Tridentate chelate π-bonded complexes of rhodium(I), iridium(I), and iridium(III) and chelate σ-bonded complexes of nickel(II), palladium(II), and platinum(II) formed by intramolecular hydrogen abstraction reactions

Abstract

2,2′-Bis( o-diphenylphosphino)bibenzyl, o-Ph 2PC 6H 4CH 2CH 2C 6H 4PPh 2- o (bdpbz), is dehydrogenated by various rhodium complexes to give the planar rhodium(I) complex ▪, from which the ligand, 2,2′-bis( o-diphenylphosphino)- trans-stilbene (bdpps) can be displaced by treatment with sodium cyanide. The stilbene forms stable chelate olefin complexes with planar rhodium(I) and iridium(I) and with octahedral iridium(III). On reaction with halide complexes of nickel(II), palladium(II) or platinum(II), the stilbene ligands ▪ (R  Ph or o-CH 3C 6H 4) lose a vinyl proton in the form of hydrogen chloride to give chelate, planar σ-vinyls of general formula MX(o-R 2PC 6H 4C CHC 6H 4PR 2- o) (M  Ni, Pd, Pt; X  Cl, Br, I) of high thermal stability; analogous methyl derivatives Pt(CH 3)(o-R 2PC 6H 4C CHC 6H 4PR 2- o) are obtained from Pt(CH 3) 2(COD) (COD  1,5-cyclooctadiene) and the stilbene ligands. The bibenzyl also forms chelate σ-benzyls MX(o-Ph 2PC 6H 4C HCH 2C 6H 4PPh 2- o) (M  Pd, Pt; X  Cl, Br, I). The 1H NMR spectra of the o-tolyl methyl groups in the compounds MX(o-R 2PC 6H 4C CHC 6H 4PR 2- o) (M  Ni, Pd, Pt; R  o-CH 3C 6H 4) vary with temperature, probably as a consequence of interconversion of enantiomers arising from restricted rotation about the MP and MC bonds. Possible mechanisms for the dehydrogenation reactions are briefly discussed.