Piperidine-appended imidazolium ionic liquids as task-specific catalysts: computational study, synthesis, and multinuclear NMR
Document Type
Article
Publication Date
7-1-2016
Abstract
Imidazolium ionic liquids (IMILs) with a piperidine moiety appended via variable length methylene spacers (with n = 1–4) were studied computationally to assess their potential to act as internal base for N-heterocyclic carbene (NHC) generation. Proton transfer energies computed by B3LYP/6-311+G(2d,p) were least endothermic for the basic-IL with n = 3, whose optimized structure showed the shortest C2-H----N(piperidine) distance. Inclusion of counter anion (Cl or NTf2) caused dramatic conformational changes to enable close contact between the acidic C2-H and the anions. To examine the prospect for internal C2-H----N coordination, multinuclear NMR data (1H, 15N, and 13C) were computed by gauge independent atomic orbitals–density functional theory (GIAO-DFT) in the gas phase and in several solvents by the PCM method for comparison with the experimental NMR data for the basic ILs (with n = 2–4) synthesized in the laboratory. These studies indicate that interactions with solvent and counter ion are dominant forces that could disrupt internal C2-H----N coordination/proton transfer, making carbene generation from these basic-ILs unlikely without an added external base. Therefore, the piperidine-appended IMILs appear suitable for application as dual solvent/base in organic/organometallic transformations that require the use of mild base, without the necessity to alkylate at C-2 to prevent N-heterocyclic carbene formation. Copyright © 2016 John Wiley & Sons, Ltd.
Publication Title
Journal of Physical Organic Chemistry
Volume
29
Issue
7
First Page
346
Last Page
351
Digital Object Identifier (DOI)
10.1002/poc.3541
ISSN
08943230
E-ISSN
10991395
Citation Information
Laali, Jamalian, A., & Borosky, G. L. (2016). Piperidine-appended imidazolium ionic liquids as task-specific catalysts: computational study, synthesis, and multinuclear NMR: Piperidine-appended Imidazolium Ionic Liquids. Journal of Physical Organic Chemistry, 29(7), 346–351. https://doi.org/10.1002/poc.3541