A series of aluminum aryloxides of types [Al­(OAr)3] and [Al­(OAr)2Cl] (Ar = 4-CH3C6H4, 4-PhC6H4, 2-iPr-C6H4, 2-tBu-C6H4, 2,6-iPr2C6H3, and 2,6-Cl2C6H3) were synthesized from commercially available reagents and structurally characterized by single X-ray diffraction studies. The structural evaluations for aluminum aryloxides revealed the formation of dinuclear clusters in the solid state. The solution behavior of the synthesized compounds was studied by multinuclear nuclear magnetic resonance (NMR) spectroscopy. The synthesized compounds were applied for the in situ generation of Ziegler–Natta catalyst systems for the ring-opening metathesis polymerization (ROMP) of nonconstrained olefins. The ligand exchange between WCl6 and Al-aryloxides followed by activation with aluminum alkyls resulted in the formation of ill-defined species showing enhanced ROMP reactivity compared to the related systems generated upon the ligand exchange between WCl6 and ArOH or isolated [W­(OAr)4Cl2]. The benefits of using newly developed systems for the ROMP of cyclic olefins are their low costs and high molecular weights for polymerization products (M w > 250 kDa). Moreover, an E/Z stereoselective control over the double CC bond in the polymeric product was achieved upon tuning the steric volume at the aryloxide ligand framework.