Structural flexibility within a sterically hindered ligand platform:: mononuclear iron(II) carboxylate complexes as subsite models for diiron(II) centers

Abstract

The synthesis and characterization of a series of mononuclear iron(II) carboxylate complexes are described. By using sterically hindered carboxylate ligands, 2,6-di( p-tolyl)benzoate (Ar TolCO 2 − ) and 2,6-di(4- tert-butylphenyl)benzoate (Ar 4-tBuPhCO 2 − ), a series of four-, five-, and six-coordinate iron(II) complexes were synthesized. The compounds are [Fe(O 2CAr Tol) 2(1-BnIm) 2] ( 3), [Fe(O 2CAr Tol) 2(1-MeBzIm) 2] ( 4), [Fe(O 2CAr 4-tBuPh) 2(2,2′-bipy) 2] ( 5), [Fe(O 2CAr Tol) 2(TMEDA)] ( 6), and [Fe(O 2CAr Tol) 2(BPTA)] (7). Structural analyses of 3– 7 revealed that the overall stereochemistry of the [Fe(O 2CAr′) 2L n ] units is dictated by electronic and steric factors of the N-donor ligands (L), as well as by the flexible coordination of the carboxylate ligands. Distinctive Mössbauer parameters obtained for these and related compounds facilitated the spectral assignment of a diiron(II) complex having asymmetric metal sites, [Fe 2(μ-O 2CAr Tol) 3(O 2CAr Tol)(2,6-lutidine)] ( 2). Well-defined mononuclear iron carboxylate complexes thus may serve as subsite models for higher nuclearity species in both synthetic and biological systems.