Palladium-catalyzed asymmetric allylic alkylation (AAA) with alkyl sulfones as nucleophiles

An efficient palladium-catalyzed AAA reaction with a simple α-sulfonyl carbon anion as nucleophiles is presented for the first time. Allyl fluorides are used as superior precursors for the generation of π-allyl complexes that upon ionization liberate fluoride anions for activation of silylated nucleophiles. With the unique bidentate diamidophosphite ligand ligated palladium as catalyst, the in situ generated α-sulfonyl carbon anion was quickly captured by the allylic intermediates, affording a series of chiral homo-allylic sulfones with high efficiency and selectivity. This work provides a mild in situ desilylation strategy to reveal nucleophilic carbon centers that could be used to overcome the pK_a limitation of “hard” nucleophiles in enantioselective transformations.

A variety of “hard” α-sulfonyl carbanions of aryl, heteroaryl and alkyl sulfones were successfully employed as nucleophiles in palladium-catalyzed asymmetric allylic alkylation with excellent enantioselectivities.     

Diboramacrocycles: reversible borole dimerisation–dissociation systems

We report that the outcome of the tin–boron exchange reaction of a mixed thiophene-benzo-fused stannole with aryldibromoboranes is associated with the steric bulk of the aryl substituent of the borane reagent, leading to either boroles or large diboracycles as products. NMR spectroscopic studies indicate that the two products can reversibly interconvert in solution, and mechanistic density functional theory (DFT) calculations reveal boroles to be intermediates in the formation of the diboracyclic products. The addition of Lewis bases to the diboracycles leads to the corresponding borole adducts, demonstrating that they react as “masked” boroles. Additionally, the reaction of the title compounds with a series of organic azides affords complex heteropropellanes, formally 2 : 1 borole-azide adducts, that deviate from the usual BN aromatic compounds formed via nitrogen atom insertion into the boroles.

Diboramacrocycles are a new form of borole dimers, participating in various addition reactions as “masked” boroles. The reaction of a less crowded diboramacrocycle with organic azides affords unprecedented complex heteropropellanes.     

An electrochemical modification strategy to fabricate NiFeCuPt polymetallic carbon matrices on nickel foam as stable electrocatalysts for water splitting

Electrochemical modification is a mild and economical way to prepare electrocatalytic materials with abundant active sites and high atom efficiency. In this work, a stable NiFeCuPt carbon matrix deposited on nickel foam (NFFeCuPt) was fabricated with an extremely low Pt load (∼28 μg cm⁻²) using one-step electrochemical co-deposition modification, and it serves as a bifunctional catalyst for overall water splitting and achieves 100 mA cm⁻² current density at a low cell voltage of 1.54 V in acidic solution and 1.63 V in alkaline solution, respectively. In addition, a novel electrolyte was developed to stabilize the catalyst under acidic conditions, which provides inspiration for the development of highly efficient, highly stable, and cost-effective ways to synthesize electrocatalysts.

Multiple metal elements immobilized into a carbon matrix to fabricate an ultra-stable water splitting electrocatalyst by one-step electrochemical modification.     

Molecular planting of a single organothiol into a “gap-site” of a 2D patterned adlayer in an electrochemical environment

The self-assembled inclusion of molecules into two-dimensional (2D) porous networks on surfaces has been extensively studied because 2D functional materials consisting of organic molecules have become an important research topic. However, the isolation of a single molecular thiol remains a challenging goal. Here, we report a method of planting and isolating organothiols onto a 2D patterned organic adlayer at an electrochemical interface. In situ scanning tunneling microscopy revealed that the phase transition of an ovalene adlayer is electrochemically induced and that the gap site created by three ovalene molecules serves as a 2D molecular template to isolate thiol molecules and to standardize the distance between them via the formation of precise selective open spaces, suggesting that electrochemical “molecular planting” opens applications for 2D patterns of isolated single organothiol molecules.

Gap sites electrochemically created in the ovalene adlayer can accept a single thiol.     

Ligand-redox assisted nickel catalysis toward stereoselective synthesis of (n+1)-membered cycloalkanes from 1,n-diols with methyl ketones

A well-defined, bench-stable nickel catalyst is presented here, that can facilitate double alkylation of a methyl ketone to realize a wide variety of cycloalkanes. The performance of the catalyst depends on the ligand redox process comprising an azo-hydrazo couple. The source of the bis electrophile in this double alkylation is a 1,n-diol, so that (n+1)-membered cycloalkanes can be furnished in a stereoselective manner. The reaction follows a cascade of dehydrogenation/hydrogenation reactions and adopts a borrowing hydrogen (BH) method. A thorough mechanistic analysis including the interception of key radical intermediates and DFT calculations supports the ligand radical-mediated dehydrogenation and hydrogenation reactions, which is quite rare in BH chemistry. In particular, this radical-promoted hydrogenation is distinctly different from conventional hydrogenations involving a metal hydride and complementary to the ubiquitous two-electron driven dehydrogenation/hydrogenation reactions.

A homogeneous nickel catalyst is described that forms (n+1)-membered cycloalkane rings from ketones and 1,n-diols following a radical-promoted pathway.     

Highly effective and chemoselective hydrodeoxygenation of aromatic alcohols

Effective hydrodeoxygenation (HDO) of aromatic alcohols is very attractive in both conventional organic synthesis and upgrading of biomass-derived molecules, but the selectivity of this reaction is usually low because of the competitive hydrogenation of the unsaturated aromatic ring and the hydroxyl group. The high activity of noble metal-based catalysts often leads to undesired side reactions (e.g., saturation of the aromatic ring) and excessive hydrogen consumption. Non-noble metal-based catalysts suffer from unsatisfied activity and selectivity and often require harsh reaction conditions. Herein, for the first time, we report chemoselective HDO of various aromatic alcohols with excellent selectivity, using porous carbon–nitrogen hybrid material-supported Co catalysts. The C–OH bonds were selectively cleaved while leaving the aromatic moiety intact, and in most cases the yields of targeted compounds reached above 99% and the catalyst could be readily recycled. Nitrogen doping on the carbon skeleton of the catalyst support (C–N matrix) significantly improved the yield of the targeted product. The presence of large pores and a high surface area also improved the catalyst efficiency. This work opens the way for efficient and selective HDO reactions of aromatic alcohols using non-noble metal catalysts.

Porous carbon–nitrogen hybrid material-supported Co catalysts can effectively promote the chemoselective hydrodeoxygenation reaction of a various of aromatic alcohols in ethanol and hydrogen atmosphere, under relatively mild conditions.     

Site-selective amination and/or nitrilation via metal-free C(sp2)–C(sp3) cleavage of benzylic and allylic alcohols

Benzylic/allylic alcohols are converted via site-selective C(sp²)–C(sp³) cleavage to value-added nitrogenous motifs, viz., anilines and/or nitriles as well as N-heterocycles, utilizing commercial hydroxylamine-O-sulfonic acid (HOSA) and Et₃N in an operationally simple, one-pot process. Notably, cyclic benzylic/allylic alcohols undergo bis-functionalization with attendant increases in architectural complexity and step-economy.

Benzylic/allylic alcohols are converted via site-selective C(sp²)–C(sp³) cleavage to value-added nitrogenous motifs, viz., anilines and/or nitriles as well as N-heterocycles, utilizing commercial hydroxylamine-O-sulfonic acid (HOSA) and Et₃N in an operationally simple, one-pot process.     

Free three-dimensional carborane carbanions

Carbon atom functionalization via generation of carbanions is the cornerstone of carborane chemistry. In this work, we report the synthesis and structural characterization of free ortho-carboranyl [C₂B₁₀H₁₁]⁻, a three-dimensional inorganic analog of the elusive phenyl anion that features a “naked” carbanion center. The first example of a stable, discrete C(H)-deprotonated carborane anion was isolated as a completely separated ion pair with a crown ether-encapsulated potassium cation. An analogous approach led to the isolation and structural characterization of a doubly deprotonated 1,1′-bis(o-carborane) anion [C₂B₁₀H₁₀]₂²⁻, which is the first example of a discrete molecular dicarbanion. These reactive carbanions are key intermediates in carbon vertex chemistry of carborane clusters.

Free three-dimensional carborane carbanions, which are inorganic siblings of deprotonated aryls with the “naked” anionic carbon atom are reported.     

Controlling cyclization pathways in palladium(ii)-catalyzed intramolecular alkene hydro-functionalization via substrate directivity

We report a series of palladium(ii)-catalyzed, intramolecular alkene hydrofunctionalization reactions with carbon, nitrogen, and oxygen nucleophiles to form five- and six-membered carbo- and heterocycles. In these reactions, the presence of a proximal bidentate directing group controls the cyclization pathway, dictating the ring size that is generated, even in cases that are disfavored based on Baldwin''s rules and in cases where there is an inherent preference for an alternative pathway. DFT studies shed light on the origins of pathway selectivity in these processes.

We report a series of palladium(ii)-catalyzed, intramolecular alkene hydrofunctionalization reactions with carbon, nitrogen, and oxygen nucleophiles to form five- and six-membered carbo- and heterocycles.     

Uncommon carbene insertion reactions

Transition-metal-catalysed carbene insertion reaction is a straightforward and efficient protocol for the construction of carbon–carbon or carbon–heteroatom bonds. Compared to the intensively studied and well-established “common” carbene insertion reactions, including carbene insertion into C–H, Si–H, N–H, O–H, and S–H bonds, several “uncommon” carbene insertion reactions, including carbene insertion into B–H, Sn–H, Ge–H, P–H, F–H, C–C, and M–M bonds, have been neglected for a long time. However, more and more studies on uncommon carbene insertion reactions have been disclosed recently, and clearly demonstrate the great synthetic potential of these reactions. The current perspective reviews the history and the newest advances of uncommon carbene insertion reactions, discusses their potential applications and challenges, and also presents an outlook of this promising field.

Transition-metal-catalysed carbene insertion reaction is a straightforward and efficient protocol for the construction of carbon–carbon or carbon–heteroatom bonds.     

Cold-catalytic antitumor immunity with pyroelectric black phosphorus nanosheets

Catalytic nanomedicine with the innate features of catalysts brings incomparable properties to biomedicine over traditional drugs. The temperature-dependent activity of catalysts provides catalytic nanomedicines with a facile strategy to control their therapeutic performance. Tuning catalytic nanomedicine by cold treatment (4–37 °C) is safe and desired for practical applications, but there is a lack of cold-catalytic platforms. Herein, with black phosphorus (BP) as a model pyroelectric nanocatalyst, we explored the potential of cold-catalysts for antitumor therapy. BP nanosheets with pyro-catalytic activity catalyze the generation of oxidative stress to activate antitumor immunity under cold treatment. Due to the cold-catalytic immunomodulation, immune memory was successfully achieved to prevent tumor metastasis and recurrence. Considering the safety and conductive depth (>10 mm) of cold in the body, pyroelectric nanocatalysts open up exciting opportunities for the development of cold-catalytic nanomedicine.

Cold-catalytic nanomedicine and the concept of cold-catalytic immunotherapy are explored with black phosphorus as a model cold catalyst.     

Enhancement of Chiroptical Responses of trans‐Bis[(β‐iminomethyl)naphthoxy]platinum(II) Complexes with Distorted Square Planar Coordination Geometry

Invited for this month''s cover picture are the groups of Masahiro Ikeshita and Takashi Tsuno at Nihon University and Yoshitane Imai at Kindai University (Japan). The cover picture shows the comparison of circularly polarized luminescence (CPL) properties of square planar platinum(II) complexes with different coordination geometry. Computational studies have been carried out to investigate these structure‐dependencies, and revealed that the distortion of the coordination geometry results into an enhancement the chiroptical responses of these compounds. Read the full text of their Research Article at 10.1002/open.202100277.

“… How does the stereochemistry of transition metal complexes affect their photophysical properties…” Find out more about the story behind the front cover research at 10.1002/open.202100277.     

Non-metal with metal behavior: metal-free coordination-insertion ring-opening polymerization

The “coordination-insertion” ring-opening polymerization (ROP) mechanism has so far been the monopoly of metal catalysts. In this work, we present a metal-free “coordination-insertion” ROP of trimethylene carbonate (TMC) and ε-caprolactone (ε-CL), as well as their sequential block copolymerization, with N-trimethylsilyl-bis (trifluoromethanesulfonyl)imide (TMSNTf₂) as the non-metallic initiator/catalyst. TMSNTf₂ was proposed to work through an unprecedented metal-free “coordination-insertion” mechanism, which involves the coordination of monomer to the Si atom of TMSNTf₂, the nucleophilic attack of the –NTf₂ group on the coordinated monomer, and the cleavage of the acyl–oxygen bond of the monomer. The proposed metal-free “coordination-insertion” ROP was studied by NMR, SEC, and MALDI-TOF analyses. In addition, the TMSNTf₂-mediated ROP of TMC and ε-CL led to linear and cyclic polymers following two-stage first-order polymerization processes, as evidenced by structural analyses and kinetics study, which further demonstrated the metal-free “coordination-insertion” mechanism.

The first metal-free “coordination-insertion” ROP of cyclic carbonate and lactones mediated by N-trimethylsilyl-bis(trifluoromethanesulfonyl)imide (TMSNTf₂) was proposed, which in the past was exclusively the monopoly of metal complex catalysts.     

A general strategy for the synthesis of α-trifluoromethyl- and α-perfluoroalkyl-β-lactams via palladium-catalyzed carbonylation

β-Lactam compounds play a key role in medicinal chemistry, specifically as the most important class of antibiotics. Here, we report a novel one-step approach for the synthesis of α-(trifluoromethyl)-β-lactams and related products from fluorinated olefins, anilines and CO. Utilization of an advanced palladium catalyst system with the Ruphos ligand allows for selective cycloaminocarbonylations to give diverse fluorinated β-lactams in high yields.

β-Lactam compounds play a key role in medicinal chemistry, specifically as the most important class of antibiotics.     

Enhanced photoreduction of water catalyzed by a cucurbit[8]uril-secured platinum dimer

A cucurbit[8]uril (CB[8])-secured platinum terpyridyl chloride dimer was used as a photosensitizer and hydrogen-evolving catalyst for the photoreduction of water. Volumes of produced hydrogen were up to 25 and 6 times larger than those obtained with the corresponding free and cucurbit[7]uril-bound platinum monomer, respectively, at equal Pt concentration. The thermodynamics of the proton-coupled electron transfer from the Pt(ii)–Pt(ii) dimer to the corresponding Pt(ii)–Pt(iii)–H hydride key intermediate, as quantified by density functional theory, suggest that CB[8] secures the Pt(ii)–Pt(ii) dimer in a particularly reactive conformation that promotes hydrogen formation.

The cucurbit[8]uril macrocycle can secure a platinum terpyridyl complex into a particularly reactive dimer that catalyzes the photoreduction of water.     

Molecularly engineered AIEgens with enhanced quantum and singlet-oxygen yield for mitochondria-targeted imaging and photodynamic therapy

Luminogens characteristic of aggregation-induced emission (AIEgens) have been extensively exploited for the development of imaging-guided photodynamic therapeutic (PDT) agents. However, intramolecular rotation of donor–acceptor (D–A) type AIEgens favors non-radiative decay of photonic energy which results in unsatisfactory fluorescence quantum and singlet oxygen yields. To address this issue, we developed several molecularly engineered AIEgens with partially “locked” molecular structures enhancing both fluorescence emission and the production of triplet excitons. A triphenylphosphine group was introduced to form a D–A conjugate, improving water solubility and the capacity for mitochondrial localization of the resulting probes. Experimental and theoretical analyses suggest that the much higher quantum and singlet oxygen yield of a structurally “significantly-locked” probe (LOCK-2) than its “partially locked” (LOCK-1) and “unlocked” equivalent (LOCK-0) is a result of suppressed AIE and twisted intramolecular charge transfer. LOCK-2 was also used for the mitochondrial-targeting, fluorescence image-guided PDT of liver cancer cells.

Luminogens characteristic of aggregation-induced emission (AIEgens) have been engineered for the development of imaging-guided photodynamic therapeutic (PDT) agents.     

Direct air capture of CO2via crystal engineering

This article presents a perspective view of the topic of direct air capture (DAC) of carbon dioxide and its role in mitigating climate change, focusing on a promising approach to DAC involving crystal engineering of metal–organic and hydrogen-bonded frameworks. The structures of these crystalline materials can be easily elucidated using X-ray and neutron diffraction methods, thereby allowing for systematic structure–property relationships studies, and precise tuning of their DAC performance.

A perspective view of direct air capture (DAC) of CO₂ and its role in mitigating climate change is presented. The article focuses on a promising approach to DAC involving crystal engineering of metal–organic and hydrogen-bonded frameworks.     

Support stabilized PtCu single-atom alloys for propane dehydrogenation

PtCu single-atom alloys (SAAs) open an extensive prospect for heterogeneous catalysis. However, as the host of SAAs, Cu suffers from severe sintering at elevated temperature, resulting in poor stability of catalysts. This paper describes the suppression of the agglomeration of Cu nanoparticles under high temperature conditions using copper phyllosilicate (CuSiO₃) as the support of PtCu SAAs. Based on quasi in situ XPS, in situ CO-DRIFTS, in situ Raman spectroscopy and in situ XRD, we demonstrated that the interfacial Cu⁺–O–Si formed upon reduction at 680 °C serves as the adhesive between Cu nanoparticles and the silicon dioxide matrix, strengthening the metal–support interaction. Consequently, the resistance to sintering of PtCu SAAs was improved, leading to high catalytic stability during propane dehydrogenation without sacrificing conversion and selectivity. The optimized PtCu SAA catalyst achieved more than 42% propane conversion and 93% propylene selectivity at 580 °C for at least 30 hours. It paves a way for the design and development of highly active supported single-atom alloy catalysts with excellent thermal stability.

This paper describes PtCu single-atom alloys supported on copper phyllosilicate via Cu⁺–O–Si. The catalyst exhibits sintering resistance in propane dehydrogenation reaction without sacrificing activity and selectivity.     

Kinetic effects of molecular clustering and solvation by extended networks in zeolite acid catalysis

Reactions catalyzed within porous inorganic and organic materials and at electrochemical interfaces commonly occur at high coverage and in condensed media, causing turnover rates to depend strongly on interfacial structure and composition, collectively referred to as “solvent effects”. Transition state theory treatments define how solvation phenomena enter kinetic rate expressions, and identify two distinct types of solvent effects that originate from molecular clustering and from the solvation of such clusters by extended solvent networks. We review examples from the recent literature that investigate reactions within microporous zeolite catalysts to illustrate these concepts, and provide a critical appraisal of open questions in the field where future research can aid in developing new chemistry and catalyst design principles.

“Solvent effects” at interfaces in heterogeneous catalysts are described by transition state theory treatments that identify kinetic regimes associated with molecular clustering and the solvation of such clusters by extended molecular networks.     

Combining palladium and ammonium halide catalysts for Morita–Baylis–Hillman carbonates of methyl vinyl ketone: from 1,4-carbodipoles to ion pairs

Here we report that Morita–Baylis–Hillman carbonates from diverse aldehydes and methyl vinyl ketones can be directly utilised as palladium-trimethylenemethane 1,4-carbodipole-type precursors, and both reactivity and enantioselectivity are finely regulated by adding a chiral ammonium halide as the ion-pair catalyst. The newly assembled intermediates, proposed to contain an electronically neutral π-allylpalladium halide complex and a reactive compact ion pair, efficiently undergo asymmetric [4 + 2] annulations with diverse activated alkenes or isatins, generally with high regio-, diastereo- and enantio-selectivity, and even switchable regiodivergent or diastereodivergent annulations can be well realised by tuning the substrate or catalyst assemblies. An array of control experiments, including UV/Vis absorption study and density functional theory calculations, are conducted to rationalise this new double activation mode combining a palladium complex and an ammonium halide as an ion-pair catalyst.

A double activation catalytic system combining a palladium complex and an ammonium halide was developed to promote the asymmetric [4 + 2] annulations of Morita–Baylis–Hillman carbonates of methyl vinyl ketone.