New Reduction Catalysis by Dinuclear Transition-metal Complexes of Gable Porphyrin

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Reduction of nitrobenzene was performed by (TPP) FeCl and gable Fe_2Cl_2 as a model reaction of NO_2^- reduction by nitrite reductase. This reaction proceeds via not azobenzene and hydrazobenzene but nitrosobenzene and phenylhydroxylamine. Significant solvent effects were observed; reaction proceeds little in THF, moderately in diglyme, but considerably in diglyme-MeOH. The catalytic activity of gable Fe_2Cl_2 is about twice of (TPP) FeCl in diglyme-MeOH(1:1), suggesting that the two active cites in gable Fe_2Cl_2 cooperatively accelerates this catalytic reduction. UV-Vis and ESR spectra suggest that active species is Fe(II) porphyrin. Hydrogenation of alpha,beta-unsaturated esters and cyclopropanation of stylene were also efficiently catalyzed by these Fe-porphyrins, yielding the saturated ester and phenylcyclopropane respectively. In these reactions, however, gable Fe_2Cl_2 exhibits almost the same catalytic activity as (TPP)FeCl.