A Cyclobutene‐1,2‐bis(imidazolium) Salt as Preligand for Palladium‐Catalyzed Cross‐Coupling Reactions: Properties and Applications

Abstract

Spectroscopic investigations and the results of calculations on the title bis-imidazolium salt, its mono-and bis-carbenes, and its interactions with palladium are presented. In addition, we report on the scope and limitations of metal-catalyzed cross-coupling reactions performed with the title bisPalladium-catalyzed cross-coupling reactions are of evergrowing importance in organic synthesis.[1] They are key steps in numerous total syntheses of natural products, pharmaceuticals, starting materials, liquid crystals, polymers, and new functional materials. Undoubtedly, the SuzukiMiyaura reaction is one of the most widely applied crosscoupling reactions and remarkable progress has been achieved in the syntheses of sterically extremely hindered biaryls, syntheses with low catalyst loadings, and cross-coupling reactions under very mild conditions.[2] In this respect, N-heterocyclic carbenes [3] play important roles as ligands due to their valuable properties, for example, their tunable electronic characteristics, ability to form complexes [4] with a broad range of electron-rich (Pd 0 , [5] Rh +[6] ) as well as electron-poor metals (Mg, [7] Be, [8] Nb [9] ), and the stability of the C carbene -metal bond. The last-mentioned property enables reactions with low catalyst loadings. Meanwhile, numerous structural modifications of N-heterocyclic carbenes and related species have been performed with a view to enhancing the electron density at the carbene center and thus influencing the σ-donating capacity of catalytically active metal complexes. Figure 1 shows some examples, the "classical" NHC imidazol-2-ylidene, the abnormal N-heterocyclic carbene (aNHC) imidazol-4-ylidene, [10] the remote Nheterocyclic carbene (rNHC) [11] pyrazol-4-ylidene, and the cyclic alkyl(amino)carbene (CAAC). [12] In the latter species,

Mechanochemical arylative detrifluoromethylation of trifluoromethylarenes

“…26 Since the Suzuki–Miyaura coupling is the most performed C–C bond formation reaction in both academia and industry, 27,28 expanding this powerful coupling reaction to efficiently involve benzonitrile remains highly sought after. 29–31…”

“…26 Since the Suzuki-Miyaura coupling is the most performed C-C bond formation reaction in both academia and industry, 27,28 expanding this powerful coupling reaction to efficiently involve benzonitrile remains highly sought after. [29][30][31] In view of our expertise in fluorine chemistry, [32][33][34][35] herein we wish to report a mechanochemically enabled direct aryla-tive detrifluoromethylation of trifluoromethylarenes. Our concept depicted in Scheme 1 proposes the in situ defluorinative conversion of ArCF 3 into ArCN (step A) and the subsequent decyanative arylation in a one-pot fashion (step B).…”