Mesoionic and N-Heterocyclic Carbenes Coordinated N Center: Experimental and Computational Analysis.

N-Heterocyclic carbenes, carbocyclic carbenes, remote N-heterocyclic carbenes and N-heterocyclic silylenes are known to form L→N coordination bonds. However, mesoionic carbenes (MICs) are not reported to form coordination bonds with cationic nitrogen. Herein, synthesis and quantum chemical studies were performed on 1,2,3-triazol-5-ylidene stabilized N center. Six compounds with MIC→N ←NHC were synthesized. Density functional theory calculations and energy decomposition analysis were carried out to explore the bonding situation between MIC and N center. The C→N bond lengths were in the range of 1.295-1.342 Å and bond dissociation energies were <400 kcal/mol. Natural bond orbital analysis supported the presence of excess electron density (>3 electrons) at the N center. The computational and X-ray diffraction analysis results confirmed the presence of divalent N character of center nitrogen and MIC→N ←NHC coordination interactions.