Anilido-Oxazoline-Ligated Iron Alkoxide Complexes for Living Ring-Opening Polymerization of Cyclic Esters with Controllability.

Anilido-oxazoline-ligated iron complexes, including bis(anilido-oxazolinate) iron(II), mononuclear iron(II) alkyl and aryloxide, as well as the dinuclear analogues, were synthesized, and their catalytic performance on ring-opening polymerization (ROP) has been studied. Transmetalation of FeCl(THF) with in situ-generated anilido-oxazolinate lithium afforded the bis(anilido-oxazolinate) iron complexes and . Half-sandwich anilido-oxazolinate iron trimethylsilylalkyl complexes and could be synthesized in good yields via taking pyridine as an L-type ligand. Treatment of with benzyl alcohol and 4-phenoxyphenol, respectively, generated the dimeric alkoxide or aryloxide complexes and , whereas the reaction with 2,4,6-trimethylphenol and 2,6-di--butyl-4-methylphenol yielded the mononuclear aryloxide complexes and , respectively. The iron alkoxide and aryloxide complexes were active single component catalysts for the ROP of ε-caprolactone (CL). Remarkably, the dinuclear complex exhibited excellent controllability, livingness, and high initiation efficiency for ROP of CL. ROP of CL derivatives by produced the corresponding polycyclic esters with good controllability, and the well-defined block copolymers could be generated by sequentially feeding different monomers. The chain initiation and propagation processes were investigated by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and kinetics analysis. In addition, a computational study was conducted to rationalize the mechanism and synergistic effect of the alkoxide-bridged bimetallic iron centers.