Disclosed are compounds useful as catalyst activators for olefin polymerization, comprising structures of the following formulae: wherein: L+ is a protonated derivative of an element of Group 15 of the Periodic Table of the Elements, additionally bearing two hydrocarbyl substituents of from 1 to 50 carbons each, or a positively charged derivative of an element of Group 14 of the Periodic Table of the Elements, said Group 14 element being substituted with three hydrocarbyl substituents of from 1 to 50 carbons each; R1 is a divalent linking group of from 1 to 40 non-hydrogen atoms; R2 independently each occurrence is a ligand group of from 1 to 50 nonhydrogen atoms with the proviso that in a sufficient number of occurrences to balance charge in the compound, R2 is L+—R1—; M1 is boron, aluminum or gallium; Arf independently each occurrence is a monovalent, fluorinated organic group containing from 6 to 100 non-hydrogen atoms; Y is a Group 15 element; and Z is a Group 14 element.