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Formation of Para-Substituted Triphenylboroxines:  A Computational Study

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posted on 2005-10-06, 00:00 authored by Jeremy Kua, Peter M. Iovine
Density functional theory (B3LYP//6-311+G*) calculations including Poisson−Boltzmann (PB) implicit solvent were applied to study the relative stability of triphenylboroxine (PhBO)3 with respect to its phenylboronic acid monomers. In solution, formation of (PhBO)3 is thermodynamically unfavorable; however, addition of an amine base results in the formation of stable 1:1 adducts of (PhBO)3 and amine. Formation of 1:2 adducts is energetically unfavorable. We find that adduct formation is more exothermic than cleavage of the boroxine ring back to its monomers. π-Electron-withdrawing groups in the para-position of the phenyl ring destabilize the boroxine ring with respect to its monomers. However, para-substituents that are net electron-withdrawing are found to stabilize formation of the 1:1 adduct.

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