Synthesis And Catalytic Activity Of Anionic-functionalized N-heterocyclic Carbene Iron(Ⅱ) Complexes

A series of iron(II) complexes supported by phenoxo- and Schiff-base-functionalized N-heterocyclic carbene, were synthesized , and fully characterized by elemental analysis, 1H NMR spectra and some of them by X-ray structural determination. Preliminary studies show that these iron(II) complexes can catalyze the ring-opening polymerization ofε-caprolactone as a single component catalyst.1. The reaction of anhydrous FeBr2 with two equivalents of in situ generated phenoxo-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 mononuclear iron(II) complexes FeL12 (3) and FeL22 (4) in good yield, respectively. Attempt to synthesize monoligand Fe(II) bromide by the 1:1 molar ratio of NaL to FeBr2 failed, only the same complexes of 3 and 4 were obtained. Both of them were characterized by elemental analysis, 1H NMR spectra and X-ray structural determination.2. The reaction of anhydrous FeBr2 with one equivalent of in situ generated salicylaldiminato-functionalized N-heterocyclic carbene [NaO-4, 6-di-C(CH3)3-C6H2CH=NCH2CH2{C(NCHCHNR)}] (R = CH3, NaL3; R = CH(CH3)2, NaL4; R = CH2Ph, NaL5) affords monoligand iron(II) bromide FeL4Br (8). FeBr2 reacts with one equivalent of in-situ generated NaL3, NaL4 and NaL5 followed with NaOAr to yield the corresponding iron(II) aryloxide complexes of FeL3(OAr) (9) , FeL4(OAr) (10) and FeL5(OAr) (11). All of them were characterized by elemental analysis. 9 and 10 by 1H NMR spectra and X-ray...