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-Ph2PC6H4CH2CH2C6H4PPh2-o (bdpbz), is dehydrogenated by various rhodium complexes to give the planar rhodium(I) complex {A figure is presented}, 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 {A figure is presented} (R Ph or o-CH3C6H4) lose a vinyl proton in the form of hydrogen chloride to give chelate, planar σ-vinyls of general formula MX(o-R2PC6H4CCHC6H4PR2-o) (M Ni, Pd, Pt; X Cl, Br, I) of high thermal stability; analogous methyl derivatives Pt(CH3)(o-R2PC6H4CCHC6H4PR2-o) are obtained from Pt(CH3)2(COD) (COD 1,5-cyclooctadiene) and the stilbene ligands. The bibenzyl also forms chelate σ-benzyls MX(o-Ph2PC6H4CHCH2C6H4PPh2-o) (M Pd, Pt; X Cl, Br, I). The 1H NMR spectra of the o-tolyl methyl groups in the compounds MX(o-R2PC6H4CCHC6H4PR2-o) (M Ni, Pd, Pt; R o-CH3C6H4) vary with temperature, probably as a consequence of interconversion of enantiomers arising from restricted rotation about the MP and MC bonds. Possible mechanisms for the dehydrogenation reactions are briefly discussed. Show more