A metallocene complex is represented by the the formula (C.sub.pR.sub.5).sub.nMX.sub.k where C.sub.p (each occurrence) is a cyclopentadienyl group; each of the five R substituents on the or each cyclopentadienyl group is independently selected from hydrogen, C.sub.1 to C.sub.30 substituted or unsubstituted hydrocarbyl, halohydrocarbyl, silylhydrocarbyl or silylhalohydrocarbyl, wherein two adjacent R substituents may be joined to form part of a saturated, partially unsaturated or aromatic monocyclic or polycyclic ring structure, and SiR'.sub.2NR''.sub.2 where each of the two R' substituents is independently selected from hydrogen, C.sub.1 to C.sub.30 substituted or unsubstituted hydrocarbyl, halohydrocarbyl, silylhydrocarbyl or silylhalohydrocarbyl, wherein two adjacent R' substituents may be joined to form part of a saturated, partially unsaturated or aromatic monocyclic or polycyclic ring structure, and each of the two R'' substituents is independently selected from C.sub.2 to C.sub.30 substituted or unsubstituted hydrocarbyl, halohydrocarbyl, silylhydrocarbyl or silylhalohydrocarbyl, wherein two adjacent R'' substituents may be joined to form part of a saturated, partially unsaturated or aromatic monocyclic or polycyclic ring structure; n is 1 or 2; M is a metal of valence m from Groups 4 to 11 of the Periodic Table of Elements, k is equal to m minus n and the or each X substituent is a univalent anionic ligand, or two X substituents are joined and bound to the metal atom to form a metallocycle ring, or two X substituents are joined to form a chelating ligand, a diene ligand, or an alkylidene ligand, provided that at least one R substituent on the or one cyclopentadienyl group is SiR'.sub.2NR''.sub.2, provided that at least one R substituent on at least one C.sub.p is SiR'.sub.2NR''.sub.2 and provided that one or the C.sub.p may be bridged by a bridging group to another C.sub.p group, or a heteroatom containing group, where the bridging group replaces one R group on the C.sub.p group(s) or a hydrogen on a heteratom containing group.