Recent Developments in the Organic Chemistry of Calcium - An Element with Unlimited Possibilities in Organometallic Chemistry?

The organocalcium chemistry developed vastly during the last decade. The preparation of the organocalcium compounds via direct synthesis (insertion of Ca into a C-X bond of phenyl halides, Grignard reaction) affords skilful procedures due to the inertia of the calcium metal and the extreme reactivity of the organocalcium derivatives. Further Suitable preparative methods include metathesis reactions of CaX2 with KR or LiR, metallation reactions of H-acidic Substrates. metal-halogen exchange reactions, and transmetallation of heavy main group atoms in their compounds with calcium metal. Possibilities to stabilize organocalcium compounds include steric shielding by bulky ligands at the periphery and electronic reduction of the nucleophilicity of the calcium-bound carbanions. Selected applications in catalysis such as hydrophosphination are also mentioned. Very recent developments and challenges in the preparation of alkaline earth metal(I) compounds are presented as well. Concepts to overcome the rather large atomization energies of the metals are discussed.