Proof of Chiral Dihydride Complexes Including Catalyst and Substrate during the Bis(phosphinite)rhodium(I)‐Catalyzed Hydrogenation of Dimethyl Itaconate

The PHIP-NMR method (PHIP = parahydrogen induced polarization) can be used to detect dihydride catalyst–substrate complexes of the general formula [Rh(PP)(XX)(H)2]BF4 (shown on the right, XX = dimethyl itaconate as substrate), which are formed in situ under hydrogenation conditions with chiral bis(phosphinite)rhodium(I) catalysts. Remarkable is the absence of typical (H,P)trans coupling (2J(H,P)trans); the RhP bond trans to HB is therefore lenthened, and the octahedral geometry distorted.