Cooperative effects of lanthanides when associated with palladium in novel, 3D Pd/Ln coordination polymers. Sustainable applications as water-stable, heterogeneous catalysts in carbon–carbon cross-coupling reactions

Abstract

Three novel porous heterobimetallic coordination polymers, [Ln2Pd3(BPDC)2(HBPDC)2(μ2-O)Cl4(H2O)6·nH2O]m (Ln=Pr, n=5 (1), Ln=Gd, n=4 (2), and Ln=Tb, n=4 (3)), were readily prepared by combining Pd(II) and Ln(III) with 2,2′-bipyridine-4,4′-dicarboxylic acid (H2BPDC) as a heteroleptic ligand, under hydrothermal conditions, and structurally characterized by means of single-crystal X-ray diffraction, FT-IR, powder X-ray diffraction, elemental analysis and thermogravimetric (TG) techniques. Single-crystal X-ray diffraction examination showed that 1–3 have similar 3D frameworks, connected via hydrogen bonding interactions, and consisting of three distinct types of building blocks: Pd(BPDC)Cl2, Pd(HBPDC)2 and a Ln dimer (Ln2O15). The new isostructural, air and water stable coordination polymers, resulting from association of lanthanides with palladium, exhibited superior but distinct capabilities as eco-friendly heterogeneous catalysts in Suzuki-Miyaura, Heck and Sonogashira cross-couplings, under green reaction conditions. Supramolecular, solid catalysts 1–3 have been recovered quantitatively from the reaction mixtures by simple filtration. Also importantly, their sustainability, utility and cost-effectiveness have been demonstrated by recycling experiments with catalyst 1 in Suzuki-Miyaura, proceeding practically without loss of activity after four runs.