Generation effects on the microstructure and product distribution in ethylene polymerization promoted by dendritic nickel catalysts

Heterogeneous Dendrimer-Based Catalysts

The present review compiles the advances in the dendritic catalysis within the last two decades, in particular concerning heterogeneous dendrimer-based catalysts and their and application in various processes, such as hydrogenation, oxidation, cross-coupling reactions, etc. There are considered three main approaches to the synthesis of immobilized heterogeneous dendrimer-based catalysts: (1) impregnation/adsorption on silica or carbon carriers; (2) dendrimer covalent grafting to various supports (silica, polystyrene, carbon nanotubes, porous aromatic frameworks, etc.), which may be performed in a divergent (as a gradual dendron growth on the support) or convergent way (as a grafting of whole dendrimer to the support); and (3) dendrimer cross-linking, using transition metal ions (resulting in coordination polymer networks) or bifunctional organic linkers, whose size, polarity, and rigidity define the properties of the resulted material. Additionally, magnetically separable dendritic catalysts, which can be synthesized using the three above-mentioned approaches, are also considered. Dendritic catalysts, synthesized in such ways, can be stored as powders and be easily separated from the reaction medium by filtration/centrifugation as traditional heterogeneous catalysts, maintaining efficiency as for homogeneous dendritic catalysts.

Synthesis of low to high molecular weight poly(1-hexene); rigid/flexible structures in a di- and mononuclear Ni-based catalyst series

Poly(1-hexene)s with a wide range of M_w and MWD using mono- and dinuclear rigid/flexible bridged Ni catalysts; structure–property relation.

Organosilicon platforms: bridging homogeneous, heterogeneous, and bioinspired catalysis

Organosilicon compounds form versatile structures such as cubic metallasiloxanes, cage-like silsesquioxanes, macromolecular nanocages, and flexible dendrimers and linear metallasiloxanes, and are useful as catalysts, ligands for metal complexes, and catalyst supports.

N-(5,6,7-Trihydroquinolin-8-ylidene)arylaminonickel dichlorides as highly active single-site pro-catalysts in ethylene polymerization

A series of N-(5,6,7-trihydroquinolin-8-ylidene)arylamine ligands was synthesized and fully characterized by NMR, IR spectroscopy and elemental analysis. Dimeric N-(5,6,7-trihydroquinolin-8-ylidene)arylaminonickel dichlorides were prepared and examined by IR spectroscopy and elemental analysis, and the molecular structures of the representative nickel complexes were determined by the single crystal X-ray diffraction. On treatment with various alkylaluminiums, all the title complexes exhibited highly active, single-site active behavior for ethylene polymerization producing polyethylene (PE) waxes. The catalytic systems using the co-catalysts diethylaluminium chloride (Et(2)AlCl) or methylaluminoxane (MAO) were investigated in detail, and the molecular weights and distributions of the PEs obtained were found to significantly rely on the nature of the different ligands present and reaction parameters such as the molar ratios of Al/Ni, reaction temperature and reaction time.

Diphenylphosphine containing macromolecules in the methoxycarbonylation of ethene: the effect of macromolecular architecture on the selectivity of the reaction

Various polyhedral oligomeric silsesquioxanes containing diphenylphosphine moieties at their periphery have been used in the methoxycarbonylation of ethene. Those with a -CH(2)CH(2)- spacer between the silicon and the phosphorus atoms (G0-8ethylPPh(2) and G1-16ethylPPh(2)) only produce methyl propanoate whilst a similar macromolecule with a -CH(2)- spacer between Si and P (G1-16methylPPh(2)) gives only copolymer. The effect of the molecular architecture is discussed in comparison with the selectivities observed when using small molecule analogues.

Synthesis and1H NMR studies of paramagnetic nickel(ii) complexes containing bis(pyrazolyl)methane ligands with dendritic substituents

The substituted bis(pyrazolyl)methane ligands RCH(3,5-Me2pz)2(R=SiMe3, CH2Ph, G1, G2, and G3; Gn=Fréchet-type dendritic wedges of generation n) have been prepared starting from H2C(3,5-Me2pz)2. Reaction of these didentate ligands with [NiBr2(DME)] is a straightforward procedure that allows the synthesis of the nickel(II) complexes [NiBr2{RCH(3,5-Me2pz)2}]. The molecular structure of compound (R=CH2Ph) has been determined by X-ray diffraction studies. The nickel centre coordinates two bromine and two nitrogen atoms in a tetrahedral environment, and the metallacycle Ni(NN)2C adopts a boat conformation with the benzyl group in an axial position. 1H NMR studies have been carried out to characterize these paramagnetic nickel compounds in solution. Valuable information about the disposition of the ligands and dendritic wedges in solution has been obtained thanks to the influence of the paramagnetic centre on the proton resonances.