Bimetallic Pd/Cu complexes of pyridylchalcogenolates and their catalytic activity in the Sonogashira reaction

Abstract

The heterobimetallic complexes [{Pd(PPh₃)₂(4-Epy)₂}{Cu(PPh₃)₂Cl}₂] (E = S, Se) were synthesized from the Cu^I complex [CuCl(PPh₃)₃] and “metallo-ligands” [PdCl(PPh₃)₂(4-Epy)] (1) and [Pd(PPh₃)₂(4-Epy)₂] (2) (Epy⁻ = 4-pyridylchalcogenolate; E = S or Se). Reaction of 2, having two free pyridyl groups, yields a cleaner product than 1, possessing only one pyridyl group. NMR spectroscopy, ESI-MS spectrometry and X-ray diffraction structures are in line with centrosymmetric molecules, a square planar Pd^II center and two tetrahedral Cu^I centers, that are bridged by two trans oriented 4-pyridylchalcogenolates. The same reaction using the chelating diphosphine ligand dppf resulted in insoluble products. The two mixed metal Pd^II–Cu^I complexes show high catalytic activity in the Sonogashira cross-coupling reactions of phenylacetylene and a variety of aryl bromides. The optimized reaction produced a TON of 470 000 and a TOF of 31 300 h⁻¹.