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 [RuCl 2 ( C CHR)L 2 ] (R = Ph or t Bu and L = PCy 3 or P i Pr 3 ) ( 1a − d ) with [H(OEt 2 ) 2 ]BAr f (BAr f - = [B{C 6 H 3 (CF 3 ) 2 -3,5} 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 [RuCl 2 (⋮CCH 2 R)L 2 ]BAr f ( 2a − d ) in almost quantitative yields. The protonation of the carboxylato derivatives [RuCl(κ 2 -O 2 CR)( C CHPh)(P i Pr 3 ) 2 ] [R = H ( 3a ), CH 3 ( 3b ), or Ph ( 3f )] with [H(OEt 2 ) 2 ]BAr f led to the formation of the five-coordinate cyclic carbene complexes [RuCl{ C(CH 2 Ph)OC(O)R}(P i Pr 3 ) 2 ]BAr f [R = H ( 6a ), CH 3 ( 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(κ 2 -O 2 CR)( C CHPh)(P i Pr 3 ) 2 ] [R = CH 2 F ( 3c ), CHF 2 ( 3d ), CF 3 ( 3e ), C 6 H 4 NO 2 -4 ( 3g ), C 6 H 4 NO 2 -2 ( 3h ), C 6 F 5 ( 3i ), and C 6 H 3 (NO 2 ) 2 -2,4 ( 3j )] with [H(OEt 2 ) 2 ]BAr f gave an equilibrium mixture of the carbyne [RuCl(κ 2 -O 2 CR)(⋮CCH 2 Ph)(P i Pr 3 ) 2 ]BAr f ( 5c − e, 5g − j ) and the isomeric, cyclic carbene complexes [RuCl{ C(CH 2 Ph)OC(O)R}(P i Pr 3 ) 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(κ 2 -O 2 CR 1 ){ C(CH 2 Ph)OC(O)R 2 }(P i Pr 3 ) 2 ]BAr f [R 1 = R 2 = CHF 2 ( 7a ), CF 3 ( 7b ); R 1 = CF 3, R 2 = H ( 7c )] were obtained on protonation of the precursors [Ru(κ 1 -O 2 CR 1 )(κ 2 -O 2 CR 2 )( C CHPh)(P i Pr 3 ) 2 ] ( 4a − c ) with [H(OEt 2 ) 2 ]BAr f . Both 7a and 7b undergo a fluxional process in solution resulting in a κ 1 /κ 2 interconversion of the carboxylato groups. The crystal and molecular structures of 2b, 5e, and 6a were determined by X-ray crystallography.