Modulating Thermostability and Productivity of Benzhydryl‐Substituted Bis(imino)pyridine‐Iron C₂H₄ Polymerization Catalysts through ortho‐C_nH_2n−1 (n=5, 6, 8, 12) Ring Size Adjustment

Abstract

Four types of benzhydryl-containing bis(arylimino)pyridineiron(II) chloride complex, [2-{CMeN(2,4,6-Me 3 C 6 H 2 )}-6-{CMeN(Ar)} C 5 H 3 N]FeCl 2 (Ar = 2,4-), discriminable by the ring size of the ortho-C n H 2nÀ 1 (n = 5, 6, 8, 12) group, have been prepared in good yield (> 85 %) via the reaction of the corresponding N,N,N'-ligand, L1-L4, with ferrous chloride tetrahydrate. All new complexes were characterized by FT-IR spectroscopy and elemental analysis. The molecular structure of Fe3 emphasizes the distorted pseudo-square pyramidal geometry bestowed to the metal center and the steric unevenness provided by the inequivalent N-mesityl and N-2,4-dibenzyhydryl-6-cyclooctylphenyl groups. Extremely high activities for ethylene polymerization were achieved at temperatures between 60 °C and 70 °C following pre-treatment of the iron(II) precatalyst with either MMAO or MAO, with the relative performance being: Fe2 > Fe1 > Fe3 > Fe4. Notably, ortho-cyclohexyl Fe2, under activation with MMAO, afforded the highest level of performance of this study reaching 2.82 × 10 7 g PE per mol (Fe) per h at 70 °C forming strictly linear and narrowly dispersed polyethylene (M w / M n = 2.0) with moderate molecular weight (11.3 kg per mol). Furthermore, runs performed using Fe1/MMAO at 90 °C saw the catalytic activity drop by around only 40 % highlighting the remarkable thermostability of these catalysts. By comparison, polymerizations performed using MAO as co-catalyst were less controlled with broader dispersities (M w /M n range: 4.8-10.1), while the molecular weights were generally higher (55.7-150.9 kg per mol). °Cwith MMAO]. Furthermore E (Scheme 1), [11d] the dibenzocycloheptyl equivalent of D, when activated with MMAO also reached optimal performance at an operating temperature of [a

Unimodal polyethylenes of high linearity and narrow dispersity by using ortho-4,4′-dichlorobenzhydryl-modified bis(imino)pyridyl-iron catalysts

“…Inspection of the data reveals the catalytic activity to initially increase with temperature reaching a peak value of 10.46 Â 10 6 g PE mol À1 (Fe) h À1 at 60 1C (entry 3, Table 2), and then decrease to 8.62 Â 10 6 g PE mol À1 (Fe) h À1 at 80 1C; this loss in performance at temperatures in excess of 60 1C can be attributed to the onset of catalyst deactivation and the lower solubility of ethylene in the solvent at these temperatures. 59 Nonetheless, the observed polymerization activity at 80 1C is greater than those of a host of cobalt or iron analogues, 51,54 which would point towards appreciable thermal stability. In terms of the molecular weight of the polyethylene, this was observed to decrease at higher run temperature, in accordance with an increased rate of chain termination (Fig.…”

“…The coordination geometry of both complexes can be described as distorted square pyramidal with N1, N2, N3 and Cl2 defining the square base and Cl1 the apical position (N(2)-Fe(1)-Cl(1): 89.611 (Fe2), 93.111 (Fe5)). 51,52 More specifically the degree of distortion can be quantified in terms of the tau value (with tau = 0 perfectly square pyramidal and tau = 1 perfectly trigonal bipyramid), 64 with Fe2 being 0.23 and Fe5 0.17. The iron atom itself sits at a distance of 0.531 Å above the basal plane for Fe2 and 0.571 Å for Fe5.…”

“…[27][28][29][30][31][32][33][34][35][36][37] In the main, two strategies have been employed with a view to improve thermal stability and activity of N,N,N-iron catalysts, namely modification of the substituents on the N-aryl groups in A or changes to the ligand framework itself. [38][39][40][41][42][43][44][45][46][47][48][49][50][51] Among these, most effort has been dedicated to the introduction of large sterically hindered substituents to the N-aryl group in A that not only retain the high catalytic activity, but also improve the thermal stability of the catalyst. 49,50 Based on research conducted by our group and others, we have found that the introduction of orthobenzhydryl (CHPh 2 ) substituents to a single N-aryl group in an unsymmetrical version of A (B, Chart 1) can be beneficial to the thermal stability of the iron catalyst.…”

Research Progress of Iron Catalysts with N,N,N‐tridentate Ligands for Ethylene Polymerization

“…One o-cycloalkyl on N-aryl group were introduced to catalysts 18 a-d to improve catalyst thermostability by the addition of steric hindrance on the ligand. [54] Complex 18 b exhibited activities as high as 2.82×10 7 g PE/(mol Fe•h) for ethylene polymerization. The order of the catalyst activity was 18 b > 18 a > 18 c > 18 d, and the catalyst showed the best catalytic performance at 70 °C (Table 2, entries [15][16][17][18].…”

“…One o‐ cycloalkyl on N‐aryl group were introduced to catalysts 18 a – d to improve catalyst thermostability by the addition of steric hindrance on the ligand [54] . Complex 18 b exhibited activities as high as 2.82×10 7 g PE/(mol Fe⋅h) for ethylene polymerization.…”