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Book Synthesis and Reactivity of Dinitrogen Oxo and Nitrido Complexes of First Row Transition Metals Supported by Hydrotris pyrazolyl borate Ligands

Download or read book Synthesis and Reactivity of Dinitrogen Oxo and Nitrido Complexes of First Row Transition Metals Supported by Hydrotris pyrazolyl borate Ligands written by Daniel Clayton Cummins and published by . This book was released on 2018 with total page 281 pages. Available in PDF, EPUB and Kindle. Book excerpt: When 9 is reacted with single oxygen atom transfer reagents the novel bridging oxo complex in the form of [TpFc,MeFe] 2(μ2-η1:η1-O) (16) is produced. 16 is only the second instance of such a FeII-O-FeII compound to have been isolated and structurally characterized. In the effort to produce additional chalcogenide compounds the complexes TpFc,MeFeOCPh3 (13) and TpFc,MeFeSCPh3 (14) were produced by salt metathesis with 3. The reaction of 14 with KH in the presence of 18-crown-6 to produce a bridging sulfide, [Tp Fc,MeFe]2(μ2-η1:η 1-S) (15). Attempts to produce imide compounds to act as isoelectronic models for terminal oxo compounds by reacting organic azides with 9 and 10 resulted in the production of tetrazene complex TpFc,MeCoN4Bn2 (17), as well as metallated azides TpFc,MeFeN3 (20) and TpFc,MeCoN3 (21).

Book Transition Metal Dinitrogen Complexes

Download or read book Transition Metal Dinitrogen Complexes written by Yoshiaki Nishibayashi and published by John Wiley & Sons. This book was released on 2019-05-06 with total page 496 pages. Available in PDF, EPUB and Kindle. Book excerpt: A comprehensive book that explores nitrogen fixation by using transition metal-dinitrogen complexes Nitrogen fixation is one of the most prominent fields of research in chemistry. This book puts the focus on the development of catalytic ammonia formation from nitrogen gas under ambient reaction conditions that has been recently repowered by some research groups. With contributions from noted experts in the field, Transition Metal-Dinitrogen Complexes offers an important guide and comprehensive resource to the most recent research and developments on the topic of nitrogen fixation by using transition metal-dinitrogen. The book is filled with the information needed to understand the synthesis of transition metal-dinitrogen complexes and their reactivity. This important book: -Offers a resource for understanding nitrogen fixation chemistry that is essential for explosives, pharmaceuticals, dyes, and all forms of life -Includes the information needed for anyone interested in the field of nitrogen fixation by using transition metal-dinitrogen complexes -Contains state-of-the-art research on synthesis of transition metal-dinitrogen complexes and their reactivity in nitrogen fixation -Incorporates contributions from well-known specialists and experts with an editor who is an innovator in the field of dinitrogen chemistry Written for chemists and scientists with an interest in nitrogen fixation, Transition Metal-Dinitrogen Complexes is a must-have resource to the burgeoning field of nitrogen fixation by using transition metal-dinitrogen complexes.

Book Reactivity and Thermochemistry of First row Transition Metal Complexes with Stable Organic Radicals

Download or read book Reactivity and Thermochemistry of First row Transition Metal Complexes with Stable Organic Radicals written by Thomas R. Porter and published by . This book was released on 2014 with total page 179 pages. Available in PDF, EPUB and Kindle. Book excerpt: Reactions involving transition metals and organic free radicals are critically important in a variety of chemical and biological processes. Because of their prevalence, there is a fundamental interest in better understanding these types of reactions to fully realize their potential for new applications. The work presented in this dissertation describes the free radical reactivity and thermochemistry of several different transition metal systems with stable organic radicals. Chapter 1 provides an introduction to transition metal reactivity involving organic free radicals. Chapter 2 describes the catalytic disproportionation of a hydroxylamine by (TMP)Fe[superscript III]-OH (TMP = meso-tetramesityl porphyrin) and some of the radical reactions that make up the catalytic cycle. Chapter 3 describes the preparation, structural characterization and thermochemistry of a previously unreported stable organic radical, [superscript t]Bu2NPArO* (2,6-di-tert-butyl-4-(4'-nitrophenyl)phenoxyl). Chapter 4 describes the preparation of several [Tp[superscript tBu]Cu[superscript II]]+ (Tp[superscript tBu] = hydro-tris(3-tert-butyl-pyrazolyl)borate) and [Tp[superscript tBuMe]Cu[superscript II]]+ (Tp[superscript tBu]Me = hydro-tris(3-tert-butyl-5-methyl-pyrazolyl)borate) alkoxide compelxes as models for potential intermediates in copper/radical alcohol oxidation catalysis. Treating these complexes with stable radicals such a [superscript t]Bu3ArO* (2,4,6-tri-tert-butyl-phenoxyl) did not result in alkoxide oxidation despite having a large driving force. From these studies, we conclude driving force is not a primary predictor for copper/radical alcohol oxidation. Chapter 5 discusses the coordination chemistry of [Tp[supercscript tBu]Cu[superscript II]]+ and [Tp[superscript tBu]Zn[superscript II]]+ with 4-nitro-phenols. With the bulky 2,6-disubstituted 2,6-di-tert-butyl-4-nitro-phenoxide, coordination to either metal occurs through a nitronate resonance form. The 2,6-unsubstituted 4-nitro-phenol binds through the phenoxide resonance form. Chapter 6 highlights the large kinetic barrier for ketone reduction or oxidation by titanocene(III/IV) and the hydrogen atom donor/acceptor, [superscript t]Bu3ArO(-H). Finally, Chapter 7 describes the selective and stoichiometric reduction of aromatic and aliphatic nitro groups by photoreduced titanium dioxide nanoparticles in acidic aqueous solutions. From thermochemical analysis, it is likely that these reactions proceed through a rate determining H+/e- transfer.

Book Synthesis and Reactivity of Imido and Oxo Complexes of Transition Metals

Download or read book Synthesis and Reactivity of Imido and Oxo Complexes of Transition Metals written by and published by . This book was released on with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Refer to the Full-Text, p.16-18.

Book Synthesis Reactivity and Catalytic Applications of Two Coordinate First Row Transition Metal Complexes

Download or read book Synthesis Reactivity and Catalytic Applications of Two Coordinate First Row Transition Metal Complexes written by Michael Isaac Lipschutz and published by . This book was released on 2015 with total page 139 pages. Available in PDF, EPUB and Kindle. Book excerpt: Recently, the development of more sustainable catalytic systems based on abundant first-row metals, especially nickel, for organic transformations has attracted significant interest. This thesis describes the development of new synthetic methods for the preparation of two-coordinate complexes of a variety of first row transition metals. The physical and spectroscopic properties of these complexes are discussed and the reactivity and catalytic applications of these compounds are also explored. Species of this type are found to catalyze a variety of useful organic transformations using inexpensive metals and ligands.

Book Synthesis and Reactivity of Low valent Titanium and Zirconium Complexes

Download or read book Synthesis and Reactivity of Low valent Titanium and Zirconium Complexes written by Tamara Elizabeth Hanna and published by . This book was released on 2007 with total page 932 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Book New Late Transition Metal Oxo and Hydrazido Complexes

Download or read book New Late Transition Metal Oxo and Hydrazido Complexes written by Hui Shan and published by . This book was released on 1998 with total page 412 pages. Available in PDF, EPUB and Kindle. Book excerpt: Rhodium/gold (1a, 1b) and iridium/gold (2) [mu] 4 -oxo complexes with diene ligands have been synthesized from reactions between [(AuPPh 3) 3 ([mu]-O)]BF 4 and [(diene)MCl] 2 (M = Rh, diene = NBD, COD; M = Ir, diene = COD). A family of platinum/gold [mu] 3 -oxo complexes with COD ligand (3a-3g), [(1,5-COD)Pt([mu]-OAuL)] 2 (BF 4) 2 (L = PPh 3, PPh 2 Pr i, PPh 2 Et, P(o-toly) 3, P(p-toly) 3, P(p-MeOPh) 3, P(p-CF 3 Ph) 3), and a gold free platinum [mu] 3 -oxo/hydroxo complex, [(1,5-COD) 4 Pt 4 ([mu] 3 -O) 2 ([mu]-OH)](BF 4) 3 (5) are also prepared from the novel oxo/halide exchange synthetic route. The structural and chemical properties of these new compounds have been studied. One of the special properties of 5 is its unique ability of reacting with unactivated olefins (e.g. ethylene, tetramethylethylene, and cyclooctadiene) to give oxidized organic products or intermediate adducts. The mechanism of olefin insertion into M-O bond is favored in the attempted rationalization of the formation of the diverse products observed in the reactions. A whole family of complexes (13a-13f), [(AuL) 6 N 2](BF 4) 2 (L = PPh 2 Pr i, PPh 2 Et, PPh 2 Me, P(p-toly) 3, P(p-MeOPh) 3, P(p-CF 3 Ph) 3), which contains dinitrogen bonding simultaneously to six metal atoms is synthesized and characterized. These compounds are studied as structural models for the coordination of dinitrogen at the center of the nitrogenase Fe-Mo cofactor cluster. The existence of our compound supports the idea that the bond order of dinitrogen is reduced from 3 to 1 on initial coordination to the inside of the cluster. The chemical properties of these new hydrazido complexes have been studied. One of the special properties of 13 is their unique ability of being reduced and protonated to generate ammonia. This reactivity makes them suitable chemical model for the reduction of dinitrogen at the active site of nitrogenase. Considerable experimental work has been devoted to the understanding of the protonation process of complex 13a, [(AuPPh 2 Pr i) 6 N 2](BF 4) 2 . Two partially protonated species, [(AuPPh 2 Pr i) 5 HN 2] 2+ and [(AuPPh 2 Pr i) 4 H 2 N 2] 2+, are determined and considered to be key intermediates in the generation of ammonia. Preliminary kinetic studies have been carried out, which led to the proposal that the formation of [(AuPPh 2 Pr i) 5 HN 2] 2+ species occur through an associate process involving the formation of a highly reactive hyper-coordinated complex, [(AuPPr i Ph 2) 6 N 2 H] 3+ [double dagger], in the transition-state.

Book Reductive Functionalization of 3D Metal Methyl Complexes and Characterization of a Novel Dinitrogen Dicopper I Complex

Download or read book Reductive Functionalization of 3D Metal Methyl Complexes and Characterization of a Novel Dinitrogen Dicopper I Complex written by Hengameh Fallah and published by . This book was released on 2017 with total page 105 pages. Available in PDF, EPUB and Kindle. Book excerpt: Reductive functionalization of methyl ligands by 3d metal catalysts and two possible side reactions has been studied. Selective oxidation of methane, which is the primary component of natural gas, to methanol (a more easily transportable liquid) using organometallic catalysis, has become more important due to the abundance of domestic natural gas. In this regard, reductive functionalization (RF) of methyl ligands in [M(diimine)2(CH3)(Cl)] (M: VII (d3) through CuII (d9)) complexes, has been studied computationally using density functional techniques. A SN2 mechanism for the nucleophilic attack of hydroxide on the metal-methyl bond, resulting in the formation of methanol, was studied. Similar highly exergonic pathways with very low energy SN2 barriers were observed for the proposed RF mechanism for all complexes studied. To modulate RF pathways closer to thermoneutral for catalytic purposes, a future challenge, paradoxically, requires finding a way to strengthen the metal-methyl bond. Furthermore, DFT calculations suggest that for 3d metals, ligand properties will be of greater importance than metal identity in isolating suitable catalysts for alkane hydroxylation in which reductive functionalization is used to form the C--O bond. Two possible competitive reactions for RF of metal-methyl complexes were studied to understand the factors that lower the selectivity of C--O bond forming reactions. One of them was deprotonation of the methyl group, which leads to formation of a methylene complex and water. The other side reaction was metal-methyl bond dissociation, which was assessed by calculating the bond dissociation free energies of M3d--CH3 bonds. Deprotonation was found to be competitive kinetically for most of the 1st row transition metal-methyl complexes (except for CrII, MnII and CuII), but less favorable thermodynamically as compared to reductive functionalization for all of the studied 1st row transition metal complexes. Metal-carbon bond dissociation was found to be less favorable than the RF reactions for most 3d transition metal complexes studied. The first dinitrogen dicopper (I) complex has been characterized using computational and experimental methods. Low temperature reaction of the tris(pyrazolyl)borate copper(II) hydroxide {iPr2TpCu}2(μ-OH)2 with triphenylsilane under a dinitrogen atmosphere gives the μ -N2 complex, {iPr2TpCu}2(μ -N2). X-ray crystallography reveals an only slightly activated N2 ligand (N-N: 1.111(6) Å) that bridges between two iPr2TpCuI fragments. While DFT studies of mono- and dinuclear copper dinitrogen complexes suggest a weak μ-backbonding between the d10 CuI centers and the N2 ligand, they reveal a degree of cooperativity in the dinuclear Cu-N2-Cu interaction.

Book Synthesis and Reactivity of Metal Complexes with Hindered Pyrazole and Imidazole Ligands

Download or read book Synthesis and Reactivity of Metal Complexes with Hindered Pyrazole and Imidazole Ligands written by Swetha Neravetla and published by . This book was released on 2010 with total page 128 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Book Synthesis and Reactivity Studies of Mono Bi and Trimetallic Complexes Supported by Oxidatively resistant Polyanionic Ligands

Download or read book Synthesis and Reactivity Studies of Mono Bi and Trimetallic Complexes Supported by Oxidatively resistant Polyanionic Ligands written by Julia Megan Stauber and published by . This book was released on 2017 with total page 296 pages. Available in PDF, EPUB and Kindle. Book excerpt: Investigations of the oxidatively-resistant hexacarboxamide cryptand, mBDCA-5t-H6, to support mono-, bi-, and trimetallic complexes are presented. Selective single metal ion insertion into the cryptand was achieved to generate the mono-Co(II) and Zn(II) complexes that contain proximal hydrogen-bonding networks enforced by the carboxamide N–H groups of the pre-organized second-coordination sphere. The cobalt(II) complex serves as a selective colorimetric turn-on fluoride sensor and represents a unique example of a transition-metal based fluoride sensor where fluoride binding takes place directly at the transition metal. The binding of fluoride is synergistic involving hydrogen-bond donors from the second-coordination sphere together with metal(II) ion coordination. Isolation of the mono-metallic Co and Zn complexes allowed for the preparation of their transition and main group metal heterobimetallic variants. Hetero- and homobimetallic complexes of cobalt(II) and zinc(II) are presented, and the reactivity of the homobimetallic complexes with O2, O−2 , and H2O2 is discussed. The cryptand was also explored as a supporting ligand for cofacially arranged divalent group 14 ions (Ge, Sn, Pb). Reaction of the di-tin(II) complex with elemental sulfur or selenium generates di-tin polychalcogenide complexes containing [mu]–E and bridging [mu]– E5 ligands (E = Se, S), where the sulfur-containing product acts reversibly as a source of S3 ∙− in DMF solution. The di-tin(II) complex also serves as a bidentate ligand for the preparation of trimetallic Sn2/M complexes (M = Ag(I), Au(I), Pd(0)). Reactivity studies of the Sn2/Pd(0) complex with substrates including CS2, S8, and 1AdC≡P are described. Terminal titanyl complexes supported by oxidatively-resistant tri- and tetrametaphosphates were prepared as molecular models of heterogeneous oxidation catalysts. These complexes react with hydrogen peroxide to produce the corresponding peroxotitanium( IV) metaphosphates, and represent rare examples of titanium oxo and peroxo systems supported by an all-oxygen ligand environment.

Book Oxidation State Roulette

Download or read book Oxidation State Roulette written by Brandon Fitchett and published by . This book was released on 2018 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The use of rare and expensive noble metals in the chemical industry as organometallic catalysts has grown exponentially in the past few decades due to their high activity, selectivity and their ability to catalyze a wide range of reactions. With this growth in use has also come a proportional growth in concern as these toxic metals inevitably leach into the environment and their negative effects on public health and our ecosystems are becoming better understood. First-row transition metal catalysts provide both environmental and economic benefits as alternatives to these noble metals due to their lower toxicity and cheaper costs. The two-electron chemistry that makes the noble metals so attractive however, is more challenging to accomplish with first-row transition metals. Intelligently designing the ligand scaffold which surrounds the metal can mitigate or even eliminate some of the shortfalls of these first-row metals. Some key features that should be considered when designing a ligand are: 1) a strong chelating ability so the ligand can stay attached to the metal, 2) incorporation of strong donors to favour low-spin complexes, 3) inclusion of hemilabile groups to allow for substrate activation and metal stabilization throughout various oxidation states, 4) redox activity to be able to donate or accept electrons, and 5) inclusion of Lewis base functionalities which are able to assist the substrate activation. Ligands which incorporate these features are known as bifunctional ligands as they can accomplish more than one function in the catalytic cycle. Developing first-row transition metal complexes containing these ligands may enable these species to replicate the reactivity and selectivity generally associated with the precious metals. Being able to replace the noble metals used in industry with these catalysts would have tremendous environmental and economic benefits. The objective of this thesis is to advance the field of bifunctional catalysis by examining the behaviour of two sterically svelte, tridentate SNS ligands containing hard nitrogen and soft sulphur donors when bonded to cobalt. Previous work with iron provides a template of the ligand behaviour to which cobalt can be compared, allowing us to contrast the effects exerted by the different metals. After an introduction to bifunctional catalysis in Chapter 1, Chapter 2 describes the reactivity of the amido ligand, SMeNHSMe, with precursors ranging from Co(I) to Co(III), all of which yielded the 19e- pseudooctahedral cobalt(II) bis-amido complex, Co(SMeN-SMe)2 characterized by 1H NMR spectroscopy, single-crystal X-ray crystallography and cyclic voltammetry. Although this complex has a similar structure as the Fe analogue, the cobalt bis-amido complex did not exhibit the same hemilabile behaviour that allowed for simple ligand substitution of one of the thioether groups. Instead it reacted reversibly with 2,2'-bipyridine while 1,2-bis(dimethylphosphino)ethane (DMPE) and 2,6-dimethylphenyl isocyanide both triggered additional redox chemistry accompanied by the loss of protonated SMeNHSMe. In contrast, protonation gave the cobalt(II) amido-amine cation, [Co(SMeNSMe)(SMeNHSMe)](NTf2), which allowed for substitution of the protonated ligand by acetonitrile, triphenylphosphine and 2,2'-bipyridine based on 1H NMR evidence. The ability of Co(SMeNSMe)2 to act as a precatalyst for ammonia-borane dehydrogenation was also probed, revealing that it was unstable under these conditions. Addition of one equivalent of DMPE per cobalt, however, resulted in better activity with a preference for linear aminoborane oligomers using ammonia-borane and, surprisingly, to a change in selectivity to prefer cyclic products when moving to methylamine-borane. Chapter 3 delves into the chemistry of the thiolate ligand, SMeNHS, which formed a new 18e- cobalt(III) pseudooctahedral complex, Co(S-NC-)(SMe)(DEPE), from oxidative addition of the Caryl-SMe bond. Scaling up this reaction resulted instead in formation of an imine-coupled [Co(N2S2)]- anion which was characterized by 1H NMR/EPR spectroscopy, single-crystal X-ray diffraction, cyclic voltammetry and DFT studies. The latter revealed an interesting electronic structure with two electrons delocalized in the ligand, demonstrating the non-innocent nature of the N2S2 ligand. While the analogous iron complex proved to be an effective pre-catalyst for the hydroboration of aldehydes with selectivity against ketones, this behaviour was not observed with [Co(N2S2)]- which gave a slower rate and less selectivity. The knowledge acquired from this thesis work has advanced the field of bifunctional catalysis by extending the application of these two SNS ligands from iron to cobalt, revealing unpredictable differences in reactivity between the metals. By comparing the behaviour of these ligands with iron and cobalt, we gain a better understanding of the chemistry that is accessible by these ligands and the applications for which they may be used. This increased knowledge contributes to our long-term goal of replacing expensive and toxic noble metals with more benign first-row transition metals, improving the sustainability of the chemical industry.