Cobalt dimers, transition metal compound

An improvement of catalyst activity, especially for the oxidation of electron-poor, deactivated systems like p-toluic acid, can be reached by addition of other transition metal compounds to the Co/Mn/Br catalyst. The most prominent additive is zirconium(IV) acetate, which by itself is totally inactive. An addition of zirconi-um(IV) acetate (ca. 15 % of the amount of cobalt) can yield reaction rates which are higher than those observed using a tenfold amount of cobalt acetate. This amazing co-catalytic effect can be attributed to the common ability of zirconium to attain greater than sixfold coordination in solution, to the high stability of Zr toward reduction, and to the ability of zirconium or Hf to redistribute the dimer/ monomer equilibrium of dimerized cobalt acetates (Co 7Co, Co VCo " systems) by forming a weak complex with the catalytically more active monomeric Co species [17]. 

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]. 

Among the most significant developments in the field of catalysis in recent years have been the discovery and elucidation of various new, and often novel, catalytic reactions of transition metal ions and coordination compounds 13, 34). Examples of such reactions are the hydrogenation of olefins catalyzed by complexes of ruthenium (36), rhodium (61), cobalt (52), platinum (3, 26, 81), and other metals the hydroformylation of olefins catalyzed by complexes of cobalt or rhodium (Oxo process) (6, 46, 62) the dimerization of ethylene (i, 23) and polymerization of dienes (15, 64, 65) catalyzed by complexes of rhodium double-bond migration in olefins catalyzed by complexes of rhodium (24,42), palladium (42), cobalt (67), platinum (3, 5, 26, 81), and other metals (27) the oxidation of olefins to aldehydes, ketones, and vinyl esters, catalyzed by palladium chloride (Wacker process) (47, 48, 49,... 

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