Solvent-Ligated Copper(II) Complexes for the Homopolymerization of 2-Methylpropene

Copper(II) complexes with weakly coordinating counter anions can be utilized as highly efficient catalysts for the synthesis of poly(2‐methylpropene) (“polyisobutene”) with a high content of terminal double bonds. These copper(II) compounds are significantly more active than the manganese(II) complexes described previously, can be applied in chlorine‐free solvents such as toluene, are easily accessible, and can be handled at room temperature and in laboratory atmospheres for brief periods, but they are sensitive to excess water, thereby losing their catalytic activity. Replacing the acetonitrile ligands by benzonitrile ligands improves the solubility and catalytic activity in nonpolar and nonchlorinated solvents. However, the benzonitrile copper(II) compounds have lower thermal stability than their acetonitrile congeners. Very active polyisobutenes with a high proportion of terminal double bonds and a fairly low polydispersity index are obtained by using 2‐methylpropene polymerization using CuII cations [CuII(NCR)6]2+ (R=CH3, Bn, C2H5) with weakly coordinating nitrile ligands and noncoordinating counterions [A]− as catalysts (examples are shown here).