Date of Award

6-2023

Degree Name

Master of Science

Department

Chemistry

First Advisor

Gellert Mezei, Ph.D.

Second Advisor

Ramakrishna Guda, Ph.D.

Third Advisor

Ekkehard Sinn, Ph.D.

Keywords

Copper, indazole, nanojar, oxoanion, pyrazole, supramolecular structure

Access Setting

Masters Thesis-Open Access

Abstract

The field of synthetic supramolecular chemistry has exploded since the first syntheses of crown ethers by Charles Pedersen in the 1960s, leading to further development in the area of macrocycles and incorporation into a vast array of metal-organic structures. Supramolecular chemistry came to the forefront of science with the 1987 Nobel Prize in Chemistry, awarded jointly to Donald J. Cram, Jean-Marie Lehn, and Charles Pedersen “for their development and use of molecules with structure-specific interactions of high selectivity.”

Nanojars are supramolecular metal-organic complexes with a high affinity for hydrophilic anions and can efficiently transfer such anions from water into organic solvents through liquid-liquid extraction. The Nanojar Project started with studying trinuclear copper-pyrazolate species, which grew into the Nanojar project from the 2004 discovery. The first identified nanojar had a structure in which a chloride anion was incarcerated within an assembly of four macrocycles made of pyrazolate, copper(II), and hydroxide subunits, templated by the anion and bound together by hydrogen bonds and weak copper-oxygen interactions. Since then, different nanojars have been synthesized and their properties have been elucidated, including solubility, anion selectivity, structure, spectral, and fluorescent properties.

The scope of this work built off the already functionalized self-assembly pathway of the copper-pyrazolate structure incarcerating oxoanions and derivatized the pathway using 1H-indazole (benzpyrazole), concentrating on the synthesis and characterization of the carbonate and sulfate oxoanion within this new nanojar structure. The copper-indazolate products were characterized primarily by electrospray-ionization mass spectrometry (ESI-MS), and secondarily with UV-visible spectroscopy, NMR, and X-Ray crystallography. This work seeks to expand the nanojar database, exploring the different physical and chemical properties of a pyrazole with a fused 3,4-aromatic benzene substituent.

The carbonate pyrazole nanojar has been a published structure for over a decade. The pyrazolate nanojars are prized for their ability to sequester oxoanions, retain their integrity through manipulations of their pyrazole spacing, and exhibit resilience in alkaline environments. One thing that has remained the same within the nanojar moiety is the fundamental backbone of the nanojar. This project investigates the synthesis and characterization of indazole nanojars by taking the already functionalized pathway of nanojar self-assembly and derivatizing the scaffold molecule of the nanojar. Some initial speculations were that the increased bulk due to the additional benzene ring could create new ring combinatorial arrays. One of the questions that immediately derived from regiochemical considerations was, what would be the stereochemical orientations of the 1H-indazole units in the macrocyclic rings? The 1H-indazole because the two nitrogen atoms bound to the copper are not linearly arranged, pointing directly outward, rather the two covalently bound nitrogen atoms on the 5-membered pyrazole ring force the benzene functional group on the indazole bicyclic molecule to adopt an orientation attaching on the left or right 3,4-position. The next question was asked: because the nanojars are not perfectly symmetrical and the top and bottom rings may have a hyperbolic parabola shape, what conformation will the indazoles take on the top and bottom periphery saddle points? Will the center ring adopt a different conformation to lower the steric hindrance of the benzene rings in any way, and will it favor specific ring sizes compared to others? It was essential to synthesize a collection of indazole nanojars with double-charged oxoanions to observe the scope of potentially incarcerated ions and assess whether selectivity could be achieved. This work attempts to answer these questions.

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