Amine-borane dehydropolymerisation catalysed by iridium POCOP complexes

Polyaminoboranes (PABs) are isosteres of polyolefins by the isoelectronic relationship between the C—C and B—N units.1 These polymeric materials have potential use as precursors to B,N-based pre-ceramics, e.g. hexagonal boron nitride (h-BN) an isostere of graphene.

This thesis describes the controlled synthesis of polyaminoborane with previously reported catalyst, Ir(tBu-POCOP)H2 (POCOP = κ3-1,3-(OPtBu2)2C6H3])4. Chapter 1 provides a summary of the synthesis of polyaminoboranes, with a focus on transition metal catalysed reactions, and the mechanisms that have previously been reported. The applications of polyaminoboranes were also discussed.

Chapter 2 introduces the kinetics of the dehydrogenation of H3B·NH2Me with Ir(tBu-POCOP)(H)2, identifying an unexpected induction period, with potential causes of this induction period discussed. The speciation of the reaction was studied by NMR spectroscopy in situ and in operando. Relevant catalytic intermediates were identified and studied for the dehydrogenation of H3B·NH2Me independently. Equilibria between the identified catalytically relevant complexes were studied and discussed in this chapter.

Chapter 3 presents the proposed mechanistic pathways for the dehydrogenation of H3B·NH2Me with Ir(tBu-POCOP)(H)2. This study will combine data from kinetic experiments, Eyring analysis, isotope labelling experiments, DFT calculations and kinetic modelling to propose a mechanism. The synthesis and characterisation of an anionic iridium trihydride complex is also reported.

Chapter 4 discusses the reaction conditions that have been identified that allow for the control of molecular weight of polyaminoborane, with a relationship based on kobs ∝ Mn. This chapter includes scale up of the reaction to 20 g with very low catalyst loadings (0.001 mol%). The synthesis of BN ceramics (boron nitride) from polyaminoboranes is also detailed in this chapter.

Chapter 5 investigates the use of Ir(POCOP) catalysts with different R-groups on the phosphine to dehydrogenate H3B·NH2Me, to determine their effect on the rate of reaction and so in turn molecular weight.