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BIS[HYDROTRIS(1-PYRAZOLYL)BORATE] COMPLEXES: INVESTIGATING TITANIUM(II) METAL CENTERS AS FUEL ATOMS IN ENERGETIC MATERIALS & IRON(II)-MEDIATED REACTIONS WITH SOLVENTS AND OXYGEN
Bacon, Alexandra Marie
Bacon, Alexandra Marie
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Thesis/Dissertation
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2023
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Chemistry
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http://dx.doi.org/10.34944/dspace/8853
Abstract
In energetic materials research, the main goal is to create novel structures with improved energetic properties compared to the current industry standards. Despite the abundance of new organic structures synthesized over the last 30 years, applications have been limited by this delicate balance of synthesis, safety, and standards. Based on this, purely organic structures appear to be reaching a limit of their explosive capacity, an idea that has been dubbed “the CHNO ceiling”. Thus, compounds synthesized decades ago remain as the industry standard. The research presented in this dissertation endeavored to mitigate this problem. Building on previous work on energetic metallic clusters, we investigated the hypothesis that an unstable, reducing, fuel metal center such as titanium(II) will lead to a large combustion exotherm. Data from bomb calorimetric measurements supports this hypothesis: for complexes of hydrotris(pyrazolyl)borate (Tp), the titanium metal center resulted in larger heat of combustion compared to iron and manganese analogs, as well as the ionic Mg(Tp)2 compound. The combustion analysis of TiTp2 also led to the creation of a new method of sample preparation for air-free calorimetry.
With data supporting the Ti(II) hypothesis, the project moved toward incorporating Ti(II) into energetic materials. The first target was more nitrogen rich analog of Tp, hydrotris(1,2,4-triazolyl)borate (Ttri).. So far, this titanium complex has not been confirmed but reaction products still need to be characterized. We attempted to ligate the energetic tetrazole to a Ti(II) center. In this case, the reduction was unsuccessful, instead synthesizing a Ti(III)Cl3-tetrazole complex. Although not energetic, the products exhibited solvatochromism and different equivalents of tetrazole gave different results.
This dissertation also examines reactions of Fe(II)Tp2 with chlorinated solvents and ethers. In the presence of sunlight, the iron complex reacted rapidly decomposed chloroform, ultimately forming [FeTp2]+, [FeCl4]-. In diethyl ether and dibutyl ether, the data suggested that Fe(II)Tp2 cleaved and oxidized. In the resulting diiron(III) complexes, each iron center maintained one original Tp ligand and were bridged by two carboxylate ions (acetate or butanoate) and one oxygen atom. These complexes highlight a previously unknown reaction of FeTp2, the mechanism of which is under investigation.
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