High Temperature Iron Ethylene Polymerization Catalysts Bearing N,N,N'-2-(1-(2,4-Dibenzhydryl-6-fluorophenylimino)ethyl)-6-(1-(arylphenylimino)ethyl)pyridines

The N,N,N'-ferrous chloride complexes,[2-{CMeN(2,4-(CHPh)_(2)-6-FC_(6)H_(2))}-6-(CMeNAr)C_(5)H_(3)N]FeCl_(2)(Ar=2,6-Me_(2)C_(6)H_(3) Fe1,2,6-Et_(2)C_(6)H_(3)Fe2,2,6-^(i)Pr_(2)C_(6)H_(3) Fe3,2,4,6-Me_(3)C_(6)H_(2) Fe4 and 2,6-Et_(2)-4-MeC_(6)H_(2) Fe5),each possessing one N-2,4-dibenzhydryl-6-fluorophenyl group,were readily synthesized from their respective unsymmetrical bis(imino)pyridines,L1-L5.Structural identification of Fe2 highlighted the variation in the steric properties provided by the dissimilar N-aryl groups.Following pre-treatment with either MAO or MMAO,complexes Fe1-Fe5 all displayed,at an operating temperature of 80℃,high activities for ethylene polymerization with levels falling in the order:Fe4> Fe1> Fe5> Fe2> Fe3.Notably,Fe4/MAO displayed the highest activity of 1.94×10^(7) g_(PE)·mol_(Fe)^(-1)·h^(-1) of the study with only a modest loss in performance at 90℃.Generally,the resulting polyethylenes were highly linear(T_(m) range:122-132℃),narrowly disperse and of low molecular weight(M_(w) range:6.73-46.04kg·mol^(-1)),with the most sterically hindered Fe3 forming the highest molecular weight polymer of the series.End-group analysis by ^(1)H-and ^(13)CNMR spectroscopy revealed saturated alkyl(n-propyl and i-propyl) and unsaturated vinyl chain ends indicative of the role of both β-H elimination and chain transfer to aluminum as termination pathways.By comparison with previou sly reported iron precatalysts with similar tridentate ligand skeletons,it is evident that the introduction of a large benzhydryl group in combination with a fluorine as the ortho-substituents of one N-aryl group has the effect of enhancing thermal stability of the iron polymerization catalyst whilst maintaining appreciable polymer molecular weight.

Investigating the Effects of Para-methoxy Substitution in Sterically Enhanced Unsymmetrical Bis(arylimino)pyridine-cobalt Ethylene Polymerization Catalysts

A group of five bis(arylimino)pyridine-cobalt(Ⅱ)chloride complexes,[2-{(2,6-(Ph_(2)CH)_(2)-4-MeOC_(6)H_(2))N=CMe}-6-(ArN=CMe)C_5 H_(3)N]CoCl_(2)(Ar=2,6-Me_(2)C_(6)H_(3)Co1,2,6-Et_(2)C_(6)H_(3)Co2,2,6-iPr_(2)C_(6)H_(3)Co3,2,4,6-Me_(3)C_(6)H_(2)Co4,2,6-Et_(2)-4-MeC_(6)H_(2)Co5),each containing one N-4-methoxy-2,6-dibenzhydrylphenyl group and one smaller sterically/electronically variable N-aryl group,have been synthesized in good yield(>71%)from the corresponding neutral terdentate nitrogen-donor precursor,L1-L5.All complexes have been characterized by^(1)H-NMR and FTIR spectroscopy with the former highlighting the paramagnetic nature of these cobaltous species and the unsymmetrical nature of the chelating ligand.The molecular structures of Co3 and Co4 emphasize the steric differences of the two inequivalent N-aryl groups and the distorted square pyramidal geometry about the metal centers.In the presence of MAO or MMAO,Co1-Co5 collectively displayed high activities for ethylene polymerization producing high molecular weight polyethylenes that,in general,exhibited narrow dispersities(M_w/M_n values:2.12-4.07).Notably,the least sterically hindered Co1 when activated with MAO was the most productive(6.92×10^(6)g_(PE)·mol^(-1)_((Co))·h^(-1))at an operating temperature of60℃.Conversely,the most sterically hindered Co3/MMAO produced the highest molecular weight polyethylene(M_w=6.29×10^(5)g·mol^(-1)).All the polymers displayed high linearity as demonstrated by their melting temperatures(>130℃)and their~1 H-and^(13)C-NMR spectra.By comparison of Co1 with its para-methyl,-chloro and-nitro counterparts,the presence of the para-methoxy substituent showed the most noticeable effect of enhancing the thermal stability of the catalyst.

Fusing Carbocycles of Inequivalent Ring Size to a Bis(imino)pyridine-Iron Ethylene Polymerization Catalyst: Distinctive Effects on Activity, PE Molecular Weight, and Dispersity

The 4,6-bis(arylimino)-1,2,3,7,8,9,10-heptahydrocyclohepta[b]quinoline-iron(II)chlorides(aryl=2,6-Me_(2)C_(6)H_(3) Fe1;2,6-Et_(2)C_(6)H_(3) Fe_(2);2,6-i-Pr_(2)C_(6)H_(3) Fe_(3);2,4,6-Me3C_(6)H_(2) Fe4;and 2,6-Et_(2)-4-Me_(2)C_(6)H_(2) Fe_(5))have been prepared in good yield by a straightforward one-pot reaction of 2,3,7,8,9,10-hexahydro-1H-cyclohepta[b]quinoline-4,6-dione,FeCl_(2)·4H_(2)O,and the appropriate aniline in acetic acid.All ferrous complexes have been characterized by elemental analysis and FT-IR spectroscopy.In addition,the structure of Fe_(3) has been determined by single crystal X-ray diffraction,which showed the iron center to adopt a distorted square pyramidal geometry with the saturated sections of the fused six-and sevenmembered carbocycles to be cis-configured.In combination with either MAO or MMAO,Fe1–Fe5 exhibited exceptionally high activities for ethylene polymerization(up to 15:86×10^(6) g(PE)mol^(−1)(Fe)h^(−1) at 40℃(MMAO)and 9:60×10^(6) g(PE)mol^(−1)(Fe)h^(−1) at 60℃(MAO))and produced highly linear polyethylene(HLPE,Tm≥128℃)with a wide range in molecular weights;in general,the MMAO-promoted polymerizations were more active.Irrespective of the cocatalyst employed,the 2,6-Me_(2)-substituted Fe1 and Fe4 proved the most active while the more sterically hindered 2,6-i-Pr_(2) Fe_(3) the least but afforded the highest molecular weight polyethylene(Mw:65.6–72.6 kg mol^(-1)).Multinuclear NMR spectroscopic analysis of the polymer formed using Fe4/MMAO at 40℃ showed a preference for fully saturated chain ends with a broad bimodal distribution a feature of the GPC trace(Mw/Mn=13:4).By contrast,using Fe4/MAO at 60℃ a vinyl-terminated polymer of lower molecular weight(Mw=14:2 kg mol^(−1))was identified that exhibited a unimodal distribution(Mw/Mn=3:8).Moreover,the amount of aluminoxane cocatalyst employed,temperature,and run time were also found to be influential on the modality of the polymer.