Download or read book Redox Properties of Several Cobalt Helicene Complexes and the Synthesis and Study of Tri cobalt Clusters in Several Oxidation States written by Matthew P. Robben and published by . This book was released on 1994 with total page 482 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Synthesis and Chemical physical Properties of Several Series of Nitrene capped Cobalt and Iron cobalt Triangular Metal Clusters written by Michael Scott Ziebarth and published by . This book was released on 1989 with total page 460 pages. Available in PDF, EPUB and Kindle. Book excerpt:

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.

Download or read book Facilitating Multi electron Reactivity at Low coordinate Cobalt Complexes Using Redox active Ligands written by Aubrey L. Smith and published by . This book was released on 2011 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: In this study, we describe a detailed investigation of cobalt complexes containing redox-active ligands. We have prepared an electronic series of the complex in three oxidation states: [CoIII(ap)2]-, CoIII(isq)(ap), and [CoIII(CH3CN)(isq)2]+. Characterization shows that the metal center remains cobalt(III) through the redox changes and indicates that the oxidation state changes occur with gain or loss of electrons from the ligand set. While CoIII(isq)(ap) reacts with halide radicals to form a new cobalt-halide bond in a single electron reaction, [CoIII(ap)2]- appears to be prone to multi-electron reactivity in reactions with sources of "Cl+". Both reactions occur with electrons derived from the ligand set. Mechanistic studies suggest a single, two electron step is responsible for the bond-formation. Similarly, [CoIII(ap)2]- reacts with alkyl halides to pseudo-oxidatively add the alkyl at the cobalt center. The product of the reaction can be isolated and fully characterized and was found to be best assigned as CoIII(alkyl)(isq)2. This assignment indicates that the reaction occurs, again, with the new bond formed with two electrons formally derived from the ligand set and with no change in oxidation state at the metal center. Mechanistic investigations of the pseudo-oxidative addition suggest the reaction is SN2-like. The reaction occurs with a wide scope of alkyl halides, including those containing beta-hydrogens. : The cross-coupling reaction of CoIII(alkyl)(isq)2 with RZnX forms a new carbon-carbon bond. Similarly, the two electron oxidized complex [CoIII(CH3CN)(isq)2]+ reacts with organozinc reagents to couple two carbon nucleophiles and form a new carbon-carbon bond. Both reactions are successful with both sp2 and sp3 carbons. When followed substoichiometrically, the homocoupling reaction can be observed to form CoIII(alkyl)(isq)2. This indicates that the homocoupling and cross-coupling reactions proceed by the same mechanism. However, both reactions have low yields. The yield of the reactions are decreased by steric bulk of the alkyl or aryl fragments or around the metal center created by substituents on the ligand. Also, while the steric congestion disfavors the addition of the first alkyl fragment, the addition of the second alkyl fragment and subsequent rapid elimination of the coupling product is almost completely inhibited. This result also implies that the coupling of the two alkyl fragments is entirely inner-sphere requiring installation of both for coupling.

Download or read book The Synthesis Structure and Properties of Some Triazido Triammine Complexes of Cobalt III written by Frederick Dominick Sancilio and published by . This book was released on 1975 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Polynuclear Cobalt Complexes as Models of a Cobalt Water Oxidation Catalyst written by Andrew Ullman and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: In the first part of the thesis, we present the synthesis of a heptanuclear cobalt cluster in two different oxidation states, Co(II)7 and a mixed valence Co(III)Co(II)6. An anomalously slow self-exchange electron transfer rate as compared to that predicted from semiclassical Marcus theory was measured, supporting a charge transfer process that is accelerated by dissociation of the anion from the oxidized cluster. This mechanism sheds light on the inverse dependence of anions in the deposition mechanism of Co-OECs. Moreover, the results address a long-standing controversy surrounding the Co2+/3+ self-exchange electron transfer reaction of the hexaaqua complex.

Download or read book Substitution and Redox Properties of Some Organoisocyanide Cobalt II Complexes written by Olayinka A. Oyetunji and published by . This book was released on 2017 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Synthesis and Study of Some Intermediate field Cobalt III Oxalato Complexes written by Marilyn Gail Moffitt and published by . This book was released on 1967 with total page 94 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Redox Study of Cobalt II cobalt III Polypyridyl Complexes in Nonaqueous Solvents written by Larry W. Long and published by . This book was released on 1978 with total page 74 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Synthesis and Reactivities of Cobalt iii Alkylperoxo Complexes Bearing Quaterpyridine Ligand written by Yunzhou Chen and published by . This book was released on 2022 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Direct use of dioxygen (O2) in functionalizing organic molecules is highly desirable. In nature, enzymes perform alkane oxidation efficiently at ambient conditions. The transition metals involved in the active sites of enzymes play vital roles in binding with O2 and transferring electrons and protons during metabolism. Many metal-oxygen species, such as hydro(alkyl) peroxo complexes, are invoked as reactive intermediates in these biological processes. Given the complexity of enzymes, studying the reactivity of these enzymes with simple synthetic coordination compounds is one of the strategies. This thesis is mainly concerned with the oxidation of alkanes and alkenes catalyzed by tailor-made cobalt(III) alkylperoxo complexes at ambient conditions. In the first part, we report the design and synthesis of the highly electrophilic cobalt(III) alkylperoxo complex, [CoIII(qpy)(OOtBu)(NCCH3)]2+ (2), supported by a planar tetradentate quaterpyridine ligand (qpy = 2,2′:6′,2′′:6′′,2′′′-quaterpyridine). This complex activates C(sp3)–H bonds of a variety of organic molecules at ambient conditions and yields a series of alkylperoxo complexes with the general formula [CoIII(qpy)(OOR)(NCCH3)]2+ [RH = Et2O (3), THF (4), tBuOMe (5), ethylbenzene (6), toluene (7), cyclopentene (8), and 3-hexyne (9)], which have been well characterized by various spectroscopic techniques including NMR, ESI-MS, UV-vis, FT-IR, and CHN elemental analysis. The structures of these complexes have also been characterized by X-ray crystallography. In the second part, the mechanism for the alkane oxidation catalyzed by [CoIII(qpy)(OOR)(NCCH3)]2+ was extensively studied at room temperature and one atmospheric pressure. NMR study reveals the reaction stoichiometry. ESI-MS study indicates exogeneous O2 is crucial with the support of 18O-labeled experiments. Kinetics study by UV-vis and a significant kinetic isotopic effect resulted for the oxidation of ethylbenzene by 2 suggest a rate-limiting hydrogen-atom abstraction from organic substrates (R′H) by [CoIII(qpy)OOR]2+ via the proximal oxygen atom of the peroxo group (i.e., [CoIII(qpy)OOR]2+ + R′H → [CoII(qpy)]2+ + R′• + ROOH). The resulting alkyl radical R′• bound with O2 to form alkyl peroxyl radical R′OO•, which was rapidly scavenged by the [CoII(qpy)]2+ to give another alkylperoxo complex [CoIII(qpy)OOR′]2+. The proposed mechanism in the peroxidation of organic molecules b y alkyl(hydro)peroxo complexes is unprecedented. In the third part, we examine the catalytic properties of [CoIII(qpy)(OOR)(NCCH3)]2+ in aerobic oxidation of various substrates. Using ethylbenzene, cumene, cyclopentene, and cyclohexene as the substrates, [CoIII(qpy)(OOR)(NCCH3)]2+ are found to be active and robust catalysts to produce the corresponding hydroperoxides, alcohols, and ketones catalytically. A turnover of >3000 is achieved in the oxidation of cyclohexene for 7 d. In the fourth part, the reactivities of [CoIII(qpy)OOR]2+ with alkenes were explored. Alkenes with weak C–H bonds (e.g., 1,4-cyclohexadiene and cycloalkenes) resulted in C–H functionalization. In case there are no weak C–Hs in the alkenes (e.g., styrene), [CoIII(qpy)OOR]2+ catalyzes the polymerization of styrenes in O2 to produce polyalkylperoxo species. The [CoIII(qpy)(OOCH(OOtBu)CH2Ph)(NCCH3)]2+ ( bisalkylperoxo 11), has complex, been isolated and characterized by ESI-MS, NMR, and X-ray crystallography. In summary, this work demonstrates the highly electrophilic character of Co(III) alkylperoxo complexes supported by the qpy ligand. Under ambient conditions, these complexes are suitable catalysts to perform aerobic peroxidation of a variety of alkanes and alkenes

Download or read book Synthesis and Oxidation of Two Tri metallic Compounds and Activation Volumes for Electron Transfer by Some Cobalt Clathrochelates in Nonaqueous Solution written by Mark A. Murguia and published by . This book was released on 1989 with total page 284 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Synthesis of a Cobalt Porphyrin Complex to be Used as a Catalyst in Reactions Involving Organic Radical Intermediates written by Noa Bar Ziv and published by . This book was released on 2019 with total page 24 pages. Available in PDF, EPUB and Kindle. Book excerpt: Radical intermediates appear frequently in organic synthesis due to the fact that they are highly reactive and can be used to generate a variety of useful products. However, the traditional synthesis of radicals involves hazardous reagents and carcinogens, and generates a large amount of waste. Therefore, it would be desirable to use safer, inexpensive, and abundant starting materials, such as alcohols, which are relatively simple to synthesize. The approach that will be studied in this research is the activation of alcohols using a cobalt metal catalyst and visible light energy to generate radical intermediates that can be used in a variety of reactions. Once a radical intermediate is obtained from the starting alcohol, it can undergo a few transformations, including the loss of carbon dioxide to effect deoxygenation or cross-coupling, or alternatively formation of various ester products. The goal of the project is to identify an efficient cobalt catalyst that gives high yields across a variety of substrates. The objective is achieved by synthesizing several cobalt complexes, testing their photochemical properties and evaluating their performance in several reactions.

Download or read book Variations on Cobalt Hexaamine CoN6 written by Chang Jin Qin and published by . This book was released on 1997 with total page 346 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Synthesis and Characterization of Cobalt based Coordination Complexes with Various Organic Linkers written by Md Faruque Hasan and published by . This book was released on 2018 with total page 166 pages. Available in PDF, EPUB and Kindle. Book excerpt: Metal-organic frameworks (MOFs) are being explored and investigated for a wide range of potential industrial applications due to the massive diversity of its structures and so many properties. Metal-organic framework compounds offer extremely large surface area, higher empty space volume, flexible networks, perfect mechanical and thermal stability, MOF can provide size or shape selectivity, and all of these are necessary for many industrial applications. In this research, different types of cobalt MOFs and coordination complexes have been synthesized with solvothermal process by fabricating cobalt (II) ion (normally metal salt) coordinated with organic ligand (normally organic carboxylate acid or basic organic compound or sometimes both and Nitrogen based third party linkers) and required solvent with subsequent heating condition. Various characterization techniques have been employed such as: single crystal X-ray diffraction (SXRD), powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), nuclear magnetic resonance (NMR), and BET surface area.

Download or read book Studies of Redox Formation and Dissociation Rates of Some Cobalt and Chromium Polypyridyl Complexes written by Robert D. Farina and published by . This book was released on 1968 with total page 312 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book A Study of the Synthesis and Reactions of Some Iron and Cobalt Complexes Containing Sulphur donor Ligands written by S. Y. Lee and published by . This book was released on 1977 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Mechanistic Studies on Reactivities of Organometallic Macrocyclic Complexes of Chromium and Cobalt written by and published by . This book was released on 1990 with total page 171 pages. Available in PDF, EPUB and Kindle. Book excerpt: Reaction pathways leading to the formation and cleavage of a transition metal-carbon bond at various oxidation states of the metal occupy a central position in understanding many enzymatic reactions and designing catalysts. The report is divided into six parts that (1) focus on the homolysis vs heterolysis of a C-Cr(III) bond, (2) describes a unique chain reaction and a S{sub E}2 reaction I2 and RCrL{sup 2+}, (3) concerns the oxidation of organochromium(III) complexes by dihalide and pseudo-dihalide radical anions generated by pulse radiolysis, (4) concentrates on the oxidation mechanism of RCr(H2O){sup 2+} and the fate of RCr(H2O){sup 3+} as well as the corresponding reduction potentials, (5) extends study of organocobalt complexes with attention to reduction induced cleavages of a transition metal-carbon bond, and (6) describes the crystallization of ((CH3)4N)(Co(dmgBF2)2py) and reports its molecular structure as determined by x-ray diffraction. 182 refs., 25 figs., 16 tabs. (BM).