Synthesis and characterization of monomeric ruthenium-based catalysts for water oxidation
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Authors
Xiao, Dan
Issue Date
2025-05
Type
Electronic thesis
Thesis
Thesis
Language
en_US
Keywords
Chemistry
Alternative Title
Abstract
Nature converts solar energy into chemical energy (in the form of carbohydrates), releases dioxygen, and fixes carbon dioxide through photosynthesis. Light-driven water oxidation, one of the most energetically demanding reactions in nature (2H2O → O2 + 4H+ + 4e-), occurs in the photosynthetic reaction center, photosystem II (PSII). The structure of PSII revealed the tetranuclear manganese-calcium-oxo (Mn4Ca-oxo) cluster in the oxygen-evolving complex (OEC) that is known to catalytically initiate the water oxidation to produce protons, electrons and the release of dioxygen. Inspired by the catalytic manganese-calcium-oxo (Mn4Ca-oxo) cluster, several catalysts for artificial water oxidation have been developed with varied metal centers. The scope of the metals includes the first-row transition metals, ruthenium, and iridium. In Chapter 1, we describe the water oxidation reaction in Nature and progress on the development of artificial water oxidation complexes over the past few decades. Among the aforementioned metals, ruthenium-based catalysts have been studied extensively to explore the structure-activity relationships in the hope of illuminating a strategy for designing an efficient catalyst for water oxidation. Based on the current molecular ruthenium models for water oxidation, we designed, synthesized and characterized a series of ruthenium complexes with a negatively charged dicarboxylate backbone.
Chapter 2 describes the synthesis and characterization of ruthenium-based complexes with symmetric backbone ligands, such as, pda2− (2,6-pyridinyldiacetate), pba2− (pyridine-2,6-bis(α-oxo) acetate) and pdc2− (2,6-pyridinedicarboxylate) with various ancillary ligands, tfmp, py, pic and dmap, differing in electron-donating ability. 1H NMR was employed to investigate the electronic effect of ancillary ligands on the protons from the backbone ligands and those from the coordinated ancillary ligand. UV-Vis spectroscopy was used to study the electronic absorption of the Ru-pba family. The UV-Vis spectra revealed that the electron-donating ability of ancillary ligands can affect the metal-ligand charge transfer (MLCT) bands. The 1H NMR spectra revealed that a stronger electron-donating ancillary ligand will result in an upfield shift of the peaks.
Chapter 3 describes the synthesis and characterization of ruthenium-based complexes with asymmetric backbone ligands, such as, cmpc2− (6-(carboxymethyl)-pyridine-2-carboxylate) and cpa2− (6-carboxy-α-oxo-2-pyridine acetate) with various ancillary ligands, tfmp, py, pic and dmap, differing in electron-donating ability. 1H NMR spectroscopy was employed to investigate the electronic effect of the ancillary ligands on the protons from the backbone ligands and those from the coordinated ancillary ligand. UV-Vis spectroscopy was used to study the electronic absorption of the Ru-cpa family. Comparison of the 1H NMR and UV-Vis spectra are presented in this chapter.
The crystal structure of the complexes revealed an O-Ru-O bite angle ranging from 172° – 178° in the complexes with little distortion of the octahedral configuration, indicating increased stability and ease of access to bind water molecules at the metal center. Functional catalytic studies of these complexes in the future will contribute insight on the structure-activity relationships and serve as a motivation for the design of novel molecular catalysts for water oxidation.
Description
May2025
School of Science
School of Science
Full Citation
Publisher
Rensselaer Polytechnic Institute, Troy, NY