Synthesis of iron complexes with bidentate N-heterocyclic carbene ligands

Transition metals such as rhodium, indium, palladium, and gold have been used to catalyze pharmaceuticals, but due to the cost and rarity of such metals, alternate transition metal bases such as iron and nickel are being examined for their potential to facilitate similar reactions. Several Fe(II) complexes were synthesized to examine Fe(II) for bond formation with bidentate carbene ligands at varying ligand bite angles. Mesityl imidazole and tert-butyl imidazole were synthesized as ligand precursors. Two types of Mesityl Bis(imidazolium) salts (MesNHC2R) were synthesized, one with a methyl linker (R = Me) and another with an ethyl linker (R = Et). Two tert-butyl bis(imidazolium) salts (tBuNHC2R) were also synthesized, with the same linker variations. 1 H NMR spectroscopy was used to characterize the salts before being transferred into a glovebox with a nitrogen atmosphere. The ligand salts were deprotonated and complexed with FeCl2. No 1H NMR signals were detected for these complexes which are likely high spin iron(II). Further work will involve the reduction of the iron(II) into iron(O) as a catalyst precursor.


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