Transition-metal catalyzed C-H activation as a means of synthesizing complex natural products.

Over the past few decades, the advent of C-H activation has led to a rethink among chemists about the synthetic strategies employed for multi-step transformations. Indeed, deploying innovative and masterful tricks against the numerous classical organic transformations has been the need of the hour. Despite this, the immense importance of C-H activation remains unfulfilled unless the methodology can be deployed for large-scale industrial processes and towards the concise, step-economic synthesis of prodigious natural products and pharmaceutical drugs. Lately, the growing potential of C-H activation methodology has indeed driven the pioneers of synthetic organic chemists into finding more efficient methods to accelerate the synthesis of such complex molecular scaffolds. This review aims to draw a general overview of the various C-H activation procedures that have been adopted for synthesizing these vast majority of structurally complicated natural products. Our objective lies in drawing a complete picture and taking the readers through the synthesis of a series of such complex organic compounds by simplified techniques, making it step-economic on a larger scale and thus instigating the readers to trigger the use of such methodology and uncover new, unique patterns for future synthesis of such natural products.

Constructing Co@TiO2 Nanoarray Heterostructure with Schottky Contact for Selective Electrocatalytic Nitrate Reduction to Ammonia.

Electrochemical nitrate (NO3 - ) reduction reaction (NO3 - RR) is a potential sustainable route for large-scale ambient ammonia (NH3 ) synthesis and regulating the nitrogen cycle. However, as this reaction involves multi-electron transfer steps, it urgently needs efficient electrocatalysts on promoting NH3  selectivity. Herein, a rational design of Co nanoparticles anchored on TiO2  nanobelt array on titanium plate (Co@TiO2 /TP) is presented as a high-efficiency electrocatalyst for NO3 - RR. Density theory calculations demonstrate that the constructed Schottky heterostructures coupling metallic Co with semiconductor TiO2  develop a built-in electric field, which can accelerate the rate determining step and facilitate NO3 - adsorption, ensuring the selective conversion to NH3 . Expectantly, the Co@TiO2 /TP electrocatalyst attains an excellent Faradaic efficiency of 96.7% and a high NH3  yield of 800.0 µmol h-1  cm-2  under neutral solution. More importantly, Co@TiO2 /TP heterostructure catalyst also presents a remarkable stability in 50-h electrolysis test.

Defective TiO2- x for High-Performance Electrocatalytic NO Reduction toward Ambient NH3 Production.

Synthesis of green ammonia (NH3 ) via electrolysis of nitric oxide (NO) is extraordinarily sustainable, but multielectron/proton-involved hydrogenation steps as well as low concentrations of NO can lead to poor activities and selectivities of electrocatalysts. Herein, it is reported that oxygen-defective TiO2 nanoarray supported on Ti plate (TiO2- x /TP) behaves as an efficient catalyst for NO reduction to NH3 . In 0.2 m phosphate-buffered electrolyte, such TiO2- x /TP shows competitive electrocatalytic NH3 synthesis activity with a maximum NH3 yield of 1233.2 µg h-1  cm-2 and Faradaic efficiency of 92.5%. Density functional theory calculations further thermodynamically faster NO deoxygenation and protonation processes on TiO2- x (101) compared to perfect TiO2 (101). And the low energy barrier of 0.7 eV on TiO2- x (101) for the potential-determining step further highlights the greatly improved intrinsic activity. In addition, a Zn-NO battery is fabricated with TiO2- x /TP and Zn plate to obtain an NH3 yield of 241.7 µg h-1  cm-2 while providing a peak power density of 0.84 mW cm-2 .

Rational Construction of Heterostructured Cu3 P@TiO2 Nanoarray for High-Efficiency Electrochemical Nitrite Reduction to Ammonia.

Electroreduction of nitrite (NO2 - ) to valuable ammonia (NH3 ) offers a sustainable and green approach for NH3 synthesis. Here, a Cu3 P@TiO2 heterostructure is rationally constructed as an active catalyst for selective NO2 - -to-NH3 electroreduction, with rich nanosized Cu3 P anchored on a TiO2 nanoribbon array on Ti plate (Cu3 P@TiO2 /TP). When performed in the 0.1 m NaOH with 0.1 m NaNO2 , the Cu3 P@TiO2 /TP electrode obtains a large NH3 yield of 1583.4 µmol h-1  cm-2 and a high Faradaic efficiency of 97.1%. More importantly, Cu3 P@TiO2 /TP also delivers remarkable long-term stability for 50 h electrolysis. Theoretical calculations indicate that intermediate adsorption/conversion processes on Cu3 P@TiO2 interfaces are synergistically optimized, substantially facilitating the conversion of NO2 - -to-NH3 .

Ambient Ammonia Synthesis via Electrochemical Reduction of Nitrate Enabled by NiCo2 O4 Nanowire Array.

NiCo2 O4 nanowire array on carbon cloth (NiCo2 O4 /CC) is proposed as a highly active electrocatalyst for ambient nitrate (NO3 - ) reduction to ammonia (NH3 ). In 0.1 m NaOH solution with 0.1 m NaNO3 , such NiCo2 O4 /CC achieves a high Faradic efficiency of 99.0% and a large NH3 yield up to 973.2 µmol h-1  cm-2 . The superior catalytic activity of NiCo2 O4 comes from its half-metal feature and optimized adsorption energy due to the existence of Ni in the crystal structure. A Zn-NO3 - battery with NiCo2 O4 /CC cathode also shows a record-high battery performance.

Amorphous Boron Carbide on Titanium Dioxide Nanobelt Arrays for High-Efficiency Electrocatalytic NO Reduction to NH3.

Electrocatalytic NO reduction is regarded as an attractive strategy to degrade the NO contaminant into useful NH3 , but the lack of efficient and stable electrocatalysts to facilitate such multiple proton-coupled electron-transfer processes impedes its applications. Here, we report on developing amorphous B2.6 C supported on a TiO2 nanoarray on a Ti plate (a-B2.6 C@TiO2 /Ti) as an NH3 -producing nanocatalyst with appreciable activity and durability toward the NO electroreduction. It shows a yield of 3678.6 µg h-1 cm-2 and a FE of 87.6 %, superior to TiO2 /Ti (563.5 µg h-1 cm-2 , 42.6 %) and a-B2.6 C/Ti (2499.2 µg h-1 cm-2 , 85.6 %). An a-B2.6 C@TiO2 /Ti-based Zn-NO battery achieves a power density of 1.7 mW cm-2 with an NH3 yield of 1125 µg h-1 cm-2 . An in-depth understanding of catalytic mechanisms is gained by theoretical calculations.

High-Performance Electrochemical NO Reduction into NH3 by MoS2 Nanosheet.

Electrochemical reduction of NO not only offers an attractive alternative to the Haber-Bosch process for ambient NH3 production but mitigates the human-caused unbalance of nitrogen cycle. Herein, we report that MoS2 nanosheet on graphite felt (MoS2 /GF) acts as an efficient and robust 3D electrocatalyst for NO-to-NH3 conversion. In acidic electrolyte, such MoS2 /GF attains a maximal Faradaic efficiency of 76.6 % and a large NH3 yield of up to 99.6 µmol cm-2 h-1 . Using MoS2 nanosheet-loaded carbon paper as the cathode, a proof-of-concept device of Zn-NO battery was assembled to deliver a discharge power density of 1.04 mW cm-2 and an NH3 yield of 411.8 µg h-1 mgcat. -1 . Calculations reveal that the positively charged Mo-edge sites facilitate NO adsorption/activation via an acceptance-donation mechanism and disfavor the binding of protons and the coupling of N-N bond.

Hierarchical Tubular Architecture Constructed by Vertically Aligned CoS2 -MoS2 Nanosheets for Hydrogen Evolution Electrocatalysis.

Developing efficient electrocatalysts for the hydrogen evolution reaction (HER) is crucial for establishing a sustainable and environmentally friendly energy system, but it is still a challenging issue. Herein, hierarchical tubular-structured CoS2 -MoS2 /C as efficient electrocatalysts are fabricated through a unique metal-organic framework (MOF) mediated self-sacrificial templating. Core-shell structured MoO3 @ZIF-67 nanorods are used both as a precursor and a sacrificial template to form the one-dimensional tubular heterostructure where vertically aligned two-dimensional CoS2 -MoS2 nanosheets are formed on the MOF-derived carbon tube. Trace amounts of noble metals (Pd, Rh, and Ru) are successfully introduced to enhance the electrocatalytic property of the CoS2 -MoS2 /C nanocomposites. The as-synthesized hierarchical tubular heterostructures exhibit excellent HER catalytic performance owing to the merits of the hierarchical hollow architecture with abundantly exposed edges and the uniformly dispersed active sites. Impressively, the optimal Pd-CoS2 -MoS2 /C-600 catalyst delivers a current density of 10 mA cm-2 at a low overpotential of 144 mV and a small Tafel slope of 59.9 mV/dec in 0.5 m H2 SO4 . Overall, this MOF-mediated strategy can be extended to the rational design and synthesis of other hollow heterogeneous catalysts for scalable hydrogen generation.

Ni2P Nanosheets on Carbon Cloth: An Efficient Flexible Electrode for Sodium-Ion Batteries.

Transition-metal phosphides have been increasingly investigated because of their high theoretical specific capacity and low potential for sodium storage. Herein, we describe the development of Ni2P nanosheets on carbon cloth (Ni2P Ns/CC), which behaves as a flexible 3D anode for sodium-ion batteries. Such a Ni2P Ns/CC delivers a high capacity of 399 mA h g-1 at 0.2 A g-1. At 2 A g-1, it still delivers 72 mA h g-1 even after 1000 cycles. The impressive performance is attributed to such a self-supported structure. Moreover, a possible conversion reaction mechanism is also carefully revealed.

Biosynthesis of Novel Ag-Cu Bimetallic Nanoparticles from Leaf Extract of Salvia officinalis and Their Antibacterial Activity.

Bimetallic nanoparticles exhibit bifunctional or synergistic effects prevailing between two metals with the capabilities of enhanced electronic, catalytic, and optical properties. Green synthetic routes have gained tremendous interest because of the noninvolvement of toxic and harmful chemical reagents in preparation. Therefore, we develop bimetallic Ag-Cu nanoparticles (Ag-Cu NPs) through an eco-friendly and biocompatible preparation method. In this study, Ag-Cu NPs have been synthesized from leaf extracts of the commonly known sage, S. officinalis. The extract has a rich phytochemical composition, including bioreducing polyphenols, flavonoids, and capping/stabilizing agents. An array of well-known spectroscopic and microscopic techniques were used to characterize the as-prepared Ag-Cu bimetallic nanoparticles, including X-ray diffraction (XRD), ultraviolet-visible spectroscopy, Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy, transmission electron microscopy, and energy-dispersive X-ray spectroscopy. The size of the Ag-Cu NPs was found to be 50 nm with a spherical shape and an almost uniform distribution. The antibacterial effect was further evaluated using agar well diffusion and disc diffusion assays. Ag-Cu NPs exhibit antibacterial and antibiofilm properties against Gram-positive and Gram-negative bacteria strains. The minimum inhibitory concentration (MIC) of Ag-Cu NPs was between 5 g/mL and 15 g/mL. The Ag-Cu NPs inhibit biofilm formation at 25 g/mL and 50 g/mL. The results of biogenic Ag-Cu NPs provide novel antibacterial activity against Gram-positive and Gram-negative bacteria, as well as antibiofilm activity. Hence, Ag-Cu NPs might serve as a novel antibacterial agent with potential antibacterial and antibiofilm properties.

High-efficiency electroreduction of nitrite to ammonia on a Cu@TiO2 nanobelt array.

Electrochemical nitrite (NO2-) reduction is a potential and sustainable route to produce high-value ammonia (NH3), but it requires highly active electrocatalysts. Herein, Cu nanoparticles anchored on a TiO2 nanobelt array on a titanium plate (Cu@TiO2/TP) are reported as a high-efficiency electrocatalyst for NO2--to-NH3 conversion. The designed Cu@TiO2/TP catalyst exhibits outstanding catalytic performance toward the NO2-RR, with a high NH3 yield of 760.5 µmol h-1 cm-2 (237.7 µmol h-1 mgcat.-1) and an excellent faradaic efficiency of 95.3% in neutral solution. Meanwhile, it also presents strong electrochemical stability during cyclic tests and long-term electrolysis.

CoO nanoparticle decorated N-doped carbon nanotubes: a high-efficiency catalyst for nitrate reduction to ammonia.

Ambient electrochemical NO3- reduction is emerging as an appealing approach toward eliminating NO3- contaminants and generating NH3 simultaneously, but its efficiency is challenged by a lack of active and selective electrocatalysts. In this work, we report CoO nanoparticle decorated N-doped carbon nanotubes as an efficient catalyst for highly selective hydrogenation of NO3- to NH3. In 0.1 M NaOH electrolyte with 0.1 M NO3-, this catalyst is capable of achieving a large NH3 yield of up to 9041.6 ± 370.7 µg h-1 cm-2 and a high faradaic efficiency of 93.8 ± 1.5%, with excellent durability. Theoretical calculations reveal the catalytic mechanisms.

In Situ Derived Co2B Nanosheet Array: A High-Efficiency Electrocatalyst for Ambient Ammonia Synthesis via Nitrate Reduction.

Ambient ammonia synthesis via electrochemical nitrate (NO3-) reduction is regarded as a green alternative to the Haber-Bosch process. Herein, we report the in situ derivation of an amorphous Co2B layer on a Co3O4 nanosheet array on a Ti mesh (Co2B@Co3O4/TM) for efficient NH3 production via selective electroreduction of NO3- under ambient conditions. In 0.1 M PBS and 0.1 M NaNO3, Co2B@Co3O4/TM exhibits a maximum Faradaic efficiency of 97.0% at -0.70 V and a remarkable NH3 yield of 8.57 mg/h/cm2 at -1.0 V, with durability for stable NO3--to-NH3 conversion over eight recycling tests and 12 h of electrolysis. Additionally, it can be applied as an efficient cathode material for Zn-NO3- batteries to produce NH3 while generating electricity. The catalytic mechanisms on Co2B@Co3O4 are further revealed by theoretical calculations.

Co-NCNT nanohybrid as a highly active catalyst for the electroreduction of nitrate to ammonia.

Electrocatalytic nitrate (NO3-) reduction has emerged as an attractive dual-function strategy to produce ammonia (NH3) and simultaneously mitigate environmental issues. However, efficient electrocatalysts with high selectivity for NH3 synthesis are highly desired. In this work, we report the Co-NCNT nanohybrid as a highly active electrocatalyst towards NO3--to-NH3 conversion. In 0.1 M NaOH solution containing 0.1 M NO3-, the Co-NCNT catalyst is capable of attaining a large NH3 yield of 5996 µg h-1 cm-2 and a high faradaic efficiency of 92% at -0.6 V versus reversible hydrogen electrode. Moreover, it displays excellent electrochemical stability.

Co nanoparticle-decorated pomelo-peel-derived carbon enabled high-efficiency electrocatalytic nitrate reduction to ammonia.

Electrocatalytic nitrate reduction is a sustainable approach to produce ammonia and remediate water pollutant nitrate. Here, we show that Co nanoparticle-decorated pomelo-peel-derived carbon is an efficient electrocatalyst for nitrate reduction to ammonia with a faradaic efficiency of 90.1% and a yield of 1.1 mmol h-1 mgcat.-1.

A FeCo2O4 nanowire array enabled electrochemical nitrate conversion to ammonia.

Electrocatalytic nitrate (NO3-) reduction not only generates high-value ammonia (NH3) but holds significant potential in the control of NO3- contaminants in natural environments. Here, a bimetallic FeCo2O4 spinel nanowire array grown on carbon cloth is proposed as an efficient electrocatalyst for the conversion of NO3- to NH3 with a high faradaic efficiency of up to 95.9% and a large NH3 yield of 4988 µg h-1 cm-2. Furthermore, it also exhibits excellent stability during 16 h electrolysis.

N-doped carbon nanotubes supported CoSe2 nanoparticles: A highly efficient and stable catalyst for H2O2 electrosynthesis in acidic media.

Electrocatalytic oxygen reduction reaction (ORR) provides an attractive alternative to anthraquinone process for H2O2 synthesis. Rational design of earth-abundant electrocatalysts for H2O2 synthesis via a two-electron ORR process in acids is attractive but still very challenging. In this work, we report that nitrogen-doped carbon nanotubes as a multi-functional support for CoSe2 nanoparticles not only keep CoSe2 nanoparticles well dispersed but alter the crystal structure, which in turn improves the overall catalytic behaviors and thereby renders high O2-to-H2O2 conversion efficiency. In 0.1 M HClO4, such CoSe2@NCNTs hybrid delivers a high H2O2 selectivity of 93.2% and a large H2O2 yield rate of 172 ppm·h-1 with excellent durability up to 24 h. Moreover, CoSe2@NCNTs performs effectively for organic dye degradation via electro-Fenton process. Electronic Supplementary Material: Supplementary material (SEM images, EDX mapping images, XPS spectrum, XRD patterns, RRDE voltammogram, Tafel plots, cyclic voltammograms, UV-Vis spectra, and Tables S1) is available in the online version of this article at 10.1007/s12274-021-3474-0.

High-Efficiency Electrosynthesis of Ammonia with Selective Reduction of Nitrate in Neutral Media Enabled by Self-Supported Mn2CoO4 Nanoarray.

Ambient ammonia synthesis by electroreduction of nitrate (NO3-) provides us a sustainable and environmentally friendly alternative to the traditional Haber-Bosch process. In this work, Mn2CoO4 nanoarray grown on carbon cloth (Mn2CoO4/CC) serves as a superior electrocatalyst for efficient NH3 synthesis by selective reduction of NO3-. When operated in 0.1 M PBS with 0.1 M NaNO3, Mn2CoO4/CC reaches a high Faraday efficiency of 98.6% and a large NH3 yield up to 11.19 mg/h/cm2. Moreover, it exhibits excellent electrocatalytic stability. Theory calculations show that the Mn2CoO4 surface has strong interaction with NO3-, which can effectively inhibit the occurrence of hydrogen evolution, beneficial for NO3--to-NH3 conversion.

Ni nanoparticle-decorated biomass carbon for efficient electrocatalytic nitrite reduction to ammonia.

Electrocatalytic nitrite (NO2-) reduction to ammonia (NH3) can not only synthesize value-added NH3, but also remove NO2- pollutants from the environment. However, the low efficiency of NO2--to-NH3 conversion hinders its applications. Here, Ni nanoparticle-decorated juncus-derived biomass carbon prepared at 800 °C (Ni@JBC-800) serves as an efficient catalyst for NH3 synthesis by selective electroreduction of NO2-. This catalyst shows a remarkable NH3 yield of 4117.3 µg h-1 mgcat.-1 and a large faradaic efficiency of 83.4% in an alkaline electrolyte. The catalytic mechanism is further investigated by theoretical calculations.

Ultrathin single-crystal PtSe2 nanosheets for high-efficiency O2 electroreduction to H2O2.

Electrochemical synthesis of H2O2via a two-electron oxygen reduction reaction (2e- ORR) has emerged as a promising alternative to the anthraquinone process. However, the strong competition from the 4e- pathway severely limits its activity and selectivity, especially for Pt-based catalysts. Herein, ultrathin single-crystal PtSe2 nanosheets were successfully prepared via an in situ selenization process using commercial Pt/C as a precursor, demonstrating an exclusive 2e- ORR pathway compared to the 4e- pathway of commercial Pt/C, delivering a high H2O2 selectivity over a wide pH range (>80%, up to 94.1%). Furthermore, in situ infrared spectroscopy results revealed Pt as an active center, accompanied by the key intermediate OOH* adsorption and HOOH formation.