Synthesis And Catalytic Activity Of Novel Iron(II) Complexes Bearing Nitrogen-based Ligands

A series of iron(II) complexes supported byβ-diketiminate or phenoxo- functionalized N-heterocyclic carbene were synthesized, respectively. All of them have been fully characterized by elemental analysis, 1HNMR spectra and some of them by X-ray structural determination. Preliminary studies show that these iron(II) complexes can be used as a single component catalyst for ring-opening polymerization ofε-caprolactone.1. Reaction of anhydrous FeCl2(THF)1.5 with two equivalents of LLi (L = [{N(C6H4R-4)C(Me)}2CH], R = Me, L1H, 1; R = Cl, L2H, 2) afforded bis-β-diketiminate iron(II) complexes of L12Fe (3) and L22Fe (4). Anhydrous FeCl2(THF)1.5 reacted with equivalent of LLi, and then followed with equivalent of NaOtBu to yield the corresponding iron(II) alkoxides of L1FeOtBu (5) and L2FeOtBu (6). Anhydrous FeCl2(THF)1.5 reacted with equivalent of [CH{N(iPr)CH}2]Cl, and then followed with equivalent of L2Li to yield the corresponding iron(II) chloride complex of L2FeCl2[CH{N(iPr)CH}2] (7). 3, 4, 5, 6和7 were fully characterized by elemental analysis and 1HNMR spectra. 3, 4, 6和7 were fully characterized by X-ray structural determination.2. Reaction of anhydrous FeCl2(THF)1.5 with equivalent of NaOtBu and HO-4-C(CH3)3-C6H2-2,6-di-[CH2{(NCHCHNR)CH}Cl]2 (R = iPr, H3L4Cl2, c; R = Bz, H3L5Cl2, d) afforded bisnuclear phenoxo-functionalized N-heterocyclic carbene iron(II) alkoxides (FeL4OtBu)2 (8) and (FeL5OtBu)2 (9). 8 and 9 were fully characterized by elemental analysis and 1HNMR spectra. 8 also has been characterized by X-ray structural determination.3. The catalytic activity of iron(II) complexes 3, 4, 5 , 6, 8 and 9 for ring-opening polymerization (ROP) ofε-CL was studied in turn. 5, 6, 8 and 9 could be used as single-component initiator for the ROP ofε-CL, Among them, 8 and 9 showed higher catalytic activity than 5 and 6. However, both of 3 and 4 have no obvious activity for ROP ofε-CL, which indicated that the Fe-N bond presented in 3 or 4 is inert toward the insertion ofε-CL.