Activation of late transition metal catalysts for olefin polymerizations and olefin/CO copolymerizations

Abstract

The late transition metal catalysts for homo- and copolymerizations of olefins expand the polymer properties and the usable monomer feedstock of early transition metal catalysts. A critical step for a polymerization is the activation of catalyst precursors and the generation of the actual active site. This perspective discusses possible activation protocols for two well-known catalyst systems, the a-diimine Ni or Pd olefin polymerization catalysts and the Pd catalysts for alkene/CO copolymerization. The general concept of catalyst activation is outlined and similarities as well as differences between single-component catalysts and in situ activated systems are highlighted.

(α-Diimine)palladium catalyzed ethylene polymerization and (co)polymerization with polar comonomers

“…Moreover, the reduced oxophilicity of the palladium center renders the catalyst capability of copolymerizing ethylene with polar-functionalized comonomers, with a majority of polar groups located at the end of branches in the final copolymers [15][16][17]26,27]. Among the best tolerated comonomers are those bearing oxygen-containing functionalities, such as acrylates [16,17], methyl vinyl ketones [16,17], and silyl vinyl ethers [28][29][30].…”

Olefin Polymerization with Non-metallocene Catalysts (Late Transition Metals)

“…Diimine Ni complexes are frequently used in combination with organoaluminum cocatalyst, where the cationic diimine Ni-alkyl complex is produced in situ similar to the metallocene catalysts. As for organoaluminum, Et 2 AlCl or Me 3 Al are usable in addition to MAO or MMAO [17]. Cationic methylpalladium complexes with diimine ligand can be isolated much more easily than the Ni complex.…”

“…Square planar Ni(II) and Pd(II) complexes with diimine ligands (Chart 4.1, 1a-1i) show high catalytic activity for ethylene polymerization [5,14,17,19]. Orthosubstituents on N-aryl groups are essential for high catalytic activity and formation of high molecular weight polymer.…”

Zwitterionic Relatives of Cationic Platinum Group Metal Complexes: Applications in Stoichiometric and Catalytic σ‐Bond Activation

“…Beyond these practical advantages, head-to-head reactivity studies involving structurally analogous cationic and zwitterionic PGM complexes also provide opportunities to assess the impact of adjusting the electronic properties of a formally cationic PGM center on metal-centered reactivity at a fundamental level, without substantially modifying the steric profile of the reactive metal coordination sphere. Despite the established utility of non-PGM zwitterions in a range of applications (most notably polymerization chemistry [9][10][11][12] ), rationally prepared PGM zwitterions have emerged only recently, owing in part to the challenge of developing effective ligation strategies for enforcing the requisite formal charge separation. However, recent advances in ancillary ligand design have enabled the preparation of several unique classes of isolable PGM zwitterions that exhibit reactivity patterns in s-bond activation chemistry that are reminiscent of, or in some cases complementary to, related cationic PGM species.…”