Schwartz's reagent

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.

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&equiv;C bond. The selectivity of the hydrozirconation of alkynes has been studied in detail. The rate of addition to unsaturated carbon-carbon bonds is terminal alkyne > terminal alkene ~ internal alkyne > disubstituted alkene. Acyl complexes can be generated by insertion of CO into the C-Zr bond resulting from hydrozirconation.

Preparation
The complex was first prepared by Wailes and Weigold. It can be purchased or readily prepared by reduction of zirconocene dichloride with lithium aluminum hydride.
 * (C5H5)2ZrCl2 +  1/4 LiAlH4  &rarr;  (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.

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