The .beta.-effect with vinyl cations: kinetic study of the protiodemetalation of silyl-, germyl-, and stannylalkynes

Dallaire, Carol; Brook, Michael A.

doi:10.1021/om00030a049

Cited by 44 publications

(22 citation statements)

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“…13 (21), 184.8 (20), 158.6 (13), 128.6 (17), 100.7 (7). These assignments are in good accordance with those reported previously.…”

Section: -(Triethylgermyl)-2-(triethylsilyl)ethyne (7)supporting

confidence: 90%

“…[6] The different reactivities of alkynylsilanes and alkynylgermanes under acidic, electrophilic, [7] or fluoridic [8] conditions are an advantage and enable their exploitation in the preparation of nonsymmetrically substituted dialkyne-containing molecules. [6a,9] The synthetic procedures for the synthesis of alkynylgermanes are still under development.…”

Section: Introductionmentioning

confidence: 99%

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A Simple Catalytic Route for Alkynylgermanes

et al. 2016

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“…13 (21), 184.8 (20), 158.6 (13), 128.6 (17), 100.7 (7). These assignments are in good accordance with those reported previously.…”

Section: -(Triethylgermyl)-2-(triethylsilyl)ethyne (7)supporting

confidence: 90%

Section: Introductionmentioning

confidence: 99%

A Simple Catalytic Route for Alkynylgermanes

et al. 2016

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“…Comparison with the corresponding trimethylsilyl analog, l-(trimethylsilylj-2-phenylethyne (7), shows the stannyl substituent to be better than the silyl group by a factor of 210 and gives a differential P-stannyVP-silyl effect of 6AG' = 3.2 kcal mol-l. These are substantial effects, but they pale in comparison to the much larger P-stannyl stablizations observed in other systems (2,3). The difference between the present result and the previously reported stannyl/silyl rate ratio of 5.1 x lo7, corresponding to ~AG'= 10.5 kcal mol-', is especially striking, for in both cases the reaction examined involved proton addition to a carbon-carbon triple bond.…”

Section: Reactivitycontrasting

confidence: 86%

The acid-catalyzed demetalation of 1-(tri-n-butylstannyl)-2-phenylethyne. A surprisingly small β-stannyl effect

Egle¹,

Gabelica²,

Kresge³

et al. 1996

Can. J. Chem.

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Abstract:Rates of conversion of 1-(tri-11-butylstanny1)-2-phenylethyne to phenylethyne in HzO and D,O solutions of perchloric acid were found to be proportional to acid concentration, giving the hydronium ion rate constant kH+ = 1.85 x lo-' M-I s-I and the isotope effect kHJkD+ = 3.10. The magnitude of this isotope effect suggests that the reaction occurs by rate-determining hydron transfer to the substrate, producing a vinyl carbocation; this carbocation then loses its tributylstanny l group, giving phenylacetylene as the only detectable aromatic product. The hydronium ion rate constant, when compared to the rates of protonation of phenylethyne and I-(trimethylsily1)-2-phenylethyne, gives a P-stannyl stabilizing effect of FAG*= 6.6 kcal mol-I and a differential P-stannyVP-silyl effect of FAG*= 3.2 kcal mol-I. These stabilizations are very much smaller than previously reported P-stannyl effects. Possible reasons for the difference are suggested.Key words: P-stannyl effect, P-silyl effect, carbocation stabilization, protodemetalation.RCsumC : On a trouvt que les vitesses de conversion du I-(tri-n-butylstanny1)-2-phtnyltthyne en phCnylCthyne, en solutions d'acide perchlorique dans du H,O et dans du D20, est proportionnelle B la concentration d'acide; la constante de vitesse de l'ion hydronium kH+ = 1,85 x 10-2 M-' s-I et I'effet isotopique kH+lkD+ = 3,10. L'amplitude de cet effet isotopique suggkre que la reaction se produit par une ttape dtterminant la vitesse au cours de laquelle il y a transfert d'un hydron au substrat conduisant B la formation d'un carbocation vinylique; ce carbocation perd alors son groupe tributylstannyle ne donnant que du phCnylacCtyl6ne comme seul produit aromatique pouvant &tre dttecte. Lorsqu'on compare la constante de vitesse de I'ion hydronium aux vitesses de protonation du phtnyltthyne et du I-(trimCthylsily1)-2-phCnyltthyne, on en dtduit l'effet stabilisant du groupe P-stannyle, FAG'= 6,6 kcal mol-I, ainsi que la difftrence entre les effets P-stannyle et P-silyle, FAG" 3,2 kcal mol-I. Ces stabilisations sont beaucoup plus faibles que celles rapportCes antkrieurement pour les effets P-stannyles. On suggkre diverses raisons possibles pour la difference.Mots clgs : effet P-stannyle, effet P-silyle, stabilisation du carbocation, protodCmttallation. [Traduit par la rtdaction]It is well known that silyl substituents in the P-position stabilize carbocations strongly (for reviews, see ref. l), and other Group IV A metals lying below silicon in the periodic table have even more powerful effects. For example, a stannyl substituent in the P-position was found to accelerate the rate of solvolysis of a cyclohexanol ester over that of the unsubstituted substrate by a factor much in excess of 1 0 '~ (2), and the remarkably large stannyllsilyl rate ratio of lo8 was observed in the protonation of metalated acetylenes (3). We were surprised to discover, therefore, that the stannyl group in 1-(tri-rz-butylstanny1)-2-phenylethyne raises the rate of vinyl cation formation by protonation of this substance...

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“…The high ipso-directing force shown by the trimethylstannyl group is probably due to the b-effect of the tin atom which makes easier the cleavage of an aryl group from the tin via an electrophilic ipso-substitution [10]. The method proposed is a straightforward and convenient route for the synthesis of unsymmetrical diaryl ketones.…”

Section: Resultsmentioning

confidence: 99%