σ3/σ5‑P Tautomerism and Coordination Behavior of α,α-Dialkyl-2-(diphenylphosphino)benzenemethanols

The previously described phosphino-alcohol α,α-dimethyl-2-(diphenylphosphino)­benzenemethanol 2 and hydridophosphorane 6 (derived from the reaction of 2-lithio­(diphenylphosphino)­benzene with (−)-fenchone) are shown by 31P­{1H} NMR saturation transfer experiments to be in equilibrium with the alternative closed chain P­(V) tautomer σ5-P 2 and open-chain P­(III) tautomer σ3-P 6, respectively. Using standard basis sets, the density function theory (DFT)-calculated equilibrium constant for σ3-P 6 ⇌ σ5-P 6 is shown to vary by several orders of magnitude; this was found to be largely dependent on the polarization functions on phosphorus and the mobile hydrogen, with the requirements for accurate modeling examined. The phosphino-alcohol 2 and the deprotonated species from treatment with BuLi react with [RuCl­(μ-Cl)­(η6-p-cymene)]2 to form unstable κ2(P,O)-complexes 9 and 12, respectively. These complexes subsequently rearrange to form a common complex (R P*,S Ru*)-10, where a phenyl substituent on phosphorus has been displaced by oxygen to generate a κP-1,3-dihydro-3,3-dimethyl-1-phenyl-2,1-benzoxaphosphole ligand coordinated to (η6-p-cymene)­RuClPh. In the case of complex 9, the HCl liberated on the formation of (R P*,S Ru*)-10 subsequently leads to a proto-demetalation reaction to generate the corresponding dichloride complex 11 and benzene. Kinetic measurements, DFT modeling, and quantum chemical topology analysis indicate that the rearrangement of complex 12 takes place in a fully concerted single step, while in the case of complex 9, a two-step process occurs via a metallophosphorane intermediate 18 featuring a κP-[(1,2-η)-phenyl]­phosphine bonding mode. In the reaction of hydridophosphorane 6 with [RuCl­(μ-Cl)­(η6-p-cymene)]2, hydridic behavior is observed, with the formation of known complex [RuCl­(η6-p-cymene)]2(μ-Cl)­(μ-H) 13, together with an alkoxyphosphonium chloride species 14. However, deprotonation of 6 with BuLi followed by reaction with [RuCl­(μ-Cl)­(η6-p-cymene)]2 follows a similar course to deprotonated 2, affording a mixture of complexes where a κP-1,3-dihydro-3,3-disubstituted-1-phenyl-2,1-benzoxaphosphole ligand is coordinated to (η6-p-cymene)­RuClPh: (S P,R Ru)-16 and (R P,R Ru)-16. Chromatographic purification, followed by reaction with HCl, converts complex (S P,R Ru)-16 to the stereochemically pure chiral-at-phosphorus ruthenium dichloride complex (S P)-17.