Synthesis And Catalytic Activities Of β-ketiminate Andβ-diketiminate Iron Complexes

Polycaprolactone (PCL) has been applied widely in biomedical and pharmaceutical industry because of its biocompatible, permeable and biodegradable properties. As a kind of efficient initiators for the ring-opening polymerization (ROP) of s-caprolactone, metal catalysts can control the ROP of s-caprolactone well by choosing appropriate ligands and center metals. Although plenty of active metal catalysts have been discussed, the residue of metal in polymers takes a toxic risk for creature, which limits the application of polycaprolactone in biomedical and pharmaceutical fields. Therefore, exploring non-toxic metal catalysts, which can initiate the ROP of ε-caprolactone in control to yield environmentally benign polycaprolactone, has great significance.In this thesis, we report a series of N-alkyl-β-ketiminate and diketiminate iron complexes nacacR2Fe(R=iPr,3b;tBu,3c; CHPh2,3e; ad,3f), nacnacR2Fe(R=CH3,4a;lPr,4b;tBu,4c; CH2CH2Ph,4d) and [nacacCH32Fe]3Li2O(5a), which were prepared by the treatments of FeCl2(THF)1.5with β-ketiminate or β-diketiminate ligands, respectively. Furthermore, the catalytic activities of the above complexes for the ROP of s-caprolactone are also investigated. Due to their paramagnetic properties, the’H NMR spectra of the high-spin iron(II) complexes show broad peaks and drifting chemical shifts, which results in the difficult identication of the protons. Therefore, these complexes have been further characterized by IR, EI-HRMS, X-ray structure determination and ICP. From the catalytic experiments we know that all of the iron complexes can initiate the ROP of s-caprolactone. Among the examined catalysts, β-ketiminate iron complexes3b,3c,3e and3f not only have higher catalytic activities than β-diketiminate iron complexes, but also achieve more than99%conversion within one hour at80℃. Besides, complex5a indicates the best catalytic activity for the ROP of s-caprolactone with more than99%conversion within5minutes at80℃, and it can yield98%monomer conversion within100minutes at room temperature, at the same time, the obtained polymers have narrow molecular weight distribution (PDI=1.06-1.28).