Reductively induced homolytic carbon–carbon bond cleavage in Co(CO)3(PPh3)(COCF3)

The chemical or electrochemical reduction of the trifluoroacetyl complex Co(CO)3(PPh3)(COCF3) 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(PPh3)(COCF3)]− 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 CF3 radical can be trapped by either benzophenone anion, forming the anion of α-(trifluoromethyl)benzhydrol, or Bu3SnH, yielding CF3H. The ultimate organometallic product is an 18-electron anion, either [Co(CO)4]− or [Co(CO)3(PPh3)]−, 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.

The reduction of Co(CO)3(PPh3)(COCF3) produces a 19e− anion which rapidly dissociates either the PPh3 or one of the CO ligands. The resulting 17e− anion undergoes one-electron reductive elimination of CF3 to restore the metal center to an 18e− configuration as [Co(CO)3L]−. The CF3 may be trapped by Bu3SnH or benzophenone anion.Figure optionsDownload as PowerPoint slide