Mechanism of N-Fluorobenzenesulfonimide Promoted Diamination and Carboamination Reactions: Divergent Reactivity of a Pd(IV) Species

Abstract

The mechanism of the Pd-catalyzed diamination and carboamination of alkenes promoted by N-fluorobenzenesulfonimide (NFBS) was investigated. Stereochemical labeling experiments established that the diamination reaction proceeds via overall syn addition of the two nitrogen groups, whereas carboamination is the result of an anti addition of arene and nitrogen to the alkene. The intermediate Pd-alkyl complex arising from aminopalladation was observed, and an X-ray crystal structure of its 2,2'-bipyridine (bipy) complex was obtained, revealing strong chelation of the amide protecting group to palladium. Aminopalladation was shown to be an anti-selective process in both the presence and the absence of added ligands, proceeding via external attack of the nitrogen on a Pd-coordinated alkene. The intermediate Pd-alkyl complex was converted to diamination product upon exposure to NFBS with inversion of configuration via oxidative addition followed by dissociation of the benzenesulfonimide anion and S(N)2 displacement of the Pd-C bond. Conversely, arylation of the Pd-alkyl complex proceeds via retention of stereochemistry, consistent with C-H activation of the arene at the Pd(IV) center. A small intermolecular isotope effect (k(H)/k(D) = 1.1) and a large intramolecular isotope effect (k(H)/k(D) = 4) were measured for this process, indicating that C-H activation occurs via a poorly selective product-determining coordination of the arene followed by a highly selective C-H activation. Competition between arenes reveals an unusual reactivity order of toluene > benzene > bromobenzene > anisole.

Iridium-Catalyzed, Intermolecular Hydroetherification of Unactivated Aliphatic Alkenes with Phenols

“…[78] Over the next two decades, several studies described palladiumcatalyzed amination reactions, but none contained evidence for a syn aminopalladation by migratory insertion of the alkene into a Pd À N bond. [79][80][81][82] Thus, migratory insertion was not thought to be part of the mechanism of palladiumcatalyzed aminations of alkenes.…”

Passive F+‐Oxidationsmittel ermöglichen die selektive reduktive Eliminierung hochvalenter Metallzentren in der Katalyse

“…[40] Sie entdeckten, dass bei Verwendung aromatischer Lösungsmittel eine ungewöhnliche oxidative Carbamidierung auftrat, bei der ein Lösungsmittelmolekül durch eine Pd-vermittelte C-H-Aktivierung funktionalisiert wurde (Schema 16). [41,42] Sie fanden heraus, dass die Be- aus. An diesem Punkt sind reduktive Eliminierungen von C-F und C-N ausreichend träge, sodass eine Abfolge von aromatischer Koordinierung, C-H-Aktivierung und reduktiver C-C-Eliminierung der bevorzugte Reaktionsweg ist, was zum carbamidierten Produkt 54 in guter Ausbeute und mit hervorragender para-Selektivät führt.…”

Oxidative Functionalization of Alkenes

“…The respective C-H activation was again of high selectivity, usually with preference for the 4-position, as shown for the case of toluene. As deduced from deuterium labeling at the former double bond, the final reductive C-C bond formation from the coordination sphere of the palladium(IV) intermediate occurs with retention of configuration [66]. Ethyl nicotinate 86 ( …”

“…Azepin was the only product that was produced using N-bromosuccinimide (NBS) as oxidant (52%). Using an isolated palladium complex from aminopalladation [66], Michael et al [83] could show that the C-Cl bond formation directly results from treatment of the alkyl palladium intermediate with NCS.…”