Group 10 metal complexes of the 3,4-bis(dicyclohexylphosphino)thiophene (dcypt) ligand: Synthesis, characterization and catalysis

Abstract

The nickel(II) (1), palladium(II) (2) and platinum(II) (3) complexes of the 3,4-bis(dicyclohexylphosphino)thiophene (dcypt) ligand were synthesized and characterized by multinuclear NMR and FT-IR spectroscopic techniques, mass spectrometry and elemental analysis. The nearly perfect square-planar geometry of the three complexes was confirmed by single-crystal X-ray diffraction analysis. Both complexes 1 (Ni) and 2 (Pd) were evaluated towards the Suzuki-Miyaura cross-coupling reaction between aryl halides and aryl boronic acids, a field that was not explored until now for metal complexes of dcypt. While the palladium(II) (pre)catalyst (2) was found very efficient for this transformation, both under “classical” (Cs₂CO₃ as base, 1,4-dioxane as solvent) and “green” (K₃PO₄ as base, tert-amyl alcohol (tAA) as solvent) reaction conditions, its nickel(II) analog (1) was only moderately active under the latter conditions (inactive under the former). Complex 2 was tolerant to both the presence of EDGs or EWGs groups on para position of the aryl halide or aryl boronic acid (72–99 %) and allowed the synthesis of polycyclic aromatic compounds. Moreover, the remarkable air-stability of dcypt and of its corresponding palladium(II) complex (2) allowed to perform Suzuki-Miyaura cross-coupling reactions under air and with a non-dried alcoholic solvent (tAA) without loss of activity.