Reactions of ruthenium benzylidenes with H2O to give benzaldehyde and (aqua)ruthenium complex

The second generation of Grubbs type catalyst, (PCy3)(H2IMes)Cl2Rudouble bond; length as m-dashCHPh (1) undergoes the Cl replacement with CH3CN to give cationic ruthenium carbene complexes, [(RCN)3(H2IMes)Rudouble bond; length as m-dashCHPh](OTf)2 (2, R = CH3 (a), Ph (b)) in the presence of AgOTf. The reaction of 2a with H2O in the presence of CH3CN gives (aqua)ruthenium complex, [Ru(H2IMes)(NCCH3) 4(H2O)](OTf)2 (3) and benzaldehyde. Benzaldehyde is also observed in the reaction of 1 with H2O. Plausible reaction pathways are suggested for the degradation of ruthenium benzylidenes to give benzaldehyde on the basis of the isotope labeling experiments.