Download or read book Synthesis and Characterization of Redox noninnocent Pyrazine diimine Iron Complexes and an Inverted Pyridine diimine Ligand written by Jaylan Billups and published by . This book was released on 2023 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Cooperativity between the metal center and the ligand has been shown in nature to be an important feature of systems that catalyze two-electron processes that first-row transition metals usually cannot catalyze on their own. In these cases, the ligand acts as a site of reactivity that in many instances can store electrons or react directly with substrates in solution. The design and study of systems where there is synergy between the metal and the ligand have been leveraged to catalyze polymerization and hydrogenation-type reactions as well as the activation of small molecules such as dihydrogen. Specifically, the pyridine(diimine) ligand scaffold has been reported to store up to three electrons on the ligand backbone that can later be used in catalysis. Wanting to expand on this work, we have designed and synthesized a new pincer that has redox-noninnocent properties similar to pyridine(diimine) ligands but incorporates a pyrazine ring instead of a pyridine ring to give rise to new electronic properties. Pyrazine(diimines) also have an uncoordinated 4-position nitrogen that can be further functionalized to fine-tune the electronic properties of the ligand. In Chapter II we will discuss bisligated iron(II) pyrazine(diimine) (PZDI) complexes in three different oxidation states where we used spectroscopic and computational techniques as well as comparison to known pyridine(diimine) iron(II) complexes to support our assignments of ligand-based reduction. Chapter III will focus on monoligated pyrazine(diimine) iron(II) complexes as compared to analogous pyrazine(diimine) systems where the central metal is manganese, cobalt, or nickel, as well as compare our pyrazine(diimine) iron(II) complexes to reported pyridine(diimine) iron(II) analogs. We have also synthesized a new inverted pyridine(diimine) ligand scaffold that has an NCN binding pocket, which will be discussed in Chapter IV. In the design of the inverted pyridine(diimine) ligand we have left in place the 4-position nitrogen from our previously described pyrazine(diimine) ligand, maintaining a Lewis basic site for functionalization. Overall, we hope to describe the results we observed with both monoligated and bisligated iron(II) pyrazine(diimine) complexes as well as discuss our approach to the design of and progress towards a new inverted pyridine(diimine) ligand scaffold.

Download or read book Synthesis Characterization and Reactivity Studies of Iron Complexes Supported by the Redox active ONO Ligand written by Janice Lin Wong and published by . This book was released on 2014 with total page 123 pages. Available in PDF, EPUB and Kindle. Book excerpt: The work reported herein primarily focuses on the development of new platforms for multi-electron reactivity using iron complexes supported by a redox-active pincer-type ligand. This dissertation details the synthesis, characterization, and reactivity of iron complexes coordinated to the redox-active [ONO] ([ONO]H3 = bis(3,5-di-[tert]-butyl-2-phenol)amine) ligand. Chapter 1 provides a general background on ligand-centered and metal-centered redox reactivity. Specifically, the characteristics of redox-active ligands and their ability to promote multi-electron reactivity at redox-inert metal centers is presented. In addition, iron-catalyzed organic transformations in which the metal center undergoes redox changes is also discussed. Finally, ligand-enabled redox reactions mediated by iron complexes containing redox-active ligands is described. Chapter 2 reports on the complexation of bis(3,5-di-[tert]-butyl-2-phenoxy)amine, [ONHO], and the redox-active [ONO] ligands by iron centers to afford a new family of iron complexes. Characterizations of each compound through a battery of analytical techniques reveal the oxidation states of the metal center and ligand. Furthermore, the electronic properties of each complex were investigated in order to evaluate their potential to facilitate multi-electron reactivity. Chapter 3 details the reactivity of the [ONO]Fe platform. Metathesis reactions are conducted with [ONO [superscript q] Fe [superscript III] X2 (X = Cl, N[SiMe3]2 complexes, demonstrating the capability of the fully-oxidized [ONO [superscript q]−1 to act as a two-electron acceptor to generate the fully reduced [ONO [superscript cat]3− that is coordinated to an iron(III) center. Similarly, oxidation of [ONO[superscript cat] Fe [superscript III] (py)3 (py = pyridine) using dihalogens result in two-electron oxidations of the tridentate ligand while the metal oxidation state remains the same. These redox reactions showcase the ability of the [ONO] ligand platform to undergo reversible two-electron oxidation state changes, allowing multi-electron reactivity to occur at the iron center. The synthesis and characterization of two novel bimetallic complexes of the form [ONO]M'[ONO]2 M (M' = Fe, Zn; M = Fe) are presented in Chapter 4. The rich redox profiles of both complexes suggest that they can potentially impart unique cooperative bimetallic reactivity. The synthetic techniques developed to prepare these complexes lay the foundation for a general method to access new bimetallic combinations that could be promising for multi-electron reactivity. Finally, Chapter 5 discusses the synthesis, characterization, and electronic comparisons between two homoleptic tris-iminosemiquinonate chromium(III) compounds. While one is coordinated to three N,N'-bis(3,5-dimethylphenyl)acenapthenediimino-semiquinonate, (dmp-ADI [superscript sq])1−, ligands, the other contains three N,N'-bis(3,5-dimethylphenyl)phenanthrenediimino-semiquinonate, (dmp-PDIsq)1− ligands. The differences in the electronic properties between each complex likely stems from variation in the diimine ligand backbones. However, further investigation is required to completely understand the complicated behaviors of such complexes, both of which apparently exhibit intramolecular anti-ferromagnetic properties.

Download or read book Synthesis and Reactivity of Group 9 Complexes Featuring Redox Non innocent Ligands written by Hagit Ben-Daat Levin and published by . This book was released on 2016 with total page 71 pages. Available in PDF, EPUB and Kindle. Book excerpt: The addition of aminoalkyl-substituted 2,6-bis(imino)pyridine (or pyridine diimine, PDI) ligands to [(COD)RhCl]2 (COD = 1,5-cyclooctadiene) resulted in the formation of rhodium monochloride complexes with the general formula (NPDI)RhCl (NPDI = iPr2NEtPDI or Me2NPrPDI). The investigation of (iPr2NEtPDI)RhCl and (Me2NPrPDI)RhCl by single crystal X-ray diffraction verified the absence of amine arm coordination and a pseudo square planar geometry about rhodium. Replacement of the chloride ligand with an outer-sphere anion was achieved by adding AgBF4 directly to (iPr2NEtPDI)RhCl to form [(iPr2NEtPDI)Rh][BF4]. Alternatively, this complex was prepared upon chelate addition following the salt metathesis reaction between AgBF4 and [(COD)RhCl]2. Using the latter method, both [(NPDI)Rh][BF4] complexes were isolated and found to exhibit K4-N,N,N,N-PDI coordination regardless of arm length or steric bulk. In contrast, the metallation of PPDI chelates featuring alkylphosphine imine substituents (PPDI = Ph2PEtPDI or Ph2PPrPDI) resulted in the formation of cationic complexes featuring K5-N,N,N,P,P-PDI coordination in all instances, [(PPDI)Rh][X] (X = Cl, BF4). Adjusting the metallation stoichiometry allowed the preparation of [(Ph2PPrPDI)Rh][(COD)RhCl2], which was characterized by multinuclear NMR spectroscopy and single crystal X-ray diffraction.

Download or read book Synthesis and Characterization of Pyridine and 4 phenylpyridine Complexes Containing the Bis diimine carbonyl osmium II Moiety written by Carmen Leung and published by . This book was released on 2010 with total page 284 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Chemical and Redox Non innocence in Iminopyridine and Bis imino pyridine Aluminum III Complexes Including Polar Bond Activation and Catalytic Dehydrogenation by superscript Ph I2P2 Al THF H superscript Ph I2P written by Thomas Winfield Myers and published by . This book was released on 2014 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: This dissertation discusses the synthesis, reactivity and characterization of iminopyridine and bis(imino)pyridine complexes of aluminum and other electrophilic main group metal ions. It is shown that aluminum complexes of iminopyridine ligands can undergo stoichiometric redox transformations while aluminum complexes of bis(imino)pyridine ligands can facilitate heterolytic substrate activation and catalytic dehydrogenation reactions. In chapter 2, the reaction of disulfides, nitrogen group transfer reagents, and zinc(II) salts with [Na(THF)6][(IP2−)2Al] (2.1c) (IP = 2,6-bis(isopropyl)-N-(2-pyridinyl-methylene)phenylamine) affords aluminum complexes of the form (IP−)2AlX (X = Cl 2.2, [mu]2-SSCN(CH3)2 2.4, SCH3 2.5, NaNTs 2.6, CCPh 2.7, N3 2.8, SPh 2.9, and NHPh 2.10). Additionally, the oxidation of (IP−)2Al(Me) (2.3) by single electron oxidants leads to formation of [(IP−)(IP)Al(Me)]+. When TrBPh4 (Tr = triphenylmethyl) is employed as the oxidant, carbon-carbon coupling between one of the IP ligands and the Tr group is observed to form [(TrIP)(IP)Al(Me)]+ (2.11). This bond formation can be reversed when bulkier anions are added, or can be avoided by using TrB(C6F5)4 and TrBAr[superscript F] as the one electron oxidants. In chapter 3, the formation of Al(III) and Ga(III) oxo intermediates are proposed resulting from the oxidation of [(IP2−)2M]− (M = Al, Ga) with pyO (pyO = pyridine-N-oxide). These reactive intermediates homolytically and heterolytically cleave C-H bonds to form [Na(DME)(THF)][(IP2−)(IP−)Al(OH)] (3.3) and (IP−)2M(OH) (M = Al 3.4, Ga 3.7). The identity of the counter cation directs the reactivity of [(IP2−)2Al]−. When [Na(DME)3][(IP2−)2Al] is employed, C-H activation of solvent is observed, while when [Bu4N][(IP2−)2Al] is employed proton abstraction from Bu4N+ is observed. The oxidation of [(IP2−)2Ga]− by pyO leads to acid base chemistry when either Na+ or Bu4N+ is employed as the counter cation. The reaction of 3.4 and 3.7 with CO2 leads to formation of [(IP−)2M]2([mu][eta]1:[kappa]2-OCO2) (M = Al 3.10, Ga 3.11). Reduction of 3.10 and 3.11 with alkali or alkali earth metals and subsequent oxidation allows for the reformation of 3.4 and 3.7. In chapter 4, the reduction of [superscript Me]IP[subscript Mes] ([superscript Me]IP[subscript Mes] = 2,6-bis(isopropyl)-N-(2-(5-mesityl-pyridinyl)-methylene)phenylamine) with sodium metal followed by metathesis with MCl[subscript n]X[subscript 3-n] (M = Al, Ga, X = Cl, CH3) leads to the formation of ([superscript Me]IP[subscript Mes−)MX2 (M = Al, X = Cl, 4.1a, 4.2a; M = Ga, X = Cl 4.5), ([superscript CH2]IP[subscript Mes]−)AlX2 (X = Cl, 4.1b, 4.2b), ([superscript Me]IP[subscript Mes]2−)MX(OEt2) (M = Al, X = Cl, 4.3, 4.4; M = Ga, X = Cl 4.6) . Unlike the IP ligand system, only one [superscript Me]IP[subscript Mes] ligand coordinates to the metal center in these complexes. Selective deprotonation of the [superscript Me]IP[subscript Mes] ligand is observed in ether solvents, while selective reduction is observed in alkane and aromatic solvents. In chapter 5, complexes of bis(imino)pyridine ligands with aluminum are presented. Reduction of [superscript Ph]I2P ([superscript Ph]I2P = 2,6-(2,6-[superscript i]Pr2-C6H3N=CPh)2C5H3N) by 2 equivalents of sodium metal followed by salt metathesis with AlCl2X (X = Cl, H) affords ([superscript Ph]I2P2−)AlX(THF) (X = Cl 5.1, H 5.2a) and ([superscript Ph]I2P2−)AlH (5.2b). The [superscript Ph]I2P2− ligands in these complexes are shown to be chemically non-innocent. The addition of polar N-H and O-H bonds across the aluminum-amido bonds leads to the formation of ([superscript Ph]HI2P2−)AlH(X) (X = NHDipp 5.3a, NHPh 5.3b, [mu]-O 5.5, OPh 5.8) (Dipp = 2,6-diisopropylphenyl). 5.2b also catalyzes the dehydrogenative coupling of benzylamine with 3.5 turnovers over 24 hours. In chapter 6, complexes of the form ([superscript Ph]I2P2−)AlX(THF) (X = H, Me) are shown to be active catalysts for the selective dehydrogenation of formic acid with an initial TOF of up to 5200 hr−1 and up to 2200 total turnovers observed. The mechanism of the transformation is examined through a series of stoichiometric reactions. In the presence of formic or acetic acid, the [superscrpt Ph]I2P2− ligand is protonated at both the amido nitrogen and at the ipso carbon position effectively hydrogenating one of the imine arms of the ligand. The Al(III) complexes of the [superscript Ph]HI2P− and [superscript Ph]H2I2P forms of the ligand favor [beta]-hydride abstraction from formate, while the Al(III) complexes of the [superscript Ph]I2P2− form of the ligand favors the reverse reaction: insertion of CO2 into the Al-H bond. The liberation of CO2 from formate is investigated through a series of deuterium labeling studies which show [beta]-hydride transfer from formate to the aluminum center. Finally, in chapter 7, the variety of electronic states adopted by complexes of methyl-substituted bis(imino)pyridine ligands is discussed. Reduction of [superscript Me]I2P ([superscript Me]I2P = 2,6-bis(1-methylethyl)-N-(2-pyridinylmethylene)phenylamine) with sodium metal leads to the formation of ([superscript Me]I2P−)Na(OEt2) (7.1). Reduction of [superscript Me]I2P by sodium metal followed by salt metathesis with MgCl2, Mg(OTf)2, AlCl3, and AlCl2H affords [([superscript Me]I2P2−)Mg(THF)](MgCl2) (7.2), ([superscript Me]I2P2−)Mg(THF)2 (7.3), ([superscript Me]I2P−)AlCl2 (7.4), ([superscript Me]I2P2−)AlCl(THF) (7.5) and ([superscript Me]I2P2−)AlH(THF) (7.6), respectively. The electronic states of 7.1 to 7.6 are shown to be dependent on the reaction conditions used to synthesize the complexes with certain conditions leading to dimer formation. Initial reactivity studies with 7.5 and 7.6 are discussed.

Download or read book Terdentate Iron Complexes written by Aaron Maurice Tondreau and published by . This book was released on 2011 with total page 409 pages. Available in PDF, EPUB and Kindle. Book excerpt: A three-electron series of four-coordinate bis(imino)pyridine iron nitrosyl complexes was synthesized. The electronic structure of this series of compounds was determined by the use of X-ray crystallography, Mössbauer, IR, NMR, and EPR spectroscopies, and corroborated by DFT calculations. (iPrPDI)Fe(NO) was determined to be an intermediate-spin ferric complex with a triplet two electron reduced bis(imino)pyridine chelate and a triplet NO-. The overall spin state of (iPrPDI)Fe(NO) is S = 1/2. The oxidation of (iPrPDI)Fe(NO) occurs at the bis(imino)pyridine chelate, and the electronic structure of the iron nucleus remains intermediate-spin ferric. The reduction of (iPrPDI)Fe(NO) also is bis(imino)pyridine chelate centered. This yields a three-electron reduced chelate, leaving the iron intermediate-spin ferric and the nitrosyl as NO-. The reduction and oxidation of compounds was carried out to yield two other three-electron series. The synthesis and characterization of [Li(OEt2)3][(iPrPDI)Fe(CH2CMe3)(N2)], (iPrPDI)Fe(CH2CMe3), and [(iPrPDI)Fe(CH2CMe3)][BPh4] allowed for the determination of the degree of chelate participation over a three-electron series pertinent to olefin polymerization. The redox events were shown to occur at the bis(imino)pyridine chelate, leaving the iron nucleus Fe(II) throughout the series. [Na15-Crown-5][(iPrPDI)Fe(CO)2], (iPrPDI)Fe(CO)2, and [(iPrPDI)Fe(CO)2][BArF24] were also synthesized. Analysis of [(iPrPDI)Fe(CO)2][BArF24] indicates that oxidation of the formally Fe(0) complex (iPrPDI)Fe(CO)2 results in the oxidation of the bis(imino)pyridine chelate to a neutral ligand, giving a formally Fe(I) species. [Na-15Crown-5][(iPrPDI)Fe(CO)2] was not structurally characterized, but EPR spectroscopy indicates that the reduction occurred at the ligand, and the iron is low spin Fe(II). Bis(imino)pyridine iron complexes also were utilized as catalysts for the hydrosilylation of ketones, aldehydes, and olefins. The hydrosilylation of ketones and aldehydes was performed with primary and secondary silanes using bis(imino)pyridine iron dialkyl complexes and pybox iron dialkyls. The hydrosilylation of olefins was performed with tertiary silanes utilizing several reduced bis(imino)pyridine iron complexes. The result was reactivity that proved to be competitive with platinum based catalysis. In several instances iron outperformed platinum in terms of selectivity and fewer side-products.

Download or read book Synthesis and Characterization of Transitional Metal Pyridine Containing Complexes with Both Catalytic and Therapeutic Applications written by Magy Amir Maurice Mekhail and published by . This book was released on 2022 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Pyridinophanes derived from pyclen are the focus of many studies as biological mimics, chelators, and catalytic precursors. Therefore, the desire to tune the reactivity of metal pyridinophane complexes has inspired modifications that include expansion of ring size and substitutions to the N-atoms. However, substitution on the pyridine moiety is largely unexplored to date. Herein, new synthetic strategies for pyclen-congeners bearing electron donating and electron withdrawing groups are introduced, resulting in doubling the number of pyridine functionalized molecules in literature. Further, the influence of such modifications on properties and reactivity of two metals (Fe(III) and Cu(II)) is described. For the Fe(III) system, 4-substitution of the pyridine ring successfully provides a regulatory handle on the electronic properties and the catalytic C-C coupling activity of the respective Fe complexes. These are the first examples of a structure-activity relationship study with the impact of electronic properties decoupled from structural properties and investigated. The Fe(III) system was also explored in a catalase mimetic study to determine the role of ligand design on the activity of the metal center through changing electronic properties and rigidity of the ligand. Varying the electronic properties of the ligand has a minor effect on catalase activity, but changes to the geometry of the complex have significant impacts on the system. This activity was also successfully observed to cellular models. The Cu(II) system was investigated as a superoxide dismutase mimic. Cu(II) Pyclen complexes, specifically, has been shown to match its coordination environment and to have high binding affinity. My studies highlight that modifications to the pyridine ring of the ligand can tune the redox potential, while exhibiting high binding stabilities and retaining the coordination environment. In fact, one of the complexes studied exhibits one of the highest SOD activities reported to date, which is hypothesized to be the result of not only the electronic properties of the Cu center but also the high binding stability exhibited by this complex. Altogether, this work focused on functionalizing the pyridine ring in pyridinophanes and studying the effect of the modifications on the electronics of metal complexes and their reactivity with both catalytic and potential therapeutic application.

Download or read book Design and Synthesis of a Series of Redox Active Tetrazine and Triazine Based Transition Metal Complexes written by Yixin Zhang and published by . This book was released on 2018 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The use of two different chelating redox active ligands, 2,6-bis(6-methyl-1,2,4,5-3-yl) pyridine (BTZP) and 2,6-bis-(5,6-dialkyl-1,2,4-triazin-3-yl)-pyridine (BTP) in heterometallic first row and second row transition metal chemistry has yielded two new families of redox active metal complexes. These complexes were found to exhibit interesting electrochemical and magnetic properties. In this thesis, Chapter 1 lays the foundation for the research presented within. This section covers the fundamentals of the ligand design, ligand synthesis and related coordination chemistry literature review. Chapters 2 and 3 report the results of the current thesis. In Chapter 2, the synthesis and characterization of a family of discrete molecules and supramolecular arrangements, employing the ligand BTZP, is presented. All of the complexes presented in Chapter 2 are successfully synthesized and characterized with electrochemical and magnetic studies. According to the electrochemical data, it is found that the classic "terpy-like" complexes with [Co(BTZP) 2]2+ formula fosters more stability in the redox process. In Chapter 3, a family of transition metal complexes with [M(BTP) 2]2+ (M=Fe or Co) inorganic cores were obtained through the employment of the ligand BTP with various anions. In addition, dimeric molecules with [CoX4(BTP)2] formula were also obtained by solvothermal synthesis. The complexes were also electrochemically characterized, with all the complexes capable of being reduced, while only [CoII(BTP)2] (ClO4)2 showed reversible redox process. Similar with BTZP, the series of BTP based complexes are also characterized through magnetic measurement. Only cobalt-based BTP complexes are paramagnetic, with [CoII(BTP)2]2+ being spin crossover active when BF4- and ClO4- are present. However, the presence of NCS- and halides lead to either antiferromagnetic interactions and ferromagnetic interactions dominating at different temperature regimes.

Download or read book Bioinspired Design of Redox active Ligands for Multielectron Catalysis written by and published by . This book was released on 2015 with total page 19 pages. Available in PDF, EPUB and Kindle. Book excerpt: Mononuclear metalloenzymes in nature can function in cooperation with precisely positioned redox-active organic cofactors in order to carry out multielectron catalysis. Inspired by the finely tuned redox management of these bioinorganic systems, we present the design, synthesis, and experimental and theoretical characterization of a homologous series of cobalt complexes bearing redox-active pyrazines. These donor moieties are locked into key positions within a pentadentate ligand scaffold in order to evaluate the effects of positioning redox non-innocent ligands on hydrogen evolution catalysis. Both metal- and ligand-centered redox features are observed in organic as well as aqueous solutions over a range of pH values, and comparison with analogs bearing redox-inactive zinc(II) allows for assignments of ligand-based redox events. Varying the geometric placement of redox non-innocent pyrazine donors on isostructural pentadentate ligand platforms results in marked effects on observed cobalt-catalyzed proton reduction activity. Electrocatalytic hydrogen evolution from weak acids in acetonitrile solution, under diffusion-limited conditions, reveals that the pyrazine donor of axial isomer 1-Co behaves as an unproductive electron sink, resulting in high overpotentials for proton reduction, whereas the equatorial pyrazine isomer complex 2-Co is significantly more active for hydrogen generation at lower voltages. Addition of a second equatorial pyrazine in complex 3-Co further minimizes overpotentials required for catalysis. The equatorial derivative 2-Co is also superior to its axial 1-Co congener for electrocatalytic and visible-light photocatalytic hydrogen generation in biologically relevant, neutral pH aqueous media. Density functional theory calculations (B3LYP-D2) indicate that the first reduction of catalyst isomers 1-Co, 2-Co, and 3-Co is largely metal-centered while the second reduction occurs at pyrazine. Taken together, the data establish that proper positioning of non-innocent pyrazine ligands on a single cobalt center is indeed critical for promoting efficient hydrogen catalysis in aqueous media, akin to optimally positioned redox-active cofactors in metalloenzymes. In a broader sense, these findings highlight the significance of electronic structure considerations in the design of effective electron-hole reservoirs for multielectron transformations.

Download or read book Synthesis Reactivity of Iron II Pyridinediimine Complexes for the Reduction of Nitrite written by Yubin Kwon and published by . This book was released on 2016 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: The activation of small molecules has been studied by the scientific field for many decades as it plays a key role in nature such as photosynthesis and respiration. Many of these reactions are catalyzed by metalloenzymes in nature where the transfer of electrons and protons are coupled for the reaction to move forward. Noncovalent interactions in the secondary coordination sphere of metalloenzymes play an important role in determining the activity and selectivity. Hydrogen bonds are the most common noncovalent interactions that metalloenzymes utilize to control the reactivity in the secondary coordination sphere. Therefore, it is important to develop compounds and catalysts that can move both protons and electrons. Recent studies have been done by several groups on the mechanism of nitrite reduction. Based on those findings, we developed a series of iron (II) pyridinediimine (PDI) complexes that contain pendant bases, with varying pKa values, located in the secondary coordination sphere. These ligands were synthesized, coordinated to iron (II) and reduced under carbon monoxide (CO) to store electrons within the ligand scaffold. These reduced complexes were then protonated to form hydrogen bonds and fine tune the reactivity. These PDI complexes that are capable of storing both electrons and protons were investigated to functionally mimic the metalloenzyme nitrite reductase. To date, the mechanism of nitrite reduction remains unknown. In an attempt to determine how nitrite binds to the metal of our PDI complex, we synthesized a dinitrosyl iron complex. The synthesis of this complex should help to determine the mechanism of nitrite reduction.

Download or read book Synthesis and Characterization of Iron Complexes Supported by Bulky Amide Ligands written by Sheree Lynell Stokes and published by . This book was released on 1998 with total page 378 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Probing the Secondary Coordination Sphere of Zn II and Fe II Pyridinediimine PDI Complexes written by Mayra Delgado and published by . This book was released on 2017 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: The transformation of many small, abundant molecules is necessary both in a biological setting and in the chemical industry. In Nature, the activation of small molecules is promoted by metalloenzymes. However, many of these chemical transformations are thermodynamically demanding and consist of multi-electron redox processes. Understanding the secondary coordination sphere has played an integral role in determining the catalytic activity and selectivity of such transformations and has led to the development of bioinspired catalysts in order to mimic the native active site of the metalloenzyme. Due to its extensive modularity, the utilization of the pyridinediimine (PDI) metal complexes was targeted in this work to study the secondary coordination sphere and its relationship to the reactivity at the metal active site. The redox-active PDI ligand scaffold containing a pendant base was used to synthesize a series of Fe(II) and Zn(II) complexes consisting of H-bond acceptors/donors in the secondary coordination sphere. The Zn(II) complexes are able to be protonated in the secondary coordination sphere, forming metal halogen hydrogen bonds (MHHBs). The use of these intramolecular H-bonds in the Zn complexes also serve to provide stabilization of the hydrosulfide (HS- ) ligand, forming a six-coordinate Zn complex. The Fe(II) complexes were reduced under CO atmosphere, followed by protonation in the secondary coordination sphere. This resulted in stable, doubly reduced protonated species, capable of moving protons and electrons in and out of the system. The protonated Fe(II) complex was poised to deliver protons and electrons necessary to investigate nitrite (NO2- ) reduction for the formation a dinitrosyl iron complex (DNIC). The reduction of nitrate (NO3- ) for the synthesis of the DNIC was also explored and used to further investigate products of the reaction. Fe(II) PDI complexes with an incorporation of Lewis acids in the secondary coordination sphere were also synthesized and characterized in order to provide a better understanding of how redox inactive metals in the secondary coordination sphere of the PDI scaffold of alters the redox activity of the complex.

Download or read book Chiral Iron Pyridine Complexes and Ruthenium Complexes with N Heterocyclic Carbene and Macrocyclic N O Donor Atom Ligands written by Kar-Yee Lam and published by . This book was released on 2017-01-26 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: This dissertation, "Chiral Iron Pyridine Complexes and Ruthenium Complexes With N-heterocyclic Carbene and Macrocyclic (N, O) Donor Atom Ligands: Synthesis, Catalytic Activity and Biological Studies" by Kar-yee, Lam, 林嘉儀, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Abstract of thesis entitled CHIRAL IRON PYRIDINE COMPLEXES AND RUTHENIUM COMPLEXES WITH N-HETEROCYCLIC CARBENE AND MACROCYCLIC(N, O) DONOR ATOM LIGANDS: SYNTHESIS, CATALYTIC ACTIVITY AND BIOLOGICAL STUDIES Submitted by Lam Kar Yee For the degree of Doctor of Philosophy at The University of Hong Kong in April 2016 Transition metal complexes are widely applied as catalysts for organic transformation reactions such as the oxygen atom and nitrene transfer reactions and there is a growing interest to develop the medicinal applications of transition metal complexes. The studies of reactive metal-oxo and metal-nitrene intermediates are important in probing the underlying reaction mechanisms. This thesis is comprised of three main parts. In the first part, iron complexes with chiral pyridine ligands, such as 4′,6-disubstituted 2,2′ 6′,2″-terpyridine (NNN ) and 4′,6,6″-trisubstituted 2,2′ 6′,2″''-terpyridine (NNN ), were studied for their catalytic activities in asymmetric epoxidation, aziridination, amidation and sulfimidation reactions. The Fe-NNN complex catalyzed intermolecular nitrene transfer/CN bond formation reactions of styrenes with PhINTs in moderate product yields. For the asymmetric intramolecular amidation, the Fe-NNN complex can catalyze intramolecular C-N bond formation using PhI(OAc) as oxidant to form five- or six-membered ring products. The highest product yield obtained was 91 %. The complete conversion of para-substituted phenyl methyl sulfides to corresponding sulfimides was observed by using the Fe-NNN 1 2 complex as catalyst. Both the Fe-NNN and Fe-NNN complexes catalyzed asymmetric epoxidation of styrene using PhIO as oxidant at 0 C. The reaction intermediates of the nitrene/oxygen transfer reactions were studied by ESI-MS and high-valent iron-ligand multiple bonded species are proposed to be the reaction intermediates. In the second part, ruthenium pincer N-heterocyclic carbene (CNC) complexes were prepared and characterized by spectroscopic means and X-ray crystallography. II 2+ Complex [Ru (CNC)(bpy)(MeCN)], in which the CNC ligand adopts a fac-coordination mode and contains reactive CH bond of bridging methylene group, was found to react with PhINTs to result in the formation of a new CN bond and cleavage of one existing NC(methylene) bond of the CNC ligand, as revealed by X-ray crystal structure determination of the ruthenium complex product. The reaction 2+ of [Ru(CNC)(bpy)(MeCN)] with PhINTs was monitored by ESI-MS, UV-vis, and NMR spectroscopy; a paramagnetic Ru(III)-amido complex was isolated, which apparently resulted from intramolecular imido/nitrene CH insertion of a Ru(IV)-imido/nitrene intermediate and was found to undergo the observed CN bond cleavage. Such type of CN bond cleavage induced by metal-mediated imido/nitrene insertion is unprecedented in literature. The final part of this thesis is the study of the anti-angiogenic and anti-metastatic properties of the ruthenium complexes. Ruthenium complexes with different oxidation states (+2 and +3) and ligands (pincer NHC and macrocyclic (N, O) donor atom ligands) were examined for their cytotoxicity and anti-angiogenesis activity. III Among the complexes studied, [Ru (N O )Cl ]Cl (Ru-1) displays promising 2 2 2 inhibi

Download or read book Rational Design Synthesis and Characterization of Amide Functionalized Pyridine and Benzimidazole Transition Metal Complexes written by Samuel S. K. Asem and published by . This book was released on 2011 with total page 576 pages. Available in PDF, EPUB and Kindle. Book excerpt: This study expands our efforts to make a new class of Pt (II) compounds analogous to cisplatin and its derivatives using sterically hindered ligands. Pt compounds in this series have been synthesized using specially designed pyridine and benzimidazole ligands. These heterocycles, amide functionalized at position 2 with aryl and alkyl pendants, rapidly change their mode of coordination depending on the pH of the medium. These ligands, synthesized using condensation chemistry, also coordinate to Co(II), Ni(H), Cu(lI), and Zn(1I) generally as anionic bis-chelates through the benzimidazole nitrogen and the carbonyl oxygen, creating a four-coordinate complex with the exception of an unusual trigonal bipyramidal Zn(H) complex. I H NMR temperature studies reveal that these ligands interconvert between imide and amide isomers and that electron withdrawing pendants favor amide isomers. Crystal structures of Co(II) and Ni(1I) complexes of N-( I-methylbenzimidazol-2-yl)cyclohexanecarboxamide, for example, show two ligands bind per metal ion when reacted with acetate and nitrate salts. The bischelates of these Ni(1I) complexes also show expansions of their coordination spheres from four to five-coordinate. Furthermore, these Ni(II) bis-chelated complexes possess square planar or distorted 4-coordinate geometries. The synthesis and properties of several new Pt (II) complexes containing these ligands will be presented. A second generation and novel complex class containing metal-binding, linker and recognition domains is reported. Both classes of Pt complexes were obtained using a synthetic methodology which favors the cis isomers. The second generation complex crystallizes in the monoclinic space group P2dn with lattice dimensions a = 17.7393(5) A, b = 11.4632(3) A, c = 19.3959(5) A and ~ = 99.794(3)°. These complexes have been characterized using physical methods that include X-ray crystallography, IH &13C NMR, Mass spectrometry, UV and IR spectroscopies. Complexes similar in structure to cisplatin and carboplatin show varying cytotoxic properties toward different cancer cell lines. Additionally, some of these new Pt complexes show comparable and promising cytotoxicity against prostate cancer cell lines.

Download or read book Synthesis Characterization and Solubility of Iron II Diimine Complexes in Aqueous methanol Mixtures written by Lay Kian Pua and published by . This book was released on 2006 with total page 50 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Synthesis Characterization and Reactivity Studies of Pyridine Bis anilide Iron Complexes written by Edward Charles Weintrob and published by . This book was released on 2012 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Pyridinediimine Complexes with Coordination Sphere Interactions Relevant to Copper and Non heme Iron Enzymes written by Pui Man Audrey Cheung and published by . This book was released on 2021 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Primary and secondary coordination sphere interactions with proximal Brønsted-Lowry acid/base sites were investigated using a family of pyridinediimine (PDI) complexes. The PDI ligands used in this project could be easily prepared by the Schiff base reactions with commercially available diamines as proton relays. Upon activation, the pendant Brønsted site and accessible electrons were arranged in a single scaffold that allowed the transportation of both protons and electrons to occur. Two new PDI complexes with morpholine (6) and pyrrolidine (7) derivatives were introduced to the pendant PDI family. The proton dissociation constant of 6Fe(CO)2 and 7Fe(CO)2 were measured [pKa (CD3CN) = 17.1 and 18.3, respectively]. The PDI complexes were subjected to reactions with nitrite and monitored via UV-Vis and IR spectroscopy, in which they exhibited much faster initial rates than some of the previously reported pendant PDI complexes. The rate enhancement effect was clearly evidenced by the stability of the corresponding mononitrosyl iron complex (MNIC) intermediate. These results had not yet been observed in other mononuclear PDI complexes and was attributed to the unique combination of proton responsivity, redox-activity and hemilability in 6 and 7.