Thermal and photochemical reactions of large metallaborane clusters and functionalizations of boron nitride nanosheets

The thermal and photochemical pathways of several metallaborane compounds and the functionalization of boron nitride nanosheets have been investigated. The nanosheets have potential applications in Dye Sensitized Solar Cells.Chapters 1 and 3 describe the thermal and photochemical pathways for two metalladecaboranes, [nido -6-Mn(CO) 3 B 9 H 13 ][NMe 4 ] (1.1) and [6-C5Me5-nido-6-RhB9H13] (3.1). Isomerization or cage closure reactions were observed depending on the reaction conditions and the transition metal employed. Characterized products include the firstnido-5 metalladecaborane and ahypercloso-metalladecaborane containing a group 7 transitional metal, compound1.3 and1.4, respectively. Other findings include the facile acid catalyzed cyclic oxonium functionalization of complex1.1, the role of complex3.1 as the catalyst for the [2+2+2] cycloadditions of terminal alkynes, and the formation ofhypercloso-rhodadecaborane3.3 which is the firsthypercloso-metalladecaborane containing the metal rhodium. Chapter 2 describes investigations of the photochemical reactions between metallaboranes and unsaturated molecules. The complex 1.1was found to photoreact with both terminal and internal alkynes to afford the carborane with general formula [7-R-8-R\u27-7,8-nido-C2B9H10][NMe4] (2) in good yield. This represents a novel method for generating the substituted nido-C2B9 complex. Besides alkynes, the investigation of the photoreactions of other unsaturated species with the complex 1.1 were found to generate the [arachno-B9H14]- (2.4) and [nido-B9H12]- (2.5) anions in different relative ratios, depending on the nature of the unsaturated molecules. The complex1.1 was also found to act as an efficient catalyst for isocyanate cyclodimerization under photo-irradiation conditions, representing the first example of a metallaborane complex to catalyse the cyclodimerization of isocyanate. In Chapter 4, an effective and simple noncovalent functionalization and solubilization of boron nitride nanosheets (BNNSs) has been achieved by using polythiophene or polyvinylpyrrolidone as a functionalization polymer with BNNSs. The BNNSs form strong π-π stacking interactions with the polythiophenes and were found to act as a bandgap tuning tool for polythiophene derivatives. A BNNS-polythiophne-TiO2 hybrid nanomaterial was achieved by the covalent binding between TiO2 nanoparticle surfaces and the BNNS-polythiophene unit containing a carboxylic acid functional group. This nanomaterial was then further incorporated into a Dye Sensitized Solar Cells (DSSCs) and the observed enhancement of the performance of the cells is discussed