Frustrated Lewis pairs derived from N-heterocyclic carbenes and Lewis acids
Frustrated Lewis pairs derived from N-heterocyclic carbenes and Lewis acids
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DOI：
10.1039/b908737k
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发表时间：
2009-01-01
影响因子：
4
通讯作者：
Stephan, Douglas W.
中科院分区：
文献类型：
--
作者：
Chase, Preston A.;Gille, Austin L.;Stephan, Douglas W.
研究了由N-杂环卡宾和一些刘易斯酸衍生的阻挫刘易斯对的化学性质。1，3-双[2，6-二异丙基]苯基]-1，3-咪唑-2-亚基（IDipp）（1）与B（C6 F5）（3）反应生成经典的刘易斯酸碱加合物（IDipp）B（C6 F5）（3）（2），该加合物不发生反应。与此相反，1，3-二叔丁基-1，3-咪唑-2-亚基（3）与B（C6 F5）（3）的结合证明形成受抑刘易斯对，并与H-2反应以高产率得到盐[ItBuH][HB（C6 F5）（3）]（4）。以类似的方式，将（3）加入到一系列胺-硼烷加合物中，包括H3 NB（C6 F5）（3）（5）、PhH 2NB（C6 F5）（3）（6）和PhH 2NB（C6 F5）（3）（7），导致去质子化并形成咪唑鎓酰胺基硼酸盐[ItBuH][H2 NB（C6 F5）（3）]（8），[ItBuH][PhHNB（C6F5）（3）]（9）和[ItBuH][Ph2NB（C6F5）（3）]（10）。胺-硼烷加合物EtNH 2 B（C6 F5）（3）（11）tBuNH（2）B（C6 F5）（3）（12）和Et 2NHB（C6 F5）（3）（13）的类似反应分别得到氨基硼烷EtHNB（C6 F5）（2）（14）tBuHNB（C6 F5）（2）（15）和Et 2NB（C6 F5）（2）（16），释放出C6 F5 H和一当量的未反应卡宾。在机理上，这些反应被认为通过类似于（8）-（10）的瞬时咪唑鎓盐进行。此外，还探讨了卡宾（3）与阳离子[CPh 3]（+）在阻挫刘易斯对化学中的结合.该化合物在室温下的反应导致[C（3）H（2）N（2）tBu（2）（C6 H5）CPh 2][B（C6 F5）（4）]（17）的立即形成，这是由卡宾攻击三苯甲基的苯环之一的对位碳引起的。将卡宾加成到[CPh 3][B（C6 F5）（4）]的苄胺加合物中导致形成[ItBuH][B（C6 F5）（4）]（18）和仲胺Ph 3CNHCH 2 Ph（19），从而提供了全碳基受抑刘易斯对的第一个实例。报道了（2）、（4）、（9）和（13）的晶体学数据。
The chemistry of frustrated Lewis pairs derived from N-heterocyclic carbenes and a number of Lewis acids has been probed. The combination of 1,3-bis[2,6-(di-iso-propyl)phenyl]-1,3-imidazol-2-ylidene (IDipp) (1) with B(C6F5)(3) was shown to give the classical Lewis acid-base adduct (IDipp) B(C6F5)(3) (2) which was unreactive. In contrast, the combination 1,3-di-tert-butyl-1,3-imidazol-2-ylidene (3) with B(C6F5)(3) proved to form a frustrated Lewis pair, and reacts with H-2 to give the salt [ItBuH][HB(C6F5)(3)] (4) in high yield. In a similar fashion, addition of (3) to a series of amine-borane adducts including H3NB(C6F5)(3) (5), PhH2NB(C6F5)(3) (6) and PhH2NB(C6F5)(3) (7) led to deprotonation and formation of imidazolium amido-borate salts [ItBuH][H2NB(C6F5)(3)] (8), [ItBuH][PhHNB(C6F5)(3)] (9) and [ItBuH][Ph2NB(C6F5)(3)] (10). Similar reactions of the amine-borane adducts EtNH2B(C6F5)(3) (11) tBuNH(2)B(C6F5)(3) (12) and Et2NHB(C6F5)(3) (13) gave the amidoboranes EtHNB(C6F5)(2) (14) tBuHNB(C6F5)(2) (15) and Et2NB(C6F5)(2) (16) respectively, with liberation of C6F5H and an equivalent of unreacted carbene. Mechanistically these reactions are thought to proceed through transient imidazolium salts similar to (8)-(10). In addition, the combination of carbene (3) and the cation [CPh3](+) in frustrated Lewis pair chemistry has been probed. Reaction of this combination at room temperature results in the immediate formation of [C(3)H(2)N(2)tBu(2)(C6H5)CPh2][B(C6F5)(4)] (17) stemming from carbene attack at a para-carbon of one of the phenyl rings of trityl. Addition of carbene to the benzyl amine adduct of [CPh3][B(C6F5)(4)] results in the formation of [ItBuH][B(C6F5)(4)] (18) and the secondary amine Ph3CNHCH2Ph (19), thus providing the first example of an all carbon-based frustrated Lewis pair. Crystallographic data for (2), (4), (9) and (13) are reported.