Schwartz's Reagent
Encyclopedia
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.
complexes can be generated by insertion of CO
into the C-Zr bond resulting from hydrozirconation. 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.
with lithium aluminium hydride
:
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's Reagent from dihydride has also been reported.
Chemical compound
A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...
with the formula
Chemical formula
A chemical formula or molecular formula is a way of expressing information about the atoms that constitute a particular chemical compound....
(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
Princeton University
Princeton University is a private research university located in Princeton, New Jersey, United States. The school is one of the eight universities of the Ivy League, and is one of the nine Colonial Colleges founded before the American Revolution....
. This metallocene
Metallocene
A metallocene is a compound typically consisting of two cyclopentadienyl anions bound to a metal center in the oxidation state II, with the resulting general formula 2M. Closely related to the metallocenes are the metallocene derivatives, e.g. titanocene dichloride, vanadocene dichloride...
is used in organic synthesis
Organic synthesis
Organic synthesis is a special branch of chemical synthesis and is concerned with the construction of organic compounds via organic reactions. Organic molecules can often contain a higher level of complexity compared to purely inorganic compounds, so the synthesis of organic compounds has...
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≡C bond. The selectivity of the hydrozirconation of alkynes has been studied in detail. 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 AcylAcyl
An acyl group is a functional group derived by the removal of one or more hydroxyl groups from an oxoacid, including inorganic acids.In organic chemistry, the acyl group is usually derived from a carboxylic acid . Therefore, it has the formula RCO-, where R represents an alkyl group that is...
complexes can be generated by insertion of CO
Carbon monoxide
Carbon monoxide , also called carbonous oxide, is a colorless, odorless, and tasteless gas that is slightly lighter than air. It is highly toxic to humans and animals in higher quantities, although it is also produced in normal animal metabolism in low quantities, and is thought to have some normal...
into the C-Zr bond resulting from hydrozirconation. 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. It can be purchased or readily prepared by reduction of zirconocene dichlorideZirconocene dichloride
Zirconocene dichloride is an organozirconium compound composed of a zirconium central atom, with two cyclopentadienyl and two chloro ligands. It is a colourless diamagnetic solid that is somewhat stable in air.-Preparation:...
with lithium aluminium hydride
Lithium aluminium hydride
Lithium aluminium hydride, commonly abbreviated to LAH or known as LithAl, is an inorganic compound with the chemical formula LiAlH4. It was discovered by Finholt, Bond and Schlesinger in 1947. This compound is used as a reducing agent in organic synthesis, especially for the reduction of esters,...
:
- (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's Reagent from dihydride has also been reported.