Chromium complexes based on thiophene–imine ligands for ethylene oligomerization.

A new set of Cr(III) complexes, {L}CrCl3(THF), based on thiophene–imine (2a, L = PhOC6H4(N═CH)‐2‐SC4H3; 2b, L = PhOC2H4(N═CH)‐2‐SC4H3; 2c, L = Ph(NH)C2H4(N═CH)‐2‐SC4H3; 2d, L = PhOC6H4(N═CH)‐2‐SC4H2‐5‐Ph; 2e, L = Ph(NH)C2H4(N═CH)‐2‐SC4H2‐5‐Ph) have been prepared and characterized using elemental analysis and infrared spectroscopy. Upon activation with methylaluminoxane, all the chromium complexes generated active systems affording a nonselective distribution of α‐olefins with turnover frequencies in the range 9500–93 500 (mol ethylene) (mol Cr)−1 h−1, and producing mostly oligomers (95.0–99.3 wt% of total products). Small amounts of polymer were produced in these oligomerization reactions (0.8–8.2 wt%). The catalytic activities were quite sensitive to the ligand environment. Moreover, the effects of oligomerization parameters (temperature, [Al]/[Cr] molar ratio, time) on the activity and on the product distribution were examined. A new set of Cr(III) complexes based on thiophene‐imine have been prepared. Upon activation with MAO, all the chromium complexes generated active systems affording a nonselective distribution of α‐olefins. Highlights: A new class of chromium precatalysts supported by thiophene–imine ligands with pendant N,O‐donor groups has been synthesized.The chromium precatalysts exhibit high selectivity for production of α‐olefins.The catalytic performance of the chromium precatalysts is strongly affected by the ligand environment.The thiophene–imine ligands have a significant effect on the K values and on the oligomer distributions. [ABSTRACT FROM AUTHOR]
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