Bis(imino)pyridines fused with 6- and 7-membered carbocylic rings as N,N,N-scaffolds for cobalt ethylene polymerization catalysts

Abstract

Mixed carbocyclic-fused bis(arylimino)pyridine-cobalt(ii) chlorides, on activation with either MAO or MMAO, displayed high activities for ethylene polymerization affording linear polyethylene waxes; high selectivity for vinyl end-groups is a feature of MAO-promoted systems.

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

“…As an alternative strategy in bis(imino)pyridine ligand design, our group has recently explored the fusion of carbocycles to the central pyridine unit in (Figure 1) as a means to form well-defined Fe-/Co-based complexes bearing singly [22][23][24][25][26][27][28][29][30] and doubly fused derivatives (e.g., B, C, D, and E in Figure 1) [31][32][33][34][35][36][37][38]. Indeed, the fused ring size has been shown to be pivotal to the catalytic activity and polymeric properties [6,[36][37][38]. Of particular note, iron-containing B [31], C [32], and D [36] can produce strictly linear polyethylenes with a wide range of molecular weights, end-group types, and activities (up to 10 7 g(PE) mol -1 (Fe) h -1 ) [6,36].…”

Exceptionally high molecular weight linear polyethylene by using N,N,N′‐Co catalysts appended with a N′‐2,6‐bis{di(4‐fluorophenyl)methyl}‐4‐nitrophenyl group

“…To explore the potential of precatalysts Co1 -Co5 to mediate the polymerization of ethylene, methylaluminoxane (MAO) and modified methylaluminoxane (MMAO) were chosen as co-catalysts; both aluminoxanes have a reputation for being among the most potent in cobalt polymerization catalysis. [26][27][28][29][30][31][32][33][34][35][36][37][38][39][40]43] The effect of the Al:Co molar ratio, reaction temperature, run time and ethylene pressure are all parameters to be investigated. The molecular weights (M w ) and molecular weight distributions (M w / M n ) of the resultant polyethylenes were determined by gel permeation chromatography (GPC), while their melt temperatures (T m ) were determined by differential scanning calorimetry (DSC).…”

“…As the temperature was raised, the catalytic activity steadily reduced reaching a minimal value of 2.85 × 10 6 g (PE) mol −1 (Co) h −1 at 60°C, which is likely attributable to partial deactivation of the active species and lower solubility of ethylene at elevated temperature. [4][5][6][7][8][9][10][11][12][13][14][15]38,[48][49][50]54,55] Nevertheless, this activity at 60°C was relatively high when compared with related cobalt catalysts at a similar operating temperature, [10,13,30,[32][33][34][35][36][37][38] highlighting the appreciable thermal stability of this catalyst. In terms of the polymer molecular weight, it was evident that increasing the temperature gave polyethylene of lower molecular weight ( Figure S1), which is in line with more rapid chain transfer/chain termination at the higher temperature compared to chain propagation.…”

“…Of particular note have been the raft of steric and electronic variations made to the ortho ‐ and para ‐positions of the N ‐aryl groups of the tridentate ligand . Elsewhere, ligand development has seen the emergence of bis(imino)pyridines fused with carbocycles that can be varied in terms of their ring size ( B , n = 0–3, Scheme ) . Collectively, these structural changes to the chelating ligand have seen important correlations with the activity and temperature stability of the active catalyst as well as the molecular weight of the polyethylene.…”

“…[25] Elsewhere, ligand development has seen the emergence of bis(imino)pyridines fused with carbocycles that can be varied in terms of their ring size (B, n = 0-3, Scheme 1). [26][27][28][29][30][31][32][33][34][35][36][37] Collectively, these structural changes to the chelating ligand have seen important correlations with the activity and temperature stability of the active catalyst as well as the molecular weight of the polyethylene.…”