Bortoli M, Wolters LP, Orian L, Bickelhaupt FM. Addition-Elimination or Nucleophilic Substitution? Understanding the Energy Profiles for the Reaction of Chalcogenolates with Dichalcogenides.
J Chem Theory Comput 2016;
12:2752-61. [PMID:
27096625 DOI:
10.1021/acs.jctc.6b00253]
[Citation(s) in RCA: 30] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
We have quantum chemically explored the mechanism of the substitution reaction between CH3X(-) and the homo- and heterodichalcogenides CH3X'X″CH3 (X, X', X″ = S, Se, Te) using relativistic density functional theory at ZORA-OLYP/TZ2P and COSMO for simulating the effect of aqueous solvation. In the gas phase, all substitution reactions proceed via a triple-well addition-elimination mechanism that involves a stable three-center intermediate. Aqueous solvation, in some cases, switches the character of the mechanism to double-well SN2 in which the stable three-center intermediate has become a labile transition state. We rationalize reactivity trends and some puzzling aspects of these elementary reactions, in particular, vanishing activation energies and ghost three-center intermediates, using the activation strain model (ASM).
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