2D sp2 Carbon‐Conjugated Porphyrin Covalent Organic Framework for Cooperative Photocatalysis with TEMPO

2D covalent organic frameworks (COFs) are receiving ongoing attention in semiconductor photocatalysis. Herein, we present a photocatalytic selective chemical transformation by combining sp² carbon‐conjugated porphyrin‐based covalent organic framework (Por‐sp²c‐COF) photocatalysis with TEMPO catalysis illuminated by 623 nm red light‐emitting diodes (LEDs). Highly selective conversion of amines into imines was swiftly afforded in minutes. Specifically, the π‐conjugation of porphyrin linker leads to extensive absorption of red light; the sp² ?C=C? double bonds linkage ensures the stability of Por‐sp²c‐COF under high concentrations of amine. Most importantly, we found that crystalline framework of Por‐sp²c‐COF is pivotal for cooperative photocatalysis with (2,2,6,6‐tetramethylpiperidin‐1‐yl)oxyl (TEMPO). This work foreshadows that the outstanding hallmarks of COFs, particularly crystallinity, could be exploited to address energy and environmental challenges by cooperative photocatalysis.     

2D sp2 Carbon-Conjugated Porphyrin Covalent Organic Framework for Cooperative Photocatalysis with TEMPO

2D covalent organic frameworks (COFs) are receiving ongoing attention in semiconductor photocatalysis. Herein, we present a photocatalytic selective chemical transformation by combining sp² carbon-conjugated porphyrin-based covalent organic framework (Por-sp²c-COF) photocatalysis with TEMPO catalysis illuminated by 623 nm red light-emitting diodes (LEDs). Highly selective conversion of amines into imines was swiftly afforded in minutes. Specifically, the π-conjugation of porphyrin linker leads to extensive absorption of red light; the sp² −C=C− double bonds linkage ensures the stability of Por-sp²c-COF under high concentrations of amine. Most importantly, we found that crystalline framework of Por-sp²c-COF is pivotal for cooperative photocatalysis with (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO). This work foreshadows that the outstanding hallmarks of COFs, particularly crystallinity, could be exploited to address energy and environmental challenges by cooperative photocatalysis.     

Promoting electrochemical reduction of CO2 to ethanol by B/N-doped sp3/sp2 nanocarbon electrode

Electrochemical reduction of CO₂ to value-added chemicals holds promise for carbon utilization and renewable electricity storage. However, selective CO₂ reduction to multi-carbon fuels remains a significant challenge. Here, we report that B/N-doped sp³/sp² hybridized nanocarbon (BNHC), consisting of ultra-small nanoparticles with a sp³ carbon core covered by a sp² carbon shell, is an efficient electrocatalyst for electrochemical reduction of CO₂ to ethanol at relatively low overpotentials. CO₂ reduction occurs with a Faradaic efficiency of 58.8%-69.1% for ethanol and acetate production at ?0.5 ～ ?0.6 V (vs. RHE), among which 51.6%-56.0% is for ethanol. The high selectivity for ethanol is due to the integrated effect of sp³/sp² carbon and B/N doping. Both sp³ carbon and B/N doping contribute to enhanced ethanol production with sp² carbon reducing the overpotential for CO₂ reduction to ethanol.     

Y(OTf)3 catalyzed substitution dependent oxidative C(sp)–C(sp) cleavage and regioselective dehydration of β-allyl-β-hydroxydithioesters: alternate route to α,β-unsaturated ketones and functionalized dienes

β-Allyl-β-hydroxydithioesters have been generated by the regioselective Grignard addition to the β-oxodithioesters. They have been successfully employed in selective C(sp³)–C(sp³) bond cleavage to construct α,β-unsaturated ketone residues by the treatment of an emerging catalyst yttrium(III)triflate for the first time. On the other hand, hetaryl substituted β-allyl-β-hydroxydithioesters led to the useful diene precursors through selective dehydration under the similar conditions.     

Efficient Water Reduction with sp3‐sp3 Diboron(4) Compounds: Application to Hydrogenations,H–D Exchange Reactions,and Carbonyl Reductions

A series of crystalline sp³‐sp³ diboron(4) compounds were synthesized and shown to promote the facile reduction of water with dihydrogen formation. The application of these diborons as simple and effective dihydrogen and dideuterium sources was demonstrated by conducting a series of selective reductions of alkynes and alkenes, and hydrogen–deuterium exchange reactions using two‐chamber reactors. Finally, as the water reduction reaction generates an intermediate borohydride species, a range of aldehydes and ketones were reduced by using water as the hydride source.     

Efficient Water Reduction with sp3‐sp3 Diboron(4) Compounds: Application to Hydrogenations,H–D Exchange Reactions,and Carbonyl Reductions

A series of crystalline sp³‐sp³ diboron(4) compounds were synthesized and shown to promote the facile reduction of water with dihydrogen formation. The application of these diborons as simple and effective dihydrogen and dideuterium sources was demonstrated by conducting a series of selective reductions of alkynes and alkenes, and hydrogen–deuterium exchange reactions using two‐chamber reactors. Finally, as the water reduction reaction generates an intermediate borohydride species, a range of aldehydes and ketones were reduced by using water as the hydride source.     

Temperature-modulated selective C(sp3)–H or C(sp2)–H arylation through palladium catalysis

Transition metal-catalysed C–H bond functionalisations have been extensively developed in organic and medicinal chemistry. Among these catalytic approaches, the selective activation of C(sp³)–H and C(sp²)–H bonds is particularly appealing for its remarkable synthetic versatility, yet it remains highly challenging. Herein, we demonstrate the first example of temperature-dependent selective C–H functionalisation of unactivated C(sp³)–H or C(sp²)–H bonds at remote positions through palladium catalysis using 7-pyridyl-pyrazolo[1,5-a]pyrimidine as a new directing group. At 120 °C, C(sp³)–H arylation was triggered by the chelation of a rare [6,5]-fused palladacycle, whereas at 140 °C, C(sp²)–H arylation proceeded instead through the formation of a 16-membered tetramer containing four 7-pyridyl-pyrazolo[1,5-a]pyrimidine–palladium chelation units. The subsequent mechanistic study revealed that both C–H activations shared a common 6-membered palladacycle intermediate, which was then directly transformed to either the [6,5]-fused palladacycle for C(sp³)–H activation at 120 °C or the tetramer for C(sp²)–H arylation at 140 °C with catalytic amounts of Pd(OAc)₂ and AcOH. Raising the temperature from 120 °C to 140 °C can also convert the [6,5]-fused palladacycle to the tetramer with the above-mentioned catalysts, hence completing the C(sp²)–H arylation ultimately.

Unprecedented 16-membered tetramer or [6,5]-fused palladacycle, mutually shadowboxing-like transformed from the shared common intermediate, accomplishes the Pd-catalysed temperature-dependent selective arylation of C(sp²)–H or C(sp³)–H.     

Understanding active chlorine species production using boron doped diamond films with lower and higher sp3/sp2 ratio

The present study was motivated by the reports that promote the use of boron doped diamond (BDD) anode for electrochemical disinfection. The discussion about the production of undesirable active chlorine species on diamond films is still open. For this reason, the influence of sp³/sp² ratio on the performance on the evolution of chlorine-related species was investigated by polarization and electrolytic techniques in order to establish whether their formation and consumption related to either chemical or electrochemical reactions. The results demonstrated that dissolved Cl₂, ClO₂⁻, ClO₂, ClO₃⁻ and ClO₄⁻ species can be electrochemically formed at both BDD electrodes. However, the concentration trends are different, indicating that the relation of sp³/sp² ratio has a key role in the electrochemical route to produce ClO₃⁻ and ClO₄⁻.     

Synthesis of sp2-Iminosugar Selenoglycolipids as Multitarget Drug Candidates with Antiproliferative,Leishmanicidal and Anti-Inflammatory Properties

sp²-Iminosugar glycolipids (sp²-IGLs) represent a consolidated family of glycoconjugate mimetics encompassing a monosaccharide-like glycone moiety with a pseudoamide-type nitrogen replacing the endocyclic oxygen atom of carbohydrates and an axially-oriented lipid chain anchored at the pseudoanomeric position. The combination of these structural features makes them promising candidates for the treatment of a variety of conditions, spanning from cancer and inflammatory disorders to parasite infections. The exacerbated anomeric effect associated to the putative sp²-hybridized N-atom imparts chemical and enzymatic stability to sp²-IGLs and warrants total α-anomeric stereoselectivity in the key glycoconjugation step. A variety of O-, N-, C- and S-pseudoglycosides, differing in glycone configurational patterns and lipid nature, have been previously prepared and evaluated. Here we expand the chemical space of sp²-IGLs by reporting the synthesis of α-d-gluco-configured analogs with a bicyclic (5N,6O-oxomethylidene)nojirimycin (ONJ) core incorporating selenium at the glycosidic position. Structure–activity relationship studies in three different scenarios, namely cancer, Leishmaniasis and inflammation, convey that the therapeutic potential of the sp²-IGLs is highly dependent, not only on the length of the lipid chain (linear aliphatic C₁₂ vs. C₈), but also on the nature of the glycosidic atom (nitrogen vs. sulfur vs. selenium). The ensemble of results highlights the α-dodecylseleno-ONJ-glycoside as a promising multitarget drug candidate.     

Hydrogen chemisorption on carbon structure with mixed sp2–sp3 hybridization: empirical potential studies

Hydrogen storage is a key technology for the advancement of hydrogen and fuel cell power technologies in transportation, stationary, and portable applications. The currents state of art shows that there is no existing material which could be used as efficient storage medium. In this paper we present a new concept of a non-conventional engineering storage solution. It is based on the recent theoretical and experimental discoveries which show existence of a new meta-stable phase of graphite with mixed sp²–sp³ hybridization called diaphite. By means of the molecular dynamics calculations with adaptive intermolecular reactive empirical bond order potential empirical potential we show that the increase of the hydrogen-carbon binding energy on diaphite is related to the transformation of local bonds geometry from sp² hybridization to sp³. We propose and discuss a scenario of fully reversible photo-stimulated process of adsorption/desorption of hydrogen on/of diaphite.     

Direct C(sp2)C(sp3) Cross‐Coupling of Diaryl Zinc Reagents with Benzylic,Primary, Secondary,and Tertiary Alkyl Halides

The direct C(sp²)? C(sp³) cross‐coupling of diaryl zinc reagents with benzylic, primary, secondary, and tertiary alkyl halides proceeded in the absence of coordinating ethereal solvents at ambient temperature without the addition of a catalyst. The C(sp²)? C(sp³) cross‐coupling showed excellent functional‐group tolerance, and products were isolated in high yields, generally without the requirement for purification by chromatography. This process represents an expedient, operationally simple method for the construction of new C(sp²)? C(sp³) bonds.     

Direct C(sp2)?C(sp3) Cross‐Coupling of Diaryl Zinc Reagents with Benzylic,Primary, Secondary,and Tertiary Alkyl Halides

The direct C(sp²) C(sp³) cross‐coupling of diaryl zinc reagents with benzylic, primary, secondary, and tertiary alkyl halides proceeded in the absence of coordinating ethereal solvents at ambient temperature without the addition of a catalyst. The C(sp²) C(sp³) cross‐coupling showed excellent functional‐group tolerance, and products were isolated in high yields, generally without the requirement for purification by chromatography. This process represents an expedient, operationally simple method for the construction of new C(sp²) C(sp³) bonds.     

Internal Peptide Late‐Stage Diversification: Peptide‐Isosteric Triazoles for Primary and Secondary C(sp3)−H Activation

Secondary C(sp³)?H arylations were accomplished by palladium catalysis with triazoles as peptide bond isosteres. The unique power of this approach is highlighted by the possibility of achieving secondary C(sp³)?H functionalizations on terminal peptides as well as the unprecedented positional‐selective C(sp³)?H functionalization of internal peptide positions, setting the stage for modular peptide late‐stage diversification.     

Iron and Manganese Catalysts for the Selective Functionalization of Arene C(sp2)−H Bonds by Carbene Insertion

The first examples of the direct functionalization of non‐activated aryl sp² C?H bonds with ethyl diazoacetate (N₂CHCO₂Et) catalyzed by Mn‐ or Fe‐based complexes in a completely selective manner are reported, with no formation of the frequently observed cycloheptatriene derivatives through competing Buchner reaction. The best catalysts are Fe^II or Mn^II complexes bearing the tetradentate pytacn ligand (pytacn= 1‐(2‐pyridylmethyl)‐4,7‐dimethyl‐1,4,7‐triazacyclononane). When using alkylbenzenes, the alkylic C(sp³)?H bonds of the substituents remained unmodified, thus the reaction being also selective toward functionalization of sp² C?H bonds.     

BODIPY Peptide Labeling by Late‐Stage C(sp3)−H Activation

Late‐stage BODIPY diversification of structurally complex amino acids and peptides was accomplished by racemization‐free palladium‐catalyzed C(sp³)?H activation. Transformative fluorescence modification proved viable by triazole‐assisted C(sp³)?H arylation in a chemo‐ and site‐selective fashion, providing modular access to novel BODIPY peptide sensors.     

Regioselective Vinylation of Remote Unactivated C(sp3)−H Bonds: Access to Complex Fluoroalkylated Alkenes

Regioselective incorporation of a particular functional group into aliphatic sites by direct activation of unreactive C?H bonds is of great synthetic value. Despite advances in radical‐mediated functionalization of C(sp³)?H bonds by a hydrogen‐atom transfer process, the site‐selective vinylation of remote C(sp³)?H bonds still remains underexplored. Reported herein is a new protocol for the regioselective vinylation of unactivated C(sp³)?H bonds. The remote C(sp³)?H activation is promoted by a C‐centered radical instead of the commonly used N and O radicals. The reaction possesses high product diversity and synthetic efficiency, furnishing a plethora of synthetically valuable E alkenes bearing tri‐/di‐/mono‐fluoromethyl and perfluoroalkyl groups.     

Hybrid Nanocarbon as a Catalyst for Direct Dehydrogenation of Propane: Formation of an Active and Selective Core–Shell sp2/sp3 Nanocomposite Structure

Hybrid nanocarbon, comprised of a diamond core and a graphitic shell with a variable sp²‐/sp³‐carbon ratio, is controllably obtained through sequential annealing treatment (550–1300 °C) of nanodiamond. The formation of sp² carbon increases with annealing temperature and the nanodiamond surface is reconstructed from amorphous into a well‐ordered, onion‐like carbon structure via an intermediate composite structure—a diamond core covered by a defective, curved graphene outer shell. Direct dehydrogenation of propane shows that the sp²‐/sp³‐nanocomposite exhibits superior catalytic performance to that of individual nanodiamond and graphitic nanocarbon. The optimum catalytic activity of the diamond/graphene composite depends on the maximum structural defectiveness and high chemical reactivity of the ketone groups. Ketone‐type functional groups anchored on the defects/vacancies are active for propene formation; nevertheless, once the oxygen functional groups are desorbed, the defects/vacancies alone might be active sites responsible for the C?H bond activation of propane.     

One-Pot Synthesis of Primary and Secondary Aliphatic Amines via Mild and Selective sp3 C−H Imination

The direct replacement of sp³ C−H bonds with simple amine units (−NH₂) remains synthetically challenging, although primary aliphatic amines are ubiquitous in medicinal chemistry and natural product synthesis. We report a mild and selective protocol for preparing primary and secondary aliphatic amines in a single pot, based on intermolecular sp³ C−H imination. The first C−H imination of diverse alkanes, this method shows useful site-selectivity within substrates bearing multiple sp³ C−H bonds. Furthermore, this reaction tolerates polar functional groups relevant for complex molecule synthesis, highlighted in the synthesis of amine pharmaceuticals and amination of natural products. We characterize a unique C−H imination mechanism based on radical rebound to an iminyl radical, supported by kinetic isotope effects, stereoablation, resubmission, and computational modeling. This work constitutes a selective method for complex amine synthesis and a new mechanistic platform for C−H amination.     

Practical Catalytic Cleavage of C(sp3)−C(sp3) Bonds in Amines

The selective cleavage of thermodynamically stable C(sp³)?C(sp³) single bonds is rare compared to their ubiquitous formation. Herein, we describe a general methodology for such transformations using homogeneous copper‐based catalysts in the presence of air. The utility of this novel methodology is demonstrated for C_α?C_β bond scission in >70 amines with excellent functional group tolerance. This transformation establishes tertiary amines as a general synthon for amides and provides valuable possibilities for their scalable functionalization in, for example, natural products and bioactive molecules.     

NiH‐Catalyzed Reductive Relay Hydroalkylation: A Strategy for the Remote C(sp3)−H Alkylation of Alkenes

The terminal‐selective, remote C(sp³)?H alkylation of alkenes was achieved by a relay process combining NiH‐catalyzed hydrometalation, chain walking, and alkylation. This method enables the construction of unfunctionalized C(sp³)?C(sp³) bonds under mild conditions from two simple feedstock chemicals, namely olefins and alkyl halides. The practical value of this transformation is further demonstrated by the large‐scale and regioconvergent alkylation of isomeric mixtures of olefins at low catalyst loadings.