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Encyclopedia > Metallocene

In chemistry, and in particular, in organometallic chemistry, a metallocene is a compound consisting of an aromatic organic ligand bound to a metal. Chemistry (in Greek: χημεία) is the science of matter that deals with the composition, structure, and properties of substances and with the transformations that they undergo. ... Organometallic chemistry is the study of chemical compounds containing bonds between carbon and a metal. ... In chemistry, an aromatic molecule is one in which electrons are free to cycle around circular arrangements of atoms, which are alternately singly and doubly bonded to one another. ... Organic has several meanings and related topics. ... In chemistry, a ligand is an atom, ion or functional group that is bonded to one or more central atoms or ions, usually metals generally through co-ordinate covalent bond. ...

A key feature of metallocenes is planar aromatic organic ligands in which multiple of the carbon atoms in the ring form metal-carbon bonds that are equivalent. An aromatic hydrocarbon (abbreviated as AH), or arene is a hydrocarbon, the molecular structure of which incorporates one or more planar sets of six carbon atoms that are connected by delocalised electrons numbering the same as if they consisted of alternating single and double covalent bonds. ... General Name, Symbol, Number carbon, C, 6 Chemical series nonmetals Group, Period, Block 14, 2, p Appearance black (graphite) colorless (diamond) Atomic mass 12. ... Properties For alternative meanings see atom (disambiguation). ...

The prototypical metallocene is ferrocene, consisting of two cyclopentadienyl rings bound on opposite sides of a central iron atom, forming an organometallic sandwich compound. In the case of ferrocene, for instance, the length and strength and bond angles about the metal-carbon bonds are identical. The nature of the bonding of the organic ligand to the metal is referred to as its "hapticity" and is indicated by the Greek letter eta. The equivalent bonding of all 5 carbon atoms of each cyclopentadienyl ring in ferrocene is denoted as eta-5. Ferrocene Fe(C5H5)2 is the prototypical metallocene, a type of organometallic chemical compound, consisting of two cyclopentadienyl rings bound on opposite sides of a central iron atom and forming an organometallic sandwich compound. ... Cyclopentadiene, with molecular formula C5H6, is a clear, colorless, liquid organic chemical, with an odor reminiscent of turpentine or camphor. ... General Name, Symbol, Number iron, Fe, 26 Chemical series transition metals Group, Period, Block 8, 4, d Appearance lustrous metallic with a grayish tinge Atomic mass 55. ...

The systematic name of ferrocene is, therefore, bis(eta-5-cyclopentadienyl)iron.

A notable feature of all metallocenes is their high thermal stability (up to and over 500°C). All neutral metallocenes are soluble in common organic solvents and can be purified by vacuum sublimation. Metallocenes of all 3d-row elements are known, but with the exception of ferrocene all of these are sensitive to air, paramagnetic and do not possess a closed-shell electron structure.

X-ray diffraction studies have shown that all metallocenes have a sandwich structure, with the cyclopentadienyl rings either eclipsed or staggered. For non-substituted metallocenes the energy difference between the staggered and eclipsed conformations is only 8 kJ/mol. Ferrocene and osmocene take on an eclipsed conformation at low temperatures, while pentamethylcyclopentadienyl ligands are always in a staggered conformation to minimize steric hindrance between the methyl groups.

A similar structure to metallocenes, including just one facially-bound planar organic ligand instead of two, are the half-sandwich compounds.

  Results from FactBites:
Metals known to form metallocene complexes are titanium, zirconium, hafnium, vanadium, chromium, molybdenum, tungsten, manganese, iron, ruthenium, osmium, cobalt, rhodium, and nickel.
The commonest metallocene is ferrocene, yellow to orange crystal melting at 173 C, is an organometallic compound of sandwich structure.
Metallocenes having catalytic site in systematic molecular structure are used as polymerization catalyst to produce uniform polymer with unique structures and physical properties.
Patents in Class 556/53 (2041 words)
This invention relates to metallocene compounds represented by formula: ##STR00001## wherein M is a group 3, 4, 5 or 6 transition metal atom, or a lanthanide metal atom, or actinide metal atom; E is a substituted or unsubstituted indenyl...
This invention relates to a metallocene compounds represented by formula: ##STR00001## wherein M is a group 3, 4, 5 or 6 transition metal atom, or a lanthanide metal atom, or actinide metal atom; E is an indenyl ligand that is substitute...
The invention relates to a metallocene catalyst in which the metal is coordinated by any η 5 cyclopentadienyl ligand characterised in that said ligand is directly or indirectly substituted by a pendant siloxy or germyloxy group wh...
  More results at FactBites »



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