Ruthenium Trispyrazolylborate Complexes. 18. Aminocarbene Ruthenium Complexes Derived from Terminal Alkynes and 2-Aminopyridines

The reactions of RuTp(COD)Cl with the bidentate ligands 2-aminopyridine (apy), 2-amino-4-picoline (apic), and 2-(methylamino)pyridine (mapy) in the presence of terminal alkynes HC⋮CR (R = Ph, n-Bu, C₆H₉) afford the cyclic aminocarbene complexes RuTp(CCH₂R-apy)Cl, RuTp(CCH₂R-apic)Cl, and RuTp(CCH₂R-mapy)Cl. This reaction proceeds most likely via the intermediacy of both a reactive RuTp complex containing a strained, and thus labile, κ²-N,N-coordinated aminopyridine ligand and a vinylidene intermediate. As side products, except for mapy, the dimeric complexes [RuTp(μ-apy)Cl]₂ and [RuTp(μ-apic)Cl]₂, featuring bridging aminopyridine ligands, were isolated. Representative complexes were characterized by X-ray crystallography.