Abstract
AbstractThe 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.
Highlights
Secondary phosphine oxides, air and moisture stable, exist as two tautomers in equilibrium, the pentavalent R1R2P(=O)H (SPO) and the trivalent phosphinous acid R1R2P(OH) (PA)
Theoretical studies on the tautomerism suggest a bimolecular mechanism via P···H···O···P or mononuclear solvent-assisted hydrogen bonding as most likely and metal atoms may favor the tautomerization as consequence of PA coordination.[2]
The formation of complex 1 a can be explained by oxidative addition of diphenyl phosphine oxide through [RhCl(bipy)], formed upon addition of bipyridine to the starting dimer rhodium(I) complex, with cod displacement
Summary
Followed by PÀ H oxidative addition and RuÀ toÀ O hydrogen transfer to afford P-coordinated PA species.[3]. We report on hydrido-diimine-Rh(III) compounds containing the (Ph2PO···H···OPPh2)-k2P system obtained through oxidative addition of diphenylphosphine oxide at Rh(I) complexes and on their reactivity towards hydride or proton abstractors. This kind of hydrido-complexes could be intermediates in alkyne hydrophosphinylation reactions
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