Chitosan microsphere-supported catalysts: design, synthesis and optimization for ethylene polymerization.

Polyolefins are the main building blocks for consumer products. Here, chitosan, a biopolymer that can be derived from abundant fishery waste, is shaped as a microspheroidal support using spray drying to facilitate ethylene polymerization. Definitive screening design was used to optimize synthesis steps efficiently.

Dinuclear group IV metal complexes based on a bis(indenyl)-(/)-stilbene platform: a potential prototype of "photoswitchable" catalysts for olefin polymerization.

The preparation of dizirconium complexes based on a novel bis(indenyl)-(/)-stilbene platform was explored. Negishi coupling between the -generated diorganozincates obtained from the respective //-(/)-dibromostilbenes and the bromo-functionalized zirconocene (η-Cp*)(η-2-methyl-4-bromoindenyl)ZrCl, or, alternatively, the preparation of bis(indene)stilbene pro-ligands {//-(/)-BisIndSB}H through Negishi coupling of the corresponding dibromostilbenes with 4-bromoindene and subsequent metallation/transmetallation with Cp*ZrCl or Zr(NMe), allowed the preparation of a series of dinuclear complexes. These were analyzed by NMR spectroscopy and some of them by iASAP-mass spectrometry and by X-ray diffraction studies.

-Symmetric {cyclopentadienyl/indenyl}-metallocene catalysts: synthesis, structure, isospecific polymerization of propylene and stereocontrol mechanism.

A series of new MeSi-bridged cyclopentadiene/indene proligands {MeSi(R-R-Cp)(R,R,R,R-Ind)H} (1a-j) with various substitutions both on the indene and cyclopentadiene moieties was prepared. The corresponding -symmetric group 4 -metallocene complexes (M = Zr, Hf), namely, {MeSi(MeCp)(Ind)}ZrCl (2a-Zr), {MeSi(MeCp)(2-Me,4-Ph-Ind)}MCl (2b-M), {MeSi(MeCp)(2-Me,4-Ph,6-Bu-Ind)}ZrCl (2c-Zr), {MeSi(MeCp)(2-Me,4-Ph,5-OMe,6-Bu-Ind)}MCl (2d-M), {MeSi(MeCp)(2-R',4-(3',5'-Bu,4'-OMe-CH),5-OMe,6-Bu-Ind)}ZrCl, R' = Me (2e-Zr), R' = Et (2f-Zr), {MeSi(2,5-Ph-3,4-Me-Cp)(2-Me,4-(3',5'-Bu,4'-OMe-CH),5-OMe,6-Bu-Ind)}ZrCl (2g-Zr), {MeSi(MeCp)(2-Me,4-(3',6'-Bu-carbazol-4'-yl)-Ind)}ZrCl (2h-Zr), {MeSi(2,5-Me,3,4-iPr-Cp)(2-Me,4-Ph-Ind)}ZrCl (2i-Zr), {MeSi(2,5-Me,3,4-iPr-Cp)(2-Me,4-Ph,6-Bu-Ind)}ZrCl (2j-Zr) and {MeSi(MeCp)(2-Me-4,5-[]anthracene-Ind)}MCl (2k-Zr) were synthesized and characterized by NMR spectroscopy and mass spectrometry. The solid-state molecular structures of 2b-Zr, 2d-Zr, 2e-Zr, 2f-Zr, 2j-Zr and 2k-Zr were determined by X-ray crystallography.

Paraffin-Inert Atmospheric Solid Analysis Probe: A Fast and Easy Approach To Characterize Extremely Air-Sensitive Organometallic Complexes by Mass Spectrometry.

Rational characterization of most organometallic compounds is hampered by their high reactivity, in particular, toward oxygen and water. Mass spectrometry experiments require physical introduction of the sample in the ionization source. So, the main challenge is to transfer air-sensitive organometallic compounds from inert atmosphere to the ionization source.

A Theoretical Outlook on the Stereoselectivity Origins of Isoselective Zirconocene Propylene Polymerization Catalysts.

The first three insertion steps of propylene for isoselective metallocenes from the one-carbon-bridged cyclopentadienyl-fluorenyl {Cp/Flu} and silicon-bridged ansa-bis(indenyl) {SBI} families were computed by using a theoretical method implementing the B3PW91 functional in combination with solvent corrections incorporated with the Solvation Model based on Density (SMD) continuum model. For C -symmetric {Cp/Flu}-type metallocenes, two mechanisms of stereocontrol were validated theoretically: more facile and more stereoselective chain "stationary" insertion (or site epimerization backskip) and less stereoselective alternating mechanisms. For the C -symmetric {SBI}-type system, the computation results were in complete agreement with the sole operating chain migratory insertion mechanism.

Functionalization of the PEG Corona of Nanoparticles by Clip Photochemistry in Water: Application to the Grafting of RGD Ligands on PEGylated USPIO Imaging Agent.

The fast development of nanomedicines requires more and more reliable chemical tools in order to accurately design materials and control the surface properties of the nano-objects used in biomedical applications. In this study we describe a smooth and simple photografting technique, i.e.

Unprecedented copper(I) bifluoride complexes: synthesis, characterization and reactivity.

To be or not to bifluoride: Two synthetic pathways to unprecedented N-heterocyclic carbene copper(I) bifluoride complexes have been developed. Catalytic tests demonstrated that copper(I) bifluorides are very efficient catalysts, which do not require any additional activating agent. The first Cu-catalyzed diastereoselective allylation of (R)-N-tert-butanesulfinyl aldimines was also established.

A three-component tandem reductive aldol reaction catalyzed by N-heterocyclic carbene-copper complexes.

[Structure: see text] An efficient catalytic system for the three-component coupling of electrophilic alkenes, aldehydes, and silane was optimized with a new family of copper N-heterocyclic carbene complexes. These catalysts do not require activation and show high activity (TOF>15,000 h-1) as well as some anti diastereoselectivity.