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Electronic influence of substitution on the pyridine ring within NNN pincer-type molecules

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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 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 ligand 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.

Graphical abstract: Electronic influence of substitution on the pyridine ring within NNN pincer-type molecules

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Article information


Submitted
11 Dec 2019
Accepted
28 Jan 2020
First published
05 Feb 2020

Dalton Trans., 2020, Advance Article
Article type
Paper

Electronic influence of substitution on the pyridine ring within NNN pincer-type molecules

T. M. Schwartz, M. E. Burnett and K. N. Green, Dalton Trans., 2020, Advance Article , DOI: 10.1039/C9DT04714J

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