In the following, we demonstrate the correlation of 51V NMR chemical shifts with redox potentials of a series of non-innocent vanadium(V) catechol complexes. Several of the complexes synthesized herein were characterized previously by both solid state and solution 51V NMR spectroscopy. An observed linear correlation between solution and solid state 51V NMR chemical shifts is consistent with the solution structure being similar to that observed in the solid state. Due to the fact that the solid state 51V NMR chemical shift describes the electronic structure of the vanadium complexes, the potential exists for the use of the 51V NMR chemical shift to characterize the properties of these compounds. The vanadium(V) catechol complexes described in this study are in fact redox active and the chemical shifts fall outside the normal populated isotropic 51V NMR chemical shift range (-300 to -700 ppm) as anticipated for complexes with non-innocent ligands. These complexes are therefore well suited for examination of the hypothesis that the 51V NMR chemical shifts of the vanadium(V) catechol complexes correlate with the redox potential of these complexes. Cyclic Voltammetry studies were performed to calculate the redox potential (E˳) of each complex in solution. The 51V NMR chemical shifts were then plotted as a function of the redox potential. A linear correlation of 51V NMR isotropic chemical shift and redox potential is observed for the three known and three novel VO(HSHED) compounds containing a non-innocent catechol ligand. These studies demonstrate that substitution of the non-innocent catechol ligand with electron-donating groups results in a downfield shift in 51V NMR spectra and a decrease in redox potential. In contrast, substitution of the catechol ligand with electron-withdrawing groups results in an upfield shift in 51V NMR and an increase in redox potential. Combined, these studies demonstrate for the first time that 51V NMR chemical shifts correlate with the redox potential of the vanadium(V) catecholates and could potentially be a useful method for characterization of the redox properties of these compounds.

Vanadium(V) catecholates: Correlating redox potential with 51V NMR chemical shifts

249th National Meeting (2015)

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