Journal article

Publication year: 2015

Pages: 5922-5927

Journal: Chemical Science

Volume number: 6

Issue number: 10

ISSN: 2041-6520

DOI Link: https://doi.org/10.1039/c5sc02205c

Publisher: Royal Society of Chemistry

Abstract: 
The electron-deficient pentaarylborole 1-(2',4',6'-tris(trifluoromethyl)phenyl)-2,3,4,5-tetraphenylborole (1) has been synthesised with the long-term aim of developing borole-based optoelectronic materials. The bulky 2,4,6-tris(trifluoromethyl)phenyl (FMes) group on the boron atom of 1 significantly improves (>600 times) its air stability relative to its mesityl analogue. Moreover, 1 shows good thermal stability without undergoing the dimerisation or isomerisation reactions reported for some other boroles. A triarylborole analogue (2), belonging to a new class of borole with the 3- and 4-positions of the BC4 ring linked by a -(CH2)(3)- group, has also been synthesised to elucidate the influence of carbon-bonded substituents on the stability of boroles. Both boroles were prepared through the reaction of Li[FMesBF(3)] and divinyldilithium reagents, a new and general method for borole syntheses. Compound 2 was found to isomerise through a [1,3]-H shift and double-bond rearrangement to an s-trans-butadienylborane species under highly basic (NaOH) conditions. The increased steric crowding at the boron centre through incorporation of the FMes group does not preclude binding of Lewis bases to either 1 or 2, as demonstrated by their fully reversible binding of pyridine. Interestingly, 1 exhibits a blue-shifted absorption spectrum, as compared with its mesityl analogue, a result contrary to previous understanding of the influence of substituent electronics on the absorption spectra of boroles. Most importantly, these boroles exhibit much greater air-stability than previously reported analogues without sacrificing the strong electron-accepting ability that makes boroles so attractive; indeed, 1 and 2 have very low reduction potentials of -1.52 and -1.69 eV vs. Fc/Fc(+), respectively.

Harvard Citation style: Zhang, Z., Edkins, R., Haehnel, M., Wehner, M., Eichhorn, A., Mailänder, L., et al. (2015) Taming the beast: fluoromesityl groups induce a dramatic stability enhancement in boroles, Chemical Science, 6(10), pp. 5922-5927. https://doi.org/10.1039/c5sc02205c

APA Citation style: Zhang, Z., Edkins, R., Haehnel, M., Wehner, M., Eichhorn, A., Mailänder, L., Meier, M., Brand, J., Brede, F., Müller-Buschbaum, K., Braunschweig, H., & Marder, T. (2015). Taming the beast: fluoromesityl groups induce a dramatic stability enhancement in boroles. Chemical Science. 6(10), 5922-5927. https://doi.org/10.1039/c5sc02205c