DFT Approach for Predicting 13C NMR Shifts of Atoms Directly Coordinated to Nickel

The aim of this work is to develop a simple density functional theory (DFT) method that can be safely applied to calculate 13C NMR shifts in diamagnetic Ni complexes. A comparative analysis of calculated vs experimental 13C NMR shifts for a wide range of nickel complexes (157 in total) was carried out. A number of functional–basis set combinations were tested. On the whole, the NMR shifts of carbon atoms directly bonded to nickel can be calculated within the framework of the Kohn–Sham theory level using a number of hybrid functionals. The linear scaling procedure significantly improves results (root-mean-square error (RMSE) = 4.0–4.6 ppm). In the complexes coordinated with solvent and/or counterions, the predictions are less accurate (RMSE = 6.4 ppm). In the Ni–diimine alkyne complexes, calculations underestimate the NMR shielding (by 7–10 ppm) possibly due to the influence of high-spin states. At the same time, pure generalized gradient approximation (GGA) functionals show limits in their predictive power, particularly for the N-heterocyclic carbenes (NHCs) and π-donating carbons. Care has to be taken when interpreting 13C NMR spectra of Ni complexes using empirical dependencies, which may be misleading.