NDLI: Mechanistic insights into the full hydrogenation of 2,6-substituted pyridine catalyzed by the Lewis acid $C_{6}F_{5}(CH_{2})_{2}B(C_{6}F_{5})

Content Provider	World Health Organization (WHO)-Global Index Medicus
Author	Li, Shuhua Zhao, Jiyang Wang, Guoqiang
Description	Author Affiliation: Zhao J ( School of Chemistry and Chemical Engineering, Key Laboratory of Mesoscopic Chemistry of Ministry of Education, Institute of Theoretical and Computational Chemistry, Nanjing University, Nanjing 210093, People's Republic of China. shuhua@nju.edu.cn.)
Abstract	The reaction mechanism for the full hydrogenation of 2-phenyl-6-methyl-pyridine catalyzed by the Lewis acid $C_{6}F_{5}(CH_{2})_{2}B(C_{6}F_{5})_{2}$ was investigated in detail by density functional theory calculations. Our calculations show that a plausible reaction pathway of the hydrogenation of pyridine contains five stages: (1) the generation of a new borane $C_{6}F_{5}(CH_{2})_{2}B(C_{6}F_{5})_{2}$ from the hydroboration of the alkene, which forms a frustrated Lewis pair (FLP) with a pyridine; (2) the activation of $H_{2}$ by FLP to yield an ion pair intermediate; (3) intramolecular hydride transfer from the boron atom to the pyridinium cation in the ion pair intermediate to produce the 1,4-dihydropyridine; (4) hydrogenation of the 1,4-dihydropyridine by the FLP to form the 1,4,5,6-tetrahydropyridine; (5) hydrogenation of the 1,4,5,6-tetrahydropyridine by the FLP to yield the final piperidine. The last two hydrogenation processes follow a similar pathway, which includes four steps: (a) proton transfer from the pyridinium moiety to the substrate; (b) dissociation of the newly generated pyridine; (c) hydride migration from the hydridoborate moiety to the protonated substrate to produce the hydrogenated product; (d) release of the hydrogenated product to regenerate the free borane. The full hydrogenation of pyridine is calculated to be exothermic by 16.9 kcal $mol^{−1},$ relative to the starting reactants. The rate-limiting step is the proton transfer in the second hydrogenation step, with a free energy barrier of 28.2 kcal $mol^{−1}$ in the gas phase (27.9 kcal $mol^{−1}$ in toluene) at room temperature and 1.0 atm. Our results can account for the observed experimental facts.
ISSN	14779226
Issue Number	19
Journal	Dalton Trans.
Volume Number	44
e-ISSN	13645447
Language	English
Publisher	Royal Society of Chemistry
Publisher Date	2015-05-21
Publisher Place	Great Britain (UK)
Access Restriction	Subscribed
Subject Keyword	Chemistry
Content Type	Text
Resource Type	Article
Subject	Inorganic Chemistry

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