Reactions of Ruthenium Acetylide and Vinylidene Complexes Containing a 2-Pyridyl Group

Two ruthenium acetylide complexes [Ru]CtC(C5H3RN) (1a, R ) H; 1b, R ) Me; [Ru] ) Cp(PPh3)2Ru) containing 2-pyridyl groups are prepared and their chemical reactivities are explored. Protonation of the ruthenium acetylide complex 1a with HBF4 takes place at both the nitrogen atom and C , giving the dicationic pyridiniumvinylidene complex {[Ru]dCdC(H)(C5H4NH)}(BF4)2 (3a). Addition of BF3 to 1a yields the Lewis acid/base adduct [Ru]CtC(C5H4NfBF3) (4a). In the presence of moisture both complexes 3a and 4a in solution transform into the cationic heterocyclic carbene complex {[Ru]dC(O)CH2(C5H4NfBF2)}BF4 (6a), for which the structure is confirmed by X-ray structure determination. The formation of 6a involves the intermediate {[Ru]dCdC(H)(C5H4NfBF2OH)}BF4 (5a), characterized by spectroscopic methods. DFT calculations show that the Gibbs free energy change of the exothermic transformation of 5a to 6a is -20.59 kcal/mol. N-Alkylation reactions of 1b with two alkyl bromides BrCH2R′ (R′ ) CHdCHCO2Me and CO2Me) yield two pyridiniumacetylide complexes {[Ru]Ct C(C5H3MeNCH2R′)}Br (7b, R′ ) CHdCHCO2Me; 7c, R′ ) CO2Me, respectively). Complex 7c, characterized by X-ray structure determination, undergoes further protonation to give the pyridiniumvinylidene complex {[Ru]dCdC(H)(C5H4NCH2R′) (8c). Interestingly, the acetylide complex 7b undergoes a C-C coupling reaction of the acetylic C with the CdC double bond to give the vinylidene complex 9b, characterized also by X-ray structure determination.