Sulfur-bonded sulfoxide complexes of rhodium(III) and rhodium(I)

Abstract

Aqueous 2-propanol solutions of RhCl3•3H2O on treatment with sulfoxides yield mer-RhCl3L3 complexes, the sulfoxide L being dimethyl (DMSO), tetramethylene (TMSO), methyl phenyl (MPSO), or (R)-methyl-p-tolyl (MPTSO); with diphenyl sulfoxide (DPSO), a [RhCl(DPSO)2]2 complex with S-bonded sulfoxide is obtained via the propanol reduction of a Rh(III) intermediate. The mer-rhodium(III) complexes in solution contain two sulfur-bonded sulfoxides (R2SO), and one oxygen-bonded sulfoxide (R2SO) that is trans to a (R2SO) ligand. The DMSO ligand in mer-RhCl3(DMSO)2(DMSO) is displaced by amides, amine oxides, and phosphine oxides; the DMSO cis to the oxygen-bonded ligands is identified in nmr by using the ring current shielding effects of OPPh2Me. Salts of [RhCl4(R2SO)2]− have been obtained with n-propyl sulfoxide and DMSO using several cations, including the symmetrically hydrogen-bridged species, [R2SO—H—OSR2]+. The cyclooctene precursor [RhCl(C8H14)2]2 has been used to synthesize [RhCl(DPSO)(C8H14)]2, [RhCl(DMSO)2]2, and [RhCl(DIOS)2]2, where DIOS is (2R,3R)-2,3-isopropylidene-2,3-dihydroxy-1,4-bis(methylsulfinyl)butane. The nature of rhodium–sulfur bonding is discussed, especially in terms of a contribution of metal–sulfur π-backbonding.