Pd nanosized particles supported on chitosan and 6-deoxy-6-amino chitosan as recyclable catalysts for Suzuki–Miyaura and Heck cross-coupling reactions

Several chitosan and 6-deoxy-6-amino chitosan-Schiff base ligands (1–4) were prepared by condensation of either 2-pyridinecarboxaldehyde or 2-(diphenylphosphino)benzaldehyde with the amino group(s) on chitosan and its derivative (6-deoxy-6-amino chitosan). The supported ligands were reacted with [PdCl2(COD)] to form chitosan-supported PdII catalysts (5–8). All the supported catalysts were air- and moisture-stable and have been characterized using elemental analysis, ICP-MS, UV–vis, FT-IR, PXRD, TGA, 31P solid state NMR and TEM. As models for the heterogenized catalysts (5 and 6), mononuclear PdII complexes (9 and 10) were also prepared via the Schiff-base condensation reaction of 1,3,4,6-tetra-O-acetyl-β-d-glucosamine hydrochloride to form 1,3,4,6-tetra-O-acetyl-β-d-glucos-2-pyridylimine and 1,3,4,6-tetra-O-acetyl-β-d-glucos-2-(diphenylphosphino)imine which were subsequently reacted with [PdCl2(COD)]. Complexes (9 and 10) and their precursors were characterized by 1H and 31P NMR, UV–vis, FT-IR spectroscopy and elemental analysis.Catalytic Suzuki–Miyaura and Heck carbon–carbon cross-coupling reactions were carried out using the supported Pd catalysts and their mononuclear analogues. The immobilized and homogeneous catalysts showed high activity for both the Suzuki–Miyaura and Heck cross-coupling reactions in organic and aqueous media. Homogeneous catalysts (9 and 10) decomposed during the first run, while the supported catalysts could be recycled and reused up to five times.

Figure optionsDownload high-quality image (88 K)Download as PowerPoint slideResearch highlights▶ Chitosan-supported Pd(II) catalysts were synthesized in good yield. ▶ The Pd(II) catalysts were characterized using various analytical techniques. ▶ High catalytic activity was exhibited in Suzuki–Miyaura and Heck coupling reactions. ▶ No Pd leaching was detected in the products as determined by ICP-MS. ▶ The catalysts could be recycled and reused up to five times with consistent activity.