Theoretical analysis on the formation and nitric oxide release of N-heterocyclic carbene nitric oxide radicals

The theoretical study on the fixation and release of nitric oxide (NO) by N-heterocyclic carbenes (NHCs) is explored by utilizing a multivariate linear regression approach. We utilized data-driven tools to establish correlations between molecular descriptors of NHC and reaction outputs of the formation and NO release of NHC nitric oxide radicals (NHCNOs). A key electronic parameter, the singlet-triplet energy gap (ΔE_ST), plays a pivotal role in the thermodynamics of NHCNO formation (ΔG_f) and NO release (ΔG_r). The activation energy models highlight HOMO energy level (E_HOMO), C–N bond length (d_C–N), and NBO charge on N atom (q^NBO_N) as crucial factors for the formation of NHCNO (ΔG^‡_f), while the activation energy for the NO release (ΔG^‡_r) significantly correlates with free energy difference (ΔG_r), resulting a strong ΔE_ST dependency. This study provides valuable insights into the thermodynamics and kinetics of NHCNO processes, offering predictive capabilities to design NHCs tailored for NO release.