Substitution effects on 1,3-disubstituted imidazol-2-ylidenes and 1,3-diarylimidazol-2-ylidenes revisited: a theoretical study at DFT level
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Effect of substituents on philicity and stability of 1,3-disubstituted imidazol-2-ylidenes and 1,3-diarylimidazol-2-ylidenes was assessed using the following calculations: adiabatic electron affinity and adiabatic ionization potential, global electrophilicity and differential orbital energy scales for philicity, and ΔES–T, ΔEHyd, ΔEiso, and ΔEH–L for stability, with the aid of density functional theory and the results were then compared with each other. In the case of 1,3-disubstituted imidazol-2-ylidene, the carbene with CH3 group has the highest nucleophilic character considering all the above scales and the highest thermodynamic stability. 1,3-Diarylimidazol-2-ylidenes with CH3O and NH2 groups have high-nucleophilic properties and high-stability; their ΔEiso values are also greater than 377 kJ/mol which means that they may be reasonable synthetic targets. While, the presence of electron donating groups at 1,3-disubstituted imidazol-2-ylidene results in ΔEiso > 377 kJ/mol. Nucleophilicity of 1,3-diarylimidazol-2-ylidenes is, to some extent, greater than that of 1,3-disubstituted imidazol-2-ylidenes.
KeywordsN-Heterocyclic carbenes Electrophilic substitutions Stability Density functional theory Carbenes
The authors gratefully acknowledge the financial support for this work from the Research Council of Malayer and Bu-Ali Sina University, Iran.
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