- Base-Free Cross-Couplings of Aryl Diazonium Salts in Methanol: PdII–Alkoxy as Reactivity-Controlling Intermediate
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Pd-catalyzed cross-coupling reactions of aryl diazonium salts are generally assumed to proceed via cationic PdII intermediates which in turn would be highly reactive in the subsequent transmetalation step. Contrary to this belief, we herein report our observation and rationalization of opposing reactivities of ArN2+ in Suzuki (=effective) and Stille (=ineffective) cross-couplings in MeOH. Our systematic experimental and computational studies on the roles of transmetalating agent, solvent, base and the likely involvement of in situ formed diazoether derivatives challenge the currently accepted mechanism. Our data suggest that the observed solvent dichotomy is primarily due to PdII-methoxy intermediates being formed, which are unreactive with arylstannanes, but highly reactive with arylboronic acids, complementing the Suzuki “Pd-oxy” mechanism with the direct demonstration of transmetalation of a PdII-alkoxy complex. Lewis acids were found to circumvent this reactivity divergence, promoting efficient couplings regardless of the employed conditions or coupling partners.
- Sanhueza, Italo A.,Klauck, Felix J. R.,Senol, Erdem,Keaveney, Sinead T.,Sperger, Theresa,Schoenebeck, Franziska
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supporting information
p. 7007 - 7012
(2021/03/01)
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- Transformations of Diazonium Salts. III. Transformations, Acid-Base Properties, and Reactivity of Nitronaphthyldiazonium Salts
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The transformations in water-alkali media, stability, acid-base properties, and activity in azocoupling of a series of nitronaphthaleneldiazonium salts are studied by preparative, spectroscopic, and kinetic methods. 4-Nitronaphthaleneldiazonium cation shows the highest acidity and the highest activity in azo-coupling. Nitro substitution in other positions much less affects the reactivity of the naphthaleneldiazonium cation. Unlike nitro derivatives of benzene series of diazo compounds, their naphthalene analogs show no effect of isomerism of diazotate anions, other conditions being equal. The experimental evidence does not allows unabiguous assignment of the ntronaphthalene diazotates to Z or E series. The transformations of nitronaphthalenediazonium salts involve addition of hydroxide anion to the ring carbon atom, which results in accumulation of the structural isomer of diazohydroxide. It is assumed that an analogous addition product arises in reaction of the diazonium cation with an azo component, and being an electrophilic species it is capable to enter azo-coupling.
- Bagal,Luchkevich,El'tsov
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p. 119 - 132
(2007/10/03)
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