Metallic complexes having indenyl ligands can be used as an ingredient of a catalyst system. The catalyst system can be used in polymerizations of ethylenically unsaturated hydrocarbon monomers that include both olefins and polyenes. Embodiments of the catalyst system can provide interpolymers that include polyene mer and from 40 to 75 mole percent ethylene mer, with a plurality of the ethylene mer being randomly distributed. The catalyst system also can be used in solution polymerizations conducted in C5-C12 alkanes, yielding interpolymers that include at least 10 mole percent ethylene mer.