Date of Graduation

12-2021

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Chemistry (PhD)

Degree Level

Graduate

Department

Chemistry & Biochemistry

Advisor/Mentor

Kilyanek, Stefan M.

Committee Member

Coridan, Robert H.

Second Committee Member

Tian, Z. Ryan

Third Committee Member

Heyes, Colin D.

Fourth Committee Member

Zheng, Nan

Keywords

Biofuels; Biomass Conversion; Catalysis; Green Chemistry; Molybdenum

Abstract

This dissertation details the development of rationally designed dioxomolybdenum catalyst active for deoxydehydration (DODH), the net reduction of diols and polyols into alkenes and dienes. Catalyst design involved variations on dioxomolybdenum(VI) supported by a dianionic meridional pincer ligand. Rational substrate scope was explored using aliphatic diols, aromatic diols, and biomass derived diols. Various reductants were tested for ability to catalyze the reaction. The substrate specific mechanism of DODH was explored utilizing NMR and in-situ infrared spectroscopy and important rate constants and rate determining steps were found to aid in the optimization of ideal reaction conditions. Catalytic activity was observed to be dependent on the ligand environment. The smaller electronically demanding ligand environment showed readily rapid reactivity for aromatic diols, but competitive side reactions and catalyst dimerization occurred. The more sterically demanding ligand environment was observed to slow the relative reaction times, decrease/block competitive side reactions, and increase the yields for specific diols. Electrochemical studies were performed on the more sterically demanding catalyst to gain a fundamental understanding of the proton transfer and electron transfer processes that are involved in transforming the molybdenum-dioxo catalyst into the active mono-oxo species. The processes may be coupled together in a proton coupled electron transfer (PCET) where the proton and electron are transferred stepwise. The catalyst was screened against a variety of Brønsted-Lowry acids within a pKa window of ~9-32 in THF. Electrochemical characterization of the molybdenum catalyst suggests a PTET mechanism. Future studies involve the further rational design of ligand environments to directly access the reduced catalytically DODH active species with minimum energy input as an efficient and alternative method to generate industrially relevant chemical precursors.

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