Synthesis and Reactivity of Coordinatively Unsaturated Dinuclear Ruthenium Bridging Imido Complexes

[Cp*Ru(μ-NHPh)]2 (Cp* = η5-C5Me5) reacted with CO, t-BuNC, Ph2SCH2, or Me3SiCCH to give the dinuclear ruthenium bridging imido complexes [(Cp*Ru)2(μ-NPh)(μ-L)] (2a, L = CO; 2b, L = t-BuNC; 2c, L = CH2; 2d, L = CCHSiMe3). Protonolysis of 2d with t-BuOH produced the parent vinylidene complex [(Cp*Ru)2(μ-NPh)(μ-CCH2)] (2e). Treatment of 2e with HOTf or MeOTf afforded the cationic alkylidyne complexes [(Cp*Ru)2(μ-NPh)(μ-CR)]OTf (2f, R = Me; 2g, R = Et). Hydride abstraction from 2c with Ph3CBF4 gave the methylidyne complex [(Cp*Ru)2(μ-NPh)(μ-CH)]BF4 (2h). X-ray structures of 2a−c and 2f revealed short Ru−N distances (1.876−1.894 Å) consistent with Ru−N multiple bonds, and the μ-alkylidyne 2f also featured short Ru−C bonds (1.929(7) and 1.914(7) Å). In addition to giving simple Lewis base adducts such as [(Cp*Ru)2(μ-NPh)(μ-CO)(PMe3)] and [(Cp*Ru)2(μ-NPh)(μ-CH2)(t-BuNC)2], these imido complexes provided an array of novel ligand coupling reactions. Thus, 2b underwent a tandem imido−isocyanide coupling and C−H activation reaction to give an amidinate complex. Complexes 2c and 2e mediated imido−CO−methylene and imido−CO−vinylidene coupling to give [{Cp*Ru(CO)2}2(μ-PhNCOCH2)] (6) and [{Cp*Ru(CO)}2(μ-PhNCOCCH2)] (7), respectively. Complex 2c also underwent a selective coupling reaction with 2 equiv of Me3SiCCH to give the μ-allenylimine complex [(Cp*Ru)2{μ-Me3SiCHCC(SiMe3)C(Me)NPh}] (8). The imido methylidyne complex coupled with 2 equiv of alkynes to give [(Cp*Ru)2{μ-HC(R1CCR2)(R2CCR1)NPh}]OTf (9a−c), a product of double alkyne cycloaddition to the Ru−N and Ru−C multiple bonds and C−C coupling of the resulting ruthena- and azaruthenacyclobutene moieties.