Dedicated to Professor Dieter Enders on the occasion of his 60th birthdayEver-increasing environmental concerns has resulted in much attention being recently directed toward the development of new protocols for the aerobic oxidation of alcohols using transition-metal catalysts.[1] Among them, palladium-based catalysts show very interesting and promising catalytic activity, and different types of palladium-based homogeneous [2] and heterogenous [3] catalysts in the form of metal complexes or nanoparticles [4] have been developed for this purpose. Accordingly, the application of palladium-based catalysts has also been well documented for the asymmetric oxidation of alcohols.[5] Although, significant progress has been achieved in improving catalytic activity, selectivity, and substrate scope, there is still the major problem that palladium agglomeration and the formation of palladium black can cause catalyst deactivation in many cases. Recently, Tsuji and co-workers have shown that novel pyridine derivatives with 2,3,4,5-tetraphenylphenyl substituents and higher dendritic units at the 3-position significantly suppress the formation of palladium black and give the highest reported turnover numbers (TON) of 1480 in the homogeneous palladium-catalyzed oxidation of alcohols in air.[2o]Very recently, we explored a new silica-based palladium(II) interphase catalyst for the aerobic oxidation of alcohols. [3g] However, this method requires high catalyst concentrations (up to 5 mol %) and it suffers from the disadvantage of a significant reduction in its reactivity after three reaction cycles. Furthermore, this catalyst did not show good catalytic activity in the aerobic oxidation of allylic alcohols. Quite recently, the use of palladium nanoparticles dispersed in an organic polymer has also been demonstrated in the aerobic oxidation of alcohols. [4a,b] However, these heterogeneous Pd systems also suffer from high catalyst loading (typically substrate/catalyst ratios are ca. 20:1) and also the organic polymers used in these systems are potentially susceptible to oxidative degradation under aerobic oxidation conditions, thus restricting catalyst recovery over a long period. Moreover, it is well known that the small particle size as well as the high surface area of nanoparticles means they are very mobile and thermodynamically susceptible to agglomeration and the formation of larger inactive particles.[6] Ordered mesoporous structures (such as MCM-41 [7] and SBA-15 [8] ) with regular channel structures and pore diameters in the range of 2 to 30 nm, their easy separation from the reaction mixtures, and their relatively high surface area, would seem to be ideal for forming a scaffold in which three-dimensional dispersions of metal nanoparticles could be supported. Furthermore, because the majority of the nanoparticles are usually formed inside the channels of ordered porous materials, the support prevents agglomeration while providing the inherent advantages of a heterogeneous catalyst such as easy recovery and product se...

Among the very few efforts for preparation of stable mesoporous metal−organic frameworks (MOFs), there is no report of an additive-free example via a surfactant-assisted templating method. On the other hand, photocatalytic aerobic oxidation of alcohols mediated by crystalline TiO 2 has been known as a green route, which has the potential to replace current technology with transition-metal-containing heterogeneous systems. Here, a simple procedure for preparation of HKUST-1 containing ordered mesoporous domains has been developed using nonionic block copolymer in DMF as the solvent. All materials have been thoroughly characterized by FTIR, FESEM, HRTEM, XRPD, EDS, and TG analysis. Subsequently, it has been demonstrated that incorporation of amorphous TiO 2 within the prepared mesoporous MOF could successfully develope a new type of photocatalyst system for selective aerobic oxidation of benzylic alcohols with moderate to high yields in sunlight irradiation.

Preparation and characterization of a variety of immobilized palladium catalyst, based on either ligand functionalized amorphous or ordered mesoporous silica, is described. The resulting Pd-loaded materials act as efficient catalyst for the oxidation of a variety of alcohols using molecular oxygen and air. Our studies show that in the case of supported palladium catalyst on hybrid amorphous silica, the nature of ligand and the solvent could effectively control the generation of nanoparticles. Furthermore, we have found that nanoparticles with smaller size and higher activity were generated from the anchored palladium precursor when the aerobic oxidation of alcohols was carried out in a,a,a-trifluorotoluene (TFT) instead of toluene. On the other hand, in the case of aerobic oxidation reactions by using supported palladium catalyst on hybrid SBA-15, the combination of organic ligand and ordered mesoporous channels resulted in an interesting synergistic effect that led to enhanced activity, prevention of Pd nanoparticles agglomeration, and finally generation of a durable catalyst.

Two novel pillared metal-organic frameworks (MOFs) including urea-functional groups are introduced. Herein, urea functional groups were incorporated into the MOF backbone by preparing urea-ditopic ligand. These frameworks (TMU-18 and TMU-19) were fabricated using the synthesized urea-containing ligand, 4,4'-Bipyridine (bpy) and 1,2-Bis(4-pyridyl)ethane (bpe), respectively using zinc nitrate as metal source. Subsequently, TMU-18 and TMU-19 were characterized by X-ray diffraction, IR spectroscopy, elemental analysis, scanning electron microscopy (SEM) and thermogravimetric analysis. Furthermore, their potential talent as organocatalysts was evaluated in the regioselective methanolysis of epoxides. 4 (urea-based ligand) is 4,4'-(carbonylbis(azanediyl))dibenzoic acid, bipy and bpe are 4,4'bipyridine and 1,2-bis(4-pyridyl)ethane, respectively, Figure 1. Experimental Section Apparatus and ReagentsAll starting materials, including 1,1'-Carbonyldiimidazole, 4-Aminobenzoic acid were purchased from commercial suppliers (Sigma-Aldrich, Merck) and used as received. The infrared spectra were recorded on a Nicolet Fourier Transform IR, Nicolet 100 spectrometer in the range 500-4000 cm -1 using the KBr disk technique. Elemental analyses (carbon, hydrogen, and nitrogen) were performed using an ECS 4010 CHN made in Costech, Italy. Melting points were obtained by a Bamstead Electrothermal type 9200 melting point apparatus and corrected.Thermogravimetric analyses (TGA) of the compounds were performed on a computer-controlled PL-STA 1500 apparatus. The 1 H-NMR spectrum was recorded on a Bruker AC-250 MHz spectrometer at ambient temperature in d 6 -DMSO and CDCl 3 . X-ray powder diffraction (XRPD) measurements were performed using a Philips Xpert diffractometer with monochromated Cu-Kα radiation (λ = 1.54056 Å). The samples were also characterized by field emission scanning electron microscope (FE-SEM) SIGMA ZEISS and TESCAN MIRA (Czech) with gold coating. Single-Crystal Diffraction.X-ray crystal structure determinations: Crystals in viscous paraffin oil were mounted on cryoloops and intensity data were collected on the Australian Synchrotron MX1 beamline at 100 K with wavelength (λ = 0.71073 Å). The data were collected using the BlueIce 24 GUI and processed with the XDS 25 software package. The structures were solved by conventional methods and refined by full-matrix least-squares on all F 2 data using SHELX97 26 or SHELX2014

Dedicated to Professor Dieter Enders on the occasion of his 60th birthdayEver-increasing environmental concerns has resulted in much attention being recently directed toward the development of new protocols for the aerobic oxidation of alcohols using transition-metal catalysts.[1] Among them, palladium-based catalysts show very interesting and promising catalytic activity, and different types of palladium-based homogeneous [2] and heterogenous [3] catalysts in the form of metal complexes or nanoparticles [4] have been developed for this purpose. Accordingly, the application of palladium-based catalysts has also been well documented for the asymmetric oxidation of alcohols.[5] Although, significant progress has been achieved in improving catalytic activity, selectivity, and substrate scope, there is still the major problem that palladium agglomeration and the formation of palladium black can cause catalyst deactivation in many cases. Recently, Tsuji and co-workers have shown that novel pyridine derivatives with 2,3,4,5-tetraphenylphenyl substituents and higher dendritic units at the 3-position significantly suppress the formation of palladium black and give the highest reported turnover numbers (TON) of 1480 in the homogeneous palladium-catalyzed oxidation of alcohols in air.[2o]Very recently, we explored a new silica-based palladium(II) interphase catalyst for the aerobic oxidation of alcohols. [3g] However, this method requires high catalyst concentrations (up to 5 mol %) and it suffers from the disadvantage of a significant reduction in its reactivity after three reaction cycles. Furthermore, this catalyst did not show good catalytic activity in the aerobic oxidation of allylic alcohols. Quite recently, the use of palladium nanoparticles dispersed in an organic polymer has also been demonstrated in the aerobic oxidation of alcohols. [4a,b] However, these heterogeneous Pd systems also suffer from high catalyst loading (typically substrate/catalyst ratios are ca. 20:1) and also the organic polymers used in these systems are potentially susceptible to oxidative degradation under aerobic oxidation conditions, thus restricting catalyst recovery over a long period. Moreover, it is well known that the small particle size as well as the high surface area of nanoparticles means they are very mobile and thermodynamically susceptible to agglomeration and the formation of larger inactive particles.[6] Ordered mesoporous structures (such as MCM-41 [7] and SBA-15 [8] ) with regular channel structures and pore diameters in the range of 2 to 30 nm, their easy separation from the reaction mixtures, and their relatively high surface area, would seem to be ideal for forming a scaffold in which three-dimensional dispersions of metal nanoparticles could be supported. Furthermore, because the majority of the nanoparticles are usually formed inside the channels of ordered porous materials, the support prevents agglomeration while providing the inherent advantages of a heterogeneous catalyst such as easy recovery and product se...