Recyclable Hypervalent Iodine Reagents in Modern Organic Synthesis

Hypervalent iodine (HVI) reagents have gained much attention as versatile oxidants because of their low toxicity, mild reactivity, easy handling, and availability. Despite their unique reactivity and other advantageous properties, stoichiometric HVI reagents are associated with the disadvantage of generating non-recyclable iodoarenes as waste/co-products. To overcome these drawbacks, the syntheses and utilization of various recyclable hypervalent iodine reagents have been established in recent years. This review summarizes the development of various recyclable non-polymeric, polymer-supported, ionic-liquid-supported, and metal–organic framework (MOF)-hybridized HVI reagents.

1 Introduction

2 Polymer-Supported Hypervalent Iodine Reagents

2.1 Polymer-Supported Hypervalent Iodine(III) Reagents

2.2 Polymer-Supported Hypervalent Iodine(V) Reagents

3 Non-Polymeric Recyclable Hypervalent Iodine Reagents

3.1 Non-Polymeric Recyclable Hypervalent Iodine(III) Reagents

3.2 Recyclable Non-Polymeric Hypervalent Iodine(V) Reagents

3.3 Fluorous Hypervalent Iodine Reagents

4 Ionic-Liquid/Ion-Supported Hypervalent Iodine Reagents

5 Metal–Organic Framework (MOF)-Hybridized Hypervalent Iodine Reagents

6 Conclusion

A Ru-Complex Tethered to a N-Rich Covalent Triazine Framework for Tandem Aerobic Oxidation-Knoevenagel Condensation Reactions

Herein, a highly N-rich covalent triazine framework (CTF) is applied as support for a Ru^III complex. The bipyridine sites within the CTF provide excellent anchoring points for the [Ru(acac)₂(CH₃CN)₂]PF₆ complex. The obtained robust Ru^III@bipy-CTF material was applied for the selective tandem aerobic oxidation-Knoevenagel condensation reaction. The presented system shows a high catalytic performance (>80% conversion of alcohols to α, β-unsaturated nitriles) without the use of expensive noble metals. The bipy-CTF not only acts as the catalyst support but also provides the active sites for both aerobic oxidation and Knoevenagel condensation reactions. This work highlights a new perspective for the development of highly efficient and robust heterogeneous catalysts applying CTFs for cascade catalysis.

Ionic-liquid-modified CMK-3 as a support for the immobilization of molybdate ions (MoO42-): Heterogeneous nanocatalyst for selective oxidation of sulfides and benzylic alcohols

A nanometric carbon CMK-3 modified with octylimidazolium ionic liquid and MoO₄^2- as a new hybrid catalyst was synthesized. The study is the first to report a successful immobilization of MoO₄⁼ on the CMK-3/OctIm as a hybrid nanocatalyst. A variety of analytical methods were utilized to determine the properties of the structure and morphology of the synthesized nanocatalyst [CMK-3/Im/MoO₄^2-]. The analytical techniques were transmission electron microscopy (TEM), scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDS), inductively coupled plasma (ICP), X-ray diffraction (XRD), N₂ isotherms (BET), IR spectroscopy and thermogravimetric analysis (TGA). CMK-3/OctIm/MoO₄^2- hybrid catalyst demonstrated a considerable catalytic activity. It is a recyclable nanocatalyst that is utilized to chemoselectively oxidize different types of sulfides to the corresponding sulfoxides and benzylic alcohols to aldehydes using the green oxidant, hydrogen peroxide (H₂O₂) in high-yields. With a little leaching and variation in activity, it is possible to recover and reuse the catalyst frequently. A combination of molybdate anion and the CMK-3 order mesoporous carbon resulted in an improvement in the performance of catalysis and ease of separation for the reaction procedure.

Needle ball-like nanostructured mixed Cu-Ni-Co oxides: Synthesis, characterization and application to the selective oxidation of sulfides to sulfoxides

A mixed nano-metal oxides of Cu-Ni-Co has been synthesized. Several characterization techniques (EDS, XRD, TEM, and SEM) have been used to provide insight into the nature and structure of the catalyst. The size of this mixed metal oxide is 22 nm. The SEM images indicate that the sample with spherical particles, of which spherical assembly is comprised of elongated rod/needle-like subunits pointing radially outward, creates a needle ball-like structure. To efficiently catalyze the selective oxidation of sulfide towards sulfoxide, this heterogeneous catalyst uses an oxidizing agent (hydrogen peroxide- H₂O₂) and a solvent (acetonitrile) in mild conditions. The influence of reaction temperature and sulfide/oxidant molar ratio was evaluated with respect to sulfide conversion and chemoselectivity towards the sulfoxide product. Under optimized conditions, product yields in the range from 70 to 97% were obtained.

Advances in Synthetic Applications of Hypervalent Iodine Compounds

The preparation, structure, and chemistry of hypervalent iodine compounds are reviewed with emphasis on their synthetic application. Compounds of iodine possess reactivity similar to that of transition metals, but have the advantage of environmental sustainability and efficient utilization of natural resources. These compounds are widely used in organic synthesis as selective oxidants and environmentally friendly reagents. Synthetic uses of hypervalent iodine reagents in halogenation reactions, various oxidations, rearrangements, aminations, C-C bond-forming reactions, and transition metal-catalyzed reactions are summarized and discussed. Recent discovery of hypervalent catalytic systems and recyclable reagents, and the development of new enantioselective reactions using chiral hypervalent iodine compounds represent a particularly important achievement in the field of hypervalent iodine chemistry. One of the goals of this Review is to attract the attention of the scientific community as to the benefits of using hypervalent iodine compounds as an environmentally sustainable alternative to heavy metals.

Peroxoniobium(v)-catalyzed selective oxidation of sulfides with hydrogen peroxide in water: a sustainable approach

Facile and selective transformation of thioethers to the corresponding sulfoxides or sulfones with 30% H₂O₂ has been achieved in an aqueous medium by using peroxoniobium(v) complexes as reusable catalysts.

Regio- and enantio-selective oxidation of diols by Candida parapsilosis ATCC 7330

Optically pure (S)-diols and their corresponding hydroxy ketones were prepared via regio- and enantio-selective oxidation of the corresponding diols using whole cells of Candida parapsilosis ATCC 7330.