Teng Wang

Direct Approaches to Nitriles via Highly Efficient Nitrogenation Strategy through C–H or C–C Bond Cleavage

Because of the importance of nitrogen-containing compounds in chemistry and biology, organic chemists have long focused on the development of novel methodologies for their synthesis. For example, nitrogen-containing compounds show up within functional materials, as top-selling drugs, and as bioactive molecules. To synthesize these compounds in a green and sustainable way, researchers have focused on the direct functionalization of hydrocarbons via C-H or C-C bond cleavage. Although researchers have made significant progress in the direct functionalization of simple hydrocarbons, direct C-N bond formation via C-H or C-C bond cleavage remains challenging, in part because of the unstable character of some N-nucleophiles under oxidative conditions. The nitriles are versatile building blocks and precursors in organic synthesis. Recently, chemists have achieved the direct C-H cyanation with toxic cyanide salts in the presence of stoichiometric metal oxidants. In this Account, we describe recent progress made by our group in nitrile synthesis. C-H or C-C bond cleavage is a key process in our strategy, and azides or DMF serve as the nitrogen source. In these reactions, we successfully realized direct nitrile synthesis using a variety of hydrocarbon groups as nitrile precursors, including methyl, alkenyl, and alkynyl groups. We could carry out C(sp(3))-H functionalization on benzylic, allylic, and propargylic C-H bonds to produce diverse valuable synthetic nitriles. Mild oxidation of C═C double-bonds and C≡C triple-bonds also produced nitriles. The incorporation of nitrogen within the carbon skeleton typically involved the participation of azide reagents. Although some mechanistic details remain unclear, studies of these nitrogenation reactions implicate the involvement of a cation or radical intermediate, and an oxidative rearrangement of azide intermediate produced the nitrile. We also explored environmentally friendly oxidants, such as molecular oxygen, to make our synthetic strategy more attractive. Our direct nitrile synthesis methodologies have potential applications in the synthesis of biologically active molecules and drug candidates.

TEMPO-catalyzed aerobic oxygenation and nitrogenation of olefins via C=C double-bond cleavage

A novel TEMPO-catalyzed aerobic oxygenation and nitrogenation of hydrocarbons via C═C double-bond cleavage has been disclosed. The reaction employs molecular oxygen as the terminal oxidant and oxygen-atom source by metal-free catalysis under mild conditions. This method can be used for the preparation of industrially and pharmaceutically important N- and O-containing motifs, directly from simple and readily available hydrocarbons.

Silver-Catalyzed Nitrogenation of Alkynes: A Direct Approach to Nitriles through CC Bond Cleavage**

The transformation of alkynes is a fundamental method that has been widely used in organic synthesis. Alkyne chemistry can be dated back to the early nineteenth century. The hydration of alkynes to ketones (Scheme 1a) and the addition reactions of alkynes (Scheme 1b) are early examples. Subsequently, various catalytic systems were developed. For example, the Pd-catalyzed Wacker-type oxidation to generate 1,2-diketones (Scheme 1c) is one of the most important industrial processes. The development of cyclization reactions such as click chemistry (Scheme 1d) has established new perspectives for the use of alkynes in drug discovery, materials science, supramolecular chemistry, polymer chemistry, and biotechnology. Furthermore, the coupling of terminal alkynes, such as the Sonogashira coupling (Scheme 1e), provides important methods for C C bond formation. The catalytic cleavage of C C bonds to produce carboxylic acids and new alkynes has also been disclosed (Scheme 1 f,g). Because of the significance and wide applications of such chemistry in organic synthesis, the exploration for new types of alkyne transformations is very attractive to researchers. Nitriles are one of the most common structural motifs in nature, and are versatile building blocks in the synthesis of natural products, pharmaceuticals, agricultural chemicals, materials, and dyes. Their importance in synthetic and medicinal chemistry has attracted considerable attention for the development of new synthetic strategies for these compounds. Azides have been widely used in organic reactions, but recent progress on the direct transformation of simple hydrocarbons into N-containing compounds through a nitrogenation strategy encouraged us to try the direct transformation of alkynes. Although metal-catalyzed C C bond cleavage involving alkyne metathesis has been disclosed, direct C C bond cleavage to form nitriles (Scheme 1h) is still unknown and remains both challenging and of great value. Herein, we report a novel and direct silver-catalyzed nitrogenation reaction of alkynes to nitriles through C C bond cleavage (Scheme 1h). The significance of the present chemistry is threefold: 1) It is the first example of a direct transformation from terminal alkynes to nitriles. 2) The application of selective C C bond cleavage in organic synthesis presents one of the most attractive and challenging projects. This chemistry provides a novel means of C C bond cleavage. 3) Compared to traditional gold salt p-acid catalysts, the silver catalyst plays a key role in this transformation. This research not only provides a new application for alkynes in organic synthesis, but also offers valuable mechanistic insights into this novel nitrogenation chemistry, which may promote the discovery of other new types of nitrogenation reactions for the construction of N-containing compounds. The initially investigated substrate for the direct nitrogenation of acetylenes was para-methoxy phenylacetylene. When the reaction is performed in the presence of Ag2CO3 using azidotrimethylsilane (TMSN3) as the nitrogen source, p-methoxy-benzonitrile (2a) was obtained in 58% yield (Table 1, entry 1). Reactions catalyzed by other transition metals, such as AuCl3, NiCl2, FeCl2, Cu(OAc)2, and Pd(OAc)2, either did not proceed or gave poor yields (Table 1, entries 2 and 3; see also the Supporting Information). Product 2a was obtained in 81% yield when DMSO was employed as the Scheme 1. Direct transformations of alkynes.

Copper-Catalyzed Oxoazidation and Alkoxyazidation of Indoles

Copper-catalyzed oxoazidation and alkoxyazidation of indoles has been developed. The dearomatization reaction which leads to versatile 3-azido indolenine and oxindole derivatives in moderate to good yields could be used in a further transformation.

Selective C sp 2Csp Bond Cleavage: The Nitrogenation of Alkynes to Amides

Breakthrough: A novel catalyzed direct highly selective C(sp2)-C(sp) bond functionalization of alkynes to amides has been developed. Nitrogenation is achieved by the highly selective C(sp2)-C(sp) bond cleavage of aryl-substituted alkynes. The oxidant-free and mild conditions and wide substrate scope make this method very practical.

MOF-derived surface modified Ni nanoparticles as an efficient catalyst for the hydrogen evolution reaction

Pyrolysis of a Ni based metal organic framework in NH3 yields Ni nanoparticles with surface nitridation together with thin carbon coating layers. The subtle surface modification significantly improves the catalytic performance for the hydrogen evolution reaction (HER). The surface modified Ni nanoparticles show a low overpotential of only 88 mV at a current density of 20 mA cm−2, which is one of the most efficient HER catalysts based on metallic Ni reported so far. The results suggest that controlled pyrolysis of MOFs is an effective method to prepare highly efficient noble metal free HER catalysts.

Iron‐Facilitated Oxidative Dehydrogenative CO Bond Formation by Propargylic C sp 3H Functionalization

The formation of carbon–heteroatom bonds is one of themost attractive and fundamental transformations in organic synthesis. For example, the construction of C O bonds plays an important role in producing alcohols, ethers, and esters in the synthesis of drugs, materials, and natural products. In general, great progress has been made in C O bond formation from carbon–halide bonds, although prefunctionalization of the substrates was often required and halidecontaining by-products were formed during the process (Scheme 1a). Thus, the alternative strategy involving direct

MOF-Derived Noble Metal Free Catalysts for Electrochemical Water Splitting

Noble metal free electrocatalysts for water splitting are key to low-cost, sustainable hydrogen production. In this work, we demonstrate that metal-organic frameworks (MOFs) can be controllably converted into catalysts for the oxygen evolution reaction (OER) or the hydrogen evolution reaction (HER). The OER catalyst is composed of FeNi alloy nanoparticles encapsulated in N-doped carbon nanotubes, which is obtained by thermal decomposition of a trimetallic (Zn2+, Fe2+, and Ni2+) zeolitic imidazolate framework (ZIF). It reaches 10 mA cm-2 at the overpotential of 300 mV with a low Tafel slope of 47.7 mV dec-1. The HER catalyst consists of Ni nanoparticles coated with a thin layer of N-doped carbon. It is obtained by thermal decomposition of a Ni-MOF in NH3. It shows low overpotential of only 77 mV at 20 mA cm-2 with low Tafel slope of 68 mV dec-1. The above noble metal free OER and HER electrocatalysts are applied in an alkaline electrolyzer driven by a commercial polycrystalline solar cell. It achieves electrolysis efficiency of 64.4% at 65 mA cm-2 under sun irradiation of 50 mW cm-2. This practical application shows the promising prospect of low-cost and high-efficiency sustainable hydrogen production from combination of solar cells with high-performance noble metal free electrocatalysts.

An efficient Co–N–C oxygen reduction catalyst with highly dispersed Co sites derived from a ZnCo bimetallic zeolitic imidazolate framework

In this work we report a highly efficient Co based catalyst for the oxygen reduction reaction (ORR) with highly dispersed Co sites on N-doped carbon. The catalyst is derived from a ZnCo bimetallic metal organic framework (MOF) by heat treatment in an inert atmosphere at 1000 °C. Zn is simultaneously eliminated during the pyrolysis due to its high volatility at high temperature, yielding a highly porous structure with homogeneous Co loading. Another effect of Zn is to disperse Co in the MOF precursor, which effectively inhibits the aggregation of Co after pyrolysis. The best ORR performance is achieved when 5% Zn is substituted by Co in the MOF precursor. The resulting catalyst shows a high half wave potential of 0.90 V vs. reversible hydrogen electrode in 0.1 M KOH solution, which is mainly attributed to the high dispersion of the ORR active Co sites.

Ultrafine Sn nanocrystals in a hierarchically porous N-doped carbon for lithium ion batteries

We report a simple method of preparing a high performance, Sn-based anode material for lithium ion batteries (LIBs). Adding H2O2 to an aqueous solution containing Sn2+ and aniline results in simultaneous polymerization of aniline and oxidation of Sn2+ to SnO2, leading to a homogeneous composite of polyaniline and SnO2. Hydrogen thermal reduction of the above composite yields N-doped carbon with hierarchical porosity and homogeneously distributed, ultrafine Sn particles. The nanocomposite exhibits excellent performance as an anode material for lithium ion batteries, showing a high reversible specific capacity of 788 mAh·g−1 at a current density of 100 mA·g−1 after 300 cycles and very good stability up to 5,000 mA·g−1. The simple preparation method combined with the good electrochemical performance is highly promising to promote the application of Sn based anode materials.