Polynuclear alkoxy-zinc complexes of bowl-shaped macrocycles and their use in the copolymerisation of cyclohexene oxide and CO 2

Abstract

The reactions between alcohols and the tetranuclear ethyl-Zn complexes of an ortho-phenylene-bridged polypyrrole macrocycle, Zn 4 Et 4 (L 1 ) 1 and the related anthracenyl-bridged macrocyclic complex, Zn 4 Et 4 (THF) 4 (L 2 ) 2 have been studied. With long-chain alcohols such as n-hexanol, the clean formation of the tetranuclear hexoxide complex Zn 4 (OC 6 H 13 ) 4 (L 1 ) 3 occurs. In contrast, the use of shorter-chain alcohols such as i-propanol results in the trinuclear complex Zn 3 (μ 2 -O i Pr) 2 (μ 3 -O i Pr)(HL 1 ) 4 that arises from demetalation; this complex was characterised by X-ray crystallography. The clean formation of these polynuclear zinc clusters allowed a study of their use as catalysts in the ring-opening copolymerisation (ROCOP) reaction between cyclohexene oxide and CO 2 . In situ reactions involving the pre-catalyst 1 and n-hexanol formed the desired polymer with the best selectivity for polycarbonate (90%) at 30 atm CO 2 , whilst the activity and performance of pre-catalyst 2 was poor in comparison.