Ruthenaphosphaalkenyls : Synthesis , structures and their conversion to η 2 - phosphaalkene complexes

The ruthenaphosphaalkenyls [Ru{P=CH(SiMe2R)}Cl(CO)(PPh3)2] (R = Me, Ph, Tol) have been prepared in good yield by the facile hydroruthenation of the respective phosphaalkynes, RMe2SiC≡P, 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{P=CH(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 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*, pz, pz) to afford the η,η-chelated pyrazolylphosphaalkene complexes [Ru{η−N:η−P,C-P(pz’)=CH(R)}(CO)(PPh3)2], which feature a 3-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.