Zinc oxide clusters encapsulated by organozinc phosphazenate assemblies

Richards, Philip I.; Boomishankar, Ramamoorthy; Steiner, Alexander

doi:10.1016/j.jorganchem.2006.12.024

Cited by 10 publications

(3 citation statements)

References 21 publications

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“…Polyanionic phosphazenates are multisite ligands that can accommodate arrays of metal centers. − They are obtained via deprotonation of hexaprotic cyclotriphosphazenes (RNH) 6 P 3 N 3 (labeled X H 6 hereafter). − The steric and electronic properties of the R groups in the ligand periphery control the size and layout of the coordinated arrangement. − The routes along which metalations can progress are manifold considering the large number of partially deprotonated ligand isomers that can exist (see Scheme ). Nonetheless, metalations often proceed along distinctive pathways; for example, reactions with butyllithium advance via the trianionic C 3 v -symmetric isomer [ X‴ H 3 ] 3– , which distributes its negative charge most effectively. − …”

Section: Introductionmentioning

confidence: 99%

Polyanionic Ligand Platforms for Methyl- and Dimethylaluminum Arrays

et al. 2019

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Trimethylaluminum finds widespread applications in chemical and materials synthesis, most prominently in its partially hydrolyzed form of methylalumoxane (MAO), which is used as a cocatalyst in the polymerization of olefins. This work investigates the sequential reactions of trimethylaluminum with hexaprotic phosphazenes (RNH)6P3N3 (=XH6) equipped with substituents R of varied steric bulk including tert-butyl (1H6), cyclohexyl (2H6), isopropyl (3H6), isobutyl (4H6), ethyl (5H6), propyl (6H6), methyl (7H6), and benzyl (8H6). Similar to MAO, the resulting complexes of polyanionic phosphazenates [XH n ] n−6 accommodate multinuclear arrays of [AlMe2]+ and [AlMe]2+. Reactions were monitored by 31P NMR spectroscopy, and structures were determined by single-crystal X-ray diffraction. They included 1H4(AlMe2)2, 1H3(AlMe2)3, 2H3(AlMe2)3, 3(AlMe2)4AlMe, 4H(AlMe2)5, 4(AlMe2)6, {5H(AlMe2)4}2AlMe, 5(AlMe2)6, 6(AlMe2)6, {7(AlMe2)4AlMe}2, and 8(AlMe2)6. The study shows that subtle variations of the steric properties of the R groups influence the reaction pathways, levels of aggregation, and fluxional behavior. While [AlMe2]+ is the primary product of the metalation, [AlMe]2+ is utilized to alleviate overcrowding or to aid aggregation. At the later stages of metalation, [AlMe2]+ groups start to scramble around congested sites. The ligands proved to be very robust and extremely flexible, offering a unique platform to study complex multinuclear metal arrangements.

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Section: Introductionmentioning

confidence: 99%

Polyanionic Ligand Platforms for Methyl- and Dimethylaluminum Arrays

et al. 2019

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“…0.2 equiv, and decreased slightly with 0.4 equiv of water. The acceleration of reactions mediated by Et 2 Zn in the presence of catalytic amounts of water has been attributed to the formation of ZnO complexes , that can transform the structure of the reactants, , catalyze the cyclopropanation acting as Lewis acids, , or both. We obtained indirect support for the catalytic capacity of related Lewis acidic species by monitoring the cyclopropanation rates in the presence of ZnO.…”

Section: Resultsmentioning

confidence: 99%

The Effect of Additives on the Zinc Carbenoid-Mediated Cyclopropanation of a Dihydropyrrole

Ramı́rez

Truc

et al. 2014

J. Org. Chem.

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The synthesis of a key intermediate in the preparation of oral antidiabetic drug Saxagliptin is discussed with an emphasis on the challenges posed by the cyclopropanation of a dihydropyrrole. Kinetic studies on the cyclopropanation show an induction period that is consistent with a change in the structure of the carbenoid reagent during the course of the reaction. This mechanistic transition is associated with an underlying Schlenk equilibrium that favors the formation of monoalkylzinc carbenoid IZnCH2I relative to dialkylzinc carbenoid Zn(CH2I)2, which is responsible for the initiation of the cyclopropanation. The factors influencing reaction rates and diastereoselectivities are discussed with the aid of DFT computational studies. The rate accelerations observed in the presence of Brønsted acid-type additives correlate with the minimization of the undesired induction period and offer insights for the development of a robust process.

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“…This could have some interesting implications for polynuclear metal complexes in areas such as catalysis. This approach might also enable the confinement of well-defined mixed-metal or metal oxide assemblies. , …”

Section: Discussionmentioning

confidence: 99%

Magnesium and Titanium Complexes of Polyanionic Phosphazenate Ligands

et al. 2010

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Polyanionic phosphazenates constitute polydentate ligands that offer several chelating sites, facilitating the accommodation of multinuclear metal arrays. Here, we describe their coordination behavior in the presence of magnesium and titanium. Reaction of the hexaprotic cyclotriphosphazene (iBuNH)6P3N3 (1) with nBu2Mg in thf in 1:2 ratio yields the dinuclear magnesium complex [(thf)Mg(iBuN)2(iBuNH)4P3N3]2 (2), while a 1:4 ratio gives the octanuclear complex [(thf)3(nBuMg)2Mg2(iBuN)6P3N3]2 (3). Both magnesium complexes exist as dimers in the solid state. In addition to metal ligand interactions, dimer 2 is supported by four hydrogen bonds (N−H···N interactions). The reaction of (CyNH)6P3N3 (4) with two equivalents of (Me2N)4Ti produces the dinuclear complex {(Me2N)2Ti}2(CyN)4(CyNH)2P3N3 (5), in which the phosphazenate ligand accommodates the two titanium atoms in tridentate coordination sites. The metalation reactions were followed by 31P NMR. Metal complexes 2, 3, and 5 were characterized by X-ray structure analysis.

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Zinc oxide clusters encapsulated by organozinc phosphazenate assemblies

Cited by 10 publications

References 21 publications

Polyanionic Ligand Platforms for Methyl- and Dimethylaluminum Arrays

Polyanionic Ligand Platforms for Methyl- and Dimethylaluminum Arrays

The Effect of Additives on the Zinc Carbenoid-Mediated Cyclopropanation of a Dihydropyrrole

Magnesium and Titanium Complexes of Polyanionic Phosphazenate Ligands

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