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Planar N‐Heterocyclic Carbene Diarylborenium Ions: Synthesis by Cationic Borylation and Reactivity with Lewis Bases
Author(s) -
Farrell Jeffrey M.,
Stephan Douglas W.
Publication year - 2015
Publication title -
angewandte chemie
Language(s) - English
Resource type - Journals
eISSN - 1521-3757
pISSN - 0044-8249
DOI - 10.1002/ange.201500198
Subject(s) - chemistry , dabco , cationic polymerization , carbene , lewis acids and bases , borylation , adduct , octane , medicinal chemistry , reactivity (psychology) , borane , hydride , stereochemistry , ring (chemistry) , polymer chemistry , organic chemistry , catalysis , alkyl , aryl , pathology , medicine , hydrogen , alternative medicine
The NHC–borane adduct (IBn)BH 3 ( 1 ) (NHC= N‐heterocyclic carbene; IBn=1,3‐dibenzylimidazol‐2ylidene) reacts with [Ph 3 C][B(C 6 F 5 ) 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 [C 3 H 2 (NCH 2 C 6 H 4 ) 2 B][B(C 6 F 5 ) 4 ] is resistant to quaternization at boron by Et 2 O coordination, but forms classical Lewis acid–base adducts with the stronger donors Ph 3 P, Et 3 PO, or 1,4‐diazabicyclo[2.2.2]octane (DABCO). Treatment of 3 with t Bu 3 P selectively yields the unusual oligomeric borenium salt trans ‐[(C 3 H 2 (NCH 2 C 6 H 4 ) 2 B) 2 (C 3 H 2 (NCHC 6 H 4 ) 2 B)][B(C 6 F 5 ) 4 ] ( 7 ).