Oxidation reactions catalysed by molybdenum(VI) complexes grafted on UiO‐66 metal–organic framework as an elegant nanoreactor

A heterogeneous catalyst was synthesized by immobilizing Mo(CO)₃ in a UiO‐66 metal–organic framework. The benzene ring of the organic linker in UiO‐66 was modified via liquid‐phase deposition of molybdenum hexacarbonyl, Mo(CO)₆, as starting precursor to form the (arene)Mo(CO)₃ species inside the framework. The structure of this catalyst was characterized using X‐ray diffraction, and chemical integrity was confirmed using Fourier transform infrared and diffuse reflectance UV–visible spectroscopic methods. The metal content was analysed with inductively coupled plasma. Field emission scanning electron microscopy was used to measure particle size and N₂ adsorption measurements to characterize the specific surface area. This catalytic system was efficiently applied for epoxidation of alkenes and oxidation of sulfides. The Mo‐containing metal–organic framework was reused several times without any appreciable loss of its efficiency.     

Covalent supporting of novel dioxo‐molybdenum tetradentate pyrrole‐imine complex on Fe3O4 as high‐efficiency nanocatalyst for selective epoxidation of olefins

A novel Mo(VI) tetradentate Schiff base complex based on two pyrrole‐imine donors was anchored covalently on Fe₃O₄ nanoparticles and characterized using physicochemical techniques. The catalytic epoxidation process was optimized in terms of the effects of solvent, reaction temperature, kind of oxidant and amount of oxidant and catalyst. Then the novel heterogeneous nanocatalyst was used for the efficient and selective catalytic epoxidation of internal alkenes (cyclohexene, cyclooctene, α‐pinene, indene and trans ‐1,2‐diphenylethene) and terminal alkenes (n ‐heptene, n ‐octene, n ‐dodecene and styrene) using tert ‐butyl hydroperoxide (70% in water) as oxidant in 1,2‐dichloroethane as solvent. The prepared nanocatalyst is very effective for the selective epoxidation of cis ‐cyclooctene with 100% conversion, 100% selectivity and turnover frequency of 1098 h⁻¹ in just 30 min. The magnetic nanocatalyst was easily recovered using an external magnetic field and was used subsequently at least six times without significant decrease in conversion.     

A green epoxidation system with poly(4‐vinylpyridine) microsphere‐supported molybdenum catalyst

The immobilization of molybdenum (Mo) compounds on poly(4‐vinylpyridine) (P4VP) microspheres for catalytic epoxidation was reported. P4VP‐supported Mo compounds were highly efficient and selective for the epoxidation of cis‐cyclooctene using hydrogen peroxide (H₂O₂) as oxygen source. When ethanol was used as solvents, outstanding catalytic activity and selectivity were observed for Mo‐containing catalysts in the epoxidation of cis‐cyclooctene. A completely green epoxidation system based on H₂O₂ and cleaner solvent has been achieved, and the heterogenized Mo catalyst can be recovered for five times without loss of its activity. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 558–562, 2010     

Molybdenum hexacarbonyl supported on functionalized multi-wall carbon nanotubes: Efficient and highly reusable catalysts for epoxidation of alkenes with tert-butyl hydroperoxide

In the present work, highly efficient epoxidation of alkenes catalyzed by Mo(CO)₆ supported on amines modified multi-wall carbon nanotubes, MWCNTs, is reported. The prepared catalysts were characterized by elemental analysis, scanning electron microscopy, FT-IR and diffuse reflectance UV-Vis spectroscopic methods. These new heterogenized catalysts, [Mo(CO)₆@amines-MWCNT], were used as highly efficient catalysts for epoxidation of alkenes with tert-BuOOH. These robust catalysts could be reused several times without loss of their catalytic activities.     

Multi-wall carbon nanotube supported tungsten hexacarbonyl: an efficient and reusable catalyst for epoxidation of alkenes with hydrogen peroxide

Highly efficient epoxidation of alkenes with H₂O₂ catalyzed by tungsten hexacarbonyl supported on multi-wall carbon nanotubes (MWCNTs) modified with 1,2-diaminobenzene is reported. The prepared catalyst, [W(CO)₆@DAB-MWCNT], was characterized by elemental analysis, scanning electron microscopy, FT-IR, and diffuse reflectance UV-Vis spectroscopic methods. The prepared catalyst was applied as an efficient catalyst for green epoxidation of alkenes with hydrogen peroxide in CH₃CN. This heterogeneous metal carbonyl catalyst showed high stability and reusability in epoxidation without loss of its catalytic activity.     

Mo (CO)6‐assisted Pd‐supported magnetic graphene oxide‐catalyzed carbonylation‐cyclization as an efficient way for the synthesis of 4(3H)‐quinazolinones

In this paper, a novel catalyst is introduced based on the immobilization of palladium on modified magnetic graphene oxide nanoparticles. The catalyst is characterized by several methods, including transmission electron microscopy, scanning electron microscopy, X‐ray fluorescence, vibrating‐sample magnetometer, Fourier transform‐infrared and dynamic light scattering (DLS) analysis. The activity of the catalyst was investigated in the synthesis of 4(3H)‐quinazolinones via Pd‐catalyzed carbonylation‐cyclization of N‐(2‐bromoaryl) benzimidamides by Mo (CO)₆. The Mo (CO)₆ is used as a carbon monoxide source for performing the reaction under mild conditions. The catalyst showed good reusability, and no change in activity was observed after 10 cycles of recovery.     

Highly efficient epoxidation of alkenes with hydrogen peroxide catalyzed by tungsten hexacarbonyl supported on multi-wall carbon nanotubes

The preparation, characterization, and catalytic activity of W(CO)₆ supported on multi-wall carbon nanotubes modified with 4-aminopyridine is reported. The catalyst, [W(CO)₅@Apy-MWCNT], was characterized by physico-chemical and spectroscopic methods and found to be an efficient heterogeneous catalyst for green epoxidation of alkenes with hydrogen peroxide in MeCN solvent. The catalyst showed good stability and reusability properties in the epoxidation reactions.     

Asymmetric Allylation of Ketones and Subsequent Tandem Reactions Catalyzed by a Novel Polymer‐Supported Titanium–BINOLate Complex

By using a novel, simple, and convenient synthetic route, enantiopure 6‐ethynyl‐BINOL (BINOL=1,1‐binaphthol) was synthesized and anchored to an azidomethylpolystyrene resin through a copper‐catalyzed alkyne–azide cycloaddition (CuAAC) reaction. The polystyrene (PS)‐supported BINOL ligand was converted into its diisopropoxytitanium derivative in situ and used as a heterogeneous catalyst in the asymmetric allylation of ketones. The catalyst showed good activity and excellent enantioselectivity, typically matching the results obtained in the corresponding homogeneous reaction. The allylation reaction mixture could be submitted to epoxidation by simple treatment with tert‐butyl hydroperoxide (TBHP), and the tandem asymmetric allylation epoxidation process led to a highly enantioenriched epoxy alcohol with two adjacent quaternary centers as a single diastereomer. A tandem asymmetric allylation/Pauson–Khand reaction was also performed, involving simple treatment of the allylation reaction mixture with Co₂(CO)₈/N‐methyl morpholine N‐oxide. This cascade process resulted in the formation of two diastereomeric tricyclic enones in high yields and enantioselectivities.     

Boehmite nano‐particles functionalized with silylpropylamine‐supported Keggin‐type heteropolyacids: Catalysts for epoxidation of alkenes

Boehmite nano‐particles with a high degree of surface hydroxyl groups were covalently functionalized by 3‐(trimethoxysilyl)‐propylamine to support H₃[PMo₁₂O₄₀], H₃[PW₁₂O₄₀], H₄[SiMo₁₂O₄₀] and H₄[SiW₁₂O₄₀] Keggin‐type heteropolyacids. After characterization of these catalysts by FT‐IR, powder X‐ray diffraction, TG/differential thermal analysis, CHN, inductively coupled plasma and transmission electron microscopy techniques, they were applied to the epoxidation of cis‐cycloocten. The progress of the reactions was investigated by gas–liquid chromatography, and the catalytic procedures were optimized for the parameters involved, such as the solvent and oxidant. The results showed that 25 mg of supported H₃[PMo₁₂O₄₀] catalyst in 1 ml C₂H₄Cl₂ with 0.5 mmol cyclooctene and 1 mmol tert‐butylhydroperoxide at reflux temperature gave 98% yield over 15 min. Recycling experiments revealed that these nanocatalysts could be repeatedly applied up to five times for a nearly complete epoxidation of cis‐cycloocten. The optimized experimental conditions were also used successfully for the epoxidation of some other alkenes, such as cyclohexene, styrene and α‐methyl styrene.     

Efficient Synthesis of Oxazolidin‐2‐one via (Chitosan‐Schiff Base)cobalt(II)‐Catalyzed Oxidative Carbonylation of 2‐Aminoalkan‐1‐ols

The (chitosan‐Schiff base)cobalt(II) complex was found to be an efficient catalyst for the oxidative carbonylation (CO/O₂) of 2‐aminoalkan‐1‐ols 1 to give oxazolidin‐2‐ones 2 , in the presence of NaI. The effects of promoters, temperature, solvents, and other reaction conditions were investigated in this study.     

Cobalt(II) acetylacetonate complex immobilized on aminosilane‐modified SBA‐15 as an efficient catalyst for epoxidation of trans‐stilbene with molecular oxygen

From environmental and economic points of view, it is highly desirable to develop a clean and efficient catalytic process to produce epoxides. An attractive approach is to use a solid, recyclable catalyst and molecular oxygen as the oxidant without any sacrificial reductant or other additives. Nonetheless, the catalysts reported up to now still cannot balance catalytic activity with epoxide selectivity. It is of great importance to explore novel catalysts with both high activity and selectivity for the epoxidation of olefins. In this work, cobalt(II) acetylacetonate (Co(acac)₂) was covalently bonded to the silica surface of SBA‐15 molecular sieve by multi‐step grafting using 3‐aminopropytrimethoxysilane (APTS) as coupling agent. Characterizations with nitrogen physisorption, X‐ray diffraction, transmission electron microscopy, Fourier transform infrared spectroscopy and thermogravimetric analysis suggested that the metal complex was successfully immobilized on the aminosilane‐modified SBA‐15 surface and the channel structure remained intact. The synthesized Co(acac)₂APTS@SBA‐15 catalyst was used in the epoxidation of trans‐stilbene (TS) with molecular oxygen. Compared to the sample prepared by the impregnation method as well as Co(acac)₂ solutions under the same reaction conditions, the Co(acac)₂ immobilized catalyst exhibited remarkably higher TS conversion and trans‐stilbene oxide (TSO) selectivity. An increase in TS conversion with Co content was observed when the Co loading was lower than 0.70% and the 0.70Co(acac)₂APTS@SBA‐15 sample exhibited the best catalytic performance. Up to 50.1% of TS conversion could be achieved within 6 h, affording TSO selectivity as high as 96.7%. The superior catalytic performance of this particular catalyst is attributed to the high activity of the immobilized Co(acac)₂ species on SBA‐15. Copyright © 2016 John Wiley & Sons, Ltd.     

Synergistic Interplay of a Non‐Heme Iron Catalyst and Amino Acid Coligands in H2O2 Activation for Asymmetric Epoxidation of α‐Alkyl‐Substituted Styrenes

Highly enantioselective epoxidation of α‐substituted styrenes with aqueous H₂O₂ is described by using a chiral iron complex as the catalyst and N‐protected amino acids (AAs) as coligands. The amino acids synergistically cooperate with the iron center in promoting an efficient activation of H₂O₂ to catalyze epoxidation of this challenging class of substrates with good yields and stereoselectivities (up to 97 % ee) in short reaction times.     

Well‐defined NHC?Pd complex‐mediated intermolecular direct annulations for synthesis of functionalized indoles (NHC = N‐hetero‐cyclic carbene)

As alternatives to the common tertiary phosphine/Pd systems, well‐defined N‐heterocyclic carbene–Pd complexes have been proven to be highly efficient precatalysts for intermolecular direct annalution of o‐haloanilines and ketones at lower catalyst loadings. A highly efficient and practical protocol for synthesis of functionalized indoles was developed using (IPr)Pd(acac)Cl as catalyst. Both o‐bromoanilines and o‐chloroanilines gave rise to efficient coupling under the reaction conditions. Related to acyclic ones, cyclic ketones coupled more effectively with o‐haloanilines. With [Pd(IPr)₂] as catalyst, the base‐sensitive groups including OH and CO₂H groups could be tolerated. Copyright © 2011 John Wiley & Sons, Ltd.     

Palladium‐Catalyzed Carbonylative [3+2+1] Annulation of N‐Aryl‐Pyridine‐2‐Amines with Internal Alkynes by CH Activation: Facile Synthesis of 2‐Quinolinones

We describe here a novel procedure for the synthesis of highly substituted 2‐quinolinones. By this newly developed approach, 2‐quinolinone derivatives were prepared in moderate to good yields by carbonylative cyclization of N‐aryl‐pyridine‐2‐amines and internal alkynes by C?H activation. Remarkably, [Mo(CO)₆] was applied as a solid CO source and the reaction proceeded in an atom economic manner.     

Reactions of Cyclohexyl Isocyanide with η5‐Substituted Cyclo‐pentadienyl MoMo Triply Bonded Complexes. Crystal Structure of [Mo(CO)2(η5‐C5H4CO2CH3)]2(μ‐η2‐CNC6H11)

Reactions of one or two equiv. of cyclohexyl isocyanide in THF at room temperature with Mo?Mo triply bonded complexes [Mo(CO)₂(η⁵‐C₅H₄R)]₂ (R=COCH₃, CO₂CH₃) gave the isocyanide coordinated Mo? Mo singly bonded complexes with functionally substituted cyclopentadienyl ligands, [Mo(CO)₂(η⁵‐C₅H₄R)]₂(μ‐η²‐CNC₆H₁₁) ( 1a , R=COCH₃; 1b , R=CO₂CH₃) and [Mo(CO)₂(η⁵‐C₅H₄R)(CNC₆H₁₁)]₂ ( 2a , R=COCH₃; 2b , R=CO₂CH₃), respectively. Complexes 1a , 1b and 2a , 2b could be more conveniently prepared by thermal decarbonylation of Mo? Mo singly bonded complexes [Mo(CO)₃(η⁵‐C₅H₄R)]₂ (R=COCH₃, CO₂CH₃) in toluene at reflux, followed by treatment of the resulting Mo?Mo triply bonded complexes [Mo(CO)₂(η⁵‐C₅H₄R)]₂ (R=COCH₃, CO₂CH₃) in situ with cyclohexyl isocyanide. While 1a , 1b and 2a , 2b were characterized by elemental analysis and spectroscopy, 1b was further characterized by X‐ray crystallography.     

Alternative Synthesis of 2‐Hydroxy‐3,5,5‐trimethylcyclopent‐2‐en‐1‐one

The 2‐hydroxy‐3,5,5‐trimethylcyclopent‐2‐en‐1‐one ( 1 ) was synthesized in 42% yield by rearrangement of epoxy ketone 10 on treatment with BF₃⋅Et₂O under anhydrous conditions. Intermediate 10 was available from the known enone 8 , either via direct epoxidation (60% H₂O₂, NaOH, MeOH; yield 50%), or via reduction to the corresponding allylic alcohol 14 (LiAlH₄, THF), followed by epoxidation ([VO(acac)₂], ^tBuOOH) and reoxidation under Swern conditions, in 37% total yield.     

Catalytic Asymmetric Epoxidation of α,β‐Unsaturated Esters with Chiral Yttrium–Biaryldiol Complexes

The full details of the asymmetric epoxidation of α,β‐unsaturated esters catalyzed by yttrium complexes with biaryldiol ligands are described. An yttrium–biphenyldiol catalyst, generated from Y(OiPr)₃–biphenyldiol ligand–triphenylarsine oxide (1:1:1), is suitable for the epoxidation of various α,β‐unsaturated esters. With this catalyst, β‐aryl α,β‐unsaturated esters gave high enantioselectivities and good yields (≤99 % ee). The reactivity of this catalyst is good, and the catalyst loading could be decreased to as little as 0.5–2 mol % (the turnover number was up to 116), while high enantiomeric excesses were maintained. For β‐alkyl α,β‐unsaturated esters, an yttrium–binol catalyst, generated from Y(OiPr)₃–binol ligand–triphenylphosphine oxide (1:1:2), gave the best enantioselectivities (≤97 % ee). The utility of the epoxidation reaction was demonstrated in an efficient synthesis of (?)‐ragaglitazar, a potential antidiabetes agent.     

Excellent alkene epoxidation catalytic activity of macrocyclic‐based complex of dioxo‐Mo(VI) on supermagnetic separable nanocatalyst

A phenoxybutane‐based Schiff base complex of cis‐dioxo‐Mo(VI) was supported on paramagnetic nanoparticles and characterized using powder X‐ray diffraction, infrared, diffuse reflectance and atomic absorption spectroscopies, scanning and transmission electron microscopies and vibrating sample magnetometry. The separable nanocatalyst was tested for the selective epoxidation of cyclohexene, cyclooctene, styrene, indene, α‐pinene, 1‐octene, 1‐heptene, 1‐dodecene and trans‐stilbene using tert‐butyl hydroperoxide (80% in di‐tert‐butyl peroxide–water, 3:2) as oxidant in chloroform. The catalyst was efficient for oxidation of cyclooctene with 100% selectivity for epoxidation with 98% conversion in 10 min. We were able to separate magnetically the nanocatalyst using an external magnetic field and used the catalyst at least six successive times without significant decrease in conversion. The turnover frequency of the catalyst was remarkable (2556 h^?1 for cyclooctene). The proposed nanomagnetic catalyst has advantages in terms of catalytic activity, selectivity, catalytic reaction time and reusability by easy separation.     

Highly Tunable Selectivity for Syngas‐Derived Alkenes over Zinc and Sodium‐Modulated Fe5C2 Catalyst

Zn‐ and Na‐modulated Fe catalysts were fabricated by a simple coprecipitation/washing method. Zn greatly changed the size of iron species, serving as the structural promoter, while the existence of Na on the surface of the Fe catalyst alters the electronic structure, making the catalyst very active for CO activation. Most importantly, the electronic structure of the catalyst surface suppresses the hydrogenation of double bonds and promotes desorption of products, which renders the catalyst unexpectedly reactive toward alkenes—especially C₅₊ alkenes (with more than 50% selectivity in hydrocarbons)—while lowering the selectivity for undesired products. This study enriches C₁ chemistry and the design of highly selective new catalysts for high‐value chemicals.     

Some Reactions of gem‐Dibromocyclopropanes and Metal Carbonyls

A series of gem‐dibromocyclopropanes were treated with various metal complexes. Among the metal complexes, Ru(CO)₂(PPh₃)₃, Ru(CO)₃(PPh₃)₂, and Mo(CO)₆ were able to remove a bromine atom from 1,1‐dibromo‐2‐phenylcyclopropanes ( 1 ) to yield a series of corresponding of 1‐bromo‐2‐phenylcyclopropanes ( 2 ). Upon the treatment of 1 with Cr(CO)₆ in DMSO, a series of allenes were obtained in good yields. The correlation between the rate of formation of allenes and the substituents on the benzene gives a negative coefficient which suggests the dibromocyclopropanes possesses as an electrophile toward to Cr(CO)₆. In the presence of Cr(CO)₆, gem‐dibromobicyclo[n,1,0]alkanes ( 4 ) in DMF or DMSO solution underwent the cleavage of carbon‐bromine bond followed by ring‐expansion and coupling reaction to form bicycloalkenes 7 .