Zirconium(IV) chloride

Zirconium(IV) chloride, also known as zirconium tetrachloride, is the inorganic compound with the formula ZrCl₄. This white high-melting solid hydrolyzes rapidly in humid air. It is a key reagent in the chemistry of zirconium.

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Structure

Unlike TiCl₄, ZrCl₄ adopts a polymeric structure wherein each Zr is octahedrally coordinated. This difference in structures, polymeric vs. molecular, is responsible for the striking difference in their properties - one being distillable, the other being a high melting solid. In the solid state, ZrCl₄ adopts a tape-like linear polymeric structure--the same structure adopted by HfCl₄. This polymer degrades readily upon treatment with Lewis bases, which cleave the Zr-Cl-Zr linkages.^[1]

Kroll process

ZrCl₄ is an intermediate in the conversion of zirconium minerals to metallic zirconium by the Kroll process. In nature, zirconium minerals invaribly exists as oxides (reflected also by the tendency of all zirconium chlorides to hydrolyze). For their conversion to bulk metal, these refractory oxides are first converted to the tetrachloride, which can be distilled at high temperatures. This conversion entails treatment of the oxide with carbon as the oxide "getter" and chlorine.

ZrO₂ + 2 C + 2 Cl₂ → ZrCl₄ + 2 CO

Chemical reactions

ZrCl₄ is the principal starting compound for the synthesis of many organometallic complexes of zironcium.^[2] Because of its polymeric structure, ZrCl₄ it is usually converted to a molecular complex before use. It forms a 1:2 complex with tetrahydrofuran: CAS [21959-01-3], mp 175-177 °C.^[3] NaC₅H₅ reacts with ZrCl₄(THF)₂ to give zirconocene dichloride, ZrCl₂(C₅H₅)₂, a versatile organozirconium complex.^[4] One of the most curious properties of ZrCl₄ is its high solubility in the presence of methylated benzenes, such as durene. This solubilization arises through the formation of π-complexes.^[5]

Uses

In organic synthesis zirconium tetrachloride is used as a weak Lewis acid for the Friedel-Crafts reaction, the Diels-Alder reaction and intramolecular cyclisation reactions.^[6] It is also used to make water-repellent textiles.

References

1. ^ N. N. Greenwood & A. Earnshaw, Chemistry of the Elements (2nd ed.), Butterworth-Heinemann, Oxford, 1997.
2. ^ New Aspects of Zirconium Containing Organic Compounds. Topics in Organometallic Chemistry, 10 Edited by Ilan Marek (Technion-Israel Institute of Technology, Haifa). Springer: Berlin, Heidelberg, New York. 2005. x + 176 pp. ISBN 3-540-22221-9.
3. ^ L. E. Manxzer, Joe Deaton, Paul Sharp, R. R. Schrock (1982). "Tetrahydrofuran Complexes of Selected Early Transition Metals". Inorganic Syntheses 21: 135-40. doi:10.1002/9780470132524.ch31.
4. ^ G. Wilkinson and J.G. Birmingham (1954). "Bis-cyclopentadienyl Compounds of Ti, Zr, V, Nb and Ta". J. Am. Chem. Soc. 76 (17): 4281-4284. doi:10.1021/ja01646a008.
5. ^ Musso, F.; Solari, E.; Floriani, C.; Schenk, K. (1997). "Hydrocarbon Activation with Metal Halides: Zirconium Tetrachloride Catalyzing the Jacobsen Reaction and Assisting the Trimerization of Alkynes via the Formation of η⁶-Arene-Zirconium(IV) Complexes". Organometallics 16: 4889-4895. doi:10.1021/om970438g.
6. ^ Bora U. (2003). "Zirconium Tetrachloride". Synlett: 1073-1074. doi:10.1055/s-2003-39323.