Oxidative Addition of Secondary Phosphine Oxides through Rh(I) Center: Hydrido-Phosphinito-Rh(III) Complexes and their Catalytic Activity in Hydrophosphinylation of Alkynes

Abstract

The reaction of [Rh(μ-Cl)(cod)]2 with diimines, differing in their steric and electronic properties, and with diphenylphosphine oxide leads to the oxidative addition products, hydrido-phosphinito-Rh(III) complexes {Rh(PPh2OH)(PPh2O)(NN)(H)Cl} (1), stabilized by the formation of a hydrogen bonded phosphinous acid-phosphinito quasi-chelate [(PO⋅⋅⋅HOP)-κ2P]. Exchange of hydride by chloride to afford {Rh(PPh2OH)(PPh2O)(NN)Cl2} (2) occurs in hydrido complexes containing low steric hindrance diimines and is inhibited for complexes containing encumbered diimines. Complexes 1 react with BF3⋅OEt2 with exchange of the acidic proton by BF2, and transformation of the quasi-chelating PO⋅⋅⋅HOP into a chelating PO-BF2-OP ligand in {Rh{(PPh2O)2BF2}(NN)(H)Cl} (3). The reaction of [Rh(μ-Cl)(nbd)]2 or [Rh(acac)(nbd)] with diphenylphosphine oxide leads to coordinatively unsaturated nortricyclyl-phosphinito-Rh(III) complexes, {Rh(PPh2OH)(PPh2O)(ntyl)(μ-Cl)}2 (4) or {Rh(PPh2OH)(PPh2O)(ntyl)(acac)} (6), respectively. Their reaction with BF3⋅OEt2 results in the corresponding {Rh{(PPh2O)2BF2}(ntyl)(μ-Cl)}2 (5) or {Rh{(PPh2O)2BF2}(ntyl)(acac)} (7). Some of these new complexes have shown catalytic activity in hydrophosphinylation of alkynes, with {Rh(PPh2OH)(PPh2O)(NN)(H)Cl} containing encumbered NN being efficient and regioselective catalysts in the hydrophosphinylation of phenylacetylene with diphenylphosphine oxide to produce (E)-diphenyl(styryl)phosphine oxide.