Auf dem Weg zu einer allgemeinen Nucleophilie‐Skala?

Phan, Thanh Binh; Breugst, Martin; Mayr, Herbert

doi:10.1002/ange.200600542

Cited by 62 publications

(57 citation statements)

References 66 publications

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“…The situation is different when other types of electrophiles are used, for example S N 2 substrates. [11] In such cases, electrophile-specific sensitivity parameters s E are important, as shown by Swain and Scott. [12] As discussed in reference [11], it depends on the type of reaction whether nucleophileCorrespondence specific (s N , see Figure 2) or electrophile-specific sensitivity parameters (s E ) are needed (or both).…”

Section: The Real Difference Between the Two Approachesmentioning

confidence: 96%

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Reply to T. W. Bentley: Limitations of the s(E+N) and Related Equations

Mayr

2011

Angew Chem Int Ed

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electrophilicity · kinetics · linear free-energy relationships · nucleophilicity · solvent effectsThe preceding commentary [1] is the forth in a series [2][3][4] that tries to discredit our approach to a semiquantitative model of polar organic reactivity. None of these publications reports new experimental results, and all deal exclusively with a reinterpretation of our kinetic data. As the detailed analysis of the manifold mistakes and incorrect statements in references [1][2][3][4] would bore the nonspecialist reader, I will comment the most important points in this response and ask the interested reader to find my comprehensive reply in the Supporting Information, which also provides a detailed validation of the statements in this reply. Let me first explain the essence of the controversy, which is not described in reference [1]. The Patz-Mayr ApproachIn recent years we have studied the kinetics of the reactions of carbocations and Michael acceptors with different types of nucleophiles, including alkenes, enol ethers, enamines, arenes, ylides, organometallic compounds, hydride donors, amines, phosphines, alcohols, alkoxides, and many more nucleophiles. The most commonly used solvents were dichloromethane, acetonitrile, DMSO, and water. The reactivities of electrophiles and nucleophiles thus studied cover a range of more than 30 orders of magnitude.[5] As bimolecular reactions in these solvents cannot be faster than 10 9 -10 10 L mol À1 s À1 (diffusion limit) and reactions slower than 10 À5 L mol À1 s À1 are difficult to measure, it is impossible to base a comprehensive nucleophilicity scale on measured rate constants for a single reference electrophile.Therefore, we have defined a series of benzhydrylium ions and quinone methides as reference electrophiles, which differ widely in reactivity. We studied the kinetics of their reactions with various nucleophiles and performed a least-squares minimization on the basis of Equation (1). [7a,b] In this equa-tion, electrophiles are characterized by one parameter (E), which we defined as solvent-independent, while nucleophiles are characterized by two parameters, the nucleophilicity parameter N and the nucleophile-specific sensitivity parameter s N (previously termed s), which are treated as solventdependent. Fixed parameters were E = 0 for (4-MeOC 6 H 4 ) 2 CH + and s N = 1.0 for 2-methyl-pent-1-ene. Reference [3] correctly describes that our basis correlation for deriving the reactivity parameters N, s N , and E was based on 209 rate constants for the reactions of 38 p nucleophiles with 23 electrophiles in the reactivity range À10 < E < 6. It is not clear why Scheme 1 in both Ref.[4] and Ref.[1] now pretend that our basis correlation was restricted to electrophiles in the narrow range of 0 < E < 6. This is not true![8] Details of our correlation are given in Appendix A of the Supporting Information.Since both s N and N are nucleophile-specific parameters, Equation (1) is equivalent to Equation (2), in which thenucleophilicity parameter Nu corresponds to log k of the...

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Section: The Real Difference Between the Two Approachesmentioning

confidence: 96%

“…[11] Linear free-energy relationships are empirical rules that describe relationships between rate constants or equilibrium constants. They can be interpreted but not derived.…”

Section: Towards a General Scale Of Nucleophilicitymentioning

confidence: 99%

Reply to T. W. Bentley: Limitations of the s(E+N) and Related Equations

Mayr

2011

Angew Chem Int Ed

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“…Furthermore, it has been shown that the reactivity order of nucleophiles towards tritylium ions (Ritchie N + ) and benzhydrylium ions (Patz-Mayr N) is roughly the same as towards CH 3 I or CH 3 Br (Swain-Scott n), [12] which indicates that the order of nucleophilicities does not depend on the hardness of the electrophilic reaction partner when the electrophilic reaction center is carbon.…”

Section: Introductionmentioning

confidence: 99%

Farewell to the HSAB Treatment of Ambident Reactivity

Mayr¹,

Breugst²,

Ofial³

2011

Angew Chem Int Ed

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The concept of hard and soft acids and bases (HSAB) proved to be useful for rationalizing stability constants of metal complexes. Its application to organic reactions, particularly ambident reactivity, has led to exotic blossoms. By attempting to rationalize all the observed regioselectivities by favorable soft-soft and hard-hard as well as unfavorable hard-soft interactions, older treatments of ambident reactivity, which correctly differentiated between thermodynamic and kinetic control as well as between different coordination states of ionic substrates, have been replaced. By ignoring conflicting experimental results and even referring to untraceable experimental data, the HSAB treatment of ambident reactivity has gained undeserved popularity. In this Review we demonstrate that the HSAB as well as the related Klopman-Salem model do not even correctly predict the behavior of the prototypes of ambident nucleophiles and, therefore, are rather misleading instead of useful guides. An alternative treatment of ambident reactivity based on Marcus theory will be presented.

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“…[9] Die durch die Benzhydrylium-Methode [6,7] ermittelten Nucleophilie-Parameter N und s können darüber hinaus für die Beschreibung von S N 2-Reaktionen genutzt werden, wenn Gleichung (1) um einen elektrophilspezifischen Steigungsparameter s E erweitert wird. [10] Die linearen Korrelationen zwischen lg k 2 und den Elektrophilie-Parametern E der Benzhydrylium-Ionen 2 in Abbildung 2 belegen, dass Gleichung (1) auch für die Reaktionen der Isocyanide 1 mit den Benzhydrylium-Ionen 2 gültig ist, was die Bestimmung der in der rechten Spalte der Tabelle 2 aufgelisteten Parameter N und s der Isocyanide 1 a-e ermöglichte.…”

Section: Dieunclassified

Nucleophilie‐Parameter von Alkyl‐ und Arylisocyaniden

2007

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Professor Lutz F. Tietze zum 65. Geburtstag gewidmet Alkyl-und Arylisocyanide haben eine einzigartige Carbenähnliche Struktur mit einem formal zweibindigen Kohlenstoffatom. Ihre elektronische Struktur kann durch die Resonanzformeln 1' und 1'' wiedergegeben werden. Sie sind leicht über eine Reihe präparativer Methoden zugänglich und wichtige Substrate wertvoller chemischer Umwandlungen wie der Passerini-und Ugi-Reaktion; [1] bei vielen dieser Reaktionen greift ein Kohlenstoff-Elektrophil an der IsocyanGruppe an.[2] Bisher gibt es nur wenige Informationen zur Thermodynamik und Kinetik derartiger Transformationen. [3][4][5] Die Benzhydrylium-Methode, die sich auf Referenzelektrophile vergleichbarer Struktur, aber sehr unterschiedlicher Reaktivität (24 Größenordnungen) stützt, wurde verwendet, um die derzeit umfassendste Nucleophilie-Skala aufzubauen.[6] Wir haben diese Methode nun genutzt, um die nucleophilen Reaktivitäten der Isocyanide 1 a-e (Ts = Toluol-4-sulfonyl) zu bestimmen.Wir beobachteten, dass die Geschwindigkeiten der Reaktionen der Isocyanide 1 a-e mit Benzhydrylium-Ionen 2 in einen für kinetische Messungen gut zugänglichen Bereich fallen, wenn die Elektrophilie-Parameter E der Benzhydrylium-Ionen 2 im Bereich À6 < E < 0 liegen. Daher wurden 2 a-h (Tabelle 1) als Referenzelektrophile für diese Versuchsreihe ausgewählt. [7] Beim Versetzen der farbigen Lösungen von 2-BF 4 und 2-ZnCl 3 mit den Isocyaniden 1 a-e in CH 2 Cl 2 verschwand die Färbung, was wir auf die Bildung der farblosen NitriliumIonen 3 zurückführen (Schema 1). In Einklang mit dieser Interpretation wurden die Iminoester 5 d und 5 e isoliert, als durch Zugabe von 1 d oder 1 e zu CH 2 Cl 2 -Lösungen von Chlorbis(4-methoxyphenyl)methan 2 a-Cl und ZnCl 2 /Et 2 O die Nitrilium-Ionen 3 d und 3 e generiert (Schema 1) und anschließend mit dem Silylketenacetal 4 umgesetzt wurden (Schema 2). Die Reaktion des Nitrilium-Salzes 3 a-ZnCl 3 mit 4 lieferte nicht den Iminoester 5 a (R = tBu), sondern führte

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Auf dem Weg zu einer allgemeinen Nucleophilie‐Skala?

Cited by 62 publications

References 66 publications

Reply to T. W. Bentley: Limitations of the s(E+N) and Related Equations

Reply to T. W. Bentley: Limitations of the s(E+N) and Related Equations

Farewell to the HSAB Treatment of Ambident Reactivity

Nucleophilie‐Parameter von Alkyl‐ und Arylisocyaniden

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