Schwartz's reagent
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| Names | |||
|---|---|---|---|
| IUPAC name
chloridobis(η5-cyclopentadienyl)hydridozirconium
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| Other names
Cp2ZrClH, zirconocene hydride
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| Identifiers | |||
| ECHA InfoCard | 100.048.599 | ||
CompTox Dashboard (EPA)
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| Properties | |||
| C10H11ClZr | |||
| Molar mass | 257.87 g/mol | ||
| Appearance | White solid | ||
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Schwartz's reagent is the common name for the chemical compound with the formula (C5H5)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. This metallocene is used in organic synthesis for various transformations of alkenes and alkynes.[1][2][3]
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] Generally, the addition of the Zr-H proceeds the syn-addition. 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] Upon alkene insertion into the zirconium hydride bond, the resulting zirconium alkyl undergoes facile rearrangement to the terminal alkyl and therefore only terminal acyl compounds can be synthesized in this way. The rearrangement most likely proceeds via β-hydride elimination followed by reinsertion.
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 aluminium hydride:
- (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.[9] An alternative procedure that generated Schwartz's Reagent from dihydride has also been reported.[10]
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): 8115–8116. 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.
{{cite journal}}: CS1 maint: multiple names: authors list (link) - ^ R. C. Sun, M. Okabe, D. L. Coffen, and J. Schwartz (1998). "Conjugate Addition of a Vinylzirconium Reagent: 3-(1-Octene-1-yl)cyclopentanone". Organic Syntheses
{{cite journal}}: CS1 maint: multiple names: authors list (link); Collected Volumes, vol. 9, p. 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.
{{cite journal}}: CS1 maint: multiple names: authors list (link) - ^ 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 (2): 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". Organic Syntheses
{{cite journal}}: CS1 maint: multiple names: authors list (link); Collected Volumes, vol. 9, p. 162. - ^ Peter Wipf, Hidenori Takahashi, and Nian Zhuang (1998). "Kinetic vs. thermodynamic control in hydrozirconation reactions" (PDF). Pure Appl. Chem. 70 (5): 1077–1082. doi:10.1351/pac199870051077.
{{cite journal}}: CS1 maint: multiple names: authors list (link)