Organozirconium Compound on:
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Organozirconium chemistry is the science of exploring the properties, structure, and reactivity of organozirconium compounds, which are
In addition to mixed Cp2Zr(CO)2, zirconium forms the binary carbonyl r(CO)6sup>2-.
Cationic hafnocene complexes,
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 so ...
s containing chemical bond
A chemical bond is a lasting attraction between atoms or ions that enables the formation of molecules and crystals. The bond may result from the electrostatic force between oppositely charged ions as in ionic bonds, or through the sharing o ...
s between carbon
Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—its atom making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Carbon makes ...
and zirconium
Zirconium is a chemical element with the symbol Zr and atomic number 40. The name ''zirconium'' is taken from the name of the mineral zircon, the most important source of zirconium. The word is related to Persian '' zargun'' (zircon; ''zar-gun'' ...
. Organozirconium compounds have been widely studied, in part because they are useful catalysts in Ziegler-Natta polymerization.
Comparison with organotitanium chemistry
Many organozirconium compounds have analogues onorganotitanium chemistry
Organotitanium chemistry is the science of organotitanium compounds describing their physical properties, synthesis, and reactions. Organotitanium compounds in organometallic chemistry contain carbon-titanium chemical bonds. They are reagents in or ...
. Zirconium(IV) is more resistant to reduction than titanium(IV) compounds, which often convert to Ti(III) derivatives. By the same token, Zr(II) is a particularly powerful reducing agent, forming robust dinitrogen complexes. Being a larger atom, zirconium forms complexes with higher coordination numbers, e.g. polymeric pZrCl3sub>n vs monomeric CpTiCl3 (Cp = C5H5).
History
Zirconocene dibromide was prepared in 1953 by a reaction of thecyclopentadienyl Cyclopentadienyl can refer to
* Cyclopentadienyl anion, or cyclopentadienide,
**Cyclopentadienyl ligand
A cyclopentadienyl complex is a coordination complex of a metal and cyclopentadienyl anion, cyclopentadienyl groups (, abbreviated as Cp−) ...
magnesium bromide and zirconium(IV) chloride
Zirconium(IV) chloride, also known as zirconium tetrachloride, () is an inorganic compound frequently used as a precursor to other compounds of zirconium. This white high-melting solid hydrolyzes rapidly in humid air.
Structure
Unlike molecular T ...
. In 1966, the dihydride Cp2ZrH2 was obtained by the reaction of Cp2Zr(BH4)2 with triethylamine
Triethylamine is the chemical compound with the formula N(CH2CH3)3, commonly abbreviated Et3N. It is also abbreviated TEA, yet this abbreviation must be used carefully to avoid confusion with triethanolamine or tetraethylammonium, for which TEA ...
. In 1970, the related hydrochloride (now called Schwartz's reagent
Schwartz's reagent is the common name for the organozirconium compound with the formula (C5H5)2ZrHCl, sometimes called zirconocene hydrochloride or zirconocene chloride hydride, and is named after Jeffrey Schwartz, a chemistry professor at Princet ...
) was obtained by reduction of zirconacene dichloride (Cp2ZrCl2) with lithium aluminium hydride
Lithium aluminium hydride, commonly abbreviated to LAH, is an inorganic compound with the chemical formula Li Al H4. It is a white solid, discovered by Finholt, Bond and Schlesinger in 1947. This compound is used as a reducing agent in organic ...
(or the related LiAlH(t-BuO)3). The development of organozirconium reagents was recognized by a Nobel Prize in Chemistry
)
, image = Nobel Prize.png
, alt = A golden medallion with an embossed image of a bearded man facing left in profile. To the left of the man is the text "ALFR•" then "NOBEL", and on the right, the text (smaller) "NAT•" then "M ...
to Ei-Ichi Negishi.
Zirconocene chemistry
The foremost applications of zirconocenes involve their use as catalysts for olefin polymerization.Schwartz's reagent
Schwartz's reagent is the common name for the organozirconium compound with the formula (C5H5)2ZrHCl, sometimes called zirconocene hydrochloride or zirconocene chloride hydride, and is named after Jeffrey Schwartz, a chemistry professor at Princet ...
( p2ZrHClsub>2) participates in hydrozirconation, which enjoys some use in organic synthesis
Organic synthesis is a special branch of chemical synthesis and is concerned with the intentional construction of organic compounds. Organic molecules are often more complex than inorganic compounds, and their synthesis has developed into one o ...
. Substrates for hydrozirconation
Schwartz's reagent is the common name for the organozirconium compound with the empirical formula, formula (C5H5)2ZrHCl, sometimes called zirconocene hydrochloride or zirconocene chloride hydride, and is named after Jeffrey Schwartz, a chemistry pr ...
are alkene
In organic chemistry, an alkene is a hydrocarbon containing a carbon–carbon double bond.
Alkene is often used as synonym of olefin, that is, any hydrocarbon containing one or more double bonds.H. Stephen Stoker (2015): General, Organic, an ...
s and alkyne
\ce
\ce
Acetylene
\ce
\ce
\ce
Propyne
\ce
\ce
\ce
\ce
1-Butyne
In organic chemistry, an alkyne is an unsaturated hydrocarbon containing at least one carbon—carbon triple bond. The simplest acyclic alkynes with only one triple bond and no ...
s. Terminal alkynes give vinyl complexes. Secondary reactions are nucleophilic addition
In organic chemistry, a nucleophilic addition reaction is an addition reaction where a chemical compound with an electrophilic double or triple bond reacts with a nucleophile, such that the double or triple bond is broken. Nucleophilic additions ...
s, transmetalation Transmetalation (alt. spelling: transmetallation) is a type of organometallic reaction that involves the transfer of ligands from one metal to another. It has the general form:
:M1–R + M2–R′ → M1–R′ + M2–R
where R and R′ can be, but ...
s, conjugate additions, coupling reaction A coupling reaction in organic chemistry is a general term for a variety of reactions where two fragments are joined together with the aid of a metal catalyst. In one important reaction type, a main group organometallic compound of the type R-M (R ...
s, carbonylation
Carbonylation refers to reactions that introduce carbon monoxide into organic and inorganic substrates. Carbon monoxide is abundantly available and conveniently reactive, so it is widely used as a reactant in industrial chemistry. The term carbo ...
, and halogenation
In chemistry, halogenation is a chemical reaction that entails the introduction of one or more halogens into a compound. Halide-containing compounds are pervasive, making this type of transformation important, e.g. in the production of polyme ...
.
Extensive chemistry has also been demonstrated from decamethylzirconocene dichloride, Cp*2ZrCl2. Well-studied derivatives include Cp*2ZrH2, p*2Zrsub>2(N2)3, Cp*2Zr(CO)2, and Cp*2Zr(CH3)2.
Zirconocene dichloride can be used to cyclise enynes and dienes to give cyclic or bicyclic aliphatic systems.
:
Alkyl and CO complexes
The simplest organozirconium compounds are the homoleptic alkyls. Salts of r(CH3)6sup>2- are known. Tetrabenzylzirconium is a precursor to many catalysts for olefin polymerization. It can be converted to mixedalkyl
In organic chemistry, an alkyl group is an alkane missing one hydrogen.
The term ''alkyl'' is intentionally unspecific to include many possible substitutions.
An acyclic alkyl has the general formula of . A cycloalkyl is derived from a cycloal ...
, alkoxy, and halide derivatives, Zr(CH2C6H5)3X (X = CH3, OC2H5, Cl).
In addition to mixed Cp2Zr(CO)2, zirconium forms the binary carbonyl r(CO)6sup>2-.
Organohafnium chemistry
Organohafnium compounds behave nearly identically to organozirconium compounds, as hafnium is just below zirconium on the periodic table. Many Hf analogues of Zr compounds are known, including bis(cyclopentadienyl)hafnium(IV) dichloride, bis(cyclopentadienyl)hafnium(IV) dihydride, and dimethylbis(cyclopentadienyl)hafnium(IV).
Cationic hafnocene complexes, post-metallocene catalyst
A post-metallocene catalyst is a kind of catalyst for the polymerization of olefins, i.e., the industrial production of some of the most common plastics. "Post-metallocene" refers to a class of homogeneous catalysts that are not metallocenes. This ...
s, are used on an industrial scale for the polymerization
In polymer chemistry, polymerization (American English), or polymerisation (British English), is a process of reacting monomer molecules together in a chemical reaction to form polymer chains or three-dimensional networks. There are many fo ...
of alkenes.
Additional reading
* *References
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