Catalytic utility of PNN-based Mn I pincer complexes in the synthesis of quinolines and transfer hydrogenation of carbonyl derivatives.

This manuscript describes the synthesis of a triazolyl-pyridine-based phosphine, N -((diphenylphosphaneyl)methyl)- N -methyl-6-(1-phenyl-1 H -1,2,3-triazol-4-yl)pyridin-2-amine, [2,6-{(PPh 2 )CH 2 N(Me)(C 5 H 3 N)(C 2 HN 3 C 6 H 5 )}] (1) (here onwards referred to as PNN) and its cationic and neutral Mn I complexes and catalytic applications. The reaction of 1 with Mn(CO) 5 Br afforded a cationic complex [Mn(CO) 3 (PNN)]Br (2), which is highly stable in solid state, but in solution it gradually loses one of the CO groups to form a neutral complex [Mn(CO) 2 (PNN)Br] (3). Complex 2 on treatment with AgBF 4 also yielded a cationic complex [Mn(CO) 3 (PNN)]BF 4 (4). These complexes efficiently promoted the synthesis of quinoline derivatives via acceptor-less dehydrogenative coupling of 2-aminobenzyl alcohol and ketones, with complex 3 showing the highest activity with a very low catalyst loading (0.03 mol%) at 110 °C. Complex 3 (0.5 mol%) also showed excellent catalytic activity in the transfer hydrogenation of ketones and aldehydes to form respective secondary and primary alcohols.