Graphitic carbon nitrides and their composites with various morphologies and bandgaps engineered for the hydrogen evolution reaction under visible light are reviewed.

On the basis of the strategy of promoting thermostability of α-diimine nickel catalyst by ligand backbone framework, a series of α-diimine nickel(II) complexes with bulky camphyl or diaryl-substituted backbones, [2,6-(R2)2C6H3−NC(R1)−C(R1)N−2,6-(R2)2C6H3]NiBr2 (1a, R1 = Ph, R2 = CH3; 2a, R1 = 4-methylphenyl, R2 = CH3; 3a, R1 = 4-fluorophenyl, R2 = CH3; 4a, R1 = camphyl, R2 = CH3; 4b, R1 = camphyl, R2 = i-Pr), were synthesized and used as catalyst precursors for ethylene polymerization. Crystallographic analysis revealed that the bulky camphyl backbone has a valid steric-effect on the nickel center by blocking the axial site for the metal center and suppressing the potential rotation of the CAr−N bond. Ethylene polymerizations catalyzed by these nickel α-diimine complexes activated by MAO were systematically investigated and the influences of the substituted backbones as well as reaction temperature on the catalytic activity, molecular weight and branching structure of the polymers were evaluated. It was found that the catalysts containing a camphyl backbone have excellent thermal stability and polymer structure control for ethylene polymerizations. Even at 80 °C, the 4b/MAO system still kept high activity and relatively stable kinetics and produced high molecular weight polyethylene. Moreover, the branching degrees and branched chain distribution of the polyethylenes obtained by the complex could also be controlled by tuning the reaction temperature.

Development of thermally stable nickel-based catalysts is highly desirable for industrial gas-phase olefin polymerizations. On the basis of the strategy of promoting the thermostability of nickel catalyst by the ligand backbone, we herein reported novel dibenzobarrelene-derived α-diimine nickel precatalysts for ethylene polymerization. Increasing the steric bulk on the ligand backbone was expected to inhibit the N-aryl rotation of the α-diimine ligands by the repulsive interactions, thus enhancing thermal stability (100 °C) and living fashion a temperatures up to 80 °C. Bulk ligand backbone also improved tolerance of nickel catalyst toward polar groups, and the α-diimine nickel catalyst containing a 2,6-t Bu-dibenzobarrelene backbone catalyzed living copolymerization of ethylene and methyl 10-undecenoate.

On the basis of different approaches for modifying α-diimine palladium catalysts, a series of methyl chloride palladium complexes with various α-diimine ligand backbones were synthesized and characterized. The corresponding cationic palladium complex chelating esters were further obtained by treatment of methyl chloride palladium complexes with methyl acrylate (MA). It was observed that decomposition of a cationic palladium complex chelating ester can occur to produce a new cationic palladium complex chelating two ligands and two counteranions, which provides a new pathway for deactivation of palladium catalysts and formation of palladium black by a fragmentation pattern with ester loss. These α-diimine palladium catalysts were employed in the homopolymerization of ethylene and copolymerization of ethylene and MA to evaluate substituent effects of the ligand backbone. A bulky camphyl α-diimine palladium catalyst was found to show better thermal stability and afford high-molecular-weight copolymer with higher incorporation of polar monomer. Longstanding living polymerization of ethylene was also achieved within 12 h using a bulky camphyl α-diimine palladium catalyst.

An unconventional organic molecule (TBBU) showing obvious long‐lived room temperature phosphorescence (RTP) is reported. X‐ray single crystal analysis demonstrates that TBBU molecules are packed in a unique fashion with side‐by‐side arranged intermolecular aromatic rings, which is entirely different from the RTP molecules reported to date. Theoretical calculations verify that the extraordinary intermolecular interaction between neighboring molecules plays an important role in RTP of TBBU crystals. More importantly, the polymer film doped with TBBU inherits its distinctive RTP property, which is highly sensitive to oxygen. The color of the doped film changes and its RTP lifetime drops abruptly through a dynamic collisional quenching mechanism with increasing oxygen fraction, enabling visual and quantitative detection of oxygen. Through analyzing the grayscale of the phosphorescence images, a facile method is developed for rapid, visual, and quantitative detection of oxygen in the air.

No abstract

Coordination insertion polymerization is unsurpassed as a straightforward method for synthesis of highvalue polyolefins by the copolymerization of ethylene and polar monomers, but poison effects of polar groups on the metal center result in a lack of fine control over the polymer architecture. Herein we reported a thermally stable dibenzobarrelene-derived α-diimine palladium catalyst for the precision synthesis of functionalized polyolefins by living copolymerization of ethylene and a variety of acrylate comonomers. The introduction of the bulky dibenzobarrelene backbone can improve migratory insertion selectivity of methyl acrylate (MA) in a 2,1-mode, thus preventing polar groups from poisoning palladium centers by stable five-membered palladacycle intermediates formed by 1,2-insertion of MA. In this living chain-walking catalyst system, the composition, molecular weight, and branching topology of the copolymer can be facilely tunable by simple variation of the ethylene pressure.

A bulky amine-imine nickel complex containing two 2,6-diisopropyl substituents after activation with MMAO or Et(2)AlCl can polymerize ethylene in a living fashion over a period of 120 minutes at room temperature or above.