A Pentacoordinate Boron-Containing π-Electron System with Cl–B–Cl Three-Center Four-Electron Bonds

Abstract

Tricoordinate boron-containing π-electron systems are an attractive class of compounds with intense fluorescence and strong electron-accepting properties. However, the impact of pentacoordination of the boron atoms on their properties has not been determined. We now disclose a B,B'-bis(1,8-dichloro-9-anthryl)-substituted 9,10-dihydro-9,10-diboraanthracene as a new pentacoordinate organoboron compound. In this skeleton, with the aid of the orthogonal arrangement of the anthryl substituent, the B and Cl atoms can form a three-center four-electron (3c-4e) Cl-B-Cl bond. The pentacoordination of the boron atom significantly perturbs the electronic structure and thereby the photophysical and electrochemical properties.

Highly Electron‐Deficient and Air‐Stable Conjugated Thienylboranes

“…The corresponding values for FBDT2 proved to be similar with average values of 0.015 e a 0 À3 and 0.050 e a 0 À5 . The relatively lower electron density for FBDT and FBDT2 in comparison to that reported by Yamaguchi for related B···Cl [17] and by Yamashita for B···O contacts [18] is likely a result of the smaller atomic radii and higher electronegativity of fluorine.…”

Recent developments in and perspectives on three-coordinate boron materials: a bright future

“…However, degradation was observed in dilute solutions (10 –5 M) of 37 during photophysical measurements. 160 Yamaguchi and co-workers found that the introduction of two chloro atoms at the 1,8-positions of the 9-naphthalenyl substituent could stabilise the boron via Cl–B interactions. This results in a weak Cl–B–Cl three-centre, four-electron bond and a nominally five-coordinate boron centre.…”

Regioselective electrophilic borylation of haloarenes

“…17 Previously, Yamaguchi and co-workers demonstrated the presence of 3c-4e bonding between boron and two proximal chlorines at comparable (2.727(4) Å) B-Cl distances in a neutral triarylborane, albeit in a significantly more linear Cl-B-Cl arrangement than that found in 2 (167.2° versus 128.0° in 2). 18 Inspection of the calculations (M06-2X/6-311G(d,p) PCM CH 2 Cl 2 ) on 2 revealed that the HOMO-8 contains a degree of bonding overlap between the ortho chlorines on Cl 2 Py and boron. However, the major bonding component in this orbital is from B-Cl π donation (Figure 1, bottom left).…”