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Synthesis and Characterization of Three-Coordinate and Related ??-Diketiminate Derivatives of Manganese, Iron, and Cobalt
Abstract
Treatment of M[N(SiMe(3))(2)](2) (M = Mn, Fe, Co) with various bulky beta-diketimines afforded a variety of new three-coordinate complexes which were characterized by UV-vis, (1)H NMR and IR spectroscopy, magnetic measurements, and X-ray crystallography. Reaction of the beta-diketimine H(Dipp)NC(Me)CHC(Me)N(Dipp) (Dipp(2)N(wedge)NH; Dipp = C(6)H(3)-2,6-Pr(i)(2)) with M[N(SiMe(3))(2)](2) (M = Mn or Co) gave Dipp(2)N(wedge)NMN(SiMe(3))(2) (M = Mn, 1; Co, 3) while the reaction of Fe[N(SiMe(3))(2)](2) with Ar(2)N(wedge)NH (Ar = Dipp, C(6)F(5), Mes, C(6)H(3)-2,6-Me(2), or C(6)H(3)-2,6-Cl(2)) afforded the series of iron complexes Ar(2)N(wedge)NFe[N(SiMe(3))(2)] (Ar = Dipp, 2a; C(6)F(5), 2b; Mes, 2c; C(6)H(3)-2,6-Me(2), 2d; C(6)H(3)-2,6-Cl(2), 2e). This represents a new synthetic route to beta-diketiminate complexes of these metals. The four-coordinate bis-beta-diketiminate complex Fe[N(wedge)N(C(6)F(5))(2)](2), 4, was also isolated as a byproduct from the synthesis of 2b. Direct reaction of the Dipp(2)N(wedge)NLi with CoCl(2) gave the "ate" salt Dipp(2)N(wedge)NCoCl(2)Li(THF)(2), 5, in which the lithium chloride has formed a complex with Dipp(2)N(wedge)NCoCl through chloride bridging. The Fe(III) species Dipp(2)N(wedge)NFeCl(2), 6, was obtained cleanly from the reaction of FeCl(3) with Dipp(2)N(wedge)NLi. Magnetic measurements showed that all the complexes have a high spin configuration. The different substituents in the series of iron complexes 2a-e allowed assignment of their paramagnetically shifted (1)H NMR spectra. The X-ray crystal structures 1-2d and 3 showed that they have a distorted three-coordinate planar configuration at the metals whereas complexes 4-6 have highly distorted four-coordinate geometries.
... Indeed, values in the same range (4.9-5.1 μ B ) have been observed for three-coordinate iron(II) β-diketiminate complexes [CH(CH 2 CNR) 2 ]-FeN(SiMe 3 ) 2 [R = C 6 F 5 , 2,6-Me 2 C 6 H 3 , 2,6-Cl 2 C 6 H 3 , 2,6diisopropylphenyl (Dipp), 2,4,6-Me 3 C 6 H 2 (Mes)]. [33] The exact same μ eff value as that for 2 (5.15 μ B ) has been found for [CH(Ph 2 PNDipp) 2 ]FeN(SiMe 3 ) 2 . [34] With the related bis(phosphinimino)methanide ligand [CH(Ph 2 PNMes) 2 ], a slightly higher effective magnetic moment of 5.25 μ B was observed. ...
... [40] Curiously, (thf) 2 NaCr[N(CH 2 CH 2 NSiMe 3 ) 3 ] and (tmeda) 2 Li 2 Cr(Me) 4 (tmeda = Me 2 NCH 2 CH 2 NMe 2 ), feature effective magnetic moments of 5.1 and 4.89 μ B , respectively. [41] The ate complex 4 with three-coordinate cobalt(II) centers features a μ eff value of 5.23 μ B , which is similar to that observed for Co[N(SiMe 2 Ph) 2 ] 2 (thf) (5.20 μ B ). [ ] 2 } 2 (μtmeda), lower effective moments were also found (4.91, [33] 4.80, [34] 4.90, [34] and 5.09 μ B , [23] respectively). However, all of the mentioned data lie above the spin-only value for a d 7 high-spin configuration of 3.87 μ B . ...
... [23] Again, β-diketiminate and bis(phosphinimino)methanide complexes [CH(CH 2 CNDipp) 2 ]-MnN(SiMe 3 ) 2 and [CH(Ph 2 PNR) 2 ]MnN(SiMe 3 ) 2 (R = Dipp, Mes) were examined by the Evans method and displayed slightly larger effective magnetic moments than 5 with μ eff = 5.65, 5.90, and 5.80 μ B , respectively. [33][34][35] The ion-separated complex [(thf) 4 Li]{Mn[C 3 H 3 (SiMe 3 ) 2 ] 3 } was investigated by SQUID magnetometry and showed a magnetic moment of 4.03 μ B at 300 K and 2.92 μ B at low temperatures. [43] This behavior was ascribed to a high-spin/lowspin equilibrium. ...
Dimetallic ate complexes were synthesized from the divalent transition metal silylamide complexes {Fe[N(SiMe3)2]2}2, Cr[N(SiMe3)2]2(thf), Co[N(SiMe3)2]2(thf)2, and {Mn[N(SiHMe2)2]2}2 (thf = tetrahydrofuran) by the addition of the corresponding lithium or sodium silylamide salt. Accordingly, donor-free LiFe[N(SiMe3)2]3 and NaMn[N(SiHMe2)2]3 as well as thf-coordinated (thf)NaCr[N(SiMe3)2]3 and (thf)NaCo[N(SiMe3)2]3 were obtained. The thf-containing mixed iron(II)/lithium bis(trimethylsilyl)amide complex (thf)LiFe[N(SiMe3)2]3 was synthesized by the simple addition of thf to the donor-free complex LiFe[N(SiMe3)2]3. All of the complexes were characterized by IR spectroscopy and elemental analysis, and the effective magnetic moments in solution were determined by the Evans method. The solid-state structures of these bis(trimethylsilyl)amido-derived complexes were additionally determined by X-ray crystallography.
... Solvents were degassed and stored over activated molecular sieves. Starting reagents L'BCl2 [34,36], LAl [1,37], LGa [2,38,39], LIn [3], and LTl [4] were prepared according to the (slightly modified) literature methods (LK was isolated and not prepared in situ). 1 H (300 MHz, 400 MHz, 600 MHz), 11 B{ 1 H} (128.5 MHz, 192.5 MHz), 13 C{ 1 H} (75.5 MHz, 100.7 MHz, 150.9 MHZ), and 19 F{ 1 H} (376.5 MHz) spectra were recorded with a Bruker Avance DPX-300, a Bruker Avance Neo 400 MHz or a Bruker Avance III HD 600 NMR spectrometer and are referenced to internal C6D6 ( 1 H: δ = 7.16, 13 C: δ = 128.06), and thf-d8 ( 1 H: δ = 3.58; 13 C: δ = 67.21). ...
... Solvents were degassed and stored over activated molecular sieves. Starting reagents L'BCl 2 [34,36], LAl [1,37], LGa [2,38,39], LIn [3], and LTl [4] were prepared according to the (slightly modified) literature methods (LK was isolated and not prepared in situ). 1 21). Heteronuclear NMR measurements were performed protium decoupled unless otherwise noted. ...
Monovalent group 13 diyls are versatile reagents in oxidative addition reactions. We report here [1,4]-cycloaddition reactions of β-diketiminate-substituted diyls LM (M = Al, Ga, In, Tl; L = HC[C(Me)NDipp]2, Dipp = 2,6-iPr2C6H3) with various 1,2-diketones to give 5-metalla-spiro[4.5]heterodecenes 1, 4–6, and 8–10, respectively. In contrast, the reaction of LTl with acenaphthenequinone gave the [2,3]-cycloaddition product 7, with Tl remaining in the +1 oxidation state. Compound 1 also reacted with a second equivalent of butanedione as well as with benzaldehyde in aldol-type addition reactions to the corresponding α,β-hydroxyketones 2 and 3, while a reductive activation of a benzene ring was observed in the reaction of benzil with two equivalents of LAl to give the 1,4-aluminacyclohex-2,4-dien 12. In addition, the reaction of L’BCl2 (L = HC[C(Me)NC6F5]2) with one equivalent of benzil in the presence of KC8 gave the corresponding 5-bora-spiro[4.5]heterodecene 13, whereas the hydroboration reaction of butanedione with L’BH2 (14), which was obtained from the reaction of L’BCl2 with L-selectride, failed to give the saturated 5-bora-spiro[4.5]heterodecane.
... The Co-Cl [C1(2)] bond distances are 2.340(3) Å, which are slightly longer than data observed in the compounds [CoL(l-Cl)] 2 [38] and CoLCl 2 Li(THF) 2 (L@(N(Dipp)C(Me)) 2 CH) (2.293-2.295 Å) [59], Fig. 1. ORTEP drawing of 1b with thermal ellipsoids drawn at the 30% probability level. ...
... The distances of Cl(1) and Cl(1) 0 to the Co-Cl(2)-Co-Li plane are equal at 4.56 Å, and the dihedral angle between Co-Cl(1) 0 -Li and Co-Cl(2)-Co-Cl(1)-Li is 75.71°. The Li-Cl and Li-O distances [2.361(15) and 1.938(17) Å] are also similar to previously reported compounds[59][60][61][62][63][64]. Regarding the b-diketiminato moiety, the bond distances Co-N [1.956(7) and 1.920(7)Å] and the bond angle N-Co-N (96.0°) are typical for b-diketiminato compounds [9-18,59-73]. ...
The lithium β-diketiminate (1c, [Li{N(2,6-iPr2C6H3)C(Ph)CHC(tBu)NH}]2 represented as (LiL)2) reacted with 3d-metal (II) chlorides to afford the corresponding compounds (2–7). All metal compounds were fully characterized by elemental, spectroscopic analyses and the single-crystal X-ray diffraction. The coordination geometries around the metals are shown to be tetrahedral within the trinuclear Co2Li compound (2), planar in ML2 (M=Co, 3), pseudo-tetrahedral conformation in the ML2 with M as Mn (4), Fe (5) or Zn (6), and square planar in the dinickel compound (7). Indicated by the trimetallic Co2Li compound 2, a six-membered ring is constructed of three metal atoms and three bridged chlorides as a twisted conformation. An inversion center is present in the centroid of the Ni2Cl2 four-membered ring within compound 7. The plausible mechanism of forming ML2 was proposed through the chloro-bridged multinuclear compounds on the basis of isolated intermediates of trinuclear (2) and dinuclearic (7) compounds. Upon treatment with methylaluminoxane (MAO), the nickel compound 7 possessed good activity towards ethylene oligomerization, whereas the other metal compounds showed moderate activities towards ethylene polymerization.
... [15] Salicylidimine ligands are synthesised through the condensation of 2, 2'-dihydroxy-[1,1'] binaphthyl-3, 3'-dicarbaldehyde, and 2, 6-dialkylanilines, and they are excellent chelat-ing agents for the synthesis of polynuclear transition metal complexes. [16][17][18] Cobalt complexes with 2, 2'-binaphthol-based ligands have a wide range of applications in oxidative catalysis due to their excellent dinucleating ability, low toxicity, and high efficiency. [19][20][21] Furthermore, cobalt complexes with various ligands have been extensively studied as chemical models of dioxygen-carrying proteins such as hemoglobin and myoglobin, as well as active oxidants in organic substrate oxidation. ...
Two well‐defined novel binuclear cobalt (II) [Co(H2L¹)]2 and [Co(H2L²)]2 compounds are presented. Binuclear cobalt (II) complexes (1–2) containing 1,1′‐binaphthyl derived tetradentate (N2O2) donor ligands H2L¹ and H2L², namely 3,3‐bis[((2,6‐diisopropylphenyl)imino)methyl]‐[1,1′‐binaphthalene‐2,2′‐dioxodicobalt(II) and 3,3′‐bis‐[((2,6‐diethyl‐phenyl)imino)‐ethyl]‐[1,1′]‐binaphtyl‐2,2′‐dioxocobalt(II) complexes were synthesized and isolated for the first time. Various spectroscopic techniques, including UV‐visible spectra, magnetic susceptibility, cyclic voltammetry, elemental analysis, mass spectrometry, and single‐crystal X‐ray diffraction were used to structurally characterize these binuclear cobalt(II) complexes. The binuclear cobalt (II) [Co(H2L¹)]2 and [Co(H2L²)]2 complexes (1–2) demonstrated excellent catalytic activity in the cyanosilylation reaction of various aryl aldehydes to value‐added cyanohydrins at room temperature under solvent‐free conditions.
... The planar threecoordinate Fe center displayed a very small NÀ FeÀ N bite angle (87.9(1)°, 88.0(1)°in both enantiomers). [31][32][33][34] The FeÀ NSi bond lengths in rac-1 (1.931 (2) (5) Å). [8] The 1,2-trans-diphenyl substituents of the backbone adopt a 153.98°angle. Single crystals of the homoleptic tetraamido ferrate 2 that were collected exhibited two different three-dimensional network structures through K + -coordination to amido-N, phenyl, and solvent moieties. ...
Amidometal complexes entertain a very rich coordination chemistry, however, applications to catalytic transformations are comparably rare. The triamido ferrate complex K[Fe(N^N)N(SiMe3)2], N^N=1,2‐diphenylethylene‐1,2‐diamido, was prepared and applied to catalytic hydrosilylations of alkenes. Mechanistic studies indicated initial silylative amide dissociation and formation of a potential iron hydride species, a step that was significantly accelerated by the presence of styrene. image
... However,i n situ UV-vis spectroscopy measurements give l max = 494 and 552 nm (for catalysis in the presenceo fH 3 N·BH 3 )o rl max = 497 and 547 nm (for catalysis in the presenceo fH Bpin);w avelengthst hat have been linked to both Fe I and Fe III b-diketiminate species. [21,23] Using the methodr eported by Scheer for the synthesis of the h 6 -toluene analogue of 1 A , [24] we obtain 87 % 3a (7.5:1 trans:cis)a fter 16 ha t6 08Cw hen 5mol %o ft his Fe I speciesi su sed in catalysis (31 %i na6.3:1 ratio after 2h); these resultsa re in-line with those obtained using the same conditions with pre-catalyst 1 (5 mol %1a nd 10 mol %H Bpin, 27 %, 5.7:1r atio after 2h;a nd 93 %, 7.6:1 ratio after 16 h) and furthers upport the proposal that the reactionp roceeds via an Fe I species. ...
Iron‐catalyzed isomerization of alkenes is reported using an iron(II) β‐diketiminate pre‐catalyst. The reaction proceeds with a catalytic amount of a hydride source, such as pinacol borane (HBpin) or ammonia borane (H3N⋅BH3). Reactivity with both allyl arenes and aliphatic alkenes has been studied. The catalytic mechanism was investigated by a variety of means, including deuteration studies, Density Functional Theory (DFT) and Electron Paramagnetic Resonance (EPR) spectroscopy. The data obtained support a pre‐catalyst activation step that gives access to an η²‐coordinated alkene FeI complex, followed by oxidative addition of the alkene to give an FeIII intermediate, which then undergoes reductive elimination to allow release of the isomerization product.
... Å that are indicative of a low-spin state for the complexes 2−5. Structurally related high-spin Fe(II) complexes have been reported to have significantly larger Fe−N distances (e.g., 1.98 Å in [(1)FeX 2 ][NBu 4 ], 15 2.02 Å in a bis(β-diketiminate)iron complex 16 ). In addition, the intraligand N−N bonds in 1−5 are slightly elongated (1.32−1.33 ...
The transition between spin states in d-block metal complexes has important ramifications for their structure and reactivity, with applications ranging from information storage materials to understanding catalytic activity of metalloenzymes. Tuning the ligand field (ΔO) by steric and/or electronic effects has provided spin-crossover compounds for several transition metals in the periodic table, but this has mostly been limited to coordinatively saturated metal centers in octahedral ligand environments. Spin-crossover complexes with low coordination numbers are much rarer. Here we report a series of four-coordinate, (pseudo)tetrahedral Fe(II) complexes with formazanate ligands and demonstrate how electronic substituent effects can be used to modulate the thermally induced transition between S = 0 and S = 2 spin states in solution. All six compounds undergo spin-crossover in solution with T1/2 above room temperature (300–368 K). While structural analysis by X-ray crystallography shows that the majority of these compounds are low-spin in the solid state (and remain unchanged upon heating), we find that packing effects can override this preference and give rise to either rigorously high-spin (6) or gradual spin-crossover behavior (5) also in the solid state. Density functional theory calculations are used to delineate the empirical trends in solution spin-crossover thermodynamics. In all cases, the stabilization of the low-spin state is due to the π-acceptor properties of the formazanate ligand, resulting in an “inverted” ligand field, with an approximate “two-over-three” splitting of the d-orbitals and a high degree of metal–ligand covalency due to metal → ligand π-backdonation. The computational data indicate that the electronic nature of the para-substituent has a different influence depending on whether it is present at the C–Ar or N–Ar rings, which is ascribed to the opposing effect on metal–ligand σ- and π-bonding.
... The resulting coordination environment of Co 2+ in the title compound is associated with insufficient crowding that prevents the elimination of chloride as a lithium salt by-product. The tendency of forming metal-halogenlithium fragments was previously reported in many cases where -ketoiminate or -diketiminate ligands have been employed (Yang et al., 2012;Eckert et al., 2004;Panda et al., 2002). ...
The crystal structure of the title compound, [CoLi(C 11 H 21 N 2 O)Cl 2 (C 4 H 8 O) 2 ], has monoclinic symmetry and comprises one heterometallic binuclear complex molecule in the asymmetric unit. The Co ²⁺ cation is bonded to one oxygen and two nitrogen atoms of a β -ketoiminato ligand and to two chlorido ligands, leading to a distorted trigonal-bipyramidal coordination sphere. One of the Cl ligands and the oxygen atom of the β -ketoiminato ligand are bridging to a Li ⁺ cation, which is further bonded to oxygen atoms of two THF molecules. The resulting coordination sphere is distorted tetrahedral. In the crystal, weak intermolecular C—H...Cl hydrogen bonds are identified that link the complex molecules into a three-dimensional network structure.
... The decafluorinated and tetrachlori-nated ligand precursors, L 2 H and L 3 H, respectively, were prepared by condensation reactions, as described in the literature. 45,46 The reaction of each of the β-diketiminate ligand precursors with 1.2−1.4 equiv of [CuMes] n (n = 4, 5) in a toluene solution generated a series of η 2 -coordinated toluene copper(I) adducts in 56−71% isolated yield (Scheme 1). ...
A series of copper(I) complexes bearing electron-deficient β-diketiminate ligands have been prepared. The study includes [{{ArNC(CR3)}2CH}Cu(η(2)-toluene)n] (Ar = Mes, R = F, n = 0.5, [12·tol]; Ar = C6F5, R = Me, n = 1, [2·tol]; Ar = 2,6-Cl2C6H3, R = H, n = 0.5, [32·tol]). Reactions of [1-3n·tol] with boranes, alanes, a zinc hydride, a magnesium hydride, and a calcium hydride generate the corresponding σ complexes ([1-3·B], [3·B'], [3·Al], [3·Al'], [1-3·Zn], [1·Mg], and [1·Ca]). These species all form reversibly, being in equilibrium with the arene solvates in solution. With the exception of the calcium complex, the complexes have all been characterized by single-crystal X-ray diffraction studies. In solution, the σ-hydride of the aluminum, zinc, magnesium, and calcium derivatives resonates between -0.12 and -1.77 ppm (C6D6 or toluene-d8, 193-298 K). For the σ-borane complexes, the hydrides are observed as a single resonance between 2 and 3.5 ppm (C6D6, 298 K) and bridging and terminal hydrides rapidly exchange on the NMR time scale even at 193 K. Quantification of the solution dynamics by van't Hoff analysis yields expectedly small values of ΔH° and negative values of ΔS° consistent with weak binding and a reversible process that does not involve aggregation of the copper species. The donor-acceptor complexes can be rationalized in terms of the Dewar-Chatt-Duncanson model. Density functional theory calculations show that the donation of σ-M-H (or E-H) electrons into the 4s-based orbital (LUMO or LUMO+1) of the copper fragment is accompanied by weak back-donation from a dxz-based orbital (HOMO or HOMO-1) into the σ*-M-H (or E-H) orbital.
... An attractive characteristic of the BDI ligand is that its preparation is both simple and modular, allowing for introduction of a variety of aryl substituents, which can confer a range of steric and electronic influences on metal complexes. The 2,6-dichlo-rophenyl analog (Ar = 2,6-Cl 2 -C 6 H 3 ; BDI Cl ) offers a more electronpoor, less hindered alternative to BDI iPr , and has been primarily applied as a supporting ligand for late-and mid-transition metal complexes [22,23]. Here, we report the use of the BDI Cl ligand to prepare group 5 imido complexes in an effort to draw synthetic and structural parallels with analogous BDI complexes. ...
A series of transition metal‐pnictogenide compounds were prepared starting from [(Dipp2NacNac)MCl] (M = Cr, Mn, Fe, Zn) (Dipp2NacNac = HC{C(Me)N(Dipp)}2) and [M´E(SiMe3)2] (M´= Li, K; E = P, As, Sb) as well as [Li(Et2O)nPH2] and [Li(tmeda)AsH2]. In the course of these investigations we were able to characterize all permutations for compounds of the composition [(Dipp2NacNac)ZnE(SiMe3)2] (E = P, As, Sb) and [(Dipp2NacNac)ZnEH2] (E = P, As). Moreover, the synthesis of selected compounds of type [(Dipp2NacNac)ME(SiMe3)2] for M = Cr, Mn, Fe and E = P‐Sb are described. As part of our efforts, we established a number of bonding motifs that are underexplored in the literature to date. All isolated compounds, were examined by NMR spectroscopy, IR spectroscopy, Elemental analysis and X‐Ray structure analysis. DFT calculations on the chromium compounds were performed to investigate the binding situation between chromium and the group 15 element in more detail.
We report the use of alkaline earth metals magnesium and calcium for the reduction of the cobalt(II) complex [iPr2NN]Co(μ–Cl)2Li(thf)2 (iPr2NN = 2,4-bis-(2,6-diisopropylphenylimido)pentyl) (1) resulting in heterotrimetallic dinitrogen complexes 2 and 3 with a rare example of [Co–N2–M–N2–Co] core where M = Mg (complex 2) and Ca (complex 3). The dinitrogen ligands in complexes 2 and 3 showed weakened N–N bonds, as judged by infrared spectroscopy and the structures of 2 and 3 were confirmed by X-ray crystallography. These cobalt complexes can be isolated as pure solids that are stable in solution of non-coordinating solvents such as n-pentane or cyclohexane, as well as THF. These results demonstrate the correlation between the binding mode of the Lewis acid and N–N weakening in heterotrimetallic dinitrogen complexes.
The reaction between diphosphorus derivatives [(ClImDipp)P2(Dipp)]OTf (1[OTf]) and [(ClImDipp)P2(Dipp)Cl] (1[Cl]) with the cyclotetraphosphido cobalt complex [K(18c‐6)][(PHDI)Co(η⁴‐cyclo‐P4)] (2) leads to the formation of complex [(PHDI)Co{η⁴‐cyclo‐P6(Dipp)(ClImDipp)}] (3), which features an unusual hexaphosphido ligand [ClImDipp=4,5‐dichloro‐1,3‐bis(2,6‐diisopropylphenyl)imidazol‐2‐yl, Dipp=2,6‐diisopropylphenyl, 18c‐6=18‐crown‐6, PHDI=bis(2,6‐diisopropylphenyl)phenanthrene‐9,10‐diimine]. Complex 3 was obtained as a crystalline material with a moderate yield at low temperature. Upon exposure to ambient temperature, compound 3 slowly transforms into two other compounds, [K(18c‐6)][(PHDI)Co(η⁴‐P7Dipp)] (4) and [(PHDI)Co{cyclo‐P5(ClImDipp)}] (5). The novel complexes 3–5 were characterized using multinuclear NMR spectroscopy and single‐crystal X‐ray diffraction. To shed light on the formation of these compounds, a proposed mechanism based on ³¹P NMR monitoring studies is presented.
We report the synthesis of 17 molybdenum and tungsten complexes supported by the ubiquitous BDI ligand framework (BDI = β-diketiminate). The focal entry point is the synthesis of four molybdenum and tungsten(V) BDI complexes of the general formula [MO(BDIR)Cl2] [M = Mo, R = Dipp (1); M = W, R = Dipp (2); M = Mo, R = Mes (3); M = W, R = Mes (4)] synthesized by the reaction between MoOCl3(THF)2 or WOCl3(THF)2 and LiBDIR. Reactivity studies show that the BDIDipp complexes are excellent precursors toward adduct formation, reacting smoothly with dimethylaminopyridine (DMAP) and triethylphosphine oxide (OPEt3). No reaction with small phosphines has been observed, strongly contrasting the chemistry of previously reported rhenium(V) complexes. Additionally, the complexes 1 and 2 are good precursors for salt metathesis reactions. While 1 can be chemically reduced to the first stable example of a Mo(IV) BDI complex 15, reduction of 2 resulted in degradation of the BDI ligand via a nitrene transfer reaction, leading to MAD (4-((2,6-diisopropylphenyl)imino)pent-2-enide) supported tungsten(V) and tungsten(VI) complexes 16 and 17. All reported complexes have been thoroughly studied by VT-NMR and (heteronuclear) NMR spectroscopy, as well as UV-vis and EPR spectroscopy, IR spectroscopy, and X-ray diffraction analysis.
Introducing charges into ligand systems fine-tunes their electronic properties and influences the solubility of their metal complexes. Herein, we present a synthesis of a dianionic, C3-symmetric ligand combining three anionic N-donors tethered to a positively charged phosphonium center. The tris-skatylmethylphosphonium (TSMP) ligand, isolated in the form of its dipotassium salt TSMPK2, is the first dianionic homoscorpionate capable of metal exchange. The potassium cations in TSMPK2 are exchangeable for other metals, which results in rich coordination chemistry. Thus, the ligand displays a bridging μ2:κ2:κ1 coordination mode with trigonal planar Cu(I) centers in the tetrameric complex [(TSMP)Cu]44-. The κ3 mode is accessed upon addition of 1 equiv. of P(OEt)3 per Cu(I) to yield the tetrahedral monomeric complex [(TSMP)CuP(OEt)3]-. Both Fe(II) and Ni(II) in pyridine give octahedral high-spin κ3 complexes with composition (TSMP)M(Py)3 (M=Fe, Ni). Displacement of three pyridine ligands in (TSMP)Fe(Py)3 for a second equivalent of TSMP gives a high-spin pseudotetrahedral 2:1 complex [(TSMP)2Fe]2- with the ligands in κ2 coordination mode. The reduction in coordination number is likely due to electrostatic repulsion of the negatively-charged indolides as well as their weaker π-accepting character as compared to pyridine.
We report on the synthesis and structural features of NMe2-modified β-diketiminate-supported boron difluoride compounds (LArBF2: LAr=[HC(NAr)2(CNMe2)2]–; LPh: Ar=Ph; LTol: Ar=p-tolyl; LXyl: Ar=m-xylyl). The title compounds were prepared in moderate yields (~65%) by insitu deprotonation of the corresponding ligands LArH using KH, followed by the addition of BF3OEt2. According to solid-state and theoretical analyses of the BF2 compounds, the lone pair at each NMe2 group is involved in electron delocalization within the central BC3N2 ring. As a result, the N-aryl substituents sterically clash with the NMe2 groups, causing this central ring to pucker. Several attempts were made to prepare heavy analogues (e.g. LArBX2, X=Cl, Br, I) but only unidentifiable product mixtures were observed. It appears that the observed steric clash between the N-aryl substituents and the NMe2 groups prevented the formation of these heavy analogues.
The coordination chemistry of the new NNP pincer ligand framework (QuiNacNacP) is explored with cobalt. Upon treatment of the cobalt(II) complex Co[QuiNacNacP]Cl with KC8, the formation of cobalt(I) dinitrogen complex Co[QuiNacNacP]N2 was observed. Co[QuiNacNacP]N2 crystallizes as a square planar (S = 0) complex with an essentially unactivated N2 ligand. In solution, the dinitrogen complex is in equilibrium with the paramagnetic T‐shaped complex Co[QuiNacNacP] (S = 1). The ability of Co[QuiNacNacP]Cl to act as a catalyst precursor in the reductive silylation of dinitrogen was also briefly explored. Reaction of ≈ 1000 equivalents KC8 with ≈ 1500 equivalents Me3SiCl (relative to Co[QuiNacNacP]Cl) under 1 atm of N2 furnished roughly 40 equivalents of N(SiMe3)3.
Li- und Fe-Paarung: Die Kopplung eines starken Lewis-sauren Eisenkatalysators mit dem Lithiumsalz LiAl(ORF)4 [ORF=(OC(CF3)3] zur Voraktivierung von Diazoreagenzien führt zu elektrophilen Eisencarbenspezies, die in der Lage sind, in nicht aktivierte aliphatische C-H-Bindungen zu insertieren. Die Reaktionen erfolgen bei 25 °C über α-Alkylmetallocarben-Intermediate und das Lithiumkation spielt eine entscheidende Rolle bei der geschwindigkeitsbestimmenden Bildung des elektrophilen Eisencarben-Intermediats.
Abstract
Combining an electrophilic iron complex [Fe(Fpda)(THF)]2 (3) [Fpda=N,N′-bis(pentafluorophenyl)-o-phenylenediamide] with the pre-activation of α-alkyl-substituted α-diazoesters reagents by LiAl(ORF)4 [ORF=(OC(CF3)3] provides unprecedented access to selective iron-catalyzed intramolecular functionalization of strong alkyl C(sp³)−H bonds. Reactions occur at 25 °C via α-alkyl-metallocarbene intermediates, and with activity/selectivity levels similar to those of rhodium carboxylate catalysts. Mechanistic investigations reveal a crucial role of the lithium cation in the rate-determining formation of the electrophilic iron-carbene intermediate, which then proceeds by concerted insertion into the C−H bond.
Combining an electrophilic iron complex [Fe(Fpda)(THF)]2 (3) [Fpda=N,N′‐bis(pentafluorophenyl)‐o‐phenylenediamide] with the pre‐activation of α‐alkyl‐substituted α‐diazoesters reagents by LiAl(ORF)4 [ORF=(OC(CF3)3] provides unprecedented access to selective iron‐catalyzed intramolecular functionalization of strong alkyl C(sp³)−H bonds. Reactions occur at 25 °C via α‐alkyl‐metallocarbene intermediates, and with activity/selectivity levels similar to those of rhodium carboxylate catalysts. Mechanistic investigations reveal a crucial role of the lithium cation in the rate‐determining formation of the electrophilic iron‐carbene intermediate, which then proceeds by concerted insertion into the C−H bond.
Coordination of redox‐active ligands to metals is a compelling strategy for making reduced complexes more accessible. In this work, we explore the use of redox‐active formazanate ligands in low‐coordinate iron chemistry. Reduction of an iron(II) precursor occurs at milder potentials than analogous non‐redox‐active β‐diketiminate complexes, and the reduced three‐coordinate formazanate‐iron compound is characterized in detail. Structural, spectroscopic and computational analysis show that the formazanate ligand undergoes reversible ligand‐centered reduction to form a formazanate radical dianion in the reduced species. The less negative reduction potential of the reduced low‐coordinate iron formazanate complex leads to distinctive reactivity with formation of a new N‐I bond that is not seen with the β‐diketiminate analogue. Thus, the storage of an electron on the supporting ligand changes the redox potential and enhances certain reactivity.
The synthesis and characterization of a new series of β-diketiminato manganese(II) compounds are explored. The reactivity, volatility, and thermal stability of these complexes, as demonstrated by TGA and sublimation, qualifies them as potential precursors for the vapor-phase growth of manganese oxide films. Relative rates of surface reactivity are explored through NMR studies, XPS, and buried volume calculations, and smaller ligands, which promote lower molecular weight complexes as well as more exposed metal centers, emerge as the most promising candidates.
The behavior of the complex (H2L)CoCl2, where H2L is a bis-(pyrazol-3-yl)pyridine, towards Bronsted bases is studied, to evaluate peripheral NH deprotonation as a route to a dianionic pincer ligand on a d7 center. Deprotonation is found to also remove chloride from cobalt, and the decreased metal coordination number is then satisfied by bimolecular reaction of the newly formed peripheral deprotonated pyrazolate nitrogen, leading to Co2 units bridged by some of the pyrazolates, in the analogous species [Co2(L)(LH)]2(L) and [Co2(L)(HL)]2[Co(L)2], but also occasionally by chloride retention, in LiCo2L2Cl. Reacting LiCo2L2Cl with tBuNC, yields monomeric LCo(tBuNC)2, shown to be a 17 valence electron species. Use of excess LiN(SiMe3)2 in deprotonation of (H2L)CoCl2 leads to a product containing a Co[N(SiMe3)2]2 substructure, which illustrates opening of the Co2L2 dimer in response to an attacking nucleophile.
The application of synthetic organic chemistry to the surface chemistry of monolayer arrays adds a novel dimension to the power of these systems for surface modification. This paper describes the elaboration of simple functionalized monolayers into dialdimine and dialdiminate ligands tethered to the monolayer surface. These ligands are then used to coordinate metal ions in an effort to form diiminate complexes with control over their environment and orientation. Ligand anchoring is best achieved through either thiol-ene photochemistry or azide-acetylene "click" chemistry. There is an influence of ligand bulk on some surface transformations, and in some cases reactions that have been reported to be effective on simple, homogeneous monolayer surfaces are not applicable to a more complex monolayer environment. The large excess of solution reagents relative to monolayer surface functionality adds another measure of difficulty to the control of interfacial reactions. In instances where the anchoring chain includes functional groups that can directly interact with metal ions, the metalation of ligand-bearing surfaces resulted in a higher metal ion content than would have been expected from binding only to the diimine ligands.
The ability to tune between different regioselectivities using a common pre-catalyst is an unusual yet highly desirable process. Herein, we report the use of an iron(II) pre-catalyst that can be used to synthesize vinyl phosphines in a Markovnikov selective manner in benzene, whereas a simple change to dichloromethane as the reaction solvent leads to the Z-selective anti-Markovnikov functionalization. Preliminary mechanistic that studies suggest Markovnikov selectivity is a radical mediated process whereas the anti-Markovnikov selectivity is not radical in nature, and is due to a change in oxidation state, are reported.
The use of hydride species for substrate reductions avoids strong reductants, and may enable nitrogenase to reduce multiple bonds without unreasonably low redox potentials. In this work, we explore the N═N bond cleaving ability of a high-spin iron(II) hydride dimer with concomitant release of H2. Specifically, this diiron(II) complex reacts with azobenzene (PhN═NPh) to perform a four-electron reduction, where two electrons come from H2 reductive elimination and the other two come from iron oxidation. The rate law of the H2 releasing reaction indicates that diazene binding occurs prior to H2 elimination, and the negative entropy of activation and inverse kinetic isotope effect indicate that H-H bond formation is the rate-limiting step. Thus, substrate binding causes reductive elimination of H2 that formally reduces the metals, and the metals use the additional two electrons to cleave the N-N multiple bond.
This contribution explores the influences of incorporating electron-withdrawing CF3 and halide groups into (β-diketiminato)iron complexes of tetrazene and isocyanide. The synthesis of a new halogenated β-diketimine (LCF3,ClH) was accomplished by two different methods, including a novel microwave-assisted synthesis that improves the yield of the difficult condensation. Treatment of an iron(II) complex of this ligand with reductant and azide gives two diiron complexes with novel tetrazenes as bridging ligands. Structural and Mössbauer data show that the bridging tetrazene is a radical anion. The halogenation of the supporting ligand also influences iron(I) complexes of the type [LFe(CNtBu)2], which are low-spin and square-planar with alkyl substituents but high-spin and pseudotetrahedral with halogen substituents. DFT calculations suggest that the changes from halogenation come from a combination of steric and electronic effects, and that the electronic influence of ligand halogenation is minor.
Spin-crossover in a pseudo-tetrahedral bis(formazanate) iron(II) complex is described. Structural, magnetic and spectroscopic analyses indicate that this compound undergoes thermal switching between an S = 0 and an S = 2 state, which is very rare in four-coordinate complexes. The transition to the high-spin state is accompanied by an increase in Fe-N bond lengths and a concomitant contraction of intraligand N-N bonds. The latter suggests that stabilization of the low-spin state is due to the -acceptor properties of the ligand. One-electron reduction of 1 leads to the formation of the corresponding anion 2, which contains a low-spin (S = ½) Fe(I) center. The findings are rationalized by electronic structure calculations using density functional theory.
Treatment of trans-[PtCl2(NCR)2] [R = Et 1, nPr 2, tBu 3, CH2Ph 4, Ph 5, p-CF3C6H4 6, NMe2 7, NEt2 8, N(CH2)5 9] with 2.5 equiv. of 2,3-diphenylmaleimidine in CH2Cl2 at room temperature for 5 min [for R = p-CF3C6H4 6, NMe2 7, NEt2 8, N(CH2)5 9] or 14 h (for R = Et 1, nPr 2, tBu 3, CH2Ph 4, Ph 5) furnishes (1,3,5,7,9-pentaazanona-1,3,6,8-tetraenato)platinum(II) [(PANT)PtII; PtCl{HN=C(R)N=CN[C(Ph)=C(Ph)]C=NC(R)=NH}] complexes 10–18. These species are formed by platinum(II)-mediated double coupling of 2,3-diphenylmaleimidine with both nitrile ligands. The formulation of the complexes was supported by satisfactory C, H, and N elemental analyses, which were in agreement with HRESI-MS, IR, and 1H and 13C{1H} NMR spectra. The structures of 10, 11·1/8nC6H14, 15, 16·CCl4, and 17·CHCl3 were determined by single-crystal X-ray diffraction. Absorption and emission studies were performed on representative complexes 10, 15, and 18, and the results show weak phosphorescence maxima at around 730–750 and 770–820 nm in CH2Cl2 and in the solid state, respectively. Further insight into the photophysical properties was gained by time-dependent density functional theory (TD–DFT) with detailed analysis of the corresponding frontier molecular orbitals for the lower-lying transition. The calculated energies of the T1 state (in terms of wavelength) are 715.8 nm for 10, 764.6 nm for 15, and 697.7 nm for 18, and these values are in good agreement with the trend of the first vibronic peaks of their phosphorescence spectra.
This article covers the last 10 years of the inorganic and coordination chemistry of manganese at oxidation states (II), (III), (IV), (V), (VI), and (VII), as well as multinuclear compounds having oxidation states (II)–(IV) with both unitary and mixed valencies. The common ligands for manganese compounds involve the donor atoms nitrogen, oxygen, and the halogens while only few are known with other group V and group VI donors. One of the major areas of expansion has been the multinuclear complexes that are relevant to such diverse fields as metalloenzymes and single-molecule magnets. Besides the small clusters, comprising two to four metal ions synthesized to model the structures and functions of manganese metalloenzymes, a lot of interest has been invested in larger clusters, not only for their biological relevance, but also for the development of materials with novel magnetic properties. Significant advances have been also been made in the chemistry of higher oxidation state manganese complexes (V), (VI), and (VII).
Keywords:
manganese;
coordination;
inorganic;
multinuclear complexes;
oxidation states (II) to (VII);
ligand
Dissolution of M(CO)3(Br)(L(Ar)) [L(Ar) = (2,6-Cl2-C6H3-NCMe)2CH2] in either acetonitrile [M = Mn, Re] or benzonitrile (M = Re) results in C-C coupling of the nitrile to the diimine ligand. When reacted with acetonitrile, the intermediate adduct [M(CO)3(NCCH3)(L(Ar))]Br forms and undergoes an intramolecular C-C coupling reaction between the nitrile carbon and the methylene carbon of the β-diimine ligand.
β-Diketiminates are widely used supporting ligands for building a range of metal complexes with different oxidation states, structures, and reactivities. This Perspective summarizes the steric and electronic influences of ligand substituents on these complexes, with an eye toward informing the design of new complexes with optimized properties. The backbone and N-aryl substituents can give significant steric effects on structure, reactivity and selectivity of reactions. The electron density on the metal can be tuned by installation of electron withdrawing or donating groups on the β-diketiminate ligand as well. Examples are shown from throughout the transition metal series to demonstrate different types of effects attributable to systematic variation of β-diketiminate ligands.
This article provides a summary of the important and interesting aspects of the inorganic and coordination chemistry of cobalt. A brief history of the element, detailing its discovery and historical uses, is given, and some general information concerning the properties of elemental cobalt is detailed. The general chemistry of cobalt is then outlined, including an overview of the common oxidation states found in inorganic compounds and complexes, a discussion of the stereochemistry, spectra and magnetism of cobalt complexes, and an outline of some analytical methods used for cobalt. The inorganic chemistry of simple cobalt salts is then described, and the coordination chemistry of cobalt, which constitutes the majority of the article, is then outlined in some detail. Coordination complexes of cobalt are detailed according to the oxidation state of the metal ion, with complexes ranging from Co(−I) to Co(V) discussed. Brief descriptions of the chemistry of each oxidation state are given, and specific examples are then outlined according to the nature of the ligand donor atom(s), with extensive references to both the primary literature and to review articles given. Thus, Co(I), Co(0), and Co(−I) complexes containing aliphatic, aromatic, and macrocyclic amine ligands, as well as Schiff-base, porphyrin, and P-donor ligands are discussed, while Co(II) complexes of carboxylate, heterocyclic, and oxygen-derived ligands are summarized. Co(III) ammine and amine complexes are described in detail, while Co(III) complexes containing O-donor ligands are also discussed. The few known Co(IV) and Co(V) complexes are outlined.Keywords:cobalt;inorganic chemistry;coordination chemistry;Werner complexes;oxidation state;ligands
A series of three-coordinate N-heterocyclic carbene bis(trimethylsilyl)amide complexes of cobalt, [Co{N(SiMe3)2}2(NHC)] (NHC = N,N′-diarylimidazolin-2-ylidene, aryl = 2,6-diisopropylphenyl, SIPr (1), aryl = mesityl, SIMes (2); κ1-N,N′-diphosphanylimidazol-2-ylidene, PCP (5); κ1-N-phosphanyl-N′-2,6-diisopropylphenylimidazol-2-ylidene, PC (6); cyclic alkyl amino carbene :C(Cy)CH2CMe2N-2,6-Pri2C6H3, cAACCy (7)) were prepared by the reaction of [Co{N(SiMe3)2}2] with the corresponding NHCs. The complexes exhibited interesting transamination reactivity in reactions with bulky 2,6-diisopropylaniline (NH2(DiPP)), where adjustment of the stoichiometry and reaction conditions resulted in the substitution of one or two N(SiMe3)2 ligands by the anilido ligand NH(DiPP), giving [Co{N(SiMe3)2}{NH(DiPP)}(NHC)] (NHC = N,N′-bis(2,6-diisopropylphenyl)imidazol-2-ylidene, IPr (8)) and [Co{NH(DiPP)}2(NHC)] (NHC = SIPr (9); IPr (10); PCP (11)). X-ray crystallography revealed trigonal-planar coordination geometry at Co for all of the new complexes and long Co-CNHC bond lengths; in the cases of 5, 8, 9, 10, and 11, intramolecular Co···H and/or H···P interactions may provide further stabilization of specific conformations. Magnetic and electron paramagnetic resonance studies showed that the three-coordinate Co(II) centers in 1-7 behave as S = 3/2 spins with strong anisotropy arising from the low symmetry of the coordination site (C2v). The anisotropy results in large values of the zero-field splitting parameter D.
A three-coordinate cobalt species, IPrCoCl{N(SiMe3)2} [1; IPr = 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene], was synthesized by the reaction of {IPrCoCl2}2 with NaN(SiMe3)2. Compound 1 is a useful starting material for low-coordinate (IPr)Co species. 1 reacts with 2,6-di-tert-butyl-4-methylphenol (BHT-H) via aminolysis of the Co-N bond to generate a three-coordinate phenoxide complex, IPrCoCl(O-2,6-(t)Bu2-4-MeC6H2) (2). The reaction of 1 with 2,6-diisopropylaniline (NH2DIPP) generates IPrCoCl(NHDIPP) (4), which undergoes disproportionation to form a mixture of 4, {IPrCoCl2}2, and IPrCo(NHDIPP)2 (3). The same product mixture is formed by the reaction of 1 with Li[NH(DIPP)], which unexpectedly proceeds by amide exchange. Compound 3 was synthesized independently by the reaction of {IPrCoCl2}2 with 4 equiv of Li[NH(DIPP)]. The reaction of 1 with the bulkier lithium 2,6-dimesitylanilide (LiNHDMP) also proceeds by amide exchange to generate IPrCoCl(NHDMP) (5), which is stable toward disproportionation. Compounds 1 and 2 exhibit trigonal-planar geometries at cobalt in the solid state. The solid-state structure of 3 also contains a trigonal-planar cobalt center and exhibits close Co---H contacts involving the methine hydrogen atoms of the NH(DIPP) groups in the axial positions. The solid-state structure of 5 features an interaction between cobalt and a flanking aryl group of the anilide ligand, resulting in pyramidalization of the cobalt center.
The bulky bis(carbene)borate ligand H2B((t)BuIm)(2) allows for the synthesis of three- and four-coordinate iron(II) complexes, including heteroleptic H2B((t)BuIm)(2)FeN(TMS)(2) and homoleptic [H2B((t)BuIm)(2)](2)Fe. The magnetic properties of these coordinatively unsaturated complexes have been characterized by SQUID magnetometry, but no evidence of single-molecule magnet behavior is observed, despite large negative uniaxial zero field splitting. The three-coordinate complex H2B((t)BuIm)(2)FeN(TMS)(2) serves as a precursor for the synthesis of the four-coordinate mixed carbene complex H2B((t)BuIm)(2)((t)Pr(2)Im)FeCl, which has a coordination environment similar to that found in tris(carbene)borate iron(II) chloride complexes. Despite this similarity, attempts to prepare the corresponding iron(IV) nitride were unsuccessful, suggesting that subtle structural factors are critical to stabilizing this species.
Although it is well established that paramagnetic NMR spectroscopy is a powerful tool to derive structural information, the methodology is still not yet universally applied to paramagnetic small molecule complexes. In this paper paramagnetic 1 H NMR spectroscopy is investigated as a convenient method for the experimental inorganic chemist to elucidate solution structures and speciation of small molecule metal complexes derived from 2,6-pyridinedicarboxylic acid as ligand. Spectra of complexes with O h geometry, in which the spin states of the metal ion range from d 3 (Cr 3+), d 5 (Fe 3+), d 6 (Fe 2+), d 7 (Co 2+) to d 8 (Ni 2+), were recorded and analyzed. For all complexes the 1 H NMR spectra give well-resolved, easy detectable lines, which depending on the spin state and electron relaxation time of the metal ion and the pH of the solution can be fairly broad. Regardless, the spectra allow complexes of 1:1 and 1:2 stoichiometries to be distinguished in spite of the metal nucleus short nuclear correlation and relaxation times, and the magnitude of the hyperfine shift spread. The pH stability profile and the ability of the complexes to undergo ligand exchange reactions were also investigated for each of the complexes. This work demonstrates that paramagnetic 1 H NMR spectroscopy is very useful for characterizing small molecule complexes and their solution chemistry without requiring a detailed analysis of the hyperfine shifts and relaxivities.
The iron complex acts as an efficient catalyst for the title reaction by a simple procedure without an additive and within short reaction time.
The synthesis, characterization, and X-ray crystal structure of HnacnacR (R = mesityl) 1 as well as the structure of the first vanadium β-diiminate dimer, di-μ-hydroxo-di(nacnacR)divanadyl(IV) (R = mesityl) 2 are reported. The reported β-diimine, 1, is prepared through a condensation reaction between 2,4,6-trimethylaniline and 2,4-pentanedione. Compound 1 crystallizes in the
space group with Z′ = 8; 2 also crystallizes in
with Z′ = 1. The vanadium(IV) in 2 has the expected distorted square pyramidal geometry. Although the hydroxide hydrogen atoms can be found in the electron difference map, the existence of the bridging hydroxide in 2 was further confirmed through bond distance comparisons and bond valence sum analysis. Compound 1 was characterized by NMR, IR, and X-ray crystallography. (HnacnacR (R = mesityl) = 4-(2,4,6-trimethylphenylimino)-2-(2,4,6-trimethylphenylamino)pent-2-ene; mesityl = 2,4,6-trimethylphenyl).
The (β-ketiminato)rhodium complex [Rh{κ2-(N,O)-(tBu)(O)CCHC(tBu)N(C6F5)}(cod)] (1) [cod = (1Z,5Z)-1,5-cyclooctadiene] and (β-diketiminato)rhodium complexes [Rh{κ2-(N,N)-(Ar)NC(Me)CHC(Me)N(Ar)}(L1)(L2)] [2: Ar = C6F5, (L1)(L2) = cod; 3: Ar = C6F5, L1 = L2 = C2H4; 4: Ar = C6F5, L1 = L2 = CNtBu; 5: Ar = 2,6-MeC6H3, L1 = L2 = CNtBu; 6a: Ar = C6F5, L1 = L2 = CO; 7a: Ar = C6F5, L1 = CO, L2 = NCMe; 8a: Ar = C6F5, L1 = CO, L2 = PEt3; 9a: Ar = C6F5, L1 = CO, L2 = NH3] were synthesized. Treatment of [Rh{κ2-(N,N)-(C6F5)NC(Me)CHC(Me)N(C6F5)}(CO)(NCMe)] (7a) with tertiary silanes HSiR3 gave the (β-diketiminato)(hydrido)(silyl)rhodium complexes [Rh{κ2-(N,N)-(C6F5)NC(Me)CHC(Me)N(C6F5)}(H)(SiR3)(CO)] (10a: R = Me; 11: R = Et; 12: R = iPr; 13: R = Ph; 14: R = OMe; 15: R = OEt). When using an excess amount of HSiMe3 the dihydridobis(silyl) complex [Rh{κ2-(N,N)-(C6F5)NC(Me)CHC(Me)N(C6F5)}(H)2(SiMe3)2] (16) was formed in addition to 10a.
Despite the growing interest in iron catalysis and hydroamination reactions, iron-catalyzed hydroamination of unprotected primary aliphatic amines and unactivated alkenes has not been reported to date. Herein, a novel well-defined four-coordinate β-diketiminatoiron(II) alkyl complex is shown to be an excellent precatalyst for the highly selective cyclohydroamination of primary aliphatic alkenylamines at mild temperatures (70-90 °C). Both empirical kinetic analyses and the reactivity of an isolated iron(II) amidoalkene dimer, [LFe(NHCH2 CPh2 CH2 CHCH2 )]2 favor a stepwise σ-insertive mechanism that entails migratory insertion of the pendant alkene into an iron-amido bond associated with a rate-determining aminolysis step.
75 Jahre nach der Entdeckung der Hydroformylierung erleben Cobalt-Katalysatoren eine Renaissance in Hydrierungen. Wir haben Arenmetallate untersucht, in denen die niedervalente Metallspezies nicht durch Heteroatom-Liganden, sondern durch einfache π-Kohlenwasserstoffe stabilisiert ist. Kaliumbis(anthracen)cobaltat 1 und -ferrat 2 sind synthetische Vorstufen für quasi-“nackte” anionische Metallspezies. Eine Aggregation wird durch (labile) Koordination der in Hydrierungen vorhandenen π-Akzeptoren (Olefine, Arene, Carbonylverbindungen) effektiv unterdrückt. Kinetische Studien, NMR-Spektroskopie und Vergiftungsexperimente in Alkenhydrierungen bestätigen die Bildung eines homogenen Katalysators aus 1, der durch Ligandenaustausch gebildet und durch Koordination an Alkene stabilisiert wird. Das zugrundeliegende Katalysatorkonzept ist komplementär zur Verwendung von Komplexen mit Heteroatom-Donorliganden in reduktiven Prozessen.
75 years after the discovery of hydroformylation, cobalt catalysts are now undergoing a renaissance in hydrogenation reactions. We have evaluated arene metalates in which the low-valent metal species is-conceptually different from heteroatom-based ligands-stabilized by π coordination to hydrocarbons. Potassium bis(anthracene)cobaltate 1 and -ferrate 2 can be viewed as synthetic precursors of quasi-"naked" anionic metal species; their aggregation is effectively impeded by (labile) coordination to the various π acceptors present in the hydrogenation reactions of unsaturated molecules (alkenes, arenes, carbonyl compounds). Kinetic studies, NMR spectroscopy, and poisoning studies of alkene hydrogenations support the formation of a homogeneous catalyst derived from 1 which is stabilized by the coordination of alkenes. This catalyst concept complements the use of complexes with heteroatom donor ligands for reductive processes.
Geometries, bonding nature, and electronic structures of (NN)Ni(O2) (NN = β-diketiminate), its cobalt(I) and copper(I) analogues, and (Ph3P)2Ni(O2) were investigated by density functional theory (DFT) and multistate restricted active space multiconfigurational second-order perturbation (MS-RASPT2) methods. Only (NN)Ni(O2) takes a CS symmetry structure, because of the pseudo-Jahn–Teller effect, while all other complexes take a C2V structure. The symmetry lowering in (NN)Ni(O2) is induced by the presence of the singly occupied δdxy–πx* orbital. In all of these complexes, significant superoxo (O2–) character is found from the occupation numbers of natural orbitals and the O–O π* bond order, which is independent of the number of d electrons and the oxidation state of metal center. However, this is not a typical superoxo species, because the spin density is not found on the O2 moiety, even in open-shell complexes, (NN)Ni(O2) and (NN)Co(O2). The M–O and O–O distances are considerably different from each other, despite the similar superoxo character. The M–O distance and the interaction energy between the metal and O2 moieties are determined by the dyz orbital energy of the metal moiety taking the valence state. The binding energy of the O2 moiety is understood in terms of the dyz orbital energy in the valence state and the promotion energy of the metal moiety from the ground state to the valence state. Because of the participations of various charge transfer (CT) interactions between the metal and O2 moieties, neither the dyz orbital energy nor the electron population of the O2 moiety are clearly related to the O–O bond length. Here, the π bond order of the O2 moiety is proposed as a good measure for discussing the O–O bond length. Because the d electron configuration is different among these complexes, the CT interactions are different, leading to the differences in the π bond order and, hence, the O–O distance among these complexes. The reactivity of dioxygen complex is discussed with the dyz orbital energy.
1H NMR spectroscopy of the synthetically important paramagnetic cobalt(II) disilylamide dimer [Co{N(SiMe3)2}2]2 (1) in benzene solution shows that it exists in equilibrium with its monomer Co{N(SiMe3)2}2 and has an association energy of −0.30 kcal mol−1. Magnetic investigations of 1 show that the Co ions are strongly coupled antiferromagnetically. The three-coordinated Lewis base complexes formed by 1—[Co{N(SiMe3)2}2L], where L = trimethylphosphine (PMe3) (2), pyridine (3), and tetrahydrofuran (THF) (4)—display high magnetic moments with large negative D-values (between −62 cm−1 and −82 cm−1). The magnetic data, together with its electronic spectrum, show that earlier studies of 1 were likely made on its THF complex [Co{N(SiMe3)2}2(THF)] (4), which is obtained if the synthesis is performed in THF.
The title compound [MeLiPrCoCH2Si(CH3)3MeLiPr = 2,4-pentane-N,N′-bis(2,6-diisopropylphenyl) ketiminato] possesses trigonal planar geometry and crystallizes in monoclinic space group P21/n with crystal cell parameters a = 10.6155(14) Å, b = 21.279(3) Å, c = 14.8057(19) Å, β = 97.196(2)°, V = 3,318.1(7) Å3, and Z = 4. The title compound is the second reported three coordinated 13 valence electron Co(II) alkyl complex and the first such complex reported with an asymmetrically bonded alkyl group. The steric effects are discussed in comparison of known similar structures of Fe, Co, and Zn.
Graphical Abstract
The title compound [MeLiPrCoCH2Si(CH3)3MeLiPr = 2,4-pentane N,N′-bis(2,6-diisopropylphenyl) ketiminato] is a three coordinated 13 valence electron Co(II) complex with the alkyl group (R = (trimethylsilyl)methylene), with an asymmetrically bonded alkyl group. The steric effects are discussed in comparison of known similar structures of Fe, Co, and Zn.
The C,N-(trimethylsilyliminodiphenylphosphoranyl)silylmethylmetal complexes [Fe(L)2] (3), [Co(L)2] (4), [ZrCl3(L)]·0.83CH2Cl2 (5), [Fe(L)3] (6), [Fe(L′)2] (7) and [Co(L′)2] (8) have been prepared from the lithium compound Li[CH(SiMe2R)P(Ph)2NSiMe3] [1a, (R = Me) {≡ Li(L)}; 1b, (R = NEt2) {≡ Li(L′)}] and the appropriate metal chloride (or for 7, FeCl3). From Li[N(SiMe3)C(Ph)C(H)P(Ph)2NSiMe3] [≡ Li(L″)] (2), prepared in situ from Li(L) (1a) and PhCN, and CoCl2 there was obtained bis(3-trimethylsilylimino- diphenylphosphoranyl-2-phenyl-N-trimethylsilyl-1-azaallyl-N,N′)cobalt(II) (9). These crystalline complexes 3–9 were characterised by their mass spectra, microanalyses, high spin magnetic moments (not 5) and for 5 multinuclear NMR solution spectra. The X-ray structure of 3 showed it to be a pseudotetrahedral bis(chelate), the iron atom at the spiro junction.
The sterically encumbered 1,2,4-(Me3C)3C5H2 (Cp′) ligand allows the synthesis of stable high spin mono(cyclopentadienyl) manganese complexes [Cp′MnX(thf)]2 (X = Cl, Br, I; 1-X). Thermal stabilities of 1-X toward ligand redistribution to [Cp2′Mn] (2) and MnX2 depend on the bridging halide ligand. The kinetic stability of 1-I in solution even at elevated temperatures is noteworthy. Complexes 1 are useful starting materials for further functionalizations. Metathesis of 1-Cl with [LiN(SiMe3)2(OEt2)]2 yields the 13 valence-electron (VE) complex, [Cp′MnN(SiMe3)2] (3), while the manganese polyhydride cluster, [{Cp′Mn}4{MnH6}], was formed in the reaction of 1-I and KHBEt3. The 17 VE [MnH6]4− core of 4 is effectively shielded by four high spin [Cp′Mn]+ units. Magnetic susceptibility studies on 4 suggest weak electron exchange coupling between the spin carriers, but the spin state of the central [MnH6]4− fragment remained ambiguous. Therefore, the electronic structure of 4 was also analyzed by broken symmetry (BS) DFT calculations, which provided strong evidence for a low spin [MnH6]4− unit in agreement with previous spectrochemical studies performed on [FeH6]4−.
Radikal mild: Der erste bei Raumtemperatur isolierbare, strukturell charakterisierte Superoxonickel(II)-Komplex 1 mit quadratisch-planarem, vierfach koordiniertem NiII-Zentrum ist zu milden Sauerstoffübertragungen über das postulierte Intermediat 2 in der Lage, das unter H-Abstraktion zum homovalenten Komplex 3 mit einem quadratisch-planar und einem tetraedrisch koordinierten NiII-Zentrum dimerisiert. L=CH{C(Me)N-2,6-iPr2C6H3}2.
A series of manganese(II) amides (1-4), derived from 2,6-diisopropylaniline (H2NAr; where Ar = 2,6-Pri2C6H3) and its N-silylated derivative H(SiMe3)NAr, has been prepared and characterized. The crystal structure of Mn[N(SiMe3)Ar]2[THF] (2) reveals a monomeric species with a planar three-coordinate Mn(II) center. Crystal data for 2: trigonal (hexagonal axes), a = 30.119(2) Å, c = 10.589(1) Å V = 8319(1) Å3, T = 153 K, space group P 31 (No. 144), Z = 9 (R/Rw = 0.053/0.050). In contrast, Mn3[N(H)Ar]4[N(SiMe3)2]2 · C7H8 (4) is shown to be a novel trinuclear compound held together by nitrogen-bridges. The two terminal Mn(II) atoms have a distorted trigonal planar arrangement of nitrogen donors whereas the central Mn(II) is surrounded by a distorted tetrahedral array of nitrogen donors. Crystal data for 4: orthorhombic, a= 21.301(5) Å b = 17.021(6) Å c = 20.519(7) Å V = 7439(4) Å3, T = 153 K, space group Pbcn (No. 60), Z = 4 (R/Rw = 0.050/0.070).
Examples of compounds with gallium–boron donor–acceptor bonds, HC[MeC(2,6-Pri2C6H3)N]2Ga→B(C6F5)33 and (η5-C5Me5)Ga→B(C6F5)34 have been prepared by treatment of the free gallanediyls with B(C6F5)3; the structures of both compounds were determined by X-ray crystallography.
Transamination reactions utilizing the compound mercuric bis(trimethylsilyl)amide, Hg{N(SiMe3)2}2, in tetrahydrofuran (THF), and the metals Na, Mg, Ca, Sr, Ba and Al have been investigated. Thus the THF solvated compounds Na[N(SiMe3)2]·THF and M[N(SiMe3)2]2·2THF, M = Mg, Ca, Sr and Ba (1-4), have been prepared. The X-ray crystal structures of 1 and the related manganese compound Mn[N(SiMe3)2]2·2THF (5) are reported. Interaction of the silylamides, 2-4, with a range of crown ethers apparently proceeded with elimination of silylamine, (Me3Si)2NH, and novel ring opening of the crown ethers, generating species containing a donor alkoxide ligand with a vinyl ether function, presumably, O(CH2CH2O)nCHCH2 (n = 3-5). The silylamides 2-4 were also cleanly converted to the corresponding alkoxides (from 1H NMR data) in reactions with stoichiometric quantities of 3-ethyl-3-pentanol.
The bulky β-diiminate ligands [(2,6-C6H3X2)NC(Me)CHC(Me)N(2,6-C6H3X2)]– (X = Me, LMe; X = Cl, LCl) have been found to be effective in stabilizing low coordination numbers (CN) in Rh and Ir complexes. The 14- complex LMeRh(COE) (COE = cyclooctene) has a three-coordinate T-shaped Rh environment and is nonagostic. Coordinative unsaturation is avoided by incorporation of a small ligand (e.g. N2, MeCN, olefins), by the intramolecular coordination of a chlorine atom in LClRh(COE), or by an agostic interaction in LMeRh(norbornene). In solution at room temperature, LMeRh(COE) undergoes rapid isomerization according to the allyl hydride mechanism; the corresponding 2,3-dimethylbutene complex actually prefers the allyl hydride structure. Rhodium(I) complexes of LMe and LCl catalyze olefin hydrogenation; hydrogenation of 2,3-dimethylbutene has been shown to be preceded by isomerization. The shielding properties of the bulky β-diiminate ligands allow direct observation of a number of reactive intermediates or their iridium analogues, including an olefin–dihydrogen complex (with Rh) and an olefin dihydride (with Ir). These observations, together with calculations on simple model systems, provide us with snapshots of a plausible hydrogenation cycle. Remarkably, hydrogenation according to this cycle appears to follow a 14-e/16-e path, in contrast to the more usual 16-e/18-e paths.
A monovalent aluminum monomer [{HC(CMeNAr)2}Al] was obtained by reduction of the corresponding aluminum(III) diiodide. The molecular structure shows a unique two-coordinate aluminum center and a planar heterocyclic Al-N-C-C-C-N six-membered ring system (see picture).A nonbonded lone pair of electrons on the Al atom indicates the Lewis base character of the aluminum center. Ar = 2,6-iPr2C6H3.
Novel chromium(III) ethene polymerization catalysts bearing bulky monoanionic N,N-chelate ligands are described.
The reaction of the β-aminoimine compound (2,6-Pri2H3C6)NC(CH3)CHC(CH3)N(C6H3-2,6-Pri2)H (1, Dipp2nacnacH; Dipp = C6H3-2,6-Pri2) with n-BuLi in diethyl ether or tetrahydrofuran afforded the solvates Dipp2nacnacLi(Et2O) (2) and Dipp2nacnacLi(THF) (3), respectively, which crystallized as monomers featuring the Li+ ions in a distorted trigonal planar environment and an essentially planar arrangement for the LiN2C3 ring. The lithiation of 1, in the absence of a donor solvent, afforded a Dipp2nacnacLi
product that crystallized in two different types of associated structures, 4a and 4b. In the dimer 4a, the Li+ ion is coordinated to the two nitrogens of the Dipp2nacnac ligand, and it is associated by coordination of lithium to a carbon of the Dipp ring of the other Dipp2nacnac unit of the dimer. In the dodecamer 4b, the asymmetric unit consists of a chain of six LiDipp2nacnac units associated by interactions of the Li+ ions with one or two carbons from a Dipp ring of the next molecule in the chain. The hexamer is linked to an identical one (generated through an inversion center) by Li+–Dipp interactions involving the first and third lithium atoms from each hexamer, thereby generating an overall dodecameric structure of a type that
was previously unknown for lithium salts. An improved yield synthesis for 1 was also developed.
Treatment of the Grignard reagent MeMgCl with the lithiates Li[L–X] (Li[L–X] = lithium β-diketiminate [HC{C(Me)NAr′}2Li] (Ar′ = 2,6-diisopropylphenyl) or lithium N,N′-diisopropylaminotroponiminate, Li[(iPr2)ATI]) in THF provided four-co-ordinate methylmagnesium complexes [Mg(η2-L–X)Me(THF)]. The β-diketiminate complex has been characterised by X-ray crystallography, however the aminotroponiminate complex is an oil. Both complexes readily react with oxygen to provide methoxide-bridged dimeric complexes [Mg(μ-OMe)(η2-L–X)]2 and the complex [Mg(μ-OMe){η2-(iPr2)ATI}]2 has structurally been characterised. The methyl-bridged dimeric complex [Mg(μ-Me){HC[C(Me)NAr′]}2]2 may be obtained by removal of THF from the adduct under vacuum at 150 °C or by treatment of the β-diketimine (L–XH) with dimethylmagnesium in toluene with elimination of methane, and has also been characterised crystallographically. In contrast to this, treatment of MgMe2 with the aminotriponimine H[(iPr2)ATI] provides only the bis-chelate complex [Mg{(iPr2)ATI}2] which has also been characterised structurally. However the methyl bridged dimer [Mg(μ-Me){η2-(iPr2)ATI}]2 may be formed by removal of THF from [MgMe{η2-(iPr2)ATI}(THF)] at 110 °C under vacuum.
The divalent lead complex [η4-Me8taa]Pb has been synthesized by metathesis of PbI2 with Li2[Me8taa] in THF (Me8taaH2=octamethyldibenzotetraaza[14]annulene). [η4-Me8taa]Pb exists as (at least) three structural modifications, namely the triclinic chloroform solvate [η4-Me8taa]Pb·CHCl3, and the primitive and C-centered orthorhombic polymorphs of the dichloromethane solvate [η4-Me8taa]Pb·CH2Cl2. The structures of each of these modifications have been determined by single crystal X-ray diffraction. Of most significance, the C-centered orthorhombic polymorph [η4-Me8taa]Pb·CH2Cl2 is subject to the existence of a false minimum in the structure solution refinement procedure, the result of which is the generation of a non-macrocyclic structure for a compound that is actually macrocyclic. Significantly, even though it does not exhibit the true connectivity of the molecule, the errant structure is characterized by a low R value and well-behaved displacement parameters. The manifestation of the false minimum is a consequence of the crystal belonging to a polar space group, which results in a “partial polar ambiguity.” As such, the result serves to emphasize that care must be taken to ensure that, for polar space groups, all atoms of the derived structure belong to a single true polar configuration, rather than a hybrid of the two possible true polar configurations.
The base-free dimethyl scandium complex supported by the bulky β-diketiminato ligand ArNC(tBu)CHC(tBu)NAr (Ar = 2,6-iPr2C6H3, 1) reacts with various equivalencies of the strong organometallic Lewis acid B(C6F5)3 to give scandium alkyl cations. With 0.5 equiv, a monocationic μ-methyl dimer (2) was observed spectroscopically. Reaction with a further 0.5 equiv of borane gives the monomeric methyl cation 3, which was fully characterized, including via X-ray crystallography. This compound is fluxional on the NMR time scale via a “ligand flip” mechanism. Reaction with another equivalent of borane gives the unique dication 4, which exhibits a static structure on the NMR time scale. Dimethyl compound 1 is a highly active catalyst precursor for ethylene polymerization under borane or MAO-type activation. Activities for this group 3 metal based catalyst approach those observed for group 4 based metallocene systems.
A new β-diketiminate ligand containing a nitro group on the carbon framework has been developed, complexation of which with cuprous ion provided a novel linear polymer copper(I) complex with an extended d−pπ system.
Reaction of {HC(MeCDippN)(2)}Ga: with N2O or S-8 produces the compounds [{HC(MeCDipDN)(2)}GaE](2) (E = O or S), which are unique examples of gallium oxide and sulfide dimers stabilized by a chelating ligand. [GRAPHICS]
The new heteroleptic divalent germanium and tin compounds L2MX [L2=PhNC(Me)CHC(Me)NPh. X=Cl; M=Ge (1), Sn (2). X=I; M=Ge (3), Sn (4)] have been synthesized and physicochemically and structurally (2) characterized. The halide ligand of all compounds can either be removed by reaction with NaBPh4 leading to the cationic Ge(II) and Sn(II) species L2M+ or may be replaced by other groups after nucleophilic substitution giving L2MR compounds [R=N(SiMe3)2; M=Ge, Sn. M=Sn; R=OSO2CF3, N3]. Reactions of 1 and 2 with elemental S8, Se or transition metal complexes M′(CO)5·THF have resulted in the isolation of the new complexes L2(Cl)ME (E=S; M=Ge, Sn. E=Se, M=Ge) and L2(Cl)MM′(CO)5 (M′=Cr, W; M=Ge, Sn).
Natrium-bis-(trimethylsilyl)-amid reagiert mit CrCl3, MnJ2, NiJ2 und CuJ in Tetrahydrofuran zu flüchtigen, sehr hydrolyse-und sauerstoffempfindlichen Disilylamiden des Cr(III), Mn(II), Ni(II) und Cu(I).
Syntheses and Crystal Structures of the Amido Complexes [Na(12-Crown-4)2][M{N(SiMe3)2}3] with M = Mn, Fe, and Co
The ionic amido complexes [Na(12-crown-4)2][M[N-(SiMe3)2}3] with M = Mn (1), Fe (2) and Co (3) were prepared by the reaction of M[N(SiMe3)2]2 (M = Mn, Co) and Fe[N-(SiMe3)2]3, respectively, with sodium bis(trimethylsilyl)amide in toluene solution in the presence of 12-crown-4. 1–3 were characterized by IR spectroscopy and by crystal structure determinations. The complexes consist of cations [Na(12-crown-4)2]+ with a sandwich-like structure and anions [M{N(SiMe3)2}3]– in which the metal atoms are planarly coordinate by the three nitrogen atoms of the bis(trimethylsilyl)amido groups.
The synthesis of three new bulky bidentate diamines, the compounds Me2Si(NHMes)2 (1), Mes(H)NCH2CH2N(H)Mes (2) (Mes = 2,4,6-Me3C6H2), and Dipp(H)NCH2CH2N(H)Dipp (3) (Dipp = 2,6-i-Pr2C6H3 is described. The addition of 2 equiv of n-BuLi to 1 or 3 results in almost quantitative yields of the novel dimeric solvent-free dilithium derivatives [{Li(Mes)N}2SiMe2]2 (4) and [Li(Dipp)NCH2CH2N(Dipp)Li]2 (5). The reaction of 1 with Mn{N(SiMe3)2}2 in the presence of LiN(SiMe3)2 gives the unusual product [Li(Mn{NMes}2SiMe2)2N(SiMe3) 2] (6), which features a dimeric Mn salt of the dianion of 1 and, in addition, a Li+ ion sandwiched between two mesityl rings. The reaction of the bulky amine 3 affords the monomeric manganese(II) amide Mn[N-(Dipp)CH2CH2N(H)Dipp]2 (7), which has a very distorted geometry at Mn as a result of the steric requirements and bonding of ligand 3. Compounds 1 and 3-7 have been characterized by X-ray crystallography. Crystallographic data with Cu Kα radiation (λ = 1.541 78 Å) for 1 and 4-6 and Mo Kα radiation (λ = 0.710 69 Å) for 3 and 7 at 130 K: 1, a = 16.401 (10) Å, b = 6.386 (2) Å, c = 9.244 (2) Å, Z = 2, orthorhombic, space group P21212: 3, a = 10.968 (3) Å, b = 11.859 (4) Å, c = 20.455 (7) Å, α = 93.61 (3)°, β = 103.41 (3)°, γ = 109.22 (3)°, Z = 4, triclinic, space group P1; 4, a = 9.360 (3) Å, b = 10.052 (2) Å, c = 11.313 (3) Å, α = 77.08 (2)°, β = 85.49 (2)°, γ = 73.50 (2)°, Z = 1, triclinic, space group P1; 5, a = 12.758 (4) Å, b = 12.828 (5) Å, c = 19.085 (8) Å, β = 103.23 (3)°, Z = 4, monoclinic, space group P21/c; 6, a = 12.918 (5) Å, b = 14.552 (5) Å, c = 13.395 (6) Å, β = 90.35 (3)°, Z = 2, monoclinic, space group P21/c; 7, a = 21.713 (12) Å, b = 13.927 (6) Å, c = 17.764 (11) Å, β = 117.51 (4)°, Z = 4, monoclinic, space group C2/c.
The reaction between {HC(MeCDippN)2}Ga: (Dipp = C6H3Pri2 -2,6) and N3SiMe3 afforded the tetrazole {HC(MeCDippN)2}GaN(SiMe3)NNN(SiMe3) 1 and its amide/azide isomer {HC(MeCDippN)2}Ga(N3)N(SiMe3) 2 2 whose stabilities are due to the unique steric properties of the [HC(MeCDippN)2]− ligand.
Treatment of ScCl3. THF3 with the lithium salts of the ligands ArNC(R)CHC(R)NAr, where Ar = 2,6-Pr-i-C6H3 and R = CH3 and Bu-t, gives LScCl2. nTHF derivatives (R = CH3, n = 1, 1a; R = Bu-t, n = 0, 1b). These compounds can be derivatized by allylation with methyllithium or benzylpotassium. The dibenzyl compound prepared from 1a, when treated with B(C6F5)(3), gives an ion pair, 4, in which the cationic scandium center is stabilized by a eta(6)-aryl interaction with the abstracted berate benzyl group.
[(Ph)2nacnac]MCl2(THF)2 ([(Ph)2nacnac] = N,N-diphenyl-2,4-pentanediimine anion; M = Ti (1a), V (1b), Cr (1c)) were prepared and their structures determined by X-ray diffraction. In the presence of excess methylaluminoxane (MAO), 1a−c catalyzed the homopolymerization of ethylene and the copolymerization of ethylene with α-olefins.
Reaction of LLi (L = ArNC(Me)CHC(Me)NAr, Ar = 2,6-Me2C6H3) with [Rh(COE)2Cl]2 (COE = cyclooctene) produces stable, three-coordinate LRh(COE) (1). At room temperature in solution, the LRh fragment moves rapidly over one face of the COE ligand via reversible allyl hydride formation.
Mono- and disubstituted bis(ketenimine) complexes of zirconium (1 and 2, respectively) can be readily prepared by reaction of these ligands (3) with Zr(NMe)4 or, in some cases, the homoleptic tetrabenzyl derivative ZrBn4. Treatment of 1 (Ar = Ph, p-CF3Ph; X = NMe2) with Me2NH·HCl and of 2 (Ar = Ph, X = NMe2) with either Me2NH·HCl or TMSCl provides the corresponding chloro derivatives in high yield. Alkyl derivatives of 2 (X = Me, Bn) can be readily prepared by reaction of the corresponding chloro derivatives with Grignard or organolithium reagents. Monocyclopentadienyl bis(ketenimine) complexes 4 (Ar = Ph, p-CF3Ph; Cp = η5-C5H5, η5-C9H7; X = Cl) were prepared from 1 (Ar = Ph, p-CF3Ph; X = Cl) by reaction with CpLi or IndLi in high yield, and methyl derivatives 4 (Ar = Ph, p-CF3Ph; Cp = η5-C5H5, η5-C9H7; X = Me) were accessible by treatment of the chloro precursors with methyllithium. The X-ray structure of 2 (Ar = Ph; X = NMe2) reveals a distorted-octahedral geometry in which the bis(ketenimine) ligands are σ-bound to the metal and the dimethylamido groups are cis to one another, and the corresponding dichloro derivative also adopts a similar structure in the solid state, whereas the bis(ketenimine) ligands adopt a distorted, η5 binding mode in the monoindenyl derivative 4 (Ar = Ph; Cp = η5-C9H7; X = Cl). Enantiomers of 2 (Ar = Ph, X = Cl) readily interconvert in solution via a Bailar-twist mechanism, as revealed by variable-temperature 1H NMR spectroscopic studies; activation parameters for this process were determined (ΔH‡ = 9.0 ± 0.45 kcal mol-1; ΔS‡ = −9.9 ± 1.0 cal mol-1 K-1).
The preparation and reaction chemistry of β-diketiminato aluminum complexes are described. (TTP)AlCl2 (1) (TTPH = 2-(p-tolylamino)-4-(p-tolylimino)-2-pentene) is formed by the treatment of AlCl3 with LiTTP. Sequential alkylation of 1 with CH3Li results in the formation of the mono- and dimethyl aluminum complexes (TTP)AlMeCl (2) and (TTP)AlMe2 (3), respectively. Only monoalkyl complexes are produced when more hindered alkyllithium reagents are used. Compounds 2 and 3 are more conveniently prepared by treating Al(CH3)3 with TTPH·HCl and TTPH, respectively. The more sterically hindered β-diketimine ligand 2-((2,6-diisopropylphenyl)amino)-4-((2,6-diisopropylphenyl)imino)-2-pentene (DDPH) also reacts smoothly with Al(CH3)3 to yield (DDP)Al(CH3)2 (4). Compound 3 undergoes methyl abstraction reactions upon addition of B(C6F5)3 or AgOTf. Cationic species formed from 3 and B(C6F5)3 are unstable and decompose to (TTP)Al(CH3)(C6F5) and MeB(C6F5)2. In contrast, (TTP)Al(CH3)(OTf) (6) is thermally stable, but the triflate group is surprisingly inert toward displacement by Lewis bases. Compounds 1, 3, 4, and 6 were crystallographically characterized. The structures all indicate that the β-diketiminato backbone is essentially planar. The pseudotetrahedral aluminum center is displaced from the plane formed by the ligand backbone in 4 by 0.72 Å.
The sterically hindered α-diimine ligand ArNC(Me)C(Me)NAr (Ar = 2,6-C6H3-iPr2) reacts with “naked Pd” precursors to give ethylene polymerization catalysts. The “β-iminoamine” ligand ArNC(Me)CHC(Me)NHAr (3) reacts with [Pd(MeCN)4](BF4)2 to give 3·HBF4 plus bimetallic complex 4, which has been characterized by X-ray crystallography. Reaction between (DME)NiBr2 and ligand 3 affords [η2-ArNC(Me)CH2C(Me)NAr]NiBr2 (5), which has been crystallographically characterized; an ethylene polymerization catalyst is formed upon addition of MAO to 5.
Reaction of the β-diketiminato lithium salt Li(OEt2)[HC(CMeNAr)2] (Ar = 2,6-i-Pr2C6H3) with GeCl2·(dioxane) and SnCl2 in diethyl ether provided the monomeric complexes [HC(CMeNAr)2]MCl (M = Ge (2), Sn (3), respectively) with a three-coordinated metal center. The reductive dehalogenation reactions of 3 with C8K and LiAlH4 afforded [HC(CMeNAr)2]2Sn (7) and [HC(CMeNAr)2]AlH2, respectively. The metathesis reactions of 3 with t-BuLi, AgSO3CF3, and NaN3 resulted in the formation of [HC(CMeNAr)2]Sn(t-Bu) (4), [HC(CMeNAr)2]Sn(OSO2CF3) (5), and [HC(CMeNAr)2]SnN3 (6), respectively. Compounds 2, 3, 5, and 7 were characterized by single-crystal X-ray structural analysis. The structures indicate that the β-diketiminato backbone is essentially planar and the metal centers reside in distorted-tetrahedral environments with one vertex occupied by a lone pair of electrons. The bond angles at the metal center are in the range 85.2(8)−106.8(2)°, and the most acute angle is associated with the bite of the chelating ligand.
Low-coordinate cationic aluminum complexes are expected to be highly electrophilic and therefore are of interest for Lewis acid catalysis, olefin polymerization, and other potential applications. The authors describe three-coordinate, base-free aluminum alkyl cations that incorporate β-diketiminate ligands. The reaction of {l{underscore}brace}HC(CMeNAr)â{r{underscore}brace}AlMeâ (1, Ar = 2.6-{sup i}Prâ-phenyl) with [PHâC][B(CâFâ)â] in CâDâ or CâDâCl proceeds by methyl abstraction and yields [{l{underscore}brace}HC(CMeNAr)â{r{underscore}brace}AlMe][B(CâFâ)â] (2) and PhâCMe. Complex 2 is soluble in CâDâCl, separates as a liquid clathrate (oil) from benzene, and was isolated as an off-white solid by the addition of hexanes to a liquid clathrate in benzene. The addition of benzene/hexanes (1:10 by volume) to the isolated powder of 2, gently heating to 50 C for 2 days, and slowly cooling the mixture yielded 2{center{underscore}dot}benzene as colorless crystals. Complex 2 crystallizes as an ion pair in which the B(CâFâ)ââ» anion binds weakly to the {l{underscore}brace}HC(CMeNAr)â{r{underscore}brace}AlMe{sup +} cation through a meta fluorine.
The reactions of the metal amides [Ti(NMe2)4], [Fe{N(SiMe3)2}3], and [(Co{N(SiMe3)2}2)2] with p-tert-butylcalix[4]areneH4 (1) have resulted in the isolation and structural characterization of the first three σ-bonded transition-metal derivatives of a calixarene. Complete exchange of the four -OH protons in 1 with [Ti(NMe2)4] gives the complex [{Ti(p-tert-butylcalix[4]arene)}2]·6PhMe (2) as orange-red crystals. The conformationally mobile cone configuration of 1 acquires rigidity in the titanium complex which exists in a dimeric form with bridging through one of the ligand oxygens resulting in a distorted tetrahedral coordination at titanium. The reactions of 1 with [Fe{N(SiMe3)J3] or [(Co{N(SiMe3)2}2)2] are more complex and involve -SiMe3 shifts from silylamide groups to a ligand oxygen giving, for iron, an unusual complex of formula [{Fe(NH3)(p-tert-butylcalix[4]areneOSiMe3)} 2]·3n-C6H14 (3) and the new cluster [Co3(p-tert-butylcalix[4]areneOSiMe3) 2(THF)]·5PhMe (4) for cobalt. The remarkable inclusion of ammonia (which derives from an -N(SiMe3)2 group) in 3 appears to be unprecedented. The cluster 4 also appears to be unique since it is the only structurally characterized cobalt alkoxide. The crystal data at 140 K, Mo Kα (λ = 0.71069 Å), are as follows: 2-a = 12.427 (5) Å, b = 13.409 (5) Å, c = 18.754 (13) Å, α = 98.60 (5)°, β = 106.26 (4)°, γ = 108.33 (3)°, Z = 2, space group P1, R = 0.067; 3-a = 12.815 (10) Å, b = 15.061 (13) Å, c = 16.870 (10) Å, α = 111.67 (6)°, β = 91.66 (6)°, γ = 111.81 (7)°, Z = 2, space group P1, R = 0.083; 4-a = 10.152 (10) Å, b = 22.551 (11) Å, c = 27.142 (11) Å, β = 105.02 (3)°, Z = 4, space group = P21/n, R = 0.14.
The synthesis, spectroscopy, and structures of several lithium salts of very bulky silylamides and some of their transition-metal derivatives are described. In addition, the structures of two of the bis(silyl)amine precursors, HN(SiMePh2)2 and HN(SiPh3)2, are reported. The lithium derivatives include the monomeric solvates Li(THF)2N(SiMePh2)2, 1, Li-(THF)2N(SiPh3)2, 2, and Li(12-crown-4)N(SiMePh2)2, 3, and the salt [Li(12-crown-4)2][N(SiPh3)2]·THF, 4, involving the free [N(SiPh3)2]- ion with a wide SiNSi angle. Four transition-metal derivatives, M[N(SiMePh2)2]2 (M = Mn, 5; Fe, 6; Co, 7) and Fe[N(SiMe2Ph)2]2, 8, are also reported. All compounds were characterized by X-ray crystallography, and the transition-metal species were further examined by 1H NMR, UV-vis, and EPR spectroscopy and magnetic measurements. The transition-metal complexes are all high spin with essentially two coordination and near linear geometries for 5, 6, and 8, whereas 7, the Co derivative, has an NCoN angle 147.0 (1)° with the possibility of further weak metal ligand interactions that could not be confirmed by 1H NMR. The structures of the silylamine precursors and the lithium salts 1 to 4 provide evidence of crowding through wide SiNSi angles in the case of the former and monomeric or dissociated structures including wide SiNSi angles for 1-4. The species 6 and 7, which were described in a preliminary communication, were the first crystalline, two-coordinate derivatives of iron and cobalt to be reported. In addition, the recently communicated structure of the ion [Ph3SiNSiPh3]- was the first of its kind. It is isoelectronic to [PPN]+ and has short (1.634 Å) Si-N bonds. Crystal data with Mo Kα (λ = 0.71069 Å) radiation at 130 K: HN(SiMePh2)2, C26H27NSi2, a = 13.683 (4) Å, b = 7.953 (1) Å, c = 22.196 (6) Å, β = 104.12 (2)°, Z = 4, monoclinic, space group P21/n, R = 0.039; 1, C34H42LiNO2Si2, a = 17.675 (4) Å, b = 12.111 (3) Å, c = 15.986 (2) Å, β = 107.89 (1)°, Z = 4, monoclinic, space group C2/c, R = 0.044; 2, C44H46LiNO2Si2, a = 24.945 (11)Å, b = 10.296 (3) Å, c = 20.658 (9) Å, β = 134.29 (2)°, Z = 4, monoclinic, space group C2/c, R = 0.048; 3, C34H42LiNO4Si2, a = 11.664 (3) Å, b = 13.971 (6) Å, c = 19.537 (7) Å, Z = 4, orthorhombic, space group Pbcn, R = 0.058; 5, C52H52MnN2Si4, a = 10.893 (1) Å, b = 15.399 (6) Å, c = 27.049 (4) Å, β = 91.73 (1)°, Z = 4, monoclinic P21/c, R = 0.040; 8, C32H44FeN2Si4, a = 15.137 (5) Å, b = 12.996 (4) Å, c = 17.662 (5) Å, β = 90.85 (2)°, Z =4, monoclinic, space group P21/c, R = 0.042.
The compound pictured, an arene-soluble potassium salt of a sterically demanding diazapentadienyl ligand, is accessible in two short steps from commercially available, inexpensive regents. The anion may compete with amidinate or Cp* ligands in solubilizing and controlling the environment of metal ions; it effectively engulfs the potassium ion while appearing to be merely bidentate. Only weak single η5 contacts to substituted phenyl groups link the monomers.
Three low-coordinate metal amides containing the bis(trimethylsilyl)amido group have been characterized by X-ray diffraction and elemental analysis. The molecular structures of [Mn(N(SiMe3)2)3Li(THF)] (1), [Mn2(N(SiMe3)2)4] (2), and [Co2(N(SiMe3)2)4] (3) have the amido group acting as both a bridging and a terminal ligand. The crystal data [Mo Kα (λ = 0.71069 Å)] at 140 K are as follows: (1) a = 11.678 (2) Å, b = 19.362 (2) Å, c = 17.020 (3) Å, β = 108.77 (1)°, Z = 4, space group P21/n; (2) a = 17.997 (2) Å, b = 14.942 (1) Å, c = 18.636 (2) Å, β = 121.24 (1)°, Z = 4 (dimers), space group C2/c; (3) a = 17.907 (3) Å, b = 14.644 (2) Å, c = 18.633 (3) Å, β = 120.47 (2)°, Z = 4 (dimers), space group C2/c. For 1-3 R = 0.031, 0.031, and 0.037, respectively. Complex 1 is the first homoleptic tris(silylamide) of manganese. Both 2 and 3 are dimeric in the solid state. All three complexes exhibit the coordination number 3 at the metal centers.
The syntheses of several first-row transition metal tellurolate derivatives incorporating the sterically encumbered ligand -TeSi(SiMe(3))(3) are described. Metathesis reactions of MCl(2)(dmpe)(2) (M = Cr, Mn, Fe) or CoBr2(PMe(3))(3) with [(THF)(2)LiTeSi(SiMe(3))(3)](2) yield M [TeSi(SiMe(3))(3)](2)(dmpe)(2) and Co[TeSi(SiMe(3))(3)](PMe(3))(3), respectively. Tellurolysis of the transition metal amides M[N(SiMe(3))(2)](2) with HTeSi(SiMe(3))(3) in the presence of Lewis bases yields M[TeSi(SiMe(3))(3)](2)L(2) (M = Mn, L = 4-tert-butylpyridine or 1/2 dmpe (dmpe 1,2-bis(dimethylphosphino)ethane);M = Fe, L = dmpe). The compounds have been characterized by a combination of NMR spectroscopy, magnetic measurements, and elemental analyses. In addition, four derivatives have been structurally characterized by X-ray crystallography. Mn[TeSi(SiMe(3))(3)](2)(dmpe)(2) crystallizes in the space group P2(1)2(1)2(1) with a=13.104(3) Angstrom, b=25.523(6)Angstrom, c=28.504(4)Angstrom, V=9533(5)Angstrom(3), d(calc)=1.33 g cm(-1), Z = 8, R = 3.90%, and R(W) = 3.96%. Crystal data for Fe[TeSi(SiMe(3))(3)](2)(dmpe)(2): space group <P(1)over bar> with a=9.556(2)Angstrom,b=9.814(2)Angstrom, c=32.990(5) A, V=2672.4(8)Angstrom(3), d(calc)=1.37 g cm(-1), Z = 2, R = 6.13%, and R(W)=7.09%. Fe[TeSi(SiMe(3))(3)](Cl)(dmpe)(2) crystallizes in the space group P2(1)/c with a=9.317(2)Angstrom, b=11.898(2)Angstrom, c=32.836(7)Angstrom, V=3637(1)Angstrom(3), d(calc)=1.40 g cm(-1), Z = 4, R=3.31%, and R(W)=3.52%. The crystal structure of Co[TeSi(SiMe(3))(3)](PMe(3))(3) was also determined; it crystallizes in the space group P2(1)/c with a=17.651(5)Angstrom, b=12.435(3)Angstrom, c=17.704(4)Angstrom, V=3418(1) A(3), d(calc)=1.29 g cm(-1), Z = 4, R=5.92%, and R(W)=7.67%
The reactions of the metal amides Mn[N(SiMe3)2]2 and Fe[N(SiMe3)2]2 with the sterically crowded boronous acids Trip2BOH and Mes2BOH (Trip = 2,4,6-i-Pr3C6H2, Mes = 2,4,6-Me3C6H2) afford the compounds [Mn(OBTrip2)(mu-OBTrip2)]2 (1) and [Fe(OBMes2)(mu-OBMes2)]2 (2), which are the first two examples of homoleptic transition-metal boryloxides. The X-ray crystal structures of compounds 1 and 2 have also been determined. The data show that both 1 and 2 are dimeric with three-coordinate Mn and Fe centers that are bound to one terminal boryloxide ligand and to two bridging boryloxide ligands. The M...M distances (3.094 (5) angstrom for Mn and 3.057 (5) angstrom for Fe) are considerably longer than those found in the amide precursors. Surprisingly, the metric features of 1 and 2 are very close to those observed in the closely related bis(aryloxo) complexes [M(OAr)2]2 (Ar = 2,4,6-t-Bu3C6H2, M = Mn (3), Fe (4)). This suggests that the M-O bonding in 1-4 is similar: furthermore, it is mainly ionic and little evidence for a pi-contribution to the M-O bond could be observed. Compounds 1 and 2 have also been characterized by magnetic measurements. Crystallographic data with Mo K-alpha radiation (lambda = 0.71069 angstrom) at 130 K: 1, a = 33.898 (11) angstrom, b = 16.985 (5) angstrom, c = 30.861 (11) angstrom, beta = 134.65 (2)-degrees, Z = 4, R = 0.088, space group C2/c; 2, a = 15.004 (5) angstrom, b = 14.957 (4) angstrom, c = 16.915 (6) angstrom, beta = 93.86 (3)-degrees, Z = 2, R = 0.074, space group P2(1)/n.
The X-ray structural characterization of the iron(II) amides [Fe{N(SiMe3)2}2]2 (1) and [Fe(NPh2)2]2 (2) and the Lewis base adduct Fe[N(SiMe3)2]2(THF) (3), as well as the syntheses of the last two compounds, is described. These complexes are rare examples of the coordination number 3 for iron. Compounds 1 and 2 are both dimeric in the solid state, with each trigonal-planar ion bound to one terminal and two bridging amides. They closely resemble the corresponding Mn(II) and Co(II) compounds. Compound 3 is monomeric in the solid state, with one THF and two amides arranged in a trigonal-planar fashion. The terminal Fe-N bond lengths in 1-3 are similar to those reported for two-coordinate iron(II) amides. The Fe-N bonds in 1 are somewhat longer than those in 2, indicating weaker association in 1. This is borne out in the solution behavior of the two compounds. Thus 1, which was studied by variable-temperature H-1 NMR spectroscopy, was seen to be a monomer in solution at 30-degrees-C. Increasing amounts of the dimer were observed at lower temperature, and calculations based on the monomer-dimer equilibrium indicate an association energy of approximately + 3 kcal mol-1 for [Fe{N(SiMe3)2}2]2. Crystal data with Mo K-alpha (lambda = 0.71069 angstrom) radiation at 130 K: 1, C24H72- Fe2N4Si8, a = 17.978 (4) angstrom, b = 14.691 (4) angstrom, c = 18.564 (5) angstrom, beta = 120.15 (2)-degree, Z = 4, monoclinic, space group C2/c, R = 0.031; 2, C48H40Fe2N4, a = 9.579 (5) angstrom, b = 10.264 (5) angstrom, c = 10.482 (6) angstrom, alpha = 91.78 (4)-degrees, beta = 110.68 (4)-degrees, gamma = 85.67 (4)-degrees, Z = 1, triclinic space group P1BAR, R = 0.039; 3, C16H44FeN2OSi4, a = 11.225 (5) angstrom, b = 13.391 (5) angstrom, c = 17.903 (8) angstrom, Z = 4, orthorhombic, space group Pcan, R = 0.061.
The reactions of the transition-metal amides M[N(SiMe3)2]2 (M = Mn, Fe) with dimesitylphosphane or dimesitylarsane, HPMes2 or HAsMes2, (Mes = 2,4,6-Me3C6H2) have been investigated. For the reactions involving 1 or 2 equiv of HPMes2, the major products are the dimers [M{N(SiMe3)2}(mu-PMes2)]2 (M = Mn (1), Fe (2)). These complexes feature three-coordinate metals with phosphide bridges and terminal amide groups. A similar product, [Mn{N(SiMe3)2}(mu-AsMes2)]2 (3), is obtained from the reaction between Mn[N(SiMe3)2]2 and either 1 or 2 equiv of HAsMes2. When Fe[N(SiMe3)2]2 is treated with 1 or 2 equiv of HAsMes2, however, tetramesityldiarsane, Mes2AsAsMes2, (4), is formed. The X-ray crystal structures of 1-4 were determined by X-ray crystallography. The metal complexes were further characterized by electronic absorption spectroscopy and magnetic data. Variable-temperature H-1 NMR spectroscopy of 1 and 4 is also reported. Crystal data with Mo K-alpha (lambda = 0.71069 angstrom) radiation at 130 K: 1, [Mn{N(SiMe3)2}(mu-PMes2)]2, C48H80Mn2N2P2Si4, a = 20.480 (14) angstrom, b = 11.808 (14) angstrom, c = 23.331 (9) angstrom, beta = 106.39 (4)degrees, Z = 4, monoclinic, space group P21/c, R = 0.053; 2, [Fe{N(SiMe3)2}(mu-PMes2)]2, C48H80Fe2N2P2Si4, a = 12.459 (3) angstrom, b = 19.438 (6) angstrom. c = 24.794 (6) angstrom, alpha = 67.43 (2)degrees, beta = 84.78 (2)degrees, gamma = 80.68 (2)degrees, Z = 4, triclinic, space group P1BAR, R = 0.099; 3, [Mn{N(SiMe3)2}(mu-AsMes2)]2, C48H80As2Mn2N2Si4, a = 20.549 (8) angstrom, b = 11.801 (6) angstrom, c = 23.467 (10) angstrom, beta = 106.01 (3)degrees, Z = 4, monoclinic, space group P2(1)/c, R = 0.070; 4, Mes2AsAsMes2, C36H44As2, a = 8.857 (2) angstrom, c = 39.715 (14) angstrom, Z = 4, tetragonal, space group P4(3)2(1)2, R = 0.072.
The preparation, reaction chemistry and ethylene polymerisation behaviour of low valent β-diketiminato chromium complexes are described. [(DDP)CrCl(µ-Cl)]2 (1) [DDPH = 2-{(2,6diisopropylphenyl)amino}-4-{(2,6-diisopropylphenyl)imino}pent-2-ene] is formed by treatment of CrCl3(THF)3 with LiDDP. Alkylation of 1 with AlMe3 results in the formation of the binuclear dimethyl complex [(DDP)CrMe(µ-Cl)]2 (2). In contrast, the attempted alkylation of 1 with benzylmagnesium chloride results in reduction to form the dichromium(II) complex [(DDP)Cr(µ-Cl)]2 (3). Depending on the conditions of crystallisation, 3 can be obtained as the THF adduct [3(THF)2·THF] or co-crystallised with a molecule of dibenzyl [3·Bz-Bz]. Cleavage of the dimeric unit in 1 can be achieved by the addition of carboxylates or β-diketonates to give [(DDP)CrCl(O2CR)(THF)] (R = Me 4a, Ph 4b) and [(DDP)CrCl({O(R)C}2CH)] (R = Me 5a, Ph 5b), respectively. Single crystal X-ray diffraction studies have been performed on 1, 2, 3(THF)2·THF, 3·Bz-Bz, 4a, and 5b. Complexes 1, 2 and 3(THF)2·THF are dimeric and have molecular C2h symmetry. Complex 3·Bz Bz is also dimeric but has its potential C2h symmetry removed by a significant tetrahedral distortion of the chromium coordination geometry. Compound 4a has an octahedral chromium centre coordinated to a single bidentate diketiminate ligand, a bidentate acetate, a chloride and a THF molecule. Complex 5b has a square pyramidal chromium with apical chloride and basal η2 diketiminate and diketonate ligands. The complex contains strong intramolecular C−H···π stabilising interactions. All the complexes are active in ethylene polymerisation on treatment with suitable aluminium activators, affording high molecular weight polyethylene.
The reaction of 14e [LMeRh(coe)] (1; LMe=ArNC(Me)CHC(Me)NAr, Ar=2,6-Me2C6H3; coe=cis-cyclooctene) with phenyl halides and thiophenes was studied to assess the competition between σ coordination, arene π coordination and oxidative addition of a C−X bond. Whereas oxidative addition of the C−Cl and C−Br bonds of chlorobenzene and bromobenzene to LMeRh results in the dinuclear species [{LMeRh(Ph)(μ-X)}2] (X=Cl, Br), fluorobenzene yields the dinuclear inverse sandwich complex [{LMeRh}2(anti-μ-η4:η4-PhF)]. Thiophene undergoes oxidative addition of the C−S bond to give a dinuclear product. The reaction of 1 with dibenzo[b,d]thiophene (dbt) in the ratio 1:2 resulted in the formation of the σ complex [LMeRh(η1-(S)-dbt)2], which in solution dissociates into free dbt and a mixture of the mononuclear complex [LMeRh(η4-(1,2,3,4)-dbt)] and the dinuclear complex [{LMeRh}2(μ-η4-(1,2,3,4):η4-(6,7,8,9)-dbt)]. The latter could be obtained selectively by the 2:1 reaction of 1 and dbt. Reaction of 1 with diethyl sulfide produces [LMeRh(Et2S)2], which in the presence of hydrogen loses a diethyl sulfide ligand to give [LMeRh(Et2S)(H2)] and catalyses the hydrogenation of cyclooctene.
Regardless of the amount of selenium used, the dihydride 1 (Ar = 2,6- iPr2C6H3) reacts to afford 2. In solution, intermolecular elimination of H2Se takes place with formation of 3, which displays a bridging Al-Se-Al moiety. Compounds 2 and 3 are the first structurally characterized organometallic compounds which contain metal-SeH units.
A short Ga−N bond with double-bond character is displayed by the first monomeric imide of gallium, which was obtained by the reaction of [{HC(MeCDippN)2}M:] (Dipp=2,6-iPr2C6H3, M=Ga; see picture) with N3-2,6-Trip2C6H3 (Trip=2,4,6-iPr3C6H2). The analogous aluminum (M=Al) compound is also readily available.
Recent results (post-1990) on the synthesis and structures of bis(trimethylsilyl)methyls M(CHR2)m (R = SiMe3) of metals and metalloids M are described, including those of the crystalline lipophilic [Na(μ-CHR2)]∞, [Rb(μ-CHR2)(PMDETA)]2, K4(CHR2)4(PMDETA)2, [Mg(CHR2)(μ-CHR2)]∞, P(CHR2)2 (gaseous) and P2(CHR2)4, [Yb(CHR2)2(OEt2)2] and [{Yb(CR3)(μ-OEt)(OEt2)}2]; earlier information on other M(CHR2)m complexes and some of their adducts is tabulated. Treatment of M(CHR2) (M = Li or K) with four different nitriles gave the X-ray-characterized azaallyls or β-diketinimates , and (LL′ = N(R)C(tBu)CHR, L′L′ = N(R)C(Ph)C(H)C(Ph)NR, LL″ = N(R)C(Ph)NC(H)C(Ph)CHR, R = SiMe3 and Ar = C6H3Me2-2,5). The two lithium reagents were convenient sources of other metal azaallyls or β-diketinimates, including those of K, Co(II), Zr(IV), Sn(IV), Yb(II), Hf(IV) and U(VI)/U(III). Complexes having one or more of the bulky ligands [LL′]−, [L′L′]−, [LL]−, [LL″]−, [L″L‴]−, [LL‴]− and [{N(R)C(tBu)CH}2C6H4-2]2− are described and characterized (LL = N(H)C(Ph)C(H)C(Ph)NH, L″L‴ = N(R)C(tBu)C(H)C(Ph)NR, LL‴ = N(R)C(tBu)CHPh). Among the features of interest are (i) the contrasting tetrahedral or square-planar geometry for and , respectively, and (ii) olefin-polymerization catalytic activity of some of the zirconium(IV) chlorides.
Several diorganoscandium complexes stabilized by the -diketiminato ligands (Ar)NC(R)-CHC(R)N(Ar) (Ar) 2,6-iPr-C 6 H 3 ; R) CH 3 (ligand a), R) tBu (ligand b)) have been synthesized. Reaction of the lithium salts of the ligands with ScCl 3 ‚3THF leads to the complexes LScCl 2 (THF) n , which may be readily alkylated to form the dialkyl derivatives. Most are isolated as base-free, four-coordinate complexes. Several have been characterized via X-ray crystallography, and a detailed discussion of their structures is presented. Steric interactions between Ar and the Sc-alkyl groups force the scandium to adopt an out-of-plane bonding mode. In solution, this is manifested via a fluxional process which equilibrates the two diastereotopic alkyl groups and ligand groups as well. The barriers to this process roughly correlate with the steric bulk of the alkyl substituents. At elevated temperatures, the dialkyl derivatives LScR 2 undergo a metalation process whereby one of the alkyl groups is eliminated as RH, and a ligand iPr group is metalated in the methyl position. These reactions are first order in scandium complex, and activation parameters of ∆H q) 19.7(6) kcal mol -1 and ∆S q) -17(2) cal mol -1 K -1 were measured for the loss of Me 4 Si from (Ligb)-Sc(CH 2 SiMe 3) 2 .
An alkane elimination reaction generates the diketiminate compound (TTP)Zr(CH 2 Ph) 3 (1) from Zr(CH 2 Ph) 4 and TTPH (TTPH) 2-p-tolylamino-4-p-tolylimino-2-pentene). The molecular structure of 1 was solved, and it shows a five-coordinate zirconium with three η 1 -coordinated benzyl groups and an η 2 -bound TTP ligand. When 1 is heated to 45 °C in hydrocarbon solvents, toluene is eliminated and the orthometalated product 2 is formed. The molecular structure of 2 indicates η 1 and η 2 benzyl groups. The variable-temperature 1 H NMR (-78 to 50 °C) spectra exhibit a single benzyl resonance. The magnitude of 1 J CH for the benzyl methylene resonance is consistent with a rapid exchange between η 1 and η 2 bonding modes in solution. Isotopic labeling experiments employing (PPP-d 10)Zr(CH 2 Ph) 3 -(3-d 10 , PPP) 2-phenylamino-4-phenylimino-2-pentenato) support direct C-H activation through a four-centered transition state. Based on kinetic experiments, C-H activation is unimolecular, and the rate-limiting step exhibits a large kinetic isotope effect: k H /k D) 5.2-(5) at 65 °C. The thermal stability of alkyl complexes is improved by replacing the ortho protons with isopropyl groups. (DDP)ZrMe 3 (5) can be prepared from (DDP)ZrCl 3 via halide metathesis using MeLi (DDP) 2-(2,6-diisopropyl)phenylamino-4-(2,6-diisopropyl)phe-nylimino-2-pentenato). The thermal stability of 5 is greatly enhanced compared to those of 1 and 3.
Bis[bis(trimethylsilyl)amido]iron(II), Fe[N(SiMe3)2]2, has been prepared from FeBr2(THF)2 and LiN(SiMe3)2. The corresponding Co(II) and Mn(II) amides are known to be dimeric in the crystalline phase, and the Co amide is known to be monomeric in freezing benzene. All three amides are monomeric in the gas phase at 130-150°C/1 Torr. Gas electron diffraction data are consistent with monomers of S4 symmetry (which implies ∠NMN = 180°) and bond distances of Mn-N = 195 (2), Fe-N = 184 (2), and Co-N = 184 (2) pm. Intraligand strain is reduced by opening of the SiNSi angle to 130° and rotation of SiMe3 groups. Comparison with the structures of the amido-bridged dimers of the Mn and Co amides shows that dimer formation is accompanied by significant elongation of the terminal M-N bonds and compression of the SiNSi valence angle of the terminal ligand by about 10°. Both changes are interpreted as evidence for ligand-ligand repulsion in the dimers. SCF MO calculations on high-spin 6A1 Mn(NH2)2 yield an equilibrium bond distance of Mn-N = 193 pm. It is concluded that the monomeric Mn amide is high spin. The SCF calculations suggest that the Mn-N bonding is very polar and that N-Mn pπ-dπ bonding is negligible. The photoelectron (PE) spectra of the Mn and Fe amides have been recorded and assigned. The similarity of the PE spectra of the Fe and Co amides to that of the Mn analogue suggests (but does not prove) that these species are high-spin 2B1 and 3A2, respectively.