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Infrared Multiphoton Dissociation Spectroscopic Analysis of Noncovalent Interactions in Organocatalysis
Author(s) -
Holland Mareike C.,
Berden Giel,
Oomens Jos,
Meijer Anthony J. H. M.,
Schäfer Mathias,
Gilmour Ryan
Publication year - 2014
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/ejoc.201402845
Subject(s) - chemistry , infrared multiphoton dissociation , organocatalysis , non covalent interactions , conformational isomerism , iminium , dissociation (chemistry) , photochemistry , computational chemistry , reactive intermediate , cucurbituril , counterion , infrared spectroscopy , stereochemistry , catalysis , enantioselective synthesis , ion , organic chemistry , hydrogen bond , molecule , supramolecular chemistry
Herein we report the first application of infrared multiple‐photon dissociation (IRMPD) spectroscopy to study noncovalent interactions in organocatalysis. Phenylalanine‐derived iminium ions, central to numerous organocatalytic processes, display dynamic conformational behavior as a consequence of stabilizing noncovalent interactions (e.g., CH–π, π–π). Electronic modulation of the aryl ring causes notable variation in the conformation; this can be detected spectroscopically and correlated with enantioselectivity. Given that these interactions, which orchestrate stereoinduction, encode for specific conformers (I, II, or III), a diagnostic IRMPD spectrum is generated: the C=O stretching frequency of the imidazole carbonyl group serves as a diagnostic marker. The calculated conformers and their respective spectra can be compared with experimental data. Consequently, valuable insight into the ubiquitous noncovalent interactions associated with MacMillan‐catalyst‐derived α,β‐unsaturated iminium ions can be obtained in the absence of solvent or counterion effects. A preliminary structure–catalysis correlation is disclosed, thus demonstrating the potential of this approach for studying reactive intermediates and facilitating catalyst design.