Polymer‐immobilized N,N′‐bis(acetylacetone)ethylenediamine cobalt(II) Schiff base complex and its catalytic activity in comparison with that of its homogenized analogue

Abstract

ABSTRACT:For the preparation of a heterogenized N,NЈ-bis(acetylacetone)ethylenediamine cobalt(II) Schiff base complex, first crosslinked polymer beads were prepared by the suspension copolymerization of styrene (48.97 mmol, 5.1 g), allyl chloride (48.97 mmol, 3.746 g), and divinyl benzene (DVB; 1.75 mmol, 0.228 g) in the presence of azobisisobutyronitrile (0.9 ϫ 10 Ϫ3 mmol, 0.15 g) as an initiator at 23 Ϯ 0.1°C under an inert atmosphere. The copolymerization of styrene, allyl chloride in the presence of gelatin (0.75 g), bentonite (2.0 g), and boric acid (2.5 g) produced beads of different crosslinked densities corresponding to the concentration of DVB in the reaction mixture. The amount of allyl chloride in the prepared beads varied from 5.40 to 7.40 mmol g Ϫ1 of beads with the amount of DVB varying from 2.0 to 0.8 mmol in the reaction mixture. A quadridentate Schiff base (acen) was prepared with ethylenediamine (5.0 mmol, 0.3 g) and acetylacetone (10.0 mmol, 1.0 g), and it was used to obtain a homogenized and heterogenized Co(II)(acen) 2 complex. The extent and arrangement of the Schiff base (acen) in the crosslinked beads depended on the availability of DVB in the reaction mixture. The amount of DVB in the reaction mixture influenced the extent of cobalt(II) ion loading, the degree of swelling, the porosity, and the pore size in the prepared beads. The beads (type IV) prepared with 1.75 mmol (0.228 g) of DVB in the reaction mixture showed a degree of swelling of 9.65% and efficiencies of loading and complexation for cobalt(II) ions of 49.4 and 85%, respectively, in comparison with beads obtained at other concentrations of DVB in the reaction mixture. The structure of free and polymer-supported Co(II)(acen) 2 complexes was verified with IR, UV, and magnetic measurements, which suggested a square planar geometry for the complexes under both conditions. The catalytic activities of the homogenized and heterogenized Co(II)(acen) 2 complexes were compared by the evaluation of the rate constant (k) for the decomposition of hydrogen peroxide. The heterogenized Co(II)(acen) 2 complex showed a high catalytic activity for the decomposition of hydrogen peroxide (k ϭ 2.02 ϫ 10 Ϫ4 s Ϫ1) in comparison with the homogenized Co(II)(acen) 2 complex (k ϭ 4.32 ϫ 10 Ϫ6 s Ϫ1). The energy of activation for the decomposition of hydrogen peroxide with the heterogenized Co(II)(acen) 2 complex was low (38.52 kJ mol Ϫ1 ) in comparison with that for the homogenized complex (73.44 kJ mol Ϫ1). In both cases, the rate of decomposition of hydrogen peroxide was directly proportional to the concentration of hydrogen peroxide and cobalt(II) ions. On the basis of experimental observations, a rate expression for the decomposition of hydrogen peroxide was derived.

Polymer anchored Schiff base complexes of transition metal ions and their catalytic activities in oxidation of phenol

“…The length of Schiff base ligands and their types has influenced the loading of metal ions [34] as well as the catalytic activity of metal complexes on polymer supports [35]. The most commonly used ligands on polymer supports are aminomethylpyridine [3,36], phosphines [37,38], diketones [39], multidentate amines [20], salen [40] and hydrazine [41]. In order to develop new catalyst for selective oxidation of phenol, attempt has been made to synthesize polymer supported N,N -bis(o-hydroxy acetophenone)ethylene diamine Schiff base complexes of iron(II), cobalt(II) and nickel(II) ions (P-HPED-M) and to characterize their catalytic activities in oxidation of phenol under different experimental conditions in comparison to unsupported metal complexes of HPED Schiff base.…”

Synthesis, spectroscopic and crystallographic characterization of the cobalt(III) ternary mixed-ligand complexes of N(4)-allyl/methyl thiosemicarbazones, N,N,N′,N′-tetramethylethylenediamine and azide

“…These bands were shifted to lower wave numbers by ca.12 cm -1 in the complexes, and a vibration m(Co-N) at 415 cm -1 corroborates coordination of the azomethine nitrogen [39,40]. A band in the region 580-584 cm -1 is assignable to Co-O [41,42]. The sharp bands assigned to m a (NH), m s (NH) vibrations attributable to N 2 H and N 4 H which are at 3,470-3,306 cm -1 in the spectra of the free thiosemicarbazones were observed in the 3,449-3,426 cm -1 region in the spectra of the complexes.…”

Aspects of Immobilisation of Catalysts on Polymeric Supports

“…The amount of cross-linking agent was found to determine the degree of swelling, the porosity, and the pore size of the support as well as the Co ion loading of the complex. [76] Detailed characterisation of the complex and the polymer showed that in homogeneous and heterogeneous conditions the Co-A C H T U N G T R E N N U N G (acen) complex was square planar, with the electronic properties of Co(II) determined by the degree of cross-linking. On such catalysts the decomposition rate of hydrogen peroxide increased not only by the presence of the polymer but also by its degree of cross-linking.…”