Date of Award

6-2018

Degree Name

Doctor of Philosophy

Department

Chemistry

First Advisor

Dr. Gellert Mezei

Second Advisor

Dr. Yirong Mo

Third Advisor

Dr. Ramakrishna Guda

Fourth Advisor

Dr. Todd Barkman

Keywords

Pyrazole synthesis, anions, nanojars

Abstract

This work is centered around nanojars, a family of nano-sized anion-incarcerating agents. It addresses various aspects of nanojar chemistry, such as synthesis strategies (including green methodologies) for pyrazole ligands needed for the preparation of nanojars, characterization and study of the mechanism of assembly of nanojars, and selective extraction of anions from water using nanojars.

Nanojars are neutral, supramolecular coordination complexes of the general formula [anion⊂ {Cu(μ-OH)(μ-pz)}n], formed by the reaction of Cu2+, HO‒ and pyrazolate ions (C3H2N2‒, pz‒) in the presence of oxoanions with large hydration energy (e.g. CO32–, SO42–, PO43–, HPO42–). Nanojars are comprised of n = 26–36 repeating units of the formula [Cu(OH)(pz)], which are arranged in stacks of three or four. The stacking of metallamacrocycles creates a hydrophilic central cavity occupied by the incarcerated anion, surrounded by a hydrophobic periphery, which provides solubility in numerous organic solvents. Nanojars are robust under neutral to extremely alkaline (pH > 14) conditions and bind certain anions with high strength. Under acidic conditions, however, nanojars reversibly break down and release the anion. Consequently, nanojars are excellent candidates for anion extraction agents.

The main objectives of this work are: (1) Synthesize and characterize various pyrazole ligands, including tethered multi-pyrazole ligand. In particular, pyrazoles with aliphatic and oligo(ethylene glycol) chains are targeted, which are expected to further expand the solubility of nanojars, in aliphatic solvents (such as ISOPARTM, suitable for industrial scale extractions) and water, respectively. (2) Prepare and characterize nanojars using the synthesized pyrazole ligands. Characterization techniques include NMR and UV–vis spectroscopy, mass spectrometry, X-ray crystallography and thermogravimetric analysis. (3) Study the mechanism of formation of nanojars, using pH titration, UV–vis spectroscopy and mass spectrometry. (4) Study the extraction of sulfate (SO42–) and carbonate (CO32–) ions from aqueousmedia by nanojars, and develop a method for selective extraction of these anions.

Besides the anticipated outcomes based on the objectives described above, a number of unforeseen, yet fundamentally significant results for the broader field of chemistry are also presented. Unexpected results during the organic synthesis work inspired computational studies, which resulted in demystification of misunderstood theoretical concepts related to the reactivity of pyrazole derivatives. Thus, the “adjacent lone pair effect”, and the drastic deprotonation reactivity difference between 3- and 5-alkylpyrazole isomers, as well as between five- and six-membered aromatic molecules, was elucidated. The unusual and contrasting reactivity of amino- and hydroxypyrazole derivatives toward aldehydes and ketones under either neutral or acidic conditions was also studied, providing not only an understanding of the mechanism of the reactions, but also a variety of novel bis- and non-scorpionate tris(pyrazolyl)methane ligands. Furthermore, the selective C-4 deuteration of pyrazole substrates by D2O was studied, and a convenient procedure for large-scale deuteration was developed.

Access Setting

Dissertation-Open Access

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