Carbene–Calcium Silylamides and Amidoboranes
Carbene–Calcium Silylamides and Amidoboranes
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DOI：
10.1021/acs.organomet.2c00464
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发表时间：
2022-10
期刊：
影响因子：
2.8
通讯作者：
Akachukwu D. Obi;Lucas A. Freeman;Samuel J. Coates;Andrew J. H. Alexis;Nathan C. Frey;D. Dickie;C. E. Webster;Robert J. Gilliard
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文献类型：
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作者：
Akachukwu D. Obi;Lucas A. Freeman;Samuel J. Coates;Andrew J. H. Alexis;Nathan C. Frey;D. Dickie;C. E. Webster;Robert J. Gilliard
研究了N-杂环卡宾（NHC）和环状（烷基）（氨基）卡宾（CAAC）与硅酰胺钙和氨基硼烷配位的立体电子效应。等摩尔量的空间无阻碍的NHC（即N,N'-二异丙基-2,3-二甲基咪唑-2-亚基）和{Ca[N(SiMe3)2]2}2或(THF)2Ca[N(SiMe3)2]2的直接络合得到(NHC)Ca[N(SiMe3)2]2(2)或 分别为(NHC)(THF)Ca[N(SiMe3)2]2(4)。光谱分析显示2和4中的电子差异可以忽略不计，并且后者可以在长时间真空下去溶剂化。类似地，CAAC 与 {Ca[N(SiMe3)2]2}2 的络合使 (CAAC)Ca[N(SiMe3)2]2(5) 成为第一个晶体学特征的 CAAC-Ca 配位络合物，但该化合物热不稳定，会迅速分解为难以处理的混合物。 {Ca[N(SiMe3)2]2}2和HNMe2BH3的反应产生了双(氨基硼烷)[Ca(NMe2BH3)2]n(6)，它不与大的卡宾反应，但很容易与未阻碍的NHCs络合，随后非无害地参与钙介导的胺硼烷脱氢偶联。值得注意的是，(NHC)2Ca(NMe2BH3)2(7)在温和加热（50℃，16小时）下分解形成[CaH2]n和富含氢化物的复合物[(NHC–BH2NMe2)Ca(NMe2BH3)2]2(8)。化合物8是由6和NHC–BH2NMe2的反应独立制备的，并且在回流苯中具有非常热稳定性（85℃，24小时）。在没有卡宾的情况下，6 和 HNMe2BH3 的脱氢偶联产生 (THF)2Ca(NMe2BH3)(NMe2BH2NMe2BH3) (9)，但随后与 NHC 的反应导致 Me2N=BH2 立即被提取并迁移到 8 的形成。
The stereoelectronic effects of N-heterocyclic carbene (NHC) and cyclic(alkyl)(amino) carbene (CAAC) coordination to calcium silylamides and amidoboranes have been investigated. The straightforward complexation of a sterically unencumbered NHC (i.e.,N,N′-diisopropyl-2,3-dimethylimidazol-2-ylidine) and {Ca[N(SiMe3)2]2}2or (THF)2Ca[N(SiMe3)2]2in equimolar amounts afforded (NHC)Ca[N(SiMe3)2]2(2) or (NHC)(THF)Ca[N(SiMe3)2]2(4), respectively. Spectroscopic analyses reveal negligible electronic differences in2and4, and the latter can be desolvated under prolonged vacuum. Similarly, CAAC complexation to {Ca[N(SiMe3)2]2}2afforded (CAAC)Ca[N(SiMe3)2]2(5) as the first crystallographically characterized CAAC–Ca coordination complex, but this compound is thermally unstable and rapidly decomposes to intractable mixtures. The reaction of {Ca[N(SiMe3)2]2}2and HNMe2BH3afforded the bis(amidoborane) [Ca(NMe2BH3)2]n(6), which does not react with bulky carbenes but readily complexes with unencumbered NHCs with subsequent non-innocent participations in calcium-mediated amine borane dehydrocoupling. Significantly, (NHC)2Ca(NMe2BH3)2(7) decomposes under mild heating (50 °C, 16 h) to form [CaH2]nand the hydride-rich complex [(NHC–BH2NMe2)Ca(NMe2BH3)2]2(8). Compound8was independently prepared from the reaction of6and NHC–BH2NMe2and is remarkably thermally stable in refluxing benzene (85 °C, 24 h). In the absence of carbenes, the dehydrocoupling of6and HNMe2BH3afforded (THF)2Ca(NMe2BH3)(NMe2BH2NMe2BH3) (9), but subsequent reactions with NHC resulted in the immediate abstraction and migration of Me2N═BH2toward the formation of8.