Premium
Base‐Free Cross‐Couplings of Aryl Diazonium Salts in Methanol: Pd II –Alkoxy as Reactivity‐Controlling Intermediate
Author(s) -
Sanhueza Italo A.,
Klauck Felix J. R.,
Senol Erdem,
Keaveney Sinead T.,
Sperger Theresa,
Schoenebeck Franziska
Publication year - 2021
Publication title -
angewandte chemie international edition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.831
H-Index - 550
eISSN - 1521-3773
pISSN - 1433-7851
DOI - 10.1002/anie.202014842
Subject(s) - transmetalation , chemistry , stille reaction , cationic polymerization , aryl , reactivity (psychology) , alkoxy group , reactive intermediate , combinatorial chemistry , solvent , medicinal chemistry , organic chemistry , catalysis , medicine , alkyl , alternative medicine , pathology
Pd‐catalyzed cross‐coupling reactions of aryl diazonium salts are generally assumed to proceed via cationic Pd II 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 ArN 2 + 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 Pd II ‐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 Pd II ‐alkoxy complex. Lewis acids were found to circumvent this reactivity divergence, promoting efficient couplings regardless of the employed conditions or coupling partners.