Electronic Influence of Substitution on the Pyridine Ring within NNN Pincer-Type Molecules

Schwartz, Timothy

Publication

Electronic Influence of Substitution on the Pyridine Ring within NNN Pincer-Type Molecules

Schwartz, Timothy

Date

2020

Additional date(s)

2020-05-19

Abstract

Pincer molecules are of increasing interest due to the modular nature of modification and range of reactivity observed when coordinated to metal ions. A subset within the family of pincer molecules use a pyridine group to bridge the outer two arms as well as provide a N-donor atom for metal binding. While the arm appendages have been studied extensively, little research has been conducted on the electronic effects of the central, substituted pyridine systems. Therefore, a series of NNN pincer-type ligands with substitution on the 4-position of the pyridine ring with - OH, -OBn, -H, -Cl, and -NO2 functional groups were synthesized and characterized through NMR spectroscopy and ESI-HRMS. Each pincer was metalated with Cu(II) salts and were evaluated through X-ray diffraction analysis, cyclic voltammetry, and density functional theory analysis. The results indicate that the relatively unstudied -OBn group demonstrates both electron- withdrawing (XRD bond lengths) and electron-donating (NMR spectroscopy) properties. The - NO2 pincer shows a redox event within experimental windows evaluated, in contrast to the other congeners studied. In addition, electron-donating groups increase the electron density around the Cu(II) center based on DFT studies and cyclic voltammetry. These findings can be applied to other pyridine-based pincer systems when considering ligand design and warrants future characterization of 4-position substituted pyridines.