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Transition Metal Carbene Complex
A transition metal carbene complex is an organometallic compound featuring a divalent organic ligand. The divalent organic ligand coordinated to the metal center is called a carbene. Carbene complexes for almost all transition metals have been reported. Many methods for synthesizing them and reactions utilizing them have been reported. The term carbene ligand is a formalism since many are not derived from carbenes and almost none exhibit the reactivity characteristic of carbenes. Described often as , they represent a class of organic ligands intermediate between alkyls and carbynes . They feature in some catalytic reactions, especially alkene metathesis, and are of value in the preparation of some fine chemicals. Classification Metal carbene complexes are often classified into two types. The Fischer carbenes named after Ernst Otto Fischer feature strong π-acceptors at the metal and being electrophilic at the carbene carbon atom. Schrock carbenes, named after Richard R. Sch ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Organometallic Compound
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 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 " metalorganic compound" refers to metal-containing compounds lacking direct metal-carbon bonds but which contain organic ligands. Metal β-diketonates, alkoxides, dialkylamides, and metal phosphine complexes are r ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Amino
In chemistry, amines (, ) are compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are formally derivatives of ammonia (), wherein one or more hydrogen atoms have been replaced by a substituent such as an alkyl or aryl group (these may respectively be called alkylamines and arylamines; amines in which both types of substituent are attached to one nitrogen atom may be called alkylarylamines). Important amines include amino acids, biogenic amines, trimethylamine, and aniline; Inorganic derivatives of ammonia are also called amines, such as monochloramine (). The substituent is called an amino group. Compounds with a nitrogen atom attached to a carbonyl group, thus having the structure , are called amides and have different chemical properties from amines. Classification of amines Amines can be classified according to the nature and number of substituents on nitrogen. Aliphatic amines contain only H and alkyl substituents. Arom ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tebbe's Reagent
Tebbe's reagent is the organometallic compound with the formula (C5H5)2TiCH2ClAl(CH3)2. It is used in the methylenation of carbonyl compounds, that is it converts organic compounds containing the R2C=O group into the related R2C=CH2 derivative. It is a red solid that is pyrophoric in the air, and thus is typically handled with air-free techniques. It was originally synthesized by Fred Tebbe at DuPont Central Research. Tebbe's reagent contains two tetrahedral metal centers linked by a pair of bridging ligands. The titanium has two cyclopentadienyl (, or Cp) rings and aluminium has two methyl groups. The titanium and aluminium atoms are linked together by both a methylene bridge (-CH2-) and a chloride atom in a nearly square-planar (Ti–CH2–Al–Cl) geometry. The Tebbe reagent was the first reported compound where a methylene bridge connects a transition metal (Ti) and a main group metal (Al).Herrmann, W.A., "The Methylene Bridge" ''Advances in Organometallic Chemistry'' 1982 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tantalum
Tantalum is a chemical element with the symbol Ta and atomic number 73. Previously known as ''tantalium'', it is named after Tantalus, a villain in Greek mythology. Tantalum is a very hard, ductile, lustrous, blue-gray transition metal that is highly corrosion-resistant. It is part of the refractory metals group, which are widely used as components of strong high-melting-point alloys. It is a group 5 element, along with vanadium and niobium, and it always occurs in geologic sources together with the chemically similar niobium, mainly in the mineral groups tantalite, columbite and coltan. The chemical inertness and very high melting point of tantalum make it valuable for laboratory and industrial equipment such as reaction vessels and vacuum furnaces. It is used in tantalum capacitors for electronic equipment such as computers. Tantalum is considered a technology-critical element by the European Commission. History Tantalum was discovered in Sweden in 1802 by Anders ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Titanium
Titanium is a chemical element with the Symbol (chemistry), symbol Ti and atomic number 22. Found in nature only as an oxide, it can be reduced to produce a lustrous transition metal with a silver color, low density, and high strength, resistant to corrosion in sea water, aqua regia, and chlorine. Titanium was discovered in Cornwall, Kingdom of Great Britain, Great Britain, by William Gregor in 1791 and was named by Martin Heinrich Klaproth after the Titan (mythology), Titans of Greek mythology. The element occurs within a number of minerals, principally rutile and ilmenite, which are widely distributed in the Earth's crust and lithosphere; it is found in almost all living things, as well as bodies of water, rocks, and soils. The metal is extracted from its principal mineral ores by the Kroll process, Kroll and Hunter process, Hunter processes. The most common compound, titanium dioxide, is a popular photocatalysis, photocatalyst and is used in the manufacture of white pigments ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nucleophile
In chemistry, a nucleophile is a chemical species that forms bonds by donating an electron pair. All molecules and ions with a free pair of electrons or at least one pi bond can act as nucleophiles. Because nucleophiles donate electrons, they are Lewis bases. ''Nucleophilic'' describes the affinity of a nucleophile to bond with positively charged atomic nuclei. Nucleophilicity, sometimes referred to as nucleophile strength, refers to a substance's nucleophilic character and is often used to compare the affinity of atoms. Neutral nucleophilic reactions with solvents such as alcohols and water are named solvolysis. Nucleophiles may take part in nucleophilic substitution, whereby a nucleophile becomes attracted to a full or partial positive charge, and nucleophilic addition. Nucleophilicity is closely related to basicity. History The terms ''nucleophile'' and '' electrophile'' were introduced by Christopher Kelk Ingold in 1933, replacing the terms ''anionoid'' and ''catio ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
N-Butyllithium
''n''-Butyllithium C4H9Li (abbreviated ''n''-BuLi) is an organolithium reagent. It is widely used as a polymerization initiator in the production of elastomers such as polybutadiene or styrene-butadiene-styrene (SBS). Also, it is broadly employed as a strong base (superbase) in the synthesis of organic compounds as in the pharmaceutical industry. Butyllithium is commercially available as solutions (15%, 25%, 1.5 M, 2 M, 2.5 M, 10 M, etc.) in alkanes such as pentane, hexanes, and heptanes. Solutions in diethyl ether and THF can be prepared, but are not stable enough for storage. Annual worldwide production and consumption of butyllithium and other organolithium compounds is estimated at 2000 to 3000 tonnes. Although butyllithium is colorless, ''n''-butyllithium is usually encountered as a pale yellow solution in alkanes. Such solutions are stable indefinitely if properly stored,. but in practice, they degrade upon aging. Fine white precipitate (li ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Aldol Reaction
The aldol reaction is a means of forming carbon–carbon bonds in organic chemistry. Discovered independently by the Russian chemist Alexander Borodin in 1869 and by the French chemist Charles-Adolphe Wurtz in 1872, the reaction combines two carbonyl compounds (the original experiments used aldehydes) to form a new β-hydroxy carbonyl compound. These products are known as '' aldols'', from the ''ald''ehyde + alcoh''ol'', a structural motif seen in many of the products. Aldol structural units are found in many important molecules, whether naturally occurring or synthetic. For example, the aldol reaction has been used in the large-scale production of the commodity chemical pentaerythritol and the synthesis of the heart disease drug Lipitor (atorvastatin, calcium salt). The aldol reaction unites two relatively simple molecules into a more complex one. Increased complexity arises because up to two new stereogenic centers (on the α- and β-carbon of the aldol adduct, marked wit ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Back Bonding
In chemistry, π backbonding, also called π backdonation, is when electrons move from an atomic orbital on one atom to an appropriate symmetry antibonding orbital on a ''π-acceptor ligand''. It is especially common in the organometallic chemistry of transition metals with multi-atomic ligands such as carbon monoxide, ethylene or the nitrosonium cation. Electrons from the metal are used to bond to the ligand, in the process relieving the metal of excess negative charge. Compounds where π backbonding occurs include Ni(CO)4 and Zeise's salt. IUPAC offers the following definition for backbonding: A description of the bonding of π-conjugated ligands to a transition metal which involves a synergic process with donation of electrons from the filled π-orbital or lone electron pair orbital of the ligand into an empty orbital of the metal (donor–acceptor bond), together with release (back donation) of electrons from an ''n''d orbital of the metal (which is of π-symmetry with re ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
D-orbital
In atomic theory and quantum mechanics, an atomic orbital is a function describing the location and wave-like behavior of an electron in an atom. This function can be used to calculate the probability of finding any electron of an atom in any specific region around the atom's nucleus. The term ''atomic orbital'' may also refer to the physical region or space where the electron can be calculated to be present, as predicted by the particular mathematical form of the orbital. Each orbital in an atom is characterized by a set of values of the three quantum numbers , , and , which respectively correspond to the electron's energy, angular momentum, and an angular momentum vector component (magnetic quantum number). Alternative to the magnetic quantum number, the orbitals are often labeled by the associated harmonic polynomials (e.g., ''xy'', ). Each such orbital can be occupied by a maximum of two electrons, each with its own projection of spin m_s. The simple names s orbital, p orbit ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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