The structure and the catalytic activity of diphenylboron cation in solution

利用非质子溶剂中的路易斯酸，在室温下对二苯基氯硼烷的硼阳离子行为进行了原位监测，通过对^<11>B、^<13>C和^<121>Sb的核磁共振光谱监测，并通过计算的和实验的^<11>B核磁共振化学位移的相关性证实了阳离子的种类。二苯氯硼烷在硝基甲烷中被强路易斯酸（SbCI_5, GaCI_3, AIBr_3）异解，得到两个硝基甲烷分子的供电子o原子稳定的硝基甲烷溶剂化二苯硼离子。硝基甲烷配位络合离子通过加入2个等量的溶剂可转化为men或THF配位络合离子，最后转化为吡啶络合离子。由于亲核试剂的配位，这些四配位的二苯硼离子没有路易斯酸。二苯基氯硼烷的氯离子在非亲核溶剂中不能萃取，在亚硝基中也不能用AICI_3和BCl_3萃取。二苯基氯硼烷与一等量吡啶在二氯甲烷中处理，得到相应的1:1加合物，用强路易斯酸萃取氯离子得到高路易斯酸三配位二苯硼离子。硝基甲烷中的三配位二苯基硼离子与硝基甲烷中的sp^3阳离子根据吡啶取代基的不同呈平衡态存在，而二氯甲烷中的sp^2二苯基硼离子仅以4-NMe_2取代H取代基的sp^2离子存在。在GIAO-HF/6-311+G(2d, p)//B3LYP/6-31+G(d)水平上，所有物质的^<11>B的化学位移与从头计算结果吻合较好，优化后的结构与^<11>B、^<13>C和^<121>Sb的核磁共振波谱一致。综上所述，初期生成的sp二苯硼离子（[Ph_2B]^+）是由溶剂和/或吡啶与正硼原子的π背键（B-O或B-N）稳定的，这些硼阳离子应该具有相当长的寿命，以sp^2（[Ph_2B(Py)]^+）或sp^3二苯硼阳离子([Ph_2B(Py)NO_2Me]^+, [Ph_2B(Py) _2]^+和[Ph_2B(Solv)_2]^+的形式存在。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