Ruthenaphosphaalkenyls: synthesis, structures, and their conversion to ?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 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 ?1,?2-chelated pyrazolylphosphaalkene complexes [Ru{?1-N:?2-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.