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

Abstract

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*TiMe 3 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.

Binuclear Ti(IV) complex with new compartmental ligand 2,6‐(bis‐CF3‐carbinol)‐4‐tert‐butylphenol as precatalysts for ethylene polymerization and its copolymerization with propylene and 5‐ethylidene‐norbornene

“…It is obvious that such a close arrangement of metal centers complicates the processes of precatalyst activation. In other words, “there is to some degree a limit to the benefits of closer metal–metal distances in bimetallic olefin polymerization catalysts.” [ 36 ] This type of ligands may be used as suitable precursors for synthesis of multinuclear heterometallic (Ti/Al or Ti/Mg) compounds. Further investigations on the reactivity of these species and this promising coordination chemistry are underway in our laboratories.…”

Rigid Triptycene-Based Di- and Trinuclear Salicylaldiminato Nickel Cooperative Polymerization Catalysts

“…It is well known that the steric environment of a catalytically active site experienced by the substrates is crucial to determine the favorable reaction pathways. In general, for reported bimetallic catalysts with rigid linkers, − the most distinctive feature is the proposed distal interaction of C–H bonds or polar functional groups (X) with the second metal (Figure , left), which not only achieves high levels of product polyolefin branching but also enhances enchainment selectivity of co-monomers (e.g., polar-substituted norbornenes, acrylates). Alternatively, Agapie et al proposed another kind of amine–olefin coordination isomerization mechanism based on the copolymerization of ethylene with unprotected polar amino olefins (AOs), where inhibitory coordination of amines at both Ni centers is disfavored because of steric repulsion…”

Synthesis of Ethylene/1-Octene Copolymers with Ultrahigh Molecular Weights by Zr and Hf Complexes Bearing Bidentate NN Ligands with the Camphyl Linker

“…In the middle 1990s, Brookhart and co-workers reported their landmark research on cationic α-diimine based Ni and Pd catalysts that builds a new era in the olefin polymerization field [5]. For example, branched polyolefins have been previously produced through copolymerization of ethylene with α-olefins by early transition metal catalysts [6][7][8][9], while Brookhart-type αdiimine based late transition metal catalysts can synthesize such branched polymers using ethylene as the only feed via the unique chain walking mechanism [10,11]. Moreover, Ni and Pd late transition metal catalysts have low oxophilicity, and thus show great potential for copolymerization of olefins with polar comonomers [12,13].…”