Synthesis, structure of functionalized N-heterocyclic carbene complexes of Fe(II) and their catalytic activity for ring-opening polymerization of ε-caprolactone

The reaction of anhydrous FeBr2 with two equivalents of in situ generated anionic aryloxo-functionalized N-heterocyclic carbene [NaO-4,6-di-C(CH3)3-C6H2-2-CH2{C(NCHCHNR)}] (R = CH(CH3)2, NaL1; R = CH2Ph, NaL2) affords two bis-ligand Fe(II) complexes FeL21 (1) and FeL22 (2) in good yield, respectively. Attempt to synthesize mono-ligand Fe(II) bromide by the 1:1 molar ratio of NaL to FeBr2 is unsuccessful, the same complexes of 1 and 2 were obtained. Both of 1 and 2 have been fully characterized by elemental analysis, 1H NMR spectra and X-ray structure determination. Preliminary studies show that 1 can catalyze the ring-opening polymerization of ε-caprolactone as a single component catalyst. The mechanism of the present ROP of ε-caprolactone has been investigated by the end group analysis.

Graphical abstractFe(II)-based N-heterocyclic carbene complexes of 1 and 2 have been synthesized and characterized by X-ray structural analysis. Complex 1 can catalyze the ring-opening polymerization of ε-caprolactone as a single component initiator.Figure optionsDownload full-size imageDownload as PowerPoint slide