Reductively induced homolytic carbon–carbon bond cleavage in Co(CO) 3(PPh 3)(COCF 3)

Abstract

The chemical or electrochemical reduction of the trifluoroacetyl complex Co(CO) 3(PPh 3)(COCF 3) involves a single electron transfer yielding trifluoromethyl radical and an anionic cobalt carbonyl complex. The mechanism is proposed to involve electron transfer followed by initial dissociation of either a carbonyl or phosphine ligand from the 19-electron [Co(CO) 3(PPh 3)(COCF 3)] − anion. The resulting 17-electron intermediate undergoes subsequent one-electron reductive elimination of trifluoromethyl radical by homolytic cleavage of the carbon–carbon bond of the trifluoroacetyl group. The CF 3 radical can be trapped by either benzophenone anion, forming the anion of α-(trifluoromethyl)benzhydrol, or Bu 3SnH, yielding CF 3H. The ultimate organometallic product is an 18-electron anion, either [Co(CO) 4] − or [Co(CO) 3(PPh 3)] −, depending upon which ligand is initially lost. Fluorine-containing products were identified and quantitated by 19F NMR while cobalt-containing products were determined by IR.