Synthesis and Structure of the Pentaisopropylcyclopentadienyl Radical

The reaction of FeCl2 with C5iPr5Na does not yield a ferrocene derivative but instead the surprisingly stable radical C5iPr. Apparently, the bulky isopropyl substituents interfere with the formation of a sandwich structure. In the crystal, the cyclopentadienyl units are stacked along the crystallographic x axis to give a “metal-free polydecker” (shown on the right).