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This dissertation details efforts in designing and tuning catalysts that have the ability to engage CO2 through a metal center and functional groups in the second coordination sphere. We attempted to improve a dinuclear copper complex that has the ability to engage CO2 through two metal centers and was previously reported as a CO2 reduction catalysts. Electron donating substitutions were made on the ligands in attempts to improve rates for the electrocatalytic reduction of CO2. These modifications led to changes in the reduction potentials and the structures of the complexes, but did not produce significant improvements in turnover frequencies or overpotentials for CO2 reduction. We attempted to improve rhodium disphosphine catalysts for the conversion of CO2 to HCOO-- by introducing ligands with proton relays. Several [Rh(P2N2)2]+ complexes were synthesized. They were structurally characterized as square planar with slight tetrahedral distortions and exhibited a reversible 2e-- Rh(I/--I) redox couple in voltammetric studies. We synthesized the HRh(P2N2)2 complexes and structurally characterized them as having distorted trigonal bipyramidal geometry. The hydricities of several of the HRh(P2N2)2 complexes were measured using equilibration experiments monitored by 31P NMR. The HRh(P2N2)2 complexes are among the most hydridic complexes the 16 e-- M(diphosphine)2 class. We compared the activity of the [Rh(P2N2)2]+ complexes for catalytic CO2 hydrogenation to formate to a [Rh(diphosphine)2]+ complex of a similar hydricity that lacked pendant amines. We found that, despite the strong reducing power of the HRh(P2N2)2 complexes, the non-pendant-amine-containing Rh complex was the best catalyst for CO2 hydrogenation. We also tested these complexes for their electrochemical CO2 reduction activity. While these complexes are energetic enough to react with CO2 when reduced, they are unstable under the high potentials necessary for their reduction. We tested Ru pincer complexes that are known to hydrogenate esters via a mechanism that involves co-operative metal-ligand interactions for their ability to reduce CO2 and methylformate electrochemically. We also synthesized and tested an Fe analogue of these complexes for electrochemical reactivity. We found that these complexes are promising candidates for further study as CO2 reduction catalysts.
Masakatsu Shibasaki, Motomu Kanai, Shigeki Matsunaga, and Naoya Kumagai: Multimetallic Multifunctional Catalysts for Asymmetric Reactions.- Takao Ikariya: Bifunctional transition metal-based molecular catalysts for asymmetric syntheses.- Chidambaram Gunanathan and David Milstein: Bond Activation by Metal-Ligand Cooperation: Design of ”Green” Catalytic Reactions Based on Aromatization-Dearomatization of Pincer Complexes.- Madeleine C. Warner, Charles P. Casey, and Jan-E. Bäckvall: Shvo’s Catalyst in Hydrogen Transfer Reactions.- Noritaka Mizuno, Keigo Kamata, and Kazuya Yamaguchi: Liquid-Phase Selective Oxidation by Multimetallic Active Sites of Polyoxometalate-Based Molecular Catalysts.- Pingfan Li and Hisashi Yamamoto: Bifunctional Acid Catalysts for Organic Synthesis.- Jun-ichi Ito, Hisao Nishiyama: Bifunctional Phebox Complexes for Asymmetric Catalysis.
Homogeneous and Heterogeneous Catalysis
This volume analyzes and summarizes recent developments in several key interfacial electrochemical systems in the areas of fuel cell electrocatatalysis, electrosynthesis and electrodeposition. The six Chapters are written by internationally recognized experts in these areas and address both fundamental and practical aspects of several existing or emerging key electrochemical technologies. The Chapter by R. Adzic, N. Marinkovic and M. Vukmirovic provides a lucid and authoritative treatment of the electrochemistry and electrocatalysis of Ruthenium, a key element for the devel- ment of efficient electrodes for polymer electrolyte (PEM) fuel cells. Starting from fundamental surface science studies and interfacial considerations, this up-to-date review by some of the pioneers in this field, provides a deep insight in the complex catalytic-electrocatalytic phenomena occurring at the interfaces of PEM fuel cell electrodes and a comprehensive treatment of recent developments in this extremely important field. Several recent breakthroughs in the design of solid oxide fuel cell (SOFC) anodes and cathodes are described in the Chapter of H. Uchida and M. Watanabe. The authors, who have pioneered several of these developments, provide a lucid presentation d- cribing how careful fundamental investigations of interfacial electrocatalytic anode and cathode phenomena lead to novel electrode compositions and microstructures and to significant practical advances of SOFC anode and cathode stability and enhanced electrocatalysis.
Highlighting the key aspects and latest advances in the rapidly developing field of molecular catalysis, this book covers new strategies to investigate reaction mechanisms, the enhancement of the catalysts' selectivity and efficiency, as well as the rational design of well-defined molecular catalysts. The interdisciplinary author team with an excellent reputation within the community discusses experimental and theoretical studies, along with examples of improved catalysts, and their application in organic synthesis, biocatalysis, and supported organometallic catalysis. As a result, readers will gain a deeper understanding of the catalytic transformations, allowing them to adapt the knowledge to their own investigations. With its ideal combination of fundamental and applied research, this is an essential reference for researchers and graduate students both in academic institutions and in the chemical industry. With a foreword by Nobel laureate Roald Hoffmann.
The thesis presented here is focused on two aspects of transition metal mediated catalysis research- one is designing homogeneous rhenium complex with suitable ligand framework for electrochemical reduction of carbon dioxide to address dual issues regarding green house gas removal and hydrocarbon fuel production; another being fabrication of heterogeneous mesoporous manganese oxide to catalyze organic fine chemical synthesis under aerobic atmospheric condition. The quest for conquering fossil fuel energy dependence leads us to develop methodologies for using CO2 as a renewable resource. Electrochemical reduction of CO2 has been considered as a promising procedure for this purpose. Coordination complexes of rhenium and α-diimine ligands are known to resolve the bottleneck of activating the thermally stable and kinetically inert CO2 molecule. In the beginning of the thesis, I have described the development of a new family of α-diimine ligand coordinated rhenium complexes that exhibits remarkable catalytic activity compared to the existing list of analogous systems. The reported compounds in this work consist of three different ligand systems- quinoline, naphthyridine and benzonaphthyridine bound to pyridine or thiazole moieties in the coordination sphere. It has been shown that rate of CO2 reduction and turn over frequency depends significantly on the nature of the ligands. Overall, complexes that have pyridine outperform those having thiazole, with the benzonaphthyridine complexes showing superior activity with rate constant and catalytic turnover of 103 orders. The second part of my thesis describes the design and application of thermally stable and tunable mesoporous manganese oxide to catalyze coupling and aromatization reactions. From the viewpoint of green chemistry, synthesizing valuable organic molecules by using no or minimum additive and maintaining mild reaction condition is of utter importance. We demonstrate synthesis of aromatic nitrogen containing heterocyclic molecules from their non aromatic counterparts by employing robust and inexpensive manganese oxide catalyst in the presence of no other oxidant/additive but air. The same manganese oxide material when fabricated to act as a support for copper oxide catalyst exhibited excellent efficiency for C-O, C-N and C-S bond formation in Ullmann type reaction. Not only the synthetic methodology but the underlying mechanism and role of lattice oxygen present in the structure of catalyst are explained in details following experimental and theoretical studies. The catalytic protocols discussed here have several advantages over the already reported procedures in terms of product separation, reusability of the catalyst, absence of additive, water as by product and air as the terminal oxidant.
A guide to the effective catalysts and latest advances in CO2 conversion in chemicals and fuels Carbon dioxide hydrogenation is one of the most promising and economic techniques to utilize CO2 emissions to produce value-added chemicals. With contributions from an international team of experts on the topic, CO2 Hydrogenation Catalysis offers a comprehensive review of the most recent developments in the catalytic hydrogenation of carbon dioxide to formic acid/formate, methanol, methane, and C2+ products. The book explores the electroreduction of carbon dioxide and contains an overview on hydrogen production from formic acid and methanol. With a practical review of the advances and challenges in future CO2 hydrogenation research, the book provides an important guide for researchers in academia and industry working in the field of catalysis, organometallic chemistry, green and sustainable chemistry, as well as energy conversion and storage. This important book: Offers a unique review of effective catalysts and the latest advances in CO2 conversion Explores how to utilize CO2 emissions to produce value-added chemicals and fuels such as methanol, olefins, gasoline, aromatics Includes the latest research in homogeneous and heterogeneous catalysis as well as electrocatalysis Highlights advances and challenges for future investigation Written for chemists, catalytic chemists, electrochemists, chemists in industry, and chemical engineers, CO2 Hydrogenation Catalysis offers a comprehensive resource to understanding how CO2 emissions can create value-added chemicals.
The use of CO2 as a chemical feedstock has been the focus of much research in recent years due to the promise for carbon neutral fuel storage in chemical bonds. Specifically, complexes of the type Re(bpy)(CO)3Cl (bpy = 2,2'-bipyridine and analogues thereof) have been studied for their ability to electrocatalytically reduce CO2 to CO. These catalysts are among the most active, selective, and robust homogeneous catalysts for CO2 reduction in the literature. Previous work has focused on mechanistic studies and determining the inductive effect of bipyridine functional groups on catalysis. The work presented in this dissertation focuses on the structural and biomimetic modification of these catalysts. In order to determine the optimal point of modification, the CO2 reduction capabilities of a series of Re(n,n'-dimethyl-bpy)(CO)3Cl (n = 3, 4, and 5) catalysts with a bpy modified at the 3, 4, and 5 positions with methyl substituents were assessed. A decreased catalytic current response in the n = 3 case can be explained by steric hindrance in the 3,3'- substituted catalyst disfavoring optimal charge transfer in the catalytic cycle. A series of rhenium catalysts were synthesized with bpy substituents amenable to common surface- and bio-conjugation techniques. Specifically, aminomethyl, groups were found to contribute to competent catalysts and were interrogated further. Interestingly, before the complex was coupled to amino acids, simple acylated amines (mimicking peptide bonds) on the 4- and 4,4'- positions of the bpy ligand were found to alter the mechanism by the rhenium catalyst operated electrochemically. Instead of a single metal site catalyzing the proton-dependent reduction of CO2 to CO and H2O, the bimetallic site, templated by hydrogen-bonding of the peptide bonds, reduces CO2 to CO and CO32- at potentials up to 240 mV more positive than previously studied catalysts of this type. The catalysts were then incorporated into amino acids and short peptides to investigate the advantageous effects of adding proton sources (tyrosine) and readily modifiable platform (peptides) on catalysis. In addition to proton sources, Lewis-acids can serve to increase the rates of catalysis; however insoluble carbonates prevent the reaction from being catalytic with respect to the Lewis acid. Macromolecules were used to bind the metal Lewis acids to prevent metal-carbonate formation over the course of the reaction. Furthermore, hydrogen-bonding could be utilized to template these heterobimetallic interactions and the preliminary work is presented.
Over the past decade the topic of energy and environment has been ackno- edged among many people as a critical issue to be solved in 21st century since the Kyoto Protocol came into e?ect in 1997. Its political recognition was put forward especially at Heiligendamm in 2007, when the e?ect of carbon dioxide emission and its hazard in global climate were discussed and shared univ- sallyascommonknowledge.Controllingtheglobalwarmingintheeconomical framework of massive development worldwide through this new century is a very challenging problem not only among political, economical, or social c- cles but also among technological or scienti?c communities. As long as the humans depend on the combustion of fossil for energy resources, the waste heat exhaustion and CO emission are inevitable. 2 In order to establish a new era of energy saving and environment benign society, which is supported by technologies and with social consensus, it is important to seek for a framework where new clean energy system is inc- porated as infrastructure for industry and human activities. Such a society strongly needs innovative technologies of least CO emission and e?cient en- 2 ergy conversion and utilization from remaining fossil energies on the Earth. Energy recycling system utilizing natural renewable energies and their c- version to hydrogen may be the most desirable option of future clean energy society. Thus the society should strive to change its energy basis, from foss- consuming energy to clean and recycling energy.