This contribution described the chemoselective reduction of secondary carboxamides to aldimines. To perform such challenging transformation, we reported a catalyzed hydrosilylation using Fe(CO)4(IMes) [IMes=1,3-bis (2,4,6-trimethylphenyl) imidazol-2ylidene] as the catalyst, diphenylsilane as the reductant under UV irradiation (365 nm) at room temperature for 16 h. Aldimines were then obtained, after a basic quench, in 40-83% isolated yields. This transformation was unprecedented at iron.

Industrial chemical production largely relies on fossil fuels, resulting in the unavoidable release of carbon dioxide (CO2) into the atmosphere. The concept of a circular carbon bioeconomy has been proposed to address this issue, wherein CO2 is captured and used as raw material for manufacturing new chemicals. Microbial cell factories and, in particular, autotrophic microorganisms capable of utilizing CO2 as the sole carbon source, emerged as potential catalysts for upcycling CO2 to valuable products. The Calvin-Benson-Bassham cycle (CBBc), the best-known CO2 fixation pathway, is widely distributed in Nature. While extensively studied, microbial engineering programmes based on the CBBc remains relatively underexplored. In this review, we discuss avenues towards biotechnological exploitation of the CBBc to engineer CO2-utilizing microbial cell factories, with a focus on chemically-derived electron donors. We also highlight the advantages and challenges of implementing the CBBc in heterotrophic microbial hosts and its potential to advance a true circular carbon bioeconomy. Moreover, based on the pathway’s architecture, we argue about the ideal value-added products to generate from this metabolic route. Studying and engineering the CBBc in both natural- and synthetic-autotrophs will enhance our understanding on this CO2 fixation pathway, enabling further exploration of biomanufacturing avenues with CO2 as feedstock.

Organonitrogen compounds are of vital importance to our lives.   For almost all organonitrogen compounds, ammonia is only the feedstock as a nitrogen source.   Ammonia is produced from dinitrogen (N2) and dihydrogen (H2) by the Haber-Bosch process, which consumes an enormous amount of energy.   As an alternative method to convert N2 into organonitrogen compounds under milder conditions, various stoichiometric reactions with transition metal complexes have been explored for the last 50 years.   However, the field of catalytic formation of organonitrogen compounds directly from N2 with transition metal complexes is still in its infancy.   This short review summarizes strategies to achieve the direct synthesis of organonitrogen compounds from N2 under mild reaction conditions using transition metal complexes ranging from stoichiometric reactions to catalytic reactions.

A simple and efficient route to achieve excellent yield and well-ordered PLAs and PCLs through the ROP of cyclic esters using bimetallic and monometallic aluminum complexes supported by functionalized P−N ligands under mild conditions.

Abstract

Described herein is an efficient ring-opening polymerization (ROP) of rac-lactide and ϵ-caprolactone (ϵ-CL) using novel bimetallic and monometallic aluminum complexes supported by functionalized P−N ligands. All the aluminum complexes were seen to be active catalysts in the ROP of both rac-lactide and ϵ-CL in toluene at 60 °C. Bimetallic aluminum complex, [Al(Me)₂{Ph₂P(Se)N(CH₂)₂N−(CH₂CH₂)₂O}(AlMe₃)] containing an uncoordinated Se atom and an auxiliary Al atom within the proximity of another central Al cation was observed to exhibit the highest catalytic activity among all the catalysts studied. Kinetic experiments, comparing bimetallic and related monometallic complexes revealed that bimetallic cooperativity among the two metallic centers in bimetallic complex plays an essential role in driving such superior reactivity. We synthesized several isoselective polylactides (PLAs) and polycaprolactones (PCLs) with controlled molecular weights and narrow molecular weight distributions and characterized by ¹H, ¹³C NMR, DSC and TGA.

An efficient heterogeneous 1 % Cuβ zeolite catalyzed double hydroamination of terminal alkynes for the synthesis of 2,3-dihydroquinazolin-4(1H)-ones is achieved in a solvent-free environment. This method offers an appealing approach to a number of di-substituted quinazolinones with decent to excellent yields.

Abstract

An effective and novel heterogeneous beta zeolite supported CuO (Cuβ) catalyzed double hydroamination of alkynes for the synthesis of 2,3-dihydroquinazolin-4(1H)-ones has been achieved in a solvent-free condition. Cuβ zeolite was synthesized by impregnation method. The synthesized Cuβ was characterized by X-ray diffraction, Fourier transformation infrared spectroscopy, transmission electron microscopy, scanning electron microscopy, and X-ray photoelectron spectroscopy. Pure Hβ (18 % yield) or Nano CuO (44 % yield) displayed poor catalytic activity, whereas 1 % Cuβ (96 % yield) showed higher catalytic activity for double hydroamination of alkynes due to the synergistic effect of CuO and Hβ zeolite in the reaction. The new protocol offers an appealing approach to a number of di-substituted quinazolinones with decent to excellent yields. The catalyst has been successfully recycled for up to 5 consecutive cycles.

Electrooxidation: β-Ni(OH)₂ petal-like nanosheets was synthesized by facile stepwise electrodeposition. It was found that the β- Ni(OH)₂ has superior ability to electrooxidize 5-hydroxymethylfurfural (HMF) due to its better lattice matching with substrate intrinsic electrocatalytic activity, as well as the adsorption of HMF. It achieves a 2,5-furandicarboxylic acid (FDCA) yield of 80.6 % under 30 mA/cm² in industrial electrolysis mode.

Abstract

The electrocatalytic selective oxidation of 5-hydroxymethylfurfural (HMF) presents a highly efficient and eco-friendly method for biomass utilization. Herein, we synthesized pure β-Ni(OH)₂ and amorphous Ni(OH)₂ on nickel foam (NF) using a facile stepwise electrodeposition technique and evaluated their catalytic performances for the oxidation of HMF to 2,5-furan dicarboxylic acid (FDCA). The β-Ni(OH)₂ nanosheets-decorated electrode (β-NiNS/NF) exhibited excellent interfacial lattice matching with the substrate nickel, resulting in enhanced electron transfer at the catalyst-substrate interface, as confirmed by electrochemical analysis. Consequently, the β-NiNS/NF electrode displayed improved intrinsic electrocatalytic activity and interfacial stability. Additionally, it demonstrated effective HMF adsorption capability. These advantageous properties led to enhanced HMF conversion, selectivity, and structural stability. Notably, the β-NiNS/NF electrode achieved an unprecedented FDCA yield of 80.6 % under relatively large current density galvanostatic electrolysis commonly used in industry. Moreover, our investigation identified a novel possible oxidation pathway during HMF electrocatalysis. This study not only showcases an efficient and scalable synthetic approach but also highlights the potential of the β-NiNS/NF electrode for industrial HMF electrocatalytic oxidation under conditions involving relatively large applied currents.

Methylation of PNP pincer arms has emerged as a new versatile tool to control steric hindrance and disable metal-ligand cooperative or ligand-centered reactivity. This Concept describes applications of the methylation approach in the control of catalytic activity and selectivity in hydrogenation, hydroboration and semihydrogenation, with Ru and Fe complexes.

Abstract

The widespread use of pyridine-based PNP pincer ligands has inspired the concept of metal-ligand cooperation (MLC), in which the reactivity at the deprotonated CH₂ (or NH) arm of the ligand is proposed to play an important role. Several groups developed a family of PNP-type pincer ligands with methylated arms which were initially introduced to test the effect of blocking MLC in catalysis, but eventually led to unexpected consequences such as stabilization of unusual oxidation states, beneficial catalytic activity, or selectivity. Analysis of the sterics imposed by introducing Me groups revealed that arm protection can be an efficient tool to control sterics around the metal as an alternative to phosphine substitution, leading to much greater steric hinderance above and below pincer's coordination plane. This Concept will describe several illustrative examples which contrast the reactivity of classical CH₂/NH-arm PNP pincers with their CMe₂/NMe-armed counterparts, in particular related to Ru-catalyzed alcohol dehydrogenative coupling, Fe-catalyzed hydrogenation, hydroboration, and alkyne semihydrogenation.

Boosting Mo₃S₄ catalysts towards H₂ production: A protocol for formic acid dehydrogenation assisted by biomimetic Mo₃S₄ clusters has been developed. Experiments and theoretical calculations pinpoint to the formate substitution products as the catalytically active species. Remarkably, the highest activity for a Mo-based homogeneous catalysts is reported.

Abstract

Formic acid is considered as a promising hydrogen storage material in the context of a green hydrogen economy. In this work, we present a series of aminophosphino and imidazolylamino Mo₃S₄ cuboidal clusters which are active and selective for formic acid dehydrogenation (FAD). Best results are obtained with the new [Mo₃S₄Cl₃(edⁱp_rp)₃](BPh₄) (4(BPh₄)) (edⁱp_rp=(2-(diisopropylphosphino)ethylamine)) cluster, which is prepared through a simple ligand exchange process from the Mo₃S₄Cl₄(PPh₃)₃(H₂O)₂ precursor. Under the conditions investigated, complex 4 ⁺ showed significantly improved performance (TOF=4048 h⁻¹ and 3743 h⁻¹ at 120 °C in propylene carbonate using N,N-dimethyloctylamine as base after 10 min and 15 min, respectively) compared to the other reported molybdenum compounds. Mechanistic investigations based on stoichiometric and catalytic experiments show that cluster 4 ⁺ reacts with formic acid in the presence of a base to form formate substituted species [Mo₃S₄Cl_3-x(OCOH)_x(edⁱp_rp)₃]⁺ (x=1–3) from which the catalytic cycle starts. Subsequently, formate decarboxylation of the partially substituted [Mo₃S₄Cl_3-x(OCOH)_x(edⁱp_rp)₃]⁺ (x=1, 2, 3) catalyst through a β-hydride transfer to the metal generates the trinuclear Mo₃S₄ cluster hydride. Dehydrogenation takes place through protonation by HCOOH to form Mo−H⋅⋅⋅HCOOH dihydrogen adducts, with regeneration of the Mo₃S₄ formate cluster. This proposal has been validated by DFT calculations.

A series of thermally exfoliated g-C₃N₄ (eg-C₃N₄) have been synthesized under various gas conditions (air/N₂) and then applied as catalyst supports to load Pd nanoparticles. In the solvent-free atmospheric selective oxidation of benzyl alcohol, 2.5Pd/eg-C₃N₄-AN catalyst afforded benzyl alcohol conversion and selectivity to benzaldehyde of 88 % and 92 %, respectively.

Abstract

Solvent-free atmospheric selective oxidation of benzyl alcohol (BZA) by molecular oxygen is a promising and green process for the synthesis of benzaldehyde (BZL). Supported Pd nanoparticles have been widely reported in the catalytic selective oxidation of BZA where the activity depends on the chemical valence and dispersion of the Pd nanoparticles. Herein, a series of thermally exfoliated g-C₃N₄ (eg-C₃N₄) have been synthesized under various gas conditions (air/N₂) and then applied as catalyst supports to load Pd nanoparticles. The physicochemical properties of the prepared Pd/eg-C₃N₄ materials have been characterized by N₂ adsorption–desorption, XRD, FT-IR, UV-vis, XPS, and TEM. Pd nanoparticles dispersed well on the supports, and the distributions of Pd and nitrogen species of the catalysts were related to the gas conditions of the supports. In the selective oxidation of BZA, 2.5Pd/eg-C₃N₄-AN catalyst afforded conversion of BZA and the selectivity to BZL of 88 % and 92 %, respectively. The metallic Pd⁰ species are considered the catalytic sites of Pd/eg-C₃N₄ in the catalytic reaction and meanwhile, the basic N_b species of eg-C₃N₄ were beneficial to the overall activity of the catalyst.

G-quadruplexes (G-4) mediated asymmetric sulfoxidation: Asymmetric sulfoxidations were performed utilizing native or modified G-4-forming nucleic acids as chiral inductors, providing proof that asymmetric reactions can occur at distinct sites of the biomolecule, yielding different enantiomers.

Abstract

Catalysis using G-quadruplexes (G-4) has shown promise as a way to perform asymmetric sulfoxidation of thioanisole derivatives. However, despite the relative simplicity of G-4, the mechanism of chiral control of sulfoxidation is still unknown, mainly because G-4 can adopt different topologies. To better understand the mechanism of G-4-catalyzed sulfoxidation, G-4 was chemically constrained into a unique topology. It was shown that either sulfoxidation can occur at the outer tetrads or at the grooves of G-4 and that different enantiomers can be generated depending on the region where catalysis occurs. By means of these G-4 mimics, the enantioselective control of the sulfoxidation reaction was unraveled.