Inorganic chemistry and catalysis
at Duquesne University
RESEARCH
Research Overview
Abundant element complexes for catalysis and materials applications
With an ever growing population and corresponding increase in demand for energy and natural resources, there is an immediate need for sustainable industrial processes that generate less waste, and leave a smaller carbon footprint. One option to achieve this is to develop more energy-efficient catalytic processes that are mediated by inexpensive, abundant catalysts, rather than those that use metals that are limited in supply, such as Pt, Pd, and Ir. As such, the primary goal of the Lummis research group will be to investigate the fundamental aspects of the reactions of main-group compounds, clusters, and abundant metal hydrides, with small molecules such as nitrogen, hydrogen, methane, ammonia, ethylene, CO, and alkenes that are either consumed or produced by energy production processes.
Development of redox-active main group catalysts
Group 13 and 14 complexes with accessible E(I)⟶E(III)/E(II)⟶E(IV) redox couples
Catalysis accounts for a significant percentage of the US GDP annually, and relies heavily on precious metals such as Pt, Pd, Rh, and Ir. Due to the expense and relative shortage of these elements, there is a growing effort to identify novel catalysts that rely on earth-abundant elements, such as those from the s- and p-blocks of the periodic table. While reactions between metals and small molecules such as hydrogen, ammonia, and ethylene were traditionally thought to be confined to the d-block, in 2005 a Ge analog of an alkyne was shown to react with dihydrogen [Power et al., J. Am. Chem. Soc. 2005, 127, 35, 12232]. This system laid the foundation for future main-group catalysis; specifically that the key to accessing as-yet undiscovered transition metal-like reactivity of the main group elements lies in the ability to tune both the energy and symmetry of their frontier molecular orbitals (FMOs). Since then, the development of p-block catalysis has been an exciting area, with an emphasis placed on Frustrated Lewis pair (FLP) methodology. Notably rarer, however, are instances where p-block compounds can reversibly activate small molecules as part of a larger catalytic cycle with oxidation/reduction occurring at the p-block element. In this project, we will look to design ligands such that they will allow for group 13 and 14 compounds to mediate these transformations.
Lewis Base adducts of binary metal hydrides and metal hydride cations
The chemistry of d- and s-block metal hydride complexes
Metal hydrides of the s- and d- block metals are synthetically useful reagents in catalytic and stoichiometric transformations, however binary metal hydrides typically suffer from lack of stability (d-block) and/or poor solubility (s-block). This project will use strongly donating Lewis Bases to stabilize well-defined, soluble M-H complexes and clusters for catalysis using inexpensive, abundant metals. In particular, the s-block metals will be targeted, and both neutral and cationic metal hydride complexes will be isolated. These compounds will be evaluated for their ability to functionalize small molecules such as carbon monoxide, carbon dioxide, and other unsaturated inorganic and organic substrates, in addition to their ability to mediate polymerization reactions for organic and inorganic substrates.
Dinitrogen activation and functionalization at early transition metal centers
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Direct reduction and functionalization of dinitrogen
Dinitrogen represents a valuable feedstock material in the synthesis of ammonia, urea and other nitrogen containing compounds, however, it is extremely challenging to reductively functionalize due to the strong N≡N triple bond. We will aim to use redox-active ligands on group 4 and 5 metals to stabilize the reactive, electron-rich intermediates required for catalytic dinitrogen activation. This will allow us to achieve full reductive cleavage of dinitrogen at the metal center with generation of terminal metal nitrides. Additionally, we will examine the viability of using dinitrogen as a direct feedstock for saturated and unsaturated N-heterocycles and other nitrogen-containing molecules and materials.