Boron-Nitrogen Analogues of Indene Containing Hydrocarbons
Date
2019-07-09
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Abstract
Boron-nitrogen (BN) containing polycyclic aromatic hydrocarbons represent an important class of compounds of fundamental and applied interest. Despite their prevalence in main group chemistry, there remain few ways to efficiently synthesize large quantities of BN containing aromatic species. We developed a method for the preparation of 3-bora-9aza-indene heterocycles based on zirconocene mediated functionalization of the ortho-CH bonds of pyridines. Unlike other methods, the boron center in these heterocycles remains functionalized with a chloride ligand allowing the compounds to be further elaborated through halide abstraction or reduction. The utility of the method was demonstrated by applying it towards the preparation of 1,5-dibora-4a,8a-diaza BN analogs of the intriguing hydrocarbon s-indacene starting from 2,5-dimethylpyrazine. This allowed us to experimentally and computationally compare the BN doped derivative to the all-carbon analogue, providing new knowledge on the effect of main group substitutions on bonding in aromatic compounds. The developed synthetic method also provided us access to a new BN doped indenide species in large scale that allowed for its reactivity to be examined in depth. It was found that the reactivity of the nucleophilic indenide depended on which electrophile it was treated with. This divergent reactivity was investigated through reactions with alkyl halides and carbon dioxide and the mechanisms determined were supported through computational methods. Inspired by the properties of the indacene species, we targeted derivatives of BN doped dihydroindeno[1,2-b]fluorene. They were synthesized via electrophilic borylation, a mildly air-sensitive technique, and the end products were handled readily under atmospheric conditions. Through transmetallation via diarylzinc reagents a series of derivatives were synthesized which show broad absorption profiles and frontier energy levels amenable to their use in organic solar cell devices. Exploratory device parameters were studied and show moderate results with PCEs reaching 2% showing the possibility of molecules containing this framework in organic electronic devices.
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Keywords
Boron, Main-group
Citation
Morgan, M. M. (2019). Boron-Nitrogen Analogues of Indene Containing Hydrocarbons (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca.