Abstract: The invention addresses Group 5 metal compounds suitable as polymerization catalysts characterized by comprising one Group 15 element polyanionic ancillary ligand and three single or multidentate univalent ligands comprising Group 14-16 elements bound to the Group 5 metal, but excluding cyclopentadienyl ligands. The invention Group 5 metal compounds can be generically represented by the chemical symbols(1) ?RJ!MR'.sub.3, and(2) ?(RJ)Zn(Q)!MR'.sub.2where M is a Group 5 transition metal, preferably vanadium; J is a Group 15 heteroatom ligand covalently bound to M, preferably nitrogen; R is a substituted or unsubstituted aryl, hydrocarbyl or organometalloid group covalently bound to J; each R' is, independently, a uninegative ligand, e.g.