Well-Defined Silica-Supported Zirconium-Benzyl Cationic Species: Improved Heterogenization of Single-Site Polymerization Catalysts

Silicon Nitride Surface Enabled Propane Dehydrogenation Catalyzed by Supported Organozirconium

Mesoporous silicon nitride (Si3N4) is a nontraditional support for the chemisorption of organometallic complexes with the potential for enhancing catalytic activity through features such as the increased Lewis basicity of nitrogen for heterolytic bond activation, increased ligand donor strength, and metal-ligand orbital overlap. Here, tetrabenzyl zirconium (ZrBn4) was chemisorbed on Si3N4, and the resulting supported organometallic species was characterized by Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS), Dynamic Nuclear Polarization-enhanced Solid State Nuclear Magnetic Resonance (DNP-SSNMR), and X-ray Absorption Spectroscopy (XAS). Based on the hypothesis that the nitride might enable facile heterolytic C-H bond activation along the Zr-N bond, this material was found to be a highly active (1.53 molpropene molZr-1 h-1 at 450 °C) and selective (99% to propylene) catalyst for propane dehydrogenation. In contrast, the homologous silica supported complex exhibited negligible activity under these conditions.

Polymethylaluminoxane organic frameworks (sMAOF) – highly active supports for slurry phase ethylene polymerisation

A series of modified solid polymethylaluminoxane (sMAO) catalyst supports have been developed for slurry phase ethylene polymerisation, using aryl di-ol modifier groups.

Catalyst-Free Approach for Hydroboration of Carboxylic Acids under Mild Conditions

Herein, we present a facile method for deoxygenative hydroboration of a broad range of carboxylic acids under very mild conditions. The most striking feature of this attractive hydroboration is that this elusive and challenging transformation was realized without catalyst and solvent. The investigation of solvent effect showed that tetrahydrofuran was also suitable for this kind of reaction. Moreover, a successful gram-scale trial may provide a very promising toolkit for carboxylic acid reduction at a large scale.

Organometallic Zirconium Compounds in an Oxygen-Rich Coordination Environment: Synthesis and Structural Characterization of Tris(oxoimidazolyl)hydroboratozirconium Compounds

A series of tris(oxoimidazolyl)hydroborato ligands, which serve as L₂X [O₃] donors, have been employed to obtain organometallic zirconium compounds in an uncommon oxygen-rich coordination environment. For example, Cp[To^MeBenz]ZrCl₂ has been synthesized via the reaction of [To^MeBenz]Na with CpZrCl₃ and bears a structural resemblance to the bent metallocene dichloride derivative Cp₂ZrCl₂. In addition, the half-sandwich counterparts [To^MeBenz]ZrCl₃ and [To^But]ZrCl₃ have been obtained by metathesis of ZrCl₄ with [To^MeBenz]Na and [To^But]Na, respectively. The structurally related zirconium benzyl compounds [To^RBenz]Zr(CH₂Ph)₃ (R = Me, Bu^t, 1-Ad) have also been synthesized via the reactions of [To^RBenz]Tl with Zr(CH₂Ph)₄, and X-ray diffraction studies demonstrate that the benzyl ligands in these compounds are conformationally flexible and exhibit a large range of Zr-CH₂-Ph bond angles (94.7-131.7°). Protolytic cleavage of one of the benzyl ligands of [To^RBenz]Zr(CH₂Ph)₃ (R = Bu^t, 1-Ad) may be achieved by treatment with [PhNHMe₂][B(C₆F₅)₄] to generate {[To^RBenz]Zr(CH₂Ph)₂}[B(C₆F₅)₄], which are catalysts for the polymerization of ethylene. The molecular structure of the ether adduct, {[To^ButBenz]Zr(CH₂Ph)₂(OEt₂)}[B(C₆F₅)₄], has been determined by X-ray diffraction. In addition to the use of tris(oxoimidazolyl)hydroborato ligands, bis(oxoimidazolyl)hydroborato ligands have also been used to obtain zirconium benzyl compounds in oxygen-rich environments, namely, [Bo^MeBenz]₂Zr(CH₂Ph)₂ and [Bo^AdBenz]₂Zr(CH₂Ph)₂.

Design, synthesis and antibacterial evaluation of honokiol derivatives

Staphylococcus aureus is a major and dangerous human pathogen that causes a range of clinical manifestations of varying severity, and is the most commonly isolated pathogen in the setting of skin and soft tissue infections, pneumonia, suppurative arthritis, endovascular infections, foreign-body associated infections, septicemia, osteomyelitis, and toxic shocksyndrome. Honokiol, a pharmacologically active natural compound derived from the bark of Magnolia officinalis, has antibacterial activity against Staphylococcus aureus which provides a great inspiration for the discovery of potential antibacterial agents. Herein, honokiol derivatives were designed, synthesized and evaluated for their antibacterial activity by determining the minimum inhibitory concentration (MIC) against S. aureus ATCC25923 and Escherichia coli ATCC25922 in vitro. 7c exhibited better antibacterial activity than other derivatives and honokiol. The structure-activity relationships indicated piperidine ring with amino group is helpful to improve antibacterial activity. Further more, 7c showed broad spectrum antibacterial efficiency against various bacterial strains including eleven gram-positive and seven gram-negative species. Time-kill kinetics against S. aureus ATCC25923 in vitro revealed that 7c displayed a concentration-dependent effect and more rapid bactericidal kinetics better than linezolid and vancomycin with the same concentration. Gram staining assays of S. aureus ATCC25923 suggested that 7c could destroy the cell walls of bacteria at 1×MIC and 4×MIC.

Preparation of monopodal and bipodal aluminum surface species by selective protonolysis of highly reactive [AlH3(NMe2Et)] on silica

The reaction of [AlH₃(NMe₂Et)] with silica treated at 200 °C leads to a well-defined bipodal aluminum hydride while with silica treated at 700 °C a mixture of mono- and bi-podal aluminum hydrides is obtained.

Modification of silica-supported tungsten neosilyl oxo precatalysts: impact of substituted phenol on activity and stability in olefin metathesis

Development of a novel and convenient strategy to access a large variety of highly active tungsten oxo olefin metathesis pre-catalysts.

The design of a bipodal bis(pentafluorophenoxy)aluminate supported on silica as an activator for ethylene polymerization using surface organometallic chemistry

A well-defined solid activator for supported metallocene polymerization catalysts.

Development of silica-supported frustrated Lewis pairs: highly active transition metal-free catalysts for the Z-selective reduction of alkynes

Supported Lewis acid/base systems based have been prepared and characterized.

Tailoring the selectivity in 2-butene conversion over supported d0 group 4, 5 and 6 metal hydrides: from dimerization to metathesis

2-Butenes are transformed in a continuous flow reactor over metal hydrides of zirconium, tantalum and tungsten supported on silica–alumina. Exceptionally high selectivity to dimeric products is obtained over supported zirconium hydride catalysts.