文献类型：期刊文献

英文题名：Enhanced Menshutkin SN2 Reactivity in Mesoporous Silica: The Influence of Surface Catalysis and Confinement

作者：Zheng, Weizhong[1,2];Yamada, Steven A.[1];Hung, Samantha T.[1];Sun, Weizhen[2];Zhao, Ling[2];Fayer, Michael D.[1]

机构：[1]Stanford Univ, Dept Chem, Stanford, CA 94305 USA;[2]East China Univ Sci & Technol, State Key Lab Chem Engn, Shanghai 200237, Peoples R China

年份：2020

卷号：142

期号：12

起止页码：5636

外文期刊名：JOURNAL OF THE AMERICAN CHEMICAL SOCIETY

收录：;EI(收录号：20201508395357);WOS:【SCI-EXPANDED(收录号:WOS:000526393100026)】；

基金：This work was funded by the Division of Chemical Sciences, Geosciences, and Biosciences, Office of Basic Energy Sciences of the U.S. Department of Energy through Grant No. DE-FG03-84ER13251 (W.Z., S.A.Y., and M.D.F.). S.T.H. was supported by the National Science Foundation through the CCI program, CHE-1740645. Part of this work was performed at the Stanford Nano Shared Facilities (SNSF), supported by the National Science Foundation under Award ECCS-1542152. We thank Stanford University and the Stanford Research Computing Center for providing computational resources for this research; the ab initio calculations were performed on the Sherlock cluster at Stanford. The MD simulations were performed on a home-built cluster in China, and we thank Cao Piao, Zhennan Wang, and Xiaohong Liu for their help with the MD simulation data transfer. W.Z. gratefully acknowledges the support from the China Scholarship Council (No. 201806740046) during his work at Stanford University. S.A.Y. gratefully acknowledges the support from a Stanford Graduate Fellowship. We thank Maolin Sha and Boning Wu for their constructive suggestions on the simulation methods and analysis code and Sean Roget for his constructive comments on the manuscript.

语种：英文

外文关键词：Hydrogen bonds - Chemical analysis - Electronic structure - Calculations - Molecular dynamics - Interface states - Rate constants - Pore size - Chlorine compounds - Silica - Surface chemistry - Infrared spectroscopy

摘要：A significant enhancement in the Menshutkin S(N)2 reaction between 1-methylimidazole (MeIm) and methyl thiocyanate (MeSCN) is observed when the reaction is confined in the nanoscale silica pores of MCM41 and SBA15. The experiments in the silica pores are conducted without the surrounding bulk reaction mixture. The influences of temperature, pore radius, and surface chemistry on the kinetics of the confined reaction are analyzed with time-dependent infrared spectroscopy, molecular dynamics simulations, and ab initio calculations. The rate constant of the pseudo-first order reaction increases with decreasing pore size, and the activation energy is found to decrease by 5.6 kJ/mol in the smallest pore studied (2.8 nm) relative to the bulk reaction. The rate constant dependence on pore size is accurately described by a two-state model in which molecules within the 4.6 angstrom interfacial layer experience a 2.4-fold rate constant increase relative to those reacting at the bulk rate further away from the interface. The removal of polar silanol groups from the silica surface via passivation with trimethylsilyl chloride results in bulk-like kinetics despite a reduction in the pore diameter, demonstrating the role of silanols as catalytic sites. Electronic structure calculations of the energy profile on a model silica surface confirm that silanol groups, particularly those of the vicinal type, can reduce the activation energy and reaction endothermicity through the donation of hydrogen bonds to the reactant, transition state, and product complexes.