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CPhos
CPhos is a phosphine ligand derived from biphenyl. It is a white solid that is soluble in organic solvents. Its palladium complexes exhibit high activity for Negishi coupling reactions involving aryl bromides, chlorides and triflates. CPhos mediated reactions performed with secondary (sp3) alkylzinc halides often give excellent yields, with low conversion to the frequently encountered primary substituted by-products. Utility in Negishi Coupling A simplified scheme showing the reaction course of isopropylzinc bromide with an aryl halide is shown below. Processes leading to byproduct formation are highlighted in red. Oxidative addition (1) of the aryl halide to the palladium-ligand complex followed by transmetalation (2) gives intermediate B which can undergo reductive elimination (3) to afford the desired isopropyl arene C. However, intermediate B can also undergo β-hydride elimination (4) to afford D, which can either reductively eliminate (3’) to afford de-halogenated ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dialkylbiaryl Phosphine Ligands
Dialkylbiaryl phosphine ligands are phosphine ligands that are used in homogeneous catalysis. They have proved useful in Buchwald-Hartwig amination and etherification reactions as well as Negishi cross-coupling, Suzuki-Miyaura cross-coupling, and related reactions. In addition to these Pd-based processes, their use has also been extended to transformations catalyzed by nickel, gold, silver, copper, rhodium, and ruthenium, among other transition metals. General features Dialkylbiaryl phosphine ligands are air-stable solids. Many are available commercially. They often can be synthesized in from inexpensive starting materials. One pot protocols have been conducted on >10 kg scales. Their enhanced catalytic activity over other ligands in palladium-catalyzed coupling reactions have been attributed to their electron-richness, steric bulk, and some special structural features. In particular, cyclohexyl, ''t''-butyl, and adamantyl groups on the phosphorus are used for this ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
SPhos
SPhos is a phosphine ligand derived from biphenyl. Its palladium complexes exhibit high activity for Suzuki coupling reactions involving aryl chlorides, which are unreactive with palladium complexes of most other phosphine ligands. The ligand has convenient handling characteristics since it is air-stable.{{cite journal , author1=Altman, R.A. , author2=Buchwald, S.L. , title = Pd-Catalyzed Suzuki-Miyaura Reactions of Aryl Halides Using Bulky Biarylmonophosphine Ligands , year = 2007 , journal = Nature Protocols , volume = 2 , issue = 12, pages = 3115–3121 , doi = 10.1038/nprot.2007.411 , pmid = 18079711 See also * XPhos XPhos is a phosphine ligand derived from biphenyl. Its palladium complexes exhibit high activity for Buchwald-Hartwig amination reactions involving aryl chlorides and aryl tosylates. Both palladium and copper complexes of the compound exhibit h ... * CPhos * Suzuki reaction References Tertiary phosphines ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Negishi Coupling
The Negishi coupling is a widely employed transition metal catalyzed cross-coupling reaction. The reaction couples organic halides or triflates with organozinc compounds, forming carbon-carbon bonds (C-C) in the process. A palladium (0) species is generally utilized as the metal catalyst, though nickel is sometimes used. A variety of nickel catalysts in either Ni0 or NiII oxidation state can be employed in Negishi cross couplings such as Ni(PPh3)4, Ni(acac)2, Ni(COD)2 etc. : :* The leaving group X is usually chloride, bromide, or iodide, but triflate and acetyloxy groups are feasible as well. X = Cl usually leads to slow reactions. :* The organic residue R = alkenyl, aryl, allyl, alkynyl or propargyl. :* The halide X' in the organozinc compound can be chloride, bromine or iodine and the organic residue R' is alkenyl, aryl, allyl, alkyl, benzyl, homoallyl, and homopropargyl. :* The metal M in the catalyst is nickel or palladium :* The ligand L in the catalyst can be triphenylp ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
XPhos
XPhos is a phosphine ligand derived from biphenyl. Its palladium complexes exhibit high activity for Buchwald-Hartwig amination reactions involving aryl chlorides and aryl tosylates. Both palladium and copper complexes of the compound exhibit high activity for the coupling of aryl halides and aryl tosylates with various amides. It is also an efficient ligand for several commonly used C–C bond-forming cross-coupling reactions, including the Negishi, Suzuki, and the copper-free Sonogashira coupling reactions. It is especially efficient and general when employed as a ( 2-aminobiphenyl)-cyclometalated palladium mesylate precatalyst complex (Buchwald's third generation precatalyst system), XPhos-G3-Pd, which is commercially available and stable to bench storage. The ligand itself also has convenient handling characteristics as a crystalline, air-stable solid.{{cite journal , author1=Altman, R.A. , author2=Fors, B.P. , author3=Buchwald, S.L. , title = Pd-Catalyzed Amination Reacti ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Transmetalation
Transmetalation (alt. spelling: transmetallation) is a type of organometallic reaction that involves the transfer of ligands from one metal to another. It has the general form: :M1–R + M2–R′ → M1–R′ + M2–R where R and R′ can be, but are not limited to, an alkyl, aryl, alkynyl, allyl, halogen, or pseudohalogen group. The reaction is usually an irreversible process due to thermodynamic and kinetic reasons. Thermodynamics will favor the reaction based on the electronegativities of the metals and kinetics will favor the reaction if there are empty orbitals on both metals. There are different types of transmetalation including redox-transmetalation and redox-transmetalation/ligand exchange. During transmetalation the metal-carbon bond is activated, leading to the formation of new metal-carbon bonds. Transmetalation is commonly used in catalysis, synthesis of main group complexes, and synthesis of transition metal complexes. Types of transmetalation There are two main types ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Negishi Coupling Mechanism
is a Japanese surname and place name. It may refer to: * Ei-ichi Negishi, a Japanese chemist who was awarded the 2010 Nobel Prize in Chemistry ** Negishi coupling, a chemical reaction discovered by Ei-ichi Negishi in 1977 * Kichitaro Negishi, a Japanese film director * , a neighborhood of Taitō, formerly a village * Negishi, a neighborhood of Isogo-ku, Yokohama, formerly a village ** Negishi Line, a railway line that runs between Yokohama and Ōfuna stations ** Negishi Station (Kanagawa) * Negishi Station (Fukushima) * Negishi (''My-HiME Destiny''), a fictional character in the light novel series ''My-HiME Destiny'' * Takashi Negishi, Japanese economist who extended general equilibrium modeling for competition and welfare ** Negishi welfare weights, a weight function developed by Takashi Negishi in 1972 that freezes income distributions * Negishi Shingorō, a Japanese martial artist ** Negishi-ryū, Japanese shurikenjutsu is a general term describing the traditional Japanes ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Insertion Reaction
An insertion reaction is a chemical reaction where one chemical entity (a molecule or molecular fragment) interposes itself into an existing bond of typically a second chemical entity ''e.g.'': : + \longrightarrow The term only refers to the result of the reaction and does not suggest a mechanism. Insertion reactions are observed in organic, inorganic, and organometallic chemistry. In cases where a metal-ligand bond in a coordination complex is involved, these reactions are typically organometallic in nature and involve a bond between a transition metal and a carbon or hydrogen. It is usually reserved for the case where the coordination number and oxidation state of the metal remain unchanged. When these reactions are reversible, the removal of the small molecule from the metal-ligand bond is called extrusion or elimination. There are two common insertion geometries— 1,1 and 1,2 (pictured above). Additionally, the inserting molecule can act either as a nucleophile or a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Beta-Hydride Elimination
β-Hydride elimination is a reaction in which an alkyl group bonded to a metal centre is converted into the corresponding metal-bonded hydride and an alkene. The alkyl must have hydrogens on the β-carbon. For instance butyl groups can undergo this reaction but methyl groups cannot. The metal complex must have an empty (or vacant) site ''cis'' to the alkyl group for this reaction to occur. Moreover, for facile cleavage of the C–H bond, a d electron pair is needed for donation into the σ* orbital of the C–H bond. Thus, d0 metals alkyls are generally more stable to β-hydride elimination than d2 and higher metal alkyls and may form isolable agostic complexes, even if an empty coordination site is available. The β-hydride elimination can either be a vital step in a reaction or an unproductive side reaction. The Shell higher olefin process relies on β-hydride elimination to produce α-olefins which are used to produce detergents. Illustrative of a sometimes undesirable ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Phosphine Ligand
A metal-phosphine complex is a In coordination complex containing one or more phosphine ligands. Almost always, the phosphine is an organophosphine of the type R3P (R = alkyl, aryl). Metal phosphine complexes are useful in homogeneous catalysis. Prominent examples of metal phosphine complexes include Wilkinson's catalyst (Rh(PPh3)3Cl), Grubbs' catalyst, and tetrakis(triphenylphosphine)palladium(0). Preparation Many metal phosphine complexes are prepared by reactions of metal halides with preformed phosphines. For example, treatment of a suspension of palladium chloride in ethanol with triphenylphosphine yields monomeric bis(triphenylphosphine)palladium(II) chloride units. : dCl2sub>n + 2PPh3 → PdCl2(PPh3)2 The first reported phosphine complexes were ''cis''- and ''trans''-PtCl2(PEt3)2 reported by Cahours and Gal in 1870. Often the phosphine serves both as a ligand and as a reductant. This property is illustrated by the synthesis of many platinum-metal complexes of triphenylph ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ligand
In coordination chemistry, a ligand is an ion or molecule (functional group) that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's electron pairs, often through Lewis bases. The nature of metal–ligand bonding can range from covalent to ionic. Furthermore, the metal–ligand bond order can range from one to three. Ligands are viewed as Lewis bases, although rare cases are known to involve Lewis acidic "ligands". Metals and metalloids are bound to ligands in almost all circumstances, although gaseous "naked" metal ions can be generated in a high vacuum. Ligands in a complex dictate the reactivity of the central atom, including ligand substitution rates, the reactivity of the ligands themselves, and redox. Ligand selection requires critical consideration in many practical areas, including bioinorganic and medicinal chemistry, homogeneous catalysis, and environmental chemi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Biphenyl
Biphenyl (also known as diphenyl, phenylbenzene, 1,1′-biphenyl, lemonene or BP) is an organic compound that forms colorless crystals. Particularly in older literature, compounds containing the functional group consisting of biphenyl less one hydrogen (the site at which it is attached) may use the prefixes xenyl or diphenylyl. It has a distinctively pleasant smell. Biphenyl is an aromatic hydrocarbon with a molecular formula (C6H5)2. It is notable as a starting material for the production of polychlorinated biphenyls (PCBs), which were once widely used as dielectric fluids and heat transfer agents. Biphenyl is also an intermediate for the production of a host of other organic compounds such as emulsifiers, optical brighteners, crop protection products, and plastics. Biphenyl is insoluble in water, but soluble in typical organic solvents. The biphenyl molecule consists of two connected phenyl rings. Properties and occurrence Biphenyl occurs naturally in coal tar, crude oil, a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Reaction Mechanism
In chemistry, a reaction mechanism is the step by step sequence of elementary reactions by which overall chemical change occurs. A chemical mechanism is a theoretical conjecture that tries to describe in detail what takes place at each stage of an overall chemical reaction. The detailed steps of a reaction are not observable in most cases. The conjectured mechanism is chosen because it is thermodynamically feasible, and has experimental support in isolated intermediates (see next section) or other quantitative and qualitative characteristics of the reaction. It also describes each reactive intermediate, activated complex, and transition state, and which bonds are broken (and in what order), and which bonds are formed (and in what order). A complete mechanism must also explain the reason for the reactants and catalyst used, the stereochemistry observed in reactants and products, all products formed and the amount of each. The electron or arrow pushing method is often used in i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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