Alkyl complexes, electron-transfer reactions

Electrogenerated monovalent Co complexes of the well-known open chain N202 Schiff base ligands salen (8), salphen (9), and their substituted derivatives undergo oxidative additions with alkyl halides. Reactions of the complex with substrates within the series RBr (R = Pr, Bu, t-Bu) proceed at different rates. The reaction occurs by an inner-sphere alkyl-bridged electron transfer, with a Co1- R+- X-transition state, which is sensitive to distortions of the complex in different configurations.124... 

The competing /3-hydrogen elimination and oxidative substitution of the acetoxyalkylpalladium(II) intermediate bear many similarities to the competing oxidative elimination and oxidative substitution mechanisms observed in electron transfer reactions of alkyl radicals with Cu(II) complexes.633,64 An alternative explanation for the competing pathways in the decomposition of the acetoxyalkylpalladium(II) intermediate can be represented by oxidative elimination versus 1-electron transfer followed by a subsequent electron or ligand transfer, that is,... 

A comparison of Eq. 54 and Scheme 36 reveals that the nickel center performs two functions. First, the nickel center acts as mediator of the two electron-transfer reactions during which S—C bonds are cleaved and formed (36 —> 37 and 39 —> 40). Second, it facilitates the formation of an acyl group from an alkyl group and CO (38 —> 39). This reaction is expected to be favored when the nickel center has a coordination number lower than 5. A low coordination number of nickel also facilitates the final release of the thioester in the consecutive reaction of 39 with excess CO, because intermediates such as complex 42 can readily form. 

The rate of polymerization of polar monomers, for example, maleic anhydride, acrylonitrile, or methyl methacrylate, can be enhanced by coraplexing them with a metal halide (zinc or vanadium chloride) or an organoaluminum halide (ethyl aluminum sesqui-chloride). These complexed monomers participate in a one-electron transfer reaction with either an uncomplexed monomer or another electron-donor monomer, for example, olefin, diene, or styrene, and thus form alternating copolymers (11) with free-radical initiators. An alternating styrene/acrylonitrile copolymer (12) has been prepared by free-radical initiation of equimolar mixtures of the monomers in the presence of nitrile-coraplexing agents such as aluminum alkyls. 

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