This review focuses on the synthesis, protection, functionalization, and application of magnetic nanoparticles, as well as the magnetic properties of nanostructured systems. Substantial progress in the size and shape control of magnetic nanoparticles has been made by developing methods such as co-precipitation, thermal decomposition and/or reduction, micelle synthesis, and hydrothermal synthesis. A major challenge still is protection against corrosion, and therefore suitable protection strategies will be emphasized, for example, surfactant/polymer coating, silica coating and carbon coating of magnetic nanoparticles or embedding them in a matrix/support. Properly protected magnetic nanoparticles can be used as building blocks for the fabrication of various functional systems, and their application in catalysis and biotechnology will be briefly reviewed. Finally, some future trends and perspectives in these research areas will be outlined.

Magnetic nanoparticles: Synthesis, protection, functionalization, and application

Nanoparticles containing magnetic materials, such as magnetite (Fe3O4), are particularly useful for imaging and separation techniques. As these nanoparticles are generally considered to be biologically and chemically inert, they are typically coated with metal catalysts, antibodies or enzymes to increase their functionality as separation agents. Here, we report that magnetite nanoparticles in fact possess an intrinsic enzyme mimetic activity similar to that found in natural peroxidases, which are widely used to oxidize organic substrates in the treatment of wastewater or as detection tools. Based on this finding, we have developed a novel immunoassay in which antibody-modified magnetite nanoparticles provide three functions: capture, separation and detection. The stability, ease of production and versatility of these nanoparticles makes them a powerful tool for a wide range of potential applications in medicine, biotechnology and environmental chemistry.

Intrinsic peroxidase-like activity of ferromagnetic nanoparticles

The Huisgen 1,3-dipolar cycloaddition reaction of organic azides and alkynes has gained considerable attention in recent years due to the introduction in 2001 of Cu(1) catalysis by Tornoe and Meldal, leading to a major improvement in both rate and regioselectivity of the reaction, as realized independently by the Meldal and the Sharpless laboratories. The great success of the Cu(1) catalyzed reaction is rooted in the fact that it is a virtually quantitative, very robust, insensitive, general, and orthogonal ligation reaction, suitable for even biomolecular ligation and in vivo tagging or as a polymerization reaction for synthesis of long linear polymers. The triazole formed is essentially chemically inert to reactive conditions, e.g. oxidation, reduction, and hydrolysis, and has an intermediate polarity with a dipolar moment of ∼5 D. The basis for the unique properties and rate enhancement for triazole formation under Cu(1) catalysis should be found in the high ∆G of the reaction in combination with the low character of polarity of the dipole of the noncatalyzed thermal reaction, which leads to a considerable activation barrier. In order to understand the reaction in detail, it therefore seems important to spend a moment to consider the structural and mechanistic aspects of the catalysis. The reaction is quite insensitive to reaction conditions as long as Cu(1) is present and may be performed in an aqueous or organic environment both in solution and on solid support.

Cu-catalyzed azide-alkyne cycloaddition.

Synthesis of metal-organic frameworks (MOFs): routes to various MOF topologies, morphologies, and composites.

Catalytic dehydrogenative cross-coupling: forming carbon-carbon bonds by oxidizing two carbon-hydrogen bonds

The development of an efficient catalytic activation (cleavage) system for C−H and C−C bonds is an important challenge in organic synthesis, because these bonds comprise a variety of organic molecules such as natural products, petroleum oils, and polymers on the earth. Among many elegant approaches utilizing transition metals to activate C−H and C−C bonds facilely, chelation-assisted protocols based on the coordinating ability of an organic moiety have attracted great attention, though they have often suffered from the need for an intact coordinating group in a substrate. In this Account, we describe our entire efforts to activate C−H or C−C bonds adjacent to carbonyl groups by employing a new concept of metal−organic cooperative catalysis (MOCC), which enables the temporal installation of a 2-aminopyridyl group into common aldehydes or ketones in a catalytic way. Consequently, a series of new catalytic reactions such as alcohol hydroacylation, oxo-ester synthesis, C−C triple bond cleavage, hydrative dime...

Metal-organic cooperative catalysis in C-H and C-C bond activation and its concurrent recovery.

This tutorial review deals with recent developments in the activation of C–C bonds in organic molecules that have been catalyzed by transition metal complexes. Many chemists have devised a variety of strategies for C–C bond activation and significant progress has been made in this field over the past few decades. However, there remain only a few examples of the catalytic activation of C–C bonds, in spite of the potential use in organic synthesis, and most of the previously published reviews have dwelt mainly on the stoichiometric reactions. Consequently, this review will focus mainly on the catalytic reaction of C–C bond cleavage by homogeneous transition metal catalysts. The contents include cleavage of C–C bonds in strained and unstrained molecules, and cleavage of multiple C–C bonds such as CC triple bonds in alkynes. Multiple bond metathesis and heterogeneous systems are beyond the scope of this review, though they are also fascinating areas of C–C bond activation. In this review, the strategies and tactics for C–C bond activation will be explained.

Transition metal-catalyzed carbon–carbon bond activation

Transition-metal-catalyzed activation of C–H and C–C bonds is a challenging area in synthetic organic chemistry. Among various methods to accomplish these processes, the approach using metal–organic cooperative catalytic systems is one of the most promising. In this protocol, organic molecules as well as transition metals act as catalysts to bring about reactions, which proceed with high efficiencies and selectivities. Various metal–organic cooperative catalytic systems developed for C–H and C–C bond activation reactions are discussed in this review. Also discussed are how each metal–organic cooperative catalyst affects the reaction mechanism and what kinds of substrates can be applied in each of the catalytic processes.

Chul Ho Jun

Papers

Metal-organic cooperative catalysis in C-H and C-C bond activation and its concurrent recovery.

Transition metal-catalyzed carbon–carbon bond activation

Metal–Organic Cooperative Catalysis in C–H and C–C Bond Activation

Microwave synthesis of hybrid inorganic–organic materials including porous Cu3(BTC)2 from Cu(II)-trimesate mixture

Intermolecular hydroacylation by transition-metal complexes