ic9b02257_si_001.pdf (19.85 MB)
Bifurcated Hydrogen-Bond-Stabilized Boron Analogues of Carboxylic Acids
journal contribution
posted on 2019-09-25, 16:34 authored by Rui Guo, Xiao Huang, Meihua Zhao, Yusheng Lei, Zhuofeng Ke, Lingbing KongThe reactivity of
a bulky m-terphenylboronic acid, DmpB(OH)2 [1; Dmp = 2,6-bis(2,4,6-trimethylphenyl)phenyl], toward
three different N-heterocyclic carbenes has been examined. The reaction
of 1 with 1 equiv of bis(2,6-diisopropylphenyl)imidazol-2-ylidene
(IPr) leads to the formation of a hydrogen-bonded carbene boronic
acid adduct, 2, featuring strong O–H···C
contacts. In contrast, more basic 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene
(IPr2Me2) and 1,3-di-tert-butylimidazol-2-ylidene
(ItBu) deprotonate 1 smoothly to afford the
rare anionic boranuidacarboxylic acids 3 and 4, respectively. Structural determination reveals that 3 and 4 bear unprecedented bifurcated hydrogen bonds
with a BO– unit as a double hydrogen-bond acceptor,
which contribute significantly to stabilization of the highly reactive
BO double bond. Quantum-mechanical calculations were conducted
to disclose the unique electronic properties of the multiple bonds,
as well as the important hydrogen bonds in these compounds.