Multimetallic Alkaline-Earth Hydride Cations

Reactions of dimeric β-diketiminato (BDI) magnesium and calcium hydrides with [(BDI)Mg]⁺[Al{OC(CF₃)₃}₄]^- provide ionic multimetallic hydride derivatives, which have been characterized by single-crystal X-ray diffraction analysis. The exclusively magnesium centered species comprises a cation in which two [(BDI)Mg]⁺ units are connected by a single μ₂-bridging hydride. In contrast, the greater lability of the calcium-containing system is underscored by the isolation of a cyclic heterotrimetallic species in which a CaH₂ moiety is coordinated by a molecule of benzene and an aryl substituent of a [{(BDI)Mg}₂H]⁺ cation. The homometallic dimagnesium species displays a greater facility toward reaction with diphenylacetylene than neutral [(BDI)MgH]₂, although the resultant crystallographically characterized vinyldimagnesium cation equilibrates into a complex mixture of neutral and ionic species in solution. An initial assessment of both systems for the hydrosilylation of 1-hexene and diphenylacetylene evidences an inferior catalytic performance of [(BDI)MgH]₂ in isolation.