Catalyst compositions and process for preparing polyolefins

A catalyst composition comprising at least one metallocene complex of general formula I or II M[X(R)n]xYp (I) wherein R is a univalent of divalent 1-20c hydrocarbyl, or a 1-20c hydrocarbyl containing substituent oxygen, silicon, phosphorus, nitrogen of sulphur atoms with the proviso that at least one R group contains a lewis base functionality and when there are two or more R groups present they may be the same or different, and when R is divalent it is directly attached to M and replaces a Y ligand, and wherein M is a Group IVA metal, Y is a univalent anionic ligand X is an organic group containing a cyclopentadienyl nucleus and for formula I n is an integer of 1 to 10 x is either 1 or 2, and for formula II, n, m and l are integers or 0 such that n +m +l >/=1, p =0-2, and z is a c1 to c4 alkylene radical or a dialkyl germanium or silicon or an alkyl phosphine or amine radical or bis-dialkylsilyl or bis-dialkylgermanyl containing hydrocarbyl groups having 1 to 4 carbon atoms bridging the cyclopentadienyl nuclei.