Organomagnesium compound

The group 2 elements are known to form organometallic compounds. Of these, organomagnesium compounds, usually in the form of Grignard reagents are widely used in organic chemistry, while the other organometallic compounds of this group are largely academic.

In many ways the chemistry of group 2 elements (the alkaline earth metals) mimics that of group 12 elements because both groups have filled s shells for valence electrons. Thus, both groups have nominal valency 2 and oxidation state +2. All group 2 elements are electropositive towards carbon and electronegativity decreases down the row. At the same time the atomic radius increases resulting in increasingly ionic character, higher coordination numbers, and increased ligand reactivity.

Many dialkyl group 2 metals are polymeric in the crystalline phase and resemble trimethylaluminium in three-center two-electron bond. In the gas-phase they are once again monomeric.

The metallocenes in this group are unusual. Bis(cyclopentadienyl)beryllium or beryllocene (Cp₂Be) with a molecular dipole moment of 2.2 D rules out a classical metallocene with two hapticity 5 ligands. Instead the compound is a so-called slip ⁵η/¹η sandwich and on top of that also fluxional up to −125 °C. While magnesocene (Cp₂Mg) is a regular metallocene, bis(pentamethylcyclopentadienyl)calcium (Cp^*)₂Ca is actually bent with an angle of 147°. This angle increases going down the row.

...
Wikipedia