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Schwartz's reagent

Schwartz's reagent

IUPAC name	Bis(η5-cyclopentadienyl)- zirconium(IV) chloride hydride
Other names	Cp2ZrClH, zirconocene chloride hydride
Identifiers
CAS number	37342-97-5
Properties
Molecular formula	C₁₀H₁₁Cl Zr
Molar mass	257.87 g/mol
Appearance	White solid
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references

Schwartz's reagent is the common name for the chemical compound with the formula (C₅H₅)₂ZrHCl. This metallocene is used in organic synthesis for various transformations of alkenes and alkynes.^[1]^[2]^[3]

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Hydrozirconation

Schwartz's reagent reacts with alkenes and alkynes via the process called hydrozirconation which formally results in the addition of the Zr-H bond across the C=C or C≡C bond. The selectivity of the hydrozirconation of alkynes has been studied in detail.^[4]^[5] The rate of addition to unsaturated carbon-carbon bonds is terminal alkyne > terminal alkene ~ internal alkyne > disubstituted alkene.^[6] Acyl complexes can be generated by insertion of CO into the C-Zr bond resulting from hydrozirconation.^[7]

Preparation

The complex was first prepared by Wailes and Weigold.^[8] It can be purchased or readily prepared by reduction of zirconocene dichloride with lithium aluminum hydride.^[9]

(C₅H₅)₂ZrCl₂ + ¹/₄ LiAlH₄ → (C₅H₅)₂ZrHCl + ¹/₄ "LiAlCl₄"

In practice this reaction also makes (C₅H₅)₂ZrH₂, which is treated with methylene chloride to give the mixed hydride chloride. An alternative procedure that generated Schwartz'd Reagent from dihydride has also been reported.^[10]

It is claimed that Schwartz's Reagent has been used in over 100 natural product syntheses.^[11]

References

^ D. W. Hart and J. Schwartz (1974). "Hydrozirconation. Organic Synthesis via Organozirconium Intermediates. Synthesis and Rearrangement of Alkylzirconium(IV) Complexes and Their Reaction with Electrophiles". J. Am. Chem. Soc. 96 (26): 8815-8116. doi:10.1021/ja00833a048.
^ J. Schwartz, and J. A. Labinger (2003). "Hydrozirconation: A New Transition Metal Reagent for Organic Synthesis". Angew. Chem. Int. Ed. 15 (6): 330-340. doi:10.1002/anie.197603331.
^ Donald W. Hart, Thomas F. Blackburn, Jeffrey Schwartz (1975). "Hydrozirconation. III. Stereospecific and regioselective functionalization of alkylacetylenes via vinylzirconium(IV) intermediates". J. Am. Chem. Soc. 97 (3): 679-680. doi:10.1021/ja00836a056.
^ R. C. Sun, M. Okabe, D. L. Coffen, and J. Schwartz (1998). "Conjugate Addition of a Vinylzirconium Reagent: 3-(1-Octene-1-yl)cyclopentanone". Org. Synth.; Coll. Vol. 9: 640.
^ Panek, J. S.; Hu, T. (1997). "Stereo- and Regiocontrolled Synthesis of Branched Trisubstituted Conjugated Dienes by Palladium(0)-Catalyzed Cross-Coupling Reaction". J. Org. Chem. 62 (15): 4912-4913. doi:10.1021/jo970647a.
^ Peter Wipf and Heike Jahn (1996). "Synthetic applications of organochlorozirconocene complexes". Tetrahedron 52 (40): 12853-12910. doi:10.1016/0040-4020(96)00754-5.
^ Christopher A. Bertelo, Jeffrey Schwartz (1975). "Hydrozirconation. II. Oxidative homologation of olefins via carbon monoxide insertion into the carbon-zirconium bond". J. Am. Chem. Soc. 97 (1): 228-230. doi:10.1021/ja00834a061.
^ P. C. Wailes and H. Weigold (1970). "Hydrido complexes of zirconium I. Preparation". Journal of Organometallic Chemistry 24: 405-411. doi:10.1016/S0022-328X(00)80281-8.
^ S. L. Buchwald, S. J. LaMaire, R. B. Nielsen, B. T. Watson, and S. M. King. "Schwartz's Reagent". Org. Synth.; Coll. Vol. 9: 162.
^ Peter Wipf, Hidenori Takahashi, and Nian Zhuang (1998). "Kinetic vs. thermodynamic control in hydrozirconation reactions". Pure Appl. Chem. 70 (5): 1077-1082.
^ A. Maureen Rouhi (1998). "Organozirconium Chemistry Arrives". C&EN News 82 (16): 162.

Categories: Metallocenes | Zirconium compounds

This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Schwartz's_reagent". A list of authors is available in Wikipedia.