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

Article abstract of DOI:10.1021/om010422x

The reaction of the dichloro(vinylidene)ruthenium compounds [RuCl₂(=C=CHR)L₂] (R = Ph or tBu and L = PCy₃ or PiPr₃) (1a-d) with [H(OEt₂)₂]BAr_f (BAr_f^- = [B{C₆H₃ (CF₃)₂3,5}₄]^-) resulted in the attack of the proton at the C_β carbon atom of the vinylidene ligand and afforded the corresponding cationic, five-coordinate carbyneruthenium complexes [RuCl₂(≡CCH₂R)L₂]BAr_f (2a-d) in almost quantitative yields. The protonation of the carboxylato derivatives [RuCl(κ²-O₂CR)(=C=CHPh) (PiPr₃)₂] [R = H (3a), CH₃ (3b), or Ph (3f)] with [H(OEt₂)₂]BAr_f led to the formation of the five-coordinate cyclic carbene complexes [RuCl{=C(CH₂Ph)OC(O)R}(PiPr₃)₂]BAr_f [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(κ²- O₂CR)(=C=CHPh)(PiPr₃)₂] [R = CH₂F (3c), CHF₂ (3d), CF₃ (3e), C₆H₄NO₂-4 (3g), C₆H₄NO₂-2 (3h), C₆F₅ (3i), and C₆H₃(NO₂)₂-2,4 (3j)] with [H(OEt₂)₂]BAr_f gave an equilibrium mixture of the carbyne [RuCl-(κ²-O₂CR)(≡CCH₂ Ph)(PiPr₃)₂]BAr_f (5c-e, 5g-j) and the isomeric, cyclic carbene complexes [RuCl{=C(CH₂Ph)OC(O)R} (PiPr₃)₂]BAr_f (6c-e, 6g-j). The position of this equilibrium significantly depends on the basicity of the carboxylato ligand. The six-coordinate cyclic carbene complexes [Ru(κ²-O₂CR¹){=C(CH₂Ph)OC(O) R²} (PiPr₃)₂]BAr_f [R¹ = R² = CHF₂ (7a), CF₃ (7b); R¹ = CF₃, R² = H (7c)] were obtained on protonation of the precursors [Ru(κ¹-O₂CR¹) (κ²-O₂CR²)(=C=CHPh) (PiPr₃)₂] (4a-c) with [H(OEt₂)₂]BAr_f. Both 7a and 7b undergo a fluxional process in solution resulting in a κ¹/κ² interconversion of the carboxylato groups. The crystal and molecular structures of 2b, 5e, and 6a were determined by X-ray crystallography.