Photochemical C–H bond activation of diruthenium bridging alkylidene complexes: Interligand H-exchange on Cp2Ru2(μ-CH2)(μ-CHR)(CO)2 (R=H, Me)

Irradiation of a double labeled diruthenium di-μ-methylene complex, Cp2Ru2(μ-CH2)(μ-*CD2)(CO)2 (5-13C,d2) (*C: 13C-enriched), caused H–D exchange between the two bridging methylene ligands to give an isomeric mixture of Cp2Ru2(μ-CHD)(μ-*CDH)(CO)2 and Cp2Ru2(μ-CD2)(μ-*CH2)(CO)2. In contrast to the photochemical hydrogen migration of 5-13C,d2, irradiation of a deuterated μ-methylene-μ-ethylidene complex, Cp2Ru2(μ-CD2)(μ-CHCH3)(CO)2 (7-d2), resulted in interligand exchange between β-hydrogen atoms of the ethylidene ligand and methylene hydrogen atoms to afford a mixture of Cp2Ru2(μ-CHD)(μ-CHCH2D)(CO)2 and Cp2Ru2(μ-CH2)(μ-CHCHD2)(CO)2. These exchange reactions can be interpreted in terms of μ-methylidyne, CpRu(CO)(μ-CH)(μ-CH2)Ru(H)Cp, and μ-alkenyl intermediates, CpRu(CO)(μ-CH)(μ-CHCH2)Ru(H)Cp, respectively. These species may be formed photochemical decarbonylation followed by migration of α- and β-hydrogen atoms of the bridging ligands to the coordinatively unsaturated ruthenium center. Subsequent CH2–H reductive elimination and free rotation of the resulting Ru–CH3 bond would cause the interligand H-exchange. Similar processes may be viable on a heterogeneous catalyst surface.