Bis(ditertiaryphosphine) complexes of rhodium(I). Synthesis, spectroscopy, and activity for catalytic hydrogenation

Abstract

Rhodium(I)–bis(ditertiaryphosphine) complexes of the general formula [Formula: see text]n = 1–4, and (+)-diop (diop = 2,3-O-isopropylidene 2,3-dihydroxy-1,4-bis(diphenylphosphino)butane) have been prepared by treating [Rh(cyclooctene)2Cl]2 with the appropriate ditertiaryphosphine. The n = 1 and n = 4 and diop species are five-coordinate in the solid state and in non-polar solvents, while the n = 2 and 3 species contain ionic chloride. The cationic complexes [Formula: see text] were prepared from the [Formula: see text] species by adding AgX (X = SbF6, PF6, BF4). Reaction of the chloro complexes with borohydride has yielded the hydrides, [Formula: see text] for the n = 2 and 3 diphosphines, and for (+)-diop. 1H and 31P nmr, as well as visible spectral data, are presented: a solvent-dependent deshielding of ortho protons of the phenyl groups is observed in some of the complexes, and the ligand CH2 protons are coupled to the rhodium in the Rh(Ph2PCH2PPh2)2+ cation; the P atom in this bis(diphenylphosphino) ligand shows an usual high field shift on coordination to rhodium.Preliminary kinetic data for catalytic hydrogenation of methylenesuccinic acid show that the cationic and hydrido complexes are more active than the corresponding chloro complexes, and that activity generally increases with increasing chain length of the diphosphine.