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 (<b>2a</b>), was synthesized via the treatment of {Cp*Ru­(μ-H)}₃(μ₃-H)₂ (<b>3</b>) (Cp* = η⁵-C₅Me₅) with propene. In the low-temperature region, VT ¹H NMR spectra showed that complex <b>2a</b> is in equilibrium with a nonclassical μ₃-vinyl complex, (CpRu)₃(μ₃-η²:η²-HCCH₂)­(μ₃-CH)­(μ-H) (<b>5a</b>), 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 <i>J</i>_C–H value (98 Hz) found for the β-carbon as well as the small <i>J</i>_H–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 (<b>2b</b>) and (CpRu)₃(μ₃-η²:η²-HCCHPh)­(μ₃-CH)­(μ-H) (<b>5b</b>) with <i>t</i>BuNC afforded a μ-styryl complex, (CpRu)₃(μ-η²-HCCHPh)­(μ₃-CH)­(μ-<i>t</i>BuNC)­(μ-H) (<b>6</b>), while analogous treatment of <b>2a</b> and <b>5a</b> resulted in the formation of μ₃-dimetalloallyl complex (CpRu)₃{μ₃-η³-CHCHCN­(H)<i>t</i>Bu}­(μ₃-CH)­(μ-H) (<b>7</b>). 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