ChemInform Abstract: Magnesium Dihalide Promoted Addition of Grignard Reagents to the Cyclopentadienyl Rings of Tungstenocene Dichloride.
Abstract
The nucleophilic alkyls in some Grignard reagents (II) can be induced to add to a cyclopentadienyl ligand in (I).
ChemInform Abstract
The nucleophilic alkyls in some Grignard reagents (II) can be induced to add to a cyclopentadienyl ligand in (I). These reactions offer convenient access to tungstenocene derivatives containing functionalized cyclopentadienyl ligands. The reactions are promoted by the addition of MgCl2, which is essential for the reproducible synthesis of (III) in good yield. Grignards such as (VII), which react at the metal to give bis-alkyls, are unaffected by added MgCl2. Studies of the reaction mechanism concerning the role of added magnesium halide suggest the formation of a double halide bridge in an intermediate. This can explain the otherwise surprising observation that the reaction of (I) with allyl-MgBr leads to predominant formation of the hydrobromide (X) with the hydrochloride (IIIa) as the minor product.
