Ligand-Free RuCl₃-Catalyzed Alkylation of Methylazaarenes with Alcohols

RuCl₃ efficiently catalyzes the alkylation of methylquinolines, methylpyridines, 2-methyl-benzooxazoles, and 2-methyl-quinoxalines with alkyl- or aryl-alcohols as alkylating agents. This synthetically useful and atom economical transformation does not require additional ligands. The mechanistic study indicated the alkylation reaction underwent a stepwise transfer hydrogenation, aldol condensation, and hydrogenation reaction pathway

Luminescent Zn(II) Coordination Polymers for Highly Selective Sensing of Cr(III) and Cr(VI) in Water

Three photoluminescent zinc coordination polymers (CPs), {[Zn₂(tpeb)₂(2,5-tdc)­(2,5-Htdc)₂]·2H₂O}_<i>n</i> (<b>1</b>), {[Zn₂(tpeb)₂(1,4-ndc)­(1,4-Hndc)₂]·2.6H₂O}_<i>n</i> (<b>2</b>), and {[Zn₂(tpeb)₂(2,3-ndc)₂]·H₂O}_<i>n</i> (<b>3</b>) (tpeb = 1,3,5-tri-4-pyridyl-1,2-ethenylbenzene, 2,5-tdc = 2,5-thiophenedicarboxylic acid, 1,4-ndc = 1,4-naphthalenedicarboxylic acid, and 2,3-ndc = 2,3-naphthalenedicarboxylic acid) were prepared from reactions of Zn­(NO₃)₂·6H₂O with tpeb and 2,5-H₂tdc, 1,4-H₂ndc, or 2,3-H₂ndc under solvothermal conditions. Compound <b>1</b> has a two-dimensional (2D) grid-like network formed from bridging 1D [Zn­(tpeb)]_<i>n</i> chains via 2,5-tdc dianions. <b>2</b> and <b>3</b> possess similar one-dimensional (1D) double-chain structures derived from bridging the [Zn­(tpeb)]_<i>n</i> chains via pairs of 1,4-ndc or 2,3-ndc ligands. The solid-state, visible emission by <b>1</b>–<b>3</b> was quenched by Cr³⁺, CrO₄^2–, and Cr₂O₇^2– ions in water with detection limits by the most responsive complex <b>3</b> of 0.88 ppb for Cr³⁺ and 2.623 ppb for Cr₂O₇^2– (pH = 3) or 1.734 ppb for CrO₄^2– (pH = 12). These values are well below the permissible limits set by the USEPA and European Union and the lowest so far reported for any bi/trifunctional CPs sensors. The mechanism of Cr³⁺ luminescence quenching involves irreversible coordination to free pyridyl sites in the CP framework, while the Cr⁶⁺ quenching involves reversible overlap of the absorption bands of the analytes with those of the excitation and/or emission bands for <b>3</b>

Ni(II)-Mediated Photochemical Oxidative Esterification of Aldehydes with Phenols

The photopromoted, Ni-catalyzed acceptorless dehydrogenation esterification of phenols and aromatic aldehydes has been achieved in an oxidant- and external photosensitizer-free manner. This reliable and atom-economical transformation was tolerant to a wide range of functional groups and proceeded efficiently to give various aryl benzoates in moderate to high yields. Additionally, this photocatalytic system displayed high activity for the hydrogen-evolution cross coupling of aliphatic aldehydes and phenols employing dual nickel and aromatic aldehyde catalysis

Exogenous Photosensitizer‑, Metal‑, and Base-Free Visible-Light-Promoted C–H Thiolation via Reverse Hydrogen Atom Transfer

Visible-light-driven, intramolecular C­(sp2)–H thiolation has been achieved without addition of a photosensitizer, metal catalyst, or base. This reaction induces the cyclization of thiobenzanilides to benzothiazoles. The substrate absorbs visible light, and its excited state undergoes a reverse hydrogen-atom transfer (RHAT) with 2,2,6,6-tetramethylpiperidine N-oxyl to form a sulfur radical. The addition of the sulfur radical to the benzene ring gives an aryl radical, which then rearomatizes to benzothiazole via RHAT

Cobalt(II) and Nickel(II) Complexes of a PNN Type Ligand as Photoenhanced Electrocatalysts for the Hydrogen Evolution Reaction

Hydrogen will be an important energy vector of the future, and improved efficiency in electrohydrolysis will accelerate this transition. In a fundamental study, we have prepared Co­(II) and Ni­(II) complexes of a new PNN type ligand N-((diphenylphosphanyl)­methyl)-2-amino-1,10-phenanthroline (dppmaphen) incorporating the photoactive 1,10-phenanthroline group and the strongly coordinating diphenylphosphine to obtain photoelectrochemical (PEC) catalysts [Co­(dppmaphen)2(NO3)2] (1) and [Ni­(dppmaphen)2Cl]Cl (2) which catalyzed the hydrogen evolution reaction (HER) in alkaline media (1 M KOH). Overpotentials (η10) of 430 (1) and 364 mV (2) could be reduced to 345 (1) and 284 mV (2) under Xe light irradiation. This irradiation generated photocurrent responses of 528 (1) and 357 uA/cm2 (2). Density function theory (DFT) calculation on the frontier orbitals of 1 and 2 were useful in understanding these differences in catalytic performance

Carboxylate-Assisted Assembly of Zinc and Cadmium Coordination Complexes of 1,3,5-Tri-4-pyridyl-1,2-ethenylbenzene: Structures and Visible-Light-Induced Photocatalytic Degradation of Congo Red in Water

Solvothermal reactions of zinc and cadmium nitrates with 1,3,5-tri-4-pyridyl-1,2-ethenylbenzene (tpeb) in the presence of various carboxylic acids including 4-iodobenzoic acid (4-HIBA), benzene-1,4-dicarboxylic acid (1,4-H2BDC), 2,5-furan­dicarboxylic acid (2,5-H2FDC), 2,5-dibromo­terephthalic acid (2,5-H2DB­TPA), 1,2-cyclohexane­dicarboxylic acid (1,2-H2CHDC), and 1,5-pentanedioic acid (1,5-H2PDC) gave rise to eight coordination complexes, viz, [Zn­(tpeb)2­(4-IBA)2]·2H2O (1), {[Cd­(NO3)­(tpeb)­(4-IBA)]·H2O}n (2), {[Cd2­(NO3)2­(tpeb)2­(1,4-BDC)]}n (3), {[Cd2­(tpeb)2­(2,5-FDC)2]·2H2O}n (4), [Cd­(tpeb)­(2,5-DBTPA)2]n (5), {[Cd2­(H2O)2­(tpeb)2­(1,2-CHDC)2]·H2O}n (6), [Zn­(tpeb)­(1,2-CHDC)]n (7), and {[Zn­(tpeb)­(1,5-PDC)]·H2O}n (8). Compound 1 is a discrete mononuclear complex with its Zn­(II) center coordinated by two pairs of tpeb and 4-IBA ligands. Compound 2 has a 2D waterfall-like network constructed from bridging [Cd­(NO3)­(4-IBA)] units with tpeb ligands. Compounds 3, 4, and 5 contain similar 1D [Cd­(tpeb)]n chains, which are linked by 1,4-BDC, 2,5-FDC, and 2,5-DBTPA bridges, respectively, forming either 2D (2 and 3) networks or a 3D (4) framework. Compound 6 holds a 2D wavelike layer structure in which dimeric [Cd2­(H2O)2­(1,2-CHDC)2] fragments are connected by two couples of tpeb ligands. Compounds 7 and 8 contain similar 2D fish-scale networks assembled from 1D chains of [Zn­(1,2-CHDC)]n or [Zn­(1,5-PDC)]n bridged by tpeb ligands. Compound 6, as a representative sample, has larger absorption in the visible light region, and can be employed to efficiently degrade Congo red in water without additional oxidizing or reducing reagents upon visible light irradiation. This photocatalyst could be recycled at least five times without evident loss of its catalytic efficiency

Coordination Polymer-Mediated Molecular Surgery for Precise Interconversion of Dicyclobutane Compounds

A Cd(II)-based coordination polymer {[Cd2(5-F-1,3-bpeb)2(FBA)4]·H2O}n (CP1) was obtained from Cd(II) salt, 5-fluoro-1,3-bis[2-(4-pyridyl)ethenyl]benzene (5-F-1,3-bpeb), and p-fluorobenzoic acid (HFBA). Within the one-dimensional chain structure of CP1, a pair of 5-F-1,3-bpeb was arranged in a face-to-face style. Upon UV irradiation and heat treatment, multiple cyclobutane isomers, including specific monocyclobutanes (1 with an endo-cyclobutane ring in CP1-1 and 1′ with an exo-cyclobutane ring in CP1-1′) and dicyclobutanes (endo,endo-dicyclobutane 2α in CP1-2α, exo,endo-dicyclobutane 2β in CP1-2β, and exo,exo-dicyclobutane 2γ in CP1-2γ) were stereoselectively produced. These isomers could be interconverted inside the CP via cutting/coupling specific bonds, which may be regarded as a type of molecular surgery. The precision of cutting/coupling relied on the thermal stability of the cyclobutanes and the alignment of the reactive alkene centers. The conversion processes were tracked through nuclear magnetic resonance, in situ powder X-ray diffraction, and IR spectroscopy. This approach can be considered as skeletal editing to construct complex organic compounds directly from one precursor