Development of Homogeneous Manganese Catalysts for Organic Transformations and Inorganic Polymerizations

The development of sustainable catalysts that exhibit exceptional activity has become a major goal of organometallic chemists. Considering their low cost and environmentally benign nature, the use of base metals in catalysis has recently been explored. This dissertation is focused on the development of manganese catalysts for organic transformations and inorganic polymerizations. Previous advances in Mn-based hydrosilylation and hydroboration catalysis are reviewed in Chapter 1 and set the stage for the experimental work described herein.In Chapter 2, the electronic structure of [(2,6-iPr2PhBDI)Mn(μ-H)]2 is explored. This compound was evaluated by density functional theory calculations, SQUID magnetometry and EPR spectroscopy at low temperature. Single crystal X-ray diffraction data was collected for related compounds that feature bridging X-type ligands. The data revealed how bridging ligands impact the Mayer bond order between the two Mn atoms and explained why [(2,6-iPr2PhBDI)Mn(μ-H)]2 is an active catalyst for organic transformations. Chapter 3 spotlights the first study to systematically demonstrate commercial aminosilane CVD precursor synthesis by way of SiH4 and amine dehydrocoupling using [(2,6-iPr2PhBDI)Mn(μ-H)]2. In addition, the study provided an efficient and halogen-free preparation of highly cross-linked polycarbosilazanes under ambient conditions. Furthermore, exceptionally pure perhydropolysilazane was directly prepared from ammonia and silane at room temperature through dehydrogenative coupling. These are also the first reported examples of Mn-catalyzed Si–N dehydrocoupling. This research was then extended to the Mn-catalyzed dehydrogenative coupling of NH3 and diamines to organic silanes. Organic polysilazanes and polycarbosilazanes were synthesized and the structures were characterized by NMR, FT-IR, and MALDI-TOF spectroscopy. The thermal properties and coating applications of the products were evaluated by TGA, DSC, X-ray powder diffraction, SEM and EDX. A turnover frequency (TOF) experiment using 0.01 mol% of [(2,6-iPr2PhBDI)Mn(μ-H)]2 revealed a maximum TOF of 300 s-1, which is the highest activity ever reported for this transformation. The last chapter highlights the first examples of nitrile dihydroboration mediated by a manganese catalyst. Using 0.5 mol% of [(2,6-iPr2PhBDI)Mn(μ-H)]2, 14 nitriles were reduced with HBPin at 80 ℃ to afford N,N-diborylamines after 24 h. A mechanism was proposed based on the isolation of [(2,6-iPr2PhBDI)Mn(NCHPh)]2 as an intermediate and further substantiated by DFT.