Direct Hydroxylation of Benzene with Hydrogen Peroxide Using Fe Complexes Encapsulated into Mesoporous Y-Type Zeolite

Mesoporous Y-type zeolite (MYZ) was prepared by an acid and base treatment of commercial Y-type zeolite (YZ). The mesopore volume of MYZ was six times higher than that of YZ. [Fe(terpy)₂]²⁺ complexes encapsulated into MYZ and YZ with different Fe contents (Fe(X)L-MYZ and Fe(X)L-YZ; X is the amount of Fe) were prepared and characterized. The oxidation of benzene with H₂O₂ using Fe(X)L-MYZ and Fe(X)L-YZ catalysts was carried out; phenol was selectively produced with all Fe-containing zeolite catalysts. As a result, the oxidation activity of benzene increased with increasing iron complex content in the Fe(X)L-MYZ and Fe(X)L-YZ catalysts. The oxidation activity of benzene using Fe(X)L-MYZ catalyst was higher than that using Fe(X)L-YZ. Furthermore, adding mesopores increased the catalytic activity of the iron complex as the iron complex content increased.     

Structures and thermochemistry of ions formed by methane chemical ionization of Fe(CO)5. Site of protonation and determination of Fe?H and Fe?CO bond dissociation energies of HFe(CO)n+ ions

High-energy collisional activation mass spectrometry of HFe(CO)₅⁺ ions shows that Fe(CO)₅ is protonated on the iron atom rather than on one of the ligands. This finding is supported by ab initio quantum chemical calculations. The value of the proton affinity of Fe(CO)₅ was measured by high-pressure mass spectrometry to be 857 kJ mol^?1. The Fe? CO bond dissociation energies for HFe(CO)_n⁺ (n = 1–5) were measured by energy-variable low-energy collisional activation mass spectrometry. The Fe? H bond dissociation energies in HFe(CO)_n⁺ ions were also determined. A synergistic effect on the strengths of the Fe? H and Fe? CO bonds in HFe(CO)⁺ is noticed. It is demonstrated that the electronically unsaturated species HFe(CO)_n⁺ (n = 3, 4) formed in exothermic proton-transfer reactions with Fe(CO)₅ form adducts with CH₄. Adducts between C₂H₅⁺ or C₃H₅⁺ and Fe(CO)_n are observed. These adducts are probably formed in direct reactions between the respective carbocations and Fe(CO)₅.     

含骨架铁ZSM-5的合成及其负载Pt催化剂在正十二烷脱氢反应中的催化性能

采用水热合成法使铁进入分子筛MFI骨架结构,成功合成出含骨架铁的分子筛Na-[Fe]-ZSM-5,并通过离子交换法负载Pt制备脱氢催化剂Pt/Na-[Fe]-ZSM-5。通过正十二烷脱氢反应,研究了该催化剂对长链烷烃脱氢制单烯烃反应的催化性能。采用N2吸附-脱附测试、X射线衍射(XRD)、傅立叶变换红外光谱(FT-IR)、氨气程序升温脱附(NH3-TPD)、吡啶吸附的红外光谱(Py-IR)、CO化学吸附、透射电子显微镜(TEM)等不同方法对催化剂进行了表征。结果表明,通过控制骨架铁含量可调控催化剂表面酸性;含骨架铁的ZSM-5分子筛载体具有抑制负载金属晶粒长大,保持金属高分散度的作用;其负载铂催化剂Pt/Na-[Fe]ZSM-5-50具有表面弱酸中心(0.69 mmol·g^-1)和高分散Pt中心,因而具有良好的长链烷烃脱氢活性、稳定性和单烯烃选择;在转化率稳定在~20%时,TOF为4.56 s^-1,单烯烃选择性为92.7%;在实验范围内,Pt/Na-[Fe]ZSM-5催化剂表面弱酸量和脱氢反应的本征活性(TOF)均随催化剂铁含量的增加而增加。     

Mono-Substitution of iron pentacarbonyl catalyzed by polynuclear iron carbonyl anions

The specific formation of LFe(CO)₄ (L = PPh₃, P(OPh)₃, P(OMe)₃ can be achieved by the reaction of Fe(CO)₅ with L in the presence of a catalytic amount of iron carbonyl anion. A convenient synthetic procedure was developed in which the iron carbonyl anion catalyst is generated in situ. It is shown that the mechanism does not proceed by the simple cleavage of the Fe₂(CO)₈^2? or Fe₃(CO)₁₁^2? anions, because triphenylphosphine reacts with these anions in the absence of Fe(CO)₅ to produce (PPh₃)₂Fe(CO)₃.     

Synthesis of a transition metal-dithionite complex, (η5-C5H5)(CO)2FeS(O)2S(O)2Fe(CO)2(η5-C5H5)

The reaction of Na[η⁵-C₅H₅Fe(CO)₂] with large excess of SO₂ in THF at ?78°C followed by warming to room temperature affords an iron—dithionite complex, (η⁵-C₅H₅)(CO)₂FeS(O)₂S(O)₂Fe(CO)₂(η⁵-C₅H₅).     

Organometalloidal derivatives of the transition metals: XI. Synthesis and crystal structures of Ph3GeSiMe3 and Ph3GeSiMe2Fe(CO)2(η5-C5H5)

Ph₃GeSiMe₃ and Ph₃GeSiMe₂Fe(CO)₂(η⁵-C₅H₅) have been synthesized and their crystal structures determined. The GeSi bond in iron (2.405(2) Å) is longer by 0.021 Å than in the simple germylsilane (2.384(1) Å). The significant shortening of the SiFe bond (2.328(1) Å) in the iron complex compared to that in the analogous Ph₃SiSiMe₂Fe(CO)₂(η⁵-C₅H₅) (2.346(1) Å) and spectroscopic data indicate an enhanced SiFe interaction.     

A trimethylsilyl group migration in the chemistry of η5-C5H5Fe(CO)2SiMe3

Reaction of η⁵-C₅H₅Fe(CO)₂SiMe₃ with either n-BuLi or lithium diisopropylamide (LDA) results in a migration of the trimethylsilyl group from iron to the complexed Cp ligand. The resulting η⁵-C₅H₄SiMe₃Fe(CO)₂ anion is readily alkylated to give σ-bonded derivatives. The unique reactivity of the trimethylsilyl systems is underscored by comparison with the behavior of η⁵-C₅H₅Fe(CO)₂Me under identical conditions. Some chemical transformations of η⁵-C₅H₄SiMe₃Fe(CO)₂R derivatives involving migratory insertion and β-hydride abstraction are also reported.     

Alkynethiolate ligands in the syntheses of iron carbonyl derivatives. Crystal structure of [(η-C5H5)Fe(CO)2(SCCSiMe3)]

The complexes [(η⁵-C₅H₅)Fe(CO)₂(SCCR)] (R=^tBu, SiMe₃) have been obtained by reaction of [(η⁵-C₅H₅)Fe(CO)₂I] and the corresponding LiSCCR. These are the first examples of mononuclear iron compounds containing alkynethiolate ligands. The crystal structure of [(η⁵-C₅H₅)Fe(CO)₂(SCCSiMe₃)] has been determined by X-ray diffraction. The role of [(η⁵-C₅H₅)Fe(CO)₂(SCCSiMe₃)] as a metalloligand in its reactions with metal carbonyls has been explored.     

Synthesis and Reactivity of Mononuclear Iron Models of [Fe]‐Hydrogenase that Contain an Acylmethylpyridinol Ligand

[Fe]‐hydrogenase has a single iron‐containing active site that features an acylmethylpyridinol ligand. This unique ligand environment had yet to be reproduced in synthetic models; however the synthesis and reactivity of a new class of small molecule mimics of [Fe]‐hydrogenase in which a mono‐iron center is ligated by an acylmethylpyridinol ligand has now been achieved. Key to the preparation of these model compounds is the successful C?O cleavage of an alkyl ether moiety to form the desired pyridinol ligand. Reaction of solvated complex [(2‐CH₂CO‐6‐HOC₅H₃N)Fe(CO)₂(CH₃CN)₂]⁺(BF₄)^? with thiols or thiophenols in the presence of NEt₃ yielded 5‐coordinate iron thiolate complexes. Further derivation produced complexes [(2‐CH₂CO‐6‐HOC₅H₃N)Fe(CO)₂(SCH₂CH₂OH)] and [(2‐CH₂CO‐6‐HOC₅H₃N)Fe(CO)₂(CH₃COO)], which can be regarded as models of FeGP cofactors of [Fe]‐hydrogenase extracted by 2‐mercaptoethanol and acetic acid, respectively. When the derivative complexes were treated with HBF₄?Et₂O, the solvated complex was regenerated by protonation of the thiolate ligands. The reactivity of several models with CO, isocyanide, cyanide, and H₂ was also investigated.     

Active Sites in Fe/ZSM-5 Zeolite

Fe/ZSM-5 zeolite has shown great potential in the selective oxidations of hydrocarbons such as methane and benzene. The various competing active sites of Fe/ZSM-5 zeolite are reviewed, including the mono-iron, oxygen-bridged [Fe, X] (X = Fe, Al) and peroxide species; in addition, the influences of H₂ pretreatment are considered. For the mono-iron species, the H₂ molecules are chemisorbed on the Fe(III) sites via the η²-binding mode. Both high- and low-spin Fe(III) ions play an important role during the H₂ reduction process whereas the former predominates in the N₂O decomposition process. As the calculated energy barriers indicate, the Fe(III) ions are facile to be reduced by H₂ pretreatment and therefore the active site of the mono-iron species should be in the FeO(OH) form. Instead, the oxygen-bridged [Fe, X] and peroxide species remain stable by H₂ pretreatment. The suitable oxygen-bridged [Fe, X] structures are screened out by comparisons with the experimental data and energy considerations from computational aspects. The geometries are in good agreement with the experimental data; meanwhile, it provides sound explanations to the distribution of the iron valence states, the thermodynamic facilitation of the “alfa-oxygen” generation by the introduction of extra-lattice Al ions as well as the shift of the Fe–Fe distances from ca. 3.06 to 2.53 Å. The superoxide species exists in Fe/ZSM-5 zeolite but not with the presence of extra-lattice Al ions. As the temperature increases, it gradually converts into the peroxide species and probably is the precursor of the peroxide species, one of the competing active sites in Fe/ZSM-5 zeolite. The clarification of active sites lays a solid foundation on the understanding of the catalytic processes and improvement of the Fe/ZSM-5 catalyst, one of the promising candidates to meet the industry challenges.     

Mechanism of the thermal decomposition of (η5-C5H5)Fe(CO)2(η1-acenaphthenyl)

The complexes (η⁵-C₅H₅)Fe(CO)₂(η¹-acenaphthenyl) (I), (η⁵-C₅H₅)Fe(CO)₂ (η¹-trans-β-deuterioacenaphthenyl) (II), and (η-C₅D₅)Fe(CO)₂, (η¹-acenaphthenyl) (XIII) have been prepared and their thermal decomposition studied in vacuo and in refluxing toluene. All three complexes decompose to produce mixtures of acenaphthene (VII), acenaphthylene (VIII), and [C₅H₅Fe(CO)₂]₂ (VI). Biacenaphthenyl (IX) is also obtained from the thermolysis of I in toluene. The formation of alkene VIII, and, to a lesser extent, alkane VII is suppressed by external CO. Thermolysis of I in toluene-d₈ and of II in vacuo and in toluene produces deuterium-enriched VII. The acenaphthene generated from the decomposition of XIII also contains deuterium. The above observations are accomodated by a mechanistic scheme involving competing β-elimination, ironcarbon bond homolysis to produce the acenaphthenyl radical, and CpH abstraction by an undetermined pathway.     

Assignment of Nonclassical [Cu(CO)(n)](+) (n = 1, 2) Complex Ions in Zeolite Cages

A time-resolved FT-IR technique combined with an isotopic tracer method has been applied to study CO adsorbates on Cu(+) ions in copper ion-exchanged zeolites. Three kinds of monocarbonyl species were found to adsorb strongly on Cu-zeolite samples after admission and subsequent evacuation of gas phase CO at room temperature. Their absorption bands were observed at 2146-2160, 2128-2150, and 2097-2129 cm(-1), respectively, dependent on the zeolite structures. In the presence of gaseous CO, the monocarbonyl species at 2146-2160 cm(-1) (so called nonclassical [Cu(CO)](+) complexes) could react with a CO molecule to form a dicarbonyl species [Cu(CO)(2)](+) with nu(sym) bands at 2169-2180 cm(-1). The reactivity of the nonclassical [Cu(CO)](+) complexes was dependent on the zeolite structures, ferrierite > mordenite > ZSM-5 > X-type left harpoon ovet right harpoon offretite/erionite left harpoon ovet right harpoon Y-type > L-type. The remaining two types of monocarbonyl species have little been affected by gas phase CO.     

Rearrangement of a P4 Butterfly Complex—The Formation of a Homoleptic Phosphorus–Iron Sandwich Complex

The versatile coordination behavior of the P₄ butterfly complex [{Cp′′′Fe(CO)₂}₂(μ,η^1:1-P₄)] ( 1 , Cp′′′=η⁵-C₅H₂^tBu₃) towards different iron(II) compounds is presented. The reaction of 1 with [FeBr₂⋅dme] (dme=dimethoxyethane) leads to the chelate complex [{Cp′′′Fe(CO)₂}₂(μ₃,η^1:1:2-P₄){FeBr₂}] ( 2 ), whereas, in the reaction with [Fe(CH₃CN)₆][PF₆]₂, an unprecedented rearrangement of the P₄ butterfly structural motif leads to the cyclo-P₄ moiety in {(Cp′′′Fe(CO)₂)₂(μ₃,η^1:1:4-P₄)}₂Fe][PF₆]₂ ( 3 ). Complex 3 represents the first fully characterized “carbon-free” sandwich complex containing cyclo-P₄R₂ ligands in a homoleptic-like iron–phosphorus-containing molecule. Alternatively, 2 can be transformed into 3 by halogen abstraction and subsequent coordination of 1 . The additional isolated side products, [{Cp′′′Fe(CO)₂}₂(μ₃,η^1:1:2-P₄){Cp′′′Fe(CO)}][PF₆] ( 4 ) and [{Cp′′′Fe(CO)₂}₂(μ₃,η^1:1:4-P₄){Cp′′′Fe}][PF₆] ( 5 ), give insight into the stepwise activation of the P₄ butterfly moiety in 1 .     

Kinetic determination of the metalmetal bond dissociation energy in bis(dicarbonyl η5-cyclopentadienyliron)

The ironiron bond energy in [C₅H₅Fe(CO)₂]₂ (I) has been determined by measuring the rate of disproportionation of the monoacetyl complex (AcC₅H₄)(C₅H₅)Fe₂(CO)₄ (II) to I and [AcC₅H₄Fe(CO)₂]₂ (III). The reaction follows first order kinetics in benzene solution in the temperature range of 60–100°C with activation parameters calculated as: ΔH^≠ = 26.9 ± 2.7 kcal mol^?1 and ▽s^≠ = 2.0 ± 3.2 cal mol^?1 deg^?1.     

Self‐Assembly Film of Zeolite Y Nanocrystals Loading Palladium on an Au Electrode for Electrochemical Applications

Nano‐scale zeolite Y crystals were synthesized, and palladium nanoparticles were prepared in the supercage of the zeolite by “ship‐in‐a‐bottle” approach. A novel method to fabricate zeolite‐modified electrode (ZME) loading Pd nanoparticles was developed, in which the zeolite Y loading Pd²⁺ ions was self‐assembled on (3‐mercaptopropyl) trimethoxysilane‐attached Au surface to form the stable and density packed multilayers (SAM‐ZME). The structures of zeolite Y and the SAM‐ZME were investigated by using TEM, XRD and SEM techniques. Pd²⁺ ions in the SAM‐ZME were converted into Pd nanoparticles (Pd_n⁰) by two steps consisting of the electrochemical reduction as well as the succeeding admission and release of CO. The redox couple [Fe(CN)₆]^3?/4? was used to probe the electron‐transfer barrier properties during self‐assembling process. Moreover, the special properties of the SAM‐ZME loading Pd_n⁰ were studied by using cyclic voltammetry and CO‐probe in situ FTIR spectroscopy. The results illustrated that Pd_n⁰ in the SAM‐ZME exhibits higher electrocatalytic activity for oxidation of adsorbed CO than that of ZME prepared in our previous study by zeolite coating method. The present study is of importance in design and preparation of SAM‐ZME, which poccesseses excellent properties for the immobilization of electrocatalysts or biomolecules.     

Structure and Reactivity of Iron(0)-Phenyltellurolate [PPN][PhTeFe(CO)4]

Anionic iron(0) tetracarbonyl with terminal phenyltellurolate ligand PhTe^?, [PhTeFe(CO)₄]^?, has been synthesized and characterized. The title compound was obtained by addition of (PhTe)₂ to [PPN][HFe(CO)₄] THF solution dropwise. [PPN][PhTeFe(CO)₄] crystallizes in the monoclinic space group C c, with a = 16.119(4) Å, b = 13.141(3) Å, c = 19.880(8) Å, β = 93.04(3)°, V = 4205(2) ų, and Z = 4. The [PhTeFe(CO)₄]^? anion is a trigonal-bipyramidal complex in which the phenyltellurolate ligand occupies an axial position with Fe-Te bond length 2.630(5) Å and the Fe-Te-C(Ph) angle is 103.4(5)°. The neutral iron(0)-telluroether compound, (PhTeMe)Fe(CO)₄, was prepared by alkylation of the [PhTeFe(CO)₄]^?. Protonation of [PhTeFe(CO)₄]^?and reaction of H₂Fe(CO)₄ and PhTe)₂ ultimately lead to formation of the known dimer Fe₂(μ-TePh)₂(CO)₆ and H₂.     

Synthesis of Isotope Enriched (CN3H6)2[57Fe(CN)5NO] starting from 57Fe

A high‐yield, mmolar‐scale synthesis of pure guanidinium nitroprusside, (CN₃H₆)₂[⁽⁵⁷⁾Fe(CN)₅NO] (GNP) from iron metal is described. The iron metal contained pieces of 95.3% ⁵⁷Fe together with normal iron so that an isotope enrichment in ⁵⁷Fe of 25% was achieved. Single‐crystals of GNP could be grown in cubic shape and dimensions of about 3 × 4 × 4 mm³. The purity of the GNP product and the intermediates K₄[⁽⁵⁷⁾Fe(CN)₆] · 3 H₂O and Na₂[⁽⁵⁷⁾Fe(CN)₅NO] · 2 H₂O was ascertained by ⁵⁷Fe Mössbauer spectroscopy as well as ¹³C, ¹⁴N and ⁵⁷Fe NMR spectroscopy. The ⁵⁷Fe NMR chemical shift for [⁽⁵⁷⁾Fe(CN)₅NO]^2– in GNP was detected at +2004.0 ppm [vs Fe(CO)₅].     

Stoichiometric vs Catalytic MeLi Reaction with the Mixture of (ẽ5‐C5H5)Fe(CO)2l and P(OR)3: Nucleophilic Methylation vs Arbuzov‐Like Dealkylation

The reaction of stoichiometric MeLi with the 1:1 mixture of (?⁵‐C₅H₅)Fe(CO)₂I/P(OR)₃ (R = Me, Et, and Ph) at ?78°C changes the bonding mode between metal and ring from (?⁵‐C₅H₅) to (?⁴‐exo‐MeC₅H₅) and the oxidation state of metal from Fe(II) to Fe(O), the novel complexes (?⁴‐exo‐MeC₅H₅)Fe(CO)₂P(C)R)₃ being obtained in 45‐57% yields. The reaction of trace MeLi with the 1:1 mixture of (?⁵‐C₅H₅)Fe(CO)₂I/P(OMe)₃ at ?78°C results in 70% yield of the phosphonate complex (?⁵‐C₅H₅)Fe(CO)₂P(O)(OMe)₂ which is an Arbuzov‐like dealkylation product from the cationic intermediate [(?⁵‐C₅H₅)Fe(CO)₂P(OMe)₃⁺] and the iodide. The amines could assist the Arbuzov‐like dealkylation of [(?⁵‐C₅H₅)Fe(CO)₂P(OMe)₃⁺] [PF₆^?] where iron‐carbamoyl intermediates are likely involved in the case of primary amines.     

Photochemistry of iron pentacarbonyl adsorbed on titanium dioxide

The photolysis of iron carbonyl (Fe(CO)₅) adsorbed on titanium dioxide (TiO₂, anatase) was studied by FT-IR spectroscopy. When adsorbed Fe(CO)₅ is illuminated by visible and near-UV light, the IR spectrum of its photolysis products is hardly observed, indicating that most of the Fe(CO)₅ is photodecomposed to iron(0) or iron oxides on TiO₂. The carbon monoxide (CO) evolution rate upon illumination depends on the wavelength of light; 433 nm light is more effective for CO evolution than 366 nm light. This result implies that the band-gap excitation of TiO₂ has little effect on the photolysis of adsorbed Fe(CO)₅, since the absorption edge of TiO₂ (anatase) lies at around 400 nm. The effects of substrates on the photolysis of adsorbed Fe(CO)₅ are discussed with reference to previous results obtained for aluminium oxide (Al₂O₃) and silicon dioxide (SiO₂), on which the photolysis leads to the formation of Fe₂(CO)₉ or Fe₃(CO)₁₂.