Hydrogenation catalysis by an iron porphyrin and its application to α,β-unsaturated esters

Abstract

Chloro(5,10,15,20-tetraphenylporphyrinato)iron(III) in tetrahydrofuran-methanol catalysed the hydrogenation of α,β-unsaturated esters by NaBH₄ to the saturated esters; turnovers of up to 4580 h^–1 have been attained for the hydrogenation of ethyl 2-methylbut-2-enoate. Deuterium labelling studies showed that the H^– of NaBH₄ and the H⁺ of MeOH add to the β- and α-carbons of the double bond. A slower hydrogenation of oct-1-ene was accompanied by isomerization to oct-2-enes. Spectroscopy (UV/VIS, ¹H NMR and ESR) suggests that hydrogenation proceeds via an iron(II) intermediate, and an alkyl-iron(II) species seems likely.