Olefins, also commonly known as alkenes, are important items of commerce.  Their many applications include employment as intermediates in the manufacture of detergents, as precursors to more environmentally friendly refined oils, as monomers, and as precursors for many other types of products.  An important subset of olefins are olefin oligomers, and one method of making olefin oligomers is via oligomerization of ethylene, which is a catalytic reaction involving various types of catalysts and/or catalyst systems.  Examples of catalysts and catalyst systems used commercially in the oligomerization of olefins include alkylaluminum compounds, certain nickel-phosphine complexes, a titanium halide with a Lewis acid (e.g., diethyl aluminum chloride), and a selective 1-hexene catalyst system containing a chromium containing compound (e.g., a chromium carboxylate), a nitrogen containing ligand (e.g., a pyrrole), and a metal alkyl (e.g., alkyl aluminum compounds). 
Several non-commercial olefin oligomerization catalyst systems are based upon metal complexes of pyridine bis-imines, metal complexes of α-diimine compounds having a metal complexing group, and selective trimerization and/or tetramerization catalyst system using a metal complex of a compound having a diphosphinylaminyl group.  These catalyst systems typically use an alkyl aluminum compound (e.g., aluminoxane) to activate the metal complexes for olefin oligomerization. 
Applications and demand for olefin oligomers (e.g., alpha olefins) continue to multiply, and competition to supply them correspondingly intensifies.  Thus, additional novel and improved catalysts and methods for olefin oligomerization are desirable.