Efficient cross-coupling of aryl Grignard reagents with aIkyl halides by recyclable ionic iron(Ⅲ) complexes bearing a bis(phenol)-functionaIized benzimidazolium cation

摘要

A novel bis(phenol)-functionalized benzimidazolium salt, 1,3-bis(3,5-di-tert-butyl-2-hydroxybenzyl)benz-imidazolium chloride (H_3LCl, 1), was designed and used to prepare ionic iron(Ⅲ) complexes of the type [H_3L][FeX_4] (X = Cl, 2; X = Br, 3). Both 2 and 3 were characterized by elemental analysis, Raman spectro-scopy, electrospray ionization mass spectrometry and X-ray crystallography. The catalytic performances of 2 and 3 in cross-coupling reactions using aryl Grignard reagents with primary and secondary alkyl halides bearing β-hydrogens were studied. This analysis shows that complex 2 has good potential for alkyl chloride-mediated coupling. In comparison, complex 3 showed slightly lower catalytic activity. After decanting the product contained in the ethereal layer, complex 2 could be recycled at least eight times without significant loss of catalytic activity.