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

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 ((LH)-H-ipr) 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(O2CCH3)(2) in KOH-CH3OH 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 H-1 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)(2)Fe](2)O as shown by H-1 NMR spectroscopy. (C) 2002 Elsevier Science Ltd. All rights reserved.