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Hydrogen‐Bond Structure and Dynamics of TADDOL Asymmetric Organocatalysts Correlate with Catalytic Activity
Author(s) -
Cha Seoncheol,
Marekha Bogdan,
Wagner Manfred,
Hunger Johannes
Publication year - 2019
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201901594
Subject(s) - hydrogen bond , intermolecular force , catalysis , intramolecular force , chemistry , molecule , solvent , diol , hydrogen , low barrier hydrogen bond , photochemistry , computational chemistry , polymer chemistry , organic chemistry
The catalytic efficiency of diol‐based organocatalysts has been shown to strongly depend on the diols molecular structure including hydrogen‐bonding, yet, the underlying molecular‐level origins have remained elusive. Herein a study on the inter‐ and intramolecular hydrogen‐bonding of two isomeric diol‐based catalysts (TADDOLs) in solution is presented: 1‐Naphthyl substituted TADDOL (1nTADDOL), which exhibits high catalytic efficiency, and 2‐naphthyl substituted TADDOL (2nTADDOL), which is a poor catalyst. Using nuclear magnetic resonance and infrared spectroscopy, comparable hydrogen‐bond strengths for both TADDOLs in solution were found, however, significantly slower bonding dynamics for 1nTADDOL. In aromatic solvents, 1nTADDOL forms less, but longer‐lived, intermolecular OH⋅⋅⋅π bonds to solvent molecules, as compared to 2nTADDOL. Thus, rather than previously suggested differences in intermolecular hydrogen‐bonding strengths, the results suggest that the hydrogen‐bonding kinetics and entropies differ for both TADDOLs, which also explains their vastly different catalytic activities.