Synthesis, structure, and property of a triruthenium cluster having a μ-alkyl ligand: Transformation of a μ 3(⊥)-alkyne ligand into a μ-alkyl ligand via a μ 3-vinylidene complex

Abstract

A triruthenium μ-alkyl complex, (Cp ∗Ru) 3(μ-η 2-HCHCH 2R)(μ-CO) 2(μ 3- CO) ( 2a, R = Ph; 2b, R = t Bu, Cp ∗ = η 5-C 5Me 5), which contains a two-electron and three-center interaction among Ru, C, and H atoms, has been synthesized by the reaction of a perpendicularly coordinated 1-alkyne complex, {Cp ∗Ru(μ-H)} 3(μ 3-η 2:η 2(⊥)-RCCH) ( 1a; R = Ph, 1b; R = t Bu), with carbon monoxide. A diffraction study for 2b clearly represented the bridging neohexyl group on one Ru–Ru edge. This μ-alkyl group exhibited dynamic behavior resulting in site-exchange of the α-hydrogen atoms between the terminal and bridging positions, which was synchronized with the migration of the μ-alkyl groups between the two ruthenium atoms. The agostic C–H bond was readily cleaved upon pyrolysis. Whereas the μ-phenethylidene intermediate resulting from the σ-C–H bond cleavage has never been observed, a μ 3-phenethylidyne complex, {Cp ∗Ru(μ-CO)} 3(μ 3-CCH 2Ph) ( 7a), and a μ 3-methylidyne complex, {Cp ∗Ru(μ-CO)} 3(μ 3-CH) ( 8), were obtained by the successive C–H/C–H and C–H/C–C bond cleavages at the μ-alkyl moiety, respectively.