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P-Chiral Phosphine
''P''-Chiral phosphines are organophosphorus compounds of the formula PRR′R″, where R, R′, R″ = H, alkyl, aryl, etc. They are a subset of chiral phosphines, a broader class of compounds where the stereogenic center can reside at sites other than phosphorus. P-chirality exploits the high barrier for inversion of phosphines, which ensures that enantiomers of PRR'R" do not racemize readily. The inversion barrier is relatively insensitive to substituents for triorganophosphines. By contrast, most amines of the type NRR′R″ undergo rapid pyramidal inversion. Research themes Most chiral phosphines are C2-symmetric diphosphines. Famous examples are DIPAMP and BINAP. These chelating ligands support catalysts used in asymmetric hydrogenation and related reactions. DIPAMP is prepared by coupling the ''P''-chiral methylphenylanisylphosphine. ''P''-Chiral phosphines are of particular interest in asymmetric catalysis. ''P''-Chiral phosphines have been investigated for two m ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Asymmetric Catalysis
Enantioselective synthesis, also called asymmetric synthesis, is a form of chemical synthesis. It is defined by IUPAC as "a chemical reaction (or reaction sequence) in which one or more new elements of Chirality (chemistry), chirality are formed in a substrate molecule and which produces the stereoisomeric (enantiomeric or diastereomeric) products in Enantiomeric excess, unequal amounts." Put more simply: it is the synthesis of a compound by a method that favors the formation of a specific enantiomer or diastereomer. Enantiomers are stereoisomers that have opposite configurations at every chiral center. Diastereomers are stereoisomers that differ at one or more chiral centers. Enantioselective synthesis is a key process in modern chemistry and is particularly important in the field of pharmaceuticals, as the different enantiomers or diastereomers of a molecule often have different biological activity. Overview Many of the building blocks of biological systems such as sugars a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Stereochemistry
Stereochemistry, a subdiscipline of chemistry, studies the spatial arrangement of atoms that form the structure of molecules and their manipulation. The study of stereochemistry focuses on the relationships between stereoisomers, which are defined as having the same molecular formula and sequence of bonded atoms (constitution) but differing in the geometric positioning of the atoms in space. For this reason, it is also known as Three-dimensional space, 3D chemistry—the prefix "stereo-" means "three-dimensionality". Stereochemistry applies to all kinds of compounds and ions, Organic chemistry, organic and Inorganic chemistry, inorganic species alike. Stereochemistry affects Biochemistry, biological, Physical chemistry, physical, and supramolecular chemistry. Stereochemistry reactivity (chemistry), reactivity of the molecules in question (dynamic stereochemistry). History In 1815, Jean-Baptiste Biot's observation of optical activity marked the beginning of organic stereochemistr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Coordination Chemistry
A coordination complex is a chemical compound consisting of a central atom or ion, which is usually metallic and is called the ''coordination centre'', and a surrounding array of chemical bond, bound molecules or ions, that are in turn known as ''ligands'' or complexing agents. Many metal-containing chemical compound, compounds, especially those that include transition metals (elements like titanium that belong to the periodic table's d-block), are coordination complexes. Nomenclature and terminology Coordination complexes are so pervasive that their structures and reactions are described in many ways, sometimes confusingly. The atom within a ligand that is bonded to the central metal atom or ion is called the donor atom. In a typical complex, a metal ion is bonded to several donor atoms, which can be the same or different. A Ligand#Polydentate and polyhapto ligand motifs and nomenclature, polydentate (multiple bonded) ligand is a molecule or ion that bonds to the central atom ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Catalysis
Catalysis () is the increase in rate of a chemical reaction due to an added substance known as a catalyst (). Catalysts are not consumed by the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recycles quickly, very small amounts of catalyst often suffice; mixing, surface area, and temperature are important factors in reaction rate. Catalysts generally react with one or more reactants to form intermediates that subsequently give the final reaction product, in the process of regenerating the catalyst. The rate increase occurs because the catalyst allows the reaction to occur by an alternative mechanism which may be much faster than the noncatalyzed mechanism. However the noncatalyzed mechanism does remain possible, so that the total rate (catalyzed plus noncatalyzed) can only increase in the presence of the catalyst and never decrease. Catalysis may be classified as either homogeneous, whose components are dispersed in the same phase (usual ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Organocatalysis
In organic chemistry, organocatalysis is a form of catalysis in which the rate of a chemical reaction is increased by an organic catalyst. This "organocatalyst" consists of carbon, hydrogen, sulfur and other nonmetal elements found in organic compounds.Special Issue: Because of their similarity in composition and description, they are often mistaken as a misnomer for enzymes due to their comparable effects on reaction rates and forms of catalysis involved. Organocatalysts which display secondary amine functionality can be described as performing either enamine catalysis (by forming catalytic quantities of an active enamine nucleophile) or iminium catalysis (by forming catalytic quantities of an activated iminium electrophile). This mechanism is typical for covalent organocatalysis. Covalent binding of substrate normally requires high catalyst loading (for proline-catalysis typically 20–30 mol%). Noncovalent interactions such as hydrogen-bonding facilitates low catalyst loa ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Homogeneous Catalyst
In chemistry, homogeneous catalysis is catalysis where the catalyst is in same phase as reactants, principally by a soluble catalyst in a solution. In contrast, heterogeneous catalysis describes processes where the catalysts and substrate are in distinct phases, typically solid and gas, respectively. The term is used almost exclusively to describe solutions and implies catalysis by organometallic compounds. Homogeneous catalysis is an established technology that continues to evolve. An illustrative major application is the production of acetic acid. Enzymes are examples of homogeneous catalysts. Examples Acid catalyst The proton is a pervasive homogeneous catalyst because water is the most common solvent. Water forms protons by the process of self-ionization of water. In an illustrative case, acids accelerate (catalyze) the hydrolysis of esters: :CH3CO2CH3 + H2O CH3CO2H + CH3OH At neutral pH, aqueous solutions of most esters do not hydrolyze at practical rates. Transition metal ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ligand
In coordination chemistry, a ligand is an ion or molecule with a 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 acids and bases, Lewis bases. The nature of metal–ligand bonding can range from covalent bond, covalent to ionic bond, 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 acids and bases, 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 (chemistry), 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 are ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Asymmetric Hydrogenation
Asymmetric hydrogenation is a chemical reaction that adds two atoms of hydrogen to a target (substrate) molecule with three-dimensional spatial selectivity. Critically, this selectivity does not come from the target molecule itself, but from other reagents or catalysts present in the reaction. This allows spatial information (what chemists refer to as chirality) to transfer from one molecule to the target, forming the product as a single enantiomer. The chiral information is most commonly contained in a catalyst and, in this case, the information in a single molecule of catalyst may be transferred to many substrate molecules, amplifying the amount of chiral information present. Similar processes occur in nature, where a chiral molecule like an enzyme can catalyse the introduction of a chiral centre to give a product as a single enantiomer, such as amino acids, that a cell needs to function. By imitating this process, chemists can generate many novel synthetic molecules that inte ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Organophosphorus Compound
Organophosphorus chemistry is the scientific study of the synthesis and properties of organophosphorus compounds, which are organic compounds containing phosphorus. They are used primarily in pest control as an alternative to chlorinated hydrocarbons that persist in the environment. Some organophosphorus compounds are highly effective insecticides, although some are extremely toxic to humans, including sarin and VX (nerve agent), VX nerve agents. Phosphorus, like nitrogen, is in pnictogen, group 15 of the periodic table, and thus phosphorus compounds and nitrogen compounds have many similar properties. The definition of organophosphorus compounds is variable, which can lead to confusion. In industrial and environmental chemistry, an organophosphorus compound need contain only an organic substituent, but need not have a direct phosphorus-carbon (P-C) bond. Thus a large proportion of pesticides (e.g., malathion), are often included in this class of compounds. Phosphorus can adopt a v ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
BINAP
BINAP (2,2′-bis(diphenylphosphino)-1,1′-binaphthyl) is an organophosphorus compound. This Optical isomerism, chiral diphosphines, diphosphine ligand is widely used in chiral synthesis, asymmetric synthesis. It consists of a pair of 2-diphenylphosphinonaphthalene, naphthyl groups linked at the 1 and 1′ positions. This C2-Symmetric ligands, C2-symmetric framework lacks a stereocenter, stereogenic atom, but has axial chirality due to restricted rotation (atropisomerism). The barrier to racemization is high due to steric hindrance, which limits rotation about the bond linking the naphthyl rings. The dihedral angle between the naphthyl groups is approximately 90°. The natural bite angle is 93°. Use as ligand in asymmetric catalysis BINAP is used in organic synthesis for enantioselective transformations catalyzed by its complex (chemistry), complexes of ruthenium, rhodium, and palladium. As pioneered by Ryōji Noyori and his co-workers, rhodium complexes of BINAP are usefu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
DIPAMP
DIPAMP is an organophosphorus compound that is used as a ligand in homogeneous catalysis. It is a white solid that dissolves in organic solvents. Work on this compound by W. S. Knowles was recognized with the Nobel Prize in Chemistry. DIPAMP was the basis for one of the first industrial scale asymmetric hydrogenation, the synthesis of the drug L-DOPA. : DIPAMP is a C2-symmetric diphosphine. Each phosphorus Phosphorus is a chemical element; it has Chemical symbol, symbol P and atomic number 15. All elemental forms of phosphorus are highly Reactivity (chemistry), reactive and are therefore never found in nature. They can nevertheless be prepared ar ... centre, which is pyramidal, bears three different substituents - anisyl, phenyl, and the ethylene group. The ligand therefore exists as the enantiomeric (''R'',''R'') and (''S'',''S'') pair, as well as the achiral ''meso'' isomer. DIPAMP was originally prepared by an oxidative coupling, starting from anisyl(phenyl)(methyl)p ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
