Organozirconium compounds are organometallic compounds containing a carbon to zirconium chemical bond. 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 in organic chemistry as an intermediate in the synthesis of chemical compounds and share characteristics with organotitanium compounds also a Group 4 element. 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 family. It was prepared in a reaction of the cyclopentadienyl magnesium bromide and zirconium(IV) chloride. Zirconocenes are used as polymerization catalysts such as Kaminsky catalysts, partly replacing organotitanium compounds.
The so-called Schwartz's reagent (1974) is a zirconocene hydrochloride and a reagent in hydrometalation reactions (called hydrozirconation) with some use in organic synthesis. Substrates for hydrozirconation are alkenes and alkynes. With terminal alkynes the terminal vinyl zirconium product is predominantly formed. Secondary reactions are nucleophilic additions, transmetalations, conjugate additions, coupling reactions, carbonylation and halogenation.
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 in benzene as an uneventful insoluble solid. In 1970 H. Weigold and P.C. Wailes prepared the hydrochloride from the dichloride (Cp2ZrCl2) and Lithium aluminium hydride (or the related LiAlH(t-BuO)3). They went on to investigate the reaction of these novel hydrides with carboxylic acids (for example to compounds like CpZr(OCOR)3) and in 1971 then arrived at their reactions with alkynes.
For example, with one equivalent of Cp2ZrClH they obtained from diphenylacetylene 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 electrophiles such as hydrochloric acid, bromine and acid chlorides to the corresponding alkane, bromoalkanes and ketones:
Organohafnium compounds behave nearly identically to organozirconium compounds. Many analogous compounds are known, including bis(cyclopentadienyl)hafnium(IV) dichloride, bis(cyclopentadienyl)hafnium(IV) dihydride, and dimethylbis(cyclopentadienyl)hafnium(IV).
- Other chemistries of carbon with other elements in the periodic table.
|Compounds of carbon with other elements in the periodic table
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