ELECTROCHEMICAL CATALYTIC REDUCTION OF ACYL CHLORIDES BY BIS(TRIMETHYLSILYLCYCLOPENTADIENYL)NIOBIUM SPECIES

Electrogenerated bis(trimethylsilylcyclopentadienyl)niobium (III) comp lexes (eta5-Me3SiC5H4)2NbX2- (X = Cl, Br, and I) have been shown to be effective catalysts for the reduction of acyl chlorides R1R2CHCOCl (R 1 = R2 = Ph and R2 = CH3, R2 = Ph). Indirect cathodic reduction yields alpha-diketones (R1R2CHCO)2, ketones R1R2CHCOCHR1R2, and alkanes (R1R 2CH)2. The formation of these derivatives involves the homolytic cleav age of the acyl chloride carbon-halogen bond, giving an acyl radical. Several mechanistic aspects are discussed: an oxidative addition of R1 R2CHCOCl to the niobium (III) complex is followed by a reductive elimi nation of the acyl radical.