Cobalt nickel dimer

Analogously, pyrazolyl-aluminate and -indate ligands have been prepared <75JCS(D)749) and their chelating properties evaluated with cobalt, nickel, copper and zinc. Gallyl derivatives of pyrazoles and indazoles have been extensively studied by Storr and Trotter e.g. 75CJC2944) who determined several X-ray structures of these compounds. These derivatives exist in the solid state as dimers, such as (212) and (288). A NMR study in acetone solution showed the existence of a slow equilibrium between the dimer (212) and two identical tautomers (289) and (290) (Section 4.04.1.5.1) (81JOM(215)157). 

Tn transition Group Villa, complexes of iron, cobalt, nickel and rhodium are active in CO3 dcoxygenation. The reactivity of a series of metal carbonyl anions with carbon dioxide has been found to parallel their relative nucleophilicities. The highly nucleophilic (CpFefCO) ] reacts to form the dimer [CpFefCO) ] 2 and carbonate, whereas (CofCO) ]" is unrcactivc [284]. 

Ethylene for polymerization to the most widely used polymer can be made by the dehydration of ethanol from fermentation (12.1).6 The ethanol used need not be anhydrous. Dehydration of 20% aqueous ethanol over HZSM-5 zeolite gave 76-83% ethylene, 2% ethane, 6.6% propylene, 2% propane, 4% butenes, and 3% /3-butane.7 Presumably, the paraffins could be dehydrogenated catalyti-cally after separation from the olefins.8 Ethylene can be dimerized to 1-butene with a nickel catalyst.9 It can be trimerized to 1-hexene with a chromium catalyst with 95% selectivity at 70% conversion.10 Ethylene is often copolymerized with 1-hexene to produce linear low-density polyethylene. Brookhart and co-workers have developed iron, cobalt, nickel, and palladium dimine catalysts that produce similar branched polyethylene from ethylene alone.11 Mixed higher olefins can be made by reaction of ethylene with triethylaluminum or by the Shell higher olefins process, which employs a nickel phosphine catalyst. 

The first example of homogeneous transition metal catalysis in an ionic liquid was the platinum-catalyzed hydroformylation of ethene in tetraethylammonium trichlorostannate (mp. 78 °C), described by Parshall in 1972 (Scheme 5.2-1, a)) [1]. In 1987, Knifton reported the ruthenium- and cobalt-catalyzed hydroformylation of internal and terminal alkenes in molten [Bu4P]Br, a salt that falls under the now accepted definition for an ionic liquid (see Scheme 5.2-1, b)) [2]. The first applications of room-temperature ionic liquids in homogeneous transition metal catalysis were described in 1990 by Chauvin et al. and by Wilkes et ak. Wilkes et al. used weekly acidic chloroaluminate melts and studied ethylene polymerization in them with Ziegler-Natta catalysts (Scheme 5.2-1, c)) [3]. Chauvin s group dissolved nickel catalysts in weakly acidic chloroaluminate melts and investigated the resulting ionic catalyst solutions for the dimerization of propene (Scheme 5.2-1, d)) [4]. 

Related compounds with other transition metals have been studied only sparsely, e.g., with nickel(II) [198], cobalt(III) [174], and rhodium(lll) [199, 200]. A series of dimeric copper(ll) complexes [[Cu(L BF2)S][X] is also known and exhibits interesting magnetic effects associated with electron spin exchange between the copper(ll) ions [201]. 

The electrochemistry of cobalt-salen complexes in the presence of alkyl halides has been studied thoroughly.252,263-266 The reaction mechanism is similar to that for the nickel complexes, with the intermediate formation of an alkylcobalt(III) complex. Co -salen reacts with 1,8-diiodo-octane to afford an alkyl-bridged bis[Co" (salen)] complex.267 Electrosynthetic applications of the cobalt-salen catalyst are homo- and heterocoupling reactions with mixtures of alkylchlorides and bromides,268 conversion of benzal chloride to stilbene with the intermediate formation of l,2-dichloro-l,2-diphenylethane,269 reductive coupling of bromoalkanes with an activated alkenes,270 or carboxylation of benzylic and allylic chlorides by C02.271,272 Efficient electroreduc-tive dimerization of benzyl bromide to bibenzyl is catalyzed by the dicobalt complex (15).273 The proposed mechanism involves an intermediate bis[alkylcobalt(III)] complex. 

The importance of metal coordination compounds in biological systems has led to the study of polydentate Schilf base complexes of cobalt(II), nickel(II), and copper(II) (204, 205). Dimers have been observed in the spectra of complexes of both tri- and tetradentate ligands [e.g., salicylaldehydeand A,A-bis(salicylidene)ethylenediamine]. The parent ions form the base peaks, and the spectra are characterized... 

The compounds discussed in this section are restricted to nickel, as the existence of palladium (I) or platinum (I) compounds has not been established. Since nickel(I) contains nine d-electrons, analogies with copper(II) might be expected, but these do not arise there are, however, certain similarities with cobalt(O), particularly in the tendency to dimerization. 

Template reactions between malonaldehydes and diamines in the presence of copper(II), nickel(II) or cobalt(II) salts yield neutral macrocyclic complexes (equation 15).99-102 Both aliphatic102 and aromatic101 diamines can be used. In certain cases, non-macrocyclic intermediates can be isolated and subsequently converted into unsymmetrical macrocyclic complexes by reaction with a different diamine (Scheme ll).101 These methods are more versatile and more convenient than an earlier template reaction in which propynal replaces the malonaldehyde (equation 16).103 This latter method can also be used for the non-template synthesis of the macrocyclic ligand in relatively poor yield. A further variation on this reaction type allows the use of an enol ether (vinylogous ester), which provides more flexibility with respect to substituents (equation 17).104 The approach illustrated in equation (15), and Scheme 11 can be extended to include reactions of (3-diketones. The benzodiazepines, which result from reaction between 1,2-diaminobenzenes and (3-diketones, can also serve as precursors in the metal template reaction (Scheme 12).101 105 106 The macrocyclic complex product (46) in this sequence, being unsubstituted on the meso carbon atom, has been shown to undergo an electrochemical oxidative dimerization (equation 18).107... 

Ethylene dimerization catalysis has, however, been more thoroughly investigated for the broader range of homogeneous catalysts. For example, active metal complexes containing titanium, nickel, iron, cobalt, rhodium, ruthenium, and palladium, are all known (133). Where possible, comparisons will be made with the relevant homogeneous catalyst systems. 

Butadiene dimerization catalysts have been quite extensively studied, although the major effort has been concentrated on homogeneous catalyst systems using complexes containing nickel (167), iron (168), cobalt (169), and palladium (170). 

Interest in these ligands stems from a desire to synthesize improved analogues of the cobalamines 100). With this in mind, 2,6-diacetylpyridine was condensed with N,N,N- f ra(aminopropyl)amine in the presence of nickel(II) or eopper(II) to afford the complex of 105, Cobalt(II) and zinc(II) have also been employed as templating agents in the synthesis of 105 101). The reaction of the nickel(II) complex of 105 with acetone results in a dimeric complex, 106101), by a process that is well established for primary amines 102). 

Complexes of 107 have been isolated for copper(II), cobalt(II), and nickel(II) cations103). Condensation of 2,6-diaminopyridine with 108 affords the dimeric macrocycle 111 (70%). No complexes have been reported for ligands 111l08) or 113104 106>. in addition, the reaction of l,3-6is[(l-imino-4,5,6,7-tetrahydro-3-iso-indoline)amino]benzene with 2,6-diaminopyridine gives 113 (70%) 104>107>. 

The formation of a dimerized extracted species was first reported for the extraction of copper(II) with propanoic acid (40, 41). Later, nickel and cobalt were found to be extracted as dimers (22), and a mixed copper(II) carboxylate dimer involving acetate and decanoate was reported (147). More recently, attention has been drawn to the extraction of heteropolynuclear metal carboxylates (90, 91). 

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