Complexes of rhodium(I) and iridium(I) containing a trans-chelating bidentate ditertiary phosphine or arsine: Internal oxidative addition of a benzylic CH bond to iridium(I)

Abstract

2,2′-Bis(diphenylphosphino)bibenzyl, o-Ph 2PC 6H 4CH 2CH 2C 6H 4PPh 2- o (bdpbz), and its arsenic analogue, o-Ph 2AsC 6H 4CH 2CH 2C 6H 4AsPh 2- o (bdabz), form monomeric complexes of rhodium(I) and iridium(I) of general formula MCl(CO)(ligand) (M = Rh, Ir; ligand = bdpbz, bdabz) in which the Group V ligands span rans-coordination sites. The rhodium(I) complexes RhCl(CO)(bdpbz) and [Rh(CO) 2(bdpbz)] + exhibit temperature-dependent 1H NMR spectra, probably owing to inversion of the nine-membered chelate ring; the estimated free energies of activation are 17.3 ± 0.3 kcal mol −1 at 93°C for the neutral complex and 13.2 ± 0.5 kcal mol −1 at about −15°C for the cationic complex. In contrast, bdpbz behaves as a cis-bidentate ligand in the complex Pt(CH 3) 2(bdpbz); the nine-membered chelate ring undergoes inversion with an estimated free energy of activation of 16.1 ± 0.1 kcal mol −1 at 69°C. The iridium(I) complex IrCl(CO)(bdpbz) isomerizes in solution at room temperature by transferring a benzylic hydrogen atom to the metal and forming a chelate metal—carbon σ-bonded complex Ir(H)Cl(CO)(o-Ph 2PC 6H 4C HCH 2C 6H 4PPh 2- o); IrCl(CO)(bdabz) behaves similarly under more forcing conditions. Cationic metallated complexes [ Ir(H)(CO) 2{o-Ph 2EC 6H 4C HCH 2C 6H 4EPh 2- o}] + (E = P, As) have been identified in solution.