Structural and 1H NMR spectroscopic characterization of bis( N-isopropylsalicylaldiminato)iron(II)

Abstract

Coordinatively unsaturated iron(II) species form reactive organometallic and coordination complexes and are integral to the reactivity of non-heme iron proteins and their synthetic analogues. Iron(II) Schiff base complexes have proven to be easily prepared and useful starting materials for such compounds. Here we report a detailed preparative procedure and the solid-state structure of the iron(II) complex of N-isopropylsalicylaldimine (L ipr H) based on the compounds first synthesized by Larkworthy (J. Chem. Soc., A (1968) 1048). The title compound is prepared by adding 2 equiv. of salicylaldehyde (salH) to Fe(O 2CCH 3) 2 in KOH–CH 3OH to produce a precursor formulated as Fe(sal) 2 which is reacted subsequently with isopropylamine in THF to form Fe(L ipr ) 2 in 34% isolated yield. A single crystal X-ray crystallographic study of Fe(L ipr ) 2 reveals a mononuclear complex with two bidentate salicylaldiminate ligands bound to an iron(II) atom in a tetrahedral coordination geometry. The 1H NMR spectrum of Fe(L ipr ) 2 in benzene- d 6 exhibits six paramagnetically shifted ligand resonances ranging from +195 to −31 ppm that are consistent with a mononuclear high spin ( S=2) iron(II) complex in solution. Upon exposure to air, Fe(L ipr ) 2 forms the oxo-bridged dinuclear iron(III) complex [(L ipr ) 2Fe] 2O as shown by 1H NMR spectroscopy.