Department of Chemistry, University of Toronto, 80 St. George St, Toronto, Ontario, M5S 3H6 (Canada).
Angew Chem Int Ed Engl. 2015 Apr 20;54(17):5214-7. doi: 10.1002/anie.201500198. Epub 2015 Mar 10.
The NHC-borane adduct (IBn)BH3 (1) (NHC= N-heterocyclic carbene; IBn=1,3-dibenzylimidazol-2ylidene) reacts with [Ph3 C][B(C6 F5 )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 [C3 H2 (NCH2 C6 H4 )2 B][B(C6 F5 )4 ] is resistant to quaternization at boron by Et2 O coordination, but forms classical Lewis acid-base adducts with the stronger donors Ph3 P, Et3 PO, or 1,4-diazabicyclo[2.2.2]octane (DABCO). Treatment of 3 with tBu3 P selectively yields the unusual oligomeric borenium salt trans-[(C3 H2 (NCH2 C6 H4 )2 B)2 (C3 H2 (NCHC6 H4 )2 B)][B(C6 F5 )4 ] (7).
NHC-硼烷加合物 (IBn)BH3（1）（NHC= 杂环卡宾；IBn=1,3-二苄基咪唑-2-亚基）通过顺序氢化物抽提和脱氢阳离子硼化反应与 [Ph3 C][B(C6 F5 )4 ] 反应，得到单环或双环闭合的 NHC-硼翁盐 2 和 3。平面双环闭合产物 [C3 H2 (NCH2 C6 H4 )2 B][B(C6 F5 )4 ] 不易被 Et2 O 配位季铵化，但可与更强的供体 Ph3 P、Et3 PO 或 1,4-二氮杂双环[2.2.2]辛烷 (DABCO) 形成经典的路易斯酸碱加合物。用 tBu3 P 处理 3 可选择性地得到不寻常的齐聚硼翁盐反式-[(C3 H2 (NCH2 C6 H4 )2 B)2 (C3 H2 (NCHC6 H4 )2 B)][B(C6 F5 )4 ]（7）。
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