Hydrochlorination of Ruthenaphosphaalkenyls: Unexpectedly Facile Access to Alkylchlorohydrophosphane Complexes

The novel ruthenaphosphaalkenyls [Ru­{PC­(H)­SiMe₂R}­Cl­(CO)­(PPh₃)₂] (R = p-C₆H₄CF₃, ⁿBu) have been prepared for the first time, and studied alongside precedent analogues (R = Me, Ph, p-tol) for their reactions with HCl. In contrast to chemistry defined for the tert-butyl congener [Ru­{PC­(H)^tBu}­Cl­(CO)­(PPh₃)₂], 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{η¹-PHCl–CH₂­SiMe₂R}­Cl­(CO)­(PPh₃)₂], extremely rare examples of coordinated “PHXR” type ligands. Where R = SiMe₃, 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_PPh3–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.