1182649-29-1Relevant articles and documents
Synthetic and Mechanistic Interrogation of Pd/Isocyanide-Catalyzed Cross-Coupling: π-Acidic Ligands Enable Self-Aggregating Monoligated Pd(0) Intermediates
Barnett, Brandon R.,Labios, Liezel A.,Stauber, Julia M.,Moore, Curtis E.,Rheingold, Arnold L.,Figueroa, Joshua S.
supporting information, p. 944 - 954 (2017/04/21)
Despite the large number of judiciously designed ligands that have been exploited in palladium-catalyzed cross-coupling protocols, the incorporation of ligands bearing appreciable π-acidic properties has remained significantly underexplored. Herein, we demonstrate that well-defined and low-coordinate Pd0 complexes supported by m-terphenyl isocyanides function as competent catalysts for the Suzuki-Miyaura cross-coupling of aryl bromides and arylboronic acids. Two-coordinate Pd(CNArDipp2)2 was active for the coupling of unhindered aryl bromides at room temperature in 2-propanol, while increasing the temperature to 60 °C allowed for the use of mono- or di-ortho-substituted aryl bromides. Oxidative addition of the aryl bromide was shown to proceed via a dissociative mechanism, implicating monoligated Pd(CNArDipp2) as the catalytically active intermediate. Attempts to access this fleeting species via activation of the PdII monoisocyanide PdCl(η3-C3H5)(CNArDipp2) with alkoxide base yielded the dinuclear PdI species (μ-C3H5)(μ-OiPr)[Pd(CNArDipp2)]2. Although dinuclear PdI complexes are often produced as off-cycle species when using complexes of the type PdCl(η3-allyl)L as precatalysts, this represents the first time that the comproportionation product (μ-allyl)(μ-Cl)[PdL]2 has been observed to undergo nucleophilic substitution with alkoxide, despite the fact that activating conditions for these precatalysts typically employ alkoxide bases. Remarkably, this alkoxide complex can undergo β-hydride elimination with expulsion of acetone and propene to produce two equivalents of catalytically active Pd(CNArDipp2), which can self-aggregate to yield the isolable tripalladium cluster Pd3(η2-Dipp-μ-CNArDipp2)3. This cluster is catalytically competent for the Suzuki-Miyaura reaction and functions as a formal source of monoligated Pd(CNArDipp2) in solution.
