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

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(PPh 2 OH)(PPh 2 O)(NN)(H)Cl} ( 1 ), stabilized by the formation of a hydrogen bonded phosphinous acid‐phosphinito quasi‐chelate [(PO⋅⋅⋅HOP)‐κ 2 P]. Exchange of hydride by chloride to afford {Rh(PPh 2 OH)(PPh 2 O)(NN)Cl 2 } ( 2 ) occurs in hydrido complexes containing low steric hindrance diimines and is inhibited for complexes containing encumbered diimines. Complexes 1 react with BF 3 ⋅OEt 2 with exchange of the acidic proton by BF 2 , and transformation of the quasi‐chelating PO⋅⋅⋅HOP into a chelating PO‐BF 2 ‐OP ligand in {Rh{(PPh 2 O) 2 BF 2 }(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(PPh 2 OH)(PPh 2 O)(ntyl)(μ‐Cl)} 2 ( 4 ) or {Rh(PPh 2 OH)(PPh 2 O)(ntyl)(acac)} ( 6 ), respectively. Their reaction with BF 3 ⋅OEt 2 results in the corresponding {Rh{(PPh 2 O) 2 BF 2 }(ntyl)(μ‐Cl)} 2 ( 5 ) or {Rh{(PPh 2 O) 2 BF 2 }(ntyl)(acac)} ( 7 ). Some of these new complexes have shown catalytic activity in hydrophosphinylation of alkynes, with {Rh(PPh 2 OH)(PPh 2 O)(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.