Synthesis of Symmetric Metallocenes from Metallic Calcium, Strontium, or Barium and Pentaisopropylcyclopentadienyl Radicals

The largest interplanar distance known to date between adjacent parallel rings of any sandwich compound (5.497(3) Å) is displayed by decaisopropylbarocene, the first heavy alkaline earth metal sandwich compound to possess axial symmetry. A new efficient metallocene formation [Eq. (1)] utilizes the free cyclopentadienyl radical [C5R5]. (R=CHMe2) as an oxidizing agent for elemental Ca, Sr, and Ba (M).