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/Ⅲ）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/Ⅲ）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（μ-Cl）₂（IPr）₂]（9）with PCy₃.The complexe 10 has been characterized by elemental analysis.