Reactivity Control of CH Bond Activation over Vanadium-Silver Bimetallic Oxide Cluster Cations

Vanadium-silver bimetallic oxide cluster ions (V(x) Ag(y) O(z) (+) ; x=1-4, y=1-4, z=3-11) are produced by laser ablation and reacted with ethane in a fast-flow reactor. A reflectron time of flight (Re-TOF) mass spectrometer is used to detect the cluster distribution before and after the reactions. Hydrogen atom abstraction (HAA) reactions are identified over VAgO(3) (+) , V(2) Ag(2) O(6) (+) , V(2) Ag(4) O(7) (+) , V(3) AgO(8) (+) , V(3) Ag(3) O(9) (+) , and V(4) Ag(2) O(11) (+) ions, in which the oxygen-centered radicals terminally bonded on V atoms are active sites for the facile HAA reactions. DFT calculations are performed to study the structures, bonding, and reactivity. The reaction mechanisms of V(2) Ag(2) O(6) (+) +C(2) H(6) are also given. The doped Ag atoms with a valence state of +1 are highly dispersed at the periphery of the V(x) Ag(y) O(z) (+) cluster ions. The reactivity can be well-tuned gradually by controlling the number of Ag atoms. The steric protection due to the peripherally bonded Ag atoms greatly enhances the selectivity of the V-Ag bimetallic oxide clusters with respect to the corresponding pure vanadium oxide systems.     

Catalytic CO Oxidation by O2 Mediated with Single Gold Atom Doped Titanium Oxide Cluster Anions AuTi2O4–6−

Gas-phase studies on catalytic CO oxidation by O₂ mediated with gold-containing heteronuclear metal oxide clusters are vital to obtain the structure−reactivity relationship of supported gold catalysts, while it is challenging to trigger the reactivity of clusters with closed-shell electronic structure in O₂ activation. Herein, we identified that CO oxidation by O₂ can be catalyzed by the AuTi₂O_4–6⁻ clusters, among which AuTi₂O₄⁻ with closed-shell electronic structure can effectively activate O₂. The reactions were characterized by mass spectrometry and quantum chemical calculations. Theoretical calculations showed that in the initial stage of O₂ activation, the Ti₂O₄ moiety in AuTi₂O₄⁻ contributes dominantly to activate O₂ into superoxide (O₂⁻⋅) without participation of the Au atom. In subsequent steps, the intimate charge transfer interaction between Au and the Ti₂O₄ moiety drives the direct dissociation of the O₂⁻⋅ unit.     

Carbon Monoxide Activation by a Molecular Aluminium Imide: C−O Bond Cleavage and C−C Bond Formation

Anionic molecular imide complexes of aluminium are accessible via a rational synthetic approach involving the reactions of organo azides with a potassium aluminyl reagent. In the case of K₂[( NON )Al(NDipp)]₂ ( NON =4,5-bis(2,6-diisopropylanilido)-2,7-di-tert-butyl-9,9-dimethyl-xanthene; Dipp=2,6-diisopropylphenyl) structural characterization by X-ray crystallography reveals a short Al−N distance, which is thought primarily to be due to the low coordinate nature of the nitrogen centre. The Al−N unit is highly polar, and capable of the activation of relatively inert chemical bonds, such as those found in dihydrogen and carbon monoxide. In the case of CO, uptake of two molecules of the substrate leads to C−C coupling and C≡O bond cleavage. Thermodynamically, this is driven, at least in part, by Al−O bond formation. Mechanistically, a combination of quantum chemical and experimental observations suggests that the reaction proceeds via exchange of the NR and O substituents through intermediates featuring an aluminium-bound isocyanate fragment.     

Photoassisted Selective Steam and Dry Reforming of Methane to Syngas Catalyzed by Rhodium–Vanadium Bimetallic Oxide Cluster Anions at Room Temperature

Photoassisted steam reforming and dry (CO₂) reforming of methane (SRM and DRM) at room temperature with high syngas selectivity have been achieved in the gas-phase catalysis for the first time. The catalysts used are bimetallic rhodium–vanadium oxide cluster anions of Rh₂VO_1–3⁻. Both the oxidation of methane and reduction of H₂O/CO₂ can take place efficiently in the dark while the pivotal step to govern syngas selectivity is photo-excitation of the reaction intermediates Rh₂VO_2,3CH₂⁻ to specific electronically excited states that can selectively produce CO and H₂. Electronic excitation over Rh₂VO_2,3CH₂⁻ to control the syngas selectivity is further confirmed from the comparison with the thermal excitation of Rh₂VO_2,3CH₂⁻, which leads to diversity of products. The atomic-level mechanism obtained from the well-controlled cluster reactions provides insight into the process of selective syngas production from the photocatalytic SRM and DRM reactions over supported metal oxide catalysts.     

Direct Dimesitylborylation of Benzofuran Derivatives by an Iridium-Catalyzed C−H Activation with Silyldimesitylborane

Direct dimesitylborylation of benzofuran derivatives by a C−H activation catalyzed by an iridium(I)/N-heterocyclic carbene (NHC) complex in the presence of Ph₂MeSi-BMes₂ afforded the corresponding dimesitylborylation products in good to high yield with excellent regioselectivity. This method provides a straightforward route to donor–(π-spacer)–acceptor systems with intriguing solvatochromic luminescence properties.     

Palladium-Catalyzed C8-Arylation of Naphthalenes through C−H Activation: A Combined Experimental and Computational Study

Herein, a direct C8-arylation reaction of 1-amidonaphthalenes is described. By using diaryliodonium salts as arylating agents, the palladium-catalyzed C−H activation reaction showed perfect C8 regioselectivity and a wide functional group tolerance. In most cases, the desired polyaromatic compounds were isolated in good to excellent yields. To explain the observed regioselectivity, DFT calculations were performed and highlighted the crucial role of the amide directing group. Finally, the utility of this method is showcased by the synthesis of benzanthrone derivatives.     

Activation of N−O σ Bonds with Transition Metals: A Versatile Platform for Organic Synthesis and C−N Bonds Formation**

N−O σ bonds containing compounds are versatile substrates for organic synthesis under transition metal catalysis. Their ability to react through both polar (oxidative addition, formation of metallanitrene, nucleophilic substitution) and radical pathways (single electron transfer, homolytic bond scission) have triggered the development of various synthetic methodologies, particularly toward synthesizing nitrogen-containing compounds. In this review, we discuss the different modes of activation of N−O bonds in the presence of transition metal catalysts, emphasizing the experimental and computational mechanistic proofs in the literature to help to design new synthetic pathways toward the synthesis of C−N bonds.     

Directed C−H Activation and Tandem Cross-Coupling Reactions Using Palladium Nanocatalysts with Controlled Oxidation

Controlled oxidation of palladium nanoparticles provided high-valent Pd^IV oxo-clusters which efficiently promote directed C−H halogenation reactions. In addition, palladium nanoparticles can undergo changes in oxidation states to provide both high-valent Pd^IV and low-valent Pd⁰ species within one system, and thus a tandem reaction of C−H halogenation and cross-coupling (C−N, C−C, and C−S bond formation) was successfully established.     

Expansion of antimonato polyoxovanadates with transition metal complexes: (Co(N3C5H15)2)2[{Co(N3C5H15)2}V15Sb6O42(H2O)]·5H2O and (Ni(N3C5H15)2)2[{Ni(N3C5H15)2}V15Sb6O42(H2O)]·8H2O

Two new polyoxovanadates (Co(N(3)C(5)H(15))(2))(2)[{Co(N(3)C(5)H(15))(2)}V(15)Sb(6)O(42)(H(2)O)]·5H(2)O (1) and (Ni(N(3)C(5)H(15))(2))(2)[{Ni(N(3)C(5)H(15))(2)}V(15)Sb(6)O(42)(H(2)O)]·8H(2)O (2) (N(3)C(5)H(15) = N-(2-aminoethyl)-1,3-propanediamine) were synthesized under solvothermal conditions and structurally characterized. In both structures the [V(15)Sb(6)O(42)(H(2)O)](6-) shell displays the main structural motif, which is strongly related to the {V(18)O(42)} archetype cluster. Both compounds crystallize in the triclinic space group P1 with a = 14.3438(4), b = 16.6471(6), c = 18.9186(6) ?, α = 87.291(3)°, β = 83.340(3)°, γ = 78.890(3)°, and V = 4401.4(2) ?(3) (1) and a = 14.5697(13), b = 15.8523(16), c = 20.2411(18) ?, α = 86.702(11)°, β = 84.957(11)°, γ = 76.941(11)°, and V = 4533.0(7) ?(3) (2). In the structure of 1 the [V(15)Sb(6)O(42)(H(2)O)](6-) cluster anion is bound to a [Co(N(3)C(5)H(15))(2)](2+) complex via a terminal oxygen atom. In the Co(2+)-centered complex, one of the amine ligands coordinates in tridentate mode and the second one in bidentate mode to form a strongly distorted CoN(5)O octahedron. Similarly, in compound 2 an analogous NiN(5)O complex is joined to the [V(15)Sb(6)O(42)(H(2)O)](6-) anion via the same attachment mode. A remarkable difference between the two compounds is the orientation of the noncoordinated propylamine group leading to intermolecular Sb···O contacts in 1 and to Sb···N interactions in 2. In the solid-state lattices of 1 and 2, two additional [M(N(3)C(5)H(15))(2)](2+) complexes act as countercations and are located between the [{M(N(3)C(5)H(15))(2)}V(15)Sb(6)O(42)(H(2)O)](4-) anions. Between the anions and cations strong N-H···O hydrogen bonds are observed. In both compounds the clusters are stacked along the b axis in an ABAB fashion with cations and water molecules occupying the space between the clusters. Magnetic characterization demonstrates that the Ni(2+) and Co(2+) cations do not significantly couple with the S = 1/2 vanadyl groups. The susceptibility data can be successfully reproduced assuming a distorted ligand field for the Co(2+) ions (1) and an O(h)-symmetric Ni(2+) ligand field (2).     

Synthesis of Polybenzoacenes: Annulative Dimerization of Phenylene Triflate by Twofold C−H Activation

Polycyclic aromatic hydrocarbons (PAHs) represent an emerging class of π-conjugated molecules in the area of optoelectronic devices and materials. Unprecedented synthetic routes to various PAHs from simple phenol derivatives by a palladium-catalyzed annulative dimerization of phenylene triflate through twofold inter- and intramolecular C−H activation have been established. The initially formed partially fused PAHs can be smoothly transformed into a variety of fully fused PAHs by the Scholl reaction. Furthermore, the reactions of phenanthrene-substituted aryl triflates proceeded regioselectively. The findings inspired the development of a rapid and efficient synthesis of polybenzoacene derivatives. This study not only allows transformation of phenyl triflates, but also discloses a new retrosynthetic strategy towards PAHs, especially polybenzoacenes.     

C−H and Si−H Activation Reactions at Ru/Ga Complexes: A Combined Experimental and Theoretical Case Study on the Ru−Ga Bond

Treatment of [Ru(COD)(MeAllyl)₂] and [Ru(COD)(COT)] with GaCp* under hydrogenolytic conditions leads to reactive intermediates which activate Si−H or C−H bonds, respectively. The product complexes [Ru(GaCp*)₃(SiEt₃)H₃] ( 1 ) and [Ru(GaCp*)₃(C₇H₇)H₃] ( 2 ) are formed with HSiEt₃ or with toluene as the solvent, respectively. While 1 was isolated and fully characterized by NMR, MS, IR and SC-XRD, 2 was too labile to be isolated and was observed and characterized in situ by using mass spectrometry, including labelling experiments for the unambiguous assignment of the elemental composition. The structural assignment was confirmed by DFT calculations. The relative energies of the four isomers possible upon toluene activation at the ortho-, meta-, para- and CH₃-positions have been determined and point to aromatic C−H activation. The Ru−Ga bond was analyzed by EDA and QTAIM and compared to the Ru−P bond in the analogue phosphine compound. Bonding analyses indicate that the Ru-GaCp* bond is weaker than the Ru-PR₃ bond.     

Continued Progress towards Efficient Functionalization of Natural and Non-natural Targets under Mild Conditions: Oxygenation by C−H Bond Activation with Dioxirane

The successful isolation and characterization of a dioxirane species in 1988 opened up one of the most attractive methods for the efficient oxidation of simple and/or structurally complex molecules. Dioxirane today rank among the most powerful tools in organic chemistry, with numerous applications in commercially important processes. They were quickly recognized as efficient oxygen transfer agents, especially for epoxidations and for a wide range of O-insertion reactions into C−H bonds. Dioxirane possess catalytic activity and appear as highly (chemo-, regio-, and stereo-) selective oxidants, despite their reactivity under mild and strictly neutral conditions being controlled by a combination of steric and electronic factors. In this review, we discuss some of the most recent and significant developments in the selective homogeneous and heterogeneous oxyfunctionalization of non-activated C−H bonds in hydrocarbons of natural and non-natural targets by using isolated dioxirane or, more generally, by using the ketones (i.e., the dioxirane precursors) as organocatalysts.     

Cobalt-Catalyzed Hiyama-Type C−H Activation with Arylsiloxanes: Versatile Access to Highly ortho-Decorated Biaryls

Versatile direct Hiyama-type C−H arylations of benzamides were accomplished with organosiloxanes by chelation-assisted cobalt catalysis. The C−H arylation featured broad substrate scope, including challenging C(sp³)−H activation, the use of γ-valerolactone as biomass-derived solvent, and selectively provided the desired biaryls, even when being highly sterically hindered.     

Influence of the Flexibility of Nickel PCP-Pincer Complexes on C−H and P−C Bond Activation and Ethylene Reactivity: A Combined Experimental and Theoretical Investigation

Using a pincer platform based on a bridgehead NHC donor with functional side arms, the combined effect of increased flexibility in six-membered pyrimidine-type heterocycles compared to the more often studied five-membered imidazole, and rigidity of phosphane side arms was examined. The unique features observed include: 1) the reaction of the azolium C_sp2−H bond with [Ni(cod)₂] affording a carbanionic ligand in [NiCl(PC_sp3^HP)] ( 8 ) rather than a carbene; 2) its transformation into the NHC, hydrido complex [NiH(PC^NHCP)]PF₆ ( 9 ) upon halide abstraction; 3) ethylene insertion into the Ni−H bond of the latter and ethyl migration to the N−C−N carbon atom of the heterocycle in [Ni(PC^EtP)]PF₆ ( 10 ); and 4) an unprecedented C−P bond activation transforming the P−C^NHC−P pincer ligand of 8 in a C−C^NHC−P pincer and a terminal phosphanido ligand in [Ni(PPh₂)(CC^NHCP)] ( 15 ). The data are supported by nine crystal structure determinations and theoretical calculations provided insights into the mechanisms of these transformations, which are relevant to stoichiometric and catalytic steps of general interest.     

K2Na3[{B6O10(OH)}{B3O4(OH)3}] ⋅ H2O: A Layered Borate Built by Mixed Oxoboron Clusters with Nonlinear-Optical Property

A new acentric borate, K₂Na₃[{B₆O₁₀(OH)}-{B₃O₄(OH)₃}] ⋅ H₂O ( 1 ) has been made under solvothermal condition. 1 has layered structure made by B₆O₁₃(OH)-based chains and B₃O₅(OH)₃-bridging clusters. Second-harmonic generation (SHG) measurements reveal that 1 is a phase-matchable nonlinear optical (NLO) material, showing the SHG signal intensity of 1.8 times that of KDP (KH₂PO₄). Besides, UV-Vis diffuse reflectance spectrum shows that 1 has the short deep UV (DUV) absorption cutoff edge of 198 nm. Thermogravimetric analysis reveals it has good thermal stability. Also 1 represents firstly mixed oxoboron clusters-made 2D layered borate with NLO property.     

Rhodium(III)-Catalyzed Atroposelective Synthesis of Biaryls by C−H Activation and Intermolecular Coupling with Sterically Hindered Alkynes

Reported herein is the atroposelective synthesis of biaryl NH isoquinolones by Rh^III-catalyzed C−H activation of benzamides and intermolecular [4+2] annulation for a broad scope of 2-substituted 1-alkynylnaphthalenes, as well as sterically hindered, symmetric diarylacetylenes. The axial chirality is constructed based on dynamic kinetic transformation of the alkyne in redox-neutral annulation with benzamides, with alkyne insertion being stereodetermining. The reaction accommodates both benzamides and heteroaryl carboxamides and proceeds in excellent regioselectivity (if applicable) and enantioselectivities (average 91.8 % ee). An enantiomerically and diastereomerically pure rhodacyclic complex was prepared and offers insight into enantiomeric control of the coupling system, wherein the steric interactions between the amide directing group and the alkyne substrate dictate both the regio- and enantioselectivity.     

Ru3(CO)12-Catalyzed Modular Assembly of Hemilabile Ligands by C−H Activation of Phosphines with Isocyanates

Hemilabile ligands have been applied extensively in transition metal catalysis, but preparations of these molecules typically require multistep synthesis. Here, modular assembly of diverse phosphine-amide ligands, including related axially chiral compounds, is first reported through ruthenium-catalyzed C−H activation of phosphines with isocyanate directed by phosphorus(III) atoms. High reactivity and regioselectivity can be obtained by using a Ru₃(CO)₁₂ catalyst with a mono-N-protected amino acid ligand. This transformation significantly expands the pool of phosphine-amide ligands, some of which have shown excellent efficiency for asymmetric catalysis. More broadly, the discovery constitutes a proof of principle for facile construction of hemilabile ligands directly from the parent monodentate phosphines by C−H activation with ideal atom, step and redox economy. Several dinuclear ruthenium complexes were characterized by single-crystal X-ray diffraction analysis revealing the key mechanistic features of this transformation.     

C−H Bond Activation by Iridium(III) and Iridium(IV) Oxo Complexes

Oxidation of an iridium(III) oxo precursor enabled the structural, spectroscopic, and quantum-chemical characterization of the first well-defined iridium(IV) oxo complex. Side-by-side examination of the proton-coupled electron transfer thermochemistry revealed similar driving forces for the isostructural oxo complexes in two redox states due to compensating contributions from H⁺ and e⁻ transfer. However, C−H activation of dihydroanthracene revealed significant hydrogen tunneling for the distinctly more basic iridium(III) oxo complex. Our findings complement the growing body of data that relate tunneling to ground state properties as predictors for the selectivity of C−H bond activation.     

Iridium-Catalyzed Enantioselective Hydroarylation of Alkenes through C−H bond Activation: Experiment and Computation

A new catalytic enantioselective hydroarylation of unactivated olefins is developed that provides rapid access to functionalized chiral dihydrobenzofurans with good yields and excellent enantioselectivities. Simple aromatic ketones or amides act as a directing group allowing the regioselective reaction at the more hindered ortho position. Tertiary benzylic stereocenters are obtained directly under mild reaction conditions and with complete atom economy from readily available starting materials.     

Synthesis and structure of a new halophosphate Sr3P3O10Cl with the flexible [P3O10]5− anions

A new halophosphate crystal Sr₃P₃O₁₀Cl was grown in molten chloride flux media. It crystallizes in the centrosymmetric orthorhombic space group Pnma (No. 62) with a = 10.617(2) Å, b = 10.736(2) Å, and c = 8.7354(17) Å. In the structure, the basic building unit is the [P₃O₁₀]⁵⁻ anion, which is consist of three PO₄ tetrahedra by sharing the corner oxygen atoms. The two Sr atoms and the Cl atom are linked to construct an infinite [Sr₃Cl]⁵⁺ chain. The [P₃O₁₀]⁵⁻ anions are interconnected with the [Sr₃Cl]⁵⁺ chains to form a three-dimensional frameworks. Additionally, the first-principle calculation was employed to obtain the band structures and densities of states.