Halogen substituted metallocene compounds are described and comprise one or more monocyclic or polycyclic ligands that are pi-bonded to the metal atom and include at least one halogen substituent directly bonded to an sp2 carbon atom at a bondable ring position of the ligand, wherein the or at least one ligand has one or more ring heteroatoms in its cyclic structure. When combined with a suitable activator, these compounds show activity in the polymerization of olefins, such as ethylene and propylene.