Modelling NMR Data of NHC Salts in Order to Determine Ligand Donor Properties

Abstract

The computational prediction of NMR spectra of a number of reported NHC salts bearing fluorine-substituted aromatic systems (fluorophenyl NHCs) and IMes (IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene). The NMR spectra of 4-fluorophenyl NHC (NHC 1), 2,4-difluorophenyl NHC (NHC 2), 2,6-difluorophenyl NHC (NHC 3), 2,4,6-trifluorophenyl NHC (NHC 4), non-fluorophenyl NHC (NHC 5), and N,N’-bis-[2,4,6-(trimethyl)phenyl]imidazol-2-ylidene (IMes) have been calculated by using three electronic tools; Mestrenova, Chemdraw professional 16.0, and NMRdb.org (a web predictor). Chemdraw professional and the web predictor failed in predicting the 13C-NMR and 19F-NMR spectra. Mnova predicted 1H,13C, and 19F-NMR successfully. The best predictor was determine by the calculating the differences between the calculated and the actual values of the chemical shifts, the low the result, the good the agreement between the tool and the literature. Consequently, mestrenova software was used to determine the electronic properties of a series of novel NHCs bearing halogen-substituted on the backbone (F-NHC, Cl-NHC, Br-NHC, and I-NHC).