Homogeneous Single-site Non-metallocene

Such examples have shown that the role of the cationic group 4 metal complexes in the coordination polymerisation of ethylene and oc-olefins with homogeneous single-site Ziegler-Natta catalysts must not be limited to those containing cyclopentadienyl-like ligands. 

2 Homogeneous Catalysts without a Metal Alkyl (or Hydride) Activator 

Homogeneous alkylaluminium (alkylaluminoxane)-free olefin polymerisation catalysts are commonly referred to as catalysts containing group 4 metallocene cationic species. These catalysts resemble the structure and properties of the respective metallocene-based Ziegler-Natta catalysts but, by definition, are not included among the latter catalysts. The development of alkylaluminium-free metallocene-based olefin polymerisation catalysts is connected with discoveries 

Homogeneous alkylaluminium-free olefin polymerisation catalysts also comprise non-metallocene cationic group 4 metal complexes such as those with benzyl ligands [162]. A distinct group of alkylaluminium-free homogeneous olefin polymerisation catalysts consists of nickel complexes [181-183], 

The essential factor determining the synthesis of cationic group 4 metallocene alkyls, [Cp 2ZrR]+, capable of olefin polymerisation is the utilisation of robust and poorly coordinating anions showing good solubility in inert aromatic solvents. The unusually low coordinating ability of such anions in ion pairs with cationic metallocenes is crucial for the catalytic activity [184]. 

---