[79950-18-8] · C13H30O3Zr · Methylzirconium Tributoxide · (MW 325.65)
(nucleophile, methylating agent)
Solubility: sol diethyl ether, tetrahydrofuran, CH2Cl2.
Form Supplied in: not commercially available.
Preparative Methods: synthesized from Zr(OBu)4 and Zirconium(IV) Chloride via ClZr(OBu)3.1 The reaction of Methyllithium with a solution of tributoxyzirconium chloride in diethyl ether at -10 °C yields the reagent (eq 1). For subsequent reactions the etheral solution of the reagent is used. Both ether and ether solutions in dichloromethane have been used as solvents in the subsequent reactions.1
Purification: used as generated in solution.
Handling, Storage, and Precautions: extremely hygroscopic, decomposed by moist air; must be handled under N2 or Ar; reagent causes burns, and is harmful if inhaled or swallowed. Use in a fume hood.
Methylzirconium tributoxide, like its higher alkyl, aryl, and vinyl homologs, is a selective nucleophile of low basicity. The selectivity is less, however, than in the titanium analogs, as seen in the preference for aldehydes in the presence of ketones (eq 2).1
Several functional groups are compatible (eq 3).
Basic nitrogen atoms in the substrate molecules do not influence the apparent basicity of the zirconium reagents as much as they do the lithium, Grignard, or titanium derivatives (eq 4).1
The alkylzirconium tributoxides are less basic than the titanium analogs, and considerably less basic than the lithium and Grignard reagents and are therefore the reagents of choice in reactions with easily enolizable ketones. In the sugar example given, the reaction is chemo- and stereospecific; only the b-methyl isomer was formed (eq 5).2 Tetramethylzirconium affords a mixture of the a- and b-stereoisomers, and other organometallic reagents failed because of enolization reactions.
Norwegian College of Pharmacy, Oslo, Norway
Frode Rise & Kjell Undheim
University of Oslo, Norway