Zirconocene-Mediated Carbonylative Coupling of Grignard Reagents

Abstract

Organozirconocenes are versatile synthetic intermediates that can undergo carbonylation to yield acyl anion equivalents. Zirconocene hydrochloride ([Cp2 ZrHCl]) is often the reagent of choice for accessing these intermediates but generates organozirconocenes only from alkenes and alkynes. This requirement eliminates a broad range of substrates. For example, organozirconocenes in which the zirconium center is bonded to an aromatic ring, a benzylic group, or an alkyl group that possesses a tertiary or quaternary carbon atom α to the carbon-zirconium bond can not be formed in this way. To provide more generalized access to acyl zirconium reagents, we explored the transmetalation of Grignard reagents with zirconocene dichloride under a CO atmosphere. This protocol generates acyl zirconium(IV) complexes that are inaccessible with the Schwartz reagent, including those derived from secondary and tertiary alkyl and aryl Grignard reagents.

Keywords: carbonylation; carbonylative coupling; iodonium salts; isomerization; zirconium complexes.