New Spiro-Borane and Spiro-Borate Derived from Dipyrromethane and Their H/D Exchange Properties
Polyhedron(2020)
摘要
The reaction between diethyldipyrromethane Et2C(C4H4N)(2) and BH3 center dot THF or the treatment of the lithium salt of dipyrromethane with BF3 center dot OEt2 in THF gave a new four coordinate boron(III) compound 1 having the spiro structure formed by one dianionic and one monoanionic dipyrromethane units. Compound 1 contains one 2H-pyrrole ring and is acidic. Hence, it readily reacts with bases such as n-Bu4NOH, NaH, DMAP or Et3N to give the spiroborate complexes 2 containing two dianionic dipyrromethane moieties. The deprotonation of 1 gives back aromaticity to the pyrrole ring. Compound 1 is rigid, a rather well resolved H-1 NMR spectrum was obtained in aromatic solvents compared to CDCl3 and peaks were assigned using 2D NOESY spectrum. Compound 1 showed fast hydrogen-deuterium exchanges at the pyrrolic positions in CDCl3/D2O or CD3CN/D2O mixture catalyzed by HBF4. However, the H/D exchange occurs in step wise fashion as shown by H-1 NMR analysis. The structures of compound 1 and 2 were confirmed by spectroscopic and X-ray diffraction methods. (C) 2020 Elsevier Ltd. All rights reserved.
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关键词
2H-pyrrole,Spiroborane,Spiroborate,H/D exchange,Aromatic solvent induced shift,NOESY,Dipyrromethane
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