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Issue 7, 2020
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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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Supplementary files

Article information


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

Dalton Trans., 2020,49, 2356-2363
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, 49, 2356
DOI: 10.1039/C9DT04714J

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