One-electron oxidation of cis- [CoR2(bipy)2]ClO4 (R = Me or Et; bipy = 2,2′-bipyridine) by organic oxidants (2,3-dichloro-5,6-dicyano-p-benzoquinone, 2,3-dicyano-p-benzoquinone, tetracyanoethylene, and tetracyano-p-quinodimethane) in acetonitrile results in the cleavage of the pair of cobalt-alkyl bonds to yield the coupled products (R-R) exclusively. A transient absorption band observed in the electron-transfer reaction of [CoEt2(bipy)2] + with tetracyanoethylene is shown to arise from a charge-transfer complex formed between [CoEt2(bipy)2]+ and tetracyanoethylene as a reaction intermediate. The logarithm of the rate constants (log k) for these electron-transfer reactions in acetonitrile at 298 K is linearly correlated with the difference in the redox potentials between [CoR2(bipy)2]+ and oxidants with a slope of -F/2.3RT (F is the Faraday constant). Based on the linear Gibbs energy relationship, mechanisms for the electron-transfer reactions are discussed with the aid of the Marcus theory, and the lifetimes of cis-[CoR2(bipy)2]2+ are estimated as ≤8 × 102 ns.
|Number of pages||6|
|Journal||Journal of the Chemical Society. Dalton Transactions|
|State||Published - 1985|