Cheng GJ, Chen P, Sun TY, Zhang X, Yu JQ, Wu YD. A combined IM-MS/DFT study on [Pd(MPAA)]-catalyzed enantioselective C-H activation: relay of chirality through a rigid framework.
Chemistry 2015;
21:11180-8. [PMID:
26186414 DOI:
10.1002/chem.201501123]
[Citation(s) in RCA: 86] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2015] [Indexed: 11/07/2022]
Abstract
A combined ion-mobility mass spectrometry (IM-MS) and DFT study has been employed to investigate the mechanism and the origin of selectivity of palladium/mono-N-protected amino acid (MPAA)-catalyzed enantioselective CH activation reactions of several prochiral substrates. We captured the [Pd(MPAA)(substrate)] complex at different stages, and demonstrated that the CH bond can be activated in the absence of an external base. DFT studies lead to the establishment of a significantly modified relay mechanism invoking a key conformational effect to account for the origin of enantioselectivity. This relay mechanism successfully accounts for the enantioselectivity for all the relevant reactions reported. The enantioselectivity originates from the rigid square-planar Pd coordination in the CH activation transition state: Bidentate MPAA and substrate coordination.
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