Ionic Liquids in Metal, Photo-, Electro-, and (Bio) Catalysis

Ionic liquids (ILs) have unique physicochemical properties that make them advantageous for catalysis, such as low vapor pressure, non-flammability, high thermal and chemical stabilities, and the ability to enhance the activity and stability of (bio)catalysts. ILs can improve the efficiency, selectivity, and sustainability of bio(transformations) by acting as activators of enzymes, selectively dissolving substrates and products, and reducing toxicity. They can also be recycled and reused multiple times without losing their effectiveness. ILs based on imidazolium cation are preferred for structural organization aspects, with a semiorganized layer surrounding the catalyst. ILs act as a container, providing a confined space that allows modulation of electronic and geometric effects, miscibility of reactants and products, and residence time of species. ILs can stabilize ionic and radical species and control the catalytic activity of dynamic processes. Supported IL phase (SILP) derivatives and polymeric ILs (PILs) are good options for molecular engineering of greener catalytic processes. The major factors governing metal, photo-, electro-, and biocatalysts in ILs are discussed in detail based on the vast literature available over the past two and a half decades. Catalytic reactions, ranging from hydrogenation and cross-coupling to oxidations, promoted by homogeneous and heterogeneous catalysts in both single and multiphase conditions, are extensively reviewed and discussed considering the knowledge accumulated until now.

Construction of Pyridine-Based Chiral Ionic Covalent Organic Frameworks as a Heterogeneous Catalyst for Promoting Asymmetric Henry Reactions

The difficulties in the separation of products from the reaction mixture and the recovery of the organic cationic ionic liquids (OCILs) catalysts still need to be addressed. Post modification of the pyridine unit in the covalent organic framework (COF) via the formation of pyridinium salts with the chiral bromoacetate led to the chiral ionic COF with OCIL "immobilized", which was utilized as a heterogeneous catalyst for asymmetric Henry reactions with high yield and excellent stereoselectivity.

Nickel(II), Copper(II) and Palladium(II) Complexes with Bis-Semicarbazide Hexaazamacrocycles: Redox-Noninnocent Behavior and Catalytic Activity in Oxidation and C-C Coupling Reactions

Nickel(II), copper(II), and palladium(II) complexes ML^H, where M = Ni (1), Cu (2), Pd (3), and ML^OMe, where M = Ni (4), Cu (5), Pd (6), have been prepared by reactions of NiCl₂·6H₂O, Cu(OAc)₂·H₂O, and PdCl₂(MeCN)₂ with 14-membered bis-semicarbazide hexaazamacrocycles H₂L^H and H₂L^OMe in dimethylformamide (DMF). The compounds were characterized by elemental analysis, ESI mass spectrometry, IR, UV-vis, and 1D (¹H, ¹³C) and 2D (¹H-¹H COSY, ¹H-¹H TOCSY, ¹H-¹H NOESY, ¹H-¹³C HSQC, ¹H-¹³C HMBC) NMR spectra (1, 3, 4, and 6), and X-ray diffraction (2, 4-6). The complexes with M^IIN₄ coordination environment have S = 0, 1/2, 0 ground states for Ni, Cu, and Pd, respectively. The electrochemical behavior of 1-6 was investigated in detail. The electronic structures of 1e-oxidized species were studied by EPR, UV-vis-NIR spectroelectrochemistry, and DFT calculations, indicating the redox-noninnocent behavior of the ligands. Compounds 1-6 were tested in the oxidation of styrene and C-C coupling (Henry and Knoevenagel condensations). Compounds 2 and 5 selectively catalyze the microwave-assisted oxidation of neat styrene to benzaldehyde (up to 88% yield), whereas the 1 and 4 catalytic systems afforded up to 99% β-nitroethanol yield with an appreciable diastereoselectivity toward the formation of the anti isomer.

Hydrosoluble Complexes Bearing Tris(pyrazolyl)methane Sulfonate Ligand: Synthesis, Characterization and Catalytic Activity for Henry Reaction

The catalytic activity of the water-soluble scorpionate coordination compounds [Cu(-NN’O-Tpms)2] (1), [Mn(Tpms)2] (2) and Li[FeCl2(-NN’N’’-Tpms)] (3) [Tpms = tris(pyrazolyl)-methane sulfonate, O3SC(pz)3], were studied towards the (Henry) reaction between benzaldehyde and nitromethane or nitroethane in aqueous medium to afford, respectively, 2-nitro-1-phenylethanol or 2-nitro-1-phenylpropanol, the latter in the syn and the anti diastereoisomeric forms. Complex 1 exhibited the highest activity under the optimum experimental conditions and was used to broaden the scope of the reaction to include several aromatic aldehydes achieving yields up to 94%.

Ni(II)-Aroylhydrazone Complexes as Catalyst Precursors Towards Efficient Solvent-Free Nitroaldol Condensation Reaction

The aroylhydrazone Schiff bases 2-hydroxy-(2-hydroxybenzylidene)benzohydrazide and (2,3-dihydroxybenzylidene)-2-hydroxybenzohydrazide have been used to synthesize the bi- and tri-nuclear Ni(II) complexes [Ni2(L1)2(MeOH)4] (1) and [Ni3(HL2)2(CH3OH)8]· (NO3)2 (2). Both complexes have been characterized by elemental analysis, spectroscopic techniques [IR spectroscopy and electrospray ionization-mass spectrometry (ESI-MS)], and single-crystal X-ray crystallography. The coordination behavior of the two ligands is different in the complexes: The ligand exhibits the keto form in 2, while coordination through enol form was found in 1. Herein, the catalytic activity of 1 and 2 has been compared with the nitroaldol condensation reaction under various conditions. Complex 2 exhibits the highest activity towards solvent-free conditions.

Wealth from waste: M. acuminata peel waste-derived magnetic nanoparticles as a solid catalyst for the Henry reaction

Biosynthesis of nanoparticles by exploiting different plant materials has become a matter of great interest in recent years and is considered as a green technology as it does not involve any harmful and toxic chemicals in the synthetic procedure. In this paper, we report a novel one-pot M. acuminata peel ash extract mediated bio-synthesis of basic iron oxide nanoparticles (MAPAE@Fe₃O₄). The nanoparticles were fully characterized by different analytical techniques such as XRF, IR, XRD, XPS, SEM, TEM, VSM and TGA. The synthesized nanoparticles exhibited high basicity due to the presence of metal oxides, primarily basic K₂O in the outer layer of Fe₃O₄ surfaces, and showed good catalytic activity for the synthesis of β-nitroalcohol via the Henry reaction at room temperature under solvent-free conditions. The catalyst was separated from the reaction medium by simply applying an external bar magnet making the process economical and less labor intensive. Furthermore, the catalyst can be reused up to the 4^th cycle without much loss of its activity.

One-pot synthesis and application of novel amino-functionalized silica nanoparticles using guanidine as amino group

The preparation of modified silica nanoparticles with guanidine was developed and used to catalyze the Henry reaction and fix quantum dots.