Sequential treatment of a previously-calcined solid oxide support (i.e. SiO2, γ-Al2O3, or mixed SiO2-Al2O3) with solutions of Cr{N(SiMe3)2}3 (0.71 wt% Cr) and a Lewis acidic alkyl aluminium-based co-catalyst (15 molar equivalents) affords initiator systems active for the oligomerisation and/or polymerisation of ethylene. The influence of the oxide support, calcination temperature, co-catalyst, and reaction diluent on both the productivity and selectivity of the immobilised chromium initiator systems have been investigated, with the best performing combination (SiO2-600, modified methyl aluminoxane-12 {MMAO-12}, heptane) producing a mixture of hexenes (61 wt%; 79% 1-hexene), and polyethylene (16 wt%) with an activity of 2403 g gCr -1 h-1. The observed product distribution is rationalised by two competing processes: trimerisation via a supported metallacycle-based mechanism and polymerisation through a classical Cossee-Arlman chain-growth pathway. This is supported by the indirect observation of two distinct chromium environments at the surface of the oxide support by a solid-state 29Si NMR spectroscopic study of the Cr{N(SiMe3)2}x/SiO2-600 pro-initiator.

中文翻译：

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催化剂载体，稀释剂和助催化剂在铬介导的异质乙烯三聚反应中的作用。

用Cr {N（SiMe3）2} 3（0.71 wt％Cr）和路易斯酸性烷基铝基溶液对先煅烧的固体氧化物载体（即SiO2，γ-Al2O3或混合SiO2-Al2O3）进行顺序处理助催化剂（15摩尔当量）提供了对乙烯的低聚和/或聚合有活性的引发剂体系。研究了氧化物载体，煅烧温度，助催化剂和反应稀释剂对固定化铬引发剂体系的生产率和选择性的影响，采用了性能最佳的组合（SiO2-600，改性甲基铝氧烷-12 {MMAO -12}，庚烷）制得己二烯（61 wt％； 79％1-己烯）和聚乙烯（16 wt％）的混合物，其活性为2403 g gCr -1 h-1。通过两个相互竞争的过程使观察到的产品分布合理化：通过支持的基于金属环的机理进行三聚，并通过经典的Cossee-Arlman链增长途径进行聚合。Cr {N（SiMe3）2} x / SiO2-600前引发剂的固态29Si NMR光谱研究间接观察了氧化物载体表面上两个不同的铬环境，这证明了这一点。