107. The reaction of diborane with the alkyl derivatives of some Group V B  elements

Hewitt, FredericW.; Holliday, A. K.

doi:10.1039/jr9530000530

Cited by 30 publications

(14 citation statements)

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“…Although this scale has been widely used because of its reference to synthetically relevant Lewis acids, it has been widely criticized for several reasons. Most notable among the problems are: 1) concerns regarding interactions between SbCl 5 and the solvent, 2) variations in the steric demands of the Lewis base on the enthalpy of formation, and 3) the observation of side reactions between certain Lewis bases and SbCl 5 . Still, these criticisms seem directed only at individual values, especially for measurements of interactions between extremely weak or strong Lewis bases, rather than the method in general.…”

Section: Toward a Scale Of Lewis Basicity: Identity Of The Lewis Basementioning

confidence: 99%

“…For example, the series SiF 4 , SiF 5 À , and SiF 6 2À has Mulliken charges at the silicon atom of + 1.19, + 1.14, and + 2.12 [31] whereas the series SiCl 4 , SiCl 5 À , and SiCl 6 2À has Mulliken charges at the silicon atom of + 0.178, + 0.279, and + 0.539, [31b] respectively. These trends are truly striking as the binding Lewis base in these cases is charged (F À and Cl À ), thus rendering the adducts formally negatively charged (and erroneously viewed as negative at the silicon atom), yet the acceptor silicon atom increases in its positive character!…”

Section: Gutmann Analysismentioning

confidence: 99%

“…For example, the trimethylphosphane-borane complex (1) possesses little of the characteristic chemical reactivity of either of the parent components (Scheme 1). [5] However, just as notable exceptions to Lewis assumptions about the octet rule exist, so do exceptions about this concept of acid-base interactions as stabilizing phenomena that lead to reduced reactivity. [6] A brief survey of the literature reveals numerous examples where stable, acid-base adducts show enhanced reactivity.…”

Section: Introductionmentioning

confidence: 96%

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Lewis Base Catalysis in Organic Synthesis

2008

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The legacy of Gilbert Newton Lewis (1875-1946) pervades the lexicon of chemical bonding and reactivity. The power of his concept of donor-acceptor bonding is evident in the eponymous foundations of electron-pair acceptors (Lewis acids) and donors (Lewis bases). Lewis recognized that acids are not restricted to those substances that contain hydrogen (Brønsted acids), and helped overthrow the "modern cult of the proton". His discovery ushered in the use of Lewis acids as reagents and catalysts for organic reactions. However, in recent years, the recognition that Lewis bases can also serve in this capacity has grown enormously. Most importantly, it has become increasingly apparent that the behavior of Lewis bases as agents for promoting chemical reactions is not merely as an electronic complement of the cognate Lewis acids: in fact Lewis bases are capable of enhancing both the electrophilic and nucleophilic character of molecules to which they are bound. This diversity of behavior leads to a remarkable versatility for the catalysis of reactions by Lewis bases.

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Section: Toward a Scale Of Lewis Basicity: Identity Of The Lewis Basementioning

confidence: 99%

Section: Gutmann Analysismentioning

confidence: 99%

Section: Introductionmentioning

confidence: 96%

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Lewis Base Catalysis in Organic Synthesis

2008

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“…Die MullikenLadungen am Siliciumatom betragen für SiF 4 , SiF 5 À und SiF 6 2À beispielsweise + 1.19, + 1.14 bzw. + 2.12, [31] für SiCl 4 , SiCl 5 À und SiCl 6 2À wurden Mulliken-Ladungen von + 0.178, + 0.279 bzw. + 0.539 am Siliciumatom ermittelt.…”

Section: Donorunclassified

“…Beispielsweise zeigt der Trimethylphosphan-Boran-Komplex (1) nur wenig von der charakteristischen chemischen Reaktivität der beiden Stammverbindungen (Schema 1). [5] Aber ebenso wie bemerkenswerte Ausnahmen zu Lewis Annahmen bezüglich der Oktettregel existieren, müssen Säure-Base-Wechselwirkungen nicht zwingend stabilisierend wirken und die Reaktivität vermindern. [6] In der Literatur findet man eine Reihe von Beispielen für stabile Säure-BaseAddukte mit erhöhter Reaktivität.…”

Section: Introductionunclassified

Lewis‐Base‐Katalyse in der organischen Synthese

2008

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Das Erbe von Gilbert Newton Lewis (1875–1946) ist im Wörterbuch der chemischen Bindung und Reaktivität allgegenwärtig. Die Bedeutung seines Konzepts der Donor‐Akzeptor‐Bindung kommt in den eponymen Grundbegriffen für Elektronenpaarakzeptoren (Lewis‐Säuren) und ‐donoren (Lewis‐Basen) zum Ausdruck. Lewis erkannte, dass Säuren nicht automatisch Wasserstoff enthalten müssen (Brønsted‐Säuren) und trug so zum Sturz des “modernen Protonenkults” bei. Seine Entdeckung läutete zunächst die Entwicklung von Lewis‐Säuren als Reagentien und Katalysatoren für organische Reaktionen ein, in den letzten Jahren wurde aber offensichtlich, dass für diese Zwecke auch Lewis‐Basen eingesetzt werden können. Bezüglich der Beschleunigung chemischer Reaktionen ergänzen Lewis‐Basen die entsprechenden Lewis‐Säuren nicht nur elektronisch: Tatsächlich können Lewis‐Basen die Elektrophilie wie auch die Nucleophilie der Verbindungen verstärken, an die sie gebunden werden. Diese unterschiedliche Reaktivität resultiert in einer bemerkenswerten Vielfalt Lewis‐Base‐katalysierter Reaktionen.

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