The imidazolium group inside the wall of a periodic mesoporous organosilica provides an excellent environment for the stabilization of ultrasmall Pt nanoparticles (<1.5 nm), and this allowed the formation of a catalyst system (i.e., Pt^(NP)@PMO-IL) with significant activity and recyclability in the selective aerobic oxidation of various alcohols in water at ambient pressure of oxygen. In particular, the catalyst exhibited high activity in the oxidation of unactivated primary alcohols and sterically encumbered secondary aliphatic alcohols, which remain challenging substrates for many catalytic aerobic protocols.

New imidazolyl-functionalized ordered mesoporous cross-linked polymers were prepared by the copolymerization of the ionic liquid 3-benzyl-1-vinyl-1H-imidazolium bromide with divinylbenzene as the cross-linker and azobisisobutyronitrile as the radical initiator in the presence of O-silylated SBA-15 as the hard template. The materials were characterized by N₂ adsorption–desorption analysis, TEM, thermogravimetric analysis, elemental analysis, and FTIR spectroscopy. The material, which benefits from the use of entrapped ionic liquid in the prepared polymer matrix in combination with its ordered mesoporous structure, is an excellent environment for the stabilization of highly dispersed Pd nanoparticles to result in a recyclable catalyst system with a significant activity in the Heck coupling reaction of aryl halides. The presence of well-distributed imidazolium functionalities in the polymeric framework might be responsible for the relatively uniform and nearly atomic scale distribution of Pd nanoparticles throughout the mesoporous structure and the prevention of Pd agglomeration during the reaction, which results in high durability, high stability, and good recycling characteristics of the catalyst. Although our catalyst system operates in a homogeneous pathway, it is also very stable and recyclable.

Simple ion exchange of the chloride anion of an ionic-liquid-functionalized magnetic nanoparticle with [PdCl₄]²⁻ provided a highly water-dispersible and magnetically separable palladium catalyst that exhibited excellent activity toward transfer hydrogenation reactions in water as a solvent. The catalyst demonstrated outstanding performance in aqueous-phase transfer hydrogenation of various nitroarenes in a highly chemo- and regioselective manner by using HCOONH₄ as a low-cost, green, and easily available hydrogen donor. Also, by using only 0.25 mol % of the catalyst and formic acid as both a hydrogen donor and formylating agent, the catalyst showed excellent activity in the one-pot, direct synthesis of N-arylformamides from nitroarenes in water as a solvent. Notably, owing to the presence of a hydrophilic ionic liquid on the surface of silica-coated iron oxide nanoparticles, the catalyst showed highly stable dispersion in water, as evidenced by the zeta potential and extremely low affinity to the organic phase. These features make this catalyst system suitable for an efficient double-separation strategy (successive extraction/final magnetic separation). The recovered aqueous phase containing the catalyst can be simply and efficiently reused in eight runs without a decrease in activity and can be easily separated from the aqueous phase at the end of the process by applying an external magnetic field.

A catalyst based on immobilization of tungstate ions (WO₄²⁻) inside the mesochannels of periodic mesoporous organosilica comprising bridged ionic liquid (1,3-bis(3-trimethoxysilylpropyl)imidazolium chloride) has been synthesized and characterized. This catalyst was then employed for the selective oxidation of organic sulfides to the corresponding sulfoxides or sulfones. The final synthesized catalyst was characterized by various techniques such as nitrogen sorption analysis, transmission electron microscopy, and thermogravimetric analysis. The catalyst was also applied to the selective oxidation of sulfides containing readily oxidizable functional groups such as hydroxyl, allylic, and even challenging aliphatic sulfides. Interestingly, it was found that on changing the reaction medium from aqueous methanol to aqueous acetonitrile, the product selectivity was changed successfully from sulfoxide to sulfone with good to excellent yields. Moreover, the catalyst can also be recovered and reused efficiently in nine subsequent reaction cycles without any remarkable decrease in the catalyst activity and selectivity.

Magnetic nanoparticles have emerged recently as an alternative for the easy separation of nanosized catalysts from reaction mixtures by employing an external magnetic field. These magnetic nanoparticles have been used as supports for catalysts and/or as part of an active catalytic site. Herein, special attention is given to identify the main synthetic steps required to develop both precious- and nonprecious-metal-catalyzed CC and CX coupling reactions by using magnetically separable catalysts.

A main-chain N-heterocyclic carbene (NHC) polymer with N-dodecyl-substituted groups was found to be a highly efficient precatalyst for cyanation of various aryl halides by using nontoxic cyanic source [K₄Fe(CN)₆] under relatively mild reaction conditions. Several aryl iodides, bromides, and activated chlorides were successfully converted to their corresponding benzonitrile derivatives without using additives (such as reducing agents or exogenous organic ligands) in good to excellent yields. Our investigations showed that changing the solvent from DMF to polyethylene glycol (PEG-200) resulted in dramatic decline of cyanation product formation to the benefit of the Ullmann homocoupling reaction. The catalyst could be reused four and five times with only slight loss of activity in cyanation and the Ullmann coupling, respectively.

Yb(OTf)₃/iPr-pybox (3b) immobilized on a self-assembled organic–inorganic hybrid silica with ionic liquid phase (SAILP) (Catalyst A) behaves as an efficient and recyclable catalyst in the enantioselective Mannich reaction of malonate esters with N-Boc aldimines to afford the corresponding products in good yields and enantioselectivities. In particular, it has been shown that the use of catalyst A resulted in much superior enantioselectivities in comparison with either 1:2 Yb(OTf)₃/3b on a periodic mesoporous organosilica with 10 percent imidazolium framework (catalyst C) or a catalyst comprising 1:1 Yb(OTf)₃/3b on SAILP under the same reaction conditions. Catalyst A could be recycled and reused at least four times with only a slight decrease in either catalytic activity or enantioselectivity.

A highly selective aerobic oxidation of 5-hydroxymethylfurfural (5-HMF) into 2,5-diformylfuran (DFF) by employing a magnetically separable 2,2,6,6-tetramethylpiperidine-N-oxide (TEMPO) catalyst (Fe₃O₄@SiO₂–TEMPO) under metal- and halogen-free conditions is described. Quantitative yields of DFF with excellent selectivities as high as >99 % were achieved under several versatile reaction conditions in a catalytic system consisting of Fe₃O₄@SiO₂–TEMPO as a catalyst, tert-butyl nitrite as a co-catalyst, acetic acid as an additive, and toluene as a solvent. The results clearly demonstrate that the present catalytic system for selective conversion of 5-HMF into DFF is comparable or even superior to the many systems based on transition-metal catalysts. In addition, the catalyst can be successfully recovered and reused in five consecutive reaction runs by an external magnetic source with keeping its catalytic performance and selectivity.

The nitroxyl radical 3-oxo-9-azabicyclo [3.3.1]nonane-N-oxyl (3-oxo-ABNO) has been prepared using a simple protocol. This organocatalyst is found to be an efficient catalyst for the aerobic oxidation of a wide variety of alcohols under metal-free conditions. In addition, the preparation and characterization of a supported version of 3-oxo-ABNO on ordered mesoporous silica SBA-15 (SABNO) is described for the first time. The catalyst has been characterized using several techniques including simultaneous thermal analysis (STA), transmission electron microscopy (TEM), and nitrogen sorption analysis. This catalyst exhibits catalytic performance comparable to its homogeneous analogue and much superior catalytic activity in comparison with (2,2,6,6-tetramethylpiperidin-1-yl)oxy (TEMPO) for the aerobic oxidation of almost the same range of alcohols under identical reaction conditions. It is also found that SABNO can be conveniently recovered and reused at least 12 times without significant effect on its catalytic efficiency.

Palladium nanoparticles supported on nanofibrillated mesoporous carbon (Pd@IFMC) were found to be highly active in heterogeneous catalysis for the Ullmann homocoupling of a broad range of aryl chlorides, bromides and iodides in aqueous medium without the need to any chemical co-reducing agents. The catalysts could be recovered and reused several times without significant loss of activity.

The catalytic activities and selectivities of two kinds of mesoporous solid acids SBA-15-PrSO₃H 1, SBA-15-Ph-PrSO₃H 2, and a periodic mesoporous organosilica (PMO) based solid acid Et-PMO-Me-PrSO₃H 3 that comprise different physicochemical surface properties were compared in an environmentally benign one-pot, three-component Biginelli reaction of aldehydes, β-ketoesters and urea or thiourea under solvent-free conditions. Among these mesoporous solid acid catalysts, 3, which has a hydrophobic/hydrophobic balance in the nanospaces (mesochannels) in which the active sites are located, is found to be a significantly more selective catalytic system in the Biginelli reaction; it produces the corresponding 3,4-dihydropyrimidin-2-one\thione (DHPM) 5 derivatives in good to excellent yields and excellent selectivities. Notably, in the case of conducting the three-component coupling reaction of benzaldehyde, metylacetoacetate and urea in the presence of 1 result in the generation of a mixture of Hantzsch dihydropyridine 4 (≈37 %) and Biginelli dihydropyrimidinone 5 (≈49 %), whereas the same reaction with 2 (catalyst loading of 1 mol % as well) furnishes the corresponding aldolic product methyl-2-benzylidene-3-oxobutanoate 6 as the major product (≈80 %) with concomitant formation of small amounts of 5 (<10 %) under essentially the same reaction conditions that are employed with catalyst 3. Water adsorption–desorption analysis of the catalysts is employed to possibly relate the observed selectivity to the difference in physicochemical properties of the materials.

A novel domino oxidative Passerini three-component reaction (OP-3CR) has been successfully developed with either primary or secondary alcohols instead of their corresponding aldehydes or ketones by using a recyclable magnetic core-shell nanoparticle supported TEMPO (2,2,6,6-tetramethyl-piperidin-1-oxyl) (MNST, 1). It has been shown that MNST is a highly effective and recyclable catalyst system in the metal- and halogen-free aerobic, oxidative, three-component Passerini reaction. To the best of our knowledge this method can be considered as the first example of a OP-3CR of alcohols under metal- and halogen-free reaction conditions. It should be also noted that there has been no precedent example of oxidative OP-3CR of secondary alcohols to their corresponding α-acyloxy carboxamides. The catalyst can be magnetically recycled and successfully reused in 14 subsequent reaction cycles with only slight decreases of its catalytic activity.

Gold nanoparticles supported on the channels of a bifunctional periodic mesoporous organosilica, were found to be a highly efficient catalyst system for the aerobic oxidation of various types of alcohols into their corresponding aldehydes and ketones at room temperature. The catalyst showed no significant loss of efficiency for the aerobic oxidation of benzyl alcohol to give benzaldehyde after 7 reaction cycles.

The preparation and characterization of a set of periodic mesoporous organosilicas (PMOs) that contain different fractions of 1,3-bis(3-trimethoxysilylpropyl)imidazolium chloride (BTMSPI) groups uniformly distributed in the silica mesoporous framework is described. The mesoporous structure of the materials was characterized by powder X-ray diffraction, transmission electron microscopy, and N₂ adsorption–desorption analysis. The presence of propyl imidazolium groups in the silica framework of the materials was also characterized by solid-state NMR spectroscopy and diffuse-reflectance Fourier-transform infrared spectroscopy. The effect of the BTMSPI concentration in the initial solutions on the structural properties (including morphology) of the final materials was also examined. The total organic content of the PMOs was measured by elemental analysis, whereas their thermal stability was determined by thermogravimetric analysis. Among the described materials, it was found that PMO with 10 % imidazolium content is an effective host for the immobilization of perruthenate through an ion-exchange protocol. The resulting Ru@PI-10 was then employed as a recyclable catalyst in the highly efficient aerobic oxidation of various types of alcohols.

A novel nano-fibrillated mesoporous carbon (IFMC) was successfully prepared via carbonization of the ionic liquid 1-methyl-3-phenethyl-1H-imidazolium hydrogen sulfate (1) in the presence of SBA-15. The material was shown to be an efficient and unique support for the palladium nanoparticle (PdNP) catalyst Pd@IFMC (2) in aerobic oxidation of heterocyclic, benzylic, and heteroatom containing alcohols on pure water at temperatures as low as 40 °C for the first time and giving almost consistent activities and selectivities within more than six reaction runs. The catalyst has also been employed as an effective catalyst for the selective oxidation of aliphatic and allylic alcohols at 70–80 °C. The materials were characterized by X-ray photoelectron spectroscopy (XPS), N₂ adsorption–desorption analysis, transmission electron microscopy (TEM), and electron tomography (ET). Our compelling XPS and ET studies showed that higher activity of 2 compared to Pd@CMK-3 and Pd/C in the aerobic oxidation of alcohols on water might be due to the presence of nitrogen functionalities inside the carbon structure and also the fibrous nature of our materials. The presence of a nitrogen heteroatom in the carboneous framework might also be responsible for the relatively uniform and nearly atomic-scale distribution of PdNPs throughout the mesoporous structure and the inhibition of Pd agglomeration during the reaction, resulting in high durability, high stability, and recycling characteristics of 2. This effect was clearly confirmed by comparing the TEM images of the recovered 2 and Pd@CMK-3.

The preparation of a novel palladium-supported periodic mesoporous organosilica based on alkylimidazolium ionic liquid (Pd@PMO-IL) in which imidazoilium ionic liquid is uniformly distributed in the silica mesoporous framework is described. Both Pd@PMO-IL and the parent PMO-IL were characterized by N₂-adsorption–desorption, diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), TEM, and solid-state NMR spectroscopy. We have demonstrated that Pd@PMO-IL is an efficient and reusable catalyst for the Suzuki–Miyaura coupling reaction of various types of iodo-, bromo-, and even deactivated aryl chlorides in water. It was also found that although the PMO-IL nanostructure acts as reservoir for soluble Pd species, it can also operate as a nanoscaffold to recapture the Pd nanoparticles into the mesochannels thus preventing extensive agglomeration of Pd. This observation might be attributed to the isolated ionic liquid units that effectively control the reaction mechanism by preventing Pd agglomeration and releasing and recapturing Pd nanoparticles during the reaction process. The catalyst can be recovered and reused for at least four reaction cycles without significant loss of activity.