Bond Activation - the Remarkable Emerging Chemistry of Bis(carboranes)

This proposal seeks to understand and build on three remarkable reactions recently discovered in the applicant's laboratory. In the first reaction an aromatic C-C bond is cleaved at room temperature in a metallacarborane (a cluster compound of [mainly] boron, carbon and metal) derived from a bis(carborane) (two linked carbon/boron clusters). The reaction is remarkable because C-C bonds in arenes are extremely strong and generally considered difficult to break. In the second reaction, again at room temperature, a different bis(carborane) molecule appears to lose two carbon vertices from one of its halves as an intact C2 unit on reduction and subsequent reaction with a metal fragment. Such decarbonation in this way is unprecedented in heteroborane chemistry. The final reaction (again room temperature) confirms unambiguoulsy decarbonation from a related monocarborane; again this is without precedent.In summary then, the first and second reactions involve bis(carboranes) and the third starts with a carborane with very strongly electron-withdrawing substituents. It seems apparent that these unprecedented reactions are in some way linked to the non-standard nature of these carboranes. Somehow the bis(carborane) and the highly modified carborane are promoting bond cleavage reactions that are traditionally very high energy processes. The chemistries of both these types of carborane are currently severely under-developed. The proposal seeks to address this situation by a thorough investigation of the reactions of bis(carboranes) and of carboranes with e-withdrawing substituents, focussing in particular on deboronation or reduction followed by metallation or capitation. We fully expect that this study will reveal other unexpected and novel reactions in addition to those recently found.Through a comprehensive synthetic chemistry programme we will seek to identify and understand the origins of the remarkable reactions we have discovered. Once we understand them we will be in a much better position to establish their generality and how they might be used.

The project is primarily concerned with academic advances but it is possible that our results could also have an impact on the chemical industry, since bond activation at ambient temperature is of considerable interest to significant parts of that industry in the context of synthesis and catalysis. For example, an outstanding problem in the petroleum industry is the difficulty in removing benzothiophene and dibenzothiophene but cleavage of the aromatic ring would facilitate that removal. Our work on decarbonation reactions could also potentially impact on catalysis if it leads to supraicosahedral monocarbon carboranes, compounds which would be expected to be superior least-coordinating anions. At HWU we benefit from the recently-created Converge programme, the specific remit of which is to to facilitate and share our research with Scottish, UK and global businesses. The project will further develop the experience and knowledge of the named RA and provide exceptional training for the PhD student. The know-how, skills and abilities of these researchers will impact on the wider community in diverse ways dependent on their ultimate career paths.