Kirill V. Axenov

Chiral Molecular Tweezers: Synthesis and Reactivity in Asymmetric Hydrogenation

We report the synthesis and reactivity of a chiral aminoborane displaying both rapid and reversible H2 activation. The catalyst shows exceptional reactivity in asymmetric hydrogenation of enamines and unhindered imines with stereoselectivities of up to 99% ee. DFT analysis of the reaction mechanism pointed to the importance of both repulsive steric and stabilizing intermolecular non-covalent forces in the stereodetermining hydride transfer step of the catalytic cycle.

Diverting Hydrogenations with Wilkinson's Catalyst towards Highly Reactive Rhodium(I) Species

The addition of Bartons base has a dramatic effect on the classic rhodium(III)-mediated hydrogenations promoted by Wilkinsons catalyst. Following the initial oxidative addition, a barrierless reductive elimination of HCl from the traditional rhodium(III) intermediates instantly produces a rhodium(I) monohydride species, which is remarkably reactive in the hydrogenation of several internal alkynes and functionalized trisubstituted alkenes. The direct formation of this species is unprecedented upon addition of molecular hydrogen and its catalytic potential has been hitherto barely explored.