Stereochemistry of Imine Reduction by a Hydroxycyclopentadienyl Ruthenium Hydride

The stereochemistry of hydrogen transfer from [2,5-Ph2-3,4-Tol2(η5-C4COD)]Ru(CO)2D to N-aryl imines to give amine complexes was shown to be mostly trans stereospecific. Stereospecific hydrogen transfer is proposed to generate an amine and a coordinatively unsaturated ruthenium intermediate in close proximity. Coordination of the amine is proposed to occur faster than lone pair inversion of the amine. In contrast, hydrogen transfer to N-alkyl imines is stereorandom. It is proposed that stereochemistry is lost in part due to the reversibility of the hydrogen transfer being faster than amine coordination.