Correlating Metal Redox Potentials to Co(III)K(I) Catalyst Performances in Carbon Dioxide and Propene Oxide Ring Opening Copolymerization

Carbon dioxide copolymerization is a front-runner CO₂ utilization strategy but its viability depends on improving the catalysis. So far, catalyst structure-performance correlations have not been straightforward, limiting the ability to predict how to improve both catalytic activity and selectivity. Here, a simple measure of a catalyst ground-state parameter, metal reduction potential, directly correlates with both polymerization activity and selectivity. It is applied to compare performances of 6 new heterodinuclear Co(III)K(I) catalysts for propene oxide (PO)/CO₂ ring opening copolymerization (ROCOP) producing poly(propene carbonate) (PPC). The best catalyst shows an excellent turnover frequency of 389 h⁻¹ and high PPC selectivity of >99 % (50 °C, 20 bar, 0.025 mol% catalyst). As demonstration of its utility, neither DFT calculations nor ligand Hammett parameter analyses are viable predictors. It is proposed that the cobalt redox potential informs upon the active site electron density with a more electron rich cobalt centre showing better performances. The method may be widely applicable and is recommended to guide future catalyst discovery for other (co)polymerizations and carbon dioxide utilizations.     

Heterodinuclear Mg(II)M(II) (M=Cr,Mn, Fe,Co, Ni,Cu and Zn) Complexes for the Ring Opening Copolymerization of Carbon Dioxide/Epoxide and Anhydride/Epoxide

The catalysed ring opening copolymerizations (ROCOP) of carbon dioxide/epoxide or anhydride/epoxide are controlled polymerizations that access useful polycarbonates and polyesters. Here, a systematic investigation of a series of heterodinuclear Mg(II)M(II) complexes reveals which metal combinations are most effective. The complexes combine different first row transition metals (M(II)) from Cr(II) to Zn(II), with Mg(II); all complexes are coordinated by the same macrocyclic ancillary ligand and by two acetate co-ligands. The complex syntheses and characterization data, as well as the polymerization data, for both carbon dioxide/cyclohexene oxide (CHO) and endo-norbornene anhydride (NA)/cyclohexene oxide, are reported. The fastest catalyst for both polymerizations is Mg(II)Co(II) which shows propagation rate constants (k_p) of 34.7 mM⁻¹ s⁻¹ (CO₂) and 75.3 mM⁻¹ s⁻¹ (NA) (100 °C). The Mg(II)Fe(II) catalyst also shows excellent performances with equivalent rates for CO₂/CHO ROCOP (k_p=34.7 mM⁻¹ s⁻¹) and may be preferable in terms of metallic abundance, low cost and low toxicity. Polymerization kinetics analyses reveal that the two lead catalysts show overall second order rate laws, with zeroth order dependencies in CO₂ or anhydride concentrations and first order dependencies in both catalyst and epoxide concentrations. Compared to the homodinuclear Mg(II)Mg(II) complex, nearly all the transition metal heterodinuclear complexes show synergic rate enhancements whilst maintaining high selectivity and polymerization control. These findings are relevant to the future design and optimization of copolymerization catalysts and should stimulate broader investigations of synergic heterodinuclear main group/transition metal catalysts.     

Copolymerization of propylene oxide and CO2 using achiral salophen Co(III) penta-florobenzoate as catalyst and tetrabutyl ammonium bromide as co-catalyst

Copolymerization of racemic propylene oxide with carbon dioxide is investigated in the presence of economically inexpensive and effective achiral salophenCo(III)X [salophen = N,N'-bis(3,5-di-tert-butylsalicylidene)-phenylenediimine, X = pentaflorobenzoate] catalyst and tetrabutyl ammonium bromide as co-catalyst. Effects of different variables like monomer to catalyst ratio, catalyst/co-catalyst ratio, temperature, pressure of CO₂ on molecular weight, yield and selectivity of poly(propylene carbonate) [PPC] have been investigated. The maximum M_w of 25.8 g/mol has been obtained at 15 bar and 50°C. All the samples were found to have excellent polydispersity near to 1.     

Copolymerization of Cyclohexene Oxide and CO(2) with a Chromium Diamine-bis(phenolate) Catalyst

A diamine-bis(phenolate) chromium(III) complex, {CrCl[O(2)NN'](BuBu)}(2) catalyzes the copolymerization of cyclohexene oxide with carbon dioxide. The synthesis of this metal complex is straightforward, and it can be obtained in high yields. This catalyst incorporates a tripodal amine-bis(phenolate) ligand, which differs from the salen or salan ligands typically used with Cr and Co complexes that have been employed as catalysts for the synthesis of such polycarbonates. The catalyst reported herein yields low molecular weight polymers with narrow polydispersities. Structural and spectroscopic details of this complex along with its copolymerization activity for cyclohexene oxide and carbon dioxide are presented.     

二氧化碳与环氧环己烷共聚的研究进展

综述了国内外用于二氧化碳与环氧环己烷共聚的各类催化剂的研究现状、进展及研发新动向.指出二氧化碳作为一种廉价、无毒、可循环利用的理想原料,利用其和环氧环己烷共聚可合成具有良好生物降解性能的脂肪族聚碳酸酯.但二氧化碳具有较高的热力学稳定性,其和环氧环己烷共聚过程在一般情况下难以实现,故迫切需要开发高效、高选择性的催化剂.     

Trinuclear salphen–chromium(III)chloride complexes as catalysts for the alternating copolymerization of epoxides and cyclic anhydrides

Although the alternating copolymerization of epoxides and cyclic anhydrides is a promising route to aliphatic polyesters, improved catalysts are required to realize commercialization of this process. Herein, trinuclear chromium complexes of salicylaldimine, in conjunction with a nucleophilic cocatalyst, are demonstrated as excellent catalysts for epoxide/cyclic anhydride copolymerization, selectively affording perfectly alternating polyesters. The effect of the distance between the chromium species is investigated by varying the bridging skeleton in a series of trinuclear salphen–Cr(III)Cl complexes for obtaining different Cr–Cr distances. Trinuclear salphenCr(III)–complexes with Cr–Cr distances of approximately 7.3 Å are found to be efficient copolymerization catalysts, even at high temperatures and extremely low catalyst loadings. In particular, a high activity of 10,620 h⁻¹ is obtained for the copolymerization of cyclohexene oxide (CHO) and phthalic anhydride (PA) under a low catalyst loading (<0.01 mol%) at 100 °C. In situ infrared spectroscopy studies suggest that the activation energy of the trinuclear Cr(III)–salphen catalyst for CHO/PA copolymerization is 15 kJ mol⁻¹ lower than that of the corresponding mononuclear catalyst owing to an intramolecular synergistic effect among the metal atoms.     

Mg(ii) heterodinuclear catalysts delivering carbon dioxide derived multi-block polymers

Carbon dioxide derived polymers are emerging as useful materials for applications spanning packaging, construction, house-hold goods and automotive components. To accelerate and broaden their uptake requires both more active and selective catalysts and greater structural diversity for the carbon dioxide derived polymers. Here, highly active catalysts show controllable selectivity for the enchainment of mixtures of epoxide, anhydride, carbon dioxide and lactone. Firstly, metal dependent selectivity differences are uncovered using a series of dinuclear catalysts, Mg(ii)Mg(ii), Zn(ii)Zn(ii), Mg(ii)Zn(ii), and Mg(ii)Co(ii), each exposed to mixtures of bio-derived tricyclic anhydride, cyclohexene oxide and carbon dioxide (1 bar). Depending upon the metal combinations, different block structures are possible with Zn(ii)Zn(ii) yielding poly(ester-b-carbonate); Mg(ii)Mg(ii) or Mg(ii)Co(ii) catalysts delivering poly(carbonate-b-ester); and Mg(ii)Zn(ii) furnishing a random copolymer. These results indicate that carbon dioxide insertion reactions follow the order Co(ii) > Mg(ii) > Zn(ii). Using the most active and selective catalyst, Mg(ii)Co(ii), and exploiting reversible on/off switches between carbon dioxide/nitrogen at 1 bar delivers precision triblock (ABA), pentablock (BABAB) and heptablock (ABABABA) polymers (where A = poly(cyclohexylene oxide-alt-tricyclic anhydride), PE; B = poly(cyclohexene carbonate), PCHC). The Mg(ii)Co(ii) catalyst also selectively polymerizes a mixture of anhydride, carbon dioxide, cyclohexene oxide and ε-caprolactone to deliver a CBABC pentablock copolymer (A = PE, B = PCHC C = poly(caprolactone), PCL). The catalysts combine high activity and selectivity to deliver new polymers featuring regularly placed carbon dioxide and biomass derived linkages.

Carbon dioxide-based multiblock polymers are synthesised, in one-pot, from a mixture of monomers using a highly selective and active heterodinuclear Co(ii)Mg(ii) catalyst.     

Effect of supercritical CO2 on the copolymerization behavior of cyclohexene oxide/CO2 and copolymer properties with DMC/Salen‐Co(III) catalyst system

The copolymerization of cyclohexene oxide (CHO) and carbon dioxide (CO₂) was carried out under supercritical CO₂ (scCO₂) conditions to afford poly (cyclohexene carbonate) (PCHC) in high yield. The scCO₂ provided not only the C1 feedstock but also proved to be a very efficient solvent and processing aid for this copolymerization system. Double metal cyanide (DMC) and salen‐Co(III) catalysts were employed, demonstrating excellent CO₂/CHO copolymerization with high yield and high selectivity. Surprisingly, our use of scCO₂ was found to significantly enhance the copolymerization efficiency and the quality of the final polymer product. Thermally stable and high molecular weight (MW) copolymers were successfully obtained. Optimization led to excellent catalyst yield (656 wt/wt, polymer/catalyst) and selectivity (over 96% toward polycarbonate) that were significantly beyond what could be achieved in conventional solvents. Moreover, detailed thermal analyses demonstrated that the PCHC copolymer produced in scCO₂ exhibited higher glass transition temperatures (T_g ～ 114 °C) compared to polymer formed in dense phase CO₂ (T_g ～ 77 °C), and hence good thermal stability. Additionally, residual catalyst could be removed from the final polymer using scCO₂, pointing toward a green method that avoids the use of conventional volatile organic‐based solvents for both synthesis and work‐up. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 2785–2793     

Oxygen bridged Homobinuclear Mn(II) compounds with Anthranilic acid: Theoretical calculations,oxidation and catalase activity

Two new homobinuclear manganese compounds with mixed ligands, [Mn₂(μ_1,1–2‐NH₂C₆H₄COO)₂(phen)₄](ClO₄)2(CH₃OH) ( 1 ), and [Mn₂(μ_1,3–2‐NH₂C₆H₄COO)₂(bipy)₄](ClO₄)2 ( 2 ) (NH₂C₆H₄COOH = anthranilic acid, bipy = 2,2′‐bipyridine, phen = 1,10‐ phenanthroline) were synthesized and thoroughly characterized by elemental analysis, IR, UV and single crystal X‐ray crystallography. X‐ray structure analysis shows that in the mono‐ and bidentate carboxylate bridged compounds, Mn–Mn distances of 1 and 2 are 3,461 Å, and 4,639 Å, respectively. The energy of the compounds was determined with a DFT (Density Functional Theory) calculation on B3LYP/6‐31G(d,p) optimized geometry by using the B3LYP/6‐31G(d,p) basis set. These compounds acts as biomimetic catalyst and show catalase‐like activity for the hydrogen peroxide dismutation at room temperature in different solvents with remarkable activity (TOF, Turnover frequency = mol of subst./(mol of cat. × time)) up to 12640 h^?1 with 1 , and 17910 h^?1 with 2 in Tris–HCl buffer). Moreover, the catalytic activity of 1 and 2 has been studied for oxidation of alcohols (cinnamyl alcohol, benzyl alcohol, cyclohexanol, 1‐octanol and 1‐heptanol) and alkenes (cyclohexene, styrene, ethyl benzene, 1‐octene and 1‐hexene) in a homogeneous catalytic system consisting t‐butylhydroperoxide (TBHP) as an oxidant in acetonitrile. Both compounds exhibited very high activity in the oxidation of cyclohexene to cyclohexanone (~80% selectivity, ~99% conversion in 1 h, TOF = 243 h^?1 and 226 h^?1) and cinnamyl alcohol to cinnamaldehyde (~64% selectivity) as the main product with very high TOF value (9180 h^?1 and 13040 h^?1 in the first minute of reaction) (~100% conversion in 0.5 h) with TBHP at 70 °C in acetonitrile, for 1 and 2 , respectively.     

Double metal cyanide complex based on Zn3[Co(CN)6]2 as highly active catalyst for copolymerization of carbon dioxide and cyclohexene oxide

Double metal cyanide complexes based on Zn₃[Co(CN)₆]₂ were prepared in the presence of different complexing agents and used in the copolymerization of carbon dioxide and cyclohexene oxide. The FTIR and ¹H NMR spectra of the products verified the formation of polycarbonate. Compared with zinc carboxylate, zinc phenoxide, and so forth, these catalysts demonstrated great enhancement of catalytic activity. Their highest turnover number and turnover frequency reached 3300 and 1650 h^?1, respectively, at 90 °C. The molar fraction of CO₂ (F_CO2) for the copolymers was about 0.44–0.47, and it varied slightly with different catalysts under a temperature of 90 °C and a pressure of 3.8 MPa. The study showed that the F_CO2 can reach 0.40 even at 0.6 MPa, and it changed slightly above 3.8 MPa. The reaction rate had little influence on the F_CO2 under our experimental conditions. A relatively low temperature was favorable for the incorporation of CO₂. The monitoring of copolymerization revealed the molecular weight was proportional to the reaction conversion. The molecular weight distribution was in the range of 4.5–6, and the reaction rate was proportional to the amount of catalyst that was used. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5284–5291, 2004     

Alternating copolymerization of carbon dioxide and cyclohexene oxide catalyzed by silicon dioxide/Zn?CoIII double metal cyanide complex hybrid catalysts with a nanolamellar structure

Air‐stable hybrid catalysts of silicon dioxide/double metal cyanide complexes (Si‐DMCCs) based on Zn₃[Co(CN)₆]₂ (ZHCC) were prepared by an in situ sol–gel method. The Si‐DMCCs showed low crystallinity and a nanolamellar structure with a thickness of ～40–60 nm. In particular, a lamellar structure of regular hexagonal shape was observed for Si‐DMCCs with low SiO₂ content. These catalysts had very high catalytic activity for alternating copolymerization of cyclohexene oxide (CHO) and carbon dioxide. A turnover number of 11,444, turnover frequency of 3815 h^?1, and apparent efficiency of 7.5 kg polymer/g ZHCC (～24.0 kg polymer/g Zn) were achieved at 3.8 MPa and 100 °C. The poly(cyclohexenylene carbonate) (PCHC) polymers obtained were completely atactic with a molecular weight (M_n) of ～10 kg/mol and polydispersity of 2.0–3.0. The PCHCs had a structure of nearly alternating CHO and CO₂ units, with a molar fraction of carbonate units of 0.44–0.47. Preliminary investigations of the mechanism suggest that nucleophilic attack by neighboring oxygen atoms is involved in copolymerization initiation with Zn? Co^III DMCCs. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3128–3139, 2008     

Copolymerization of carbon dioxide and cyclohexene oxide catalyzed by chromium complexes bearing semirigid [ONSO]‐type ligands

Chromium complexes supported by tetradentate dianionic imine‐thioether‐bridged bis(phenol) ligands were prepared and employed in the synthesis of poly(cyclohexene carbonate) via the copolymerization of CO₂ and cyclohexene oxide. The catalytic activity, product selectivity, and kinetic behaviors of these [ONSO]Cr^III complexes have been systematically investigated. Results indicate the presence of electron‐withdrawing substituents on the ligands to enhance catalytic activity and polymer selectivity. A turnover frequency of 100 h^?1 is observed at a temperature of 110 °C, producing polycarbonate with >60% selectivity. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1938–1944     

Study of electronic effect in bifunctional catalysts for the copolymerization of CO2 and PO/CHO

Carbon dioxide (CO₂) is an easily available renewable carbon source that can be used as a comonomer in the catalytic ring-opening polymerization of epoxides to form aliphatic polycarbonates. Herein, a series of new Salen-Co(III) bifunctional catalysts were synthesized for the first time, and they were studied to catalyze the copolymerization of CO₂ and propylene oxide (PO)/cyclohexene oxide (CHO). At the same time, the effects of reaction conditions (electronic effect, temperature, time) on catalytic activity and selectivity were investigated. The results show that the Salen-Co(III) complexes with electron-withdrawing groups have higher selectivity and activity for propylene carbonate (PPC)/cyclohexylene carbonate (PCHC). At the same time, the Salen-Co(III) complexes can better catalyze the copolymerization of CHO and CO₂ than that of PO and CO₂. The catalytic efficiency of the four complexes increased with increasing temperature, and the best reaction condition is 80°C, 30 min and 2 MPa of CO₂.     

Mechanistic investigation and reaction kinetics of the low-pressure copolymerization of cyclohexene oxide and carbon dioxide catalyzed by a dizinc complex

The reaction kinetics of the copolymerization of carbon dioxide and cyclohexene oxide to produce poly(cyclohexene carbonate), catalyzed by a dizinc acetate complex, is studied by in situ attenuated total reflectance infrared (ATR-IR) and proton nuclear magnetic resonance ((1)H NMR) spectroscopy. A parameter study, including reactant and catalyst concentration and carbon dioxide pressure, reveals zero reaction order in carbon dioxide concentration, for pressures between 1 and 40 bar and temperatures up to 80 °C, and a first-order dependence on catalyst concentration and concentration of cyclohexene oxide. The activation energies for the formation of poly(cyclohexene carbonate) and the cyclic side product cyclohexene carbonate are calculated, by determining the rate coefficients over a temperature range between 65 and 90 °C and using Arrhenius plots, to be 96.8 ± 1.6 kJ mol(-1) (23.1 kcal mol(-1)) and 137.5 ± 6.4 kJ mol(-1) (32.9 kcal mol(-1)), respectively. Gel permeation chromatography (GPC), (1)H NMR spectroscopy, and matrix-assisted laser desorption/ionization time-of-flight (MALDI-ToF) mass spectrometry are employed to study the poly(cyclohexene carbonate) produced, and reveal bimodal molecular weight distributions, with narrow polydispersity indices (≤1.2). In all cases, two molecular weight distributions are observed, the higher value being approximately double the molecular weight of the lower value; this finding is seemingly independent of copolymerization conversion or reaction parameters. The copolymer characterization data and additional experiments in which chain transfer agents are added to copolymerization experiments indicate that rapid chain transfer reactions occur and allow an explanation for the observed bimodal molecular weight distributions. The spectroscopic and kinetic analyses enable a mechanism to be proposed for both the copolymerization reaction and possible side reactions; a dinuclear copolymerization active site is implicated.     

Polymeric catalyst with polymerization-enhanced Lewis acidity for CO2-based copolymers

Ring-opening copolymerization of CO₂ and epoxides is a promising way to manufacture high value-added materials. Despite a variety of catalyst systems have been reported, the reaction is still limited by low activity and polymer selectivity. Herein, a strategy of polymerization-enhanced Lewis acidity is reported to construct a series of highly efficient polymeric aluminum porphyrin catalysts (PAPCs). The characterization of the coordination equilibrium constant (K_eq) showed significantly enhanced Lewis acidity of PAPC (K_eq = 18.2 L/mol) compared to the monomeric counterpart (K_eq = 6.4 L/mol), accompanied with increased turnover frequency (TOF) from 136 h⁻¹ to 5500 h⁻¹. Through detailed regulation of Lewis acidity, the highly Lewis acidic PAPC-OTs displayed a record high TOF of 30,200 h⁻¹ with polymer selectivity of up to 99%.     

Alternating copolymerization of carbon dioxide and propylene oxide under bifunctional cobalt salen complexes: Role of Lewis base substituent covalent bonded on salen ligand

Alternating copolymerization of propylene oxide (PO) and carbon dioxide (CO₂) was realized under mild conditions with a moderate turnover frequency (TOF), employing sole bifunctional cobalt salen complexes containing Lewis acid metal center and covalent bonded Lewis base on the ligand. Variation of the covalent bonded Lewis base substituents on the salen ligands could tailor the catalytic activity with TOF changing from 19.3 to 34.9 h^?1, polymeric/cyclic carbonate selectivity from 95.3 to 72.8%, and the head‐to‐tail structure in the polymer from 72.2 to 86.0%. The IR analysis confirmed that the Lewis base moiety on one molecule could coordinate with cobalt center of adjacent molecule, playing similar role to the Salen metal complex/Lewis base binary catalytic system. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 359–365, 2010     

Lanthanide Complexes Supported by a Trizinc Crown Ether as Catalysts for Alternating Copolymerization of Epoxide and CO2: Telomerization Controlled by Carboxylate Anions

A new family of heterometallic catalysts based on trimetalated macrocyclic tris(salen) ligands and rare‐earth metals was prepared and structurally characterized. The LaZn₃ system containing anionic ligands such as acetate plays a critical role in catalyzing the alternating copolymerization of cyclohexene oxide (CHO) and CO₂ with a high proportion of carbonate linkages. Among the lanthanide metals, the CeZn₃ system exhibits high catalytic activity with a turnover frequency (TOF) of over 370 h^?1. NMR analysis of the complex and end‐group analysis of the polymer suggest that the acetate ligands are rapidly exchanged, not only among coordinated acetates, but also between coordinated acetates and added carboxylate anions. These unique properties make this the first example of telomerization for the copolymerization of CHO and CO₂.     

Electrocatalytic Reduction of CO2 to Acetic Acid by a Molecular Manganese Corrole Complex

The controlled electrochemical reduction of carbon dioxide to value added chemicals is an important strategy in terms of renewable energy technologies. Therefore, the development of efficient and stable catalysts in an aqueous environment is of great importance. In this context, we focused on synthesizing and studying a molecular Mn^III‐corrole complex, which is modified on the three meso‐positions with polyethylene glycol moieties for direct and selective production of acetic acid from CO₂. Electrochemical reduction of Mn^III leads to an electroactive Mn^II species, which binds CO₂ and stabilizes the reduced intermediates. This catalyst allows to electrochemically reduce CO₂ to acetic acid in a moderate acidic aqueous medium (pH 6) with a selectivity of 63 % and a turn over frequency (TOF) of 8.25 h^?1, when immobilized on a carbon paper (CP) electrode. In terms of high selectivity towards acetate, we propose the formation and reduction of an oxalate type intermediate, stabilized at the Mn^III‐corrole center.     

(Tetramethyltetraazaannulene)chromium chloride: a highly active catalyst for the alternating copolymerization of epoxides and carbon dioxide

A tetramethyltetraazaannulene complex incorporating a chromium(III) metal center has been shown to be highly active toward the copolymerization of cyclohexene oxide and carbon dioxide to afford poly(cyclohexene carbonate) in the presence of [PPN]N3 [PPN+=bis(triphenylphosphoranylidene)ammonium] as a cocatalyst. An asymptotical rate increase was observed, leveling at 2 equiv of cocatalyst with a maximum turnover frequency of 1300 h(-1) at 80 degrees C. A benefit of this new catalyst system over that of the previously studied less-active (salen)CrX system is that the (tmtaa)CrCl catalyst has a much lower propensity toward the formation of a cyclic carbonate byproduct throughout the copolymerization reaction.     

Polymer Supported Schiff Base Complexes of Iron(III), Cobalt(II) and Nickel(II) Ions and their Catalytic Activity in Oxidation of Phenol and Cyclohexene

The polymer supported transition metal complexes of N,N′‐bis (o‐hydroxy acetophenone) hydrazine (HPHZ) Schiff base were prepared by immobilization of N,N′‐bis(4‐amino‐o‐hydroxyacetophenone)hydrazine (AHPHZ) Schiff base on chloromethylated polystyrene beads of a constant degree of crosslinking and then loading iron(III), cobalt(II) and nickel(II) ions in methanol. The complexation of polymer anchored HPHZ Schiff base with iron(III), cobalt(II) and nickel(II) ions was 83.30%, 84.20% and 87.80%, respectively, whereas with unsupported HPHZ Schiff base, the complexation of these metal ions was 80.3%, 79.90% and 85.63%. The unsupported and polymer supported metal complexes were characterized for their structures using I.R, UV and elemental analysis. The iron(III) complexes of HPHZ Schiff base were octahedral in geometry, whereas cobalt(II) and nickel(II) complexes showed square planar structures as supported by UV and magnetic measurements. The thermogravimetric analysis (TGA) of HPHZ Schiff base and its metal complexes was used to analyze the variation in thermal stability of HPHZ Schiff base on complexation with metal ions. The HPHZ Schiff base showed a weight loss of 58% at 500°C, but its iron(III), cobalt(II) and nickel(II) ions complexes have shown a weight loss of 30%, 52% and 45% at same temperature. The catalytic activity of metal complexes was tested by studying the oxidation of phenol and epoxidation of cyclohexene in presence of hydrogen peroxide as an oxidant. The supported HPHZ Schiff base complexes of iron(III) ions showed 64.0% conversion for phenol and 81.3% conversion for cyclohexene at a molar ratio of 1∶1∶1 of substrate to catalyst and hydrogen peroxide, but unsupported complexes of iron(III) ions showed 55.5% conversion for phenol and 66.4% conversion for cyclohexene at 1∶1∶1 molar ratio of substrate to catalyst and hydrogen peroxide. The product selectivity for catechol (CTL) and epoxy cyclohexane (ECH) was 90.5% and 96.5% with supported HPHZ Schiff base complexes of iron(III) ions, but was found to be low with cobalt(II) and nickel(II) ions complexes of Schiff base. The selectivity for catechol (CTL) and epoxy cyclohexane (ECH) was different with studied metal ions and varied with molar ratio of metal ions in the reaction mixture. The selectivity was constant on varying the molar ratio of hydrogen peroxide and substrate. The energy of activation for epoxidation of cyclohexene and phenol conversion in presence of polymer supported HPHZ Schiff base complexes of iron(III) ions was 8.9 kJ mol^?1 and 22.8 kJ mol^?1, respectively, but was high with Schiff base complexes of cobalt(II) and nickel(II) ions and with unsupported Schiff base complexes.