Chromium Catalysts Supported by a Nonspectator NPN Ligand: Isolation of Single‐Component Chromium Polymerization Catalysts

Albahily, Khalid; Koç, Ece; Al-Baldawi, Danya; Savard, Didier; Gambarotta, Sandro; Burchell, Tara J.; Duchateau, Robbert

doi:10.1002/anie.200800845

Cited by 63 publications

(34 citation statements)

References 44 publications

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“…The structure of 4 is a uranium(IV) centre with the metallocene ligand framework and a bis(amido)phosphane ligand in a pseudo-tetrahedral environment. [54][55][56] The uranium-nitrogen bond distances of 2.277( 4 36 The P-N bond distances are 1.734(4) and 1.741(4)Å, much longer than the 1.600(3)Å found in 3, indicative of a P-N single bond.…”

Section: Resultsmentioning

confidence: 95%

Divergent uranium- versus phosphorus-based reduction of Me₃SiN₃ with steric modification of phosphido ligands

et al. 2020

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Section: Resultsmentioning

confidence: 95%

Divergent uranium- versus phosphorus-based reduction of Me₃SiN₃ with steric modification of phosphido ligands

et al. 2020

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“…Reduction of the metal center is rather expected as it is often observed when trivalent chromium precursors are treated with alkyl aluminum reagents. [6,14] The catalytic activity of complexes 1 a-Me and 2 a-Me was low because of their poor solubility in both methylcyclohexane (MeCy) and toluene. Test reactions that were carried out on the precipitated ligand-CrCl 3 adducts showed no difference in catalytic behavior to the in situ generated species.…”

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confidence: 99%

A Highly Selective Ethylene Tetramerization Catalyst

Shaikh¹,

Albahily²,

Sutcliffe³

et al. 2012

Angew Chem Int Ed

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The issue of selectivity has been the most challenging aspect of ethylene oligomerization since its discovery.[1] In the last three decades, trimerization systems with high selectivity have been discovered, [2] but tetramerization catalysts with high selectivity remain elusive. [3] Central to the future success of this endeavor is to understand the factors responsible for the selectivity of the catalytic cycle. [4] Trivalent chromium complexes are the catalyst precursors that are most commonly used for these transformations. In the presence of alkyl aluminum activators, these species are reduced to the divalent state (responsible for nonselective oligomerization and/or polymerization) or the monovalent state (responsible for selectivity).[5] To complicate the scenario, there is also the possibility for these monovalent and divalent species to undergo disproportionative redox processes that give inactive zero-valent chromium together with higher-valent species that are readily available for further cycles of reduction/reoxidation.[6] Because of the presence of such a redox dynamism in the catalytic cycle, the ancillary ligand system determines the selectivity by preferentially stabilizing one particular oxidation state. For example, when highly reactive monovalent species are provided with a sufficiently long lifetime, selective oligomerization is initiated by the so-called redox reaction/ring-expansion mechanism. [2,5,7] As mentioned above, selective ethylene tetramerization remains exceedingly rare. With a maximum of around 77 % in the case of the process developed by SK Energy,[3d] the selectivity is definitely good, but still far from the levels obtained with the trimerization systems. In addition, the unavoidable formation of polymers poses serious reactorfouling problems that complicate industrial application. The same redox reaction/ring expansion mechanism that accounts for the selectivity of the trimerization cycle has also been invoked for the rationalization of the tetramerization. [3b, 8] Following this mechanism, it is conceivable that high selectivity cannot be reached. The selectivity in this mechanism is determined by the rate of the reduction/elimination step compared to the rate of further ring expansion. If the sevenmembered ring is capable of expanding readily into the ninemembered ring, it is hard to imagine why additional expansion should not occur equally fast. [9] In the end, a distribution of oligomers is to be expected and 1-octene may be a dominant product.Rosenthal and co-workers [10] first emphasized this problem and postulated an alternative mechanism for the highly selective formation of 1-octene. According to their hypothesis, a dimetallic system with two low-valent chromium centers that are not linked with each other may independently form two five-membered metallacycles. Cooperative dimetallic reductive elimination selectively affords 1-octene. It is by following this fascinating hypothesis that we have recently for the first time observed the formation of 1-octene that was un...

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“…Figure 13. N^N and N^P-chelated chromium precatalysts, 43 -45 [128 -130] Duchateau and Gambarotta employed the bis-chelated chromium complex, 44a as a precursor to 44b and 44c ( Figure 13) [129]. When activated with MAO, 44a yielded a statistical distribution of ethylene oligomers (including waxes) with very high activity.…”

Section: N^n and N^p-ligands And Their Cr Precatalystsmentioning

confidence: 99%

Recent advances in homogeneous chromium catalyst design for ethylene tri-, tetra-, oligo- and polymerization

Bariashir

Huang

Solan

et al. 2019

Coordination Chemistry Reviews

114

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This review focuses on recent progress made using well-defined molecular chromium complexes that, upon suitable activation, can catalyze the tri-, tetra, oligo-and/or polymerization of ethylene. In particular, emphasis will be placed on the tuning of the performance characteristics of these homogeneous catalysts through structural modifications made to the multidentate ligand manifold (e.g., donor atoms, charge, backbone and strain) and the effects these changes have on the resulting ethylene derivatives. While the ability of these catalysts to mediate the formation of high molecular weight linear polyethylene continues to see many developments, their capacity to form polyethylene waxes and oligomers has witnessed some major advances. Moreover, the impressive selectivity of some chromium systems to generate commercially important 1-hexene and more recently 1-octene has seen the implementation of this technology at the industrial level. The types of precatalysts to be discussed will be divided broadly on the basis of their ability to generate either polymers/oligomers or short chain αolefins; the effects of co-catalyst and reaction conditions (e.g., temperature, pressure, solvent) on catalytic activity and selectivity, will be also developed. In addition, current proposals as to the mechanistic details displayed by these versatile chromium catalysts will be highlighted.

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Chromium Catalysts Supported by a Nonspectator NPN Ligand: Isolation of Single‐Component Chromium Polymerization Catalysts

Cited by 63 publications

References 44 publications

Divergent uranium- versus phosphorus-based reduction of Me₃SiN₃ with steric modification of phosphido ligands

Divergent uranium- versus phosphorus-based reduction of Me₃SiN₃ with steric modification of phosphido ligands

A Highly Selective Ethylene Tetramerization Catalyst

Recent advances in homogeneous chromium catalyst design for ethylene tri-, tetra-, oligo- and polymerization

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Chromium Catalysts Supported by a Nonspectator NPN Ligand: Isolation of Single‐Component Chromium Polymerization Catalysts

Cited by 63 publications

References 44 publications

Divergent uranium- versus phosphorus-based reduction of Me3SiN3 with steric modification of phosphido ligands

Divergent uranium- versus phosphorus-based reduction of Me3SiN3 with steric modification of phosphido ligands

A Highly Selective Ethylene Tetramerization Catalyst

Recent advances in homogeneous chromium catalyst design for ethylene tri-, tetra-, oligo- and polymerization

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Divergent uranium- versus phosphorus-based reduction of Me₃SiN₃ with steric modification of phosphido ligands

Divergent uranium- versus phosphorus-based reduction of Me₃SiN₃ with steric modification of phosphido ligands