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DFT Study of Ni-Al Bimetallic-Catalyzed Selective meta-C(sp2)-H Alkenylation of Pyridine: Mechanism and
Ailin Gao1, Jiaxin Lu1, Qing Li2
1Department of Chemistry, Key Laboratory of Advanced Energy Materials Chemistry (Ministry of Education), College of Chemistry, Nankai University, Tianjin300071, P. R. China.
Abstract:
The mechanism of Ni-Al bimetallic-catalyzed selective meta-C(sp2)-H bond alkenylation of pyridine has been investigated using DFT calculations. The reaction constructs macrocyclic intermediates using a bifunctional NHC ligand and a pyridine substrate, which selectively generates the meta-C(sp2)-H alkenylated pyridine products. Calculations show that the pyridine meta-C(sp2)-H bond activation involves a ligand-to-ligand hydrogen transfer (LLHT) mechanism, rather than a stepwise oxidative addition mechanism, and the rate-determining step of the reaction is the reductive elimination process. In addition, to disclose the regioselectivity for the C(sp2)-H bond alkenylation, the reaction mechanisms for the disfavored pyridine para-C(sp2)-H and ortho-C(sp2)-H alkenylation reactions have also been calculated. It was found that the rate-determining step for both the para- and ortho-substituted pathways is likewise the reductive elimination process. Studies reveal that the regioselectivity is governed by the stability of macrocyclic templates regulated by appropriate levels of ring strain.
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