Stabilization of a Borafluorene Anion with Carbenes

  • Author: Angewandte Chemie International Edition
  • Published Date: 05 May 2021
  • Copyright: Wiley-VCH GmbH
thumbnail image: Stabilization of a Borafluorene Anion with Carbenes


"Now Available with a Negative Charge"

The incorporation of boron into polycyclic aromatic hydrocarbon (PAH) systems leads to interesting chromophoric and fluorescing materials for optoelectronics, including organic light-emitting diodes (OLEDS) and field-effect transistors, as well as polymer-based sensors. David J. D. Wilson, Latrobe University, Melbourne, Australia, Robert J. Gilliard Jr., University of Virginia, Charlottesville, USA, and colleagues have introduced a new anionic organoborane compound. The synthesis of the borafluorene succeeded through the use of carbenes.


Borafluorene is a particularly interesting boron-containing building block. It is a system of three carbon rings: two six-membered rings and one central five-membered ring incorporating a boron atom. While neutral, radical, and cationic borafluorene compounds are quite easy to produce, there have been few examples of anionic borafluorene compounds to date. A better understanding of their chemistry is important for advances in redox-dependent applications and could lead to new materials with unique bonding or optical properties. However, the relatively high reactivity of borafluorene anions makes their synthesis challenging. The researchers succeeded in the isolation and structural characterization of these elusive anions.




Carbene-Stabilized Anions

The starting point for the team's synthesis is 9-bromo-9-borafluorene, which has a bromine atom attached to its boron atom. This is treated with a very strong reducing agent (potassium graphite, sodium naphthalenide, or lithium naphthalenide) in the presence of carbenes. The anionic borafluorenes formed in the reduction are stabilized by the carbenes (pictured).


As the team demonstrated, the carbene–borafluorene anions can also be used as chemical building blocks. This makes it possible to produce new compounds that are not otherwise accessible with previously known starting materials. For example, compounds with bonds between boron and gold, selenium, or germanium were generated. A reaction with a diketone led to a ring closure and bonding of the boron atom to both ketone oxygens, forming a spirocyclic boron compound.


 

 

Article Views: 1209

Sign in Area

Please sign in below

Additional Sign In options

Please note that to comment on an article you must be registered and logged in.
Registration is for free, you may already be registered to receive, e.g., the newsletter. When you register on this website, please ensure you view our terms and conditions. All comments are subject to moderation.

Article Comments - To add a comment please sign in

If you would like to reuse any content, in print or online, from ChemistryViews.org, please contact us first for permission. more

Follow on Facebook Follow on Twitter Follow on YouTube Follow on LinkedIn Follow on Instagram RSS Sign up for newsletters

Magazine of Chemistry Europe (16 European Chemical Societies) published by Wiley-VCH