Oxidative addition reactions of trans-halogenodicarbonyl(triphenylphosphine)rhodium complexes

Abstract

The new complex trans-[RhCl(CO)₂(PPh₃)](I), obtained by chlorine-bridge splitting of [Rh(CO)₂Cl]₂ with PPh₃, undergoes a series of oxidative additions with such molecules X–Y as halogens, Ph–l, and Cl–CO₂Et to give adducts of the type [RhXYCl(CO)₂(PPh₃)]. The addition of hydrogen chloride in dichloromethane affords [RhCl₃(CO)₂(PPh₃)]. Acetyl chloride in the same solvent adds on (I) to give [RhCl₂(CO)(COMe)(PPh₃), 0·5CH₂Cl₂]. Addition of methyl iodide involves rearrangement of the methyl-rhodium(III) adduct to the acetyl-rhodium complex [RhCll(CO)(COMe)(PPh₃)], which is presumably five-co-ordinate. The product of the addition of ethyl chloroformate to (I), [RhCl₂(CO)₂(CO₂Et)(PPh)₃], reacts with dry HCl in chloroform to give the labile cation [RhCl₂(CO)₃(PPh₃)]⁺ which is converted into the neutral [RhCl₃(CO)₂(PPh₃)] on standing in solution with evolution of carbon monoxide. Complex (I) undergoes metathesis of the halogen to give trans-[RhX(CO)₂(PPh₃)](X = Br and I). The latter reacts with bromine or iodine to give [RhX₃(CO)₂(PPh₃)](X = Br and I). Near- and far-i.r. data are discussed.