Pincer–Ruthenium Catalyzed Selective α‐Alkylation of Nitriles

Abstract The catalytic α‐alkylation of benzyl nitriles with benzyl alcohols has been investigated with NNN pincer–ruthenium (Ru) complexes based on bis (imino)pyridine and 2,6‐ bis (benzimidazole‐2‐yl)pyridine ligands. The complex [ Cy2 NNN(RuCl 2 (PPh 3 )] was found to be the most efficient in comparison to other considered catalysts, leading to a 99% yield of α‐alkylated nitrile with 100% selectivity in the presence of 3 mol% KO t Bu in 1 mL of toluene at 140 °C within 2 h of reaction. While the release of PPh 3 appears to be pivotal, mercury drop experiments point to the well‐defined molecular nature of the pincer–Ru catalyst. The reaction demonstrates first‐order dependence of rate on the concentration of [ Cy2 NNN(RuCl 2 (PPh 3 )], KO t Bu, benzyl alcohol, and benzyl nitrile. DFT calculations indicate that the formation of α‐alkylated nitrile via the alcoholysis path with a barrier of 28.7 kcal/mol is the rate‐determining step (RDS) owing to equilibrium‐driven reasons despite the hydrogenolysis path being kinetically comparable (Δ G 140 ‡ = 29.0 kcal/mol). These barriers are in good agreement with the experimentally determined barrier of 29.6 kcal/mol.