A Base and Solvent-Free Ruthenium-Catalyzed Alkylation of Amines

A (pyridyl)­phosphine-ligated
ruthenium­(II) catalyst is reported
for the chemoselective benzylic N-alkylation of amines, via a hydrogen-borrowing
mechanism. The catalyst operates under mild conditions, neat, and
without a base or other additive. These conditions offer remarkable
functional group compatibility for applications in organic synthesis,
including reactions involving phenols and anilines, which are very
difficult to achieve. Mechanistic studies suggest that, unlike other
catalysts for this reaction, the redox steps are fast and reversible
while imine formation is slow. We perceive that this is the origin
of the selectivity realized with these reaction conditions.