Carbamoyl-Substituted N-Heterocyclic Carbene Complexes of Palladium(II):  Application to Sonogashira Cross-Coupling Reactions

Abstract

[reaction: see text]. The first examples of N-carbamoyl-substituted heterocyclic carbene Pd(II) complexes are described. These thermal and hydrolytically stable complexes are readily prepared from carbamoyl imidazolium salts and efficiently promote Sonogashira cross-coupling reactions under mild conditions. Cesium carbonate is also shown to be an effective base for the coupling of aryl bromides.

Robust and Electron‐Rich cis‐Palladium(II) Complexes with Phosphine and Carbene Ligands as Catalytic Precursors in Suzuki Coupling Reactions

“…There are several examples of cis PPh 3 /carbene Pd II complexes in the literature. [46][47][48][49] Examples of trans phosphine/carbene Pd 0 [50] and Pd II [30] complexes are also known. However, cis PCy 3 /carbene Pd II complexes, such as 10 and 11 are unprecedented in the literature.…”

Palladium Complexes of N‐Heterocyclic Carbenes as Catalysts for Cross‐Coupling Reactions—A Synthetic Chemist's Perspective

“…[115] A similar approach was taken by Andrus and co-workers: The catalyst prepared from a bulky imidazolium salt (218, Scheme 56) and [PdCl 2 (PPh 3 ) 2 ] promoted the coupling of various iodo-and bromosubstituted arenes and alkenes with terminal acetylenes (Scheme 66). [202] Surprisingly, SIPr·HCl (13, Table 1) showed only moderate activity.…”

“…In a similar fashion, heating 112 with Pd(OAc) 2 resulted in the unusual complex 113 (Scheme 37). [115] Decomposition of the second equivalent of the N-carbamoylimidazolium salt by acetic acid (produced during the formation of the singly ligated Pd-NHC complex) to N-methylimidazole and N-acetylpyrrolidine, followed by complexation of the singly ligated Pd-NHC species with N-methylimidazole most likely accounts for this unusual transformation.…”

C(sp2)‐C(sp) and C(sp)‐C(sp) Coupling Reactions Catalyzed by Oxime‐Derived Palladacycles

“…[6] Very recently, Plenio and colleagues [7] have presented a new and very efficient catalytic system for the Sonogashira coupling of activated and non-activated aryl chlorides with terminal acetylenes, based on the combination Na 2 PdCl 4 /(1-Ad) 2 PBn/CuI (1-Ad 1-adamantyl, Bn benzyl). On the other hand, N-heterocyclic carbene palladium(II) complex 1, [8] has also been shown to mediate the Sonogashira coupling of aryl bromides with different alkynes at 80 0 C in DMF under inert atmosphere, in the presence of 2 mol % of CuI and 1 mol % of PPh 3 . However, and in order to simplify the reaction protocol, copper-free methodologies have lately attracted most attention, as the use of copper(I) salts as co-catalysts usually induces the homocoupling reaction (Glasertype [4] ) of terminal alkynes to diynes in the presence of oxygen as well as the precipitation of catalytically inactive palladium black.…”