Reactive Palladium Carbenes: Migratory Insertion and Other Carbene–Hydrocarbyl Coupling Reactions on Well‐Defined Systems

Abstract

Palladium complexes with carbene ligands are among the best known and more extensively used catalysts. Those carbenes are usually NHC or N,N-disubstituted derivatives and their use relies on the robust nature of the carbene ligands and their role as auxiliary ligands that modify the metal's electronic and steric features. In contrast, there are other types of carbenes that, when coordinated to palladium, lead to transformations in which the carbene fragment is involved. In the last decade, palladium-catalyzed reactions have been extended to the use of carbene precursors that can be functionalized with [a]

Highly electrophilic silver carbenes

“…35 However, most of the reported silver carbene chemistry is solely based on diazo compounds stabilized by at least one electron-withdrawing group. As confirmed by numerous reports from Aggarwal, Barluenga, Valdés, Wang, Shao, Langer, Pilania, Zhou, Zhu, Jiang, and others, 36–52 N -sulfonylhydrazones derived from aldehydes and ketones are the most explored diazo precursors under the catalysis of palladium, copper, and rhodium, due to their easy availability, bench stability, and operational safety. In recent years, the Bi group first exploited silver catalysis in carbene transfer reactions of N -sulfonylhydrazones and unexpectedly discovered that silver has a weak coordination effect on carbene carbon, leading to a series of highly efficient donor carbene transfer reactions.…”

Palladium-Catalyzed Oxidative Coupling of Dibenzosiloles with α-Diazo Esters: Formal Replacement of the Silyl Group with Carbenes

“…On the other hand, diazo compounds, which are commonly utilized as carbene precursors, have emerged as nucleophilic cross-coupling partners in transition-metal-catalyzed reactions in recent years . In these transformations, the diazo substrates react with organometallic species to generate metal carbene intermediates, from which C–C bonds are formed via a rapid migratory insertion process . While such transformations are powerful in constructing a C–C bond on the carbenic center, it is challenging to generate two C–C bonds on the carbenic carbon.…”

“…4 In these transformations, the diazo substrates react with organometallic species to generate metal carbene intermediates, from which C−C bonds are formed via a rapid migratory insertion process. 5 While such transformations are powerful in constructing a C−C bond on the carbenic center, it is challenging to generate two C−C bonds on the carbenic carbon. For generating two C−C bonds on a carbenic center in carbene-based cross-coupling reactions, cascade reactions provide a possible approach, in which the metal carbene migratory insertion is followed by transmetalation and reductive elimination (Scheme 1b).…”

Reactivity of Carbenes in Aqueous Nanomicelles Containing Palladium Nanoparticles

“…Cross-couplings comprising metal–carbene migratory insertion have aroused significant interest during the past decade, which is likely due to noteworthy applications of resulting products in medicinal chemistry and material science. − However, most of these reactions involve the use of toxic solvents such as 1,4-dioxane, DMF, and benzene under harsh conditions. Due to the involvement of reactive Pd–carbene intermediates, the achievement of such transformations in aqueous micellar media might be expected to be challenging and perhaps has hence remained elusive.…”

“…32−34 However, most of these reactions involve the use of toxic solvents such as 1,4-dioxane, DMF, and benzene under harsh conditions. Due to the involvement of reactive Pd− carbene intermediates, 35 the achievement of such transformations in aqueous micellar media might be expected to be challenging and perhaps has hence remained elusive.…”