Mechanistic Studies on Pd(MPAA)-Catalyzed Enantioselective C–H Activation Reactions

A combined ion-mobility mass spectrometry (IM-MS) and DFT study has been carried out to investigate Pd/MPAA(mono-N-protected amino acid)-catalyzed direct asymmetric C–H activation reactions of several prochiral substrates. The IM-MS experiments reveal that the activation of C–H bond can be achieved in PdII(MPAA)(substrate) complex which supports that the N-protecting group acts as proton acceptor. DFT studies lead to the establishment of a chirality relay model which successfully explains the enantioselectivity for all the relevant reactions studied. The enantioselectivity originates from the rigidity of the bidentate MPAA and rigid coordination of the substrate. The effect of bulkiness of the N-protecting group on enantioselectivity is also discussed.