A quest for stable bicyclic carbenes with one, two, and three carbenic centers at theoretical level

Estimating structure, stability, and electronic properties on halogenated derivatives of 2-germabicyclo[1.1.1.]pentane-2-ylidenes at density functional theory

In this computational survey, substituent effects of group 17 on the stability (singlet-triplet energy gaps, ΔE_s-t) and reactivity of singlet (s) and triplet (t) forms of 2-germabicyclo[1.1.1.]pentane-2-ylidenes are considered by using B3LYP/6-311 +  + G**, B3LYP/aug-cc-pvtz, and B3LYP/def2-TZVP level of theories. In all germylene structures, singlets appear more stable than their corresponding triplet congeners, revealing a singlet ground state and the order of stability appears to be 1,3,4,4,5,5-hexachloro-2-germabicyclo[1.1.1.]pentane-2-ylidenes (3) > 1,3,4,4,5,5-hexabromo-2-germabicyclo[1.1.1.]pentane-2-ylidenes (4) > 1,3,4,4,5,5-hexafluoro-2-germabicyclo[1.1.1.]pentane-2-ylidenes (2) > 1,3,4,4,5,5-hexaiodo-2-germabicyclo[1.1.1.]pentane-2-ylidenes (5) > 2-germabicyclo[1.1.1.]pentane-2-ylidenes (1), at the three levels of theory. The positive and negative effects on germylene stability are LP_{(F, Cl, Br, and I)} → LP^*_G̈e and σ_(C-Ge) → σ^*_{(C-F, Cl, Br, and I)} interactions, respectively. The results of our calculations show that every singlet germylene with high LP_{(F, Cl, Br, and I)} → LP^*_G̈e interactions has higher electrophilicity. Also, in going from the most electronegative F to the least electronegative I, the nucleophilicity index (N) for germylene increases. Finally, this survey introduces that germylene 4 _s with rather high band gap (ΔE_HOMO-LUMO = 97.19 kcal/mol), nucleophilicity (2.20 eV), and stability (ΔE_s-t = 76.95 kcal/mol) has high proton affinity (171.55 kcal/mol) that can be applied as multidentate ligands and it is hoped that this will prompt experimental attention toward its.