Remote Dibenzocycloheptyl Substitution On A Bis(Arylimino)Pyridyl-Iron Ethylene Polymerization Catalyst; Enhanced Thermal Stability And Unexpected Effects On Polymer Properties

Four examples of para-dibenzocycloheptyl-substituted 2,6-bis(arylimino)pyridyl-iron(ii) chloride complexes, [2,6-{(2-R-1,4-(C15H13),6-(RC6H2)-C-2)N = CMe}(2)C5H3N]FeCl2 (R-1 = R-2 = Me Fe1, Et Fe2, iPr Fe3, R-1 = Me, R-2 = Et Fe4), have been synthesized and characterized by a combination of IR spectroscopy, elemental analysis and single crystal X-ray diffraction. The molecular structures of Fe2 and Fe4 highlight not only their pseudo-square pyramidal geometries but also the variation in configuration of the two remote dibenzo-fused cycloheptyl rings. When activated with MAO or MMAO, Fe1-Fe4 displayed very high activities for ethylene polymerization by operating effectively at 70 degrees C/10 atm [up to 7.14 x 10(7) g(PE) mol(-1)(Fe) h(-1)] producing high molecular weight linear polyethylene (as high as 98.7 kg mol(-1)) with a single melting temperature (T-m: >129.7 degrees C) as well as various levels of vinyl unsaturation. Even at temperatures up to 100 degrees C, the polymerization activity remained high [up to 1.46 x 10(7) g(PE) mol(-1)(Fe) h(-1)] underlining the good thermal stability of this catalyst class. By contrast at P-C2H4 = 1 atm, all polyethylenes produced using Fe1-Fe4 at run temperatures between 20-60 degrees C exhibited two melting point values with either MAO (T-m1 93.5-116.2 degrees C, T-m2 124.9-130.0 degrees C) or MMAO (T-m1 65.1-85.9 degrees C, T-m2 116.8-122.8 degrees C) in line with the bimodality of the lower molecular weight polymers. In particular, when MMAO was employed as a co-catalyst, the polyethylene displayed a wax-like composition and displayed a very narrow dispersity (M-w/M-n range: 1.1-1.6).