Chemo-, Stereo- and Regioselective Fluoroallylation/Annulation of Hydrazones with gem-Difluorocyclopropanes via Tunable Palladium/NHC Catalysis

Defluorinative manipulation of polyfluorinated molecules has shown great promise due to its granting of synthetic versatility to inert C−F bonds. The development of chemo-, stereo- and regioselective strategies to realize highly efficient formation of either the linear/branched or E/Z products from gem-difluorocyclopropanes (gem-F₂CPs) is a challenging task. Herein, we have realized palladium/NHC-catalyzed fluoroallylation/annulation of hydrazones with gem-F₂CPs that incorporate the hydrazone N₂ moiety into the products. The thermodynamically unstable fluorinated E-allylation products with aryl ketone hydrazones were obtained for the first time, while the di-alkyl ketone hydrazones yielded the monofluorinated products with branched selectivity under similar reaction conditions. With aldehyde hydrazones, two kinds of pyrazoles were obtained via a defluorinative allylation/annulation cascade, in which different carbon atoms of gem-F₂CPs could be incorporated into the pyrazole rings regiospecifically. DFT calculations revealed that the divergent selectivity was kinetically controlled and the final C−C bond formation proceeded through a 7-membered TS.     

Palladium-Catalyzed Enantio- and Regioselective Ring-Opening Hydrophosphinylation of Methylenecyclopropanes

Transition metal-catalyzed hydrofunctionalization of methylenecyclopropanes (MCPs) has presented a considerable challenge due to the difficult manipulation of regioselectivity and complicated reaction patterns. Herein, we report a straightforward Pd-catalyzed ring-opening hydrophosphinylation reaction of MCPs via highly selective C−C bond cleavage. This method allows for rapid and efficient access to a wide range of chiral allylic phosphine oxides in good yields and high enantioselectivities. Additionally, density functional theory (DFT) calculations were performed to elucidate the reaction mechanism and the origin of enantioselectivity.     

Deacylative Thiolation by Redox-Neutral Aromatization-Driven C−C Fragmentation of Ketones

Herein we report the development of deacylative thiolation of diverse methyl ketones. The reaction is redox-neutral, and heavy-metal-free, which provides a new way to introduce thioether groups site-specifically to unactivated aliphatic positions. It also features excellent functional group tolerance and broad substrate scope, thus allowing late-stage derivatization. The process benefits from efficient condensation between the activation reagent and ketone substrates, which triggers aromatization-driven C−C fragmentation and rapid radical coupling with thiosulfonates. Experimental and computational mechanistic studies suggest the involvement of a radical chain pathway.     

Boron-Centered Lewis Superacid through Redox-Active Ligands: Application in C−F and S−F Bond Activation

A series of redox-responsive ferrocenyl-substituted boranes and boronic esters were synthesized. Oxidation of the ferrocenyl ligand to the ferrocenium resulted in a drastic increase in the Lewis acidity beyond the strength of SbF₅, which was investigated experimentally and computationally. The resulting highly Lewis acidic boron compounds were used for catalytic C−F and S−F bond activation.     

Selective Four-Electron Reduction of Oxygen by a Nonheme Heterobimetallic CuFe Complex

We report herein the first nonheme CuFe oxygen reduction catalyst ([Cu^II(bpbp)(μ-OAc)₂Fe^III]²⁺, CuFe−OAc ), which serves as a functional model of cytochrome c oxidase and can catalyze oxygen reduction to water with a turnover frequency of 2.4×10³ s⁻¹ and selectivity of 96.0 % in the presence of Et₃NH⁺. This performance significantly outcompetes its homobimetallic analogues (2.7 s⁻¹ of CuCu−OAc with %H₂O₂ selectivity of 98.9 %, and inactive of FeFe−OAc ) under the same conditions. Structure-activity relationship studies, in combination with density functional theory calculation, show that the CuFe center efficiently mediates O−O bond cleavage via a Cu^II(μ-η¹ : η²-O₂)Fe^III peroxo intermediate in which the peroxo ligand possesses distinctive coordinating and electronic character. Our work sheds light on the nature of Cu/Fe heterobimetallic cooperation in oxygen reduction catalysis and demonstrates the potential of this synergistic effect in the design of nonheme oxygen reduction catalysts.     

Efficient Photocatalytic Cleavage of Lignin Models by a Soluble Perylene Diimide/Carbon Nitride S-Scheme Heterojunction

3,4,9,10-Perylenetetracarboxylic dianhydride (PDI) is one of the best n-type organic semiconductors and an ideal light-driven catalyst for lignin depolymerization. However, the charge localization effect and the excessively strong intermolecular aggregation trend in PDI result in rapid electron-hole (e⁻−h⁺) recombination, which limits photocatalytic performance. Herein, polymeric carbon nitride/polyhedral oligomeric silsesquioxane PDI (p-CN/P-PDI) S-scheme heterojunction photocatalyst was prepared by the solvent evaporation-deposition method for C−C bond selective cleavage of lignin β-O-4 model. Based on the material characterization results, the synergic role of polyhedral oligomeric silsesquioxane (POSS) and S-scheme heterojunction maintains appropriate aggregation domains, achieves better solar light utilization, faster charge-transfer efficiency, and greater redox capacity. Notably, the 3 % p-CN/P-PDI heterostructure exhibits a remarkable enhancement in cleavage conversion efficiency, achieving approximately 16.42 and 2.57 times higher conversion rates compared to polyhedral oligomeric silsesquioxane modified PDI (POSS-PDI) and polymeric carbon nitride (p-CN), respectively.     

Reversible Boron-Insertion into Aromatic C−C Bonds

Formation of borabicyclo[3.2.0]heptadiene derivatives was achieved via boron-insertion into aromatic C−C bonds in the photo-promoted skeletal rearrangement reaction of triarylboranes bearing an ortho-phosphino substituent (ambiphilic phosphine-boranes). The borabicyclo[3.2.0]heptadiene derivatives were fully characterized by NMR and X-ray analyses. The dearomatized products were demonstrated to undergo the reverse reaction in the dark at room temperature, realizing photochemical and thermal interconversion between triarylboranes and boron-doped bicyclic systems. Experimental and theoretical studies revealed that sequential two electrocyclic reactions involving E/Z-isomerization of an alkene moiety proceed via a highly strained trans-borepin intermediate.     

Trifluoromethylation of Carbonyl and Unactivated Olefin Derivatives by C(sp3)−C Bond Cleavage

Herein, we report a Cu-mediated trifluoromethylation of carbonyl-type compounds and unactivated olefins enabled by visible-light irradiation via σ C(sp³)−C bond-functionalization. The reaction is distinguished by its modularity, mild conditions and wide scope—even in the context of late-stage functionalization—thus offering a complementary approach en route to valuable C(sp³)−CF₃ architectures from easily accessible precursors.     

Direct C−C Double Bond Cleavage of Alkenes Enabled by Highly Dispersed Cobalt Catalyst and Hydroxylamine

The utilization of a single-atom catalyst to break C−C bonds merges the merits of homogeneous and heterogeneous catalysis and presents an intriguing pathway for obtaining high-value-added products. Herein, a mild, selective, and sustainable oxidative cleavage of alkene to form oxime ether or nitrile was achieved by using atomically dispersed cobalt catalyst and hydroxylamine. Diversified substrate patterns, including symmetrical and unsymmetrical alkenes, di- and tri-substituted alkenes, and late-stage functionalization of complex alkenes were demonstrated. The reaction was successfully scaled up and demonstrated good performance in recycling experiments. The hot filtration test, catalyst poisoning and radical scavenger experiment, time kinetics, and studies on the reaction intermediate collectively pointed to a radical mechanism with cobalt/acid/O₂ promoted C−C bond cleavage as the key step.     

Merging Manganese and Iminium Catalysis: Selective Hydroalkenylation of Unsaturated Aldehydes and Ketones

The use of synergistic catalytic strategy can usually circumvent the intrinsic limitations of one catalytic system. In this communication, we disclose a cooperative catalysis strategy of manganese and iminium catalysis to realize selective hydroalkenylation of unsaturated aldehydes and ketones. Its success stems from the LUMO activation of unsaturated carbonyl compounds with secondary amines as the organocatalyst and the synergistic HOMO activation of alkenylboronic acids with Mn₂(CO)₈Br₂. This protocol exhibits several synthetic advances, e.g., simple operation, good functional group compatibility and good regioselectivity. The theoretical calculation indicates the migratory insertion followed by demetallation-isomerization process is kinetically more favorable than Michael-like nucleophilic addition. The use of proline-derived organocatalyst can deliver the desired products in moderate enantioselectivity.     

Thioethers as Dichotomous Electrophiles for Site-Selective Silylation via C−S Bond Cleavage

The development of aryl alkyl sulfides as dichotomous electrophiles for site-selective silylation via C−S bond cleavage has been achieved. Iron-catalyzed selective cleavage of C(aryl)−S bonds can occur in the presence of β-diketimine ligands, and the cleavage of C(alkyl)−S bonds can be achieved by t-BuONa without the use of transition metals, resulting in the corresponding silylated products in moderate to excellent yields. Mechanistic studies suggest that Fe−Si species may undergo metathesis reactions during the cleavage of C(aryl)−S bonds, while silyl radicals are involved during the cleavage of C(alkyl)−S bonds.     

A Cooperative Rhodium/Secondary Phosphine Oxide [Rh/P(O)nBu2] Template for Catalytic Hydrodefluorination of Perfluoroarenes

The selective activation of C−F bonds under mild reaction conditions remains an ongoing challenge of bond activation. Here, we present a cooperative [Rh/P(O)nBu₂] template for catalytic hydrodefluorination (HDF) of perfluoroarenes. In addition to substrates presenting electron-withdrawing functional groups, the system showed an exceedingly rare tolerance for electron-donating functionalities and heterocycles. The high chemoselectivity of the catalyst and its readiness to be deployed at a preparative scale illustrate its practicality. Empirical mechanistic studies and a density functional theory (DFT) study have identified a rhodium(I) dihydride complex as a catalytically relevant species and the determining role of phosphine oxide as a cooperative fragment. Altogether, we demonstrate that molecular templates based on these design elements can be assembled to create catalysts with increased reactivity for challenging bond activations.     

An Efficient Direct Arylation Polycondensation via C−S Bond Cleavage

The direct arylation polycondensation (DArP) has become one of the most important methods to construct conjugated polymers (CPs). However, the homocoupling side-reactions of aryl halides and the low regioseletive reactivities of unfunctionalized aryls hinder the development of DArP. Here, an efficient Pd and Cu co-catalyzed DArP was developed via inert C−S bond cleavage of aryl thioethers, of which robustness was exemplified by over twenty conjugated polymers (CPs), including copolymers, homopolymers, and random polymers. The capture of oxidative addition intermediate together with experimental and theoretic results suggested the important role of palladium (Pd) and copper (Cu) co-catalysis with a bicyclic mechanism. The studies of NMR, molecular weights, trap densities, two-dimensional grazing-incidence wide-angle X-ray scattering (2D-GIWAXS), and the charge transport mobilities revealed that the homocoupling reactions were significantly suppressed with high regioselectivity of unfunctionalized aryls, suggesting this method is an excellent choice for synthesizing high performance CPs.     

Electrooxidative Activation of B−B Bond in B2cat2: Access to gem-Diborylalkanes via Paired Electrolysis

This report describes the unprecedented electrooxidation of a solvent (e.g., DMF)-ligated B₂cat₂ complex, whereby a solvent-stabilized boryl radical is formed via quasi-homolytic cleavage of the B−B bond in a DMF-ligated B₂cat₂ radical cation. Cyclic voltammetry and density functional theory provide evidence to support this novel B−B bond activation strategy. Furthermore, a strategy for the electrochemical gem-diborylation of gem-bromides via paired electrolysis is developed for the first time, affording a range of versatile gem-diborylalkanes, which are widely used in synthetic society. Notably, this reaction approach is scalable, transition-metal-free, and requires no external activator.     

Cationic Rhodium(I) Tetrafluoroborate Catalyzed Intramolecular Carbofluorination of Alkenes via Acyl Fluoride C−F Bond Activation**

The C−F bond of acyl fluorides can be cleaved and added across tethered alkenes in the presence of a cationic rhodium(I) tetrafluoroborate catalyst. This 1,2-carbofluorination reaction offers a powerful method for the synthesis of tertiary alkyl fluoride derivatives with an atom economy of 100 %. Mechanistic studies indicate that the concerted action of a rhodium cation and a tetrafluoroborate anion is key for the success of this catalytic cleavage and formation of C−F bonds in a controlled manner.     

Oxidatively Induced Selective Carbon-Carbon Bond Formation From Isolated Rhodium(III) Complexes

This work focuses on oxidatively induced regioselective intramolecular C−C bond formations based on the Rh^III complexes synthesized from dirhodium(II) trifluoroacetate with 2-arylpyridines. With the selection of electron-donating groups on the arene rings of 2-arylpyridines, the unusual meta-ortho C−C bond-forming was favored, which led to the formation of meta-substituted 2-arylpyridine homocoupling dimers. On the contrary, the electron-withdrawing groups have tendency to occur conventional ortho-ortho bond-forming, resulting in the formation of new Rh^III complexes possessing the intriguing Rh^III(TFA)₃ fragment. Preliminary mechanistic experiments suggest that the sequential oxidation of Rh^III occurred in the reaction.     

Visible-Light-Induced N-Heterocyclic Carbene-Catalyzed Single Electron Reduction of Mono-Fluoroarenes

Fluoroarenes are abundant and readily available feedstocks. However, due to the high reduction potentials of mono-fluoroarenes, their photoreduction remains a continuing challenge, motivating the development of efficient activation modes to address this issue. This report presents the blue light-induced N-heterocyclic carbene (NHC)-catalyzed single electron reduction of mono-fluoroarenes for biaryl cross-couplings. We discovered that under blue light irradiation, NHC/tBuOK combination could construct powerful photoactive architectures to promote single electron transfer for C_aryl−F bond reduction via forming highly reducing NHC radical anion. Notably, the strategy was also successful to reduce C_aryl−O, C_aryl−N, and C_aryl−S bonds for biaryl cross-couplings.     

N-(Morpholine-4-dithio)phthalimide: A Shelf-Stable,Bilateral Platform Molecule Enabling Access to Diverse Unsymmetrical Disulfides**

Synthetic methods for unsymmetrical disulfides are greatly needed owing to their applications in drug discovery, linker chemistry, and materials sciences. In this study, a new shelf-stable and easy-to-prepare bilateral disulfurating platform molecule, N-(morpholine-4-dithio)phthalimide, has been developed for the divergent synthesis of unsymmetrical disulfides. The amino and imide leaving groups of this reagent can be orthogonally transformed. Under acidic conditions, the amino moiety undergoes selective protonation and thus can be displaced by various carbon nucleophiles, such as allyl trimethylsilanes, alkynyl silanes, and electron-rich arenes, leaving the phthalimide moiety untouched. Meanwhile, the phthalimide leaving group is amenable to substitution under basic or neutral conditions. The combination of these transformations provides rapid access to diverse unsymmetrical disulfides through two C−S bond-forming reactions.     

Nickel-Catalyzed Selective C(sp2)−F Bond Alkylation of Industrially Relevant Hydrofluoroolefin HFO-1234yf

The selective transition-metal catalyzed C−F bond functionalization of inexpensive industrial fluorochemicals represents one of the most attractive approaches to valuable fluorinated compounds. However, the selective C(sp²)−F bond carbofunctionalization of refrigerant hydrofluoroolefins (HFOs) remains challenging. Here, we report a nickel-catalyzed selective C(sp²)−F bond alkylation of HFO-1234yf with alkylzinc reagents. The resulting 2-trifluoromethylalkenes can serve as a versatile synthon for diversified transformations, including the anti-Markovnikov type hydroalkylation and the synthesis of bioactive molecule analogues. Mechanistic studies reveal that lithium salt is essential to promote the oxidative addition of Ni⁰(L_n) to the C−F bond; the less electron-rich N-based ligands, such as bipyridine and pyridine-oxazoline, feature comparable or even higher oxidative addition rates than the electron-rich phosphine ligands; the strong σ-donating phosphine ligands, such as PMe₃, are detrimental to transmetallation, but the less electron-rich and bulky N-based ligands, such as pyridine-oxazoline, facilitate transmetallation and reductive elimination to form the final product.     

Versatile Reaction Pathways of 1,1,3,3,3-Pentafluoropropene at Rh(I) Complexes [Rh(E)(PEt3)3] (E=H,GePh3, Si(OEt)3, F,Cl): C-F versus C-H Bond Activation Steps

The reaction of the rhodium(I) complexes [Rh(E)(PEt₃)₃] (E=GePh₃ ( 1 ), H ( 6 ), F ( 7 )) with 1,1,3,3,3-pentafluoropropene afforded the defluorinative germylation products Z/E-2-(triphenylgermyl)-1,3,3,3-tetrafluoropropene and the fluorido complex [Rh(F)(CF₃CHCF₂)(PEt₃)₂] ( 2 ) together with the fluorophosphorane E-(CF₃)CH=CF(PFEt₃). For [Rh(Si(OEt)₃)(PEt₃)₃] ( 4 ) the coordination of the fluoroolefin was found to give [Rh{Si(OEt)₃}(CF₃CHCF₂)(PEt₃)₂] ( 5 ). Two equivalents of complex 2 reacted further by C−F bond oxidative addition to yield [Rh(CF=CHCF₃)(PEt₃)₂(μ-F)₃Rh(CF₃CHCF₂)(PEt₃)] ( 9 ). The role of the fluorido ligand on the reactivity of complex 2 was assessed by comparison with the analogous chlorido complex. The use of complexes 1 , 4 and 6 as catalysts for the derivatization of 1,1,3,3,3-pentafluoropropene provided products, which were generated by hydrodefluorination, hydrometallation and germylation reactions.