Palladium-Catalyzed C−H Functionalization of Pyridine <i>N</i>-Oxides: Highly Selective Alkenylation and Direct Arylation with Unactivated Arenes

Palladium-Catalyzed C−H Functionalization of Pyridine N-Oxides: Highly Selective Alkenylation and Direct Arylation with Unactivated Arene

Palladium-Catalyzed C−H Functionalization of Pyridine <i>N</i>-Oxides: Highly Selective Alkenylation and Direct Arylation with Unactivated Arenes

Palladium-Catalyzed C−H Functionalization of Pyridine N-Oxides: Highly Selective Alkenylation and Direct Arylation with Unactivated Arene

Synthesis of Condensed Pyrroloindoles via Pd-Catalyzed Intramolecular C−H Bond Functionalization of Pyrroles

Synthesis of Condensed Pyrroloindoles via Pd-Catalyzed Intramolecular C−H Bond Functionalization of Pyrrole

Sn-3.0Ag-0.5Cu Solder Enriched with Tb₄O₇ Nanoparticles for Mini-Light Emitting Diode Packaging

In this study, we perform innovative addition of Tb4O7 nanoparticles (NPs) into the Sn-3.0 wt % Ag-0.5 wt % Cu (SAC305) alloy for attaching a 1608 mini-LED chip to a Cu pad of a printed circuit board (PCB). The Tb4O7 NP-reinforced SAC305 solder alloy was prepared by a melting and casting route. The spreading ratio (SR) of the Tb4O7 NP-reinforced SAC305 solder was assessed using the JIS-Z-3197 standard. The melting and tensile properties of the nanomodified solders were also evaluated. The microstructural observations showed that as Tb4O7 NPs were gradually added to the Sn-rich matrix, the β-Sn-grain area became finer due to the adsorption of high surface active Tb4O7 NPs on the β-Sn grain and intermetallic compounds (IMCs). The findings showed that the produced Tb4O7 NP-reinforced SAC305 solder had a 6 °C depression in melting temperature over the pristine SAC305 alloy. The SR of the nanomodified solders was increased up to 90.5% at the optimal concentration of Tb4O7 NPs in the SAC305 matrix. A delayed microstructural coarsening and the inhibited Cu–Sn atomic interdiffusion at the joint interface were observed, which resulted in an enhancement of tensile and shear strength by 8.18 and 9.24%, respectively. The results indicate that addition of 0.3 wt % Tb4O7 NPs is needed to realize the optimum set of microstructural and thermodynamic reliability of a mini-LED/Cu chip joint

Highly Efficient and Versatile Synthesis of Polyarylfluorenes via Pd-Catalyzed C−H Bond Activation

A facile protocol for the Pd-catalyzed preparative synthesis of fluorene derivatives has been developed. While a wide range of fluorenes were easily obtained with high efficiency and selectivity under mild conditions, excellent functional group tolerance was also demonstrated. On the basis of Hammett and KIE studies, the present reaction is proposed to proceed via a base-assisted deprotonative metalation pathway

Halide-Bridged Binuclear HX-Splitting Catalysts

Two-electron mixed-valence compounds promote the rearrangement of the two-electron bond photochemically. Such complexes are especially effective at managing the activation of hydrohalic acids (HX). Closed HX-splitting cycles require proton reduction to H₂ and halide oxidation to X₂ to be both accomplished, the latter of which is thermodynamically and kinetically demanding. Phosphazane-bridged Rh₂ catalysts have been especially effective at activating HX via photogenerated ligand-bridged intermediates; such intermediates are analogues of the classical ligand-bridged intermediates proposed in binuclear elimination reactions. Herein, a new family of phosphazane-bridged Rh₂ photocatalysts has been developed where the halide-bridged geometry is designed into the ground state. The targeted geometries were accessed by replacing previously used alkyl isocyanides with aryl isocyanide ligands, which provided access to families of Rh₂L₁ complexes. H₂ evolution with Rh₂ catalysts typically proceeds via two-electron photoreduction, protonation to afford Rh hydrides, and photochemical H₂ evolution. Herein, we have directly observed each of these steps in stoichiometric reactions. Reactivity differences between Rh₂ chloride and bromide complexes have been delineated. H₂ evolution from both HCl and HBr proceeds with a halide-bridged Rh₂ hydride photoresting state. The H₂-evolution efficiency of the new family of halide-bridged catalysts is compared to a related catalyst in which ligand-bridged geometries are not stabilized in the molecular ground state, and the new complexes are found to more efficiently facilitate H₂ evolution

Halide-Bridged Binuclear HX-Splitting Catalysts

Two-electron mixed-valence compounds promote the rearrangement of the two-electron bond photochemically. Such complexes are especially effective at managing the activation of hydrohalic acids (HX). Closed HX-splitting cycles require proton reduction to H₂ and halide oxidation to X₂ to be both accomplished, the latter of which is thermodynamically and kinetically demanding. Phosphazane-bridged Rh₂ catalysts have been especially effective at activating HX via photogenerated ligand-bridged intermediates; such intermediates are analogues of the classical ligand-bridged intermediates proposed in binuclear elimination reactions. Herein, a new family of phosphazane-bridged Rh₂ photocatalysts has been developed where the halide-bridged geometry is designed into the ground state. The targeted geometries were accessed by replacing previously used alkyl isocyanides with aryl isocyanide ligands, which provided access to families of Rh₂L₁ complexes. H₂ evolution with Rh₂ catalysts typically proceeds via two-electron photoreduction, protonation to afford Rh hydrides, and photochemical H₂ evolution. Herein, we have directly observed each of these steps in stoichiometric reactions. Reactivity differences between Rh₂ chloride and bromide complexes have been delineated. H₂ evolution from both HCl and HBr proceeds with a halide-bridged Rh₂ hydride photoresting state. The H₂-evolution efficiency of the new family of halide-bridged catalysts is compared to a related catalyst in which ligand-bridged geometries are not stabilized in the molecular ground state, and the new complexes are found to more efficiently facilitate H₂ evolution

Ternary Pt−Fe−Co Alloy Electrocatalysts Prepared by Electrodeposition: Elucidating the Roles of Fe and Co in the Oxygen Reduction Reaction

An electrodeposition-based protocol for the synthesis of ternary Pt−Fe−Co electrocatalysts for the oxygen reduction reaction (ORR) has been developed. The eletrodeposition method suits the purpose of fast catalyst screening and mechanism studies. Here, we survey the composition effect of Fe and Co atoms in ternary Pt−Fe−Co alloy electrocatalysts on the electrocatalytic activity toward the ORR in terms of geometric (Pt−Pt distance) and electronic (core-level binding energy, d-band center) aspects. A wide range of Pt−Fe−Co catalysts can easily be obtained using electrodeposition under simple and mild conditions. Among the various compositions, Pt85Fe10Co5 catalyst shows excellent mass activity that is 3.5 times higher than that of pure Pt. Interestingly, the ORR kinetic current density reveals a double-volcano plot as a function of alloy composition. Extended X-ray absorption fine structure (EXAFS) spectroscopy and high-resolution X-ray photoelectron spectroscopy (HRXPS) experiments were conducted to explain the abnormal double-volcano behavior. The results also reveal that the d-band center of Pt85Fe10Co5 is downshifted by about 0.1 eV compared to that of Pt, which explains its superior activity toward the ORR

Halogen Photoelimination from Sb^V Dihalide Corroles

Main-group p-block metals are ideally suited for mediating two-electron reactions because they cycle between M^<i>n</i> and M^<i>n</i>+2 redox states, as the one-electron state is thermodynamically unstable. Here, we report the synthesis and structure of an Sb^III corrole and its Sb^VX₂ (X = Cl, Br) congeners. Sb^III sits above the corrole ring, whereas Sb^V resides in the corrole centroid. Electrochemistry suggests interconversion between the Sb^III and Sb^VX₂ species. TD-DFT calculations indicate a HOMO → LUMO+2 parentage for excited states in the Soret spectral region that have significant antibonding character with respect to the Sb–X fragment. The photochemistry of <b>2</b> and <b>3</b> in THF is consistent with the computational results, as steady-state photolysis at wavelengths coincident with the Soret absorption of Sb^VX₂ corrole lead to its clean conversion to the Sb^III corrole. This ability to photoactivate the Sb–X bond reflects the proclivity of the pnictogens to rely on the Pn^III/V couple to drive the two-electron photochemistry of M–X bond activation, an essential transformation needed to develop HX-splitting cycles

Phosphorus-Ligand Redox Cooperative Catalysis: Unraveling Four-Electron Dioxygen Reduction Pathways and Reactive Intermediates

The reduction of dioxygen to water is crucial in biology and energy technologies, but it is challenging due to the inertness of triplet oxygen and complex mechanisms. Nature leverages high-spin transition metal complexes for this, whereas main-group compounds with their singlet state and limited redox capabilities exhibit subdued reactivity. We present a novel phosphorus complex capable of four-electron dioxygen reduction, facilitated by unique phosphorus-ligand redox cooperativity. Spectroscopic and computational investigations attribute this cooperative reactivity to the unique electronic structure arising from the geometry of the phosphorus complex bestowed by the ligand. Mechanistic study via spectroscopic and kinetic experiments revealed the involvement of elusive phosphorus intermediates resembling those in metalloenzymes. Our result highlights the multielectron reactivity of phosphorus compound emerging from a carefully designed ligand platform with redox cooperativity. We anticipate that the work described expands the strategies in developing main-group catalytic reactions, especially in small molecule fixations demanding multielectron redox processes