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

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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.