Author ORCID Identifier
Date of Graduation
Eberly College of Arts and Sciences
Six Group 4 metallocene derivatives of group 4 incorporating a redox active benzene-1,2-thiolate ligand (bdt) were prepared. These complexes were characterized using one- and two-dimensional nuclear magnetic resonance (NMR) spectroscopy. Additionally, X-ray crystallographic analyses of these complexes, with the exception of Cp2Zrbdt (Cp = cyclopentadienyl), reveal C2v symmetric structure in the solid-state. All species display electronic absorption bands that are ligand-to-metal charge transfer (LMCT) in character well into the visible region. Spectroscopic data combine with time dependent-density functional theory calculations showed fluctuation in solution which promotes non-radiative energy loss and leads to the absence of emission in solution at room temperature. Cyclic voltammograms have one reversible reduction event that is metal-centered. Except for Cp*2Hfbdt (Cp* = permethylcyclopentadienyl), the remaining five complexes exhibit an irreversible oxidation event.
(MePMPMe)2ZrBn2 (MePMPMe = 3,5-dimethyl-2-(2-pyridyl)pyrrolide; Bn = benzyl) was synthesized and characterized via X-ray crystallography and NMR spectroscopy. The complex has LMCT absorption in the blue light region and is photoactive upon irradiation with blue LED. Photolysis of (MePMPMe)2ZrBn2 in the presence of excess diphenylacetylene proceeds with the formation of (MePMPMe)2(η4-C4Ph4) – the first zirconium complex featuring a coordinated cyclobutadienyl ligand. Using 4-methylbenzyl bromide as a mild oxidant, (MePMPMe)2ZrBr2 was cleanly made. A mixture of bibenzyl byproducts suggests a radical mechanism. Testing disulfide substrates lead to the formation of two new multinuclear zirconium thiophenolate complexes identified via X-ray crystallography.
Expanding the substrate scope of the photoreaction by less substituted alkyne such as 1-phenyl-1-propyne, phenylacetylene, and ethynylanisole derivatives resulted in catalytic trimerization, forming benzene derivatives that are generally selective toward one isomer. Precatalyst (MePMPMe)2ZrBn2 can also tolerate benzonitrile. Preliminary experiments with 1,6-heptadiene also catalytically produced a new organic product. CO addition produced a new zirconium species that is NMR silent. Overall, the photoreaction selectivity and fast reactivity are specific to the photochemical pathway compared to thermal condition or using KC8 reductant to reduce the Zr center. Using photoactive (MePMPMe)2ZrBn2 can form new zirconium complexes and catalytically generate organic molecules with complimentary selectivity to using late transition metals catalysts. With further exploration, this methodology can be a useful tool in inorganic and organic synthesis.
Do, P. Minh N., "Photophysics and Photochemistry Enabled by Ligand-to-Metal-Charge-Transfer: Unusual Carbon-Carbon Bond Formation at a Zirconium Center" (2022). Graduate Theses, Dissertations, and Problem Reports. 11592.