Chromium complexes based on thiophene–imine ligands for ethylene oligomerization

Abstract

A new set of Cr(III) complexes, {L}CrCl3(THF), based on thiophene–imine (2a, L = PhOC6H4(N═CH)‐2‐SC4H3; 2b, L = PhOC2H4(N═CH)‐2‐SC4H3; 2c, L = Ph(NH)C2H4(N═CH)‐2‐SC4H3; 2d, L = PhOC6H4(N═CH)‐2‐SC4H2‐5‐Ph; 2e, L = Ph(NH)C2H4(N═CH)‐2‐SC4H2‐5‐Ph) have been prepared and characterized using elemental analysis and infrared spectroscopy. Upon activation with methylaluminoxane, all the chromium complexes generated active systems affording a nonselective distribution of α‐olefins with turnover frequencies in the range 9500–93 500 (mol ethylene) (mol Cr)−1 h−1, and producing mostly oligomers (95.0–99.3 wt% of total products). Small amounts of polymer were produced in these oligomerization reactions (0.8–8.2 wt%). The catalytic activities were quite sensitive to the ligand environment. Moreover, the effects of oligomerization parameters (temperature, [Al]/[Cr] molar ratio, time) on the activity and on the product distribution were examined.

Bis(pyrazolyl)thioether/amine‐chromium(III) catalysts bearing pendantO‐ andN‐donor group for oligomerization and polymerization of ethylene

“…Thus, several families of bidentate and tridentate ligands based on a wide variety of donor‐group combinations have been disclosed in the literature objecting to produce highly active catalyst systems that are capable to produce selectively α‐olefins. [ 16–36 ] Alternatively, introduction of hemilabile pendant donor groups at the ligand framework have been done to improve the catalytic performance of chromium complexes. [ 37–45 ] For instance, Braunstein and Hor reported Cr(III) complexes supported by bis(pyrazol‐1‐yl)methane containing ether or thioether pendant group which are active for ethylene trimerization to 1‐hexene with high selectivity (>99.6%) (A, Chart 1).…”

1‐Decene oligomerization by new complexes bearing diamine‐diphenolates ligands: Effect of ligand structure

“…In the paper described herein, we aimed to design and prepare new diamine-diphenolate ligands, to be considered salan derivative ligands, typically ligands that contain same substituents on the phenolate arms and different linkage between nitrogen atoms and study the structure and catalytic properties of their resulting titanium catalysts (see Scheme 1), in the higher olefins up to 1-decene oligomerization. [20][21][22][23] Our goals were gaining more insight into the activity of salan catalysts with changing ligand structure and possibly synthesizing complexes which will be capable to produce controllable molecular weight 1-decene based oligomers. [24] 2…”

Chromium Complexes Supported by Phenyl Ether‐Pyrazolyl [N,O] Ligands as Catalysts for the Oligo‐ and Polymerization of Ethylene

“…[ 13–16 ] In this way, significant efforts have been dedicated to the synthesis of new families of ligands based on a wide variety of donor‐group combinations aiming to generate more efficient chromium catalyst systems that are capable of selectively forming α‐olefins with high productivities. [ 17–81 ] In particular, chromium catalysts stabilized by pyrazolyl‐based tridentate ligands have been successfully synthetized and their catalytic application in ethylene oligomerization explored in details. [ 51,81–91 ] Selected examples are presented in Chart 1.…”