Understanding Small Molecule Activation Promoted by Heavier Benzene 1,4-diides: Interplay Between Diradical Character and Aromaticity.

The intricate relationship between diradical character, aromaticity, and reactivity in annulated heavier Group 14 benzene-1,4-diides, that is, [(ADC)E]2 (E = Si, Ge, Sn), based on an anionic dicarbene framework, (ADC = PhC{N(Ar)C}2: Ar = aryl), has been investigated through Density Functional Theory and ab initio calculations. The diradical character of both homo- [(ADC)E]2 and heteroleptic [(ADC)2EE'] systems (E ≠ E') has been accurately computed, while the aromaticity of their corresponding closed-shell (CS) and open-shell (OS) singlet states has been evaluated using magnetic descriptors. Additionally, the key factors governing dihydrogen activation and cycloaddition with acetylene have been quantitatively analyzed in detail by applying the combination of the Activation Strain Model (ASM) of reactivity and Energy Decomposition Analysis (EDA) methods. The findings reveal a direct correlation between reactivity and diradical character, both of which increase down Group 14.