Cyclohexene catalysts, cobalt complexes

The catalytic conversion of trons-1,2-dibromocyclohexane (DBCH) to cyclohexene with macrocyclic cobalt complexes [6, 58] was used as a probe to investigate the kinetics of mediated electrochemical reactions in microemulsions. The P/Q catalyst couples were macrocyclic cobalt complexes Co L/Co L such as cobalt corrins, salen, porphyrins, and phthalocyanines. 

Turnover rates for the reduction of DBCH to cyclohexene mediated by the PLL-Co film in bicontinuous SDS microemulsions were controlled by the difference between the reduction potential of the reactant and E° of the catalyst in the film, similar to dissolved cobalt complex catalysts. High conductivity and low viscosity of the bulk microemulsion also facilitated fast catalyst turnover. 

Phosphinecarbonyl complexes of cobalt have long been known to act as hydrogenation catalysts. In a recent study involving cyclohexene the kinetics of its hydrogenation by the complex [CoH(CO)2(PBun3)2] were studied. Unlike the systems described above, the carbonyl complexes generally require elevated temperature and pressure. The proposed mechanism is given in Scheme 6. 

Example 11.1. Hydroformylation of cyclohexene with phosphine-substituted cobalt hydrocarbonyl catalyst. The most probable network of cyclohexene hydroformylation catalyzed by a phosphine-substituted cobalt hydrocarbonyl is shown on the facing page. HCo(CO)3Ph (cat) is in equilibrium with the CO-deficient HCo(CO)2Ph (cat ) and CO. For greater generality, quasi-equilibrium of these species with the 7r-complex, X, is not assumed. Actual hydroformylation olefin — aldehyde proceeds via a Heck-Breslow pathway (cycle 6.9 that includes the trihydride, X2) but without... 

Phthalocyanlnes. Gebler (18) has reported the attachment of a variety of metal phthalocyanines to both 8% and 20% dlvlnylbenzene polystyrene copolymer beads. The attachment of the phthalocyanine unit was either ly a sulfonamide or a sulfone linkage. Nickel, vanadyl, cobalt, iron and manganese complexes were formed in this way. Since solution aggregation accounts for a diminution of the catalytic activity, it was anticipated that polymer immobilization would Increase reactivity. Such an effect was not observed and little advantage over the homogeneous catalysts could be observed in the oxidation of cyclohexene. Oxidations of thiols by immobilized phthalocyanines have been reported (19-20) by both Schutten and Brouwer. 

Sun, X.-K. Zhang, X.-H. Wei, R.-J. Du, B.-Y Wang, Q. Fan, Z.-Q. Qi, G.-R. Mechanistic Insight into Initiation and Chain Transfer Reaction of COj/Cyclohexene Oxide Copolymerization Catalyzed by Zinc-Cobalt Double Metal Cyanide Complex Catalysts. J. Polymer Sci. Part A Polymer Chem. 2012, 50,2924-2934. 

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