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(∥)-HCî-≡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 J_C-H value (98 Hz) found for the β-carbon as well as the small J_H-H value for the α-vinyl proton. Treatment of the equilibrated mixture of phenyl-substituted complexes (CpRu)₃{μ₃-η²(∥)-HCî- ≡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{μ ₃-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.