Hafnium vs. Zirconium, the Perpetual Battle for Supremacy in Catalytic Olefin Polymerization: A Simple Matter of Electrophilicity?

• Main Authors: Antonio Vittoria, Georgy P. Goryunov, Vyatcheslav V. Izmer, Dmitry S. Kononovich, Oleg V. Samsonov, Francesco Zaccaria, Gaia Urciuoli, Peter H. M. Budzelaar, Vincenzo Busico, Alexander Z. Voskoboynikov, Dmitry V. Uborsky, Christian Ehm, Roberta Cipullo
• Format: Article
• Language: English
• Published: MDPI AG 2021-08-01
• Series: Polymers
• Subjects: hafnocenes; olefin polymerization; iPP; molecular catalysts; QSAR; high-temperature performance
• Online Access: https://www.mdpi.com/2073-4360/13/16/2621

The performance of <i>C</i>₂-symmetric <i>ansa</i>-hafnocene catalysts for isotactic polypropylene typically deteriorates at increasing temperature much faster than that of their zirconium analogues. Herein, we analyze in detail a set of five Hf/Zr metallocene pairs—including some of the latest generation catalysts—at medium- to high-polymerization temperature. Quantitative structure–activity relationship (QSAR) models for stereoselectivity, the ratio allyl/vinyl chain ends, and 2,1/3,1 misinsertions in the polymer indicate a strong dependence of polymerization performance on electrophilicity of the catalyst, which is a function of the ligand framework and the metal center. Based on this insight, the stronger performance decline of hafnocenes is ascribed to electrophilicity-dependent stabilization effects.