Progress toward bismuth-based radical initiators and metallopolymers

Abstract

Organobismuthanes have long been established as complexes known for it’s accessibility , lowmaterial cost, non-toxicity, as well as the synthetic versatility which has been applied to a growing number of applications. In our synthesis, we utilize previously developed techniques that take advantage of bulkier aryl substituents in diaryl bismuth compounds to prevent scrambling of the products. This has led to the development of affordable materials with highly desirable properties, some of which can be selectively attuned toward specified requirements that have potential applications in polymer and pharmaceutical chemistry. In the first chapter, we examine metallopolymers bearing diarylbismuth substituents and their physical properties. We hypothesized that modifications to these metallopolymers 4 will augment the solubility, allowing for variations in physical properties. First, we explored the copolymerization of diphenyl bismuth styrene (Ph2BiSty) and ditolyl bismuth styrene (Tol2BiSty) with methyl-methacrylate (MMA) to produce p-Ph2BiSty-co-MMA, p-Tol2BiSty-co-MMA, pPh2BiSty, and p-Tol2BiSty. These experiments produced (co)polymers that were found to be insoluble and unsuitable for characterization techniques to be applied. Our second attempt to develop on these systems led to the incorporation of the mesityl aryl group into the bismuth side chain resulting in the synthesis of the dimesityl bismuth styrene (Mes2BiSty) monomer, which was co-polymerized with 4-methyl styrene (MS) and 4-bromostyrene (BS). Similar to the outcomes of the phenyl and tolyl co-MMA co-polymer, the p-Mes2BiSty-co-MS/BS copolymers have similar solubility and homogeneity issues,. In the second chapter, bismuth-based radical promoters are reviewed for their reactivity towards the dehydrocoupling of silanes and TEMPO or PhOH. We also report that a select few of these bismuth-based promoters, in sub-stoichiometric quantities, have the ability to initiate and mediate polymerization of styrene. We report here five non-hypervalent, well-defined, diaryl bismuth radical promoters dimesityl bismuth phenyl thiolate (1-SPh), bis(2,4,6-triisopropylphenyl) bismuth phenyl thiolate (2-SPh), dimesityl bismuth hexamethyl-2,6terphenyl thiolate (1-SHMT), dimesitylbismuth isobutyronitrile (1-IBN), and bis(2,4,6-triisopropylphenyl) bismuth isobutyronitrile (2-IBN). These complexes demonstrate reactivity under thermal and photochemical conditions for the dehydrocoupling of PhSiH3 with PhOH and were found to afford low to moderate reaction turnover. Furthermore, we found two of these complexes (1-SPh and 2- iv SPh) to be somewhat reactive in the dehydrocoupling of PhSiH3 with TEMPO only under photoirradiation conditions, while the other complexes were completely inactive.