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 (Delta E-ST), plays a pivotal role in the thermodynamics of NHCNO formation (Delta G(f)) and NO release (Delta G(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(N)(NBO)) as crucial factors for the formation of NHCNO (Delta(f)G double dagger), while the activation energy for the NO release (Delta G(r)double dagger) significantly correlates with free energy difference (Delta G(r)), resulting a strong Delta E-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.