- Reactions of aryl phenylacetates with secondary amines in MeCN. Structure-reactivity relationship in the ketene-forming eliminations and concurrent E2 and E1cb mechanisms
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Elimination reactions of aryl esters of arylacetic acids 1 and 2 promoted by R2NH in MeCN have been investigated kinetically. The reactions are second-order and exhibit β = 0.44-0.84, β(lg) = 0.41-0.50, and ρ(H) = 2.0-3.6. Bronsted β and β(lg) decrease with the electron-withdrawing ability of the β-aryl substituent. Hammett ρ(H) values remain nearly the same, but the β(lg) value increases as the base strength becomes weaker. Both ρ(H) and β decrease with the change of the leaving group from 4-nitrophenoxide to 2,4-dinitrophenoxide. The results are consistent with an E2 mechanism and a reaction coordinate with a large horizontal component corresponding to proton transfer. When the base-solvent system is changed from R2NH-MeCN to R2NH/R2NH2+-70 mol% MeCN(aq), the Bronsted β, ρ(H), and β(lg) decrease. Finally, the ketene-forming elimination reactions from p-nitrophenyl p-nitrophenylacetate promoted by R2NH/R2NH2+ buffers in 70 mol% MeCN(aq) have been shown to proceed by concurrent E2 and E1cb mechanisms.
- Cho, Bong Rae,Kim, Yong Kwan,Yoon, Choon-Ock Maing
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p. 691 - 697
(2007/10/03)
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- Chemistry of diamino-ligated methylpalladium(II) alkoxides and aryloxides (Part II): Methoxide formation and carbonylation reactions
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Reaction of N-ligated methylpalladium(II) alkoxide and aryloxide complexes [Pd(Me)(OR)(N ～ N)] (R = Ph, CH(CF3)2; N ～ N = tmeda (N,N,N′,N′-tetramethylethylenediamine) or bpy (2,2′-bipyridyl)) with carbon monoxide produces the corresponding methylesters in high yields. The insertion takes place either into the Pd-Me bond (aryloxide complexes) or into the Pd-OR bond (alkoxide complexes). Methylpalladium(II) methoxide complexes [Pd(Me)(OMe)(N ～ N)] (N ～ N = tmeda, bpy) have been generated in situ by aryloxide- or alkoxide-methanol exchange reactions for which the equilibrium constants have been determined. The bpy-ligated methylpalladium methoxide complex undergoes insertion of CO producing either a methylpalladium methoxycarbonyl complex [Pd(Me)(CO2Me)(bpy)] (at -60°C) or an acylpalladium methoxycarbonyl complex [Pd(COMe)(CO2Me)(bpy)] (at -25°C); both carbonylated species could be isolated and characterized at low temperature.
- Kapteijn, Gerardus M.,Dervisi, Athanasia,Verhoef, Michel J.,Van Den Broek, M.A. Frederik H.,Grove, David M.,Van Koten, Gerard
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p. 123 - 131
(2007/10/03)
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