The sensitive balance between five-coordinate carbene and six-coordinate carbyne ruthenium complexes formed from ruthenium vinylidene precursors

The reaction of the dichloro(vinylidene)ruthenium compounds [RuCl2(=C=CHR)L -2] (R = Ph or tBu and L = PCY3 or PiPr(3)) (1a-d) with [H(OEt2)(2)]BArf- ( BArf = [B{C6H3(CF3)(2)-3,5}4}(-)) resulted in the attack of the proton at t he C-beta carbon atom of the vinylidene ligand and afforded the correspondi ng cationic, five-coordinate carbyneruthenium complexes [RuCl2-CCH2R)L-2]BA rf (2a-d) in almost quantitative yields. The protonation of the carboxylato derivatives [RuCl(kappa (2)-O2CR)(=C=CHPh)(PiPr(3))(2)] [R = H (3a), CH3 ( 3b), or Ph (3f)] with [H(OEt2)(2)]BArf led to the formation of the five-coo rdinate cyclic carbene complexes [RuCl-{=C(CH2Ph)OC(O)R}(PiPr(3))(2)]BArf [ R = H (6a), CH3 (6b), or Ph (6f)], which are formed via nucleophilic attack of the carboxylato ligand to a cationic carbyneruthenium intermediate. The protonation of the related vinylidene compounds [RuCl(kappa (2)-O2CR)(=C=C HPh)(PiPr(3))(2)] [R = CH2F (3c), CHF2 (3d), CF3 (3e), C6H4NO2-4 (3g), C6H4 NO2-2 (3h), C6F5 (3i), and C6H3(NO2)(2)-2,4 (3j)] with [H(OEt2)(2)]BArf gav e an equilibrium mixture of the carbyne [RuCl(kappa (2)-O2CR)(drop CCH2Ph)( PiPr(3))(2)]BArf (5c-e, 5g-j) and the isomeric, cyclic carbene complexes [R uCl{=C(CH2Ph)OC(O)R}(PiPr(3))(2)]BArf (6c-e, 6g-j). The position of this eq uilibrium significantly depends on the basicity of the carboxylato ligand. The six-coordinate cyclic carbene complexes [Ru(kappa (2)-O2CR1){=C(CH2Ph)O C(O)R-2}(PiPr(3))(2)]BArf [R-1 = R-2 = CHF2 (7a), CF3 (7b); R-1 = CF3, R-2 = H (7c)] were obtained on protonation of the precursors [Ru(kappa (1)-O2CR 1)(kappa (2)-O2CR2)(=C=CHPh)(PiPr(3))(2)] (4a-c) with [H(OEt2)(2)]BArf. Bot h 7a and 7b undergo a fluxional process in solution resulting in a kappa (1 )/kappa (2) interconversion of the carboxylato groups. The crystal and mole cular structures of 2b, 5e, and 6a were determined by X-ray crystallography .