ms other than hydrogen; [0006] p is 1 or 2; [0007] when p is 1, M* is hydrogen, an alkali metal or an alkaline earth metal halide, and, when p is 2, M* is an alkaline earth metal; said M* being bound to at least one of the non-fused, ring-carbons of the cyclopentadienyl ring, (1); [0008] Cp is the aromatic ligand group derived from Cp* by removal of M*; [0009] M is a metal selected from Groups 3-1