Oxygen Effect in Heteromultimetallic Catalysis: Oxygen-Bridged Catalysts for Olefin Polymerization Process

Abstract

Generation of highly Lewis acidic metal center in a catalytic system has been one of the key challenges in olefin polymerization. Highly acidic metal center can easily bind with a nucleophilic monomer and starts the polymerization process. With this objective in mind, we categorically designed and synthesized catalysts containing enhanced Lewis acidic metal centers of catalytically active metal centers with enhanced Lewis acidity. We have developed a carefully designed synthetic approach of introducing oxygen between two different metal centers to produce multimetallic systems. The attachment of the oxygen between the two metal centers also brings the metals into close proximity at the molecular level, resulting in a pronounced chemical communication between the metals. The compounds containing covalently bridged metal centers have often modified the fundamental properties of the individual metal atoms and exhibit “cooperativity” that is difficult to achieve. The synthetic strategy involves the isolation of different hydroxides as precursors for multimetallic systems. By taking the advantage of oxophilicity of Group-4 metals and Bronsted acidic character of M(O–H) species, new class of heterometallic complexes have been assembled. Many of these isolated complexes demonstrated excellent catalytic activity in olefin and styrene polymerization. Computational studies reveal that the improvement in the catalytic properties is a result of the presence of a more electrophilic metal center, which is essential for the catalysis.