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Transition-metal Allyl Complex
Transition-metal allyl complexes are coordination complexes with allyl and its derivatives as ligands. Allyl is the radical with the connectivity CH2CHCH2, although as a ligand it is usually viewed as an allyl anion CH2=CH−CH2−, which is usually described as two equivalent resonance structures. Examples The allyl ligand is commonly in organometallic chemistry. Usually, allyl ligands bind to metals via all three carbon atoms, the hapticity, η3-binding mode. The η3-allyl group is classified as an LX-type ligand in the Green LXZ Covalent bond classification method, ligand classification scheme, serving as a 3e– donor using neutral electron counting and 4e– donor using ionic electron counting. Scope Commonly, allyl ligands occur in mixed ligand complexes. Examples include (η3-allyl)Mn(CO)4 and Cyclopentadienyl allyl palladium, CpPd(allyl). Substituents on the allyl group are also common, e.g. 2-methallyl. Homoleptic complexes * bis(allyl)nickel * bis(allyl)palladium * ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Oxidative Addition
Oxidative addition and reductive elimination are two important and related classes of reactions in organometallic chemistry. Oxidative addition is a process that increases both the oxidation state and coordination number of a metal centre. Oxidative addition is often a step in catalytic cycles, in conjunction with its reverse reaction, reductive elimination. Role in transition metal chemistry For transition metals, oxidative reaction results in the decrease in the d''n'' to a configuration with fewer electrons, often 2e fewer. Oxidative addition is favored for metals that are (i) basic and/or (ii) easily oxidized. Metals with a relatively low oxidation state often satisfy one of these requirements, but even high oxidation state metals undergo oxidative addition, as illustrated by the oxidation of Pt(II) with chlorine: : tCl4sup>2− + Cl2 → tCl6sup>2− In classical organometallic chemistry, the formal oxidation state of the metal and the electron count of the complex both in ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nickel
Nickel is a chemical element; it has symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel is a hard and ductile transition metal. Pure nickel is chemically reactive, but large pieces are slow to react with air under standard conditions because a passivation layer of nickel oxide forms on the surface that prevents further corrosion. Even so, pure native nickel is found in Earth's crust only in tiny amounts, usually in ultramafic rocks, and in the interiors of larger nickel–iron meteorites that were not exposed to oxygen when outside Earth's atmosphere. Meteoric nickel is found in combination with iron, a reflection of the origin of those elements as major end products of supernova nucleosynthesis. An iron–nickel mixture is thought to compose Earth's outer and inner cores. Use of nickel (as natural meteoric nickel–iron alloy) has been traced as far back as 3500 BCE. Nickel was first isolated and classifie ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Inorganic Syntheses
''Inorganic Syntheses'' is a book series which aims to publish "detailed and foolproof" procedures for the synthesis of inorganic compounds. Although this series of books are edited, they usually are referenced like a journal, without mentioning the names of the checkers (referees) or the editor. A similar format is usually followed for the series '' Organic Syntheses''. Volumes See also * Organic SynthesesReferences {{chem-book-stub Book series introduced in 1939 ...[...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Allyl Palladium Chloride
Allylpalladium(II) chloride dimer (APC) is a chemical compound with the formula hapticity.html" ;"title="hapticity">η3-C3H5)PdClsub>2. This yellow air-stable compound is an important catalyst used in organic synthesis.Tatsuno, Y.; Yoshida, T.; Otsuka, S. "(η3-allyl)palladium(II) Complexes" Inorganic Syntheses, 1990, volume 28, pages 342-345. It is one of the most widely used transition metal allyl complexes. Structure The compound has a dimeric structure that is centrosymmetric. Each allyl group lies in a plane at an angle of about 111.5° to the square formed by the palladium and carbon atoms, and the Pd–C distances are all equal. Its unit cell is monoclinic. Synthesis The compound is prepared by purging carbon monoxide through a methanolic aqueous solution of sodium tetrachloropalladate (prepared from palladium(II) chloride and sodium chloride), and allyl chloride. :2 Na2PdCl4 + 2 CH2=CHCH2Cl + 2 CO + 2 H2O ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Polymorphism (materials Science)
In crystallography, polymorphism is the phenomenon where a compound or element can crystallize into more than one crystal structure. The preceding definition has evolved over many years and is still under discussion today. Discussion of the defining characteristics of polymorphism involves distinguishing among types of transitions and structural changes occurring in polymorphism versus those in other phenomena. Overview Phase transitions (phase changes) that help describe polymorphism include polymorphic transitions as well as melting and vaporization transitions. According to IUPAC, a polymorphic transition is "A reversible transition of a solid crystalline phase at a certain temperature and pressure (the inversion point) to another phase of the same chemical composition with a different crystal structure." Additionally, Walter McCrone described the phases in polymorphic matter as "different in crystal structure but identical in the liquid or vapor states." McCrone also def ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tetrabenzylzirconium
Tetrabenzylzirconium is an organozirconium compound with the formula Zr(CH2C6H5)4. The molecule features diamagnetic Zr(IV) bonded to four benzyl ligands. It is an orange air- and photo-sensitive solid, which is soluble in hydrocarbon solvents. The compound is a precursor to catalysts for the polymerization of olefins. Structure, synthesis, reactions X-ray crystallography demonstrates that the benzyl ligands are highly flexible: one polymorph features four η2-ligands, whereas another has two η1- and two η2-benzyl ligands. The compound is prepared by combining benzylmagnesium chloride and zirconium tetrachloride in diethyl ether.{{cite book , doi=10.1002/047084289X.rn01555, chapter=Tetrabenzylzirconium , title=Encyclopedia of Reagents for Organic Synthesis , year=2013 , last1=Mashima , first1=Kazushi , last2=Tsurugi , first2=Hatato , isbn=978-0471936237 Tetrabenzylzirconium readily undergoes protonolysis, e.g. with hydrogen chloride The Chemical compound, compound h ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
X-ray Crystallography
X-ray crystallography is the experimental science of determining the atomic and molecular structure of a crystal, in which the crystalline structure causes a beam of incident X-rays to Diffraction, diffract in specific directions. By measuring the angles and intensities of the X-ray diffraction, a crystallography, crystallographer can produce a three-dimensional picture of the density of electrons within the crystal and the positions of the atoms, as well as their chemical bonds, crystallographic disorder, and other information. X-ray crystallography has been fundamental in the development of many scientific fields. In its first decades of use, this method determined the size of atoms, the lengths and types of chemical bonds, and the atomic-scale differences between various materials, especially minerals and alloys. The method has also revealed the structure and function of many biological molecules, including vitamins, drugs, proteins and nucleic acids such as DNA. X-ray crystall ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Wurtz Coupling
In organic chemistry, the Wurtz reaction, named after Charles Adolphe Wurtz, is a coupling reaction in which two alkyl halides are treated with sodium metal to form a higher alkane. : 2 R−X + 2 Na → R−R + 2 NaX The reaction is of little value because yields are low. Exceptions are some intramolecular versions, such as 1,6-dibromohexane + 2 Na → cyclohexane + 2 NaBr. A related reaction, which combines alkyl halides with aryl halides is called the Wurtz–Fittig reaction. Despite its very modest utility, the Wurtz reaction is widely cited as representative of reductive coupling. Mechanism The reaction proceeds by an initial metal–halogen exchange, which is described with the following idealized stoichiometry: : R−X + 2 M → RM + MX This step may involve the intermediacy of radical species R·. The conversion resembles the formation of a Grignard reagent. The RM intermediates have been isolated in several cases. The radical is susceptible to diverse reactions. The org ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Allylmagnesium Bromide
Allylmagnesium bromide is a Grignard reagent used for introducing the allyl group. It is commonly available as a solution in diethyl ether. It may be synthesized by treatment of magnesium with allyl bromide while maintaining the reaction temperature below 0 °C to suppress formation of hexadiene. Allyl chloride can also be used in place of the bromide to give allylmagnesium chloride. These reagents are used to prepare transition-metal allyl complex, metal allyl complexes. References Further reading * {{cite book , author = Chabot, P. , editor1=Rakita, P. E. , editor2=Silverman, G. , chapter = 7. Infrared and Raman Spectroscopy , title = Handbook of Grignard Reagents , year = 1996 , pages = 93–102 , location = New York, N.Y. , publisher = Marcel Dekker , isbn = 0-8247-9545-8 Organomagnesium compounds Allyl compounds Bromides ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Salt Metathesis Reaction
A salt metathesis reaction (also called a double displacement reaction, double replacement reaction, or double decomposition) is a type of chemical reaction in which two ionic compounds in aqueous solution exchange their component ions to form two new compounds. Often, one of these new compounds is a precipitate, gas, or weak electrolyte, driving the reaction forward. :AB + CD -> AD + CB \mathitA_\mathitD_\mathit + \mathitC_\mathitB_\mathit --> In older literature, the term double decomposition is common. The term double decomposition is more specifically used when at least one of the substances does not dissolve in the solvent, as the ligand or ion exchange takes place in the solid state of the reactant. For example: :AX(aq) + BY(s) → AY(aq) + BX(s). Types of reactions Counterion exchange Salt metathesis is a common technique for exchanging counterions. The choice of reactants is guided by a solubility chart or lattice energy. HSAB theory can also be used to predict ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
