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

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.