Non-cyclopentadienyl organometallic compounds of calcium, strontium and barium

The use of sterically demanding ligands has allowed the organometallic compounds of the heavy alkaline-earth metals calcium, strontium and barium to emerge from the shadow cast by the far better studied organomagnesium Grignard reagents. Metallocenes and other cyclopentadienyl-based complexes have been the most intensively investigated, but in the past decade a wealth of new non-cyclopentadienyl compounds have been characterized. A broad range of structure types are known, encompassing σ- and π-bound anionic ligands, and Lewis base adducts with neutral donors. In this review, crystallographically characterized complexes are discussed, and current interpretations of the bonding in heavier Group 2 element compounds are examined. Recent applications of non-cyclopentadienyl compounds in organic synthesis are surveyed.