Anilido-Oxazoline-Ligated\nIron Alkoxide Complexes\nfor Living Ring-Opening Polymerization of Cyclic Esters with Controllability

Anilido-oxazoline-ligated\niron complexes, including bis(anilido-oxazolinate)\niron(II), mononuclear iron(II) alkyl and aryloxide, as well as the\ndinuclear analogues, were synthesized, and their catalytic performance\non ring-opening polymerization (ROP) has been studied. Transmetalation\nof FeCl<sub>2</sub>(THF)<sub>1.5</sub> with in situ-generated anilido-oxazolinate\nlithium afforded the bis(anilido-oxazolinate) iron complexes <b>1</b> and <b>2</b>. Half-sandwich anilido-oxazolinate iron\ntrimethylsilylalkyl complexes <b>3</b> and <b>4</b> could\nbe synthesized in good yields via taking pyridine as an L-type ligand.\nTreatment of <b>3</b> with benzyl alcohol and 4-phenoxyphenol,\nrespectively, generated the dimeric alkoxide or aryloxide complexes <b>5</b> and <b>6</b>, whereas the reaction with 2,4,6-trimethylphenol\nand 2,6-di-<i>tert</i>-butyl-4-methylphenol yielded the\nmononuclear aryloxide complexes <b>7</b> and <b>8</b>,\nrespectively. The iron alkoxide and aryloxide complexes were active\nsingle component catalysts for the ROP of ε-caprolactone (CL).\nRemarkably, the dinuclear complex <b>5</b> exhibited excellent\ncontrollability, livingness, and high initiation efficiency for ROP\nof CL. ROP of CL derivatives by <b>5</b> produced the corresponding\npolycyclic esters with good controllability, and the well-defined\nblock copolymers could be generated by sequentially feeding different\nmonomers. The chain initiation and propagation processes were investigated\nby matrix-assisted laser desorption/ionization time-of-flight mass\nspectrometry and kinetics analysis. In addition, a computational study\nwas conducted to rationalize the mechanism and synergistic effect\nof the alkoxide-bridged bimetallic iron centers.