Organometallic zinc compounds are attractive catalysts for various polymerizations, such as ring-opening copolymerizations (ROCOP) or ring-opening polymerizations (ROP). This is due to the compounds’ low toxicity, low cost, and lack of redox chemistry. As catalysts for the ROCOP of CO₂ and epoxides, they can help to re-use captured CO₂, and by controlling the nature of the bond between Zn and the initiating group or the polymer chain end, they enable the controlled synthesis of block copolymers from a monomer mixture.

Charlotte K. Williams, Oxford University and Imperial College London, UK, and colleagues have synthesized di-zinc-bis(phenyl) and di-zinc-bis(pentafluorophenyl) complexes (example pictured), which differ by the electron-withdrawing fluoryl substituents. The complexes were synthesized by combining a macrocyclic organic ligand with either ZnPh₂ or Zn(C₆F₅)₂.

The team investigated the complexes’ reactivity towards small molecules such as CO₂, cyclohexene oxide, and alcohols. They found that the catalyst system without fluoryl substituents readily inserted CO₂ to form carboxylates, but also reacted with alcohols to generate Zn-alkoxide species to initiate polymerizations. Both catalysts were able to initiate the ROCOP of cyclohexene oxide/CO₂ and other monomer combinations, as well as the ROP of cyclic esters.

• Di-Zinc-Aryl Complexes: CO₂ Insertions and Applications in Polymerisation Catalysis,
  Charles Romain, Jennifer A. Garden, Gemma Trott, Antoine Buchard, Andrew J. P. White, Charlotte K. Williams,
  Chem. Eur. J. 2017.
  DOI: 10.1002/chem.201701013