Displacement of the labile acetone ligand from [Rh(diene)(PPh3)(acetone)]A (diene = 1,5-cyclooctadiene (COD), norbornadiene (NBD); A = PF6−, SbF6−) allows facile coordination of dialkyl or alkyl aryl sulfoxides, and [Rh(diene)(PPh3)(sulfoxide)]+ complexes have been synthesized using dimethyl sulfoxide (DMSO), tetramethylene sulfoxide (TMSO), di-n-propyl sulfoxide (NPSO), (S,S;S,R)-(+)-2-methylbutyl methyl sulfoxide (MBMSO), methyl phenyl sulfoxide (MPSO), (R)-(+)-methyl-p-tolyl sulfoxide (MPTSO), and (R)-t-butyl p-tolyl sulfoxide (TBPTSO).Diaryl sulfoxides appear to coordinate in solution but no solid compounds could be isolated. The upfield shifts of the sulfoxide resonances (1H nmr), reflecting shielding by the adjacent phenyl groups of PPh3, and the decrease in ν(SO) on coordination, are indicative of O-bonding in all cases. Infrared data indicate that the frequency shift of ν(SO) upon O-coordination is roughly proportional to the strength of the metal–oxygen bond for a range of transition metal DMSO and TMSO complexes.