Pietsch Sabrina, Paul Ursula, Cade Ian A, Ingleson Michael J, Radius Udo, Marder Todd B
Institut für Anorganische Chemie, Julius-Maximilians-Universität Würzburg, Am Hubland, 97074 Würzburg (Germany).
School of Chemistry, The University of Manchester, Manchester M13 9PL (UK).
Chemistry. 2015 Jun 15;21(25):9018-21. doi: 10.1002/chem.201501498. Epub 2015 May 8.
We report the isolation and detailed structural characterization, by solid-state and solution NMR spectroscopy, of the neutral mono- and bis-NHC adducts of bis(catecholato)diboron (B2 cat2 ). The bis-NHC adduct undergoes thermally induced rearrangement, forming a six-membered -B-C=N-C=C-N-heterocyclic ring via C-N bond cleavage and ring expansion of the NHC, whereas the mono-NHC adduct is stable. Bis(neopentylglycolato)diboron (B2 neop2 ) is much more reactive than B2 cat2 giving a ring expanded product at room temperature, demonstrating that ring expansion of NHCs can be a very facile process with significant implications for their use in catalysis.
我们报告了通过固态和溶液核磁共振光谱对双（儿茶酚根）二硼（B2 cat2）的中性单氮杂环卡宾和双氮杂环卡宾加合物进行的分离和详细结构表征。双氮杂环卡宾加合物会发生热诱导重排，通过碳氮键断裂和氮杂环卡宾的环扩张形成一个六元 -B-C=N-C=C-N- 杂环，而单氮杂环卡宾加合物是稳定的。双（新戊二醇根）二硼（B2 neop2）比 B2 cat2 反应活性高得多，在室温下就能生成环扩张产物，这表明氮杂环卡宾的环扩张可能是一个非常容易的过程，对其在催化中的应用具有重要意义。
