Mixed bis-imine pyridine ligands of formula (I), wherein Z.sub.1, which is different from Z.sub.2, is an optionally substituted aryl group; and Z.sub.2 comprises an optionally substituted heterohydrocarbyl moiety, or an optionally substituted aryl group in combination with a metal, said optionally substituted aryl group being .pi.-co-ordinated to the metal; ##STR00001## mixed bis-imine pyridine complexes comprising a ligand of formula (I); mixed ionic bis-imine pyridine complexes comprising a ligand of formula (I); and processes for the production of alpha olefins from ethylene, using said complexes.