Toshiaki Kitano

Electron transfer chemistry of hydride and carbanion donors. Hydride and carbanion transfer via electron transfer

Abstract The hydride transfer from 1,5-dihydroriboflavin-2′,3′,4′,5′-tetra-acetate (FlH 2 ) to various hydride acceptors (tetracyano- p -quinodimethane, tetracyanoethylene, and p -benzoquinone derivatives) in deaerated acetonitrile proceeds via electron transfer from FlH 2 to hydride acceptors followed by proton and electron transfer. The formation of transient radical ion pair has been detected directly in the reactions of 1,5-dihydroriboflavin-2′,3′,4′,5′-tetra-acetate (FlH 2 ) with some hydride acceptors in deaerated acetonitrile, providing unequivocal evidence for an electron transfer pathway in the overall two-electron redox reactions of FlH 2 with hydride acceptors. The formal carbanion transfer from alkylcobalt(III) complexes to cobalt(III) porphyrin has also been shown to proceed via electron transfer, followed by the cleavage of cobaltcarbon bonds of alkylcobalt(IV) complexes and the subsequent bond formation between alkyl radical and cobalt(II) porphyrin to yield alkylcobalt(III) porphyrins. The rate constants of the overall carbanion transfer from alkylcobalt(III) complexes to cobalt(III) porphyrin agree well with those predicted by the Marcus theory for the rates of outer-sphere electron transfer reactions. In contrast with the case of alkylcobalt(III) complexes, the rate constants of the carbanion transfer from tetraalkyltin compounds (R 4 Sn) are 10 2 –10 13 times faster than those predicted by the Marcus theory depending on the size of alkyl group of R 4 Sn. The polar versus ET pathway is discussed in terms of the difference between outer-sphere versus inner-sphere electron transfer mechanisms based on the Marcus theory.

Mechanisms of reductive methylation of NAD+ analogues by a trans-dimethylcobalt(III) complex

Various NAD+ analogues are readily reduced by a trans-dimethylcobalt(III) complex, trans-[CoMe2(L)](L = 11-hydroxy-2,3,9,10-tetramethyl-1,4,8,11-tetraazaundeca-1,3,8,10-tetraene-1-olate), to yield the corresponding methylated NADH analogues, while cis-dialkyl- or monoalkylcobalt(III) complexes show no reactivity towards NAD+ analogues. The charge distribution of the NAD+ analogues, as well as the thermodynamic stability of the products, is shown to be an important factor in determining the isomer distribution of the methylated products. The observed second-order rate constants for the reduction of NAD+ analogues by trans-[CoMe2(L)] in acetonitrile at 298 K are much larger than those estimated for outer-sphere electron transfer from trans-[CoMe2(L)] to NAD+ analogues.

Photo-induced one-electron reduction of 10-methylacridinium ion with group 14 dimetallic compounds using visible irradiation

Efficient one-electron reduction of the 10-methylacridinium ion, with group 14 dimetallic compounds (Me3MM′Me3; M,M′= Sn, Ge, Si), is initiated by electron transfer to the singlet excited state of the 10-methylacridinium ion in acetonitrile with irradiation by visible light to yield 10,10′-dimethyl-9,9′-biacridine selectively.