Bimetallic Main-Group And Early Transition Metal Catalysis For Biorenewable Polymers And Biomass Conversion



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The environmental ramifications of the rapid expansion of fossil fuel-based materials have ushered in new demand for sustainable polymers and chemical feedstocks. Likewise, the development of new catalysts for the derivatization of renewable monomers and their polymerization represents a leading avenue towards sustainable materials with commercially relevant properties. This dissertation describes the synthesis of some novel binucleating ligands and their bimetallic complexes for the controlled polymerization of biorenewable monomer lactide, as well as a redox cooperative bimetallic vanadium catalyst for the degradation of lignin. First, a method for the preparation of bis(pyrazolyl)alkanes was developed based on the nucleophile-catalyzed condensation reaction between aldehydes and bis(pyrazolyl)methanones. Isolation of a key carbamate intermediate supported a proposed mechanism of two separate organocatalyzed cycles. Furthermore, tolerance of a variety of steric groups and aldehydes allowed access to polydentate heteroscorpionate ligands in one step under mild conditions. Using this method, a steric library of binucleating ligands based on the BINOL framework were prepared and their dizinc and dimagnesium complexes were characterized. These complexes were highly active for the polymerization of lactide with excellent control over molecular weight and dispersity. Importantly, kinetic analyses revealed significantly improved reactivity for the bimetallic complexes compared to structurally analogous monometallic ones, promising for a cooperativity enhanced mechanism. Additionally, new monometallic complexes of zinc and magnesium based on bulky phenol and indole ligands prepared by the same method were described and their polymerization activity briefly investigated. Finally, a novel bis(vanadyl) complex was developed, characterized, and studied in the aerobic decomposition of a lignin model compound. Magnetometry and calculation studies revealed unique ferromagnetic coupling between metal centers and a low singlet-triplet gap. Additionally, comparative reactivity studies against monometallic vanadium(IV)- and (V) structural analogues reveal marked increases in rate, highly suggestive of redox cooperativity.



Bimetallic Catalysis, Biorenewable Materials


Portions of this document appear in: Tansky, Maxym, Zipeng Gu, and Robert J. Comito. "Metal-free, mild, and selective synthesis of bis (pyrazolyl) alkanes by nucleophile-catalyzed condensation." The Journal of Organic Chemistry 86, no. 2 (2020): 1601-1611.