Matching Items (6)
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- All Subjects: Catalysis
- All Subjects: Frequency Selective Surfaces
- Creators: Jones, Anne
- Creators: Trovitch, Ryan J
Description
The search for highly active, inexpensive, and earth abundant replacements for existing transition metal catalysts is ongoing. Our group has utilized several redox non-innocent ligands that feature flexible arms with donor substituents. These ligands allow for coordinative flexibility about the metal centre, while the redox non-innocent core helps to overcome the one electron chemistry that is prevalent in first row transition metals. This dissertation focuses on the use of Ph2PPrDI, which can adopt a κ4-configuration when bound to a metal. One reaction that is industrially useful is hydrosilylation, which allows for the preparation of silicones that are useful in the lubrication, adhesive, and cosmetics industries. Typically, this reaction relies on highly active, platinum-based catalysts. However, the high cost of this metal has inspired the search for base metal replacements. In Chapter One, an overview of existing alkene and carbonyl hydrosilylation catalysts is presented. Chapter Two focuses on exploring the reactivity of (Ph2PPrDI)Ni towards carbonyl hydrosilylation, as well as the development of the 2nd generation catalysts, (iPr2PPrDI)Ni and (tBu2PPrDI)Ni. Chapter Three presents a new C-O bond hydrosilylation reaction for the formation of silyl esters. It was found the (Ph2PPrDI)Ni is the most active catalyst in the literature for this transformation, with turnover frequencies of up to 900 h-1. Chapter Four explores the activity and selectivity of (Ph2PPrDI)Ni for alkene hydrosilylation, including the first large scope of gem-olefins for a nickel-based catalyst. Chapter Five explores the chemistry of (Ph2PPrDI)CoH, first through electronic structure determinations and crystallography, followed by an investigation of its reactivity towards alkyne hydroboration and nitrile dihydroboration. (Ph2PPrDI)CoH is the first reported cobalt nitrile dihydroboration catalyst.
ContributorsRock, Christopher L (Author) / Trovitch, Ryan J (Thesis advisor) / Kouvetakis, John (Committee member) / Pettit, George R. (Committee member) / Arizona State University (Publisher)
Created2018
Description
The addition of aminoalkyl-substituted α-diimine (DI) ligands to bis(1,5 cyclooctadiene) nickel (or (COD)2Ni) resulted in the formation of two new nickel complexes with the general formula of (Me2NPrDI)2Ni and (PyEtDI)2Ni. Investigation of these complexes by 1H NMR spectroscopy revealed diimine coordination but also the absence of amine arm coordination. Using the 1H NMR spectra in conjunction with structures determined through single crystal X-ray diffraction, the electronic structure of both complexes was described as having a Ni(II) metal center that is antiferromagnetically coupled to 2 DI radical monoanions. A greater ligand field was sought by replacing the pendant amines with phosphine groups on the DI ligands. This yielded ligands with the general formula (Ph2PPrDI) and (Ph2PEtDI). Upon addition to (COD)2Ni, each ligand immediately displaced both COD ligands from the Ni0 center to produce new κ4 N,N,P,P complexes, (Ph2PPrDI)Ni and (Ph2PEtDI)Ni, as observed via single crystal X-ray diffraction and NMR spectroscopy. Reduction of the DI backbone was observed in both complexes, with both complexes being described as having a Ni(I) metal center that is antiferromagnetically coupled to a DI radical monoanion. In addition to alkylphosphine substituted DI ligands, the coordination of a pyridine diimine (PDI) ligand featuring pendant alkylphosphines was also investigated. The addition of (Ph2PPrPDI) to (COD)2Ni produced a new paramagnetic (μeff = 1.21 μB), κ4-N,N,N,P complex identified as (Ph2PPrPDI)Ni. Reduction of the PDI chelate was observed through single crystal X-ray diffraction with the electronic structure described as having a low-spin Ni(I) metal center that is weakly coupled to a PDI radical monoanion (SNi = 1/2). The ability of the three Ni complexes to mediate the hydrosilylation of several unsaturated organic substrates was subsequently investigated. Using a range of catalyst loadings, the hydrosilylation of various substituted ketones afforded a mixture of both the mono- and di-hydrosilylated products within 24 hours, while the hydrosilylation of various substituted aldehydes afforded the mono-hydrosilylated product almost exclusively within hours. (Ph2PEtDI)Ni and (Ph2PPrPDI)Ni were identified as the most effective catalysts for the hydrosilylation of aldehydes at ambient temperature using catalyst loadings of 1 mol%.
ContributorsPorter, Tyler Mathew (Author) / Trovitch, Ryan (Thesis director) / Jones, Anne (Committee member) / Mujica, Vladimiro (Committee member) / Barrett, The Honors College (Contributor) / Department of Chemistry and Biochemistry (Contributor)
Created2014-05
Description
Industrial interest in electrocatalytic production of hydrogen has stimulated considerable research in understanding hydrogenases, the biological catalysts for proton reduction, and related synthetic mimics. Structurally closely related complexes are often synthesized to define structure-function relationships and optimize catalysis. However, this process can also lead to drastic and unpredictable changes in the catalytic behavior. In this paper, we use density functional theory calculations to identify changes in the electronic structure of [Ni(bdt)(dppf)] (bdt = 1,2-benzenedithiolate, dppf = 1,1ʹ-bis(diphenylphosphino)ferrocene) relative to [Ni(tdt)(dppf)] (tdt = toluene-3,4-dithiol) as a means to explain the substantially reduced electrocatalytic activity of the tdt complex. An increased likelihood of protonation at the sulfur sites of the tdt complex relative to the Ni is revealed. This decreased propensity of metal protonation may lead to less efficient metal-hydride production and subsequently catalysis.
ContributorsHerringer, Nicholas Stephen (Author) / Jones, Anne (Thesis director) / Mujica, Vladimiro (Committee member) / Pilarisetty, Tarakeshwar (Committee member) / School of Molecular Sciences (Contributor) / Barrett, The Honors College (Contributor)
Created2018-05
Description
The late first row transition metals, being inexpensive and environmentally benign, have become very attractive for sustainable catalyst development. However, to overcome the detrimental one electron redox processes exhibited by these metals, the employment of redox non-innocent chelates turned out to be very useful. The Trovitch group has designed a series of pentadentate bis(imino)pyridine ligands (pyridine diimine, PDI) that are capable of binding the metal center beyond their 3-N,N,N core and also possess coordination flexibility. My research is focused on developing PDI-supported manganese catalysts for organic transformations and renewable fuel production.
The thesis presents synthesis and characterization of a family of low valent (PDI)Mn complexes. Detailed electronic structure evaluation from spectroscopic and crystallographic data revealed electron transfer from the reduced metal center to the accessible ligand orbitals. One particular (PDI)Mn variant, (5-Ph2PPrPDI)Mn has been found to be the most efficient carbonyl hydrosilylation catalyst reported till date, achieving a maximum turnover frequency of up to 4950 min-1. This observation demanded a thorough investigation of the operative mechanism. A series of controlled stoichiometric reactions, detailed kinetic analysis, and relevant intermediate isolation suggest a mechanism that involves oxidative addition, carbonyl insertion, and reductive elimination. Noticing such remarkable efficiency of the (PDI)Mn system, it has been tested for application in renewable fuel generation. A modest efficiency for H2 production at an apparent pH of 8.4 have been achieved using a cationic Mn complex, [(Ph2PPrPDI)Mn(CO)]Br. Although, a detailed mechanistic investigation remained challenging due to complex instability, a set of relevant Mn(-I) intermediates have been isolated and characterized thoroughly.
The dissertation also includes synthesis, characterization, and electronic structure evaluation of a series of Triphos supported iron complexes. Using this pincer chelate and either 2,2’-bipyridine (bpy) or 1,3,5,7-cyclooctatetraene (COT), a set of electronically interesting complexes have been isolated. Detailed electronic structure investigation using spectroscopy, magnetometry, crystallography, and DFT calculations revealed redox non-innocent behavior in the Bpy and COT ligands. Additionally, CO binding to the (Triphos)Fe system followed by reaction with borohydride reagents allowed for the isolation of some catalytically relevant and reactive iron hydride complexes.
The thesis presents synthesis and characterization of a family of low valent (PDI)Mn complexes. Detailed electronic structure evaluation from spectroscopic and crystallographic data revealed electron transfer from the reduced metal center to the accessible ligand orbitals. One particular (PDI)Mn variant, (5-Ph2PPrPDI)Mn has been found to be the most efficient carbonyl hydrosilylation catalyst reported till date, achieving a maximum turnover frequency of up to 4950 min-1. This observation demanded a thorough investigation of the operative mechanism. A series of controlled stoichiometric reactions, detailed kinetic analysis, and relevant intermediate isolation suggest a mechanism that involves oxidative addition, carbonyl insertion, and reductive elimination. Noticing such remarkable efficiency of the (PDI)Mn system, it has been tested for application in renewable fuel generation. A modest efficiency for H2 production at an apparent pH of 8.4 have been achieved using a cationic Mn complex, [(Ph2PPrPDI)Mn(CO)]Br. Although, a detailed mechanistic investigation remained challenging due to complex instability, a set of relevant Mn(-I) intermediates have been isolated and characterized thoroughly.
The dissertation also includes synthesis, characterization, and electronic structure evaluation of a series of Triphos supported iron complexes. Using this pincer chelate and either 2,2’-bipyridine (bpy) or 1,3,5,7-cyclooctatetraene (COT), a set of electronically interesting complexes have been isolated. Detailed electronic structure investigation using spectroscopy, magnetometry, crystallography, and DFT calculations revealed redox non-innocent behavior in the Bpy and COT ligands. Additionally, CO binding to the (Triphos)Fe system followed by reaction with borohydride reagents allowed for the isolation of some catalytically relevant and reactive iron hydride complexes.
ContributorsMukhopadhyay, Tufan K (Author) / Trovitch, Ryan J (Thesis advisor) / Buttry, Daniel (Committee member) / Pettit, George (Committee member) / Arizona State University (Publisher)
Created2016
Description
The honors thesis presented in this document describes an extension to an electrical engineering capstone project whose scope is to develop the receiver electronics for an RF interrogator. The RF interrogator functions by detecting the change in resonant frequency of (i.e, frequency of maximum backscatter from) a target resulting from an environmental input. The general idea of this honors project was to design three frequency selective surfaces that would act as surrogate backscattering or reflecting targets that each contains a distinct frequency response. Using 3-D electromagnetic simulation software, three surrogate targets exhibiting bandpass frequency responses at distinct frequencies were designed and presented in this thesis.
ContributorsSisk, Ryan Derek (Author) / Aberle, James (Thesis director) / Chakraborty, Partha (Committee member) / Electrical Engineering Program (Contributor, Contributor) / Barrett, The Honors College (Contributor)
Created2021-05
Description
The ability of magnetic resonance imaging (MRI) to image any part of the human body without the effects of harmful radiation such as in CAT and PET scans established MRI as a clinical mainstay for a variety of different ailments and maladies. Short wavelengths accompany the high frequencies present in high-field MRI, and are on the same scale as the human body at a static magnetic field strength of 3 T (128 MHz). As a result of these shorter wavelengths, standing wave effects are produced in the MR bore where the patient is located. These standing waves generate bright and dark spots in the resulting MR image, which correspond to irregular regions of high and low clarity. Coil loading is also an inevitable byproduct of subject positioning inside the bore, which decreases the signal that the region of interest (ROI) receives for the same input power. Several remedies have been proposed in the literature to remedy the standing wave effect, including the placement of high permittivity dielectric pads (HPDPs) near the ROI. Despite the success of HPDPs at smoothing out image brightness, these pads are traditionally bulky and take up a large spatial volume inside the already small MR bore. In recent years, artificial periodic structures known as metamaterials have been designed to exhibit specific electromagnetic effects when placed inside the bore. Although typically thinner than HPDPs, many metamaterials in the literature are rigid and cannot conform to the shape of the patient, and some are still too bulky for practical use in clinical settings. The well-known antenna engineering concept of fractalization, or the introduction of self-similar patterns, may be introduced to the metamaterial to display a specific resonance curve as well as increase the metamaterial’s intrinsic capacitance. Proposed in this paper is a flexible fractal-inspired metamaterial for application in 3 T MR head imaging. To demonstrate the advantages of this flexibility, two different metamaterial configurations are compared to determine which produces a higher localized signal-to-noise ratio (SNR) and average signal measured in the image: in the first configuration, the metamaterial is kept rigid underneath a human head phantom to represent metamaterials in the literature (single-sided placement); and in the second, the metamaterial is wrapped around the phantom to utilize its flexibility (double-sided placement). The double-sided metamaterial setup was found to produce an increase in normalized SNR of over 5% increase in five of six chosen ROIs when compared to no metamaterial use and showed a 10.14% increase in the total average signal compared to the single-sided configuration.
ContributorsSokol, Samantha (Author) / Sohn, Sung-Min (Thesis director) / Allee, David (Committee member) / Jones, Anne (Committee member) / Barrett, The Honors College (Contributor) / Electrical Engineering Program (Contributor)
Created2022-05