The association of pyridine and of 2,4,6-trimethylpyridine (collidine) with a pyramidal triarylborane belonging to the 9-boratriptycene family is investigated by NMR spectroscopy and by X-ray diffraction analysis. Despite of the large size of the ortho-disubstituted collidine Lewis base and of the large steric hindrance of the boron Lewis superacid used (9-boratriptycene-10-sulfonium), the superacidity at its boron atom is enabling the formation of a B-N bond and is resulting in a very stabe Lewis adduct. Single- crystal X-ray diffraction analysis revealed an exceptional deformation of the collidine moiety with a deviation from planarity of nearly 41° between the pyridine C−N bonds and the ortho-methyl groups C−Me bonds, which is even resulting a small twist of the collidine six-membered heteroaromatic ring into a boat-like conformation. Computational investigations indicate that the steric repulsions are reducing the Gibbs free energy of Lewis adduct formation by approximately 50 kJ mol−1.
|Zeitschrift fuer Anorganische und Allgemeine Chemie
|Published - 2 May 2023
- Lewis adducts
- frustrated Lewis pairs
- Lewis acids
- Frustrated Lewis pairs
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Technological Platform Physical Chemistry and characterization
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