In organometallic chemistry, metallacyclopentanes are compounds with the formula LnM(CH2)4 (Ln = ligands, and M = metal). They are a type of metallacycle. Metallacyclopentanes are intermediates in some metal-catalysed reactions in homogeneous catalysis.
Traditionally, metallacyclopentanes are prepared by dialkylation of metal dihalides with 1,4‐bis(bromomagnesio)butane or the related dilithio reagent. [2] The complex Ni(bipyridine)C4H8 is prepared by the oxidative addition of 1,4-dibromobutane to Ni(0) precursors. [1] Metallacyclopentanes also arise via the dimerization of ethylene within the coordination sphere of a low-valence metal center. This reaction is relevant to the catalytic production of butenes and related alkenes.
Unsubstituted metallacyclopentanes adopt conformations related to cyclopentane itself: open-envelope conformation and a twisted open-envelope structure. [3]
Early examples of metallacyclopentanes come from studies of the Ni-catalyzed linear- and cyclo-dimerization of ethylenes. Linear dimerization proceeds via beta-hydride elimination of the nickelacyclopentane (Ph3P)Ni(CH2)4 whereas cyclodimerization to give cyclobutane proceeds by reductive elimination from the related (Ph3P)2Ni(CH2)4. [4] Another example of a metallacyclopentane is the titanocene derivative Cp 2Ti(CH2)4. [5]
Metallacyclopentanes are intermediates in the metal-catalysed dimerization, trimerization, and tetramerization of ethylene to give 1-butene, 1-hexene, and 1-octene, respectively. These compounds are of commercial interest as comonomers, used in the production of polyethylene. [6]
In the evolution of heterogeneous alkene metathesis catalysts, metallacyclopentanes are invoked as intermediates in the formation of metal alkylidenes from ethylene. Thus, metallacyclopentane intermediates are proposed to isomerize to metallacyclobutanes, which can eliminate alkene giving the alkylidene. [7]
In organic chemistry, an alkene, or olefin, is a hydrocarbon containing a carbon–carbon double bond. The double bond may be internal or in the terminal position. Terminal alkenes are also known as α-olefins.
In organic chemistry, a diene ; also diolefin, dy-OH-lə-fin) or alkadiene) is a covalent compound that contains two double bonds, usually among carbon atoms. They thus contain two alkene units, with the standard prefix di of systematic nomenclature. As a subunit of more complex molecules, dienes occur in naturally occurring and synthetic chemicals and are used in organic synthesis. Conjugated dienes are widely used as monomers in the polymer industry. Polyunsaturated fats are of interest to nutrition.
A Ziegler–Natta catalyst, named after Karl Ziegler and Giulio Natta, is a catalyst used in the synthesis of polymers of 1-alkenes (alpha-olefins). Two broad classes of Ziegler–Natta catalysts are employed, distinguished by their solubility:
In organic chemistry, a carbene is a molecule containing a neutral carbon atom with a valence of two and two unshared valence electrons. The general formula is R−:C−R' or R=C: where the R represents substituents or hydrogen atoms.
In organic chemistry, hydrocyanation is a process for conversion of alkenes to nitriles. The reaction involves the addition of hydrogen cyanide and requires a catalyst. This conversion is conducted on an industrial scale for the production of precursors to nylon.
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In organometallic chemistry, a metallacycle is a derivative of a carbocyclic compound wherein a metal has replaced at least one carbon center; this is to some extent similar to heterocycles. Metallacycles appear frequently as reactive intermediates in catalysis, e.g. olefin metathesis and alkyne trimerization. In organic synthesis, directed ortho metalation is widely used for the functionalization of arene rings via C-H activation. One main effect that metallic atom substitution on a cyclic carbon compound is distorting the geometry due to the large size of typical metals.
Zirconocene dichloride is an organozirconium compound composed of a zirconium central atom, with two cyclopentadienyl and two chloro ligands. It is a colourless diamagnetic solid that is somewhat stable in air.
Organosilver chemistry is the study of organometallic compounds containing a carbon to silver chemical bond. The theme is less developed than organocopper chemistry.
A metal-phosphine complex is a 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).
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Hydrophosphination is the insertion of a carbon-carbon multiple bond into a phosphorus-hydrogen bond forming a new phosphorus-carbon bond. Like other hydrofunctionalizations, the rate and regiochemistry of the insertion reaction is influenced by the catalyst. Catalysts take many forms, but most prevalent are bases and free-radical initiators. Most hydrophosphinations involve reactions of phosphine (PH3).
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In organic chemistry, hydrovinylation is the formal insertion of an alkene into the C-H bond of ethylene :
In organic chemistry, alkylidene is a general term for divalent functional groups of the form R2C=, where each R is an alkane or hydrogen. They can be considered the functional group corresponding to mono- or disubstituted divalent carbenes, or as the result of removing two hydrogen atoms from the same carbon atom in an alkane.
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