Organozirconium chemistry

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. 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; their use partly replaced traditional heterogeneous Ziegler-Natta catalysts. Cp2ZrH2 was obtained in 1966 by the reaction of (Cp)2Zr(BH4)2 with triethylamine. In 1970 the related hydrochloride (now called Schwartz's reagent) was obtained by reduction of zirconacene dichloride (Cp2ZrCl2) with 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. Schwartz's reagent (2) was subsequently found to participate in hydrozirconation, which enjoys with some use in organic synthesis. Substrates for hydrozirconation are alkenes and alkynes. With terminal alkynes the terminal vinyl zirconium product predominates. Secondary reactions are nucleophilic additions, transmetalations, conjugate additions, coupling reactions, carbonylation and halogenation. Zirconocene dichloride can be used to cyclise enynes and dienes to give cyclic or bicyclic aliphatic systems. Organohafnium compounds behave nearly identically to organozirconium compounds, as hafnium, which is just below zirconium on the periodic table, has similar chemical properties to zicronium. 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 catalysts, are used on an industrial scale for the polymerization of alkenes.