Nickel Amino-Bis(phenol) Complexes for Copolymerization of Cyclohexene Oxide and Phthalic Anhydride

A series of air-stable nickel(II) complexes with various tetradentate diamino-bis(phenol)/(phenolate) ligands and coligands were synthesized. Six of these Ni[O2NN'] complexes were structurally characterized by single-crystal X-ray diffraction. The Ni[O2NN'] complexes were screened as catalysts for ring-opening copolymerization (ROCOP) of cyclohexene oxide (CHO) and phthalic anhydride (PA), utilizing bis(triphenylphosphine)iminium chloride (PPNCl) as a cocatalyst. It was determined that the catalytic activity for the Ni[O2NN'] complexes depended primarily on the coordinating coligands/counterions and the presence of a cocatalyst. Ni[O2NN'] complexes with acetate or chloride coligands selectively formed high molar mass polyesters with narrow dispersities (e.g. Mn = 14.5 kg mol-1 and Đ = Mw/Mn = 1.17), but only in the presence of the PPNCl cocatalyst. Ni[O2NN'] complexes with perchlorate counterions formed polymers containing a mixture of ester and ether linkages in the presence of PPNCl cocatalyst, and instead selectively formed polyether when no cocatalyst was used.