Pyrazolate‐Based Dinuclear α‐Diimine‐Type Palladium(II) and Nickel(II) Complexes – a Bimetallic Approach in Olefin Polymerisation

Abstract

Ni 2 Br 3 ] 3 . Complexes 1a -4a can be described as bimetallic versions of Brookhart-type a-diimine palladium complexes, where dissociation into mononuclear species is prevented by the dinucleating scaffold and the proximate metal ions are suitably positioned to work in concert during substrate transformation. Upon activation of the complexes with MAO and exposure to ethylene, polyethylene is formed. Whereas the palladium complexes display moderate activities, nickel complexes are very active. From structure/activity correlations it is evident that the presence of backbone substitutents at the pyrazolate scaffold as well as bulky ortho aryl substituents is advantageous for polymerisation. Overall, activities of the Ni complexes and the microstructure of the polymer obtained (total branching, T m and molecular weights) are still rather similar to the data reported previously for mononuclear cationic diimine nickel complexes.

A Unique Pd4 Platform with CH3 and μ‐CH2 Groups and Its CC Coupling Reaction with Simple Olefins

“…Elemental analyses were carried out with a Heraeus CHN-O-RAPID instrument. Complex A was prepared as reported; [6] all other reagents were purchased from commercial sources and used as supplied.…”

Bulky Pyrazolate‐Based Compartmental Ligand Scaffolds: Encapsulation of an Edge‐Sharing Cu6O2 Bitetrahedral Core

“…[3][4][5][6] In this context we have recently prepared a series of novel pyrazole-diimine ligands L with bulky aryl substituents at the imine-N and variable backbone substituents R, together with their nickel(II) and palladium(II) complexes (e.g., A). [7][8][9] These complexes can be viewed as bimetallic versions of the prominent α-diimine-derived Brookhart-type precatalysts for olefin polymerization, and indeed some pyrazolate-based bimetallic systems have been shown to exhibit high activity in the polymerization of ethylene. [8] In the case of nickel and if aryl substituents are not too bulky, species {LNi 2 X 3 } (X = Cl, Br) tend to aggregate to give tetra-or hexanuclear complexes such as [LNi 2 X 3 ] 3 with unusual nickel halide structural motifs.…”

A Unique Pd4 Platform with CH3 and μ‐CH2 Groups and Its CC Coupling Reaction with Simple Olefins

“…[1] While much of the work in this field is inspired by natural enzymes that contain multinuclear active sites, [2] recent years have also seen growing interest and impressive progress in the development of non-biomimetic binuclear complexes for two-center organometallic catalysis, [3,4] including the homogeneous polymerization of olefins. [5,6] An interesting situation arises for multinuclear complexes that contain more than two metal ions, as little is known about the synergetic effects in such systems.…”

“…[8] We have recently introduced a series of pyrazole-based ligands that possess appended imine donor functions with bulky aryl substituents. [6,9] These systems can be described as having two adjacent binding compartments akin to the a-diimine type, and their bi-or oligonuclear palladium(II) and nickel(II) complexes, after activation with methylalumoxane (MAO), indeed serve as highly active catalysts for olefin polymerization. [6] We were interested in elucidating details of the activation process as well as possible internuclear effects in the activated species.…”

“…[6,9] These systems can be described as having two adjacent binding compartments akin to the a-diimine type, and their bi-or oligonuclear palladium(II) and nickel(II) complexes, after activation with methylalumoxane (MAO), indeed serve as highly active catalysts for olefin polymerization. [6] We were interested in elucidating details of the activation process as well as possible internuclear effects in the activated species. Therefore we investigated the methylation of a representative pyrazolate-based dipalladium(II) complex A (Scheme 1)…”