α-Alkylation of Nitriles with Alcohols Catalyzed by NNN′ Pincer Ru(II) Complexes Bearing Bipyridyl Imidazoline Ligands

A series of unsymmetrical NNN′ ruthenium(II) complexes supported by a tridentate bipyridyl imidazoline ligand with variable steric hindrance ( 2a–c; R 1 = t Bu, i Pr, or Bn) and electronic effect ( 2d–h; R 2 = H, CH 3, OCH 3, Br, or NO 2 ) were prepared. The molecular structures of ligands 1f and 1g, and Ru complex 2a were further determined by X-ray single-crystal diffraction. The catalytic activity of these eight complexes for α-alkylation of nitriles with alcohols was evaluated, which could be controlled by the substituents on the imidazoline moiety. Ru complex 2h bearing a strong electron-withdrawing group (R 2 = NO 2 ) demonstrated the highest catalytic activity, with alkylated nitriles achieved in up to 97% yield.