Structural characterization and investigation of iron(III) complexes with nitrogen and phosphorus based ligands in atom transfer radical addition (ATRA)

The solid state molecular structures of (FeCl3)-Cl-III complexes with 2,2'-bipyridine, 1,10-phenanthroline, 5-methyl-1,10-phenanthroline, bis(2-pyridylmethyl) amine, tris(2-pyridylmethyl) amine and 1,2bis(diphenylphosphino) ethane were reported. Most complexes adopted a distorted octahedral geometry, often incorporating coordinated solvent molecules (acetonitrile, methanol or water). Rearrangement involving ligand and/or halide exchange was also observed resulting in the formation of complexes in which the anion commonly contained [(FeCl4)-Cl-III]. The isolated iron(III) complexes showed moderate activity in the ATRA of carbon tetrachloride to alpha-olefins in the presence of free-radical diazo initiator (AIBN) and were largely inactive for styrene and methyl acrylate. Furthermore, the activity was relatively independent on the nature and denticity of complexing ligand, and similar to (FeCl3)-Cl-III in the presence of stoichiometric amounts of tetrabutylammonium chloride. Kinetic results coupled with cyclic voltammetry suggested that [(FeCl4)-Cl-III] anions could be responsible for catalytic activity in these systems. (C) 2011 Elsevier B. V. All rights reserved.