Planar N‐Heterocyclic Carbene Diarylborenium Ions: Synthesis by Cationic Borylation and Reactivity with Lewis Bases |
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| Authors: | Dr. Jeffrey M. Farrell Prof. Dr. Douglas W. Stephan |
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| Affiliation: | 1. Department of Chemistry, University of Toronto, 80 St. George St, Toronto, Ontario, M5S 3H6 (Canada);2. Chemistry Department, Faculty of Science, King Abdulaziz University, Jeddah 21589 (Saudi Arabia) |
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| Abstract: | The NHC–borane adduct (IBn)BH3 ( 1 ) (NHC= N‐heterocyclic carbene; IBn=1,3‐dibenzylimidazol‐2ylidene) reacts with [Ph3C][B(C6F5)4] through sequential hydride abstraction and dehydrogenative cationic borylation(s) to give singly or doubly ring closed NHC–borenium salts 2 and 3 . The planar doubly ring closed product [C3H2(NCH2C6H4)2B][B(C6F5)4] is resistant to quaternization at boron by Et2O coordination, but forms classical Lewis acid–base adducts with the stronger donors Ph3P, Et3PO, or 1,4‐diazabicyclo[2.2.2]octane (DABCO). Treatment of 3 with tBu3P selectively yields the unusual oligomeric borenium salt trans‐[(C3H2(NCH2C6H4)2B)2(C3H2(NCHC6H4)2B)][B(C6F5)4] ( 7 ). |
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| Keywords: | boranes borylation carbenes frustrated Lewis pairs steric hindrance |
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