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Deckers, Patrick J. W.; Hessen, Bart; Teuben, Jan H.

doi:10.1002/1521-3757(20010702)113:13<2584::aid-ange2584>3.3.co;2-s

Cited by 7 publications

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“…Hemilabile chelates feature a mix of strong and weak donors, completing the metal coordination sphere with a weak donor that can be displaced by substrate to initiate catalysis. In many cases, hemilability provides an ideal balance of activity and stability, particularly with alkene substrates in olefin isomerization, oligomerization, and metathesis . The hemilabile donor acts as a “gate” that mediates substrate binding based on the metal–ligand bond strengths of the particular donor and the chelate size.…”

Section: Methodsmentioning

confidence: 99%

An Ion‐Responsive Pincer‐Crown Ether Catalyst System for Rapid and Switchable Olefin Isomerization

Kita

Miller

2017

Angew Chem Int Ed

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Rapid, selective, and highly controllable iridium-catalyzed allylbenzene isomerization is described, enabled by tunable hemilability based on alkali metal cation binding with a macrocyclic "pincer-crown ether" ligand. An inactive chloride-ligated complex can be activated by halide abstraction with sodium salts, with the resulting catalyst [κ -( NCOP )Ir(H)] exhibiting modest activity. Addition of Li provides a further boost in activity, with up to 1000-fold rate enhancement. Ethers and chloride salts dampen or turn off reactivity, leading to three distinct catalyst states with activity spanning several orders of magnitude. Mechanistic studies suggest that the large rate enhancement and high degree of tunability stem from control over substrate binding.

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Section: Methodsmentioning

confidence: 99%

An Ion‐Responsive Pincer‐Crown Ether Catalyst System for Rapid and Switchable Olefin Isomerization

Kita

Miller

2017

Angew Chem Int Ed

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“…A significant innovation was developed in 2001, when Hessen's group reported a highly selective arene-substituted Cp titanium complex catalyst, namely [(η 5 -C 5 H 4 C(Me) 2 RTiCl 3 ]/MAO, that can be switched from an ethylene polymerization catalyst into an ethylene trimerization catalyst, producing 1-C 6 , by simply changing the ligand substituent R from methyl to phenyl group. [9] In 2002, the same group synthesized [(η 5 -C 5 H 3 R(bridge)ArTiCl 3 ] complexes activated by methylaluminoxane (MAO) co-catalyst that produced 1-C 6 with an excellent productivity and selectivity (up to 99%). [10,11] The only by-products are C 10 fraction and a trace amount of polyethylene.…”

Section: Introductionmentioning

confidence: 99%

Optimization of ethylene trimerization using catalysts based on TiCl₃/half‐sandwich ligands

Azimnavahsi

Mohamadnia

2018

Applied Organom Chemis

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Catalytic trimerization of ethylene using three titanium‐based complexes [η5‐C9H6C(R)thienyl]TiCl3 with various types of bridges (R = cyclo‐C5H10 (C1), cyclo‐C4H8 (C2) and (CH3)2 (C3)) has been successfully optimized and compared. First of all, three benzofulvene precursors, C9H6C(R), were synthesized. Then the corresponding indenyl‐based ligands were obtained via the reaction of the precursors with thienyllithium. The final titanium‐based catalysts display a distorted tetrahedral geometry, as expected for Ti(IV), with the ligand coordinated with a hemilabile behaviour. The structures of the compounds were confirmed on the basis of various analyses. The effect of catalyst concentration, ethylene pressure, reaction temperature and nature of the bridge as the significant factor affecting coordination and orientation of thienyl group relative to the metal centre on 1‐hexene (1‐C6) productivity and selectivity was investigated. Results revealed that the bulky bridge groups such as cyclo‐C5H10 and cyclo‐C4H8 are appropriate for ethylene trimerization due to the closer coordination of sulfur atom with Ti, especially in cationic state, and catalyst C2 with cyclo‐C4H8 bridge exhibits moderate productivity equal to 785 kg 1‐C6 (mol Ti)−1 h−1. According to the results, ethylene at a pressure of 10 bar, 50°C and 1.5 μmol of catalyst were selected as the best conditions for obtaining 1‐C6 with high productivity and selectivity. The presence of indenyl enhances the thermal stability of the catalysts and preserves their activity in higher temperatures such as 50 and 80°C.

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“…Such ligands will provide a stabilizing donor for reactive cationic catalysts and yet be labile in the presence of substrate olefin. Recently, Hessen and coworkers have employed a hemilabile ligand to develop the first ethylene trimerization catalyst [50][51][52] in which a pendant arene fragment on a cyclopentadienyl ligand stabilizes a cationic titanium(II) intermediate (Scheme 1). Employing a related strategy we have shown that pendant arene substituents on phosphinimide ligands can act as hemilabile ligands (Scheme 1) 34, 53 to stabilize reduced Ti centers and coordinatively unsaturated Ti(IV) cations.…”

Section: Introductionmentioning

confidence: 99%

Phosphinimide complexes with pendant hemilabile donors: synthesis, structure and ethylene polymerization activity

et al. 2009

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The phosphines tBu(2)P(CH(2))(3)ECH(2)Ph (E = O (1), S (2)) converted to the corresponding phosphinimines (Me(3)SiN)PtBu(2)(CH(2))(3)ECH(2)Ph, E = O (3), S (4)) which were used to prepared the titanium complexes Cp'TiCl(2)NPtBu(2)(CH(2))(3)ECH(2)Ph, (E = O, Cp' = Cp (5), Cp* (6); E = S, Cp' = Cp (7), Cp* (8)). These species were subsequently methylated to the corresponding dimethyl-derivatives (9)-(12). Activation of (9)-(12) with both B(C(6)F(5))(3) and [Ph(3)C][B(C(6)F(5))(4)] was studied. For example, the [CpTiMe(NPtBu(2)(CH(2))(3)OCH(2)Ph)][MeB(C(6)F(5))(3)] (13) reacted with THF to give [CpTiMe(THF)(NPtBu(2)(CH(2))(3)OCH(2)Ph)][MeB(C(6)F(5))(3)] (14). Similar reactions gave the stable ion pairs [Cp'TiMe(NPtBu(2)(CH(2))(3)XCH(2)Ph)][MeB(C(6)F(5))(3)] (X = O, Cp' = Cp*, (15); X = S Cp' = Cp, (16), Cp*(17)) and [Cp'TiMe(NPtBu(2)(CH(2))(3)XCH(2)Ph)][B(C(6)F(5))(4)] (X = O, Cp' = Cp, (18); Cp*(19); X = S, Cp' = Cp, (20), Cp* (21)). The dihalide complexes (5)-(8), activated with MAO, proved to be ethylene polymerization catalysts of moderate activities. The dialkyl titanium complexes (9)-(12) activated with B(C(6)F(5))(3) or [Ph(3)C][B(C(6)F(5))(4)], gave catalysts that exhibited substantially higher activity and high molecular weight polyethylene. Polymerization at 60 degrees C rather than 30 degrees C significantly increased activity as well. The impact of the hemilabile donor with respect to catalyst activity is discussed. Crystallographic studies of (5) and (6) are reported.

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Cited by 7 publications

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An Ion‐Responsive Pincer‐Crown Ether Catalyst System for Rapid and Switchable Olefin Isomerization

An Ion‐Responsive Pincer‐Crown Ether Catalyst System for Rapid and Switchable Olefin Isomerization

Optimization of ethylene trimerization using catalysts based on TiCl₃/half‐sandwich ligands

Phosphinimide complexes with pendant hemilabile donors: synthesis, structure and ethylene polymerization activity

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Cited by 7 publications

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An Ion‐Responsive Pincer‐Crown Ether Catalyst System for Rapid and Switchable Olefin Isomerization

An Ion‐Responsive Pincer‐Crown Ether Catalyst System for Rapid and Switchable Olefin Isomerization

Optimization of ethylene trimerization using catalysts based on TiCl3/half‐sandwich ligands

Phosphinimide complexes with pendant hemilabile donors: synthesis, structure and ethylene polymerization activity

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Optimization of ethylene trimerization using catalysts based on TiCl₃/half‐sandwich ligands