Hydrogenation of carbon-heteroatom unsaturated bonds: An assessment of consistency of density functional methods

Hydrogenation of unsaturated carbon-heteroatom bonds, CX, is the general process for which we assess consistency of quantum chemical calculations in the context of B(C6F5)3-catalyzed reduction of imines with H2. According to the mechanism of the reaction, computational uncertainty of energies of hydrogenation of imines, i.e. the difference between results obtained with different methods, contributes to method-related uncertainties of the computed relative energies of key H2-activating species. For this reason, it is desirable to know the magnitude of methodological dependence/uncertainty of energies of hydrogenation. Calculations were performed with a number of different density functionals, such as M05-2X, M06-2X, B3LYP, B3PW91, BH&HLYP, MPW1K, MPW1PW91, HCTH407 and PBE, on a number of relevant imines and ketones/aldehydes. Additionally, second-order Møller–Plesset perturbation theory was also evaluated. The results quantitatively reveal the manner in which the form of a method affects the calculated energy change and that there is substantial difference between results obtained with different methods even for structurally simple species.

Graphical abstractThe relation between the form of density functionals, namely M05-2X, M06-2X, B3LYP, B3PW91, BH&HLYP, MPW1K, MPW1PW91, HCTH407 and PBE, and the calculated energy change in hydrogenation of unsaturated carbon-heteroatom bonds was assessed for a series of 12 imines (selected according to Stephan's H2-addition reactions) as well as a series of 11 ketones/aldehydes.Figure optionsDownload full-size imageDownload high-quality image (149 K)Download as PowerPoint slide