Electronic Effect of Fluoro Substituents on Chromium(lll) Complexes bearing ?-Diketiminate Ligands for Ethylene Polymerization

摘要

A series of new chromium(III) complexes bearing fluoro-substituted ?-diketiminate iigands have been synthesized and characterized by IR and elemental analyses. When activated by modified methylaluminoxane (MMAO), these Cr complexes exhibited moderate or high activities for ethylene polymerization (up to 370 gmmol~(-1)-h~(-1)). Various reaction parameters such as reaction temperature and Al/Cr ratio were investigated in detail. Further more, it was found for the first time that the catalytic behaviors of Cr complexes can be greatly influenced by the electronic effect of fluoro substituents. The introduction of electron-withdrawing fluoro groups to ligands can improve the catalytic performances compared with those bearing alkyl groups, but incorporation of more fluoro atoms would then decrease the catalytic activities.