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

Depending on the temperature, the twofold deprotonation of 1,1′‐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′‐methylenebis(3‐methyl‐4‐trimethylsilylimidazole‐2‐thione) ( 2 ) and 1,1′‐methylenebis(3‐methyl‐5‐trimethylsilylimidazole‐2‐thione) ( 3 ). The cyclic dimethylsilyl‐bridged derivative 1,1′‐methylene‐5,5′‐dimethylsilylenebis(3‐methylimidazole‐2‐thione) ( 4 ) can also be obtained, corroborating the 5/5′ 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 n BuLi at ambient temperature in solution (THF). 1 H and 7 Li pulsed field‐gradient spin‐echo (PGSE) NMR, 7 Li– 1 H 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.