Substituent-controlled donor binding and local reactivity in N-heterocyclic carbene copper amide complexes: a DFT...

Carbene-metal-amide (CMA) complexes provide compact two-coordinate coinage-metal platforms in which an amide donor, a carbene acceptor, and a d¹⁰ metal bridge are coupled within the same molecular scaffold. The present work examines whether para-substitution of the amide-bound aryl fragment can serve as a ground-state design handle to modulate donor-acceptor polarization, local reactivity, and neutral donor binding in N-heterocyclic carbene copper amide complexes. Within the ωB97X-D/def2-TZVP gas-phase model used here, the parent complex is predicted to be a bent minimum with an amide-rich donor manifold, a carbene-centered acceptor region, and Cu(I)-like d¹⁰ character. Condensed Fukui analysis identifies the carbene side as the preferred electron-accepting domain and the amido fragment as the dominant electron-donating region. Explicit small-molecule tests further show that weak CH₃CN coordination is tolerated, O-protonation is perturbative, and N-protonation disrupts the original CMA scaffold. In the donor-bound substituted series, the p-CF₃ derivative gives a slightly tighter and more persistent CH₃CN adduct than the p-OMe derivative, whereas p-OMe produces the softer donor-acceptor framework. These conclusions are interpreted as qualitative intraseries trends rather than as a complete benchmark across methods or coinage metals.

Geometry optimizations, harmonic frequency analyses, single-point refinements, Kohn-Sham frontier-orbital calculations, Mulliken population analyses, natural bond orbital calculations, and finite-difference Fukui-function evaluations were carried out using Q-Chem 5.4 at the ωB97X-D/def2-TZVP level in the gas phase. Global conceptual-DFT descriptors were derived from frontier-orbital energies, and local Fukui indices were obtained from the Mulliken charges of neutral, N+1, and N-1 states on the parent geometry. No secondary density functional or explicit-solvent benchmark was included in the present work; this limitation is discussed explicitly in the revised manuscript.