Computational Evaluation of Me₂TCCP as Lewis acid

Supramolecular adducts between dimethyl-2,2,3,3-tetracyanocyclopropane (Me₂TCCP) with 21 small (polar) molecules and 10 anions were computed with DFT (B3LYP-D3/def2-TZVP). Their optimized geometries were used to obtain interaction energies, and perform energy decomposition and `atoms-in-molecules' analyses. A set of 38 other adducts were also evaluated for comparison purposes. Selected examples were further scrutinized by inspection of the molecular electrostatic potential maps, Noncovalent Interaction index plots, the Laplacian, the orbital interactions, and by estimating the Gibbs free energy of complexation in hexane solution. These calculations divulge the thermodynamic feasibility of Me₂TCCP adducts and show that complexation is typically driven by dispersion with less polarized partners, but by orbital interactions when more polarized or anionic guests are deployed. Most Me₂TCCP adducts are more stable than simple hydrogen bonding with water, but less stable than traditional Lewis adducts involving Me₃B, or a strong halogen bond such as with Br₂. Several bonding analyses showed that the locus of interaction is found near the electron poor sp³-hydridized (NC)₂C-C(CN)₂ carbon atoms. An empty hybrid sigma*/pi* orbital on Me2TCCP was identified that can be held responsible for the stability of the most stable adducts due to donor-acceptor interactions.