Bi- and tri-dentate imino-based iron and cobalt pre-catalysts for ethylene oligo-/polymerization

Abstract

Recent progress on the use of iron and cobalt complex precatalysts for ethylene reactivity is reviewed. The review is organized in terms of the denticity of the chelate ligands 10 employed, with particular reference to the influence of the ligand frameworks and their substituents on the catalytic performance for ethylene oligomerization/polymerization catalysis. The majority of the systems bear tri-dentate ligation at the iron/cobalt centre, though it is clear that bi-dentate 15 iron/cobalt complex pre-catalysts have also attracted significant attention. Such systems produce in most cases highly linear products ranging from oligomeric α-olefins to high molecular weight polyethylene, and as such are promising candidates for both academic and industrial 20 considerations.

Pyridine–oxazoline and quinoline–oxazoline ligated cobalt complexes: Synthesis, characterization, and 1,3-butadiene polymerization behaviors

“…Additionally, the catalytic activity and selectivity of catalysts mainly depend on the steric and electronic nature of the active site. In recent years, research interest has been focused on the design and synthesis of well-defined single-site catalysts in order to gain precise control of the catalysis behavior and polymer composition [12][13][14][15]. Since the discovery of bis(arylimino)pyridine ligated Co(II) and iron(II) complexes as effective catalysts for ethylene polymerization/oligomerization [16,17], a variety of transition metal complexes bearing α-diimine, pyridinediimine, and their derivatives have been synthesized and exploited as catalyst precursors for olefin polymerization [18][19][20][21][22][23][24].…”

Correlating net charges and the activity of bis(imino)pyridylcobalt complexes in ethylene polymerization

“…The late-transition metal pre-catalysts could make thermodynamically processes feasible is through opening a lower activation energy pathway to achieve demanding reaction activity [4]. Many efforts have been devoted to iron and cobalt complex pre-catalysts because of their potential applications [5][6][7][8], in which highly active pre-catalysts are generally demanded. From experimental aspects, it is still relied on massive derivatives of ligands to finely control various factors of metal complex pre-catalysts; moreover, the optimization of catalytic parameters would be required to revaluate the real catalytic scales of complexes synthesized.…”

Recent advances in thermally robust, late transition metal‐catalyzed olefin polymerization

“…Fe and Co are both inexpensive, earth‐abundant transition metals that have intrigued researchers in the field of olefin polymerization catalysis. Depending on the identity of their coordinating ligand, catalysts containing these metals have proven to produce polyolefins and α ‐olefin oligomers; however, only those that produce polyolefins are discussed in this review. These catalysts are typically activated using MAO, which yields highly active species that can produce linear, high‐molecular‐weight polyethylene .…”

“…Depending on the identity of their coordinating ligand, catalysts containing these metals have proven to produce polyolefins and α ‐olefin oligomers; however, only those that produce polyolefins are discussed in this review. These catalysts are typically activated using MAO, which yields highly active species that can produce linear, high‐molecular‐weight polyethylene . Generally speaking, it is not uncommon for Fe‐based catalysts to exhibit faster activity than their Co‐based counterparts, though this is not always true .…”

“…To address this, several recent reports have shown that the thermal stability of Fe‐ and Co‐based catalysts may be enhanced using various ligand‐tuning‐based strategies. Many of those recent reports are discussed below, while a more comprehensive review can be found in the literature …”