How Close Is Too Close? Polymerization Behavior and Monomer-Dependent Reorganization of a Bimetallic Salphen Organotitanium Catalyst

The binuclear salphen Ti polymerization catalyst N,N′-1,2-phenylene[(salicylideneaminato)Ti(Cp*)Me2)]2 (2) is synthesized by reaction of salphen-H2 with Cp*TiMe3. Mononuclear [N-(2,6-diisopropyl)phenyl(salicylideneaminato)]Ti(Cp*)Me2 (1) serves as a control. Activation studies of 2 with cocatalyst Ph3C+B(C6F5)4– yield the cationic polymerization-inactive complex [N,N′-1,2-phenylene(salicylideneaminato)Ti(Cp*)]+B(C6F5)4– (4) and polymerization-active Cp*TiMe2+B(C6F5)4–. Polymerization studies comparing 2 with Cp*TiMe3 suggest that, within the catalytic time frame, while 2 retains bimetallic character under an ethylene atmosphere, it rapidly decomposes to 4 and Cp*TiMe2+ in the presence of 1-hexene. These monomer-dependent reorganization results highlight the importance of olefin polymerization activation mechanistic studies while providing insight for improved bimetallic catalyst design.

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