(Ferrocenylpyrazolyl)zinc(II) acetate complexes as initiators and catalysts for the ring opening polymerization of ϵ-caprolacton.

• (Ferrocenylpyrazolyl)zinc(II) acetate complexes.
• Catalysts and initiators for caprolactone ring opening polymerization.
• Ferrocenylpyrazolyl capped poly(caprolactones).

The reaction of Zn(OAc)2 with 3-ferrocenylpyrazol-1-ylmethylenepyridine (L1), 3-ferrocenyl-5-methylpyrazol-1-ylmethylenepyridine (L2), 3-ferrocenylpyrazol-1-ylethylamine (L3) and 3-ferrocenyl-5-pyrazol-1-ylethylamine (L4) afford the corresponding zinc complexes [Zn(CH3COO)2(L1)] (1), [Zn(CH3COO)2(L2)] (2), [Zn(CH3COO)2(L3)] (3), and [Zn(CH3COO)2(L4)] (4). These zinc complexes behave as catalysts or initiators for the ring opening polymerization of ϵ-caprolactone, depending on the nature of the ligands, to produce polymers that are capped with α,ω-dihydroxy, hydroxyl or ferrocenylpyrazolylethylamino end groups. Complexes 1 and 2 were found to act as catalysts when the [CL]/[C] ratios were varied from 100 to 800 to produce PCL with α,ω-dihydroxy and nearly the same molecular weight. Complexes 3 and 4 on the other hand act as initiators to produce a mixture of PCL that have polymers with ferrocenylpyrazolylethylamino and a hydroxyl as end groups as the major component of the mixture and minor species with α,ω-dihydroxy end group.

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