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

We have scrutinized eighteen new derivatives of carbenes with one, two, and three carbenic centers and compared their structural and thermodynamic parameters, at B3LYP/6-311++G** level of theory. All novel carbene scrutinized show singlet ground stat, and the highest stability belongs to 1,2,3,4-tetraazabicyclo[1.1.1]-5-pentanylene ( 9 ) (Δ E s-t = 47.95 kcal/mol). This stability can be related to their σ − bond and intermolecular interactions. This bond arose from a tendency of nonbonding electrons of nitrogen (N (E or G) ) to empty p orbital of the carbenic center. In addition, carbene 16 s and 17 s because of three coordinate covalent bonds with their carbenic centers have low nucleophilicity ( N ). The increase in band gaps (Δ Ε HOMO–LUMO ) is correlated with an increase in Δ Ε s–t values. The purpose of the present work was to assess the influence of 1 to 4 nitrogen substituents on the stability (Δ E s-t ), Δ Ε HOMO–LUMO , N , electrophilicity ( ω ), and isodesmic reactions. Finally, our investigation introduces novel carbenes that can be applied as cumulated multi-dentate ligands.