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Hitchcock PB Hu J Lappert MF Severn JR 《Dalton transactions (Cambridge, England : 2003)》2004,(24):4193-4201
Treatment of [Li(L1)]2 (1) or K(L2) (2) with SnX2 in Et2O yielded the heteroleptic beta-diketiminatotin(II) halides Sn(L1)Cl (3a), Sn(L1)Br (3b) or Sn(L2)Cl (4), even when an excess of the alkali metal beta-diketiminate was used [L1={N(R)C(Ph)}2CH, L2={N(R)C(Ph)CHC(But)N(R)}, R = SiMe3]. From and half an equivalent each of SnCl2.2H2O and SnCl2, or one equivalent of SnCl2.2H2O, the product was Sn(L3)Cl (5) or Sn(L4)Cl (6), in which one or both of the N-R bonds of L1 had been hydrolytically cleaved; the compound Sn(L5)Cl (7) was similarly obtained from and an equivalent portion of SnCl2.2H2O [L3={N(R)C(Ph)CHC(But)N(H)}, L4={N(H)C(Ph)CHC(But)N(H)} and L5={N(H)C(Ph)}2CH]. The halide exchange between 3a and 3b, studied by two-dimensional (119)Sn{1H}-NMR spectroscopy, is attributed to implicate a (mu-Cl)(mu-Br)-dimeric intermediate or transition state. The 13C{1H}-NMR spectra of or showed two distinct resonances for each group, which coalesced on heating, corresponding to DeltaG(338 K)= 69.4 (3a) or 72.8 (3b) kJ mol(-1). The chloride ligand of was readily displaced by treatment with NaNR2, CF3SO3H or CH2(COPh)2, yielding Sn(L1)X [X = NR2 (8), O3SCF3 (9) or {OC(Ph)}2CH (10)]. Oxidative addition of sulfur or selenium to gave the tin(IV) terminal chalcogenides Sn(E)(L1)(NR2)[E = S (11) or Se (12)]. The X-ray structures of the cocrystal of 3a/3b and of the crystalline compounds 5, 6, 8, 11 and are presented, as well as multinuclear NMR spectra of each of the new compounds. 相似文献
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Formation of Octameric Methylaluminoxanes by Hydrolysis of Trimethylaluminum and the Mechanisms of Catalyst Activation in Single‐Site α‐Olefin Polymerization Catalysis
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Dr. Janne T. Hirvi Prof. Manfred Bochmann Dr. John R. Severn Prof. Mikko Linnolahti 《Chemphyschem》2014,15(13):2732-2742
Hydrolysis of trimethylaluminum (TMA) leads to the formation of methylaluminoxanes (MAO) of general formula (MeAlO)n(AlMe3)m. The thermodynamically favored pathway of MAO formation is followed up to n=8, showing the major impact of associated TMA on the structural characteristics of the MAOs. The MAOs bind up to five TMA molecules, thereby inducing transition from cages into rings and sheets. Zirconocene catalyst activation studies using model MAO co‐catalysts show the decisive role of the associated TMA in forming the catalytically active sites. Catalyst activation can take place either by Lewis‐acidic abstraction of an alkyl or halide ligand from the precatalyst or by reaction of the precatalyst with an MAO‐derived AlMe2+ cation. Thermodynamics suggest that activation through AlMe2+ transfer is the dominant mechanism because sites that are able to release AlMe2+ are more abundant than Lewis‐acidic sites. The model catalyst system is demonstrated to polymerize ethene. 相似文献
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Influence of the particle size of the MgCl2 support on the performance of Ziegler catalysts in the polymerization of ethylene to ultra‐high molecular weight polyethylene and the resulting polymer properties
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An Philippaerts Richard Ensinck Nicolas Baulu Astrid Cordier Kersten Woike Romain Berthoud Gert De Cremer John R. Severn 《Journal of polymer science. Part A, Polymer chemistry》2017,55(16):2679-2690
A highly systematic size series of Ziegler catalysts with similar porosities and surface textures are synthesized by varying the stirring speed during the MgCl2 support synthesis. Besides the mean particle size, the only substantial difference observed between the various catalysts is the size and number of nodules per particle. Varying the mean diameter of the catalyst particles between 1.5 and 11.9 µm, leads to a pronounced impact on the activity in ultra‐high molecular weight polyethylene (UHMWPE) polymerization, while the Mw capabilities are only affected to a limited extend. In addition, it is observed that both the Mws as the polymer bulk density (BD) increases during the course of the polymerization. This particularity allows to optimize the Mw and/or BD at a set polymer size, by tuning the catalyst particle size. This is particularly interesting in UHMWPE production, as control of the morphological and structural properties of the UHMWPE reactor powders are critical for efficient processing as well as the performance of the final product. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 2679–2690 相似文献
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Herwig Häusler R. Pamela Kawakami Eva Mlaker Wayne B. Severn Tanja M. Wrodnigg Arnold E. Stütz 《Journal of carbohydrate chemistry》2013,32(4-5):435-449
1. INTRODUCTION Infectious diseases have remained a serious problem for society and concerned government organisations. Due to the dramatic increase of international transport of goods and passengers, dangerous microbial species and infectious diseases can be rapidly distributed over large distances. According to estimations by the World Health Organisation (WHO), nearly 50,000 people are killed by infectious diseases daily. After having been kept at bay for decades, tuberculosis has returned to claim over three million lives per year. In addition, approximately thirty new infectious diseases such as Legionnaire's disease, HIV, or borreliosis have emerged during the past two decades.1 Furthermore, long-known species, for example mycobacteria, the causative agents of such diseases as tuberculosis and leprosy, have acquired a high level of resistance to most commonly employed anti-infective agents. Because of the abundance of pathogenic microorganisms, a tremendous fraction of the pharmaceutical market is devoted to anti-infective drugs. Of a $73 billion total global market of chiral drugs, antibiotics are the largest fraction ($20 billion) closely followed only by cardiovascular therapeutics ($17.5 billion).1 相似文献
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Peter B. Hitchcock Michael F. Lappert Mikko Linnolahti John R. Severn Patrick G.H. Uiterweerd Zhong-Xia Wang 《Journal of organometallic chemistry》2009,694(21):3487-3499
Tin(II) compounds containing the ligands [CH(C6H3Me2-2,5)C(But)NSiMe3]− (≡ L1), [CH(Ph)C(Ph)NSiMe3]− (≡L2), [CH(SiMe3)P(Ph)2NSiMe3]− (≡ L3),
(≡ L4), [C(Ph)C(Ph)NSiMe3]2− (≡ L5), and [C(SiMe3)P(Ph)2NSiMe3]2− (≡ L6) are reported: the transient SnBr(L1) (1) and SnBr(L2) (2), Sn(L1)2 (3) [P.B. Hitchcock, J. Hu, M.F. Lappert, M. Layh, J.R. Severn, J. Chem. Soc., Chem. Commun. (1997) 1189], the labile Sn(L2)2 (4), [Sn(L5)]2 (5), SnCl(L3) (6), Sn(L3)2 (7), [Sn(L6)]2 (8), Sn(L4)2 (9) and Pb(L4)2 (10). They were prepared from (i) SnBr2 and K(L1) (1, 3) or K(L2) (2, 4, 5); (ii) SnCl2 and Li(L3) (6–9); or (iii) PbCl2 and Li(L4) (10). Each of 1, 3 and 5–10 has been characterised by multinuclear NMR spectra; 3, 5, 6, 8, 9 and 10 by EI-mass spectra, but only 3, 5, 8, 9 and 10 were isolated pure and furnished X-ray quality crystals. Of greatest novelty are the title binuclear fused tricyclic ladder-like compounds 5 and 8. Quantum chemical calculations, on alternative pathways to 5 from 2 and to 8 from 7, are reported. 相似文献
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