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Fragment of the crystal packing of complex 1 illustrating the intermolecular hydrogen bonding pattern.
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The mono-, di-, tri-, tetra- and polynuclear copper(II) triethanolamine (H(3)tea) complexes [Cu(H(2)tea)(N-3)] (1), [Cu-2(H(2)tea)(2)(XC6H4COO)(2)]center dot 2H(2)O (X = 4-H 2a, 4-CH3 2b, 3-Cl 2c), [Cu-3(H(2)tea)(2)-(4-OC6H4COO)(2)(H2O)center dot 4H(2)O (3), [O subset of Cu-4(tea)(4)(BOH)(4)][BF4](2) (4) and [Cu-2(H(2)tea)(2){mu-C6H4(COO)(2)-1,4}(n...
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Context 1
... geometry is completed by an azide ligand trans to the amino nitrogen N1, the N1 À Cu À N2 angle of 177.57(5)8 being essentially linear. The mononuclear units are held together by O À H · · · O intermolecular hydrogen bonds forming a polynuclear network (Figure 2) with the shortest Cu À Cu separation of 4.435(2) , which is in the range of 4 -5 found for the trinuclear clusters of some multicopper oxidases. [23] The Cu À O1 and Cu À O2 lengths of ca. ...
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http://pubs.rsc.org/en/content/articlelanding/2014/ra/c4ra08303b#!divAbstract
Organic and inorganic entities have been hybridized using 3-aminopropyltriethoxysilane (APTES) linker for the synthesis of three novel organic–inorganic hybrid catalysts [Cu(II), Co(II) and Ni(II)]. During the course of the synthesis, the static inorganic moiety was funct...
Citations
... It may be due to that the acid activates the catalyst and accelerates the oxidation reaction through the ligand protonation. [55] Based on the results, the ratio n(HCl)/n(catalyst) = 30 was used in the further experiment. ...
... To explore the mechanism of catalyst catalyzing oxidation of styrene, carbon radical trapping agents, such as CBrCl 3 and TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl) and an oxygen radical trapping agent (Ph 2 NH), were used in the radical reaction in the same molar ratio as the substrate. [55,57] It was found that the reaction could be inhibited when Ph 2 NH was introduced into the reaction system and the repression on the conversion was up to 96.3% (Table 4, Entry 4). The addition of CBrCl 3 and TEMPO leads to a lower inhibition effect, commonly from 50% to 60% (Table 4, Entries 2 and 3). ...
Four coordination compounds, [Cu (Hmthd)2Cl]n (1), [Cu3(mthd)2Br]n (2), [Ag (mthd)]n (3), and [Ag2(mthd)I]n (4) (Hmthd=2‐mercapto‐5‐methyl‐1,3,4‐thiadiazole), were synthesized and characterized by inductively coupled plasma (ICP) elemental analyses, powder X‐ray diffraction (PXRD) and Fourier transform Infra‐red (FT‐IR) spectroscopies. These resulting coordination compounds can act as efficient catalysts for the oxidation of olefins with tert‐butyl hydroperoxide (TBHP) as oxidant. Wherein, compound 2 performed extremely enhanced catalytic activity for oxidation of styrene at 80°C. Moreover, the addition of an appropriate amount of acid can promote the protonation of ligands and activate the two Ag‐containing catalysts to improve their catalytic efficiencies. Experimental results indicate that catalyst 2 has a low activation energy and excellent recycle catalytic property. Radical trap experiments were performed to verify that free radicals participate in the oxidation of styrene.
... 23 It is noteworthy that some copper(II) amino alcoholate complexes have found application in catalysis, 33 as exemplified by their catalytic role in the oxidative transformation of alkanes. [34][35][36] We reported recently on the reactions of zinc(II) quinaldinate with two amino alcohols, 3-amino-1-propanol and 2-methylaminoethanol. 37 Through the use of quinaldinate (abbreviated throughout the text as quin À ), the anionic form of quinaldinic acid (Scheme 1), which usually binds in a N,O-chelating manner and thereby occupies two binding sites in the metal's coordination sphere, the possible reaction outcomes were highly limited. As a follow-up, zinc(II) was replaced with copper(II) which is known for its redox activity. ...
Reactions between [Cu(quin) 2 (H 2 O)] (quin – = the anionic form of quinoline-2-carboxylic acid) and a series of aliphatic amino alcohols have yielded structurally very diverse copper(II) complexes, labelled a – g . The single-crystal X-ray...
... Although in comparison with homogeneous systems such as those reported herein, heterogeneous catalysts offer the advantage of catalyst reuse and recyclability, however, they are more prone to undesirable over-oxidation and the production of side products [4][5][6]. Various homogeneous copper-based catalytic systems have been developed over the years and used to catalyse Cy-H peroxidation at low temperatures with low to moderate yields [7][8][9][10][11][12][13][14][15][16][17][18][19][20]. Table 1 shows the development of homogeneous copper catalysed systems for the mild oxidation of cyclohexane to its products. ...
... Then we studied the influence of varying the oxidant concentration on the catalytic process. The results presented in Fig. 1 [15,[17][18][19]. ...
... An exploration of previous reports on this subject has shown that catalyst concentrations above 1 mol% were associated with slower reactions, decreased conversions supplemented by low turnover values, all of which were attributed to the decomposition of available active sites at higher concentrations of a catalyst [15,18,19,43]. In summary, a precatalyst concentration of 1 mol% was adopted for the remainder of this study. ...
A set of facile room temperature catalytic systems for the oxidation of cyclohexane C–H bonds was developed from in situ generated triazole-functionalised Schiff base copper complexes. The combination of a new triazolium-functionalised Schiff base, [(E)-3-methyl-1-propyl-4-(2-(((2-(pyridin-2-yl)ethyl)imino)methyl)phenyl)-1H-1,2,3-triazol-3-ium hexafluorophosphate(V), 2] with a range of bench-top Cu(I) and Cu(II) salts (Cu2O, CuO, Cu(CH3CN)4PF6, CuSO4·5H2O, Cu2(OAc)4·2H2O, CuCl2, Cu(NO3)2·3H2O) as catalysts were screened under varying reaction conditions for the peroxidation of cyclohexane using hydrogen peroxide as a green source of oxygen. High conversions to oxidised products were obtained with up to 80% in 6 h for the 2/CuSO4·5H2O system at 1 mol% catalyst concentration under optimised reaction conditions. All the copper salts yielded the ketone–alcohol (K–A) oil containing varying ratios of cyclohexanol and cyclohexanone. The results also showed that at room temperature, the various in situ generated copper catalysts exclusively yielded only the K–A oil. Furthermore, by changing the reaction temperature to reflux in acetonitrile and depending on the starting substrate (cyclohexane, cyclohexanol or cyclohexanone), 23–100% of adipic acid was also obtained. The kinetics study for the peroxidation reaction reveals activation energy of 12.29 ± 2 kJ/mol following a copper initiated radical mechanism.
Graphic Abstract
... Owing to the intrinsic inertness of C-H bonds, harsh reaction conditions are often required at high temperatures and pressures [10], while particulate methane monooxogenase (pMMO), an enzyme that bears a multicopper cluster with an N,O-environment, constitutes a paradigmatic example of a catalyst for selective C-H oxidation under mild conditions [11,12]. Some monomeric, dimeric, trimeric, and tetrameric copper complexes have been tested as catalysts for the oxidative reaction of cyclohexane [13][14][15][16][17][18][19]. The type of ligand and the configuration of the complexes play crucial roles in the catalytic performance of copper complexes. ...
The mixed-ligand copper(II) iminodiacetates [Cu(ida)(2-mim)(H2O)2]·H2O (1), [Cu(ida)(2-mim)2]·2H2O (2), [Cu(ida)(2-mim)(H2O)]n·4.5nH2O (3), and [Cu2(ida)2(2-mim)2]n·nH2O (4) (H2ida = iminodiacetic acid, 2-mim = 2-methylimidazole) were obtained from neutral or alkaline solutions at different temperatures. The novel complex 4 contains very small holes with diameters of 2.9 Å, which can adsorb O2 selectively and reversibly between 1.89 to 29.90 bars, compared with the different gases of N2, H2, CO2, and CH4. This complex is stable up to 150 °C based on thermal analyses and XRD patterns. The four complexes show catalytic activities that facilitate the conversion of cyclohexane to cyclohexanol and cyclohexanone with hydrogen peroxide in a solution. The total conversion is 31% for 4.
... The chemistry of 3d-metal clusters has attracted continuing interest from many groups around the world, [1][2] due to the aesthetically pleasing structures that many such complexes exhibit, [3][4] and relevance of these clusters to catalysis, [5][6][7][8][9][10][11] luminescence, [12][13] magnetism [14][15][16][17][18][19][20] and metal-containing proteins in biology. [21][22][23][24] Among the many 3d-metal clusters being studied, the Co II and Zn II clusters with cubane structures or containing cubane motiff have received particular interest, because many such Co II complexes [25][26][27][28] dispay Single-molecule magnetic (SMM) behaviors and some Zn II cubanes exhibit facinating photoluminescient properties. ...
The employment of 1‐((2‐hydroxybenzylidene)amino)‐2,3‐dihydro‐1H‐inden‐2‐ol (H2L) in ZnII and CoII coordination chemistry is reported. Two complexes of compositions [Zn4L4] (1) and [Co4L4] (2) have been synthesized under solvothermal conditions, and fully characterized by X‐ray single crystal diffraction, IR and elemental analysis. They both possess a defect dicubane core. The luminescence studies suggest strong emission for 1 in the solid state at room temperature. Variable temperature (2.0–300 K) magnetic studies for 2 indicate weak ferromagnetic CoII⋅⋅⋅CoII exchange interactions.
... Peroxidative oxidation of alkanes is a promising approach for the synthesis of the corresponding alcohols and ketones. In particular, oxidation with environmentally friendly oxidants, such as hydrogen peroxide (H2O2) or dioxygen [68][69][70][71], is a topic of great interest, and the use of copper complexes as catalysts [19,28,44,45,47,48] is particularly promising. However, the catalytic efficiency has still to be improved, which accounts for another aim of the current study. ...
... Moreover, in view of the multi-copper nature of particulate methane monooxygenase (pMMO), an enzyme that catalyzes the oxidation of alkanes to alcohols, particular attention [47][48][49][50][72][73][74][75] should be paid to multinuclear copper catalysts, a topic which also concerns this work. ...
... For shorter reaction times, such a behavior supports the predominance of a non-free radical pathway conceivably associated with a metal-centered oxidant instead of a free HO • radical [58]. Various mechanistic possibilities can be postulated [47,48,57,58]. ...
Reaction of the o-[(o-hydroxyphenyl)methylideneamino]benzenesulfonic acid (H2L) (1) with CuCl2·2H2O in the presence of pyridine (py) leads to [Cu(L)(py)(EtOH)] (2) which, upon further reaction with 2,2’-bipyridine (bipy), pyrazine (pyr), or piperazine (pip), forms [Cu(L)(bipy)]·MeOH (3), [Cu2(L)2(μ-pyr)(MeOH)2] (4), or [Cu2(L)2(μ-pip)(MeOH)2] (5), respectively. The Schiff base (1) and the metal complexes (2–5) are stabilized by a number of non-covalent interactions to form interesting H-bonded multidimensional polymeric networks (except 3), such as zigzag 1D chain (in 1), linear 1D chain (in 2), hacksaw double chain 1D (in 4) and 2D motifs (in 5). These copper(II) complexes (2–5) catalyze the peroxidative oxidation of cyclic hydrocarbons (cyclooctane, cyclohexane, and cyclohexene) to the corresponding products (alcohol and ketone from alkane; alcohols, ketone, and epoxide from alkene), under mild conditions. For the oxidation of cyclooctane with hydrogen peroxide as oxidant, used as a model reaction, the best yields were generally achieved for complex 3 in the absence of any promoter (20%) or in the presence of py or HNO3 (26% or 30%, respectively), whereas 2 displayed the highest catalytic activity in the presence of HNO3 (35%). While the catalytic reactions were significantly faster with py, the best product yields were achieved with the acidic additive.
... Adding a small amount of nitric acid (20 mM) in the oxidation solution, increased the yield slightly and shows some tuning ability toward the alcohol product is possible; similar results were found in solution. 31 However, we found an easy alternative method by using methanolic NaBH 4 in the washing step (by sonication for 5 min) of the copper-catalyzed oxidized surfaces. This yielded further a reduction in the water static contact angle to 72 ± 2° (Table S1). ...
Plastics, such as cyclic olefin copolymer (COC), are becoming an increasingly popular material for microfluidics. COC is used, in part, because of its (bio)-chemical resistance. However, its inertness and hydrophobicity can be a major downside for many bioapplications. In this paper, we show the first example of a surface-bound selective C-H activation of COC into alcohol C-OH moieties under mild aqueous conditions at room temperature. The nucleophilic COC-OH surface allows for subsequent covalent attachments, such as of a H-terminated silane. The resulting hybrid material (COC-Si-H) was then modified via a photolithographic hydrosilylation in the presence of ω-functionalized 1-alkenes to form a new highly stable, solvent-resistant hybrid surface.
... Complexes of TEA with metal salts possess catalytic activity and can be used as selective catalysts for the peroxidative oxidation of alkanes under mild conditions [34,35], as efficient catalysts for the hydroxylation of aryl iodides and bromides in water [36], and for selective oxidation of alkylarenes to phenyl ketones under mild reaction conditions [37]; and as catalysts of electrochemical reduction of oxygen [38]. ...
Two new zinc-containing complexes [Zn2(TEA)(C6H5COO)3] (1) and ([Zn(TEA)(H2O)2]SO4)·H2O (2) were synthesized and characterized by IR spectroscopy, elemental analysis, DSC and TG analysis. Their structure was determined by single-crystal X-ray diffraction. In the binuclear, mixed-ligand [Zn2(TEA)(C6H5COO)3] complex, one zinc atom is six-coordinated by nitrogen and three oxygen atoms of tetradentate triethanolamine (TEA) and two oxygen atoms of two different benzoate ligands, forming the distorted octahedron of the ZnNO5 type. The second zinc atom is five-coordinated, forming the distorted trigonal bipyramid. Two zinc atoms are bridged by two carboxylate groups of two benzoate ligands and one oxygen atom of the deprotonated hydroxyethyl group of TEA. Cationic complex 2 consists of [Zn(TEA)(H2O)2]²⁺ cations and SO4²⁻ anions. The coordination polyhedron around the zinc atom corresponds to a distorted octahedron (ZnNO5 type). The TEA ligand is tetradentately coordinated to the cation, forming three chelate rings. The coordination sphere of the Zn cation is completed by two aqua ligands.
... In order to attempt to increase the activity of R-Cu 2+ in the solvent-free MW-assisted peroxidative oxidation of 1-phenylethanol, we have investigated the influence of different additives (co-catalysts ) on the acetophenone product yield (Fig. 4). For this purpose, heteroaromatic N-based acids, such as 2-pyridinecarboxylic acid (Hpic) and 2-pyrazinecarboxylic acid (Hpca), or bases such as pyridine , 3,5-dimethyl-1H-pyrazole, pyridazine, piperidine and triethylamine were tested, since they have been reported [54][55][56][57][58][59][60][61]to act as promoters in peroxidative oxidations of cyclic, linear and branched saturated hydrocarbons and alcohols (primary and secondary ones). The heteroaromatic N-based acids, Hpic and Hpca, demonstrated an inhibitory effect on the reaction, and e.g. the presence of 200 lM of acid (Hpic and Hpca) ((n(acid)/(n(catalyst R-Cu 2+ )) = 20) results in an important yield drop (5% and 6%, Fig. 4 , entries 2 and 3, respectively) compared to the reaction carried out under the same conditions (10 lM of catalyst, 80 °C, MW, 1 h) but in the absence of any additive (30%, Fig. 4 , entry 1). ...
... Mild peroxidative oxidation over copper triethanolamine complexes achieves II/III yields and TONs up to 39% (total) and 380, respectively, which exceeds the activity of most other copper catalysts. 235 In the presence of methyltrioxorhenium (MTO), cyclohexane is oxidized by anhydrous H 2 O 2 in acetonitrile in air to give CHHP as the main product. 236 The incorporation of organic metal complexes into molecular sieves pores and cavities, leading to systems that mimic the unique characteristics of enzymes, are also used to oxidize cyclohexane 237 (cfr. ...
Adipic acid, which is a very important commodity chemical, is traditionally manufactured industrially by an aged and unsustainable multistep process that involves homogeneous catalysts, aggressive oxidants (concentrated nitric acid) and the production of large quantities of the greenhouse gas nitrous oxide. Much research and development into alternative and cleaner process routes to adipic acid have been carried out over the past 70 years. Improved reaction schemes have invoked variations in fossil raw materials (from benzene and phenol to cyclohexane, cyclohexanol, cyclohexanone, cyclohexene, butadiene, and adiponitrile, etc.), oxidants (O2, air, H2O2, t-BuOOH, ozone), catalysts (homogeneous, heterogeneous, phase transfer, biomimetic) and reaction conditions (low temperature, atmospheric pressure, and solvent-, metal-, halide-, and corrosion-free). No single proposed alternative pathway—some of which are purely academic—simultaneously addresses the problems of petrochemical origin, toxic starting materials or reagents, generation of environmentally incompatible byproducts, use of forcing reaction conditions, and cost in an entirely satisfactory manner, despite very intense efforts. Recently, more benign bio-based reaction pathways have been proposed starting from renewables, such as glucose or vegetable oils (which will be discussed in Part 2 of this series).
