Selective Activation of the C−H Bond in Methane by Single Platinum Atomic Anions

Mass spectrometric analysis of the anionic products of interaction between platinum atomic anions, Pt^?, and methane, CH₄ and CD₄, in a collision cell shows the preferred generation of [PtCH₄]^? and [PtCD₄]^? complexes and a low tendency toward dehydrogenation. [PtCH₄]^? is shown to be H?Pt?CH₃^? by a synergy between anion photoelectron spectroscopy and quantum chemical calculations, implying the rupture of a single C?H bond. The calculated reaction pathway accounts for the observed selective activation of methane by Pt^?. This study presents the first example of methane activation by a single atomic anion.     

Catalytic Reaction Rates Controlled by Metal Oxidation State: C−H Bond Cleavage in Methane over Nickel‐Based Catalysts

The role of low concentrations of carbon complexes in hydrocarbon decomposition over transition metal surfaces has been a topic of much debate over the past decades. It is also a mystery as to whether or not electric fields can enhance hydrocarbon conversion in an electrochemical device at lower than normal reforming temperatures. To provide a “bottom‐up” fundamental insight, C−H bond cleavage in methane over Ni‐based catalysts was investigated. Our theoretical results show that the presence of carbon or carbide‐like species at the interface between the Ni cluster and its metal‐oxide support, as well as the application of an external positive electric field, can significantly increase the Ni oxidation state. Furthermore, the first C−H bond cleavage in methane is favored as the local oxidation state of Ni increases. Thus, the presence of a low concentration of carbon species, or the addition of a positive electric field will improve the hydrocarbon activation process.     

Selective C−H Functionalization of Methane and Ethane by a Molecular SbV Complex

Owing to the strong nonpolar bonds involved, selective C?H functionalization of methane and ethane to esters remains a challenge for molecular homogeneous chemistry. We report that the computationally predicted main‐group p‐block Sb^V(TFA)₅ complex selectively functionalizes the C?H bonds of methane and ethane to the corresponding mono and/or diol trifluoroacetate esters at 110–180 °C with yields for ethane of up to 60 % with over 90 % selectivity. Experimental and computational studies support a unique mechanism that involves Sb^V‐mediated C?H activation followed by functionalization of a Sb^V‐alkyl intermediate.     

Hydrogen Bond Directed ortho‐Selective C−H Borylation of Secondary Aromatic Amides

Reported is an iridium catalyst for ortho‐selective C?H borylation of challenging secondary aromatic amide substrates, and the regioselectivity is controlled by hydrogen‐bond interactions. The BAIPy ‐Ir catalyst forms three hydrogen bonds with the substrate during the crucial activation step, and allows ortho‐C?H borylation with high selectivity. The catalyst displays unprecedented ortho selectivities for a wide variety of substrates that differ in electronic and steric properties, and the catalyst tolerates various functional groups. The regioselective C?H borylation catalyst is readily accessible and converts substrates on gram scale with high selectivity and conversion.     

Iridium‐Catalyzed Direct C−H Amidation Polymerization: Step‐Growth Polymerization by C−N Bond Formation via C−H Activation to Give Fluorescent Polysulfonamides

We report a powerful strategy for activation of C−H bonds to produce polysulfonamides by an atom‐economical and green method using iridium‐catalyzed direct C−H amidation polymerization (DCAP). After screening various directing groups, additives, silver salts, concentrations, and temperatures to optimize DCAP, high‐molecular‐weight (up to 149 kDa) and defect‐free polysulfonamides were synthesized from various bis‐sulfonyl azides. Although these polymers do not have conventional fluorescent conjugated cores, they emit blue light with large Stokes shifts and high quantum yields upon photoexcitation owing to an excited‐state intramolecular proton‐transfer process.     

Diastereoselective C−H Bond Amination for Disubstituted Pyrrolidines

We report herein the improved diastereoselective synthesis of 2,5‐disubstituted pyrrolidines from aliphatic azides. Experimental and theoretical studies of the C−H amination reaction mediated by the iron dipyrrinato complex (^AdL)FeCl(OEt₂) provided a model for diastereoinduction and allowed for systematic variation of the catalyst to enhance selectivity. Among the iron alkoxide and aryloxide catalysts evaluated, the iron phenoxide complex exhibited superior performance towards the generation of syn 2,5‐disubstituted pyrrolidines with high diastereoselectivity.     

An Annulative Synthetic Strategy for Building Triphenylene Frameworks by Multiple C−H Bond Activations

C−H activation is a versatile tool for appending aryl groups to aromatic systems. However, heavy demands on multiple catalytic cycle operations and site‐selectivity have limited its use for graphene segment synthesis. A Pd‐catal‐ yzed one‐step synthesis of functionalized triphenylene frameworks is disclosed, which proceeds by 2‐ or 4‐fold C−H arylation of unactivated benzene derivatives. A Pd₂(dibenzylideneacetone)₃ catalytic system, using cyclic diaryliodonium salts as π‐extending agents, leads to site‐selective inter‐ and intramolecular tandem arylation sequences. Moreover, N ‐substituted triphenylenes are applied to a field‐effect transistor sensor for rapid, sensitive, and reversible alcohol vapor detection.     

Photoinduced Remote Functionalisations by Iminyl Radical Promoted C−C and C−H Bond Cleavage Cascades

A photoinduced cascade strategy leading to a variety of differentially functionalised nitriles and ketones has been developed. These reactions rely on the oxidative generation of iminyl radicals from simple oximes. Radical transposition by C(sp³)−(sp³) and C(sp³)−H bond cleavage gives access to distal carbon radicals that undergo S_H2 functionalisations. These mild, visible‐light‐mediated procedures can be used for remote fluorination, chlorination, and azidation, and were applied to the modification of bioactive and structurally complex molecules.     

A Cobalt(I) Pincer Complex with an η2‐Caryl−H Agostic Bond: Facile C−H Bond Cleavage through Deprotonation,Radical Abstraction,and Oxidative Addition

The synthesis and reactivity of a Co^I pincer complex [Co(ϰ³P,CH,P‐P(CH)P^NMe‐iPr)(CO)₂]⁺ featuring an η²‐ C_aryl−H agostic bond is described. This complex was obtained by protonation of the Co^I complex [Co(PCP^NMe‐iPr)(CO)₂]. The Co^III hydride complex [Co(PCP^NMe‐iPr)(CNtBu)₂(H)]⁺ was obtained upon protonation of [Co(PCP^NMe‐iPr)(CNtBu)₂]. Three ways to cleave the agostic C−H bond are presented. First, owing to the acidity of the agostic proton, treatment with pyridine results in facile deprotonation (C−H bond cleavage) and reformation of [Co(PCP^NMe‐iPr)(CO)₂]. Second, C−H bond cleavage is achieved upon exposure of [Co(ϰ³P,CH,P‐P(CH)P^NMe‐iPr)(CO)₂]⁺ to oxygen or TEMPO to yield the paramagnetic Co^II PCP complex [Co(PCP^NMe‐iPr)(CO)₂]⁺. Finally, replacement of one CO ligand in [Co(ϰ³P,CH,P‐P(CH)P^NMe‐iPr)(CO)₂]⁺ by CNtBu promotes the rapid oxidative addition of the agostic η²‐C_aryl−H bond to give two isomeric hydride complexes of the type [Co(PCP^NMe‐iPr)(CNtBu)(CO)(H)]⁺.     

Concise Synthesis of Polysubstituted Carbohelicenes by a C−H Activation/Radical Reaction/C−H Activation Sequence

Disclosed herein is the merging of C?H activation and radical chemistry, enabling rapid access to a structurally diverse family of fused carbohelicenes through the fusion of α‐acetylnaphthalenes with alkynes under oxidative conditions. This cascade process exhibits exquisite chemoselectivity and regioselectivity. The reaction pathway was analyzed by intermediate separations, control experiments, radical trapping, EPR, MALDI‐TOF‐MS, and ESI‐HRMS experiments, and shown to involve a C2?H activation/radical reaction/C8?H activation relay.     

Copper‐Mediated Decarboxylative Coupling of Benzamides with ortho‐Nitrobenzoic Acids by Directed C−H Cleavage

A copper‐mediated decarboxylative coupling of benzamides with ortho ‐nitrobenzoic acids by 8‐aminoquinoline‐directed C−H cleavage has been developed. This reaction proceeds smoothly with only a copper salt to produce the corresponding biaryl compounds in good yields. The products can be easily transformed into various nitrogen‐containing heterocyclic compounds. Moreover, the combination of copper and a suitable base promotes a decarboxylative C−H arylation and cyclization sequence to deliver phenanthridinone derivatives in one pot.     

Ruthenium‐Catalyzed para‐Selective C−H Alkylation of Aniline Derivatives

The para ‐selective C−H alkylation of aniline derivatives furnished with a pyrimidine auxiliary is herein reported. This reaction is proposed to take place via an N−H‐activated cyclometalate formed in situ. Experimental and DFT mechanistic studies elucidate a dual role of the ruthenium catalyst. Here the ruthenium catalyst can undergo cyclometalation by N−H metalation (as opposed to C−H metalation in meta ‐selective processes) and form a redox active ruthenium species, to enable site‐selective radical addition at the para position.     

Structural Basis for Copper–Oxygen Mediated C−H Bond Activation by the Formylglycine‐Generating Enzyme

The formylglycine‐generating enzyme (FGE) is a unique copper protein that catalyzes oxygen‐dependent C−H activation. We describe 1.66 Å‐ and 1.28 Å‐resolution crystal structures of FGE from Thermomonospora curvata in complex with either Ag^I or Cd^II providing definitive evidence for a high‐affinity metal‐binding site in this enzyme. The structures reveal a bis‐cysteine linear coordination of the monovalent metal, and tetrahedral coordination of the bivalent metal. Similar coordination changes may occur in the active enzyme as a result of Cu^I/II redox cycling. Complexation of copper atoms by two cysteine residues is common among copper‐trafficking proteins, but is unprecedented for redox‐active copper enzymes or synthetic copper catalysts.     

C−H and C−F Bond Activation Reactions of Fluorinated Propenes at Rhodium: Distinctive Reactivity of the Refrigerant HFO‐1234yf

The reaction of [Rh(H)(PEt₃)₃] ( 1 ) with the refrigerant HFO‐1234yf (2,3,3,3‐tetrafluoropropene) affords an efficient route to obtain [Rh(F)(PEt₃)₃] ( 3 ) by C?F bond activation. Catalytic hydrodefluorinations were achieved in the presence of the silane HSiPh₃. In the presence of a fluorosilane, 3 provides a C?H bond activation followed by a 1,2‐fluorine shift to produce [Rh{(E)‐C(CF₃)=CHF}(PEt₃)₃] ( 4 ). Similar rearrangements of HFO‐1234yf were observed at [Rh(E)(PEt₃)₃] [E=Bpin ( 6 ), C₇D₇ ( 8 ), Me ( 9 )]. The ability to favor C?H bond activation using 3 and fluorosilane is also demonstrated with 3,3,3‐trifluoropropene. Studies are supported by DFT calculations.     

Amidinyl Radical Formation through Anodic N−H Bond Cleavage and Its Application in Aromatic C−H Bond Functionalization

We report herein an atom‐economical and sustainable approach to access amidinyl radical intermediates through the anodic cleavage of N−H bonds. The resulting nitrogen‐centered radicals undergo cyclizations with (hetero)arenes, followed by rearomatization, to afford functionalized tetracyclic benzimidazoles in a highly straightforward and efficient manner. This metal‐ and reagent‐free C−H/N−H cross‐coupling reaction exhibits a broad substrate scope and proceeds with high chemoselectivity.     

Unprecedented Reaction Pathway of Sterically Crowded Calcium Complexes: Sequential C−N Bond Cleavage Reactions Induced by C−H Bond Activations

Five bis(quinolylmethyl)‐(1H ‐indolylmethyl)amine (BQIA) compounds, that is, {(quinol‐8‐yl‐CH₂)₂NCH₂(3‐Br‐1H ‐indol‐2‐yl)} ( L¹H ) and {[(8‐R³‐quinol‐2‐yl)CH₂]₂NCH(R²)[3‐R¹‐1H ‐indol‐2‐yl]} ( L^2–5H ) ( L²H : R¹=Br, R²=H, R³=H; L³H : R¹=Br, R²=H, R³=i Pr; L⁴H : R¹=H, R²=CH₃, R³=i Pr; L⁵H : R¹=H, R²=n Bu, R³=i Pr) were synthesized and used to prepare calcium complexes. The reactions of L^1–5H with silylamido calcium precursors (Ca[N(SiMe₂R)₂]₂(THF)₂, R=Me or H) at room temperature gave heteroleptic products ( L^{1, 2} )CaN(SiMe₃)₂ ( 1 , 2 ), ( L^{3, 4} )CaN(SiHMe₂)₂ ( 3 a , 4 a ) and homoleptic complexes ( L^{3, 5} )₂Ca ( D3 , D5 ). NMR and X‐ray analyses proved that these calcium complexes were stabilized through Ca⋅⋅⋅C−Si, Ca⋅⋅⋅H−Si or Ca⋅⋅⋅H−C agostic interactions. Unexpectedly, calcium complexes (( L^3–5 )CaN(SiMe₃)₂) bearing more sterically encumbered ligands of the same type were extremely unstable and underwent C−N bond cleavage processes as a consequence of intramolecular C−H bond activation, leading to the exclusive formation of (E )‐1,2‐bis(8‐isopropylquinol‐2‐yl)ethane.     

Chelation versus Non‐Chelation Control in the Stereoselective Alkenyl sp2 C−H Bond Functionalization Reaction

A hydroxy group chelation‐assisted stereospecific oxidative cross‐coupling reaction between alkenes was developed under mild reaction conditions. In the presence of palladium catalyst, the alkenes tethered with hydroxy functionality can couple efficiently with electron‐deficient alkenes to form the corresponding multi‐substituted olefin products. The hydroxy group on the substrate could play dual roles in reaction, acting as the directing group for alkenyl C−H bond activation and controlling the stereoselectivity of the products.