An Estimate of the Reduction Potential of B(C₆F₅)₃ from Electrochemical Measurements on Related Mesityl Boranes

Abstract

MesB(C6F5)2 (1) has been prepared from MesMgBr and FB(C6F5)2·OEt2, while Mes2B(C6F5) (2) is readily available from CuC6F5 and Mes2BBr. The reduction potential E° of 1 vs Cp2Fe0/+ in THF is −1.72 V, while that of 2 is −2.10 V, and that of Mes3B (3) is −2.73 V. 11B and 1H NMR show that neither 1 nor 2 binds THF significantly. These results have been used to estimate the reduction potential of B(C6F5)3 in THF as −1.17 V vs Cp2Fe0/+ or as −0.64 V vs SCE.

The Reduction Chemistry of Ferrocenylborole

“…borole has never been reported before, except for a borafluorene that features an annulated molecular backbone. [11,17] This first reduction potential of 1 is significantly less negative than that observed for triarylboranes, which generally feature a reversible reduction processes around E 0 1/2 = À2.7 V. [8] This observation is consistent with the enhanced electron deficiency of the boron atom in 1 as a result of the 4 p-electron antiaromaticity. This reduction potential is also more positive than that reported for 9-(2,4,6-tri-tert-butylphenyl)borafluorene (E 0 1/2 = À2.2 V vs. Fc/Fc + ), thus demonstrating the difference in antiaromaticity between non-annulated and annulated boroles.…”

Benzo‐ and Naphthoborepins: Blue‐Emitting Boron Analogues of Higher Acenes

“…The 11 B NMR spectra feature signals characteristic of three-coordinate, neutral boron nuclei [14] at 64.3, 67.7, and 66.7 ppm for 3 a-c, respectively. [15] While the spectroscopic data are consistent with planar structures, X-ray crystallographic analysis [16] of each compound reveals bowed geometries; this deformation is likely due to packing effects (see below) rather than a ground-state preference for this geometry. Figure 1 shows the molecular structures of 3 b and 3 c, while Figure 2 illustrates key intermolecular packing interactions; 3 a [15] is similar to 3 c and will not be discussed in detail.…”

Multidimensional potential of boron-containing molecules in functional materials

“…The corresponding radical anions [BX 3 ] •-are isoelectronic with the much studied methyl radicals [CX 3 ] • and with aminium radical cations [NX 3 ] •+ ; reactions of triarylboranes with alkali metals have thus been studied sporadically over the past decades. 2,14,[20][21][22][23] Follow-up reactions 20 to the electron transfer such as B-aryl bond dissociation and association to form borates can preclude the observation of corresponding radical anions, which may yet be stabilised following familiar strategies from organic radical chemistry, i.e. steric shielding to prevent bimolecular reactivity, and spin delocalization through π conjugation.…”