Electronic and Ligand Properties of Skeletally Substituted Cyclic (Alkyl)(Amino) Carbenes (CAACs) and Their Reactivity towards Small Molecule Activation: A Theoretical Study

Quantum chemical calculations have been carried out to understand the ligand properties of skeletally modified cyclic alkyl amino carbenes. The stability of these carbenes has been assessed from an evaluation of their singlet-triplet and stabilization energy values. Ylide substituted carbenes are found to be more stable than non-ylidic ones in their optimized singlet state. Nucleophilicity and electrophilicity indices values were evaluated in order to further investigate the reactivity of these carbenes. The calculated values of proton affinities and the degree of gallium pyramidalization in the carbene-GaCl3 adducts correlate well with the sigma-basicity of these carbenes. The reactivity of nonylidic carbenes toward the activation of both H-2 and NH3 are calculated to be more favourable compared to that of parent CAAC. On the other hand, ylide anchored carbenes are found to be unsuccessful toward the activation of both H-2 and NH3.