Reaction of potassium tetracarbonylhydridoferrate with aryl halides: mechanistic study and extension to the catalytic carbonylation of iodobenzene by a bimetallic Fe(CO)5-Co2(CO)8 system

Article abstract of DOI:10.1021/om00047a070

Potassium tetracarbonylhydriodoferrate, KHFe(CO)₄, reacts with aryl iodides in wet methanol to yield the corresponding arenes. This reaction is catalytic under carbon monoxide (1 atm) in the presence of an excess of base. Mechanistic investigations, both by IR analysis and by electrochemical experiments, show that the reaction involves an electron transfer from HFe(CO)₄^- to the aryl halide to generate the corresponding radical anion. The resulting aryl radical either abstracts an hydrogen atom from potassium methoxide of combines with the [HFe(CO)₄] radical species to form ArFe(H)(CO)₄, which yields ArH by reductive elimination. The catalytic carbonylation of iodobenzene to benzoic acid can be performed under very mild conditions by a bimetallic system, viz. HFe(CO)₄^--Co(CO)₄^-. The observed synergetic effect is believed to involve first an electron transfer from HFe(CO)₄^- to iodobenzene and generation of a phenyl radical, followed by reaction with Co(CO)₄^-, which acts as the actual carbonylation catalyst. In agreement with these hypotheses, the carbonylation of bromobenzene, which on its own is unreaction under these conditions, can be promoted by the presence of iodobenzene.