Oxidation Of Adamantane Research Articles

Structural and electronic promotion with alkali cations of silica-supported Fe(III) sites for alkane oxidation

Promoters and precursors can control oxide phase, dispersion, and per-site reactivity of supported oxide catalysts. Previously, dispersed FeOx–SiO2 resulted from Fe3+ ethylenediaminetetraacetate (FeEDTA−) precursors, with NaFeEDTA giving enhanced dispersion and oxidation rates vs. NH4FeEDTA. Here, catalysts were synthesized by sequential alkali deposition and Fe3+ impregnation. At up to 0.9Fenm−2 from NH4FeEDTA and equimolar alkali, UV–visible and H2 TPR were consistent with isolated Fe3+ and small FeOx clusters. Omitting alkali, using Fe(NO3)3, or using Fe/alkali >1 gave evidence of larger agglomerates. For Fe/alkali ≤1 on non-porous SiO2, initial turnover frequencies in adamantane oxidation using H2O2 were independent of surface density. TOF increased as 6.3, 8.8, 15.4, and 20.9 (±0.3)ks−1 for Li+, Na+, K+, and Cs+, respectively, increasingly linearly with decreasing electronegativity. These results give a synthesis–structure–function taxonomy with alkali as an electronic and structural promoter of dispersed FeOx species for alkane selective oxidation.

Surface speciation and alkane oxidation with highly dispersed Fe(III) sites on silica

When highly dispersed, supported Fe oxides are selective alkane oxidation catalysts, but new syntheses are required to reliably produce such materials. Here, highly dispersed, supported Fe3+ catalysts are prepared via incipient wetness impregnation of SiO2 with aqueous Fe complexes of ethylenediaminetetraacetic acid (FeEDTA), followed by calcination. With Na+ countercations, UV–visible diffuse reflectance spectra are entirely below 300nm and H2 temperature-programmed reduction only shows reduction at ∼630°C for all loadings up to 2.15wt%, the maximum loading for a single impregnation cycle. These characteristics indicate isolated sites not seen for Fe(NO3)3 precursors even at 0.3wt%. NH4+ countercations lead to amorphous oxide oligomers and a minority species with unusual reducibility at 310°C. Na+ countercations produce ‘single-site’ behavior in adamantane oxidation using H2O2 with a specific turnover frequency of 9.2±0.8ks−1, constant for all Fe loadings and approximately 10 times higher than that of other well-dispersed Fe/SiO2 materials. Similar turnover frequencies are obtained when counting only the highly reducible species on the NH4+-derived catalyst, allowing these sites to be tentatively assigned as small, undercoordinated clusters that are both easily reduced and participate in alkane oxidation, reminiscent of Fe-exchanged MFI zeolites.

Nickel(ii) complexes of tripodal 4N ligands as catalysts for alkane oxidation using m-CPBA as oxidant: ligand stereoelectronic effects on catalysis

Several mononuclear Ni(II) complexes of the type [Ni(L)(CH(3)CN)(2)](BPh(4))(2) 1-7, where L is a tetradentate tripodal 4N ligand such as N,N-dimethyl-N',N'-bis(pyrid-2-ylmethyl)ethane-1,2-diamine (L1), N,N-diethyl-N',N'-bis(pyrid-2-ylmethyl)ethane-1,2-diamine (L2), N,N-dimethyl-N'-(1-methyl-1H-imidazol-2-ylmethyl)-N'-(pyrid-2-ylmethyl)ethane-1,2-diamine (L3), N,N-dimethyl-N',N'-bis(1-methyl-1H-imidazol-2-ylmethyl)ethane-1,2-diamine (L4), N,N-dimethyl-N',N'-bis(quinolin-2-ylmethyl)ethane-1,2-diamine (L5), tris(benzimidazol-2-ylmethyl)amine (L6) and tris(pyrid-2-ylmethyl)amine (L7), have been isolated and characterized using CHN analysis, UV-Visible spectroscopy and mass spectrometry. The single-crystal X-ray structures of the complexes [Ni(L1)(CH(3)CN)(H(2)O)](ClO(4))(2) 1a, [Ni(L2)(CH(3)CN)(2)](BPh(4))(2) 2, [Ni(L3)(CH(3)CN)(2)](BPh(4))(2) 3 and [Ni(L4)(CH(3)CN)(2)](BPh(4))(2) 4 have been determined. All these complexes possess a distorted octahedral coordination geometry in which Ni(II) is coordinated to four nitrogen atoms of the tetradentate ligands and two CH(3)CN (2, 3, 4) or one H(2)O and one CH(3)CN (1a) are located in cis positions. The Ni-N(py) bond distances (2.054(2)-2.078(3) Å) in 1a, 2 and 3 are shorter than the Ni-N(amine) bonds (2.127(2)-2.196(3) Å) because of sp(2) and sp(3) hybridizations of the pyridyl and tertiary amine nitrogens respectively. In 3 the Ni-N(im) bond (2.040(5) Å) is shorter than the Ni-N(py) bond (2.074(4) Å) due to the stronger coordination of imidazole compared with the pyridine donor. In dichloromethane/acetonitrile solvent mixture, all the Ni(ii) complexes possess an octahedral coordination geometry, as revealed by the characteristic ligand field bands in the visible region. They efficiently catalyze the hydroxylation of alkanes when m-CPBA is used as oxidant with turnover number (TON) in the range of 340-620 and good alcohol selectivity for cyclohexane (A/K, 5-9). By replacing one of the pyridyl donors in TPA by a weakly coordinating -NMe(2) or -NEt(2) donor nitrogen atom the catalytic activity decreases slightly with no change in the selectivity. In contrast, upon replacing the pyridyl nitrogen donor by the strongly σ-bonding imidazolyl or sterically demanding quinolyl/benzimidazolyl nitrogen donor, both the catalytic activity and selectivity decrease, possibly due to destabilization of the intermediate [(4N)(CH(3)CN)Ni-O˙](+) radical species. Adamantane is selectively (3°/2°, 12-17) oxidized to 1-adamantanol, 2-adamantanol and 2-adamantanone while cumene is selectively oxidized to 2-phenyl-2-propanol. In contrast to cyclohexane oxidation, the incorporation of sterically hindering quinolyl/benzimidazolyl donors around Ni(ii) leads to a high 3°/2° bond selectivity for adamantane oxidation. A linear correlation between the metal-ligand covalency parameter (β) and the turnover number has been observed.

Selective hydroxylation of alkanes catalyzed by iron(IV)corrole

The complex meso-tris(pentafluorophenyl)corrolatoiron(IV)chloride [(F 15TPC)FeCl] emerged as efficient catalyst in hydroxylating alkanes at room temperature. Cyclohexane and adamantane have been oxidized to the corresponding alcohols using m-chloroperbenzoic acid ( m-CPBA) as terminal oxidant. Cyclohexane has been converted to cyclohexanol in 50% yield with 100% selectivity. Adamantane has also been hydroxylated up to 75% overall yield under identical reaction condition. Significantly high regioselectivity in adamantane oxidation has been observed. The reactive intermediates have been quantitatively trapped by 2,4,6-tri- t-butylphenol (TTBP). Kinetic analysis of the (F 15TPC)FeCl-catalyzed oxidation of TTBP has found consistent with rapid reaction of organic substrate with an intermediate formed in the first and rate-determining step.

Adsorption of Cu 2+ on spherical Fe-MCM-41 and its application for oxidation of adamantane

Fe-MCM-41 with varying Si/Fe ratios (20, 50, 70 and 90) were prepared by using cetyltrimethylammoniumbromide (CTAB) as the structure-directing agent (SDA), tetraethylorthosilicate (TEOS) as the silica source and ethanol as co-surfactant in alkaline medium. The characterization was done by SEM; UV–vis diffused reflectance and FT-IR. Adsorption of copper solutions with varying parameters such as concentration, temperature and pH were performed over Fe-MCM-41 samples. The experimental data fitted well to the Langmuir and Freundlich adsorption isotherm. Fe-MCM-41 having Si/Fe ratio (90) showed highest copper adsorption capacity at pH 5.5, Cu 2+ concentration of 59.6 ppm and temperature 323 K. Fe-MCM-41(90)–Cu(59.6) was tested as a catalyst for oxidation of adamantane using hydrogen peroxide as the oxidant. The GC analyses revealed significant conversion of 32.5% and selectivity of 54% towards formation of 1-adamantanol.

Oxidation of alkane using Pt/Eu 2O 3/TiO 2/SiO 2 catalyst with O 2 and H 2 in acetic acid under mild conditions

A new solid catalyst of Pt/Eu 2O 3/TiO 2/SiO 2 for oxidation of alkane was developed. Oxidation of adamantane using the multi-components supported catalyst with O 2 and H 2 was studied in acetic acid at 313 K. Several multi-components supported catalysts were prepared and tested the oxidation activity. It is found that loading order of Eu 2O 3, TiO 2 and Pt on the SiO 2 support strongly affected the oxidation catalysis. The active catalysts model was proposed from TEM-EDS analysis that very small Pt particles well dispersed on amorphous Eu 2O 3 and TiO 2 on the SiO 2 support. Eu and Ti oxides concertedly activated O 2 with electrons supplied from H 2 on Pt, and active oxygen species efficiently oxidized adamantane and other alkanes to oxygenated compounds. Active oxygen species could not be identified but its reactivity was studied. It showed radical nature for oxidation of alkanes and a cleavage of C–H bond was the rate-determining step during the oxidation.

Reinvestigation of a Ru2-Incorporated Polyoxometalate Dioxygenase Precatalyst, “[WZnRu2III(H2O)(OH)(ZnW9O34)2]11−”: Evidence For Marginal, ≤0.2 Equivalents of Ru Incorporation Plus Faster Catalysis by Physical Mixtures of [RuII(DMSO)4Cl2] and the Parent Polyoxometalate [WZn3(H2O)2(ZnW9O34)2]12−

A 1997 Nature paper (Nature 1997, 388, 353-355) and subsequent 1998 J. Am. Chem. Soc. paper (J. Am. Chem. Soc. 1998, 120, 11969-11976) reported that a putative Ru(2)-substituted polyoxoanion, "[WZnRu(2)(III)(H(2)O)(OH)(ZnW(9)O(34))(2)](11-)", (1), is an all inorganic dioxygenase able to incorporate one O(2) into two adamantane CH bonds to yield 2 equiv of 1-adamantanol as the primary product. In a subsequent 2005 Inorg. Chem. publication (Inorg. Chem. 2005, 44, 4175-4188), strong evidence was provided that the putative dioxygenase chemistry is, instead, the result of classic autoxidation catalysis. That research raised the question of whether the reported Ru(2) precatalyst, 1, was pure or even if it contained two Ru atoms, since Ru is known to be difficult to substitute into polyoxoanion structures (Nomiya, K.; Torii, H.; Nomura, K.; Sato, Y. J. Chem. Soc. Dalton Trans. 2001, 1506-1521). After our research group had contact with three other groups who also had difficulties reproducing the reported synthesis and composition of 1, we decided to re-examine 1 in some detail. Herein we provide evidence that the claimed 1 actually appears to be the parent polyoxoanion [WZn(3)(H(2)O)(2)(ZnW(9)O(34))(2)](12-) with small amounts of Ru (</=0.2 atoms) either substituted into the parent complex or present as a small amount of a Ru(n+) impurity, at least in our and two other group's hands. The evidence obtained, on three independent samples prepared from two research groups including ours, includes elemental analysis on the bulk samples, single crystal X-ray diffraction, elemental analysis on single crystals from the same batch used for X-ray diffraction, (183)W NMR, and adamantane oxidation oxygen uptake and product determination studies. Also re-examined herein are the two previously reported crystal structures of 1 that appear to be very similar to the structure of the parent polyoxoanion, [WZn(3)(H(2)O)(2)(ZnW(9)O(34))(2)](12-). Furthermore, we report that trace Ru alone, in the form of [Ru(DMSO)(4)Cl(2)], or that the parent polyoxoanion [WZn(3)(H(2)O)(2)(ZnW(9)O(34))(2)](12-) alone, are capable of producing the same products. More significantly, a simple physical mixture of [WZn(3)(H(2)O)(2)(ZnW(9)O(34))(2)](12-) plus the average 0.13 equiv of Ru found by analysis added as the [Ru(DMSO)(4)Cl(2)] starting material is a ca. 2-fold kinetically more competent catalyst than is "[WZnRu(2)(III)(H(2)O)(OH)(ZnW(9)O(34))(2)](11-)", (1). In short, the evidence is strong that the putative "[WZnRu(2)(III)(H(2)O)(OH)(ZnW(9)O(34))(2)](11-)", (1), which underlies the previously reported all-inorganic dioxygenase catalysis claim, is probably not correct. That does not mean that 1 cannot or even does not exist, but just that (a) no reliable synthesis of it exists if it has actually been made before, and (b) that a simple mixture of the [Ru(DMSO)(4)Cl(2)] plus [WZn(3)(H(2)O)(2)(ZnW(9)O(34))(2)](12-) precursors gives about 2-fold faster catalysis of adamantane hydroxylation that occurs by, the evidence suggests, a radical-chain autoxidation mechanism rather than via the previously claimed, novel all-inorganic-based dioxygenase catalysis.

Chemoselective and biomimetic hydroxylation of hydrocarbons by non-heme μ-oxo-bridged diiron(iii) catalysts using m-CPBA as oxidant

Three novel non-heme micro-oxo-bridged diiron(III) complexes [Fe2(micro-O)(L1)2] 2, where H2(L1) is N,N'-o-phenylenebis(salicylideneimine), [Fe2(micro-O)(L2)2].2H2O 4, where H2(L2) is N,N'-o-phenylenebis(3,5-di-tert-butylsalicylideneimine), and [Fe2(micro-O)(L3)2] 6, where H2(L3)=1,4-bis(2-hydroxybenzyl)-1,4-diazepane, have been isolated and studied as catalysts for the selective oxidative transformation of alkanes into alcohols using m-choloroperbenzoic acid (m-CPBA) as co-oxidant. The mononuclear iron(III) complexes [Fe(L1)Cl] 1 and [Fe(L4)Cl] 7, where H2(L4)=1,4-bis(2-hydroxy-3,5-di-tert-butylbenzyl)-1,4-diazepane, have been also isolated and those corresponding to the dimeric complexes 4 and 6 have been generated in CH3CN solution and characterized as [Fe(L2)Cl] 3 and [Fe(L3)Cl] 5 by using ESI-MS, absorption and EPR spectral and electrochemical methods. The molecular structures of 4 and 6 have been successfully determined by single crystal X-ray diffraction. Both 4 and 6 possess the Fe-O-Fe structural motif with each iron atom possessing a distorted square pyramidal coordination geometry. The steric constraint at the iron(III) center in 6 is higher than that in 4 as understood from the values of the trigonality structural index (tau: 4, 0.226, 0.273; 6, 0.449) due to the higher steric congestion built by the diazapane back bone. The micro-oxo-to-Fe(III) LMCT band for 4 is observed around 622 nm (epsilon, 1830 M(-1) cm(-1)) in methanol but is not observed in CH3CN solution and it is blue-shifted to around 485 nm (epsilon, 5760 M(-1) cm(-1)) in 6, possibly due to the higher Fe-O-Fe bond angle in the latter (4, 177.4; 6, 180 degrees). The Fe(III)/Fe(II) redox potentials of the dinuclear complexes (E1/2: 2, -0.606; 4, -0.329; 6, -0.889 V) are more negative than those for their corresponding mononuclear complexes (E1/2: 1, -0.300 V; 3, -0.269; 5, -0.289 V) due to O2- coordination. Interestingly, upon addition of peroxides (H2O2, t-BuOOH) and the peracid m-CPBA, the intensity of the phenolate-to-Fe(III) LMCT band for 2 and 6 decreases but does not exhibit any appreciable change for 4. In the presence of m-CPBA cyclohexane is selectively (A/K, 12.2) oxidized by the dimeric complex to cyclohexanol (A, CyOH) and a small amount of the further oxidized product cyclohexanone (K, CyO). However, interestingly, the corresponding monomeric complex affords enhanced yields of both CyOH and CyO but with a lower selectivity (A/K=1.7) and also 1-chlorocyclohexane via oxidative ligand transfer (OLT). The oxidation of adamantane by 4 affords exclusively 1-adamantanol (50.5%) and 2-adamantanol (9.5%) with enhanced yields over 12 h. In contrast, 3 provides 1-adamantanol (32.4%) and 2-adamantanol (14.8%) and adamantanone (14.6%) in addition to 1-chloroadamantane (14.1%) as the OLT product. The secondary C-H bond of ethylbenzene is randomly activated by both 3 and 4 to give 1-phenylethanol and acetophenone. Also, oxidation of cumene with tertiary C-H bonds to give 2-phenyl-2-propanol and the further oxidized product acetophenone is illustrated by invoking the iron-phenoxyl radical species as invoked for metalloporphyrin-catalyzed systems. The strong chemoselectivity in C-H bond activation of alkanes by 4has been illustrated by invoking the involvement of a high-valent iron-oxo intermediate generated by using m-CPBA rather than the conventional oxidants H2O2 and t-BuOOH. In contrast to 4, the complexes 2 and 6 fail to effect the oxidation of hydrocarbons in the presence of H2O2, t-BuOOH and m-CPBA as the co-oxidant.

Highly Selective Production of 2-Adamantanone by Photocatalytic Oxidation of Adamantane

Abstract 2-Adamantanone was selectively produced by photocatalytic oxidation of adamantane in acetic acid using TiO2 powders. The reactions were carried out at ambient and acetic acid reflux temperatures with and without an oxidant. Adding oxidant in refluxing acetic acid under irradiation remarkably increased conversion and selectivity. Rutile TiO2 powders showed better conversion and selectivity in the presence of H2O2. The total conversion was 67% and the highest selectivity of 2-adamantanone was 89%.

Oxidation of adamantane with O 2 catalysed by VO(acac) 2 and reactivity of active species in acetic acid

The oxidation of adamantane (470 mM) catalysed by VO(acac) 2 (0.5 mM) with 1 atm O 2 in acetic acid at 393 K was studied. The major product was 1-adamantanol, and minor ones were 2-adamantanol and 2-adamantanone. The selectivity for 1-adamantanol (3°-selectivity) was almost constant at 75% under all oxidation conditions. The VO(acac) 2 catalyst functioned efficiently in the oxidation with a turnover number (TON) of 440 over 600 min. The oxidation rate of adamantane was enhanced by 5.5 times by the addition of CF 3SO 3H (2.2 mM) to acetic acid. Reactivities of various alkanes in the presence of VO(acac) 2 catalyst and product selectivities indicated the contribution of electrophilic active species in the oxidation. The rate-determining step was dissociation of the C–H bond of alkane by electrophilic active V species. The activity of the VO(acac) 2 catalyst is significantly different from the autoxidation promoter, Co(acac) 3. A reaction scheme for the oxidation is proposed on the basis of the reactivities and UV–vis and ESR spectroscopic studies.

High production of adamantane oxygenates in propionic acid using VO(acac) 2 and Eu(OTf) 3 with O 2

VO(acac) 2 with 1 atm O 2 catalysed the oxidation of adamantane to adamantanone, adamantanols and its esters in propionic acid at 353–393 K. Propionic acid was a more suitable solvent for the oxidation than acetic, butyric, valeric, or hexanoic acids. The maximum yield of oxygenates was 65% (3300 TON) in 360 min. Adamantane solubilities and chemical stabilities of carboxylic acid were important for the oxidation; however, the coordination of carboxylic anions with the vanadium catalyst strongly affected the oxidation activity. The oxidation rate of adamantane was enhanced 3.8 times by the addition of the Eu(OTf) 3 co-catalyst. The product selectivity for various oxidations of alkane and UV–vis spectroscopic studies of V species indicated that an active species was electrophilic vanadium peroxide species coordinated propionic anion and OTf.

Oxidation of adamantane catalysed by imidazolylporphyrinatoiron(III) complexes and structural studies of 5-coordinating iron(III) porphyrin

Oxidation of adamantane with phenylperacetic acid was carried out in the presence of three imidazolyltriarylporphyrinatoiron(III) complexes having pentafluorophenyl, phenyl, and mesityl (2,4,6-trimethylphenyl) groups as meso-substituents and three corresponding tetraarylporphyrinatoiron(III) complexes. The yield of 1- and 2-adamantanols was 76% in the case of chloro-5-(1-methyl-2-imidazolyl)-10,15,20-tri(pentafluorophenyl)porphyrinatoiron(III) (ImTPFPP–Fe(III)Cl), whereas the yield was only 26% in the case of chloro-5,10,15,20-tetra(pentafluorophenyl)porphyrinatoiron(III) in the presence of 100 eq. N-methylimidazole. The apparent effect of the appended imidazolyl group is discussed in terms of a 5-coordinated dimer of ImTPFPP–Fe(III)Cl, which was observed in the 1H and 19F NMR, and UV–vis spectra.

Oxyfunctionalisation of adamantane using inorganic–organic hybrid materials based on isopoly and heteropoly anions: Kinetics and mechanistic studies

Oxyfunctionalisation of adamantane with 30% aq.H2O2 in butyronitrile solvent was efficiently catalyzed by inorganic–organic hybrid materials synthesized by the immobilisation of isopoly (WOx = sodium tungstate, MoOx = sodium molybdate and VOx = sodium metavanadate) and heteropoly anions (V1 = H4[PMo11VO40]·32·5H2O,and V3 = H6[PMo9V3O40]·34H2O, STA = silicotungstic acid, TPA = tungstophosphoric acid and MPA = molybdophosphoric acid) onto mesoporous silica (SBA-15). These catalysts were well characterized by standard techniques and it was found that polyoxometalate has been retained all its bulk characteristics upon immobilisation onto mesoporous silica. Among the catalysts 10-molybdo-2-vanadophosphoric acid (H5[PMo10V2O40]·32·5H2O) immobilized onto amine-functionalized SBA-15 gave the highest activity under the conditions in the liquid phase oxidation of adamantane with 30% aq.H2O2 in butyronitrile solvent and gave mainly 1-adamantanol. Kinetic parameter measurements were performed by following initial rate approach for determining the rate dependence of the reaction. In situ UV-vis and electron paramagnetic resonance (EPR) spectroscopic studies carried out showed that the vanadium (V) superoxo intermediate species formed was responsible for the CH bond activation of adamantane to give 1-adamentanol. Based on this, a plausible mechanism for the oxidation of adamantane to 1-adamantanol has been proposed. The catalysts leaching studies carried out by following a standard procedure ruled out any contribution by the active vanadium species that could leach into the reaction medium and catalysts were truly functioned as heterogeneous catalysts.

Oxidation of adamantane with hypobromous acid generated in situ from CHnBr4−n and H2O in the presence of molybdenum complexes

Adamantan-1-ol (II) can be synthesized by catalytic oxidation of adamantane (I) with such oxidants as oxygen, hydrogen peroxide, alkyl hydroperoxides, and iodosylbenzene in the presence of Co, Mn, Fe, and Ru complexes [1–12]. Catalytic oxidation of adamantane (I) generally gives mixtures of products. For example, the oxidation of I with atmospheric oxygen in pyridine–acetic acid in presence of an iron catalyst and zinc at 40°C afforded a mixture of adamantan-1-ol and adamantan-2-ol whose ratio ranged, depending on the conditions, from 10 : 1 to 24.8 : 1, the overall yield being 6–16% [8].

Efficient Oxidation of Adamantanes by Sodium Nitrite with Molecular Oxygen in Trifluoroacetic Acid

Oxidation of adamantanes by oxygen was effectively achieved by use of sodium nitrite as a catalyst in trifluoroacetic acid (TFA) to give 1-adamantyl trifluoroacetates, from which adamantanols were obtained in good yields. A catalytic amount of sodium nitrite was essential and TFA was the best solvent among solvents examined for this oxidation.

Fast Catalytic Hydroxylation of Hydrocarbons with Ruthenium Porphyrins

Ruthenium porphyrin complexes such as carbonylruthenium(II) tetrakispentafluorophenylporphyrin [Ru(II)(TPFPP)(CO)] were found to be efficient catalysts for the hydroxylation of alkanes in the presence of 2,6-dichloropyridine N-oxide as the oxidant under mild, nonacidic conditions. Up to 14 800 turnovers (TO) and rates of 800 TO/min were obtained for the hydroxylation of adamantane. The hydroxylation of cis-decalin afforded cis-9-decalol and cis-decalin-9,10-diol, exclusively, thus, excluding a long-lived radicals mechanism. The kinetics of product evolution in a typical catalytic oxygenation showed an initial induction period followed by a fast, apparently zero-order phase with maximum rates and high efficiencies. Deuterium isotope effects (kH/kD) in the range of 4.2-6.4 were found for the hydroxylation of alkanes. A Hammett treatment of the data for the oxidation of para-substituted toluene derivatives showed a linear correlation with a highly negative rho+ value of -2.0. On the basis of kinetic and spectroscopic evidence, Ru(VI)(TPFPP)(O)2, Ru(II)(TPFPP)(CO), and Ru(IV)(TPFPP)Cl2 observed during catalysis were ruled out as candidates for the active catalyst responsible for the high efficiencies and turnover rates in the oxidation reactions. The fastest rates of adamantane hydroxylation with 2,6-dichloropyridine N-oxide were achieved by the reductive activation of Ru(IV)(TPFPP)Cl2 with a zinc amalgam. This redox activation is consistent with the formation of an active Ru(III) intermediate in situ by a one-electron reduction of the Ru(IV) porphyrin. EPR spectra characteristic of Ru(III) have been observed upon the reduction of Ru(IV)(TPFPP)Cl2 with a zinc amalgam. In the adamantane oxidation mediated with Ru(III)(TPFPP)(OEt), it was found that, during this process, the Ru(III) porphyrin was gradually converted to a dioxoRu(VI) porphyrin. Concomitant with this conversion, the reaction rates decreased. Catalyst activation was also stimulated by autoxidation of the solvent CH2Cl2. On the basis of these data, a mechanism is proposed that incorporates a "fast" cycle involving metastable Ru(III) and oxoRu(V) intermediates and a "slow" oxidation cycle, mediated by oxoRu(IV) and trans-dioxoRu(VI) porphyrin complexes.

Mono- and binuclear complexes of iron(ii) and iron(iii) with an N4O ligand: synthesis, structures and catalytic properties in alkane oxidation

Three mononuclear iron complexes and one binuclear iron complex, [Fe(tpoen)Cl].0.5(Fe2OCl6) (1), [Fe(tpoen)Cl]PF6 (2), Fe(tpoen)Cl3 (3) and [[Fe(tpoen)]2(mu-O)](ClO4)4 (4) (tpoen = N-(2-pyridylmethoxyethyl)-N,N-bis(2-pyridylmethyl)amine), were synthesized as functional models of non-heme iron oxygenases. Crystallographic studies revealed that the Fe(II) center of 1 is in a pseudooctahedral environment with a pentadentate N4O ligand and a chloride ion trans to the oxygen atom. The Fe(III) center of 3 is ligated by three nitrogen atoms of tpoen and three chloride ions in a facial configuration. Each Fe(III) center of 4 is coordinated with four nitrogen atoms and an oxygen atom of tpoen with the Fe-O-Fe angle of 172.0(3) angstroms. Complexes 2, 3 and 4 catalysed the oxidation of cyclohexane with H2O2 in the total TNs of 24-36 with A/K ratios of 1.9-2.4. Under the same conditions they also catalysed both the oxidation of ethylbenzene to benzylic alcohol and acetobenzene with good activity (30-47 TN) and low selectivity (A/K 0.7), and the oxidation of adamantane with moderate activity (15-18 TN) and low regioselectivity (3 degrees/2 degrees 3.0-3.2). With mCPBA as oxidant the catalytic activities of 2, 3 and 4 increased 1.8 to 2.3-fold for the oxidation of cyclohexane and ethylbenzene and 6.3 to 7.5-fold for the oxidation of adamantane. Drastic enhancement of the regioselectivity was observed in the oxidation of adamantane (3 degrees/2 degrees 18.5-30.3).

Development of Visible Light Sensitive TiO&lt;sub&gt;2&lt;/sub&gt; Photocatalysts and Their Sensitization Using Fe&lt;sup&gt;3+&lt;/sup&gt; Ions

Titanium dioxide photocatalysts are promising substrates for photodegradation of pollutants in water and air, but show photocatalytic activities only under UV light. To utilize a wider range of incident wavelengths such as solar light, development of photocatalysts active under visible light is very important. Chemically modified titanium dioxide photocatalysts were prepared containing anatase phase with S (S4+) substituted for some lattice Ti atoms or N substituted for some lattice O atoms. These catalysts showed strong absorption of visible light and high activities for degradation of 2-propanol in aqueous solution and partial oxidation of adamantane under irradiation at wavelengths longer than 440 nm. The oxidation states of the S and N atoms incorporated into the TiO2 particles were determined to be mainly S4+ and N3− from XPS spectra, respectively. The photocatalytic activities of S- or N-doped TiO2 photocatalysts with adsorbed Fe3+ ions were markedly improved for oxidation of 2-propanol compared to those of S- or N-doped TiO2 without Fe3+ ions under a wide range of incident wavelengths, including UV light and visible light. The photocatalytic activity reached maximum with 0.90 wt% Fe3+ ions adsorbed on S-doped TiO2, and 0.36 wt% Fe3+ ions on N-doped TiO2. Furthermore, redox treatment of S- or N-doped TiO2 photocatalysts with adsorbed Fe3+ ions by reduction with NaBH4 followed by air oxidation resulted in further improvements in photocatalytic activities. In this case, the optimum amounts of Fe3+ were 2.81 and 0.88 wt% on the surfaces of S- and N-doped TiO2 photocatalysts, respectively.

Oxidation of adamantane with 1 atm molecular oxygen by vanadium-substituted polyoxometalates

The oxidation of adamantane with molecular oxygen as a sole oxidant was efficiently promoted by catalyst precursors of vanadium-substituted Keggin-type phosphomolybdates such as H 4PVMo 11O 40, H 5PV 2Mo 10O 40, and H 6PV 3Mo 9O 40 in butyronitrile. The major product was a tertiary C H bond oxygenated product of 1-adamantanol, and secondary C H bond oxygenated products were also formed. The total yield of oxygenated products for the oxidation of adamantane in the presence of H 5PV 2Mo 10O 40 reached 84%. NMR and IR data show that the vanadium-substituted phosphomolybdates, such as H 4PVMo 11O 40 and H 5PV 2Mo 10O 40, decompose to form the monomeric vanadium species ( V V O 2 + (main) and V IVO 2+) and PMo 12 O 40 3 − Keggin anion. The reaction mechanism involving a radical species was proposed from ESR and kinetic data. The catalysts initially abstract the hydrogen of adamantane to form the adamantyl radical and reduced catalysts. This step would be promoted mainly by the vanadium species, such as V V O 2 + , and the phosphomolybdates, PMo 12 O 40 n − , enhance the activity. The adamantyl radical formed promotes the successive formation of the key intermediates, such as adamantyl radical and hydroperoxide species.

Synthesis, characterization, and catalytic oxygenation activity of dinuclear iron(III) complex supported by binaphthol-containing chiral ligand

Abstract A diiron(III) complex supported by a new dinucleating ligand containing a chiral binaphthol spacer has been synthesized and characterized by elemental analysis and spectroscopic methods (ESI-MS, CD, and UV–vis). The complex has a (μ-oxo)(μ-carboxylato) doubly bridged diiron(III) core, the structural motif of which resembles that of the active site of sMMO and related diiron enzymes. Catalytic oxidation of alkanes with m-CPBA proceeded very efficiently to give the corresponding alcohols as the major products together with ketones as minor products. The alcohol-selectivity (alcohol/ketone = 3.8–8.8) as well as the kinetic deuterium isotope effect (kH/kD = 3.0 for the oxidation of cyclohexane) and significantly high regioselectivity (tertiary carbon/secondary carbon = 17.1) in the oxidation of adamantane strongly suggested a reaction mechanism involving a highly reactive metal-based oxidant rather than an autooxidation mechanism involving free radical species.