Turning on ROP activity in a bimetallic Co/Zn complex supported by a [2+2] Schiff-base macrocycle
Abstract and Figures
The homo-dinuclear complexes [(MLBr)][MBr3(NCMe)]·MeCN (M = Co or Zn), where LH2 = {[2-(OH)-5-R)-C6H2-1,3-(CH)2][O(2-C6H4N)2]}2 (R = Me, tBu) were found to be inactive for the ring opening polymerization (ROP) of the...
![Figure S1. Molecular structure of minor orange product [CoBrL Me ][CoBr3(NCMe)]·4MeCN (1Me·](https://www.researchgate.net/publication/335214543/figure/fig1/AS:11431281103091085@1669608677191/Figure-S1-Molecular-structure-of-minor-orange-product-CoBrL-Me-CoBr3NCMe4MeCN_Q320.jpg)
![Figure S3. Molecular structure of [ZnBrL Me ][ZnBr3(NCMe)]·MeCN (3Me·MeCN). Thermal ellipsoids are](https://www.researchgate.net/publication/335214543/figure/fig2/AS:11431281103122236@1669608677349/Figure-S3-Molecular-structure-of-ZnBrL-Me-ZnBr3NCMeMeCN-3MeMeCN-Thermal_Q320.jpg)
![Figure S4. Molecular structure of [ZnBrL tBu ][ZnBr3(NCMe)]·MeCN (3tBu·MeCN). Solvent omitted for](https://www.researchgate.net/publication/335214543/figure/fig3/AS:11431281103103542@1669608677597/Figure-S4-Molecular-structure-of-ZnBrL-tBu-ZnBr3NCMeMeCN-3tBuMeCN-Solvent_Q320.jpg)
![Figure S5. Molecular structure of [CoBrL tBu ][Co0.68Zn0.32Br3(NCMe)]·0.25MeCN (4tBu·0.25MeCN)](https://www.researchgate.net/publication/335214543/figure/fig4/AS:11431281103131906@1669608677731/Figure-S5-Molecular-structure-of-CoBrL-tBu-Co068Zn032Br3NCMe025MeCN_Q320.jpg)
![Figure S6. Molecular structure of [CoL Me (NCMe)(µ-Br)ZnBr]·3MeCN (5Me·3MeCN).](https://www.researchgate.net/publication/335214543/figure/fig5/AS:11431281103097958@1669608678607/Figure-S6-Molecular-structure-of-CoL-Me-NCMe-BrZnBr3MeCN-5Me3MeCN_Q320.jpg)
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... Homo-dinuclear Co and Zn complexes and the heterobimetallic Co-Zn complex bearing Schiff base macrocycles (Fig. 34) and their application in d-valerolactone (VL) and CL ROP were reported by Redshaw's group. [93] The synthesis of homodinuclear complexes was that Schiff base macrocycle reacted with ZnBr 2 and CoBr 2 , respectively, to form complex 77 and complex 78. Complex 78 reacted with Me 2 Zn to form hetero-bimetallic Co-Zn complex 79. ...
Multinuclear metal complexes can effectively improve the catalytic activity of catalysts for ring-opening polymerization (ROP) of cyclic esters. If the catalytic metal centers are close enough to each other, they divide the labor of coordination-insertion reactions in polymerization processes. If the catalytic metal centers are too far apart, and the ligands connecting the catalytic metal centers can have resonance, their positive charge properties affect each other and thus affect the catalytic polymerization reaction in the same manner that electron-withdrawing groups do. This review focused on recent reports of multinuclear metal catalysts in ROP that exhibited higher catalytic activity than did mononuclear metal catalysts. The dilemma faced by the development of novel multinuclear metal complexes, and the strategies and the attention for designing catalysts are also provided.
... Mixed Zn/Co heterobimetallic complexes upheld by [2+2] Schiff base macrocycles (63 and 64, Fig. 13) [124] have been accounted for. These complexes demonstrated effective action in the ROP of ε-CL and δ-VL at 130 ºC within the sight of BnOH as co-activator. ...
The advancement of direct synthetic approaches toward the controllable synthesis of multimetallic complexes turns into an earlier and significant undertaking before the inside and out investigations of novel properties and functions of multimetallic complexes. As an elective methodologies for the synthesis of multimetallic complexes have incorporated the utilization of large macrocycles with more than one binding site and furthermore the connecting of macrocycles through interfacing units. This review highlights the arising patterns in the synthesis and uses of multimetallic macrocyclic complexes, including bi- and tri-metallic gatherings just as bigger obvious metal clusters and polymeric species.
... Schiff base macrocycles are considered as "privileged ligands" 14 because of their ease of preparation, i.e., condensation between aldehydes/ketones and amines to form the "−RC=N−" linkage. This has led to the Schiff base chemistry receiving much attention over the years, and such compounds have been widely employed in luminescence sensing, 15 biomaterial, 16 catalytic chemistry, 17 and so on. Of note is the discovery by Ni et al. of a Schiff base macrocyclic host that can serve as a probe for Cu 2+ and Fe 3+ ion sensing. ...
Different combinations of organomagnesium reagents and zinc bromide react with either 1,3-dimethoxy-4-tert-butylcalix[4]areneH2 (L(OMe)2H2) or trialkoxycalix[4]arenes (L(OR)3H) (R = n-Pr, n-pentyl) to afford mixed-metal calix[4]arene systems. Intruiging molecular structures are formed...
The first-row transition-metal ions Mn2+-Cu2+ could serve as effective templates to construct three types of double-[1 + 1], [2 + 2], and [1 + 1] Schiff-base dinuclear macrocyclic complexes in the presence of dialdehydes with different pendant arms and a common 1,8-diamine. The extremely flexible nature of macrocyclic ligands allows for the multiple template-directed syntheses, but the final products could be finely tuned by the subtle variations of Mn2+-Cu2+ ions in a 3d-electronic configuration, radius, and coordination number/geometry as well as the auxiliary (pendant-armed and anionic) template effect at the same time. Two borderlines are observed at the Co2+ ion for forming double-[1 + 1] and [2 + 2] metallacycles involving the H2pdd precursor and the [1 + 1] Cu2+ complex for double-[1 + 1] and [2 + 2] macrocycles containing the H2hpdd unit, respectively. The structural diversity is originated from the non-perfect match between [1 + 1]/[2 + 2] Schiff-base macrocycles and dinuclear metal centers; hence, a compromise between the metal coordination modes and alterations of the ligand conformation takes place.
The solvothermal reaction of Zn(NO3)2·6H2O with 5-aminoisophthalic acid and 4,4/-bipyridyl (4,4/-bipy) led to the self-assembly of the known 3-D hybrid H-bonded/covalent structure {[Zn(5-AIP)(4,4/-bipy)0.5]·DMF}n (1·DMF), but with DMF here (rather than...
In this research, two new 1D coordination polymers of Mn(II), [Mn(LH)2(µ1,5-dca)2]n (1) and [Mn(LH)2(µ1,3-N3)(CH3OH)(N3)]n (2) were synthesized and characterized by elemental analysis, spectroscopic methods, single crystal X-ray analysis and magnetic measurements (LH = 1-[(E)-(5-chloro-2-pyridyl)iminiomethyl]-2-naphtholate). These compounds were synthesized by the reaction of LH, MnCl2·4H2O and NaN(CN)2 (for compound 1) or NaN3 (for compound 2) in 1:1:2 M ratio in methanol. The spectroscopic and structural studies indicated that strong intramolecular proton transfer from naphtholic oxygen to the imine nitrogen is occurred in the ligand and due to this; the nitrogen atom of imine functionality is not coordinated to the metal core. As a result, the ligand is coordinated to the metal core as monodentate neutral ligand. The proton transfer process was attributed to the strong electron withdrawing properties of 5-chloropyridine ring. In the structure of compound 1 and 2, the manganese ions are connected to each other through µ1,5-dca and µ1,3-azide bridges, respectively to form 1D coordination polymers. The magnetic measurements showed the presence of antiferromagnetic interactions between Mn∙∙∙Mn cores in both of the obtained 1D coordination polymers, whereat the exchange interaction is an order of magnitude stronger in azido compared to dicyanamido bridged compound (–3.7 cm⁻¹ vs. –0.30 cm⁻¹).
Reaction of [2+2] and [6+6] Schiff-base macrocycles with FeBr2 are reported, together with preliminary studies of the applications of the iron-containing products. In particular, we have investigated peroxidase-like activity and determination of H2O2, as well as their ability to act as catalysts for ring opening polymerization of cyclic esters.
The ring-opening copolymerization of carbon dioxide and epoxides is a useful means to make aliphatic polycarbonates and to add-value to CO 2 . Recently, the first heterodinuclear Zn(ii)/Mg(ii) catalyst showed greater activity than either homodinuclear analogue (J. Am. Chem. Soc.2015, 137, 15078-15081). Building from this preliminary finding, here, eight new Zn(ii)/Mg(ii) heterodinuclear catalysts featuring carboxylate co-ligands are prepared and characterized. The best catalysts show very high activities for copolymerization using cyclohexene oxide (TOF = 8880 h ⁻¹ , 20 bar CO 2 , 120 °C, 0.01 mol% catalyst loading) or cyclopentene oxide. All the catalysts are highly active in the low pressure regime and specifically at 1 bar pressure CO 2 . The polymerization kinetics are analysed using in situ spectroscopy and aliquot techniques: the rate law is overall second order with a first order dependence in both catalyst and epoxide concentrations and a zero order in carbon dioxide pressure. The pseudo first order rate coefficient values are compared for the catalyst series and differences are primarily attributed to effects on initiation rates. The data are consistent with a chain shuttling mechanistic hypothesis with heterodinuclear complexes showing particular rate enhancements by optimizing distinct roles in the catalytic cycles. The mechanistic hypothesis should underpin future heterodinuclear catalyst design for use both in other (co)polymerization and carbon dioxide utilization reactions.
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Schiff base macrocycles are emerging as useful scaffolds for binding two or more catalytic metals in close proximity. Such coordination chemistry allows for the evaluation of potentially beneficial catalytic cooperative effects. In the field of ring opening polymerization (ROP) of cyclic esters, only a handful of metal systems bound by Schiff base [2 + 2] type macrocycles have been studied. Nevertheless, results to date have, for certain metals, identified some interesting structure activity relationships, whilst for other systems results have revealed particular combinations of metals and macrocycles to be virtually inactive. This perspective review takes a look at two types of recently-reported Schiff base macrocycles that have been employed as pro-ligands in the metal-catalyzed ROP of cyclic esters, specifically ε-caprolactone and rac-lactide.
The preparation of heterodinuclear complexes, especially those comprising early-late transition metals coordinated by a simple or symmetrical ancillary ligand, represents a fundamental challenge and an opportunity to prepare catalysts benefitting from synergic properties. Here, two new mixed titanium(iv)-zinc(ii) complexes, [LTi(O(i)Pr)2ZnEt] and [LTi(O(i)Pr)2ZnPh], both coordinated by a diphenolate tetra(amine) macrocyclic ligand (L), are prepared. The synthesis benefits from the discovery that reaction of the ligand with a single equivalent of titanium tetrakis(iso-propoxide) allows the efficient formation of a mono-Ti(iv) complex, [LTi(O(i)Pr)2]. All new complexes are characterized by a combination of single crystal X-ray diffraction, multinuclear NMR spectroscopy and mass spectrometry techniques. The two heterobimetallic complexes, [LTi(O(i)Pr)2ZnEt] and [LTi(O(i)Pr)2ZnPh], feature trianionic coordination by the macrocyclic ligand and bridging alkoxide groups coordinate to both the different metal centres. The heterodinuclear catalysts are compared to the mono-titanium analogue, [LTi(O(i)Pr)2], in various polymerization reactions. In the alternating copolymerizations of carbon dioxide and cyclohexene oxide, the mono-titanium complex is totally inactive whilst the heterodinuclear complexes show moderate activity (TOF = 3 h(-1)); it should be noted the activity is measured using just 1 bar pressure of carbon dioxide. In the ring opening polymerization of lactide and ε-caprolactone, the mono-Ti(iv) complex is totally inactive whilst the heterodinuclear complexes show moderate-high activities, qualified by comparison to other known titanium polymerization catalysts (l-lactide, kobs = 11 × 10(-4) s(-1) at 70 °C, 1 M in [lactide]) and ε-caprolactone (kobs = 5 × 10(-4) s(-1) at 70 °C, 0.9 M in [ε-caprolactone]).
The molecular structures of a number of solvates of the [2 + 2] Schiff-base macrocycles {[2-(OH)-5-(R)-C6H2-1,3-(CH)2][O(2-C6H4N)2]}2 (R = Me L(1)H2, tBu L(2)H2, Cl L(3)H2), formed by reacting 2,6-dicarboxy-4-R-phenol with 2,2'-oxydianiline (2-aminophenylether), (2-NH2C6H4)2O, have been determined. Reaction of L(n)H2 with two equivalents of AlR'3 (R' = Me, Et) afforded dinuclear alkylaluminium complexes [(AlR'2)2L(1-3)] (R = R' = Me (), R = tBu, R' = Me (), R = Cl, R' = Me (), R = Me, R' = Et (), R = tBu, R' = Et (), R = Cl, R' = Et ()). For comparative studies, reactions of two equivalents of AlR'3 (R' = Me, Et) with the macrocycle derived from 2,2'-ethylenedianiline and 2,6-dicarboxy-R-phenols (R = Me L(4)H2, tBu L(5)H2) were conducted; the complexes [(AlMe)(AlMe2)L(5)]·2¼MeCN (·2¼MeCN) and [(AlEt2)2L(4)] () were isolated. Use of limited AlEt3 with L(3)H2 or L(5)H2 afforded mononuclear bis(macrocyclic) complexes [Al(L(3))(L(3)H)]·4toluene (·4toluene) and [Al(L(5))(L(5)H)]·5MeCN (·5MeCN), respectively. Use of four equivalents of AlR'3 led to transfer of alkyl groups and isolation of the complexes [(AlR'2)4L(1'-3')] (R = L(2'), R' = Me (); L(3'), R' = Me (); L(1'), R' = Et (); L(2'), R' = Et (); L(3'), R' = Et ()), where L(1'-3') is the macrocycle resulting from double alkyl transfer to imine, namely {[2-(O)-5-(R)C6H2-1-(CH)-3-C(R')H][(O)(2-(N)-2'-C6H4N)2]}2. Molecular structures of complexes ·2¼MeCN, , ·4toluene, ·5MeCN and ·1¾toluene·1¼hexane are reported. These complexes act as catalysts for the ring opening polymerisation (ROP) of ε-caprolactone and rac-lactide; high conversions were achieved over 30 min at 80 °C for ε-caprolactone, and 110 °C over 12 h for rac-lactide.
Understanding how to moderate and improve catalytic activity is critical to improving degradable polymer production. Here, di- and monozinc catalysts, coordinated by bis(imino)diphenylamido ligands, show remarkable activities and allow determination of the factors controlling performance. In most cases, the dizinc catalysts significantly out-perform the monozinc analogs. Further, for the best dizinc catalyst, the ligand conformation controls activity: the catalyst with "folded" ligand conformation shows turnover frequency (TOF) values up to 60 000 h(-1) (0.1 mol % loading, 298 K, [LA]=1 m), whilst that with a "planar" conformation is much slower, under similar conditions (TOF=30 h(-1) ). Dizinc catalysts also perform very well under immortal conditions, showing improved control, and are able to tolerate loadings as low as 0.002 mol % whilst conserving high activity (TOF=12 500 h(-1) ).
A series of heterodinuclear complexes are reported where both Zn(II) and a metal from Group 1 or 2 are chelated by a macrocyclic diphenolate-tetra-amine ligand. The complexes are characterized in the solid state, where relevant by single crystal X-ray crystallography and elemental analysis, and in solution, using NMR spectroscopy and mass spectrometry. The complex synthesis is achieved by reaction of the ligand with diethyl zinc to form the monozinc complex, in situ, followed by subsequent coordination of the second metal; this method enables heterodinuclear conversions >90% as determined by NMR spectroscopy. Alternatively, the same heterodinuclear complexes are accessed by reaction between the two homodinuclear complexes at elevated temperatures for extended periods. These findings suggest that most of the heterodinuclear complexes are the thermodynamic reaction products; the only exception is the Na(I)/Zn(II) complex which is unstable with respect to the homodinuclear counterparts. The catalytic activities and selectivity of the stable heterodinuclear complexes are compared, against each other and the relevant homodinuclear analogues, for the ring-opening copolymerization of CO2 and CHO. Nearly all the heterodinuclear complexes are less active than the dizinc analogues, but the Mg(II)/Zn(II) catalyst is more active. The co-ligand influences the product selectivity, with iodide ligands resulting in cyclic carbonate formation and carboxylate ligands giving a high selectivity for polycarbonate.
This perspective review discusses metallocalix[n]arene complexes that have been employed in either α-olefin polymerization or in the ring opening polymerization (ROP) of cyclic esters over the last 5 years. Synthesis, molecular structure and catalytic potential are discussed. For α-olefin polymerization, systems based on early transition metals in combination with calix[n]arenes (n = 4, 6 or 8), depleted calix[4]arenes or thia/sulfinyl/sulfonyl calix[4]arenes have been reported, and in some cases, are highly active. For the ROP studies, a number of the systems, typically of the early transition metals, only exhibit activity under robust conditions, whereas other systems, for example those of magnesium, demonstrate exceptional activity, immortal behaviour and intriguing stereoselectivity.
Homodinuclear catalysts have good precedent for epoxide and carbon dioxide/anhydride copolymerizations; in contrast, so far pure heterodinuclear catalysts are unknown. The synthesis and properties of a heterodinuclear Zn(II)/Mg(II) complex coordinated by a symmetrical macrocyclic ligand are reported. It shows high polymerization selectivity, control, and significantly greater activity compared to either of the homodinuclear analogues or any combinations of them. Indeed, compared to a 50:50 mixture of the homodinuclear complexes, it shows 5 times (CO2/epoxide) or 40 times (anhydride/epoxide) greater activity.
The [2 + 2] Schiff-base macrocycles [2,2'-(CH2CH2)(C6H4N[double bond, length as m-dash]CH)2-2,6-(4-RC6H2OH)]2 ((R)H2), upon reaction with MnCl2 (two equivalents) afforded the bimetallic complex [Cl3Mn(μ-Cl)Mn((Me)H2)] () or the salt complex [Cl3Mn(NCMe)][MnCl((tBu)H2)] (). Under similar conditions, use of the related [2 + 2] oxy-bridged macrocycle [2,2'-O(C6H4N[double bond, length as m-dash]CH)2-4-RC6H2OH] ((R)H2), afforded the bimetallic complexes [(MnCl)2(R)] (R = Me , tBu ), whilst the macrocycle derived from 1,2-diaminobenzene and 5,5'-di-tert-butyl-2,2'-dihydroxy-3,3'-methylenedibenzaldehyde (H4) afforded the complex [(MnCl)2()]·2MeCN (·2MeCN). For comparative studies, the salt complexes [2,6-(ArNHCH)2-4-MeC6H2O][MnCl3(NCMe)] (Ar = 2,4-Me2C6H3, ) and {[(2-ArN[double bond, length as m-dash]CH),6-(ArNHCH)-4-Me-C6H2O]MnCl}2[MnCl4]·8CH2Cl2 (Ar = 4-MeC6H4, ·8CH2Cl2) were prepared. The crystal structures of are reported (synchrotron radiation was necessary for complexes , and ). Complexes (not ) were screened for their potential to act as pre-catalysts for the ring opening polymerization (ROP) of ε-caprolactone; , and , were inactive, whilst and exhibited only poor activity with low conversion (<15%) at temperatures above 60 °C.