The structure and the catalytic activity of diphenylboron cation in solution

本文研究了二苯基氯硼烷的一种新的硼阳离子行为，利用刘易斯酸在室温下的非质子溶剂中，通过现场监测^&lt；11&gt；B，^&lt；13&gt；C和^&lt；121&gt；Sb核磁共振谱，并通过计算值与实验值的相关性，证实了阳离子物种的存在。在硝基甲烷中，强Lewis酸(SbCl5、GaCl3、AlBr3)与二苯基氯硼烷发生异构化反应，生成了由两个硝基甲烷分子的给电子体O原子稳定的二苯基硼离子。通过加入2种当量的溶剂，硝基甲烷配位的配位离子可以转化为MeCN或THF配位的配位离子，最终转化为吡啶配位离子。由于亲核试剂的配位作用，这些四配位的二苯基硼离子不具有Lewis酸性。二苯基氯硼烷中氯离子的提取不能在非亲核溶剂中进行，AlCl3和BCl3甚至在亚硝基…中也不能进行。更理智一些。二苯基氯硼烷与一个当量的吡啶在二氯甲烷中反应得到相应的1：1加合物，该加合物通过用强Lewis酸提取氯离子而得到高Lewis酸性的三配位二苯基硼离子。三配位的二苯基硼离子与硝基甲烷中的硝基配位的sp3阳离子存在平衡，这取决于吡啶中的取代基；而在二氯甲烷中，对于4-NME2到H取代基，三配位的二苯基硼离子仅以sp2二苯基的形式存在。在GIAO-HF/6-311+G(2d，p)//B3LYP/6-31+G(D)水平上，所有物种的实验^&lt；11&gt；B化学位移与从头计算结果吻合较好，优化后的结构与^&lt；11&gt；B，^&lt；13&gt；C和^&lt；121&gt；SB核磁共振谱相一致。总之，初始生成的二苯基硼离子([Ph_2B]^+)是通过溶剂(S)和/或吡啶(S)与正硼原子的π后键(B-O或B-N)稳定的，这些硼阳离子应该有相当长的寿命以SP^2([Ph_2B(Py)]^+)或SP^3二苯基硼阳离子([Ph_2B(Py)NO_2Me]^+，[Ph_2B(Py)_2]^+)和[Ph_2B(Solv)_2]^+的形式存在。较少

A novel boron cationic behavior of diphenylchloroborane has been investigated by utilyzing the Lewis acids in aprotic solvents at room temperature, by monitoring ^<11>B, ^<13>C, and ^<121>Sb NMR spectroscopy in-situ, and the cationic species was confirmed by a correlation between the calculated and the experimental ^<11>B NMR chemical shifts. The heterolysis of diphenylchloroborane by the strong Lewis acid (SbCI_5, GaCI_3, AIBr_3) in nitromethane gave the nitromethane solvated diphenylboronium ion stabilized by electron donating O-atom of two nitromethane molecules. The nitromethane coordinated complex-ion can be converted into MeCN or THF coordinated complex-ion by adding 2 equivalents of solvents, and finally to the pyridine complex-ion. These four-coordinate diphenylboronium ions have no Lewis acidity due to coordination of nucleophiles. The abstraction of chloride ion from diphenylchloroborane did not proceed in non- nucleophilic solvents nor with AICI_3 and BCl_3 even in nitrometh … More ane. Treatment of diphenylchloroborane with one equivalent of pyridine in dichloromethane afforded the corresponding 1:1 adduct that gave highly Lewis acidic tricoordinate diphenylborenium ion by abstraction of chloride ion with the strong Lewis acid. The tricoordinate diphenylborenium ion existed in an equilibrium with the nitrometane-coordinate sp^3 cation in nitromethane depending on the substituent in pyridine while that in dichloromethane exists solely as sp^2 diphenylborenium ion for 4-NMe_2 to H substituent. The experimental ^<11>B chemical shifts of all species were in good agreement with the ab initio calculation results at the level of GIAO-HF/6-311+G(2d, p)//B3LYP/6-31+G(d), and the optimized structures were compatible with the ^<11>B, ^<13>C and ^<121>Sb NMR spectroscopy. In conclusion, the sp diphenylborinium ion ([Ph_2B]^+) incipiently produced was stablized by the π back-bonding (B-O or B-N) from solvent(s) and/or pyridine(s) to positive boron atom and these boron cation species should have an appreciably long life to exist as sp^2([Ph_2B(Py)]^+) or sp^3 diphenylboron cation ([Ph_2B(Py)NO_2Me]^+, [Ph_2B(PY)_2]^+), and [Ph_2B(Solv)_2]^+). Less