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

Abstract

Four unsymmetrical examples of bis(arylimino)pyridines that each possess an ortho-cycloalkyl substituent of unique ring size, 2-{CMeN(2,4,6-Me 3 C 6 H 2 )}-6-{CMeN(2,4-(CHPh 2 ) 2 -6-RC 6 H 2 )}C 5 H 3 N (R = cyclopentyl L1, cyclohexyl L2, cyclooctyl L3, cyclododecyl L4), have been prepared and employed as reactants in the formation of the corresponding cobaltous chloride complexes, (N,N,N 0 ) CoCl 2 (Co1-Co4). Structural characterization of Co2 and Co3 spotlights the five-coordinate geometry and the steric disparity imposed on the metal center by the inequivalent N-mesityl and N-2,4-dibenzyhydryl-6-cycloalkylphenyl groups. Co1-Co4 all proved productive precatalysts for ethylene polymerization achieving optimal performance at a temperature of 60 C on activation with either MAO or MMAO. Cyclopentyl-containing Co1 displayed the highest level (up to 10.3 Â 10 6 g PE per mol [Co] per h), whereas its cyclododecyl counterpart Co4 the lowest (down to 0.14 Â 10 6 g PE per mol [Co] per h).Strictly linear polyethylenes were produced with molecular weights spanning the range 22.0-36.0 kg per mol for Co1-Co4/MAO and 22.6-33.6 kg per mol for Co1-Co4/MMAO, with cyclohexyl Co2 producing the highest values with either activator. With the exception of the polymer produced using Co4, all catalysts afforded narrow unimodal distributions (M w /M n range: 1.7-2.2) for the polyethylenes in line with single site active species. By contrast, Co4 bearing the largest and conformationally flexible cycloalkyl group formed polyethylenes that were distinctly bimodal, which would imply the presence of two active species. End-group analysis of lower molecular weight polymer samples

Exploring Long Range para-Phenyl Effects in Unsymmetrically Fused bis(imino)pyridine-Cobalt Ethylene Polymerization Catalysts

“…Other key signals include the chain end methyl (H f ) that is visible most upfield at δ 0.98. Notably, from the integral ratio of H b :H f (1/7.95) (Figure 10), the molar ratio of unsaturated to fully saturated polyethylene can be calculated as 6/5 (see Supporting Information) [30,39,58]. On this basis, β-H transfer to the metal or monomer presents the main termination pathway when compared to chain transfer to aluminum (Scheme 3) [2,51,54].…”

“…The origin of this behavior was uncertain but was tentatively attributed to a self-immobilization phenomenon [38]. With regard to specific changes to the N,N,N ligand framework, most efforts have focused on varying the steric and electronic properties of the N-aryl substituents belonging to A, with an aim to enhance the thermal stability and increase the activity of their cobalt and iron catalysts [21][22][23][24][25][26][27][28][29][30]. More recently, considerable efforts have been directed towards the development of carbocyclic-fused bis(imino)pyridine ligands, as the size of the fused ring can affect the catalyst performance and product type (e.g., C [17,18,[31][32][33] and D [34][35][36], Scheme 1).…”

Non-Symmetrically Fused Bis(arylimino)pyridines with para-Phenyl Substitution: Exploring Their Use as N′,N,N″-Supports in Iron Ethylene Polymerization Catalysis

“…Evidently, the latter observation highlights the involvement of β-H elimination to metal or monomer during chain termination [24]. Moreover, by considering the integral ratio of vinyl H b to methyl chain-end H f (1/18.82) [29,37,38], the molar ratio of the unsaturated polymer chain to the saturated polymer chain can be determined as 0.379 (see SI), a value that implies the additional presence of a fully saturated polymer in line with chain transfer to aluminum being also operational [4,5]. Further support for these assignments was provided by the 13 C NMR spectrum, which reveals a high-intensity peak around δ 29.43 ppm, which corresponds to the -(CH 2 ) n -repeat unit, along with lower intensity peaks at δ 13.72, 22.38, and 31.66 ppm for an n-propyl end-group and weaker downfield peaks at δ 113.85 and 138.78 ppm for a terminal vinyl group (Figure 10) [24].…”

Thermally Stable and Highly Efficient N,N,N-Cobalt Olefin Polymerization Catalysts Affixed with N-2,4-Bis(Dibenzosuberyl)-6-Fluorophenyl Groups

“…In most cases, these structural modifications have been concerned with the N-aryl groups and, in particular, the influence of substituents with differing steric and electronic properties [1,2,5,[8][9][10][11][12][13][14][15][16][17][18][19][20][21][22]. As a more recent modification, the fusion of carbocyclic rings to the central pyridine in A has seen improvements in both catalytic performance and thermal stability [23][24][25][26][27][28][29][30][31][32][33][34][35]. As an on-going theme in our research, we have been interested in developing families of unsymmetrical bis(imino)pyridine-iron and -cobalt complexes that contain one fixed N-aryl group and the other variable.…”