The development of transition-metal-catalyzed organic transformations based on the first-row transition metals such as Fe, Co, Ni, and Cu is of importance because of their relatively low cost and toxicity relative to precious metals.[1] The strongly sdonating N-heterocyclic carbenes (NHCs) offer a good opportunity to tune the reactivity and selectivity of transition-metal catalysts.[2] A large number of NHC complexes of precious metals have recently been prepared and characterized, and their catalytic applications in various organic transformations have been widely studied. In contrast, catalytic processes based on NHC complexes of non-noble metals such as manganese, iron, and cobalt have not been well studied. [3, 4] One of the reasons is that NHC complexes of the first-row metals have to be prepared from free carbenes [5, 6] or through reactions of basic metal acetates, alkoxides, or amides with imidazolium salts.[7] The generation of free carbenes often requires special bases, and handling unstable free carbenes requires harsh conditions. The second route is also restricted because metal acetates, alkoxides, and amides are not always available, and such metal salts are moisturesensitive. The most popular approach to noble-metal-NHC complexes is the transmetalation of NHCs from silver complexes that can be synthesized by treating Ag 2 O with the imidazolium salts.[2] However, the carbene-transfer reactions of silver-NHC complexes with light metal salts such as Mn, Fe, and Co are not simple. Thus, the development of practical and convenient synthetic approaches to NHC complexes of non-noble metals is highly desired.As a continuation of our research on the nickel and palladium chemistry of NHCs, [8] we herein report practical and convenient synthetic procedures of divalent iron, cobalt, nickel, and copper complexes by direct reactions of metal powders with imidazolium salts or silver-NHC complexes. 2 [M = Fe (1); Co (2); Ni (3)] in 51.7-94.1 % yields (Scheme 1). Complexes 1-3 could also be obtained in similar yields by simply mixing H 2 L1(PF 6 ) 2 , Ag 2 O, and metallic powders in acetonitrile. The procedure is simple, and the unreacted metal powders and silver can be easily removed by filtration. Further studies revealed that compounds 1-3 could be prepared by directly treating H 2 L1(PF 6 ) 2 with the corresponding metal powders in air (Scheme 2). The acidity of imidazolium salts is too weak for the reactions of imidazolium salts with metals (M = Fe, Co, Ni, and Cu) to release H 2 to be dynamically preferred. However, the reactions took place smoothly upon exposure to an O 2 atmosphere with the formation of water.The three complexes are isostructural with each other, and their 1 H and 13 C NMR spectra show almost the same resonance signals due to pyridine and imidazolylidene moieties. The imidazolylidene backbone protons appear as two doublets at d = 8.62 and 8.13 ppm.13 C NMR spectra show singlets at d = 159.1, 159.1, and 158.9 ppm for 1-3, respectively, which is characteristic of metal-carbenic carbon a...

Plant viral diseases cause tremendous decreases in crop yield and quality. Natural products have always been a valuable source for lead discovery in medicinal and agricultural chemistry. A series of pimprinine alkaloids and their derivatives were prepared and identified by nuclear magnetic resonance (NMR) spectroscopy and high-resolution mass spectrometry (HR-MS). The antiviral activities of these alkaloids against tobacco mosaic virus (TMV) were systematically investigated for the first time. Most of the compounds exhibited higher antiviral activities than ribavirin. Compounds 5l, 9h, and 10h, which had similar or higher antiviral activities than ningnanmycin (perhaps the most widely used antiviral agent at present), emerged as new antiviral pilot compounds. This systematic structure–activity-relationship research lays the foundation for simplifying the structure of these alkaloids. The ring-open products, acylhydrazones 9a–9u, were also found to possess good antiviral activities. Moreover, all the synthesized compounds displayed broad-spectrum fungicidal activities. This study provides important information for the research and development of pimprinine alkaloids as novel antiviral agents.

Electrochemical reduction of molecular O2 to hydrogen peroxide (H2O2) offers a promising solution for water purification and environmental remediation. Here, we design a hierarchical free‐standing single‐Co‐atom (with Co–N4 coordination) electrode for oxygen reduction reaction (ORR) via a two‐electron pathway to make H2O2 in acidic media. The current density of the single‐Co‐atom electrode reached 51 mA/cm2 at 0.1 V vs reversible hydrogen electrode, lasting for more than 10 hours of continuous operation with H2O2 selectivity greater than 80%. Toward practical application, the single‐Co‐atom electrode was directly used to assemble an electrochemical cell to produce H2O2 at a rate of 676 mol/kgcat/h with a cell voltage of about 1.6 V.

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