Polynuclear alkoxy-zinc complexes of bowl-shaped macrocycles and their use in the copolymerisation of cyclohexene oxide and CO2

The reactions between alcohols and the tetranuclear ethyl-Zn complexes of an ortho-phenylene-bridged polypyrrole macrocycle, Zn4Et4(L-1) 1 and the related anthracenyl-bridged macrocyclic complex, Zn4Et4(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(OC6H13)(4)(L-1) 3 occurs. In contrast, the use of shorter-chain alcohols such as i-propanol results in the trinuclear complex Zn-3((2)-(OPr)-Pr-i)(2)((3)-(OPr)-Pr-i)(HL1) 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 CO2. 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 CO2, whilst the activity and performance of pre-catalyst 2 was poor in comparison.