Electronic Effects in Multidentate Pyridinol and N-Heterocyclic Carbene Based Ligands for Transition Metal Catalyzed Carbon Dioxide Reduction

Electronic Effects in Multidentate Pyridinol and N-Heterocyclic Carbene Based Ligands for Transition Metal Catalyzed Carbon Dioxide Reduction
Author: Chance M Boudreaux
Publisher:
Total Pages:
Release: 2021
Genre: Electronic dissertations
ISBN:
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The design of new catalysts with high catalytic efficiency and robustness towards carbon dioxide (CO2) reduction is of paramount importance. A full understanding of the requirements for creating a catalyst of this type is a missing gap in the knowledge base which prevents progress in synthesizing solar fuels. Our research hypothesis is that through the control of steric and electronic factors we can design better catalysts using various transition metals. Multidentate ligands composed of pyridyl bound to N-heterocyclic carbene rings are a synthetically flexible scaffold capable of testing our hypotheses. The systematic tuning of this scaffold will elucidate the factors necessary to improve active catalysts and extend our results to more complex systems. These ligand motifs are also commonly seen in many active catalysts for CO2 reduction. Therefore, the systemic investigation of the properties that lead to higher activity in scaffolds containing these motifs can concurrently suggest improvements for many systems already available.Reduction catalysts, supported by a CNC-pincer moiety, are some of the most robust catalysts in the literature while maintaining good catalytic activity. The CNC-pincer scaffold have shown tremendous results with electronic tunability of the pyridyl N atom through para substitution of the pyridinol ring. A ruthenium(II) catalyst utilizing the CNC pincer has shown 250 turn-over numbers of carbon monoxide (CO) over 40 h with a catalyst loading of 100 ℗æM. The cobalt(I) systems are slower; however, they are even more robust than the ruthenium analog producing 203 TON of CO2 over 72 h with a catalyst loading of 1 ℗æM. Notably, the cobalt catalyst utilizes an inexpensive, less toxic, and earth abundant metal center compared to ruthenium. Another scaffold, with NCCN donors binding in a tetradentate fashion, is currently being investigated with nickel(II) and cobalt(II) metal centers. These studies are producing a better understanding of the catalyst structure needs for a solar to chemical fuel catalyst to enable a carbon-neutral fuel cycle within our current fuel infrastructure. This catalytic system will constitute an artificial photosynthesis scheme by producing fuels and other useful chemicals from carbon dioxide, mimicking how plants store solar energy in glucose.

Transition Metal Complexes of Neutral eta1-Carbon Ligands

Transition Metal Complexes of Neutral eta1-Carbon Ligands
Author: Remi Chauvin
Publisher: Springer
Total Pages: 260
Release: 2009-12-18
Genre: Science
ISBN: 364204722X
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Contents: Yves Canac and Remi Chauvin: Neutral eta1-carbon ligands: beyond carbon monoxide; Esteban P. Urriolabeitia: Ylide Ligands; Wolfgang Petz and Gernot Frenking: Carbodiphosphoranes and related ligands; Mareike C. Jahnke and F. Ekkehardt Hahn: Chemistry of N-Heterocyclic Carbene Ligands; Tsuyoshi Kato, Eddy Maerten, Antoine Baceiredo: Non-NHCs stable singlet carbene ligands; Victorio Cadierno, Sergio E. García-Garrido: All-Carbon-Substituted Allenylidene and Related Cumulenylidene Ligands; Victorio Cadierno, Sergio E. García-Garrido: Heteroatom-Conjugated Allenylidene and Related Cumulenylidene Ligands.

Exploration of N-heterocyclic Carbene Complexes of Iron and Cobalt in Catalysis and Non-traditional Organometallic Chemistry

Exploration of N-heterocyclic Carbene Complexes of Iron and Cobalt in Catalysis and Non-traditional Organometallic Chemistry
Author: Jacob A. Przyojski
Publisher:
Total Pages: 180
Release: 2016
Genre: Cobalt catalysts
ISBN: 9781339718736
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Earth-abundant transition metal catalysts are not as well understood or developed as those involving precious metal systems. In order to develop a method of evaluating transition metal catalyzed reactions employing earth-abundant elements, several catalyst systems composed of N-heterocyclic carbene (NHC) supported Fe(II), Fe(III), and Co(II) compounds have been synthesized and characterized. The primary N-heterocyclic carbenes used were 1,3-dimesitylimidazole-2-ylidene (IMes) and 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene (IPr). Selection of the appropriate NHC ligand with respect to steric bulk afforded both monomeric and chloride bridged dimeric halide species. Derivatives of these ligands, including a chlorinated (IPrCl, IMesCl) or saturated (SIPr, SIMes) backbone, were also employed. Low-coordinate hydrocarbyls of these Fe(II) and Co(II) compounds were isolated and crystallized including, but not limited to [Fe(IPr)(TMS(CH2))2], [Fe(IPr)Bn2], [Co(IPr)(TMS(CH2))2], and analogues involving carbene ligand variation. The NHC supported metal halide species were catalytically active and efficient in a variety carbon-carbon cross coupling reactions. Isolated metal-hydrocarbyls afforded the opportunity to investigate the mechanisms of carbon-carbon cross-coupling by this series of well-defined earth-abundant transition metal catalysts. Mechanistic studies of the Fe-NHC system were consistent with an FeII/III couple based mechanism. Low oxidation states of cobalt NHC compounds were explored, affording new Co(I) and Co(0) complexes [Co2(IPr)2] and [CoCl(IPr)2].

Electronic Properties and Redox Chemistry of Various Late Transition Metal Complexes

Electronic Properties and Redox Chemistry of Various Late Transition Metal Complexes
Author: Andrew James Wessel
Publisher:
Total Pages: 311
Release: 2017
Genre: Electronic dissertations
ISBN:
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Inorganic and organometallic catalysis plays an important role in energy related catalysis including transformations like water oxidation, proton and carbon dioxide reduction, and oxidative methane oligomerization. In order to understand and improve catalysts, this dissertation focuses on the development of alternate polydentate ligands and their late transition metal complexes and a full study on their electrochemical properties. Two polydentate pyridinophane ligands, N,N'-di(2-methylpyridine)-2,11-diaza[3.3](2,6)pyridinophane, PicN4,and N-(2methylpyridine)-N'-methyl-2,11-diaza[3.3](2,6)pyridinophane, PicMeN4, were synthesized to stabilize uncommon oxidation states. Unlike previous RN4 ligands, these polydentate ligands employed functionalized amines to interact with the metal center to increase stability. PicN4 when bound with copper formed a complex with a highly reversible CuII/I redox couple. The self-exchange rate constant for this redox couple was determined in the goal of comparing to copper containing electron transfer enzymes. Similarly, the silver complex PicN4AgI was also synthesized in which the PicN4 ligand stabilized the AgI/II redox couple. These pyridinophane ligands maximized magnetic moment by stabilizing d5 manganese and iron complexes as possible MRI contrast agents. A mononuclear NiIII complex was isolated. NiIII is a commonly proposed intermediate in cross-coupling reactions. Palladium when bound to both PicN4 and PicMeN4, the binding mode for the PdII dictated the stability of the redox couples. PicN4Pd was reduced to a mononuclear PdI while the asymmetric PicMeN4PdII preferentially is oxidized. Additionally, PicMeN4Pd undergoes a C-H activation spontaneously through a proposed concerted metalation deprotonation mechanism.

Novel Di(N-heterocyclic Carbene) Ligands and Related Transition Metal Complexes

Novel Di(N-heterocyclic Carbene) Ligands and Related Transition Metal Complexes
Author: Marco Monticelli
Publisher:
Total Pages: 0
Release: 2017
Genre:
ISBN:
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The PhD, a collaboration between the University of Padova and the University of Strasbourg, is focused on the chemistry of di(N-heterocyclic carbene) ligands and can be divided in four families of ligands that constitute the four chapters: i) metal complexes (Cu(I), Ag(I), Au(I), Ir(III), Ru(II)) with di(N-heterocyclic carbene) ligands bearing a rigid phenylene bridge between the carbene units; ii) metal complexes (Cu(I), Ag(I), Au(I), Ru(II)) combining an imidazole-based NHC ligand functionalized with a triazole in the 5 position of the backbone; iii) metal complexes (Ag(I), Au(I), Pd(II)) with heteroditopic ligands based on imidazol-2-ylidene and 1,2,3-triazol-5-ylidene moieties connected with a propylene bridge; iv) bis(benzoxazolium) proligands and attempted synthesis of related transition metal complex.

The Effect of Backbone Design on Carbene Reactivity

The Effect of Backbone Design on Carbene Reactivity
Author: Dominika Nini Lastovickova
Publisher:
Total Pages: 378
Release: 2016
Genre:
ISBN:
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The ability of N-heterocyclic carbenes (NHCs) to act as organocatalysts as well as versatile ligands in transition metal-mediated processes led us to explore the effect of the NHCs backbone design on the electronic properties and the consequent reactivity of these NHC moieties. Bielawski and others have previously shown that the incorporation of carbonyls into the NHC scaffold enhanced the electrophilicity of the carbenoid center to generate an isolable, ambiphilic N,N' -diamidocarbene (DAC), which was shown to activate various small molecules. For this reason, we explored the ability of DAC to activate compounds containing early p-block elements. At ambient temperature, the DAC activated the Si-H bonds of various silanes to afford the corresponding DAC-silane adducts. The DAC was also found to form a coordination complex with aluminum trichloride and a structurally-rich, tris(aluminum) species was obtained upon exposure of the DAC to trimethylaluminum. Additionally, the DAC promoted the B-H bond activation of various BH3 complexes and the B-B bond of bis(pinacolato)diboron, constituting the first such examples for an isolable carbene. The resultant DAC-BH3 adducts contained datively coordinated Lewis bases and facilitated the hydroboration of various olefins under mild conditions and in the absence of exogenous initiators. Furthermore, we have synthesized a series of Ru-based complexes containing a quinone-annulated NHC ligand to provide redox-controlled analogues of the Grubbs' II, III, and Hoveyda-Grubbs II generation catalysts. All of the aforementioned complexes were shown to be active ring-opening metathesis polymerization (ROMP) catalysts. Moreover, in its neutral state, the redox-switchable analogue of Grubbs' III generation catalyst was shown to selectively promote the polymerization of 1,5-cyclooctadiene (COD) while the addition of a reductant inhibited the ROMP of COD. Remarkably, the opposite pattern was observed for the polymerization of norbornene imide derivatives as the ROMP of these monomers was enhanced upon the reduction of the redox-switchable analogue of Grubbs' III. Additionally, the neutral state of the redox-switchable analogue of Hoveyda-Grubbs II generation catalyst was shown to selectively facilitate ring-closing metathesis reactions, which could be reversibly inhibited upon the introduction of a suitable reducing agent.