A multimetallic iron(ii)–lithium complex as a catalyst for ε-caprolactone polymerization

Abstract

Treatment of the lithium salt of β-ketimine with FeCl(THF) in the presence of LiN(SiMe) and water affords the multimetallic iron(ii)-lithium complex 1, [(L)Fe]LiO [where L = MeC(O)CHC(NMe)Me]. In complex 1 three separated (L)Fe units are bound together by one LiO species, which leads to the formation of an interesting {FeLiO} core structure. Complex 1 can be used as a single-component initiator for the ring-opening polymerization of ε-caprolactone at room temperature, achieving a monomer conversion of 98% within 100 min, and a narrow molecular weight distribution (PDI = 1.28) of the resulting polymer.

Amides as Non-polymerizable Catalytic Adjuncts Enable the Ring-Opening Polymerization of Lactide With Ferrous Acetate Under Mild Conditions

“…Fe(II) and Fe(III) compounds have been proposed as a less toxic alternative to Sn-based catalysts in the ROP of lactones, such as dilactide (Gibson et al, 2002; Wang et al, 2005; Chen et al, 2006; Hege and Schiller, 2014; Geng et al, 2016). The toxicity of tin compounds is related to disturbance of the iron and copper metabolism, as well as the potential denaturation of proteins by reaction with free thiols (Westrum and Thomassen, 2002; Buck et al, 2003).…”

Iron–Aryloxide Complex Bearing Bis(dipyrromethene) Ligands for the Ring-Opening Polymerization of ε-Caprolactone

“…Iron alkoxides have been found to trigger the ring-opening of CL efficiently and to perform chain propagation through a common coordination-insertion mechanism (Scheme ). ,,− Earlier studies demonstrated that the activity of iron catalysts toward CL polymerization greatly affected the molecular weight and polydispersity of the products. − Fine-tuning the electronic properties of the iron center through modulation of its oxidation state and the design of auxiliary ligands significantly controls the outcome. , To date, well-studied molecular iron alkoxide systems for CL polymerization remain rare, ,,, and the most representative examples are the iron catalysts based on the bis(imino)pyridine ligand , and N , N ′-bis(trimethylsilyl)-benzamidinate …”

“…26−29 Finetuning the electronic properties of the iron center through modulation of its oxidation state and the design of auxiliary ligands significantly controls the outcome. 42,47 To date, wellstudied molecular iron alkoxide systems for CL polymerization remain rare, 26,27,30,31 and the most representative examples are the iron catalysts based on the bis(imino)pyridine ligand 31,42 and N,N′-bis(trimethylsilyl)-benzamidinate. 26 As an analogue of a porphyrin scaffold, a dipyrromethene (dipyrrin) framework is a suitable chelating ligand for iron.…”

“…Poly­(ε-caprolactone) (PCL) is a valuable and sustainable material. , As it undergoes degradation under physiological conditions by hydrolysis of the ester bonds, many biomedical applications of PCL in tissue engineering and drug delivery systems have been achieved. − Such long-chain aliphatic polyesters are also attractive for use in packaging material, which could replace traditional olefin-based polymers, thus minimizing plastic pollution. − As the most straightforward synthetic method, ring-opening polymerization (ROP) of ε-caprolactone (CL) has received much attention . A variety of metal catalysts, including Mg, , Al, − Zn, − Sn, , Ti, − Zr, , V, Fe, − Mo, , W, as well as actinides , and lanthanides, , have been studied in connection with the polymerization of CL. To date, effective cheap catalysts with low toxicity are still in demand for the polymerization .…”

The Role of Alkoxide Initiator, Spin State, and Oxidation State in Ring-Opening Polymerization of ε-Caprolactone Catalyzed by Iron Bis(imino)pyridine Complexes

“…As catalysts, iron-based complexes are appealing as iron is earth-abundant and exhibits versatile chemical reactivity . However, the few iron catalysts reported for lactone polymerizations thus far − have exhibited low activities and/or yielded broad molecular weight distributions (polymerizations of lactide and cyclic carbonates have also been reported ,, ). Nevertheless, iron-based systems remain of special interest because they offer unique opportunities for tuning of the catalyst spin state, overall charge, and oxidation stateeither of the metal or the ligandover a broad range of accessible redox potentials.…”