Adjusting Ortho-Cycloalkyl Ring Size in a Cycloheptyl-Fused N,N,N-Iron Catalyst as Means to Control Catalytic Activity and Polyethylene Properties

Abstract

Five examples of bis(arylimino)tetrahydrocyclohepta[b]pyridine dichloroiron(II) complex, [2-{(Ar)N=CMe}-9-{N(Ar)}C10H10N]FeCl2 (Ar = 2-(C5H9)-4,6-(CHPh2)2C6H2Fe1, 2-(C6H11)-4,6-(CHPh2)2C6H2Fe2, 2-(C8H15)-4,6-(CHPh2)2C6H2Fe3, 2-(C12H23)-4,6-(CHPh2)2C6H2Fe4, and 2,6-(C5H9)2-4-(CHPh2)C6H2Fe5), incorporating ortho-pairings based on either benzhydryl/cycloalkyl (ring sizes ranging from 5 to 12) or cyclopentyl/cyclopentyl groups, have been prepared in reasonable yield by employing a simple one-pot template strategy. Each complex was characterized by FT-IR spectroscopy, elemental analysis, and for Fe3 and Fe5 by single crystal X-ray diffraction; pseudo-square pyramidal geometries are a feature of their coordination spheres. On treatment of Fe1–Fe5 with modified methylaluminoxane (MMAO) or methylaluminoxane (MAO), a range in catalytic activities for ethylene polymerization were observed with benzhydryl/cyclopentyl-containing Fe1/MMAO achieving the maximum level of 15.3 × 106 g PE mol−1 (Fe) h−1 at an operating temperature of 70 °C. As a key trend, the activity was found to drop as the ortho-cycloalkyl ring size increased: Fe1C5H9/CHPh2~Fe5C5H9/C5H9 > Fe2C6H11/CHPh2 > Fe3C8H15/CHPh2 > Fe4C12H23/CHPh2. Furthermore, strictly linear polyethylenes (Tm > 126 °C) were formed with molecular weights again dependent on the ortho-cycloalkyl ring size (up to 55.6 kg mol−1 for Fe1/MAO); narrow dispersities were a characteristic of all the polymers (Mw/Mn range: 2.3–4.7), highlighting the well-controlled nature of these polymerizations.

Boosting activity, thermostability, and lifetime of iron ethylene polymerization catalysts through gem‐dimethyl substitution and incorporation of ortho‐cycloalkyl substituents

“…By maintaining the Al:Fe molar ratio at 2000:1, the activity quickly increased to a maximum level of 15.40 × 10 6 g of PE (mol of Fe) −1 h −1 at 60°C. Above 60°C the catalytic activity only slightly lessened, which was consistent with the partial deactivation of the active species [ 34,35,46,47 ] and/or the lower solubility of ethylene at the higher temperature (Figure 2). [ 48–50 ] The reason for these significant variations in catalytic performance at different reaction temperatures (especially for 30°C) is unclear but could possibly be due to the degree of activation of the precatalyst that rapidly increases with temperature.…”

α,α'‐Bis (imino)‐2,3:5,6‐bis (pentamethylene)pyridines appended with benzhydryl and cycloalkyl substituents: Probing their effectiveness as tunable N,N,N‐supports for cobalt ethylene polymerization catalysts

“…The bis (arylimino)‐2,3:5,6‐bis(pentamethylene)pyridylcobalt (II) chloride complexes, [2,3:5,6‐{C 4 H 8 C(NAr)} 2 ]CoCl 2 (Ar = 2,6‐(C 5 H 9 ) 2 –4‐(CHPh 2 )C 6 H 2 Co1 , 2‐(C 5 H 9 )‐4,6‐(CHPh 2 ) 2 C 6 H 2 Co2 , 2‐(C 6 H 11 )‐4,6‐(CHPh 2 ) 2 C 6 H 2 Co3 , 2‐(C 8 H 15 )‐4,6‐(CHPh 2 ) 2 C 6 H 2 Co4 , 2‐(C 12 H 23 )‐4,6‐(CHPh 2 ) 2 C 6 H 2 Co5 ), were prepared by employing a single‐pot procedure [ 13,30–33 ] involving the reaction of α,α'‐dioxo‐2,3:5,6‐bis (pentamethylene)pyridine, the corresponding 2‐cycloalkylaniline and cobalt dichloride in acetic acid at reflux (Scheme 1). All complexes have been isolated in reasonable yield (19%–49%) and characterized by FT‐IR spectroscopy, elemental analysis and, in the case of Co1 , by single crystal X‐ray diffraction.…”

“…), were prepared by employing a single-pot procedure [13,[30][31][32][33] involving the reaction of α,α'-dioxo-2,3:5,6-bis (pentamethylene)pyridine, the corresponding 2-cycloalkylaniline and cobalt dichloride in acetic acid at reflux (Scheme 1). All complexes have been isolated in reasonable yield (19%-49%) and characterized by FT-IR spectroscopy, elemental analysis and, in the case of Co1, by single crystal X-ray diffraction.…”

“…Indeed, the earlier finding that the molecular weight of the polyethylene generated gradually decreased with an increase in the Al: Co molar ratio (runs 2 and 6-9, Table 2; runs 3 and 7-9, Table 3) suggests that chain transfer to aluminum is important and, moreover, would account for saturated polymer. [19,31]…”

Ring size enlargement in an ortho‐cycloalkyl‐substituted bis(imino)pyridine‐cobalt ethylene polymerization catalyst and its impact on performance and polymer properties

“…With respect to the molecular weight of the polyethylene generated, it is apparent that higher polymerization run temperatures lead to lower molecular weight polymers, an observation that is again consistent with temperatureinduced chain transfer (Figure 5). [40][41][42][43][44][45][46] When compared with that seen with Co3/MAO over the same set of temperatures, the range in molecular weights of the polymers is narrower with MMAO (42.3-19.0 kg per mol vs. 56.1-21.7 kg per mol [MAO]). Nonetheless, their dispersities at the different temperatures remained narrow in line with site active species (M w /M n range: 1.6-1.9).…”