Alternating ring-opening copolymerization of cyclohexene oxide with phthalic anhydride catalyzed by iron(III) salen complexes

A series of three iron(III) salen complexes was synthesized and successfully used for copolymerization of cyclohexene oxide and phthalic anhydride. Catalytic systems based on an iron(III) salen complex in combination with 4-(dimethylamino)pyridine (DMAP) or bis(triphenylphosphine)iminium chloride (PPNCl) cocatalysts produced purely alternating copolymer with narrow molar mass distributions. [N,N′-Bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexylenediamine] iron(III) chloride was the most active complex and afforded the copolymer even in the absence of the cocatalysts. Other iron complexes were completely inactive in absence of a cocatalyst. Both DMAP and PPNCl alone were able to catalyze the copolymerization, affording purely alternating copolymers in good yields.