Date of Award
Doctor of Philosophy (PhD)
Polymers incorporating main group elements offer different and interesting properties compared to their all carbon analogues. For example, π-conjugated polymers incorporating phosphorus in the main chain of the polymer have generated interest due to their unique thermal and electronic properties, which primarily result from delocalization of the phosphorous lone pair within aromatic units. Similarly, interest in polysilanes stems from conductivity resulting from σ electron delocalization, though current methods of preparation for both of these types of materials are lacking. In this dissertation, both early and late transition-metal compounds were used to dehydrocouple phosphine and silane substrates. The use of dehydrocoupling catalysis as a method for the synthesis of main group element-linked polymers was explored utilizing substrates designed to engender solubility in their polymeric products. Progress towards the preparation of silane- and phosphine-based conjugated materials via dehydrocoupling catalysis is reported.
Catalytic reactions of bisphosphinite pincer-ligated iridium compounds p-XR(POCOP)IrHCl (POCOP) = 2,6-(R2PO)2C6H3, R = iPr, tBu, X = H, COOMe, H, NMe2with primary and secondary silanes have been performed. Compounds featuring the less sterically demanding iPr-substituted ligands facilitate silane redistribution reactions, but dehydrocoupling catalysis is observed for more encumbered silane substrates or with aggressive removal of H2. The bulkier tBu-substituted compounds are silane dehydrocoupling precatalysts that also undergo competitive redistribution with less hindered substrates. Products generated from reactions utilizing tBu ligated Ir include low molecular weight oligosilanes with varying degrees of redistribution present or disilanes when employing more sterically demanding substrates. The interplay of steric and electronic effects of the POCOP ligand on the silane product distribution will be presented.
In previous work by our group, a triamidoamine-supported zirconium catalyst,[κ5-(Me3SiNCH2CH2)2NCH2CH2NSiMe2CH2]Zr, 1 has been shown to be effective in catalyzing the formation of phosphorus–element bonds via dehydrocoupling. Substrates including 2,5-bisphosphinofuran and 1,4-bisphosphinobenzene were dehydrocoupled to yield hyperbranched polyphosphine products. Efforts to characterize these products have been limited due to poor solubility. Rational substrate design incorporating aliphatic sidechains in primary phosphine linker molecules to engender solubility has been accomplished. Treatment of these second generation substrates with 1 or [Cp*2ZrH3]Li, 2 leads to sluggish reactions reaching moderate conversions to diphosphine products. The working hypothesis is that steric congestion during the bond forming step hinders additional bond-formation. Efforts toward the characterization and utilization of these insoluble materials as metal ion scavengers will be presented.
Number of Pages
Mucha, Neil, "Catalytic Main Group Element Bond Formation Reactions Toward the Preparation of Conjugated Materials" (2015). Graduate College Dissertations and Theses. 469.