Ligand Electronic Effects on Late Transition Metal Polymerization Catalysts

Abstract

A series of bis-(aryl)-R-diimine ligands were synthesized bearing a range of electrondonating and -withdrawing substituents to systematically investigate the ligand electronic effects on late transition metal olefin polymerization catalysts. Their palladium(II) complexes were prepared and characterized. Electronic perturbations were verified by analysis of the 1 H and 13 C NMR chemical shifts of the corresponding methyl chloride complexes and the CO stretching frequencies of the corresponding cationic carbonyl complexes, which were found to correlate strongly with the Hammet substituent constant (σ p ) of the substituent on the ligand. The palladium(II) complexes of the functionalized R-diimine ligands were employed in the polymerization of ethylene and the copolymerization of ethylene with methyl acrylate. For ethylene homopolymerization, higher molecular weight was obtained with catalysts bearing more strongly electron-donating ligands. It was observed for the first time that the ligand electronic structure of the catalysts had a significant effect on topology of the polyethylene formed. More dendritic polyethylene was obtained with catalysts bearing more strongly electron-withdrawing ligands. This provides a fundamentally different approach (catalyst approach) to control polyolefin branching topology, which complements our previous strategy of controlling polymer topology by polymerization conditions. For the copolymerization of ethylene with methyl acrylate, strong correlations were observed in the incorporation ratio of methyl acrylate; catalysts bearing strongly electron-donating ligands afforded copolymers with higher incorporation of the polar comonomer. These catalysts also exhibited far greater activity in the presence of polar monomers than catalysts bearing more weakly donating ligands possessing withdrawing substituents, which were deactivated completely when methyl acrylate concentrations were sufficiently high.

Synthesis and Evaluation of Arylimino Pyridine Nickel(II) Catalysts: Influence of Substituents on Polyethylene Structure

“…However, calculating the catalytic activity and tacking into account the ethylene pressure (in Kg-PE/mol-Ni.atm.h), it can be seen that, except for the C2 complex system, all the others do not increase the catalytic activity at higher ethylene pressure. In general, increasing the ethylene concentration tends to facilitate insertion and reduce the walking chain, reducing the number of branches and thus increasing the degree of crystallinity of polyethylene [21,22].…”

Polymer Microstructure Control in Catalytic Polymerization Exclusively by Electronic Effects of Remote Substituents

“…Ethylene of 3.5 grade supplied by Gerling Holz + Co was used without further purification. Molecular weights of obtained polyethylenes were determined by 1 H and 13 C NMR spectroscopic analyses and GPC vs. linear polyethylene standards on a PL220 instrument equipped with mixed B columns using trichlorobenzene/0.0125 % BHT at 160 8C.…”

“…1 H and 13 C NMR analyses of obtained polyethylenes were conducted in 1,1,2,2-tetrachloroethane-d 2 at 130 8C in presence of 0.5 w % CrA C H T U N G T R E N N U N G (acac) 3 as a relaxation aid. Differential scanning calorimetry (DSC) of obtained polymers was performed on a Netzsch DSC 204 F1 with a heating/cooling rate of 10 8C min…”

Electrophilic RhI catalysts for arene H/D exchange in acidic media: Evidence for an electrophilic aromatic substitution mechanism

“…were prepared according to literature procedures [72], 4-nitroDAB was confirmed to reported NMR data [73].…”