Structures of square-pyramidal acyl and octahedral alkyl intermediates in the decarbonylation of acid halides by chlorotris(triphenylphosphine)rhodium(I)

Abstract

Oxidative addition of acetyl chloride to the compound [RhCl(PPh₃)₃] leads to the formation of two acetyl- and one methyl-rhodium species, all isomeric, before reductive elimination of methyl chloride occurs to give [RhCl(CO)(PPh₃)₂]. The structures of all the compounds have been determined using i.r. and both ¹H and ³¹P n.m.r. spectroscopy. The effects of changing the nature of the acid halide and the tertiary phosphine have been determined as have thermodynamic parameters for the ‘carbonyl-insertion’ reactions involved. The X-ray crystal structure of the compound [RhCl₂(COCH₂CH₂Ph)(PPh₃)₂] demonstrates essentially a square pyramid with trans-basal chlorides, trans-basal phosphines, and an apical acyl group.