Degree

Doctor of Philosophy (PhD)

Department

Chemistry

Document Type

Dissertation

Abstract

A variety of pyridyltriazole ligands are readily available via click type cycloaddition of alkynylpyridines and azides. We made functionalized tetradentate m-xylylenebis(pyridyltriazole) (m-xpt) ligands with NH2 and NMe2 electron-donating and NO2 electron-withdrawing substituents on the pyridine moieties. Complexation of these ligands with Cu(II) gives dimeric macrocycles with square pyramidal geometry at Cu centers. Previous work in our lab with the unsubstituted [Cu2(m-xpt)2(NO3)2]2+ complex showed reduction to Cu(I) by using ascorbate as reducing agent. Oxidation of the Cu(I) solution in air results in formation of an oxalate-bridged dimer, [Cu2(m-xpt)2(C2O4)]2+. Formation of the oxalate was attributed to reductive coupling of CO2 molecules. However, in this study we report results indicating that this claim is incorrect and the copper(I) complex does not react with CO2. Instead, the oxalate was formed from ascorbate (or dehydroascorbic acid) by reaction with O2. In addition, in the absence of ascorbate and/or its oxidation products the copper(I) complex oxidizes to Cu(II), and with transformation of CO2 to carbonate a trimer, [Cu3(m-xpt)3(CO3)]4+, forms. Similar results were obtained with the new functionalized complexes.

In another study, we made different ruthenium complexes with pyridyltriazole ligands. Most of the complexes were isolated as crystals and analyzed by X-ray crystallography. High-valent ruthenium complexes made by oxidation of Ru(II) or Ru(III) precursors have been employed as catalyst for oxidation of water to O2. We tested the two isomers of [Ru(tpy)(bpt)(H2O)]2+ (bpt = benzylpyridyltriazole) for water oxidation; formation of oxygen bubbles was observed from an acidic solution of one of the isomers when excess of ceric ammonium nitrate oxidant was employed.

Date

6-6-2020

Committee Chair

Maverick, Andrew W.

DOI

10.31390/gradschool_dissertations.5289

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