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Synthesis Reactivity And Multi Electron Redox Behavior Of A Bisphenoxyamide Ligand Coordinated To A Tantalum Metal Center
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Book Synopsis Synthesis, Reactivity, and Multi-electron Redox Behavior of a Bis(phenoxy)amide Ligand Coordinated to a Tantalum Metal Center by : Ryan A. Zarkesh
Download or read book Synthesis, Reactivity, and Multi-electron Redox Behavior of a Bis(phenoxy)amide Ligand Coordinated to a Tantalum Metal Center written by Ryan A. Zarkesh and published by . This book was released on 2012 with total page 150 pages. Available in PDF, EPUB and Kindle. Book excerpt: This dissertation describes the synthesis and reactivity of tantalum metal complexes containing a tridentate redox-active ligand. Fundamental studies have focused on utilizing the redox-active ligand to store multiple electron equivalents for oxidative addition and reductive elimination reactions. Chapter 1 provides an introduction to the characteristics of redox-active ligands and provides an overview of group transfer reactions involving redox-active ligands. The previous published results of bidentate redox-active ligands coordinated to Group IV d0 metals are discussed in terms of their decomposition side reactions. Chapter 2 describes the coordination of a known tridentate redox-active bis(phenoxy)amide ligand, (ONO), to a d0 tantalum(V) metal center and the examination of the redox properties of the resulting chloro oxidation products by electrochemical and spectroscopic methods. Chapter 3 examines the reactivity of the (ONO)TaR2 complexes in the general context of organometallic chemistry with a focus on protonolysis and reactivity with aryl azides, a known source of nitrene fragments upon oxidation. Chapter 4 examines the reactivity of the (ONO)TaX2 (X = Me, Cl) compounds with bulky diazoalkanes, a known carbene transfer reagent. The (ONO)TaCl2 complex proved to be a competent catalyst to generate cyclopropanes from styrene and the corresponding diazoalkane. Chapter 5 explores the utilization of the (ONO) ligand to store electron equivalents for the catalytic nitrene-nitrene coupling reactions with organoazides to afford organodiazenes. Finally, Chapter 6 addresses the electronic considerations of a related redox-active triamido ligand in an effort to tune the ligand's redox potentials.
Book Synopsis Synthesis and Ligand-Enabled Reactivity of Transition Metal Complexes Bearing a Redox-Active Bis(phenoxy)amide Ligand by : Aaron M. Hollas
Download or read book Synthesis and Ligand-Enabled Reactivity of Transition Metal Complexes Bearing a Redox-Active Bis(phenoxy)amide Ligand written by Aaron M. Hollas and published by . This book was released on 2016 with total page 188 pages. Available in PDF, EPUB and Kindle. Book excerpt: The work described herein focuses on the ability of redox-active ligands to enable multi-electron reactivity at transition metal centers. A parallel theme is the effect of ancillary ligands on controlling and modulating the electronic structure of the redox-active ligand and metal center in addition to ancillary ligand effects as they relate to controlling the primary coordination sphere of the metal. (Abstract shortened by ProQuest.).
Book Synopsis The Synthesis of Coordination and Organometallic Compounds for Two- Electron Thermal and Photochemical Redox Reactions by : Douglas Harold Motry
Download or read book The Synthesis of Coordination and Organometallic Compounds for Two- Electron Thermal and Photochemical Redox Reactions written by Douglas Harold Motry and published by . This book was released on 1995 with total page 266 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Metal-ligand Redox Interaction in the Multielectron Chemistry of Porphyrinogen Coordination Compounds by : Julien Bachmann
Download or read book Metal-ligand Redox Interaction in the Multielectron Chemistry of Porphyrinogen Coordination Compounds written by Julien Bachmann and published by . This book was released on 2006 with total page 257 pages. Available in PDF, EPUB and Kindle. Book excerpt: (Cont.) Crystallographic analysis shows that both anionic oxidation states contain the reduced ligand, whereas the dicationic state is based on the oxidized ligand (with two C - C bonds). Paramagnetic NMR confirms the structures in solution. Spectroscopies (EPR, Mössbauer) allow the assignment of well-defined individual oxidation and spin states states for the metal within each overall oxidation state of the complex (Chapter VI). The iron porphyrinogen dication is an oxidant based on an iron(II) center; it oxidizes iodide to diiodine (Chapter VII). The cobalt(II) porphyrinogen dianion can take up two protons, then photoreact to yield reduction of at least one proton to a metalbound hydride, as evidenced by infrared spectroscopy (Chapter VIII). Overall, the results afford a picture of metal-porphyrinogens including structure, electronic structure, and reactivity. The ligand supplements the central metal ion by functioning as a multielectron reservoir. Therefore, the (metal-based) coordination and (ligand-based) redox properties of a given porphyrinogen.
Book Synopsis Electronic Structure and Reactivity of Transition Metal Complexes Incorporating Pro-radical Bis-phenoxide Ligands by : Ryan Michael Clarke
Download or read book Electronic Structure and Reactivity of Transition Metal Complexes Incorporating Pro-radical Bis-phenoxide Ligands written by Ryan Michael Clarke and published by . This book was released on 2018 with total page 194 pages. Available in PDF, EPUB and Kindle. Book excerpt: Transition metal complexes with pro-radical ligands have received considerable research attention due to their interesting electronic structures, photophysical properties, and applications in catalysis. The relative ordering of metal and ligand frontier orbitals in a complex incorporating pro-radical ligands dictates whether oxidation/reduction occurs at the metal centre or at the ligand. Many metalloenzymes couple redox events at multiple metal centres or between metals and pro-radical ligands to facilitate multielectron chemistry. Owing to the simplicity of the active sites, many structural and functional models have been studied. One class of pro-radical ligand that has been investigated extensively are bis-imine bis-phenoxide ligands (i.e. salen) due to their highly modular syntheses. In this thesis, projects related to the synthesis, electronic structure, and reactivity of mono and bimetallic complexes incorporating the salen framework are explored. Chapter 2 presents a systematic investigation of the effects of geometry on the electronic structure of four bis-oxidized bimetallic Ni salen species. The tunability of their intense intervalence charge transfer (IVCT) transitions in the near infrared (NIR) by nearly 400 nm due to exciton coupling in the excited states is described. For the first time, this study demonstrates the applicability of exciton coupling to ligand radical systems absorbing in the NIR region. Chapter 3 investigates the ground-state electronic structure of a bis-oxidized Co dimer. Enhanced metal participation to the singly occupied molecular orbitals results in both high spin Co(III) and Co(II)-L• character in the ground state, and no observable band splitting in the NIR due to exciton coupling. Finally, Chapter 4 describes a series of oxidized nitridomanganese(V) salen complexes with different para ring substituents (R = CF3, tBu, and NMe2), demonstrating that nitride activation is dictated by remote ligand electronics. Upon one-electron oxidation, electron deficient ligands afford a Mn(VI) species and nitride activation, whereas an electron-rich ligand results in ligand based oxidation and resistance to N coupling of the nitrides. This study highlights the alternative reactivity pathways that pro-radical ligands impose on metal complexes and represents a key step in the use of NH3 as a hydrogen storage medium. The results presented herein provide a starting point for further efforts in reactivity with the salen platform.
Book Synopsis Small Molecule Binding to Electrophilic Trigonal Pyramidal Platinum, Palladium, and Nickel by : Charlene Tsay
Download or read book Small Molecule Binding to Electrophilic Trigonal Pyramidal Platinum, Palladium, and Nickel written by Charlene Tsay and published by . This book was released on 2013 with total page 266 pages. Available in PDF, EPUB and Kindle. Book excerpt: Chapter 1 A general introduction to the concepts and background of several types of transition metal complexes that motivate and inform the research described herein. These include a-complexes and molecular adducts of dinitrogen, dihydrogen, and carbon dioxide. Chapter 2 Trigonal bipyramidal platinum(II) complexes of the monoanionic, tetradentate, triphosphine [SiPR3 ([SiP3R]- = [(2-R2PC6H4)3Si]-; R = Ph, iPr) ligand are prepared and shown to provide access to cationic species with divergent behavior. The less electron-rich phenyl-substituted ligand renders the platinum center extremely electrophilic, leading to structurally characterized examples of weakly-donating ligands bound in the fifth, apical coordination site. Of particular interest is the structure of the toluene adduct, which suggests a possible interaction between the platinum center and an aryl C-H bond. When the ligand phosphines are instead substituted by the more electron-rich isopropyl groups, the electrophilicity of the cationic platinum is shown to be mitigated, allowing access to a four-coordinate, trigonal pyramidal platinum center. The crystallographically characterized geometry for this divalent platinum is in contrast to the canonical square planar configuration for d8, 16-electron transition metal complexes. The palladium analogue is also synthesized and shown to possess the same coordination. Chapter 3 Cationic nickel complexes of the [SiPR3] ligand are synthesized and, in contrast to their platinum and palladium congeners, facilitate the surprising binding of molecular dinitrogen to electrophilic nickel(II) centers. The extremely high stretching frequencies of these bound N2 moieties attest to their minimal activation, and the stability of these complexes is shown to arise from increased adonation from the N2 to the cationic nickel center, which compensates for the relative lack of it back-bonding that stabilizes N2 adducts in less electrophilic systems. These cationic nickel species are additionally shown to form thermally stable adducts of molecular dihydrogen. The relative binding strengths of N2 and H2 to these nickel centers are explored and shown to be modulated by the ligand phosphine substituents. Furthermore, evidence of linear binding of carbon dioxide is presented, representing an electrophilic approach to carbon dioxide activation that is in contrast to the low-valent, nucleophilic metal paradigm. Chapter 4 The four-coordinate neutral nickel boratrane (TPiPrB = (2-iPr2PC6H4)3B) reported in the literature represents an isostructural counterpart to the cationic {[SiiPr3]Ni}+ species presented in Chapter 3. Though these two compounds are formally separated by two oxidation states of nickel, the Lewis-acidic nature of the Z-type borane ligand in (TP'PrB)Ni renders it valence-isoelectronic with {[SiiPr3]Ni}+. The reactivity toward N2 and H2 of (TPiPr'B)Ni, as well as that of the new compound (TPPhB)Ni, is explored and discussed in context of what is observed for the {[SiPR3]Ni}+ system. The neutral (TPiPr'B)Ni, while presumably a better [pi] back-bonder than cationic {I[SiPip' 3]Ni}T, is demonstrated not to bind N2, though a very weak, fluxional interaction with H2 at low temperature is hypothesized. The more electrophilic (TP PhB)Ni exhibits room temperature interactions with both N2 and H2, though the nature of these interactions has yet to be confirmed. These results thus underline the importance of [sigma]-donation in stabilizing N2 and H2 adducts of poorly 7r back-bonding metal centers. Chapter 5 Cobalt(I) complexes of [SiPR3] provide an additional isostructural, isoelectronic point of comparison to the cationic nickel species presented in Chapter 3. The dinitrogen adducts [SiP'i' 3]Co(N2) and [SiPPh3]Co(N2), previously reported from our laboratory, feature strongly bound N2 ligands that are not labile to vacuum. The corresponding dihydrogen adducts are generated slowly under an H2 atmosphere. The intact nature of both dihydrogen ligands, which also are not labile to vacuum, is reflected in their NMR spectroscopic parameters. The thermal stability of these compounds enabled crystallization of [SiPi'' 3]Co(H2) which, along with the related (TP'i'B)Co(H2) complex also developed in our laboratory, represent the first structurally characterized dihydrogen adducts of cobalt. Additional comparisons are made between the relative N2 and H2 binding strengths of this system and those of the structurally and electronically related family of [SiPR3] and (TpRB) metal complexes. Appendix A The asymmetric dinucleating ligand [NOPPh], designed to contain both a hard, N-donor binding site and a soft-P-donor binding site, is synthesized and shown to form a diiron complex that features asymmetric bonding to the bridging acetates. The corresponding symmetric, allphosphine dinucleating ligand [POPPh], proves to be more conducive to further study, and provides access to the symmetric diiron, di-([mu]-bromide) starting material {[POPPh ]Fe 2Br2} {BArF4 }. Addition of hydrazine generates the asymmetric, unbridged N2H4 adduct, which features localized diamagnetic and paramagnetic iron centers. The conformation of this species additionally demonstrates the flexibility of this ligand framework. Reduction of the diiron(II) starting material in the presence of PMe3 results in formation of a putative asymmetric iron(O)/iron(I) dimetallic complex, in which an N2 molecule is bound to the diamagnetic iron center, while the PMe3 is ligated to the high-spin iron center and rendered NMR silent. The N2 ligand is shown to be reversibly displaced by H2 , suggesting the formation of a dihydrogen adduct, as well as by CO2, which is postulated to bind as a bent, [eta]2(C,O) ligand.
Book Synopsis Synthesis and Characterization of Redox-noninnocent Pyrazine(diimine) Iron Complexes and an Inverted Pyridine(diimine) Ligand by : Jaylan Billups
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.
Book Synopsis The Synthesis, Reactivity and Redox Behaviour of Tetraazaannulene Transition Metal Complexes by : Andrew J. Grist
Download or read book The Synthesis, Reactivity and Redox Behaviour of Tetraazaannulene Transition Metal Complexes written by Andrew J. Grist and published by . This book was released on 1992 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Oxidation State Roulette by : Brandon Fitchett
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.
Book Synopsis Expanding the Chemistry of D0 Transition Metals Through Redox-active Ligands by : Nicole Annette Ketterer
Download or read book Expanding the Chemistry of D0 Transition Metals Through Redox-active Ligands written by Nicole Annette Ketterer and published by . This book was released on 2008 with total page 368 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Synthesis and Reactivity of Group 9 Complexes Featuring Redox Non-innocent Ligands by : Hagit Ben-Daat Levin
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.
Book Synopsis Synthesis of Low-coordinate Transition Metal Bis(alkoxide) Complexes and Their Reactivity Toward Small Molecules by : Maryam Yousif
Download or read book Synthesis of Low-coordinate Transition Metal Bis(alkoxide) Complexes and Their Reactivity Toward Small Molecules written by Maryam Yousif and published by . This book was released on 2017 with total page 217 pages. Available in PDF, EPUB and Kindle. Book excerpt: This dissertation focused on the synthesis of new transition metal complexes in bis(alkoxide) ligand environments and the investigation of their reactivity in nitrene-group transfer catalysis and small molecule activation. Treatment of Cr(N(SiMe3)2)2(THF)2 with two equivalents of HOR (OR = OCtBu2Ph) led to the formation of the chromium(II) alkoxide dimer, Cr2(OR)4. Upon the reaction with bulky aryl and alkyl azides, Cr2(OR)4 led to the stable Cr(IV) mono(imido) complexes, Cr(OR)2(NR), featuring trigonal planar metal centers. In contrast, less bulky aryl azides led to the formation of chromium (VI) bis(imido) complexes Cr(OR)2(NR)2, independent of the amount of azide used. Chromium(IV) mono(imido) species Cr(OR)2(NR) is capable of nitrene transfer to isocyanides to form asymmetric carbodiimides (RNCNR'). When excess isocyanide is added to Cr(OR)2(NR), a new chromium(II) complex, Cr(OR)2(CNR2)4, was identified by X-ray crystallography. This tetrakis(isocyanide) chromium(II) complex is also capable of forming carbodiimide when azide is introduced. Efficient catalytic formation of carbodiimides was obtained using 2.5 mol% of Cr2(OR)4 for the mixtures of bulky organoazides and isocyanides; no catalytic reactivity was observed for the non-bulky aryl azides. DFT calculations suggest that trigonal CrIV(OR)2(NR) intermediate is the key species in the reaction mechanism as, due to it coordinative unsaturation, it allows isocyanide binding to the metal, which enables subsequent C-N bond formation. A bulkier alkoxide ligand HOR' (R = CtBu2(3,5-Ph2Ph)) was synthesized by lithium halogen exchange reaction. The protonolysis of the metal complexes, M(N(SiMe3)2(THF)x, with HOR' enabled an easy isolation of new bis(alkoxide) precursors M(OR')2(THF)2 (where M = Cr, Co, Fe) featuring cis-divacant octahedral geometry. The chemistry of the iron bis(alkoxide) compound Fe(OR')2(THF)2 with the variety of aryl azides was investigated.
Book Synopsis 1. Ortho-linked Polyaryloxide and Sterically Hindered Biphenoxide Ligands-synthesis and Metal Coordination Chemistry ; 2. Synthesis, Characterization, and Reactivity of Bis[hydrotris(pyrazol-1-yl)borato]titanium(II) by : Ajay Kayal
Download or read book 1. Ortho-linked Polyaryloxide and Sterically Hindered Biphenoxide Ligands-synthesis and Metal Coordination Chemistry ; 2. Synthesis, Characterization, and Reactivity of Bis[hydrotris(pyrazol-1-yl)borato]titanium(II) written by Ajay Kayal and published by . This book was released on 2002 with total page 574 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Syntheses of Novel Bis(alkylimino)acenaphthene (BIAN) and Tetrakis(arylimino)pyracene (TIP) Ligands and Studies of Their Redox Chemistry by : Kalyan Vikram Vasudevan
Download or read book Syntheses of Novel Bis(alkylimino)acenaphthene (BIAN) and Tetrakis(arylimino)pyracene (TIP) Ligands and Studies of Their Redox Chemistry written by Kalyan Vikram Vasudevan and published by . This book was released on 2009 with total page 496 pages. Available in PDF, EPUB and Kindle. Book excerpt: The evolution of the present work began with the syntheses of novel bis(alkylimino)acenaphthene (BIAN) ligands. At the outset of this research, despite the presence of dozens of aryl-BIAN ligands in the literature, there were as of yet no reported BIAN ligands bearing alkyl substituents. Given the nearly ubiquitous use of transition metal complexes of alkyl diazabutadiene (DAB) ligands for e.g. catalysis and as ligands for carbene chemistry, interest was generated in developing this emerging field of synthetic chemistry. Initial studies focused on the synthesis of alkyl-BIAN ligands since the traditional synthetic approaches that had been developed for aryl-BIAN ligands were unsuccessful for the alkyl analogues. As an alternate synthetic route, it was decided to employ amino- and imino-alane transfer reagents which had previously proved successful for the conversion of C=O into C=N-R functionalities. While this transfer route had proved successful to synthesize moderate yields of highly fluorinated DAB ligands, it was unknown how or whether this methodology would apply in the case of alkylated BIAN systems. Over the past decade, there has been a surge of interest regarding lanthanide complexes that are capable of undergoing spontaneous electron transfer processes. There are several reports in the literature that describe the ability of Ln(II) ions to undergo spontaneous oxidation, thereby causing one-electron reduction of the coordinated ligand and generally resulting in the corresponding Ln(III) complex. The present work focused on an enhanced understanding of the electronic communication between the lanthanide and the attached ligand. Particular emphasis was placed on defining the resulting oxidation states and the manner in which delocalized electrons of the radical anion species travel over a conjugated system. This fundamental information was gleaned from single-crystal X-ray diffraction studies and magnetic moment measurements that were obtained using the Evans method. Additional insights stemmed from the use of more classical techniques such as IR and NMR spectroscopy. In favorable cases, the presence or absence of spectral peaks can permit assignment of the lanthanide oxidation state. Accordingly, the research plan was to synthesize a series of BIAN-supported decamethyllanthanocene complexes with the goal of learning how to control the spontaneous charge transfer that had been reported in the literature. A longer term goal was to develop a bifunctional ligand of the BIAN type that was capable of accommodating two lanthanide or main group element moieties. Systems with tunable electronic interactions between lanthanide or main group elements are of interest because they offer the prospect of extended delocalization of electron density. Systems of this type have potential applications as e.g. molecular wires and single-molecule magnets. Indeed, such systems have been investigated by using bis(bipyridyl) and bis(terpyridyl) ligands to support two redox-active moieties. However, in the present work, it was recognized that a bifunctional BIAN-type ligand might be of considerable interest as the supporting structure for studying the communication between lanthanide or main group element moieties. A synthesis of variously substituted tetrakis(imino)pyracene (TIP) ligands was therefore undertaken. The flat, rigid nature of the TIP ligands rendered them ideal scaffolds for studying the redox behavior and electronic communication between lanthanide or main group element centers. The new TIP ligand class also proved to be useful for the assembly of the first example of a metallopolymer based on a BIAN-type ligand.
Book Synopsis Synthesis, Reactivity and Computational Studies of Redoxactive Indium Thiolate Complexes by : Padmapriya Srinivasan
Download or read book Synthesis, Reactivity and Computational Studies of Redoxactive Indium Thiolate Complexes written by Padmapriya Srinivasan and published by . This book was released on 2022 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Green Chemistry initiatives have recently been at the forefront of both industrial and academic communities in order to address fundamental scientific challenges of protecting human health and the environment. The Twelve Principles of Green Chemistry, of which catalysis is a primary tenet and the main motivation for this project, has led the path to reduce waste production in the chemical industry. The principle of catalysis states that catalytic reactions necessarily produce less waste than stoichiometric reactions. Traditionally, precious and toxic heavy transition metals such as platinum and palladium have been used as metal centres in catalysts because of their stability, favourable redox properties, and ease of characterization. These concerns prompted this research in finding more environmentally friendly alternatives as metal centres in catalysis, such as main group complexes. Indium is a heavy main group metal that is environmentally benign. It is most stable in the +3 oxidation state and, notably, does not possess other readily accessible oxidation states. To make indium complexes redox-active, so-called "non-innocent" redox-active ligands are being explored. The current work seeks to synthesize a series of redox-active indium catalysts with varied steric bulk about the indium centre and different redox-active ligands. The goals of this study are to first synthesize and structurally characterize organometallic indium compounds with the redox-active ligand 2-amninobenzenethiol, and then test the reactivity of indium complexes with dithiolate ligands using mild oxidizing agents. A third goal is to use DFT methods to rationalize the synthesized complexes in terms of structure, reactivity, bonding motifs, and in interpreting the experimental spectroscopic data.
Book Synopsis Studies on the Synthesis and Reactivity of Tantalum and Ruthenium Complexes Containing Pyrrolyl and Indolyl Ligands by : Keith Gregory Parker
Download or read book Studies on the Synthesis and Reactivity of Tantalum and Ruthenium Complexes Containing Pyrrolyl and Indolyl Ligands written by Keith Gregory Parker and published by . This book was released on 1995 with total page 340 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Design, Synthesis, and Reactivity of Bimetallic Complexes of Dimethylplatinum(II) Containing Ditopic Ligands by : Matthew S. McCready
Download or read book Design, Synthesis, and Reactivity of Bimetallic Complexes of Dimethylplatinum(II) Containing Ditopic Ligands written by Matthew S. McCready and published by . This book was released on 2015 with total page 658 pages. Available in PDF, EPUB and Kindle. Book excerpt: This thesis describes a study of monometallic and bimetallic dimethylplatinum(II) complexes containing ditopic nitrogen donor ligands. This work details the design and synthesis of side-to-side and cofacial arranged ligands and their respective coordination chemistry. The study of the synthesis, characterization and reaction mechanisms of the various dimethylplatinum(II) complexes is outlined in detail with special emphasis focused on the reactivity of the complexes towards oxidative addition. The ditopic ligand 6-dppd, 1,4-di(2-pyridyl)-5,6,7,8,9,10- hexahydrocycloocta[d]pyridazine, was observed to coordinate only a single equivalent of a platinum(II) center. The inability to coordinate a second equivalent, even through an assisted bridging atom, is presumed to be due to a steric clash between the free pyridyl group and the cyclooctyl backbone. In attempts to make heterobimetallic complexes of 6-dppd, the complex [PtMe2(6-dppd)] was observed to react preferentially with mercuric halides by oxidative addition rather than coordination of the mercuric salt in the second coordination site giving complexes [PtXMe2(HgX)(6-dppd)] where X = Br, Cl, OAc. This indicates that the platinum center is actually a better nucleophile than the free pyridyl nitrogen atom. The oxidative addition of solvent dichloromethane was also observed showing the enhancedreactivity of [PtMe2(6-dppd)]. Finally, [PtMe2(6-dppd)] was treated with DCl at low temperature to give the deuteridoplatinum(IV) complex. The deuteridoplatinum(IV) complex reductively eliminates methane in solution and extensive H/D exchange occurs into the CH4 product at low temperature indicating very easy reversibility of the exchange between hydridomethylplatinum(IV) and methaneplatinum(II) complexes. The abstraction of a chloride ligand from [PtClMe(6-dppd)] led to the formation of a complex dimer structure endo, endo-[Pt2Me2(?2-?3-6-dppd)2][OTf]2. This process allowed for the formation of a bimetallic platinum(II) complex which retained the initial stereochemistry. The protonolysis of [PtMe2(6-dppd)] with one equivalent of HOTf led to the generation of methane gas and the concomitant formation of both endo, endo-[Pt2Me2(?2-?3-6-dppd)2][OTf]2 and exo, exo-[Pt2Me2(?2-?3-6-dppd)2][OTf]2. The structures of the exo isomeric clamshell dimers appeared much less sterically hindered in the solid state and were observed experimentally and computationally to be the thermodynamically preferred isomers. The mechanism, selectivity and reversibility of this isomerism process was explored in detail. The reactions of [PtMe2(6-dppd)] with alkyl bromides RCH2Br, which possess hydrogen bonding functionality, result in the formation of stable organoplatinum(IV) complexes capable of forming supramolecular structure via hydrogen bonding. Both intra and inter molecular hydrogen bonding is observed in the formation of supramolecular architectures which self-assemble in the solid state through additional?-stacking and weak secondary interactions. The new anthracene derived ditopic ligands, bpad = N1,N8-bis(pyridin-2- ylmethylene)anthracene-1,8-diamine and adpa = (N, N)-4,4'-(anthracene-1,8-diylbis(ethyne- 2,1-diyl))-bis(N-(pyridin-2-ylmethylene)aniline) were prepared, characterized and used to coordinate dimethylplatinum(II) centers giving cofacial bimetallic complexes of dimethylplatinum(II). [Pt2Me4(bpad)] was shown to degrade over time in solution through a proposed metalation event involving the anthracene backbone. The oxidative addition of a variety of substrates was performed using [Pt2Me4(adpa)] giving stable diplatinum(IV) complexes as characterized by 1H NMR spectroscopy. The new xanthene derived ditopic ligands, ppxda = 2,7-di-tert-butyl-9,9-dimethyl-N4,N5-bis(4-(pyridin-2- ylmethyleneamino)phenyl)-xanthene-4,5-dicarboxamide and pmxda = 2,7-di-tert-butyl-9,9- dimethyl-bis(pyridine-2-ylmethylene)-9H-xanthene-4,5-diamine were prepared characterized and used to ligate two equivalents of a dimethylplatinum(II) center. Diplatinum complexes of both ligands were shown to easily undergo oxidative addition to give the corresponding diplatinum(IV) complexes which adopt the anti orientation. The syn alignment of metal centers was accessible through the abstraction of halides ligands and incorporation of bridging groups as is the case for the pyrazine bridged bimetallic platinum complex [Pt2Me6(C4H4N2)(pmxda)][OSO2CF3]2.
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