Engineering a Small HOMO–LUMO Gap and Intramolecular C−H Borylation by Diborene/Anthracene Orbital Intercalation

The diborene 1 was synthesized by reduction of a mixture of 1,2‐di‐9‐anthryl‐1,2‐dibromodiborane(4) (6) and trimethylphosphine with potassium graphite. The X‐ray structure of 1 shows the two anthryl rings to be parallel and their π(C14) systems perpendicular to the diborene π(B=B) system. This twist...

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Bibliographic Details
Published in:Angewandte Chemie International Edition 2017-06, Vol.56 (27), p.8009-8013
Main Authors: Wang, Sunewang R., Arrowsmith, Merle, Böhnke, Julian, Braunschweig, Holger, Dellermann, Theresa, Dewhurst, Rian D., Kelch, Hauke, Krummenacher, Ivo, Mattock, James D., Müssig, Jonas H., Thiess, Torsten, Vargas, Alfredo, Zhang, Jiji
Format: Article
Language:English
Subjects:
Absorption
Absorption spectra
Anthracene
Bonding
boron
borylation
Conformation
Conjugation
C−H functionalization
diborenes
Engineering
Graphite
HOMO–LUMO gap
Intercalation
Molecular orbitals
Oxidation
Phosphine
Potassium
Selenium
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Summary:The diborene 1 was synthesized by reduction of a mixture of 1,2‐di‐9‐anthryl‐1,2‐dibromodiborane(4) (6) and trimethylphosphine with potassium graphite. The X‐ray structure of 1 shows the two anthryl rings to be parallel and their π(C14) systems perpendicular to the diborene π(B=B) system. This twisted conformation allows for intercalation of the relatively high‐lying π(B=B) orbital and the low‐lying π* orbital of the anthryl moiety with no significant conjugation, resulting in a small HOMO–LUMO gap (HLG) and ultimately a C−H borylation of the anthryl unit. The HLG of 1 was estimated to be 1.57 eV from the onset of the long wavelength band in its UV/Vis absorption spectrum (THF, λonset=788 nm). The oxidation of 1 with elemental selenium afforded diboraselenirane 8 in quantitative yield. By oxidative ion of one phosphine ligand by another equivalent of elemental selenium, the B−B and C1−H bonds of 8 were cleaved to give the cyclic 1,9‐diborylanthracene 9. Gap engineering: An anthryl‐substituted diborene was isolated as dark‐green crystals with a remarkably small HOMO–LUMO gap (HLG) of 1.57 eV. An unprecedented intramolecular C−H borylation with the B−B bond in the corresponding diboraselenirane was observed after oxidative ion of a phosphine ligand.
ISSN:1433-7851
1521-3773
DOI:10.1002/anie.201704063