N-Heterocyclic Carbenes−Borane Complexes: A New Class of Initiators for Radical Photopolymerization

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• 作者：Mohamad-Ali Tehfe ; Malika Makhlouf Brahmi ; Jean-Pierre Fouassier ; Dennis P. Curran ; Max Malacria ; Louis Fensterbank ; Emmanuel Lacte ; Jacques Laleve
• 刊名：Macromolecules
• 出版年：2010
• 出版时间：March 9, 2010
• 年：2010
• 卷：43
• 期：5
• 页码：2261-2267
• 全文大小：894K
• 年卷期：v.43,no.5(March 9, 2010)
• ISSN：1520-5835

文摘

Newly discovered N-heterocyclic carbene-boryl radicals (NHC-BH₂^•) derived from readily available N-heterocyclic carbene−boranes are found to be efficient initiators for acrylate photopolymerization. Laser flash photolysis (LFP) experiments were used to generate three carbene-boryl radicals, which were characterized by their transient absorption spectra with the aid of DFT calculations. Rate constants were measured for the generation of the carbene-boryl radicals by hydrogen abstraction with tert-butoxyl radical, a ketophosphonyl radical, and triplet benzophenone. Rate constants were also measured for the reactions of the carbene-boryl radicals with oxygen, three alkenes, two alkyl chlorides, and diphenyliodonium hexafluorophosphate. The observed trends were interpreted with the aid of measured oxidation potentials of the carbene−boranes and calculated ionization potentials of the carbene-boryls. N-Heterocyclic carbene−boranes show excellent potential as both photopolymerization co-initiators and mediators of small molecule radical reactions, and these results will help guide further development in both fields.