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Host–Guest Exchange of Viologen Guests in Porphyrin Cage Compounds as Studied by Selective Exchange Spectroscopy (1D EXSY) NMR
Author(s) -
Swartjes Anne,
White Paul B.,
Lammertink Marijn,
Elemans Johannes A. A. W.,
Nolte Roeland J. M.
Publication year - 2021
Publication title -
angewandte chemie
Language(s) - English
Resource type - Journals
eISSN - 1521-3757
pISSN - 0044-8249
DOI - 10.1002/ange.202010335
Subject(s) - chemistry , dissociation (chemistry) , steric effects , viologen , reaction rate constant , nuclear magnetic resonance spectroscopy , porphyrin , molecule , two dimensional nuclear magnetic resonance spectroscopy , host–guest chemistry , photochemistry , crystallography , stereochemistry , kinetics , organic chemistry , supramolecular chemistry , physics , quantum mechanics
Dynamics in complexes of porphyrin cage compounds and viologen‐derived guest molecules are investigated by selective exchange NMR spectroscopy (1D EXSY). Exchange rates were found to be independent of excess guest concentration, revealing a dissociative exchange mechanism, which is accompanied by negative activation entropies, indicating significant reorganization of the host–guest complex during dissociation. Nonsymmetric viologen guests with bulky head groups had more unidirectional binding and slower exchange rates than guests with less‐bulky head groups. Thermodynamic and kinetic studies revealed that the exchange process is primarily driven by the thermodynamics of binding and that guest binding can be influenced by introducing steric and electronic groups on the host . Exchange studies with guests bearing a polymer chain revealed that both slippage and full dissociation takes place and the rate constants for both processes were determined. The slippage rate constant revealed that for smaller guests exchange takes place nearly exclusively under thermodynamic control.