The ruthenaphosphaalkenyls [Ru{PCH-(SiMe2R)}Cl(CO)(PPh3)2] (R = Me, Ph, Tol) have been prepared in good yield by the facile hydroruthenation of the respective phosphaalkynes, RMe2SiCP, with [RuHCl(CO)-(PPh3)3]; all three compounds have been structurally characterized in the solid state. Complemented by DFT studies of these, and the precedent [Ru{PCH(tBu)}Cl(CO)(PPh3)2], the phosphaalkenyl moieties have been established unequivocally to behave as one-electron donors to the coordinately unsaturated, 15-electron “RuCl(CO)(PPh3)2” fragment, corroborating an earlier demonstration of nucleophilic character at phosphorus within the tert-butyl system. Notwithstanding, the ruthenaphosphaalkenyls are shown to react with the nucelophiles Lipz′ (pz′ = pz, pz*, pzH,CF3, pzMe,CF3) to afford the η1,η2-chelated pyrazolylphosphaalkene complexes [Ru{η1-N:η2-P,C-P(pz′)CH(R)}(CO)(PPh3)2], which feature a three-membered metallacyclic (Ru−C−P) core. The nature of these novel compounds is discussed, alongside preliminary insight into the process by which they are formed
