Synthesis of New Hemilabile Tetradentate Sulfur Functionalized N-heterocyclic Carbene Ligands for Transition Metal Catalysis PDF Download
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Author: Edward Cross
Publisher:
ISBN:
Category : Carbenes (Methylene compounds)
Languages : en
Pages :
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Author: Edward Cross
Publisher:
ISBN:
Category : Carbenes (Methylene compounds)
Languages : en
Pages :
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Author:
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ISBN:
Category :
Languages : en
Pages :
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The discovery of N-heterocyclic carbenes (NHC) has dramatically affected the world of catalysis. Their inherent properties that make them excellent auxiliary ligands for catalytic processes have countless laboratories worldwide probing and exploiting every notable feature they possess. However, while there is no shortage of attention in this field of research, there has been considerably less interest in NHCs with an ability chelate to metals via a mixed-donor ligand architecture. Thus, this thesis describes the synthesis and application of a ligand set comprised of bidentate mixed-donor NHC ligands. The ligands prepared all contain a mesitylimidazol-2-ylidene core unit, but incorporate different donor-functionalized tethers. These mixed-donor NHC ligands are synthesized by using a strong base, such as KN(SiMe3)2, to deprotonate the imidazolium salt precursors. This strategy was used to effectively prepare 1-mesityl-3-(2-(mesitylamino)ethyl)imidazol-2-ylidene, Mes[CNH] and 1-mesityl-3-(2-aminoethyl)imidazol-2-ylidene, Mes[CNH2]. Mes[CNH] was found to be a convenient proligand for the synthesis of various M-NHC (M = Rh, Ir, Ru, Pd, Ni, Fe, Ag, Li) compounds. These Mes[CNH]-M complexes demonstrated the hemilabile character of the Mes[CNH] ligand forming complexes that incorporated either a coordinated or uncoordinated amino tether. Mes[CNH]M(diene)Cl, Mes[CN]M(diene) and [Mes[CNH]M(diene)]BF4(M = Rh, Ir; diene = 1,5-cyclooctadiene, 2,5-norbornadiene) were synthesized and investigated for their ability to perform hydrogenation and hydrosilylation reactions with various substrates. Mes[CNH]Ru(=CHPh)(PCy3)Cl2, Mes[CNH]Ru(=CHPh)(py)Cl2 (py = pyridine) and Mes[CNH]Ru(=CHPh)(PMe3)Cl2 were also synthesized and fully characterized. The activity of the former two Ru complexes was studied for their ability to catalyze ring-closing metathesis (RCM) and ring-opening metathesis polymerization (ROMP) reactions. In addition, the phosphine dissociation rate of Mes[CNH]Ru(=CHPh)(PCy3).
Author: Frank Glorius
Publisher: Springer
ISBN: 3540369309
Category : Science
Languages : en
Pages : 240
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In this book leading experts have surveyed major areas of application of NHC metal complexes in catalysis. The authors have placed a special focus on nickel- and palladium-catalyzed reactions, on applications in metathesis reactions, on oxidation reactions and on the use of chiral NHC-based catalysts. This compilation is rounded out by an introductory chapter and a chapter dealing with synthetic routes to NHC metal complexes.
Author: Pengfei Ai
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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The purpose of this work was the synthesis of N,N'-diphosphanyl-functionalized NHC ligands andtheir coordination chemistry. The novel stable and rigid tridentate N,N'-diphosphanyl-imidazol-2-ylidene was synthesized and experimental and computational information on its stability weregained. It served as a unique platform for the synthesis of novel mono-, di-, tri-, penta-, hexanuclear complexes with the coinage metals (Cu, Ag and Au), exhibiting rare structural features. The mono- and dinuclear complexes with one or two dangling P-donors provided rational access to heterotrinuclear complexes. All these coinage metal complexes have short metal-metalseparations, indicating the presence of d10-d10 interactions, and display excellent luminescentproperties. Partial or complete transmetallation of the homotrinuclear Cu or Ag complexes withPd(0) precursors led to hetero-trinuclear complexes with d10-d10 interactions. In addition to itsbridging behavior, this ligand also showed its chelating behavior in Pd or Cr(III) complexes. Thelatter displayed superior performance in ethylene oligomerization than the Cr(II) complexes andgave mostly oligomers.
Author: Steven Nolan
Publisher: Thieme
ISBN: 3132414034
Category : Science
Languages : en
Pages : 816
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The field of N-heterocyclic carbenes, whether in transition-metal catalysis or organocatalysis, is rapidly evolving towards applications, but is also still very active on the catalyst development front. Significant advances have been made over the past two decades and the development of these reactions has dramatically improved the efficiency of organic synthesis. N-Heterocyclic carbene based catalysts are now widely applied in the area of synthesis of both natural products and therapeutic agents. "Science of Synthesis: N-Heterocyclic Carbenes in Catalytic Organic Synthesis" presents the most commonly used and significant metal- or non-metal-catalyzed reactions for modern organic synthesis. The basic principles and current state-of-the-art of the methods are covered. Scope, limitations, and mechanism of these reactions are discussed and key experimental procedures are included. Typical examples of target synthesis are often provided to show the utility and inspire further applications.
Author: Michael Holtz-Mulholland
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 151
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Author: Sebastian Martin Gischig
Publisher:
ISBN:
Category :
Languages : en
Pages : 372
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Author: Kai Yang Wan
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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In this thesis, the synthetic protocol for a new class of enantiopure, primary-amine tethered N-heterocyclic carbene (NHC) ligands is described. The synthesis, coordination chemistry, and applications in catalysis for three ligands from this class with general formula (S,S)/(R,R)-H2N-CHPh-CHPh-NHC (NHC = -NCHCHN(C)R, R = Me, tBu, or Mes) are reported. The imidazolium salt of these ligands can be prepared in high yield and purity from the SN1 reaction between chiral sulfamidates and the corresponding N-substituted imidazoles. The method of coordination of the NHC ligands to metals depends on the acidity of the C-H functional in the imidazolium salts. Silver and copper compounds can be prepared in high yield with the ligand to the metal ratio of 2:1 or 1:1. Ruthenium, iridium, and rhodium complexes can also be prepared via transmetallation from the silver or copper reagents, intramolecular base deprotonation, or C-H oxidative addition. Four ruthenium complexes and two iridium complexes based on these ligands were proven active for ketone hydrogenation, under relatively mild condition (50°C, 25 bar H2(g)). Three half-sandwich ruthenium compounds containing Cp (cyclopentadienyl) or Cp* (1,2,3,4,5-pentamethylcyclopentadienyl) are highly active aryl and alkyl hydrogenation catalysts with TOF (turnover frequency) up to 67 s-1, TON (turnover number) up to 104, and ee (enantiomeric excess) up to 86%. An experimental and computational study of the half-sandwich ruthenium systems suggests that the heterolytic splitting of dihydrogen over the metal-amido bond and hydride transfer from the catalyst to the substrate can both be rate-determining. An alcohol-assisted mechanism was also calculated to explain the rate enhancement when the catalysis was conducted in polar, protic solvents such as 2-PrOH. A full experimental and computational study was also performed for a Fe(P-NH-P') system. Similarly, heterolytic splitting and hydride transfer are the two most energy demanding transition states. In addition, the enantiodetermining step (EDS) of this asymmetric ketone hydrogenation catalyst was calculated, and the origins of enantioselectivity were summarized as steric repulsion, the high compressibility of the backbone, and H-bond contributed stabilization.
Author: Halliru Ibrahim
Publisher:
ISBN:
Category : Aromatic amines
Languages : en
Pages : 248
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