A successful DFT calculation of carbon-13 NMR chemical shifts and carbon-fluorine spin-spin coupling constants in (η6-fluoroarene)tricarbonylchromium complexes

Carbon-13 isotropic shielding constants and carbon-fluorine spin-spin coupling constants for fluorobenzene (1), 3-dimethylaminofluorobenzene (2) and 4-dimethylaminofluorobenzene (3) as well as for their tricarbonylchromium complexes (3-6) have been calculated using DFT method with B3LYP and/or BHandH functionals and 6-311++G(2d, p) basis set. In the case of the complexes, the calculations have been performed for two expected orientations of the tricarbonylchromium tripod with respect to the benzene ring. It has been found that, when using B3LYP functional, the experimental C-13 NMR chemical shifts for all the investigated compounds can be well reproduced, provided that for the complexes the populations of conformers are adjusted during the experiment/theory correlation. The population parameters determined this way follow perfectly the expectations based on the literature knowledge of the effects of the benzene ring substituents. The calculations with BHandH functional have not been able to reproduce the C-13 NMR chemical shifts of carbonyl carbons in tricarbonylchromium complexes. On the other hand, BHandH is a functional of choice in calculations of carbon-fluorine spin-spin coupling constants. All such constants, including the through-space coupling constants between the carbonyl carbons and fluorine, have been reproduced very well. This last coupling constant has been calculated for various relative orientations of carbonyl and C-F bond and a strong angular dependence of this constant has been found.