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.