[Ru(NHC)(xantphos)(CO)H-2] complexes: intramolecular C-H activation and applications in C-C bond formation

摘要

Treatment of [Ru(PPh3)(xantphos)(CO)H-2] (1) with the N-heterocyclic carbenes (NHCs) IEt2Me2 (1,3-diethyl-4,5-dimethylimidazol-2-ylidene), (IPr2Me2)-Pr-i (1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene) and IMes (1,3-dimesitylimidazol-2-ylidene) at elevated temperature affords the C-H activated carbene complexes [Ru(NHC)'(xantphos)(CO)H] (2-4). In contrast, ICy (1,3-dicyclohexylimidazol-2-ylidene) reacts with 1 to give the substitution product [Ru(ICy)(xantphos)(CO)H-2] (6), which can be converted into the C-H activated species [Ru(ICy)'(xantphos)(CO)H] (7) upon thermolysis in the presence of H2C=CHSiMe3. Addition of H-2 to 2 yields [Ru(IEt2Me2)(xantphos)(CO)H-2] (5), while H-2 reacts with 7 to reform 6. Complexes 2-4 and 7 catalyse the Knoevenagel reaction of PhCH2OH with (BuC)-Bu-t(O)CH2CN, although they prove to be somewhat less active than the phosphine complex 1.