Ruthenium Nanoparticles Immobilized on Nano-silica Functionalized with Thiol-Based Dendrimer: A Nanocomposite Material for Oxidation of Alcohols and Epoxidation of Alkenes

Functionalized Silicas for Metal-Free and Metal-Based Catalytic Applications: A Review in Perspective of Green Chemistry

Heterogeneous catalysis plays a key role in promoting green chemistry through many routes. The functionalizable reactive silanols highlight silica as a beguiling support for the preparation of heterogeneous catalysts. Metal active sites anchored on functionalized silica (FS) usually demonstrate the better dispersion and stability due to their firm chemical interaction with FSs. Having certain functional groups in structure, FSs can act as the useful catalysts for few organic reactions even without the need of metal active sites which are termed as the covetous reusable organocatalysts. Magnetic FSs have laid the platform where the effortless recovery of catalysts is realized just using an external magnet, resulting in the simplified reaction procedure. Using FSs of multiple functional groups, we can envisage the shortened reaction pathway and, reduced chemical uses and chemical wastes. Unstable bio-molecules like enzymes have been stabilized when they get chemically anchored on FSs. The resultant solid bio-catalysts exhibited very good reusability in many catalytic reactions. Getting provoked from the green chemistry aspects and benefits of FS-based catalysts, we confer the recent literature and progress focusing on the significance of FSs in heterogeneous catalysis. This review covers the preparative methods, types and catalytic applications of FSs. A special emphasis is given to the metal-free FS catalysts, multiple FS-based catalysts and magnetic FSs. Through this review, we presume that the contribution of FSs to green chemistry can be well understood. The future perspective of FSs and the improvements still required for implementing FS-based catalysts in practical applications have been narrated at the end of this review.

Synthesis and Structures of Ruthenium Carbonyl Complexes Bearing Pyridine-Alkoxide Ligands and Their Catalytic Activity in Alcohol Oxidation

Reaction of Ru₃(CO)₁₂ with two equiv of 6-bromopyridine alcohols 6-bromopyCHROH [(R = C₆H₅ (L1); R = 4-CH₃C₆H₄ (L2); R = 4-OMeC₆H₄ (L3); R = 4-ClC₆H₄ (L4); (R = 4-CF₃C₆H₄ (L5); R = 2-OMeC₆H₄ (L6); R = 2-CF₃C₆H₄ (L7)] and 6-bromopyC(Me)₂OH (L8) in refluxing xylene afforded novel trinuclear ruthenium complexes [6-bromopyCHRO]₂Ru₃(CO)₈ (1a-1g) and [6-bromopyC(Me)₂O]₂Ru₃(CO)₈ (1h). These complexes were characterized by FT-IR and NMR spectroscopy as well as elemental analysis. The structures of all the complexes were further confirmed by X-ray crystallographic analysis. In the presence of tert-butyl hydroperoxide (TBHP) as the source of oxidant, complexes 1a-1h displayed high catalytic activities for oxidation of primary and secondary alcohols and most of oxidation reactions could be completed within 1 h at room temperature.

Ruthenium Supported on Ionically Cross-linked Chitosan-Carrageenan Hybrid MnFe2O4 Catalysts for 4-Nitrophenol Reduction

Herein, we report a facile procedure to synthesize the hybrid magnetic catalyst (Ru@CS-CR@Mn) using ruthenium (Ru) supported on ionically cross-linked chitosan-carrageenan (CS-CR) and manganese ferrite (MnFe2O4) nanoparticles with excellent catalytic activity. The ionic gelation of CS-CR is acting as a protecting layer to promote the encapsulation of MnFe2O4 and Ru nanoparticles by electrostatic interactions. The presence of an active metal and a CS-CR layer on the as-prepared Ru@CS-CR@Mn catalyst was well determined by a series of physicochemical analyses. Subsequently, the catalytic performances of the Ru@CS-CR@Mn catalysts were further examined in the 4-nitrophenol (4-NP) reduction reaction in the presence of sodium borohydride (reducing agent) at ambient temperature. The Ru@CS-CR@Mn catalyst performed excellent catalytic activity in the 4-NP reduction, with a turnover frequency (TOF) values of 925 h−1 and rate constant (k) of 0.078 s−1. It is worth to mentioning that the Ru@CS-CR@Mn catalyst can be recycled and reused up to at least ten consecutive cycles in the 4-NP reduction with consistency in catalytic performance. The Ru@CS-CR@Mn catalyst is particularly attractive as a catalyst due to its superior catalytic activity and superparamagnetic properties for easy separation. We foresee this catalyst having high potential to be extended in a wide range of chemistry applications.

Recent Progress in Application of Molybdenum-Based Catalysts for Epoxidation of Alkenes

Epoxides are important industrial intermediates applied in a variety of industrial processes. During the production of epoxides, catalysts have played an irreplaceable and unique role. In this review, the historic progress of molybdenum-based catalysts in alkene epoxidation are covered and an outlook on future challenge discussed. Efficient catalysts are demonstrated including soluble molybdenum complexes, polyoxometalates catalysts, molybdenum-containing metal organic frameworks, silica supported molybdenum-based catalysts, polymer supported molybdenum-based catalysts, magnetic molybdenum-based catalysts, hierarchical molybdenum-based catalysts, graphene-based molybdenum containing catalysts, photocatalyzed epoxidation catalysts, and some other systems. The effects of different solvents and oxidants are discussed and the mechanisms of epoxidation are summarized. The challenges and perspectives to further enhance the catalytic performances in alkenes epoxidation are presented.

Ruthenium carbonyl complexes supported by pyridine-alkoxide ligands: synthesis, structure and catalytic oxidation of secondary alcohols

Five novel trinuclear ruthenium carbonyl complexes were synthesized and their application in oxidation of secondary alcohols was also researched.