Organometallic complexes are described which are useful as pre-polymerization catalysts which may form part of olefin polymerization catalyst systems. The catalyst systems find use in the polymerization of ethylene, optionally with one or more C.sub.3-12 alpha-olefin comonomers. The organometallic complexes can be represented by formula X:

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wherein L* is a bridging group containing at least one cycloalkylene, heterocycloalkylene, arylene or heteroarylene group. The olefin polymerization catalyst system is effective at polymerizing ethylene with alpha-olefins in a solution phase polymerization process at high temperatures and produces ethylene copolymers with high molecular weight and high degrees of alpha-olefin incorporation. Pre-metallation compounds, metallation processes and synthetic methods to make the organometallic complexes as well as polymerization processes are also described.

A machine learning model predicts a K value for a new iron ethylene oligomerization catalyst structure, where the K value has not yet been experimentally determined.

Phosphino-quinoline-pyridine ligands and compositions that include complexes, the complexes including a phosphino-quinoline-pyridine ligand and a metal coordinated to the ligand are disclosed. Methods of oligomerization, such as methods of oligomerizing alpha-olefins, performed in the presence of a complex that includes a phosphino-quinoline-pyridine ligand are also disclosed.

A machine learning model predicts a K value for a new iron ethylene oligomerization catalyst structure, where the value has not yet been experimentally determined.