Pd-Iminocarboxylate Complexes and Their Behavior in Ethylene Polymerization

Investigation of catalytic reaction of ethylene dimerization to butene-1 by use of DCPDS as a modifier based on response surface methodology

Butene-1 is one of the most important petrochemical industry products that is produced in different ways. Ethylene is an important source of Butene-1 production through the oligomerization process. In this study, to reduce the by-product of the polymer produced and to improve the catalyst yield, the dicyclopentyldimethoxysilane (DCPDS) modifier in the presence of a homogeneous titanium tetra butoxide/triethyl aluminum catalyst and a combination of dichloromethane (as a promoter) in a high-pressure Buchi reactor were used. Gas chromatography was used for liquid and gas phase analysis in the reactor. The design of experiments was performed with the Box-Behnken design technique (BBD) based on the response surface method (RSM). In this method, four effective factors of catalyst concentration, modifier, promoter, and temperature were evaluated. The results of the analysis of variance for the answers of ethylene conversion rate, selectivity, polymer production rate, and yield showed that there is a good agreement between the actual values and the values obtained from the model. Optimization using design expert software showed values of 85.6, 88.5, 2.43, and 75.78% for ethylene conversion rate, selectivity, polymer content and yield, respectively, which showed an error of less than one percent compared to the laboratory results. Comparison of the catalyst performance with and without DCPDS and DCM showed that the presence of these two compounds together with the catalyst, in addition to increasing by 4, 6, and 9% for conversion, selectivity of Butene-1 and yield, respectively, reduced the production of the undesirable polymer in the reactor from 136 mg to 2.4 mg.

Controlled di-lithiation enabled synthesis of phosphine-sulfonamide ligands and implications in ethylene oligomerization

Catalyst design for ethylene oligomerization has attracted significant interest. Herein, we report the synthesis of phosphine-sulfonamide-derived palladium complexes and examine their performance in ethylene oligomerization. Arresting a dilithiation intermediate of N-(2-bromophenyl)-4-methylbenzenesulfonamide (1) at -84 °C selectively produced N-(2-(bis(2-methoxyphenyl)phosphanyl)phenyl)-4-methylbenzenesulfonamide (L1A). However, the same reaction at -41 °C delivered a different ligand; 2-(bis(2-methoxyphenyl)phosphanyl)-4-methyl-N-phenylbenzenesulfonamide (L2A). The generality of our strategy has been demonstrated by preparing N-(2-(diphenylphosphanyl)phenyl)-4-methylbenzenesulfonamide (L1B) and 2-(diphenylphosphanyl)-4-methyl-N-phenylbenzenesulfonamide (L2B). Subsequently, L1A and L1B were treated with a palladium precursor to yield 5-membered complexes C1 and C2, respectively. In contrast, L2A upon treatment with palladium produced a 6-membered metal complex C3. Thus, a small library of 7 palladium complexes (C1-C7) were synthesized by varying the donor moiety (pyridine, DMSO, and acetonitrile). The identity of palladium complexes was unambiguously ascertained using a combination of spectroscopic and analytical methods, including single-crystal X-ray diffraction. The performance of the complexes C1-C7 was investigated in ethylene oligomerization and almost all of them were found to be active. The resultant ethylene oligomers were characterized using 1H and 13C NMR, MALDI-ToF-MS, and GPC. Detailed screening of reaction parameters revealed 100 °C and 40 bars ethylene to be optimal conditions. Complex C5 outperformed other complexes and produced ethylene oligomers with a molecular weight of 1000-1900 g mol-1.