Catalyst composition

A catalyst composition comprising the reaction product of:

• a) an organometallic complex of the formula:
• ##STR11## wherein:
• M is a metal of Group 4 of the Periodic Table of the Elements having an oxidation state of +3 or +4, bound in an .eta..sup.5 bonding mode to Cp;
• n is zero or one, depending on the oxidation state of M;
• R'" is hydride or C.sub.1-20 hydrocarbyl;
• Cp is a cyclopentadienyl-, indenyl-, tetrahydroindenyl-, fluorenyl-, or octahydrofluorenyl-group, covalently substituted with a divalent moiety, R", having from 1 to 50 atoms and being covalently bonded to Y, Cp further may be substituted with from 1 to 4 alkyl, halogen, aryl, haloalkyl, alkoxy, aryloxy or silyl groups containing up to 20 non-hydrogen atoms;
• and
• Y is a divalent substituent selected from the group consisting of --NR--, --PR--, --O-- and --S--, wherein R is C.sub.1-20 hydrocarbyl, and Y together with R", Cp and M forms a metallocycle;
• and
• X, if any, is a monovalent substituent selected from the group consisting of hydride, halo, alkyl, aryl, silyl, germyl, aryloxy, alkoxy, amide, siloxy, phosphine groups, and mixtures thereof, said groups having up to 20 non-hydrogen atoms;
• b) an active compound or complex, B', capable of converting the organometallic complex a) into a cationic complex of the formula:
• ##STR12## where Cp, M, Y, X and n are as previously defined, and A.sup.- is the anion resulting from the combination of B' and R which is abstracted from complex a) or A.sup.- is the counterion from complex B';
• and
• c) an alumoxane;
• the molar ratio of b):a) being from 0.1:1 to 50:1, and the ratio of c):a) being from 1:1 to 10,000:1.