Solvent effects on catalytic activity of manganese porphyrins with cationic,anionic and uncharged meso substituents: Indirect evidence on the nature of active oxidant species

Oxidation of cyclohexene and styrene with sodium periodate and tetra‐n‐butylammonium periodate (TBAP) catalyzed by MnT(3‐MePy)P(OAc), MnT(4‐SO₃)PP(OAc) and MnTPP(OAc) has been studied in water, methanol, acetonitrile and dichloromethane as solvents. The results show significant dependence of the product distribution on the type of solvent and the electronic nature of the aryl substituents introduced at the porphyrin periphery. While the oxidation of cyclohexene and styrene in the presence of MnT(3‐MePy)P(OAc) and MnTPP(OAc) in water (also in methanol) gave the corresponding epoxides as nearly the sole product, performing the reactions in the presence of MnT(4‐SO₃)PP(OAc) yielded the products of allylic oxidation, cyclohexene‐2‐ol and cyclohexene‐2‐one and acetophenone as the major products. In the case of styrene, performing the reaction in the presence of MnT(4‐SO₃)PP(OAc), MnT(3‐MePy)P(OAc) and MnTPP(OAc) in acetonitrile gave a mixture of styrene oxide and acetophenone as the products. Under the same conditions, the oxidation of cyclohexene afforded cyclohexene oxide as approximately the exclusive product. Furthermore, the oxidation of olefins in dichloromethane gave the corresponding epoxide as the exclusive products. The product distributions observed in the protic and aprotic solvents were used to provide indirect evidence on the relative contribution and reactivity of high valent manganese oxo and periodato Mn(III) porphyrin species to the oxidation reactions.     

Oxidation of olefins and sulfides with different oxidants catalyzed by meso-tetra(n-propyl)porphyrinatomanganese(III) acetate: comparison with meso-tetra(phenyl)porphyrinatomanganese(III) acetate

In this study, the catalytic activity of meso-tetra(n-propyl)porphyrinatomanganese(III) acetate, MnT(n-pr)(OAc) in oxidation of olefins and sulfides with tetra-n-butylammonium Oxone (TBAO), tetra-n-butylammonium periodate (TBAP), aqueous hydrogen peroxide, sodium periodate and Oxone in the presence of imidazole (ImH) has been studied. The comparison of catalytic performance of MnT(n-pr)P(OAc) and MnTPP(OAc) in oxidation of olefins with TBAP shows that while the latter is four times more efficient than the former, the extent of oxidative degradation of the former is ca. 3.5 times greater than the latter. The use of excess amount of styrene resulted in only a ca. 10 % increase in the catalyst stability, suggesting a mainly intramolecular mechanism for the catalyst degradation. On the other hand, in the case of TBAO, the oxidative degradation of the former is four times greater than the latter, but the catalytic performance of the latter for the oxidation of cyclohexene was only ca. 2 times larger than the former. This observation shows that the decreased catalytic performance of MnT(n-pr)P(OAc) relative to MnTPP(OAc) is essentially due to the high degree of degradation of the former. Due to the high degree of catalyst degradation, oxidation of olefins with periodate and Oxone in the presence of the two manganese porphyrins in aqueous solution (or with hydrogen peroxide in dichloromethane) gave little or no product. Oxidation of sulfides with TBAO and TBAP in the presence of MnT(n-pr)P(OAc) showed a conversion of ca. 15 % for the catalytic oxidation of sulfides to sulfones.     

Axial base‐controlled catalytic activity,oxidative stability and product selectivity of water‐insoluble manganese and iron porphyrins for oxidation of styrenes in water under green conditions

A series of water‐insoluble iron(III) and manganese(III) porphyrins, FeT(2‐CH₃)PPCl, FeT(4‐OCH₃)PPCl, FeT(2‐Cl)PPCl, FeTPPCl, MnT(2‐CH₃)PPOAc, MnT(4‐OCH₃)PPOAc, MnT(2‐Cl)PPOAc and MnTPPOAc, in the presence of imidazole (ImH), F^?, Cl^?, Br^? and acetate were used as catalysts for the aqueous‐phase heterogeneous oxidation of styrenes to the corresponding epoxides and aldehydes with sodium periodate. Also, the effect of various reaction parameters such as reaction time, molar ratio of catalyst to axial base, type of axial base, molar ratio of olefin to oxidant and nature of metal centre on the activity and oxidative stability of the catalysts and the product selectivity was investigated. Higher catalytic activities were found for the iron complexes. Interestingly, the selectivity towards the formation of epoxide and aldehyde (or acetophenone) was significantly influenced by the type of axial base. Furthermore, Br^? and ImH were found to be the most efficient co‐catalysts for the oxidation of olefins performed in the presence of the manganese and iron porphyrins, respectively. The optimized molar ratio of catalyst to axial base was different for various axial bases. Also, the order of co‐catalyst activity of the axial bases obtained in aqueous medium was different from that reported for organic solvents. The use of a convenient axial base under optimum reaction catalyst to co‐catalyst molar ratio in the presence of the manganese porphyrin gave the oxidative products with a conversion of ca 100% in a reaction time of less than 3 h. However, the catalytic activity of the iron porphyrins could not be effectively improved by increasing the catalyst to co‐catalyst molar ratio.     

A practical innovative method for highly selective oxidation of alkenes and alkanes using Fe (III) and Mn (III) porphyrins supported onto multi‐wall carbon nanotubes as reusable heterogeneous catalysts

Functionalized multi‐walled carbon nanotubes were used for covalent immobilization of meso‐tetrakis(4‐carboxyphenyl) porphyrinatoiron (III) chloride [Fe (TCPP)Cl] and meso‐tetrakis(4‐carboxyphenyl) porphyrinatomanganese (III) acetate [Mn (TCPP)OAc]. The full characterization of the hybrid porphyrinic nanomaterials, by Fourier transform‐infrared and UV–Vis spectroscopy, transmission electron microscopy, thermogravimetry and flame atomic absorption spectrometry is described. The oxidation of alkenes and alkanes with molecular oxygen as green oxidant in the presence of Mn‐ and Fe‐catalysts has been studied in a comparative manner. The Fe‐catalyst was shown to have higher catalytic activity compared with the Mn‐catalyst. In addition, both separable solid catalysts can be recovered and reused at least 10 times along with good yields.     

Manganese porphyrins/mesoporous amberlyst 15 nanocomposites: Robust biomimetic catalysts for aqueous oxidation of olefins

In this study, the manganese complexes of N-methylated meso-tetra(2-, 3-, or 4 pyridyl)porphyrins, immobilized into the pores of the sodium salt of mesoporous amberlyst 15 nanoparticles (nanoAmbSO₃Na), nanoAmbSO₃@MnT(2-MePy)P (OAc), nanoAmbSO₃@MnT(3-MePy)P (OAc), and nanoAmbSO₃@MnT(4-MePy)P (OAc), were synthesized and characterized by field-emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDX), thermal gravimetric analysis (TGA), nitrogen adsorption/desorption porosimetry analysis, and diffuse reflectance UV–vis spectroscopy. FESEM images revealed a particle size less than ~40 nm for the nanocomposites. The results of BET are in accord with the occupation of the larger pores of the polymer matrix in the case of MnT(2-MePy)P (OAc) as the most sterically demanding metalloporphyrin of the series, and the smaller pores in the case of the other ones. The immobilized manganese porphyrins were used as catalysts for the oxidation of olefins with sodium periodate in the presence of imidazole (ImH) as the co-catalyst. The negligible oxidative destructions of the immobilized manganese porphyrins under the oxidative conditions allowed the comparison of the inherent catalytic activity of the metalloporphyrins, decreased as nanoAmbSO₃@MnT(4-MePy)P (OAc) > nanoAmbSO₃@MnT(3-MePy)P (OAc) ≫ nanoAmbSO₃@MnT(2-MePy)P (OAc). Contrary to the general belief that electron-deficient metalloporphyrins are more efficient catalysts than the electron-rich ones, the most electron-deficient metalloporphyrin of the series, that is, nanoAmbSO₃@MnT(2-MePy)P (OAc), showed the lowest catalytic activity. Due to the high oxidative stability of the immobilized manganese porphyrins, ring opening of epoxide competes with the epoxidation reaction to decrease the yield of epoxide at longer reaction times than the optimized one.     

Template‐free anion‐controlled synthesis of Pd (II) nano‐aggregates for the antifouling polymerization of CO and ethylene

The reaction of [(domppp) Pd (OAc)₂] [domppp = 1,3‐bis (di‐o‐methoxyphenylphosphino)propane] and imidazolium‐functionalized carboxylic acids containing various anions (Br^?, PF₆^?, SbF₆^? and BF₄^?) resulted in the formation of nano‐sized Pd (II) aggregates under template‐free conditions. The rate of formation of aggregates can be modulated by changing the anion, affecting the rate of polymerization of CO and olefins without fouling. Herein, we describe the analysis of Pd (II) catalysts by dynamic light scattering, atomic force microscopy, X‐ray photoelectron spectroscopy and X‐ray crystallography, and co‐ and terpolymerization results including the catalytic activity, and bulk density and molecular weight of polymers.     

Carbon–carbon coupling reactions catalyzed by supported Pd porphyrins

The tetrakis(4‐N‐methylpyridinium)porphyrinatopalladium(II) iodide, [Pd(TMPyP)]I₄, supported on Dowex 50WX8 and Amberlite IR‐120 ion‐exchange resins, was used as heterogeneous, recyclable and active catalyst for the Suzuki–Miyaura and Heck cross‐coupling reactions. These catalysts were applied to coupling of various aryl halides with phenylboronic acid and styrene in Suzuki and Heck reactions, respectively, and the corresponding products were obtained in excellent yields and short reaction times. The catalysts could be recovered easily by simple filtration and reused several times without significant loss of their catalytic activity. The catalysts were characterized by diffuse‐reflectance UV–visible spectroscopy and scanning electron microscopy, and their stability was confirmed by TGA. Copyright © 2014 John Wiley & Sons, Ltd.     

Biomimetic Decarboxylation of Carboxylic Acids with PhI（OAc）2 Catalyzed by Manganese Porphyrin [Mn（TPP）OAc]

Manganese（Ⅲ） meso-tetraphenylporphyrin acetate [Mn（TPP）OAc] served as an effective catalyst for the oxidative decarboxylation of carboxylic acids with （diacetoxyiodo）benzene [PhI（OAc）2] in CH2CI2-H2O（95：5, volume ratio）. The aryl substituted acetic acids are more reactive than the less electron rich linear carboxylic acids in the presence of catalyst Mn（TPP）OAc. In the former case, the formation of carbonyl products was complete within just a few minutes with 〉97% selectivities, and no further oxidation of the produced aldehydes was achieved under these catalytic conditions. This method provides a benign procedure owing to the utilization of low toxic（diacetoxyiodo） benzene, biologically relevant manganese porphyrins, and carboxylic acids.     

Catalytic activity of Mn(III) and Fe(III) complexes of meso-tetra(n-propyl)porphyrin in oxidation of olefins: Meso-alkyl substituent in comparison with the alkenyl and aryl ones

Catalytic activity of Mn(III) and Fe(III) complexes of meso-tetra(n-propyl)porphyrin, MnT(n-Pr)P(X) and FeT(n-Pr)P(X) (X = Cl, SCN, OAc) in oxidation of olefins with tetra-n-butylammonium periodate at room temperature has been studied. The influence of different parameters including the molar ratio of catalyst to imidazole, type of counter ion (X) and oxidative stability of metalloporphyrins on the efficiency of the catalysts was investigated. The results of competitive oxidation of cis- and trans-stilbene suggest the presence of a high-valent Mn-oxo as the predominant oxidant species in equilibrium with a six coordinate complex, MnT(n-Pr)P(ImH)(IO₄) in the case of MnT(n-Pr)P(OAc). An unusual preference for trans-stilbene over cis-stilbene was observed in the reaction catalyzed by FeT(n-Pr)P(OAc). Control reaction indicated a significant cis- to trans-isomerization (81%) in oxidation of cis-stilbene catalyzed by FeT(n-Pr)P(OAc) which may explain the observed unusual cis to trans-stilbene oxide ratio. While oxidation of cyclooctene and styrene led to the exclusive formation of the corresponding epoxides, oxidation of cyclohexene gave 2-cyclohexe-1-ol and cyclohexene oxide as the products. However, the results of this study clearly demonstrate the key role played by the group substituted at the meso positions of metalloporphyrins on their catalytic activity, apart from the electron-donating or electron-withdrawing properties of the substituents.     

Bio‐safe synthesis of linear and branched PLLA

The catalytic activities of Bi(III) acetate (Bi(OAc)₃) and of creatinine towards the ring‐opening polymerization of L ‐lactide have been compared with those of a stannous (II) ethylhexanoate ((SnOct)₂)‐based system and with those of a system catalyzed by enzymes. All four were suitable catalysts for the synthesis of high and moderate molecular weight poly(L ‐lactide)s and the differences in reactivity and efficiency have been studied. Linear and branched poly(L ‐lactide)s were synthesized using these bio‐safe initiators together with ethylene glycol, pentaerythritol, and myoinositol as coinitiators. The polymerizations were performed in bulk at 120 and 140 °C and different reactivities and molecular weights were achieved by adding different amounts of coinitiators. A molecular weight of 105,900 g/mol was achieved with 99% conversion in 5 h at 120 °C with a Bi(OAc)₃‐based system. This system was comparable to Sn(Oct)₂ at 140 °C. The reactivity of creatinine is lower than that of Bi(OAc)₃ but higher compared with enzymes lipase PS (Pseudomonas fluorescens). A ratio of Sn(Oct)₂M_o/I_o 10,000:1 was needed to achieve a polymer with a reasonable low amount of tin residue in the precipitated polymer, and a system catalyzed by creatinine at 140 °C has a higher conversion rate than such a system. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1214–1219, 2010     

NaY Zeolite Functionalized by Sulfamic Acid/Cu(OAc)2 as a Novel and Reusable Heterogeneous Hybrid Catalyst in Efficient Synthesis of Bis,Tris, and Tetrakis(indolyl)methanes, 3,4‐Dihydropyrimidin‐2(1H)‐ones,and 2‐Aryl‐1H‐benzothiazoles

An efficient acid‐catalyzed synthesis of some bis, tris, and tetrakis(indolyl)methanes, 3,4‐dihydropyrimidin‐2(1H )‐ones, and 2‐aryl‐1H ‐benzothiazoles is reported using NaY zeolite functionalized by sulfamic acid/Cu(OAc )₂ (NaY zeolite‐NHSO₃H /Cu(OAc )₂) in excellent yield. The heterogeneous catalyst has a simple work‐up procedure and could be recycled and reused for six reaction cycles.     

Further study on the synthesis of F-containing porphyrins and their catalytic activity on oxidation of cyclohexene

Reaction of tetrakis(p-allyloxyphenyl)porphyrin and perfluoroalkanesulfonyl bromides givestetrakis(p-polyfluoroalkoxylphenyl)substituted porphyrins.The yields are over 90%.The synthesis ofthe metal ion complexes of these F-containing porphyrins is also reported.Preliminary results on thestudy of the catalytic activity of the manganese(Ⅲ)complexes of various fluorinated porphyrins onoxidation of cyclohexene indicate that the introduction of R_F group into porphyrin contributes to thestability of the catalysts.     

The catalysis of some novel polystyrene-supported porphyrinatomanganese(III) in hydroxylation of cyclohexane with molecular oxygen

Some novel polystyrene-supported porphyrinatomanganese(III) in which alkyl group is bonded to the surface of polystyrene, PS-[Mn(HPTPP)Cl](C_nH_2n+1) (n=2, 6, 8, 18), have been synthesized. Their catalytic activities to hydroxylate cyclohexane in PS-[Mn(HPTPP)Cl](C_nH_2n+1)–O₂–ascrobate system have been found to be higher compared with corresponding non-supported porphyrinatomanganese(III) and increase with the increase of the length of alkyl. These results are discussed in the point of view of metalloporphyrin microenvironment.     

Biomimetic Decarboxylation of Carboxylic Acids with PhI(OAc)2 Catalyzed by Manganese Porphyrin [Mn(TPP)OAcl

Manganese(Ⅲ) meso-tetraphenylporphyrin acetate [Mn(TPP)OAc] served as an effective catalyst for the oxidative decarboxylation of carboxylic acids with (diacetoxyiodo)benzene [Phl(OAc)2] in CH2C12-H2O(95:5,volume ratio),The aryl substituted acetic acids are more reactive than the less electron rich linear carboxylic acids in the presence of catalyst Mn(TPP)OAc,In the former case,the formation of carbonyl products was complete within just a few minutes with ＞97% selectivities,and no further oxidation of the produced aldehydes was achieved under these catalytic conditions,This method provides a benign procedure owing to the utilization of low toxic(diacetoxyiodo)benzene,biologically relevant manganese porphyrins,and carboxylic acids.     

Ferrocene‐tagged ionic liquid stabilized on silica‐coated magnetic nanoparticles: Efficient catalyst for the synthesis of 2‐amino‐3‐cyano‐4H‐pyran derivatives under solvent‐free conditions

An advanced novel magnetic ionic liquid based on imidazolium tagged with ferrocene, a supported ionic liquid, is introduced as a recyclable heterogeneous catalyst. Catalytic activity of the novel nanocatalyst was investigated in one‐pot three‐component reactions of various aldehydes, malononitrile and 2‐naphthol for the facile synthesis of 2‐amino‐3‐cyano‐4H‐pyran derivatives under solvent‐free conditions without additional co‐catalyst or additive in air. For this purpose, we firstly synthesized and investigated 1‐(4‐ferrocenylbutyl)‐3‐methylimidazolium acetate, [FcBuMeIm][OAc], as a novel basic ferrocene‐tagged ionic liquid. This ferrocene‐tagged ionic liquid was then linked to silica‐coated nano‐Fe₃O₄ to afford a novel heterogeneous magnetic nanocatalyst, namely [Fe₃O₄@SiO₂@Im‐Fc][OAc]. The synthesized novel catalyst was characterized using ¹H NMR, ¹³C NMR, Fourier transform infrared and energy‐dispersive X‐ray spectroscopies, X‐ray diffraction, and transmission and field emission scanning electron microscopies. Combination of some unique characteristics of ferrocene and the supported ionic liquid developed the catalytic activity in a simple, efficient, green and eco‐friendly protocol. The catalyst could be reused several times without loss of activity.     

Catalytic Performance and Dispersion Behavior of Supported Nano‐Amorphous Alloy NiB/MCM‐41 Catalysts Prepared by Chemical Reductive Deposition

Supported nano‐amorphous alloy NiB/MCM‐41 catalysts were prepared by chemical reductive deposition. The as‐prepared catalysts were characterized by XRD, SEM, TEM, EDAX, ICP, and N₂ adsorption‐desorption. The amorphous alloy structure of NiB active sites, mesoporous structure of catalysts, and higher BET area have been proved by the experiments. The catalysts have given excellent catalytic activity and selectivity in the production of 3‐(N‐benzyl)‐amino‐4‐methoxy‐ acetanilide from 3‐amino‐4‐methoxy‐acetanilide and benzaldehyde.     

Epoxidation of styrene catalyzed by manganese (III) porphyrins supported on chloromethylated polystyrene resin bearing crown ether groups,

Metalloporphyrins and crown ether groups were simultaneously supported on chloromethylated polystyrene resin to produce a series of polymer-supported catalysts. The synthesis of these catalysts has been studied. The influence of pH, concentrations of NaOCl and phase transfer catalysts on the epoxidation of styrene catalyzed by these catalysts has also been investigated. The experimental results show that manganese(III) porphyrin bound to chloromethylated polystyrene which bears crown ether groups is effective catalysts for the epoxidation of styrene by sodium hypochlorite. The introduction of crown ether groups increases the catalytic efficiency of supported metalloporphyrins. The kinetics of epoxidation catalyzed by supported manganese(III) porphyrins obeys Michaelis-Menten equation—the characteristic of enzyme-driven reaction.     

Fe3O4@dopa (dopa = dopamine hydrochloride) functionalized Mn(III) Schiff base complex: A promising magnetically separable heterogeneous catalyst for oxidative transformations

A chiral Schiff base complex has been prepared by treating (R)-1,2-diaminopropane with 3,5-dichlorosalicylaldehyde in ethanol, followed by addition of manganese chloride hexahydrate to generate a homogeneous catalyst, [MnL(Cl)(H₂O)] (HMN). Crystal structure of the complex reveals its mononuclear nature. Circular dichroism (CD) studies indicate that the ligand and its corresponding complex contain an asymmetric center. The catalytic activity of HMN toward epoxidation of alkenes, oxidation of alcohols and oxidation of alkanes has been investigated in the presence of iodosylbenzenediacetate (PhI(OAc)₂), in acetonitrile. In the present work we found yields to be much higher compared to our previous approaches. For further adaptation, we attached our efficient homogeneous catalyst with surface modified magnetic nanoparticles (Fe₃O₄@dopa) and thereby obtained a new magnetically separable nanocatalyst Fe₃O₄@dopa@MnLCl (FDM). This catalyst has been characterized and its oxidation ability assessed in similar conditions as those used for the homogeneous catalyst. Enantiomeric excess in epoxide yield reveals retention of chirality of the active site of Fe₃O₄@dopa@MnLCl. The catalyst can be recovered by magnetic separation and recycled several times without significant loss of catalytic activity.     

Living ring‐opening polymerization of lactides catalyzed by guanidinium acetate

Hexabutyl guanidinium acetate (HBG · OAc) was synthesized and successfully used as a catalyst for the ring‐opening polymerization (ROP) of lactides. The experimental results indicated that the guanidinium salt HBG · OAc showed satisfactory catalytic behavior. Polymerization in bulk (120 °C, 18 h) produced polylactides with moderate molecular weights (number‐average molecular weight = 2.0 × 10⁴) and very narrow molecular weight distributions (polydispersity index = 1.07–1.12). A kinetic study of polymerization in bulk with HBG · OAc as an initiator revealed that the polymerization possessed typical characteristics of living polymerization. A ROP mechanism by HBG · OAc was proposed on the basis of the additive effect of the polymerization and the ¹H NMR characterization of the microstructure of the product polymers. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3775–3781, 2004     

Effect of Nano‐support and Type of Active Metal on Reforming of CH4 with CO2

Two series of Co and Ni based catalysts supported over commercial (ZrO₂, CeO₂, and Al₂O₃) nano supports were investigated for dry reforming of methane. The catalytic activity of both Co and Ni based catalysts were assessed at different reaction temperatures ranging from 500—800 °C; however, for stability the time on stream experiments were conducted at 700 °C for 6 h. Various techniques such as N₂ adsorption‐desorption isotherm, temperature‐programmed reduction (H₂‐TPR), temperature‐programmed desorption (CO₂‐TPD), temperature‐programmed oxidation (TPO), X‐ray diffraction (XRD), thermogravimetric analysis (TGA) were applied for characterization of fresh and spent catalysts. The catalytic activity and stability tests clearly showed that the performance of catalyst is strongly dependent on type of active metal and support. Furthermore, active metal particle size and Lewis basicity are key factors which have significant influence on catalytic performance. The results indicated that Ni supported over nano ZrO₂ exhibited highest activity among all tested catalysts due to its unique properties including thermal stability and reducibility. The minimum carbon deposition and thus relatively stable performance was observed in case of Co‐Al catalyst, since this catalyst has shown highest Lewis basicity.