Comparative Investigation of η⁶‑Arene Tethered Ru(II) Complexes with Different Tethered Heteroatoms for Ethylene Polymerization Catalysis: Experimental and DFT Studies

η6-Arene tethered ruthenium(II) complexes (η6-C6H5(CH2)3SCH3RuCl2) (1), (η6-C6H5(CH2)3N(CH3)2RuCl2) (2), and [(η6-C6H5(CH2)3OCH3RuCl2)]2 (3) with coordinating oxygen, sulfur, and nitrogen heteroatoms in the tethered arms have been compared for olefin polymerization. Complexes 1 and 2 are active for olefin polymerization while oxygen-containing complex 3 is inactive. The nitrogen-containing complex, 2, is 1.5-fold more active than the sulfur-containing complex 1. The polymers obtained are composed of two different fractions, a high molecular weight fraction (Mn ∼ 55–262 kg·mol–1) and a low molecular weight fraction (Mn ∼ 276–848 g·mol–1). The polydispersities of both fractions are narrow, indicating a single-site catalyst. DFT calculations were carried out on complexes 1 and 2 to determine the migratory insertion barriers. Complex 2 was found to have a migratory insertion barrier of the chain propagation of 19.4 kcal·mol–1, while complex 1 was found to be 21.8 kcal·mol–1. Theoretical calculations are in agreement with the experimental polymerization activity results.