Three-Coordinate Aluminum Is Not a Prerequisite for Catalytic Activity in the Zirconocene-Alumoxane Polymerization of Ethylene

Harlan, C. Jeff; Bott, Simon G.; Barron, Andrew R.

doi:10.1021/ja00129a008

Cited by 266 publications

(216 citation statements)

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“…The centrosymmetric structure of the rhombododecahedral Al 4 As 6 Li 4 skeleton in 3 may be viewed as close packing of the anionic RAs 2À particles (arsanediides) with Li and HAl 2 ions. The topography of the cluster skeleton is identical with that of the donor-solventfree dimeric triarsanide aggregate [(iPr 3 Si ± AsLi) 3 GetBu] 2 , [14] Scheme 2. Formation of 3 and structure of 6.…”

mentioning

confidence: 85%

“…For instance, the alumoxanes [tBuAl(m 3 -O)] n (n 6, 7, 9) can act as cocatalysts in the Pd-catalyzed conversion of CO and ethene to furnish polyketone polymers [2] and are functional models of MAO (methylalumoxane) which is a cocatalyst in the Ziegler ± Natta polmerization process. [3] However, structure ± reactivity relationships concerning aluminum and gallium pnictide cage compounds have been investigated far less than the chalcogenides of type A [4] and the imino derivatives B. [5,6] Hitherto phosphaimino derivatives of gallane were known, which are tetrameric and adopt the cubane-like structure C. [7] We report here on the first hexameric arsinoalanes andgallanes 1 a ± c, and on the phosphorus homologue 1 d, in which the Al and Ga centers are each bonded to one H atom (Scheme 1).…”

Section: Introductionmentioning

confidence: 99%

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Novel Molecular Clusters Having Aluminum-Phosphorus, Aluminum-Arsenic, and Gallium-Arsenic Skeletons, and Synthesis of an Al4As6Li4 Rhombododecahedron

et al. 1998

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The cyclocondensation reaction of the primary silylarsanes 4 a, b with the trimethylamine adducts of alane (5 a) leads, under liberation of H 2 , to the four-membered 1,3-diarsa-2,4-dialuminetane heterocycles 2 a, b. The latter derivatives were characterized by NMR spectroscopy and a single-crystal X-ray diffraction analysis. Compound 2 a consists of a puckered four-membered Al 2 As 2 ring, which contains threecoordinate As and four-coordinate Al centers and, surprisingly, the NMe 3 groups are cis oriented. Upon heating of 2 a, b in toluene, the NMe 3 groups at the Al centers are readily cleaved and the resulting unsolvated Al 2 As 2 rings trimerize, affording the novel hexagonal prismatic Al 6 As 6 cluster compounds 1 a, b. The latter were characterized by ( 1 H, 27 Al) NMR and IR spectroscopy, and the structure of 1 a was established by a X-ray diffraction analysis. The conversion of the silylarsane 4 a with the amine ± gallane 5 b and of the silylphosphane 4 c with the amine ± alane 5 a, respectively, gives directly, that is, without NMR-spectroscopically detectable intermediates, the hexameric arsagallane and phosphaalane clusters 1 c and 1 d, respectively. They are isostructural with 1 a. Interestingly, the d ( [LiAlH 4 ] in the molar ratio of 1:1 in Et 2 O as solvent gives, under elimination of H 2 , access to the unusual novel heteroaggregate 3, which has a rhombododecahedral Al 4 As 6 Li 6 skeleton. The structure of 3 was established by X-ray diffraction. Surprisingly, the same reaction of the starting materials in 1,2-dimethoxyethane instead of Et 2 O as solvent leads to an unusual triple ion pair compound.

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mentioning

confidence: 85%

Section: Introductionmentioning

confidence: 99%

Novel Molecular Clusters Having Aluminum-Phosphorus, Aluminum-Arsenic, and Gallium-Arsenic Skeletons, and Synthesis of an Al4As6Li4 Rhombododecahedron

et al. 1998

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“…Notably, the [(DIPH)AlMe] 2 dimer has MAO-like features such as bridging O atoms and terminal methyl groups. Similar to Barron's (tBuAlO) 6 model system [33] [Equation (2)], it may show latent Lewis acidity by breaking the four-membered (Al-O) 2 ring; however, no reaction or interaction between [(DIPH)AlMe] 2 and Cp* 2 ZrMe 2 is observed by NMR spectroscopy. This shows that latent Lewis acidity requires structures with annealed four-membered rings that are significantly more strained and, therefore, more reactive.…”

Section: Synthesis and Characterization Of The Al-o-zr Catalystmentioning

confidence: 98%

“…[31][32][33] These cages [Equation (2)] do not contain highly Lewis acidic low-coordinate Al, but they can activate Cp 2 ZrMe 2 by so-called latent Lewis acidity: two adjoining four-membered rings open to create a three-coordinate Lewis acidic Al site. The reaction product of (tBuAlO) 6 and Cp 2 ZrMe 2 has been characterized by multidimensional NMR spectroscopy [Equation (2)].…”

Section: Introductionmentioning

confidence: 99%

Oxide‐Bridged Heterobimetallic Aluminum/Zirconium Catalysts for Ethylene Polymerization

2015

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Protein‐based pharmaceuticals typically display high selectivity and low toxicity, but are also characterized by low oral availability, mainly because of enzymatic degradation in the gastrointestinal tract and poor permeability across the intestinal wall. One way to increase the proteolytic stability of peptides and proteins is by intramolecular crosslinking, such as the introduction of disulfide bridges. However, disulfide bridges are at risk of thiol‐disulfide exchange or reduction during production, purification, and/or therapeutic use, whereas thioether bridges are expected to be stable under the same conditions. In this study, thioether crosslinking was investigated for a 46 aa albumin‐binding domain (ABD) derived from streptococcal protein G. ABD binds with high affinity to human serum albumin (HSA) and has been proposed as a fusion partner to increase the in vivo half‐lives of therapeutic proteins. In the study, five ABD variants with single or double intramolecular thioether bridges were designed and synthesized. The binding affinity, secondary structure, and thermal stability of each protein was investigated by SPR‐based biosensor analysis and CD spectroscopy. The proteolytic stability in the presence of the major intestinal proteases pepsin (found in the stomach) and trypsin in combination with chymotrypsin (found in pancreatin secreted to the duodenum by the pancreas) was also investigated. The most promising crosslinked variant, ABD_CL1, showed high thermal stability, retained high affinity in binding to HSA, and showed dramatically increased stability in the presence of pepsin and trypsin/chymotrypsin, compared to the ABD reference protein. This suggests that the intramolecular thioether crosslinking strategy can be used to increase the stability towards gastrointestinal enzymes.

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“…20 -22 The abstracted Cl is also postulated to be trapped and stabilized in multicoordinate alumoxane complex(es). 20,21 In Method 3, the preactivation of Et(Ind) 2 ZrCl 2 by MAO in solution first forms, through the same mechanism referred to in Method 2, the crown alumoxane complex(es) 23 (Cation 2), which then anchor(s) with the silica surface OH groups.…”

Section: Zrcl]mentioning

confidence: 99%

XPS investigation of the electronic environment in selected heterogenized zirconocene catalysts

Atiqullah

Faiz

Akhtar

et al. 1999

Surf. Interface Anal.

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Ethylbisindenyl zirconium dichloride (Et(Ind)2ZrCl2) and the MAO methylalumoxane (MAO) co‐catalyst were heterogenized on Davision silica 955 partially dehydroxylated at 275 °C, following the concept of equilibrium adsorption. The influence of MAO on the electronic environment resulting from the heterogenization was investigated using XPS. Heterogenization of Et(Ind)2ZrCl2 and MAO on the above silica generated two types of zirconocenium cations (Cation 1 and Cation 2), independent of the heterogenization methods. Based on the postulated surface chemistry, Cation 1 is presumed to be in the form of an ion‐pair [SiO]−[Et(Ind)2ZrCl]+, whereas Cation 2 is presumed to be a trapped multi‐coordinated crown complex of MAO. In the absence of MAO, only Cation 1 is formed. The present study provides some support for the postulated surface chemistry regarding heterogenization of Et(Ind)2ZrCl2 and MAO on silica. Copyright © 1999 John Wiley & Sons, Ltd.

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Three-Coordinate Aluminum Is Not a Prerequisite for Catalytic Activity in the Zirconocene-Alumoxane Polymerization of Ethylene

Cited by 266 publications

References 0 publications

Novel Molecular Clusters Having Aluminum-Phosphorus, Aluminum-Arsenic, and Gallium-Arsenic Skeletons, and Synthesis of an Al4As6Li4 Rhombododecahedron

Novel Molecular Clusters Having Aluminum-Phosphorus, Aluminum-Arsenic, and Gallium-Arsenic Skeletons, and Synthesis of an Al4As6Li4 Rhombododecahedron

Oxide‐Bridged Heterobimetallic Aluminum/Zirconium Catalysts for Ethylene Polymerization

XPS investigation of the electronic environment in selected heterogenized zirconocene catalysts

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