Synthesis And Catalysis Of Functionalized N-heterocyclic Carbene Complexes Of Iron

A series of enolate-functionalized N-heterocyclic carbene precursors- corresponding imidazole salts had been synthesized. And then, the mono-nuclear iron(II) complexes possessing the bis-NHC ligands had been prepared via a new ligand-exchange method in high yields. Some of them were fully characterized by single X-ray structural determination. Preliminary studies show that these iron(II) complexes can be used as a single component catalyst for the ring-opening polymerization ofε-caprolactone.1. The reactions of 1-alkylimidazole or 1-arylimidazole with a series ofα-bromoacetophenone afforded corresponding imidazole salts [4-R-C6H4COCH2-(CH{(NCHCHNR'))Br] (R = OCH3, R'= iPr, H2L1Br; R = F, R'= iPr ,H2L2Br; R = H, R'= CH2Ph , H2L3Br; R = OCH3, R'= CH2Ph, H2L4Br; R = F, R'= CH2Ph, H2L5Br; R = OCH3, R'= Dipp, H2L6Br; R = F, R'= Dipp, H2L7Br) in a easy way with high yields. The treatment of N-phenacyl-imidazoles with an excess of allyl bromide afforded corresponding imidazole salts [4-R-C6H4COCH2-(CH{(NCHCHN C3H5))Br] (R = OCH3, H2L8Br; R = F, H2L9Br).2. The reaction of NaFe(OtBu)3,NaOtBu with the corresponding imidazole salts in 1:1:2 molar ratio in THF at room temperature afforded a series of mono-nuclear bis-ligands Fe(II) complexes of FeL12 (1), FeL22 (2), FeL32 (3), FeL42 (4), FeL52 (5), FeL62 (6), FeL72 (7), FeL82 (8) and FeL92 (9) in high yields, respectively. All of them were initiately characterized by elemental analysis, IR and melt point. Some of them were further characterized by single X-ray structural determination. The present work provided a facile one-step route to iron(II)-based enolate-functionalized N-heterocyclic carbene complexes.3. Attempts to synthesize mono-ligand Fe(II) alkoxide of L1FeOtBu or L2FeOtBu by the reaction of NaFe(OtBu)3 with H2L1Br or H2L2Br in 1:1 molar ratio were unsuccessful, respectively. The same complexes of 1 and 2 were obtained in lower yields. 4. Preliminary studies show that the new enolate chelating N-heterocyclic carbene complexes of iron(II) can be used as single component catalysts for the ring-opening polymerization ofε-caprolactone. It has been found that the structures of these complexes showed great effects on their catalytic activities.