Ind represents an indenyl group, R??? represents a substituent, other than hydrogen, bound to the Ind group at the 2-position, Cp represents a cyclopentadienyl group, M represents a transition metal from group 3 and the lanthanides of the Period System of Elements, Q represents a ligand to M, and k is an integer linked to the valence of M, wherein k equals the valence of M minus two divided by the