2006 Fiscal Year Final Research Report Summary
The structure and the catalytic activity of diphenylboron cation in solution
| Project/Area Number |
17550039
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Organic chemistry
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| Research Institution | Kyushu University : |
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Principal Investigator |
FUJIO Mizue Kyushu Univ., Researcher Inst.for Materials Chem.and Eng., Researcher, 先導物質化学研究所, 研究員 (10029887)
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| Project Period (FY) |
2005 – 2006
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| Keywords | Boron Cation / B-11 NMR Chemical Shift / Lewis Acidity / ab initio Calculation / Lewis Acid Catalyst |
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| Research Abstract |
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
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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
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Research Products
(14 results)
