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: [NNH/NNHN]Mo(CO)(4/3) (Mo1-Mo3), [NNHN]Mo(CO)(2)Br (Mo4-Mo5), [NNH]Mo(CO)(eta(3)-C3H5)Br (Mo6) and [NNHN/S]Mo(CO)(PPh3)(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, PPh3 and CO. This structural evolution provided the complex [Mo(NNH)(eta(3)-C3H5)(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.

Automated summary

Molybdenum complexes with various structural features were developed and showed high activity in the transfer hydrogenation reaction. The products can be easily purified by removing the byproduct.