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.

Copper nanocatalysts applied in coupling reactions: a mechanistic insight

Copper-based nanocatalysts have seen great interest for use in synthetic applications since the early 20th century, as evidenced by the exponential number of contributions reported (since 2000, more than 48 000 works published out of about 81 300 since 1900; results from SciFinder using "copper nanocatalysts in organic synthesis" as keywords). These huge efforts are mainly based on two key aspects: (i) copper is an Earth-abundant metal with low toxicity, leading to inexpensive and eco-friendly catalytic materials; and (ii) copper can stabilize different oxidation states (0 to +3) for molecular and nanoparticle-based systems, which promotes different types of metal-reagent interactions. This chemical versatility allows different pathways, involving radical or ionic copper-based intermediates. Thus, copper-based nanoparticles have become convenient catalysts, in particular for couplings (both homo- and hetero-couplings), transformations that are involved in a remarkable number of processes affording organic compounds, which find interest in different fields (medicinal chemistry, natural products, drugs, materials, etc.). Clearly, this richness in reactivity makes understanding the mechanisms more complex. The present review focuses on the analysis of reported contributions using monometallic copper-based nanoparticles as catalytic precursors applied in coupling reactions, paying attention to those shedding light on the reaction mechanism.

Ni nanoparticle supported reduced graphene oxide as a highly active and durable heterogeneous material for coupling reactions

We report the loading of highly air stable Ni(0) nanoparticles (average particle size = 11 nm) on the surface of a reduced graphene oxide (RGO) material. The material was characterized using different techniques, including Raman spectroscopy, XRD, TEM, SEM, and HRTEM analysis. The Ni(0)@RGO catalyst showed superb efficiency towards Kumada-Corriu C-C cross-coupling reactions, with 92% yield of 4-methoxybiphenyl at 60 °C. The recycled material can be reused up to the 5^th cycle after regeneration by calcination, without loss of activity.

The Beneficial Sinergy of MW Irradiation and Ionic Liquids in Catalysis of Organic Reactions

The quest for sustainable processes is becoming more and more important, with catalysis playing a major role in improving atom economy and reducing waste. Organic syntheses with less need of protecting/de-protecting steps are highly desirable. The combination of microwave irradiation, as energy source, with ionic liquids, as both solvents and catalysts, offered interesting solutions in recent years. The literature data of the last 15 years concerning selected reactions are presented, highlighting the importance of microwave (MW) technology coupled with ionic liquids.

Efficient conversion of fructose into 5-hydroxymethylfurfural over WO3/reduced graphene oxide catalysts

A sustainable and efficient catalyst for converting carbohydrates to a renewable platform chemical 5-hydroxymethylfurfural (HMF) is the goal in the study of biomass recycling.