Organozirconium compounds are organometallic compounds containing a carbon

Carbon

Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...

 to zirconium

Zirconium

Zirconium is a chemical element with the symbol Zr and atomic number 40. The name of zirconium is taken from the mineral zircon. Its atomic mass is 91.224. It is a lustrous, grey-white, strong transition metal that resembles titanium...

 chemical bond

Chemical bond

A chemical bond is an attraction between atoms that allows the formation of chemical substances that contain two or more atoms. The bond is caused by the electromagnetic force attraction between opposite charges, either between electrons and nuclei, or as the result of a dipole attraction...

. Organozirconium chemistry is the corresponding science exploring properties, structure and reactivity of these compounds. In general organozirconium compounds are stable and non-toxic. They are used organic chemistry

Organic chemistry

Organic chemistry is a subdiscipline within chemistry involving the scientific study of the structure, properties, composition, reactions, and preparation of carbon-based compounds, hydrocarbons, and their derivatives...

 as an intermediate in the synthesis of chemical compounds and share characteristics with organotitanium compound

Organotitanium compound

Organotitanium compounds in organometallic chemistry contain carbon to titanium chemical bonds. Organotitanium chemistry is the science of organotitanium compounds describing their physical properties, synthesis and reactions...

s also a Group 4 element

Group 4 element

The Group 4 elements are a group of chemical elements in the periodic table. In the modern IUPAC nomenclature, Group 4 of the periodic table contains titanium , zirconium , hafnium and rutherfordium . This group lies in the d-block of the periodic table...

. Organozirconium compounds have been widely studied, in part because they are useful catalysts in Ziegler-Natta polymerization.

The first organozirconium compound discovered (1953) was zirconocene dibromide, belongs to the metallocene

Metallocene

A metallocene is a compound typically consisting of two cyclopentadienyl anions bound to a metal center in the oxidation state II, with the resulting general formula 2M. Closely related to the metallocenes are the metallocene derivatives, e.g. titanocene dichloride, vanadocene dichloride...

 family. It was prepared in a reaction of the cyclopentadienyl magnesium bromide and zirconium(IV) chloride

Zirconium(IV) chloride

Zirconium 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:...

. Zirconocenes are used as polymerization

Polymerization

In polymer chemistry, polymerization is a process of reacting monomer molecules together in a chemical reaction to form three-dimensional networks or polymer chains...

 catalysts such as Kaminsky catalyst

Kaminsky catalyst

A Kaminsky catalyst is a catalytic system for alkene polymerization discovered in 1980. Kaminsky catalysts are based on metallocenes of group 4 transition metals with methylaluminoxane . These catalysts are a type of Ziegler-Natta catalyst, but they are homogeneous and show extremely high activity...

s, partly replacing organotitanium compounds.

Hydrozirconation

The so-called Schwartz's reagent

Schwartz's Reagent

Schwartz's reagent is the common name for the chemical compound with the formula 2ZrHCl, sometimes described zirconocene hydrochloride or zirconocene chloride hydride and is named after Jeffrey Schwartz, who is currently a professor in Chemistry at Princeton University...

 (1974) is a zirconocene hydrochloride and a reagent in hydrometalation

Hydrometalation

Hydrometalation is a type of chemical reaction in organometallic chemistry in which a chemical compound with a hydrogen to metal bond adds to a compounds with an unsaturated bond like an alkene forming a new compound with a carbon to metal bond ]]...

 reactions (called hydrozirconation) with some use in organic synthesis

Organic synthesis

Organic synthesis is a special branch of chemical synthesis and is concerned with the construction of organic compounds via organic reactions. Organic molecules can often contain a higher level of complexity compared to purely inorganic compounds, so the synthesis of organic compounds has...

. Substrates for hydrozirconation are alkene

Alkene

In organic chemistry, an alkene, olefin, or olefine is an unsaturated chemical compound containing at least one carbon-to-carbon double bond...

s and alkyne

Alkyne

Alkynes are hydrocarbons that have a triple bond between two carbon atoms, with the formula CnH2n-2. Alkynes are traditionally known as acetylenes, although the name acetylene also refers specifically to C2H2, known formally as ethyne using IUPAC nomenclature...

s. With terminal alkynes the terminal vinyl zirconium product is predominantly formed. Secondary reactions are nucleophilic addition

Nucleophilic addition

In organic chemistry, a nucleophilic addition reaction is an addition reaction where in a chemical compound a π bond is removed by the creation of two new covalent bonds by the addition of a nucleophile....

s, transmetalation

Transmetalation

Transmetalation is a general chemical reaction type in organometallic chemistry describing the exchange of ligands between two metal centers....

s, conjugate additions, coupling reaction

Coupling reaction

A coupling reaction in organic chemistry is a catch-all term for a variety of reactions where two hydrocarbon fragments are coupled with the aid of a metal catalyst...

s, carbonylation

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.-Organic chemistry:...

 and halogenation

Halogenation

Halogenation is a chemical reaction that incorporates a halogen atom into a molecule in substitution of hydrogen atom. Halogenation takes place in the gas phase. There are four types of halogenation: fluorination, chlorination, bromination, and iodination...

.

History

The development of zirconium hydrides obviously preceded that of hydrozirconation. The first such hydride, Cp₂ZrH₂, was developed in 1966 by M.G.H. Wallbridge in a reaction of (Cp)₂Zr(BH₄)₂ with triethylamine

Triethylamine

Triethylamine is the chemical compound with the formula N3, commonly abbreviated Et3N. It is also abbreviated TEA, yet this abbreviation must be used carefully to avoid confusion with triethanolamine, for which TEA is also a common abbreviation....

 in benzene

Benzene

Benzene is an organic chemical compound. It is composed of 6 carbon atoms in a ring, with 1 hydrogen atom attached to each carbon atom, with the molecular formula C6H6....

 as an uneventful insoluble solid. In 1970 H. Weigold and P.C. Wailes prepared the hydrochloride from the dichloride (Cp₂ZrCl₂) and Lithium aluminium hydride

Lithium aluminium hydride

Lithium aluminium hydride, commonly abbreviated to LAH or known as LithAl, is an inorganic compound with the chemical formula LiAlH4. It was discovered by Finholt, Bond and Schlesinger in 1947. This compound is used as a reducing agent in organic synthesis, especially for the reduction of esters,...

 (or the related LiAlH(t-BuO)₃). They went on to investigate the reaction of these novel hydrides with carboxylic acid

Carboxylic acid

Carboxylic acids are organic acids characterized by the presence of at least one carboxyl group. The general formula of a carboxylic acid is R-COOH, where R is some monovalent functional group...

s (for example to compounds like CpZr(OCOR)₃) and in 1971 then arrived at their reactions with alkyne

Alkyne

Alkynes are hydrocarbons that have a triple bond between two carbon atoms, with the formula CnH2n-2. Alkynes are traditionally known as acetylenes, although the name acetylene also refers specifically to C2H2, known formally as ethyne using IUPAC nomenclature...

s.

For example, with one equivalent of Cp₂ZrClH they obtained from diphenylacetylene

Diphenylacetylene

Diphenylacetylene is the chemical compound C6H5C≡CC6H5. The molecule consists of phenyl groups attached to both ends of an alkyne. It is a colorless crystalline material that is widely used as a building block in organic and as a ligand in organometallic chemistry.-Preparation:Several...

 the corresponding alkenylzirconium as a mixture of cis and trans isomer. With two equivalents of hydride the endproduct was a mixture of erythro and threo zircono alkanes:

In 1974 Donald W. Hart and Jeffrey Schwartz realized how these compounds could be used in organic synthesis by reacting the organozirconium intermediates with electrophile

Electrophile

In general electrophiles are positively charged species that are attracted to an electron rich centre. In chemistry, an electrophile is a reagent attracted to electrons that participates in a chemical reaction by accepting an electron pair in order to bond to a nucleophile...

s such as hydrochloric acid

Hydrochloric acid

Hydrochloric acid is a solution of hydrogen chloride in water, that is a highly corrosive, strong mineral acid with many industrial uses. It is found naturally in gastric acid....

, bromine

Bromine

Bromine ") is a chemical element with the symbol Br, an atomic number of 35, and an atomic mass of 79.904. It is in the halogen element group. The element was isolated independently by two chemists, Carl Jacob Löwig and Antoine Jerome Balard, in 1825–1826...

 and acid chlorides to the corresponding alkane

Alkane

Alkanes are chemical compounds that consist only of hydrogen and carbon atoms and are bonded exclusively by single bonds without any cycles...

, bromoalkanes and ketone

Ketone

In organic chemistry, a ketone is an organic compound with the structure RCR', where R and R' can be a variety of atoms and groups of atoms. It features a carbonyl group bonded to two other carbon atoms. Many ketones are known and many are of great importance in industry and in biology...

s:

The corresponding organoboron and organoaluminum compounds were already known but these are air-sensitive and/or pyrophoric whereas organozirconium compounds are not.

Scope

In one study the usual regioselectivity

Regioselectivity

In chemistry, regioselectivity is the preference of one direction of chemical bond making or breaking over all other possible directions. It can often apply to which of many possible positions a reagent will affect, such as which proton a strong base will abstract from an organic molecule, or where...

 of an alkyne hydrozirconation is reversed with the addition of zinc chloride

Zinc chloride

Zinc chloride is the name of chemical compound with the formula ZnCl2 and its hydrates. Zinc chlorides, of which nine crystalline forms are known, are colorless or white, and are highly soluble in water. ZnCl2 itself is hygroscopic and even deliquescent. Samples should therefore be protected from...

:

One example of a one-pot

One-pot synthesis

In chemistry a one-pot synthesis is a strategy to improve the efficiency of a chemical reaction whereby a reactant is subjected to successive chemical reactions in just one reactor...

 hydrozirconation - carbonylation - coupling is depicted below:

With certain allyl alcohol

Allyl alcohol

Allyl alcohol is an organic compound with the structural formula CH2=CHCH2OH. Like many alcohols,it is a water soluble, colourless liquid, but it is more toxic than typical small alcohols. Allyl alcohol is used as a raw material for the production of glycerol, but is used as a precursor to many...

s, the alcohol

Alcohol

In chemistry, an alcohol is an organic compound in which the hydroxy functional group is bound to a carbon atom. In particular, this carbon center should be saturated, having single bonds to three other atoms....

 group is replaced by nucleophilic carbon forming a cyclopropane

Cyclopropane

Cyclopropane is a cycloalkane molecule with the molecular formula C3H6, consisting of three carbon atoms linked to each other to form a ring, with each carbon atom bearing two hydrogen atoms...

ring:

Organohafnium chemistry

Organohafnium compounds are nearly identical to organozirconium compounds in that these two metals are extremely similar chemically. Cationic hafnocene complexes are relevant to alpha-olefin polymerization. Typical catalysts are bis(cyclopentadienyl)hafnium(IV) dichloride, bis(cyclopentadienyl)hafnium(IV) dihydride, and dimethylbis(cyclopentadienyl)hafnium(IV).

See also

• Other chemistries of carbon with other elements in the periodic table.