Orthometallated palladium trimers in C–C coupling reactions

A series of trimeric palladium complexes of the [Pd3(μ-Cl)4(P–C)2] (P–C = orthometallated aryl phosphite) formula have been prepared and structurally characterized using 31P NMR and ESI-MS methods. The structure of [Pd3(μ2-Cl)4{k2-P,C–P(O–o-CH3C6H3)(O–o-CH3C6H4)2}2], 1c, was determined by X-ray diffraction. It is compared with the structure of the dimeric complex [Pd2(μ-Cl)2{k2-P,C–P(O–m-CH3C6H3)(O–m-CH3C6H4)2}2], 3b. The trimeric palladium complexes very efficiently catalyzed the Suzuki–Miyaura and Hiyama reactions in ethane-1,2-diol and the Sonogashira cross-coupling in ionic liquids. The mercury test confirmed the homogeneous pathway of the Suzuki–Miyaura reaction, although Pd(0) nanoparticles were observed by TEM in the post-reaction mixture.

Graphical abstractSynthesis and structural characterization of trimeric orthometallated palladium phosphito complexes of the type [Pd3(μ-Cl)4(P-C)2]. The trimeric palladium complexes act as very efficient catalysts of Suzuki-Miyaura and Hiyama reactions in ethane-1,2-diol. High catalytic activity of trimeric palladium complexes in Sonogashira cross-coupling in ionic liquids was evidenced. The homogeneous pathway of the Suzuki-Miyaura reaction was confirmed by the Hg(0) test, although Pd(0) nanoparticles were formed at the end of the catalytic process.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Synthesis of new palladium trimeric complexes. ► Efficient catalysts for Suzuki–Miyaura and Hiyama reactions. ► Catalysts for Sonogashira reaction in ionic liquids. ► Homogeneous pathway of the catalytic reaction.