Degree

Doctor of Philosophy (PhD)

Department

Chemistry

Document Type

Dissertation

Abstract

Hydroformylation is the conversion of an alkene to an aldehyde with the use of a metal catalyst and syngas. Syngas is composed of H2 and CO commonly in a 1:1 ratio. Hydroformylation is one of the largest homogenously catalyzed reactions every year. The aldehydes produced are key intermediates in dyes, pharmaceuticals, and other industrial commodities. Current hydroformylation catalysts are composed of monovalent rhodium and cobalt metal complexes. Where rhodium catalysts are more active than cobalt catalysts, rhodium is also much more expensive than cobalt. Overall stability and metal deposition are two challenges that occur with monovalent catalysts. In 2020 Hood et al. discovered a divalent cobalt hydroformylation catalyst that has a unique cationic charge. This catalyst is supported by a bisphosphine ancillary ligand: [HCo(CO)3(P ͡ P)]+. This Co(II) catalyst produced higher catalytic activity than Co(I) catalysts. The higher valent nature of the metal center is proposed to increase the stability of the catalyst which could lead to higher catalytic activity at more mild conditions. However, there were challenges with the reproducibility of the synthesis that resulted in inconsistent results. One of the challenges was the unknown number of dioxanes present on the precursor [Co(acac)(dioxane)4]BF4 to the precatalyst [Co(acac)(dppBz)]BF4 which causes complications with reliably characterizing the complex. One way the stability of the precursor was improved was to switch to pyridine from dioxane. This led to a stronger binding coordinating solvent within the primary coordination sphere and subsequentially led to an easier characterization and crystallization of the complex. The precursor synthesized with pyridine ([Co(acac)(py)4]BF4) had less ligand fluctuation and a more predictable ligand field. With the more stable pyridine precursor, a precatalyst ([Co(acac)(dppBz)(py)]BF4) could be synthesized. Another purity challenge includes a byproduct (Co(acac)2(dppBz)) that is formed when the precatalyst was synthesized. This byproduct has not been able to be separated from the precatalyst. With modification to the synthesis, an analytically pure Co(II) precatalyst can be produced consistently. With the modifications to the synthesis, the hydroformylation system can be studied more reliably which has led to the study of activation conditions, solvent additives, and order of addition.

Date

4-19-2025

Committee Chair

Chambers, Matthew

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Available for download on Monday, March 27, 2028

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