Efficient transfer hydrogenation of ketones using molybdenum complexes by comprehensively verifying the auxiliary ligands.

Molybdenum complexes ligated with N 1 , N 1 -dialkyl- N 2 -(5,6,7,8-tetrahydroquinolin-8-yl)ethane-1,2-diamines and auxiliary ligands, providing various structural features, were developed: [NN H /NN H N]Mo(CO) 4/3 (Mo1-Mo3), [NN H N]Mo(CO) 2 Br (Mo4-Mo5), [NN H ]Mo(CO)(η 3 -C 3 H 5 )Br (Mo6) and [NN H N/S]Mo(CO)(PPh 3 ) 2 (Mo7-Mo8). All the complexes were highly active in the transfer hydrogenation (TH) of a model substrate (acetophenone), providing excellent yields of 1-phenylethanol. The structural variation in the ligand framework had a modest effect on the catalyst performance as compared to the changes in the auxiliary ligands Br, PPh 3 and CO. This structural evolution provided the complex [Mo(NN H )(η 3 -C 3 H 5 )(CO) 2 Br] (Mo6) as the most effective catalyst not only for the transfer hydrogenation of acetophenone but also for a wide range of diverse ketones (up to 43 examples). Moreover, easy purification of the products by only removing the acetone byproduct is another noteworthy feature of this environmentally friendly route.