Effect of Para-Substituents and Solvent Polarity on the Formation of Triphenylboroxine·Amine Adducts

Abstract

Density functional theory (B3LYP//6-311+G) calculations including Poisson-Boltzmann implicit solvent and NMR were used to study the formation of a series of para-substituted triphenylboroxine.amine adducts with respect to their phenylboronic acid monomers and free amine in solution. Our calculations suggest that the intermediate prior to forming trimer.amine is a dimer.amine adduct. Formation of dimer.amine can proceed via two pathways. Electron-donating substituents favor dimerization of two monomers before addition of the amine, and electron-withdrawing substituents favor formation of a monomer.amine adduct before addition of the second monomer. We also find that pi-electron acceptors destabilize formation of the dimer and trimer with respect to its monomers. Electron-withdrawing substituents favor adduct formation. Adduct formation is enthalpically stabilized by increasing the polarity of the solvent but differential solubility of the monomer compared to trimer.amine also has an effect on the equilibrium constant.

Heats of formation for the boronic acids R–B(OH)2 and boroxines R3B3O3 (R=H, Li, HBe, H2B, H3C, H2N, HO, F, and Cl) calculated at the G2, G3, and G4 levels of theory

“…However, based on the GC-MS and NMR investigations by Tokunaga et al . (7,8) and the DFT calculations by Kua and coworkers (9–11) on arylboroxine formation, this dehydration is not expected to be exothermic. Indeed, our recent MP2/aug-cc-pVTZ calculations suggest the reaction is significantly endothermic, with a $\mathrm{normal\Delta }{H}_{298}^0$ of +12.2 kcal/mol.…”

Thermodynamics of Boroxine Formation from the Aliphatic Boronic Acid Monomers R–B(OH)2 (R = H, H3C, H2N, HO, and F): A Computational Investigation

“…Despite the widespread applications of both aryl 20,22 and aliphatic 10,11,17–20 boroxines, few experimental or computational studies on the thermodynamics and kinetics of their formation from monomeric boronic acids have been reported 24–29 . Recently, Kua and coworkers 24–27 carried out a series of calculations (primarily at the B3LYP/6-311+G( d ) level) to help clarify the thermodynamics and kinetics for the formation of boroxines from aryl boronic acids.…”

“…Recently, Kua and coworkers 24–27 carried out a series of calculations (primarily at the B3LYP/6-311+G( d ) level) to help clarify the thermodynamics and kinetics for the formation of boroxines from aryl boronic acids. Thanks to these computational results and the experimental findings of the Tokunaga group 28,29 , it is now clear that the formation of boroxines from a variety of aryl boronic acids is endothermic in vacuo and in aqueous media.…”

Dynamic Iminoboronate‐Based Boroxine Chemistry for the Design of Ambient Humidity‐Sensitive Self‐Healing Polymers

“…[27,28] Although simple imines are very sensitivet ow ater owing to the hydrolysis reaction, it has been shownt hat the dative bond within iminoboronate species makest he imine product more robust against hydrolysis due to an enhanced thermodynamic stability. [30][31][32] Therefore, we planned to use the iminoboronate linkaget od esign the boroxine-based dynamic crosslinked network andw ee xpected that the boroxine BÀOb onds would conserve their dynamic feature even though Lewis acid-base interactions involve boron atoms and could consequently disrupt the reversion process. Furthermore, the construction of such iminoboronate adducts from boronic acid and amine moieties remains relatively simple and straightforward under mild conditions.…”