Advanced NMR Methods and DFT Calculations on the Regioselective Deprotonation and Functionalization of 1,1′-Methylenebis(3-methylimidazole-2-thione)

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• 作者：Mona Bauer ; Dejan Premužić ; Gü ; nther Thiele ; Bernhard Neumü ; ller ; Ralf Tonner ; &Aacute ; lvaro Raya-Bar&oacute ; n ; Ignacio Fern&aacute ; ndez and Istemi Kuzu
• 刊名：European Journal of Inorganic Chemistry
• 出版年：2016
• 出版时间：August 2016
• 年：2016
• 卷：2016
• 期：23
• 页码：3756-3766
• 全文大小：1762K
• ISSN：1099-0682c

文摘

Depending on the temperature, the twofold deprotonation of 1,1&prime;-methylenebis(3-methylimidazole-2-thione) (1) and the subsequent reaction with 2 equiv. of trimethylsilyl chloride (TMSCl) gives two different bis-TMS-functionalized isomers, namely, 1,1&prime;-methylenebis(3-methyl-4-trimethylsilylimidazole-2-thione) (2) and 1,1&prime;-methylenebis(3-methyl-5-trimethylsilylimidazole-2-thione) (3). The cyclic dimethylsilyl-bridged derivative 1,1&prime;-methylene-5,5&prime;-dimethylsilylenebis(3-methylimidazole-2-thione) (4) can also be obtained, corroborating the 5/5&prime; addition under certain conditions. All compounds have been examined by multinuclear 1D and 2D NMR experiments (1–4) together with single-crystal X-ray diffraction (3 and 4). Additionally, the dilithiated species 5 was synthesized by reacting 1 with 2 equiv. of <em>nem>BuLi at ambient temperature in solution (THF). ¹H and ⁷Li pulsed field-gradient spin-echo (PGSE) NMR, ⁷Li–¹H heteronuclear Overhauser spectroscopy (HOESY), gradient heteronuclear multiple quantum correlation (gHMQC) and gradient heteronuclear multiple bond correlation (gHMBC) experiments showed that 5 exists as a monomeric contact ion pair (CIP) in THF solution. On the contrary, the X-ray diffraction analysis of 5 revealed a polymeric chain, which can be described as [{5(thf)₂}₂]_∞. Quantum chemical DFT and MP2 calculations were also conducted to determine the energies required for the deprotonation of 1. These results explain the regioselective deprotonation of 1 by CIP formation depending on the temperature and fully support the results of the synthetic and spectroscopic experiments.