Superelektrophile

Oláh, George A.

doi:10.1002/ange.19931050604

Cited by 68 publications

(44 citation statements)

References 123 publications

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“…d(Si-F) in 5: 1.755/1.763 [10] ), was für eine Si-F-Bindungsordnung kleiner eins spricht. Zum Vergleich: Der Si-F-Abstand in Me 3 SiÀF entspricht mit 1.600(1) einer typischen Si-F-Einfachbindung. [16] In pentakoordinierten, fluorverbrückten, anionischen Bissiliconaten fanden Tamao et al immer einen kleinen (1.700-1.898 ) und einen großen Si-F-Abstand (2.090-2.369 ).…”

Section: Angewandte Chemieunclassified

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Bissilylierte Haloniumionen: [Me₃SiXSiMe₃][B(C₆F₅)₄] (X=F, Cl, Br, I)

2009

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Ionen des Typs [R À X À R]+ mit X = Halogen werden als Haloniumionen bezeichnet. Sie treten sowohl cyclisch als auch offenkettig auf, bilden eine bedeutende Klasse von Oniumionen [1,2] und spielen eine wichtige Rolle in der präparativen Chemie, z. B. als Zwischenstufen bei Friedel-Crafts-Alkylierungen und Lewis-Säure-katalysierten Halogenierungen. [3] Die stabilen, langlebigen Dialkylchloronium-, -bromoniumund -iodoniumionen können sogar als Salze isoliert werden. Ihre Synthese gelingt durch Umsetzen des Halogenalkans im Überschuss mit einer starken Lewis-Säure (LS) in schwach nucleophilen Lösungsmitteln (SNLs) oder supersauren Medien (Schema 1 A).[3] Stabile Dialkylfluoroniumionen sind in kondensierter Phase noch nicht bekannt, was der hohen Elektronegativität von Fluor zugeschrieben wird, die zur Alkylierung einer C-H-oder C-C-Bindung führt. Überra-schenderweise gibt es keine Strukturdaten von Dialkylhaloniumionen. Nur wenige arylsubstituierte Chloronium-und Bromoniumionen wurden mittels Einkristallröntgenstruk-turanalyse untersucht (Schema 2); dagegen sind viele vollständig charakterisierte Salze, die Iodoniumionen enthalten, bekannt.

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Section: Angewandte Chemieunclassified

“…[23] Dies bedeutet, dass geringfügige Wechselwirkungen des Kations mit der Umgebung im Kristall einen großen Einfluss auf den Si-X-Si-Winkel haben können. Darüber hinaus spiegelt der Si-X-Si-Winkel die sterische Abstoßung des Me 3 das I-Atom mehr als die Hälfte zum Gesamtladungstransfer bei (Tabelle 2).…”

Section: Angewandte Chemieunclassified

Bissilylierte Haloniumionen: [Me₃SiXSiMe₃][B(C₆F₅)₄] (X=F, Cl, Br, I)

2009

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“…1). The mechanism is formulated analogously to that elucidated by Olah (1993) for the reversible formation of H, and a carbonium cation from alkanes in superacids (reaction b).…”

Section: Chi=h4mptmentioning

confidence: 99%

Hydrogen Isotope Effects in the Reactions Catalyzed by H₂‐forming N⁵,N¹⁰‐Methylenetetrahydromethanopterin Dehydrogenase from Methanogenic Archaea

Klein

Hartmann

Thauer

1995

European Journal of Biochemistry

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H,-forming N',N"'-methylenetetrahydromethanopterin dehydrogenase from methanogenic Archaea, which is a novel hydrogenase containing neither nickel nor iron-sulfur clusters, catalyzes the reversible reduction of N5,N"'-methenyltetrahydomethanopterin (CH=H,MPT.') with H, to N',N"'-methylenetetrahydromethanopterin (CH,=H,MPT) and a proton (AGO' = -5.5 kJ/mol). The enzyme also catalyzes a CH-H,MPT+-dependent H,/H' exchange. We report here on kinetic deuterium isotope effects in these reactions. When CH=H,MPT' reduction was performed with DZ instead of H2, V,,,., and the K,,, did not change. A primary isotope effect of 1 was found at all pH and temperatures tested and independent of whether H,O or DZO was the solvent. The findings indicate that a step other than the activation of H, was rate-determining in CH=H,MPT+ reduction with H,. This was substantiated by the observation that also the CH=H,MPT+-dependent H,/H+ exchange reaction did not exhibit an appreciable deuterium isotope effect. V,,,,, for CH,=H,MPT dehydrogenation to CH-H,MPT+ and H2 was only 2-3 times higher than for CD2=H,MPT dehydrogenation to CD-H,MPT' and HD. Such a small primary isotope effect indicates that the breakage of the C-H bond in the methylene group of CH2=H,MPT was only rate-limiting when hydrogen was substituted by a deuterium.

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“…This reaction involves acyclic carbometallation of a ''super-acidic'' [119,303] Zr-Al bimetallic system (Scheme 3.7). Several years later, Dzhemilev reported a seemingly analogous reaction of Zrcatalyzed carbomagnesiation of alkenes with EtMgBr (Scheme 3.88) [65,304].…”

Section: Historical and Mechanistic Background Of Carbometallation Ofmentioning

confidence: 99%

Pd‐Catalyzed Cross‐Coupling with Organometals Containing Zn, Al, Zr, and so on – The Negishi Coupling and Its Recent Advances

Kamada

Kim

et al. 2013

Metal‐Catalyzed Cross‐Coupling Reactions and More

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The Pd-or Ni-catalyzed cross-coupling reactions of organometals containing Zn, Al, Zr, and B as well as related reactions of those containing Mg and several other metals collectively have emerged as arguably the most widely applicable organic skeleton construction method discovered and developed over the past several decades, allowing synthetic chemists to prepare practically all types of organic compounds. In this chapter, some of the seminal and critically important discoveries and early developments in the 1970s as well as their current scope are briefly discussed. Some of the notable discoveries and developments include (i) identification of superior properties of Pd as a critical element for crosscoupling relative to Ni, (ii) the broad scope of Pd-or Ni-catalyzed cross-coupling with respect to metal countercations including Zn, Al, Zr, B, and Mg, (iii) the hydrometallation-Pd-catalyzed cross-coupling sequential processes for selective syntheses of alkenes, dienes, oligoenes, and oligoenynes, (iv) double metal catalysis involving Pd or Ni and added metal compounds containing Zn, In, Li, and others, and (v) realization of high turnover numbers (TONs) (≥10 3 -10 9 ) through the use of chelating phosphines, such as bis-[2-(diphenylphosphino)phenyl] ether (DPEphos) and 1,1 -Bis(diphenylphosphino)ferrocene (dppf).The Zr-catalyzed alkyne carboalumination and the Zr-catalyzed asymmetric carboalumination of alkenes (ZACA reaction) have provided efficient and selective routes to (E)-trisubstituted alkenylalanes and 2-substituted chiral alkylalanes, respectively. These reactions provide two additional examples of prototypical transition metal-catalyzed organometallic reactions. Significantly, they can be readily combined with the Pd-or Ni-catalyzed cross-coupling for the synthesis of trisubstituted alkenes embracing a wide variety of natural products, such as terpenoids, carotenoids, and others, as well as various chiral organics including deoxypolypropionates and saturated terpenoids. The Zr-catalyzed alkyne carboalumination has been applied to the synthesis of a large number (>100) of natural products, while the ZACA reaction has been transformed from a mere scientific novelty to a full-fledged asymmetric synthetic method that is catalytic in both transition metal (Zr) and chiral auxiliaries through a series of breakthroughs.

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Superelektrophile

Cited by 68 publications

References 123 publications

Bissilylierte Haloniumionen: [Me₃SiXSiMe₃][B(C₆F₅)₄] (X=F, Cl, Br, I)

Bissilylierte Haloniumionen: [Me₃SiXSiMe₃][B(C₆F₅)₄] (X=F, Cl, Br, I)

Hydrogen Isotope Effects in the Reactions Catalyzed by H₂‐forming N⁵,N¹⁰‐Methylenetetrahydromethanopterin Dehydrogenase from Methanogenic Archaea

Pd‐Catalyzed Cross‐Coupling with Organometals Containing Zn, Al, Zr, and so on – The Negishi Coupling and Its Recent Advances

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Superelektrophile

Cited by 68 publications

References 123 publications

Bissilylierte Haloniumionen: [Me3SiXSiMe3][B(C6F5)4] (X=F, Cl, Br, I)

Bissilylierte Haloniumionen: [Me3SiXSiMe3][B(C6F5)4] (X=F, Cl, Br, I)

Hydrogen Isotope Effects in the Reactions Catalyzed by H2‐forming N5,N10‐Methylenetetrahydromethanopterin Dehydrogenase from Methanogenic Archaea

Pd‐Catalyzed Cross‐Coupling with Organometals Containing Zn, Al, Zr, and so on – The Negishi Coupling and Its Recent Advances

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Bissilylierte Haloniumionen: [Me₃SiXSiMe₃][B(C₆F₅)₄] (X=F, Cl, Br, I)

Bissilylierte Haloniumionen: [Me₃SiXSiMe₃][B(C₆F₅)₄] (X=F, Cl, Br, I)

Hydrogen Isotope Effects in the Reactions Catalyzed by H₂‐forming N⁵,N¹⁰‐Methylenetetrahydromethanopterin Dehydrogenase from Methanogenic Archaea