Direct Synthesis of Heavy Grignard Reagents: Challenges, Limitations, and Derivatization.

The direct synthesis of organocalcium compounds (heavy Grignard reagents) by the reduction of organyl halides with activated calcium powder succeeded in a straightforward manner for organic bromides and iodides that are bound at sp -hybridized carbon atoms. Extension of this strategy to alkyl halides was very limited, and only the reduction of trialkylsilylmethyl bromides and iodides with activated calcium allowed the isolation of the corresponding heavy Grignard reagents. Substitution of only one hydrogen atom of the methylene moiety by a phenyl or methyl group directed this reduction toward the Wurtz-type coupling and the formation of calcium halide and the corresponding C-C coupling product.

Triangles and Squares for a Unique Molecular Crystal Structure: Unsupported Two-Coordinate Lithium Cations and CC Agostic Interactions in Cyclopropyllithium Derivatives.

Understanding and controlling the aggregation state is germane to alkyllithium chemistry. Lewis base-free alkyllithium compounds normally form tetrahedral tetramers or octahedral hexamers in the solid state with the lithium cations being three-coordinate. We report that the unsupported cyclopropyl derivative 1-(trimethylsilyl)cyclopropyllithium [{μ-c-C(SiMe )C H }Li] (1), synthesized by the reduction of 1-(phenylthio)-1-(trimethylsilyl)cyclopropane, crystallizes as a tetramer in the space group I-4 with the two-coordinate lithium atoms forming a square.

Coupling and Dearomatization of Pyridines at a Transient η -Cyclopropene/Bicyclobutane Zirconocene Complex.

This paper reports on stereospecific coupling reactions between an η -cyclopropene ligand and pyridine derivatives, which are preferred to alternative C-H bond activation reactions. The dicyclopropylzirconocene complex [Cp Zr(c-C H ) ] (1) eliminates cyclopropane to generate the η -cyclopropene/bicyclobutane intermediate [Cp Zr(η -c-C H )] (A). A does not activate any pyridine C-H bonds, but rather pyridine inserts into a Zr-C bond of A, yielding an azazirconacycle with a dearomatized pyridyl group [Cp Zr{κ -N,C -(2-c-C H )-C H N}] (2).

α-CC agostic structures and aggregation diversity in cyclopropyllithium derivatives.

In the presence of thf or tmeda and depending on experimental conditions, 1-phenylcyclopropyllithium may be crystallised as either dinuclear or tetranuclear species both exhibiting α-CC agostic distortions towards tricoordinate lithium cations. In thf solution, deaggregation of the dinuclear complex takes place to yield a well-defined mononuclear species [Li(thf)3(c-CPhC2H4)].