Lewis acidity enhancement of triarylborane by appended phosphine oxide groups.


A series of mono-, di-, and tri-phosphine oxide substituted triarylboranes, Mes2BAr (1), MesBAr2 (2), and BAr3 (3) (Ar = 4-(Ph2PO)-2,6-Me2-C6H2) were prepared to investigate the effect of a phosphine oxide group (Ph2PO) on Lewis acidity enhancement of triarylboranes. The X-ray crystal structure of 3 revealed peripheral decoration of Ph2PO groups with a C3-axis perpendicular to the trigonal boron center. UV/Vis absorption and PL spectra indicated a significant contribution of π(Mes or phenylene) → pπ(B) charge transfer in the lower-energy electronic transition. The reduction potential measured by cyclic voltammetry showed apparent LUMO stabilization by introduction of phosphine oxide groups, the extent of which gradually increased with the increasing number of phosphine oxide groups. Lewis acidity enhancement was also supported by the gradual increase in fluoride ion affinity in the order 3 > 2 > 1. Theoretical calculations suggest that introduction of a Ph2PO group into a triarylborane significantly enhances the Lewis acidity of the boron center via an inductive electron-withdrawing effect and this effect is additive for multiple phosphine oxide groups.

DOI: 10.1039/c5dt00042d

Cite this paper

@article{Kwak2015LewisAE, title={Lewis acidity enhancement of triarylborane by appended phosphine oxide groups.}, author={Jaewoo Kwak and Nguyen Van Nghia and Junseong Lee and Hyoseok Kim and Myung Hwan Park and Min Hyung Lee}, journal={Dalton transactions}, year={2015}, volume={44 10}, pages={4765-72} }