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Sigma-bond Metathesis
In organometallic chemistry, sigma-bond metathesis is a chemical reaction wherein a metal-ligand sigma bond undergoes metathesis (exchange of parts) with the sigma bond in some reagent. The reaction is illustrated by the exchange of lutetium(III) methyl complex with a hydrocarbon (R-H): :(C5Me5)2Lu-CH3 + R-H → (C5Me5)2Lu-R + CH4 This reactivity was first observed by Patricia Watson, a researcher at duPont.{{cite journal, author=Watson, Patricia, title=Methane exchange reactions of lanthanide and early-transition-metal methyl complexes, journal=Journal of the American Chemical Society, year=1983, volume=32, pages=6491–6493, doi=10.1021/ja00359a023 The reaction is mainly observed for complexes of metals with d0 configuration, e.g. complexes of Sc(III), Zr(IV), Nb(V), Ta(V), etc. f-Element complexes also participate, regardless of the number of f-electrons. The reaction is thought to proceed via cycloaddition. Indeed, the rate of the reaction is characterized by a highly n ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Organometallic Chemistry
Organometallic chemistry is the study of organometallic compounds, chemical compounds containing at least one chemical bond between a carbon atom of an organic molecule and a metal, including alkali, alkaline earth, and transition metals, and sometimes broadened to include metalloids like boron, silicon, and selenium, as well. Aside from bonds to organyl fragments or molecules, bonds to 'inorganic' carbon, like carbon monoxide (Metal carbonyl, metal carbonyls), cyanide, or carbide, are generally considered to be organometallic as well. Some related compounds such as transition metal hydrides and metal phosphine complexes are often included in discussions of organometallic compounds, though strictly speaking, they are not necessarily organometallic. The related but distinct term "metalorganics, metalorganic compound" refers to metal-containing compounds lacking direct metal-carbon bonds but which contain organic ligands. Metal β-diketonates, alkoxides, dialkylamides, and metal p ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chemical Reaction
A chemical reaction is a process that leads to the chemistry, chemical transformation of one set of chemical substances to another. When chemical reactions occur, the atoms are rearranged and the reaction is accompanied by an Gibbs free energy, energy change as new products are generated. Classically, chemical reactions encompass changes that only involve the positions of electrons in the forming and breaking of chemical bonds between atoms, with no change to the Atomic nucleus, nuclei (no change to the elements present), and can often be described by a chemical equation. Nuclear chemistry is a sub-discipline of chemistry that involves the chemical reactions of unstable and radioactive Chemical element, elements where both electronic and nuclear changes can occur. The substance (or substances) initially involved in a chemical reaction are called reagent, reactants or reagents. Chemical reactions are usually characterized by a chemical change, and they yield one or more Product (c ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sigma Bond
In chemistry, sigma bonds (σ bonds) or sigma overlap are the strongest type of covalent chemical bond. They are formed by head-on overlapping between atomic orbitals along the internuclear axis. Sigma bonding is most simply defined for diatomic molecules using the language and tools of symmetry groups. In this formal approach, a σ-bond is symmetrical with respect to rotation about the bond axis. By this definition, common forms of sigma bonds are s+s, pz+pz, s+pz and dz2+dz2 (where z is defined as the axis of the bond or the internuclear axis). Quantum theory also indicates that molecular orbitals (MO) of identical symmetry actually mix or ''hybridize''. As a practical consequence of this mixing of diatomic molecules, the wavefunctions s+s and pz+pz molecular orbitals become blended. The extent of this mixing (or hybridization or blending) depends on the relative energies of the MOs of like symmetry. For homodiatomics ( homonuclear diatomic molecules), bonding σ orbit ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lutetium
Lutetium is a chemical element; it has symbol Lu and atomic number 71. It is a silvery white metal, which resists corrosion in dry air, but not in moist air. Lutetium is the last element in the lanthanide series, and it is traditionally counted among the rare earth elements; it can also be classified as the first element of the 6th-period transition metals. Lutetium was independently discovered in 1907 by French scientist Georges Urbain, Austrian mineralogist Baron Carl Auer von Welsbach, and American chemist Charles James. All of these researchers found lutetium as an impurity in ytterbium. The dispute on the priority of the discovery occurred shortly after, with Urbain and Welsbach accusing each other of publishing results influenced by the published research of the other; the naming honor went to Urbain, as he had published his results earlier. He chose the name ''lutecium'' for the new element, but in 1949 the spelling was changed to ''lutetium''. In 1909, the priority was ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Rory Waterman (chemist)
Rory Waterman is an American chemist. He is a full professor and associate dean of inorganic, organometallic, and catalysis at the University of Vermont. Early life and education Waterman attended the University of Rochester for his Bachelor of Science and the University of Chicago for his Ph.D. After completing his doctoral degree in 2004, he accepted a two-year Miller Research Fellowship at the University of California, Berkeley. Career Waterman joined the University of Vermont's (UVM) college of arts and sciences as an assistant professor of chemistry in 2006. His research at UVM focuses on finding new ways to build chemical bonds, specifically in the chemical element Phosphorus. As a result of his research, he received the 2009 Alfred P. Sloan Award for outstanding early career scientists. Beyond this, Waterman also established research opportunities for Vermont high school and University of Vermont undergraduate students which resulted in him winning the 2009 Cottrell Scholar ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cycloaddition
In organic chemistry, a cycloaddition is a chemical reaction in which "two or more Unsaturated hydrocarbon, unsaturated molecules (or parts of the same molecule) combine with the formation of a cyclic adduct in which there is a net reduction of the Multiplicity (chemistry)#Molecules, bond multiplicity". The resulting reaction is a cyclization reaction. Many but not all cycloadditions are Concerted reaction, concerted and thus pericyclic. Nonconcerted cycloadditions are not pericyclic. As a class of addition reaction, cycloadditions permit carbon–carbon bond formation without the use of a nucleophile or electrophile. Cycloadditions can be described using two systems of notation. An older but still common notation is based on the size of linear arrangements of atoms in the reactants. It uses parentheses: where the variables are the numbers of linear atoms in each reactant. The product is a cycle of size . In this system, the standard Diels-Alder reaction is a (4 + 2)-cyc ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Entropy Of Activation
In chemical kinetics, the entropy of activation of a reaction is one of the two parameters (along with the enthalpy of activation) that are typically obtained from the temperature dependence of a reaction rate constant, when these data are analyzed using the Eyring equation of the transition state theory. The standard entropy of activation is symbolized and equals the change in entropy when the reactants change from their initial state to the activated complex or transition state ( = change, = entropy, = activation). Importance Entropy of activation determines the preexponential factor of the Arrhenius equation for temperature dependence of reaction rates. The relationship depends on the molecularity of the reaction: * for reactions in solution and unimolecular gas reactions *: , * while for bimolecular gas reactions *: . In these equations is the base of natural logarithms, is the Planck constant, is the Boltzmann constant and the absolute temperature. is the ideal gas ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Transition State
In chemistry, the transition state of a chemical reaction is a particular configuration along the reaction coordinate. It is defined as the state corresponding to the highest potential energy along this reaction coordinate. It is often marked with the double dagger (‡) symbol. As an example, the transition state shown below occurs during the SN2 reaction of bromoethane with a hydroxide anion: The activated complex of a reaction can refer to either the transition state or to other states along the reaction coordinate between reactants and products, especially those close to the transition state. Peter Atkins and Julio de Paula, ''Physical Chemistry'' (8th ed., W.H. Freeman 2006), p.809 According to the transition state theory, once the reactants have passed through the transition state configuration, they always continue to form products. History of concept The concept of a transition state has been important in many theories of the rates at which chemical re ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Redox
Redox ( , , reduction–oxidation or oxidation–reduction) is a type of chemical reaction in which the oxidation states of the reactants change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a decrease in the oxidation state. The oxidation and reduction processes occur simultaneously in the chemical reaction. There are two classes of redox reactions: * Electron transfer, Electron-transfer – Only one (usually) electron flows from the atom, ion, or molecule being oxidized to the atom, ion, or molecule that is reduced. This type of redox reaction is often discussed in terms of redox couples and electrode potentials. * Atom transfer – An atom transfers from one Substrate (chemistry), substrate to another. For example, in the rusting of iron, the oxidation state of iron atoms increases as the iron converts to an oxide, and simultaneously, the oxidation state of oxygen decreases as it accepts electrons r ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Carbon–hydrogen Bond Activation
In organic chemistry and organometallic chemistry, carbon–hydrogen bond activation ( activation) is a type of organic reaction in which a carbon–hydrogen bond is Bond cleavage, cleaved and replaced with a bond (X ≠ H is typically a main group element, like carbon, oxygen, or nitrogen). Some authors further restrict the term C–H activation to reactions in which a C–H bond, one that is typically considered to be "unreactive", interacts with a transition metal center M, resulting in its cleavage and the generation of an organometallic species with an M–C bond. The organometallic intermediate resulting from this step (sometimes known as the activation step) could then undergo subsequent reactions with other reagents, either ''in situ'' (often allowing the transition metal to be used in a Catalysis, catalytic amount) or in a separate step, to produce the Late-stage functionalization, functionalized product. The alternative term functionalization is used to describe any ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Metal-catalyzed σ-bond Rearrangement
The metal ion-catalyzed σ-bond rearrangement is a collection of chemical reactions that occur with highly strained organic compounds are treated with metal ions like Ag+, Rh(I), or Pd(II) based reagents.Michael B. Smith, Jerry March, March's Advanced Organic Chemistry, 5th Ed., John Wiley & Sons, Inc., 2001, p. 1459. +2ring openings are sometimes observed: : These rearrangements proceed via oxidative addition of strained rings. Such processes are related to the activation of cyclopropanes by transition metals. See also * Cyclobutane * Cubane * Cuneane Cuneane () is a Saturated and unsaturated compounds, saturated hydrocarbon with the Chemical formula, formula and a Molecular geometry, 3D structure resembling a wedge, hence the name. Cuneane may be produced from cubane by metal-ion-catalyzed � ... * Sigma bond metathesis References {{DEFAULTSORT:Metal-ion-catalyzed sigma-bond rearrangement Ring expansion reactions ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
