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Schwartz's reagent

Introduction

Template:Chembox new 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]

Hydrozirconation

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 Cā‰”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

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 ā†’ (C5H5)2ZrHCl + 1/4 “LiAlCl4“

In practice this reaction affords also (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

References

  1. ā†‘ 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”. Journal of the American Chemical Society. 96 (26): 8815ā€“8116. doi:10.1021/ja00833a048.
  2. ā†‘ J. Schwartz, and J. A. Labinger (2003). “Hydrozirconation: A New Transition Metal Reagent for Organic Synthesis”. Angew. Chem. Int. Ed. 15 (6): 330ā€“340. doi:10.1002/anie.197603331.
  3. ā†‘ Donald W. Hart, Thomas F. Blackburn, Jeffrey Schwartz (1975). “Hydrozirconation. III. Stereospecific and regioselective functionalization of alkylacetylenes via vinylzirconium(IV) intermediates”. JACS. 97 (3): 679ā€“680. http://pubs.acs.org/cgi-bin/searchRedirect.cgi/jacsat/1975/97/i03/pdf/ja00836a056.pdf
  4. ā†‘ 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, Coll. Vol. 9: 640.
  5. ā†‘ 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): 4912ā€“4913. doi:10.1021/jo970647a.
  6. ā†‘ Peter Wipf and Heike Jahn (1996). “Synthetic applications of organochlorozirconocene complexes”. Tetrahedron. 52 (40): 12853ā€“12910. doi:10.1016/0040-4020(96)00754-5.
  7. ā†‘ 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): 228ā€“230. http://www.orgsyn.org/orgsyn/pdfs/CV9P0162.pdf
  8. ā†‘ P. C. Wailes and H. Weigold “Hydrido complexes of zirconium I. Preparation” Journal of Organometallic Chemistry 1970 Volume 24, Pages 405-411. doi:10.1016/S0022-328X(00)80281-8.
  9. ā†‘ S. L. Buchwald, S. J. LaMaire, R. B. Nielsen, B. T. Watson, and S. M. King (1998). “Schwartz’s Reagent”. Organic Syntheses, Coll. Vol. 9: 162. http://www.orgsyn.org/orgsyn/pdfs/CV9P0162.pdf
  10. ā†‘ Peter Wipf,* Hidenori Takahashi, and Nian Zhuang (1998). “Kinetic vs. thermodynamic control in hydrozirconation reactions”. Pure & Appl. Chem. 70 (5): 1077ā€“1082.http://www.iupac.org/publications/pac/1998/pdf/7005×1077.pdf
  11. ā†‘ “ORGANOZIRCONIUM CHEMISTRY ARRIVES”. C&E News: 162. 1998. http://pubs.acs.org/cen/nlw/8216sci1.html
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