This invention relates to a catalyst system for the production of polyolefins comprising:(A) a Group IV B transition metal component represented by one of the two general formulae ##STR00001## wherein(C.sub.5H.sub.5-y-xR.sub.x) is a cylopentadienyl ring(JR'.sub.z-l-y) is a heteroatom ligand in which J is an element with a coordination number of three from Group V-A or an element with a coordination number of two rom Group VI-A of the Periodic Table of Elements,each Q is independently, hydride, C.sub.1--C.sub.20 hydrocarbyl radicals, substituted hydrocarbyl radials wherein one or more hydrogen atoms is replaced by an electron withdrawing group, or C.sub.1--C.sub.20 hydrocarbyl-substituted metalloid radicals wherein the metalloid is selected from the group consisting of germanium and silicon, provided that Q is not a substituted or unsubstituted cyclopentadienyl ring, or both Q together may be an alkylidene, olefin, acetylene or a cyclometallated hydrocarbyl;"y" is 0 or 1; when "y" is 1, T is a covalent bridging group containing a Group IV-A or V-A element;L is a neutral Lewis base; and "w" is a number from 0 to 3;(B) an activator compound comprising (1) a cation; and (2) a compatible noncoordinating anion.