Iron Complexes Bearing A Bulky Imidazolium Cation:Synthesis,Characterization And Catalysis

A series of novel iron-based complexes bearing a bulky imidazolium cation have been synthesized.The catalytic performances of these iron complexes in the cross-coupling reaction of aryl Grignard reagents with alkyl halides as well as in the carboxylation of aromatic heterocyclic C-H bonds with CO₂ have been investigated.1.The reaction of the bulky imidazolium salt?1a?with one equivalent of anhydrous FeCl₂or FeCl₃ afforded the corresponding ionic iron?II/??complexes 1?[HIPr^*][FeCl₃]??IPr^*=1,3-bis?2,6-bis?diphenylmethyl?-4-methylphenyl?imidazo-2-ylidene?and 3?[HIPr^*][FeCl₄]?containing a bulky imidazolium cation.The reaction of the bulky imidazolium salt?1a?with Fe Br_n?n=2,3?and NaBr?in 1:1:3 molar ratio?afforded the corresponding ionic iron?II/??complexes 2?[HIPr^*][FeBr₃]?and 4?[HIPr^*][FeBr₄]?.The reaction of the bulky imidazolium salt?1a?with FeCl₂ and phosphine(PPh₃ or PCy₃)?in 1:1:1 molar ratio?afforded ionic iron?II?complexes 5?[HIPr^*][Fe?PPh₃?Cl₃]?and 6?[HIPr^*][Fe?PCy₃?Cl₃]?containing a bulky imidazolium cation and phosphine ligand;The bulky imidazolium salt?1a??Fe Br₂ and NaBr?in 1:1:3 molar ratio?were stired for 6 h and then add one equivalent of phosphine(PPh₃ or PCy₃)afforded ionic iron?II?complexes 7?[HIPr^*][Fe?PPh₃?Br₃]?and 8?[HIPr^*][Fe?PCy₃?Br₃]?containing a bulky imidazolium cation and phosphine ligand.Except 3 and 4,other complexes are sensitive to air and moisture.All of these complexes have been characterized by elemental analysis.Both of complexes 3 and 4 are also characterized by melting point,electrospray ionization mass spectrometry and X-ray crystallography.2.It was found that complexes 1-8 were efficient catalysts for the cross-coupling reaction of aryl Grignard reagents with alkyl halides.3.It was found that mono?imino?-functionalized imidazolium salts 1j was efficient catalysts for the carboxylation reaction of aromatic heterocyclic C-H bonds with CO₂.4.The synthesis of iron?II?complexe 10 containing N-heterocyclic carbene?NHC?ligand and phosphine ligand has been tried by the reaction of dimeric species[Fe₂Cl₂??-Cl?₂?IPr?₂]?9?with PCy₃.The complexe 10 has been characterized by elemental analysis.