Synthesis and Dynamic Properties of a Triruthenium Complex Containing μ3‑η2(∥)-Ethyne and μ3‑Methylidyne Ligands: Equilibrium of an Ethyne–Hydrido Complex with a Nonclassical μ3‑Vinyl Complex

A triruthenium complex containing μ3-η2(∥)-ethyne and μ3-methylidyne ligands, (CpRu)3{μ3-η2(∥)-HCCH}­(μ3-CH)­(μ-H)2 (2a), was synthesized via the treatment of {Cp*Ru­(μ-H)}3(μ3-H)2 (3) (Cp* = η5-C5Me5) with propene. In the low-temperature region, VT 1H NMR spectra showed that complex 2a is in equilibrium with a nonclassical μ3-vinyl complex, (CpRu)3(μ3-η2:η2-HCCH2)­(μ3-CH)­(μ-H) (5a), which features an interaction between one of the β-vinyl protons and a Ru center. The presence of the unusual 3c-2e interaction of the β-C–H bond of the vinyl group is strongly supported by the small JC–H value (98 Hz) found for the β-carbon as well as the small JH–H value for the α-vinyl proton. Treatment of the equilibrated mixture of phenyl-substituted complexes (CpRu)3{μ3-η2(∥)-HCCPh}­(μ3-CH)­(μ-H)2 (2b) and (CpRu)3(μ3-η2:η2-HCCHPh)­(μ3-CH)­(μ-H) (5b) with tBuNC afforded a μ-styryl complex, (CpRu)3(μ-η2-HCCHPh)­(μ3-CH)­(μ-tBuNC)­(μ-H) (6), while analogous treatment of 2a and 5a resulted in the formation of μ3-dimetalloallyl complex (CpRu)3{μ3-η3-CHCHCN­(H)tBu}­(μ3-CH)­(μ-H) (7). These results imply that the coordinatively saturated μ3-η2(∥)-alkyne−μ3-alkylidyne complex can generate a vacant site via the migration of a hydrido ligand onto an alkyne ligand to yield a μ-vinyl intermediate.