Synthesis and Reactions of N-Heterocyclic Carbene Boranes

• Published in: Angewandte Chemie International Edition 2011-10, Vol.50 (44), p.10294-10317
• Main Authors: Curran, Dennis P., Solovyev, Andrey, Makhlouf Brahmi, Malika, Fensterbank, Louis, Malacria, Max, Lacôte, Emmanuel
• Format: Article
• Language: English
• Subjects: boron; Chemical bonds; Lewis pairs; N-heterocyclic carbenes; radicals
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.201102717

Boranes are widely used Lewis acids and N‐heterocyclic carbenes (NHCs) are popular Lewis bases, so it is remarkable how little was known about their derived complexes until recently. NHC‐boranes are typically readily accessible and many are so stable that they can be treated like organic compounds rather than complexes. They do not exhibit “borane chemistry”, but instead are proving to have a rich chemistry of their own as reactants, as reagents, as initiators, and as catalysts. They have significant potential for use in organic synthesis and in polymer chemistry. They can be used to easily make unusual complexes with a broad spectrum of functional groups not usually seen in organoboron chemistry. Many of their reactions occur through new classes of reactive intermediates including borenium cations, boryl radicals, and even boryl anions. This Review provides comprehensive coverage of the synthesis, characterization, and reactions of NHC‐boranes. Forget everything you know about boron chemistry …︁ NHC‐boranes (see picture) are different. Functionalities that are not usually present in organoboron compounds can be easily introduced. New classes of rare boron‐based reactive intermediates (cations, radicals, and anions) have emerged. And NHC‐boranes are promising as reagents and catalysts in organic synthesis and as co‐initiators in radical polymerization.