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.