Hydrochlorination of Ruthenaphosphaalkenyls: Unexpectedly Facile Access to Alkylchlorohydrophosphane Complexes

The novel ruthenaphosphaalkenyls [Ru­{PC­(H)­SiMe<sub>2</sub>R}­Cl­(CO)­(PPh<sub>3</sub>)<sub>2</sub>] (R = <i>p</i>-C<sub>6</sub>H<sub>4</sub>CF<sub>3</sub>, <i><sup>n</sup></i>Bu) have been prepared for the first time, and studied alongside precedent analogues (R = Me, Ph, <i>p</i>-tol) for their reactions with HCl. In contrast to chemistry defined for the <i>tert</i>-butyl congener [Ru­{PC­(H)<sup><i>t</i></sup>Bu}­Cl­(CO)­(PPh<sub>3</sub>)<sub>2</sub>], which initially adds a single equivalent of HCl across the Ru–P linkage, all five silyl derivatives undergo spontaneous addition of a second equivalent to afford [Ru­{η<sup>1</sup>-PHCl–CH<sub>2</sub>­SiMe<sub>2</sub>R}­Cl­(CO)­(PPh<sub>3</sub>)<sub>2</sub>], extremely rare examples of coordinated “PHXR” type ligands. Where R = SiMe<sub>3</sub>, a distorted octahedral geometry with a conformationally restricted “PHXR” ligand is observed crystallographically; this structure is appreciably retained in solution, as determined from multinuclear NMR spectroscopic features, which include a Karplus-like P<sub>PPh3</sub>–Ru–P–H spin–spin coupling dependence. Computational data suggest a silyl-induced increase in negative charge density at the phospha­alkenic carbon, rather than an intrinsic thermodynamic driver, as the likely origin of the disparate reactivity.