Ru(II) complexes of N-alkylated TsDPEN ligands in asymmetric transfer hydrogenation of ketones and imines.

N-Alkylated TsDPEN derivatives bearing a small alkyl group act as highly efficient ligands in Ru(II) complexes for the asymmetric transfer hydrogenation of imines and ketones. A larger alkyl group serves to significantly reduce the activity of the catalyst; however, high enantiomeric excesses are still obtained. An X-ray crystal structure of the N-benzyl derivative reveals a conformation that permits hydrogen transfer through a six-membered transition state. A transition state structure for the imine reduction process is proposed.