A variety of metallocene catalyst precursors have been developed to prepare olefin polymers. Metallocene catalyst precursors are organometallic coordination complexes containing one or more cycloalkadienyl groups in association with a metal atom, usually a transition metal atom. Catalyst compositions containing metallocene catalyst precursors are highly useful in the preparation of polyolefins, producing relatively homogeneous copolymers at excellent polymerization rates while allowing one to tailor closely the final properties of the polymer as desired.
However, due to the very costly nature of metallocene catalyst precursors, it would be desirable to identify non-metallocene, non-cycloalkadienyl catalyst precursors having the desirable qualities of metallocene catalyst precursors, and yet provide additional opportunities for tailoring the active site to be more selective by imparting to it specific steric and electronic attributes. Such non-metallocene catalyst precursors would be useful to gain more flexible control over ligand coordination to help accommodate and lower key activation barriers or raise undesirable ones to, for example, favor monomer insertion over chain termination, or affect stereo/regio-selectivity. It would also be desirable to have more synthetic options available to minimize synthetic byproducts, prevent ligand decomposition, and delay catalyst deactivation without sacrificing catalyst performance or polymer properties.
Although a number of researchers have identified non-cycloalkadienyl ligands, some of which have been used to form metal complexes, very few have resulted in catalyst precursors having activities comparable to metallocenes. However, applicant has now identified the specific electronic properties required of non-metallocene, non-cycloalkadienyl catalyst precursors to provide them with the advantageous properties of conventional metallocenes. In addition, the ability to tune catalyst and polymer properties, such as activity, selectivity, molecular weight, molecular weight distribution, branching architecture, and the like, as desired is provided by adjusting the electronic profile of the non-cycloalkadienyl anionic ligand or the non-cycloalkadienyl catalyst precursor.