Asymmetric Hydrogenation Catalyzed by a Rhodium Complex of (R)‐(tert‐Butylmethylphosphino)(di‐tert‐butylphosphino)methane: Scope of Enantioselectivity and Mechanistic Study.

The rhodium complex of (R)-(tert-butylmethylphosphino)(di-tert-butylphosphino)methane used in Rh-catalyzed asymmetric hydrogenation of representative substrates 3−14 demonstrated high catalytic activity coupled with wide scope and nearly perfect enantioselectivity. Mechanistic studies (NMR and DFT computations) were carried out in order to investigate the mechanism of the enantioselection in the asymmetric hydrogenation of (Z)-α-acetamidocinnamate (3). Although catalyst−substrate complexes 15a,b with the double bond coordinated near the non-“chiral” phosphorus atom were formed as kinetic products upon the addition of 3 to solvate complex 2 at −100 °C, they rapidly rearranged to more stable isomers 15c,d with the double bond coordinated near the “chiral” phosphorus atom. The thermodynamic and kinetic parameters of the interconversion between 15c and 15d were determined by NMR; mainly, the interconversion occurred intramolecularly via nonchelating catalyst−substrate complexes 16. The equilibrium between 15d...