Hydrophobicityon the kinetics of acid-catalyzed aquation of pyridyl-imines iron(II)
complexes in aqueous and binary aqueous methanolmixtures
Kinetics of the acid-catalyzed aquation of bis-N,N’,N’’-(pyridin-2-ylmethylene-quinolin-8-yl-imine) iron(II) iodide dihydrate (1), bis-N,N’,N’’-((1-pyridin-2-yl-ethylidene)-quinolin-8-yl-imine) iron(II) iodide dihydrate (2) or bis-N,N’,N’’-((phenyl-pyridin-2-yl-methylene)-quinolin-8-yl-imine) iron(II) iodide dihydrate (3) have been investigated spectrophotometrically. The rate law and the relevant mechanism were suggested in aqueous media and aqua-methanol binary mixtures. The acid-catalyzed aquation revealed pseudo-first order kinetics with rate law kobs = k2(H+). The rate trends and activation parameters are consistent with the complexes stability discussed according to the substituent effect of the complexes (R = H, CH3 or Ph).
Iron-tridentate imine complexes provide useful structural and electronic models for the similarly coordinated sites found in the heme iron enzymes. They have high a catalytic activity towards the asymmetric oxidation of organic alcohols and alkenes (1). Since their structures and catalytic activity are analogous to those of iron porphyrins (2), pyridyl-imines and diimines have found considerable applications in, e.g. medicine, photo-, magnetic (3, 4), electrochemistry (5) analytical chemistry for the determination of iron(II) ions (6). Synthesis and fundamental chemical studies of low spin iron(II) imine complexes have not yet widely been investigated (7).
Kinetics of a variety of reactions of low-spin iron(II) complexs of N,N’-bidentate ligands and their derivatives have been extensively studied (8), whereas, little studies have been devoted to the acid-catalyzed aquation of iron(II) tridentate imine complexes in literature (9-12). The solvent effects (13-14) on such kinetics of the acid-catalyzed aquation of low-spin iron(II) complexes of N,N’-bidentate ligands as 2,2’-bipyridyl (15), 1,10-phenanthroline or Schiff base ligand ...