Pd-functionalized polydopamine-coated polyurethane foam: a readily prepared and highly reusable structured catalyst for selective alkyne semi-hydrogenation and Suzuki coupling under air

A polyurethane foam (PUF) was coated with a thin layer of polydopamine (PDA), and Pd strongly anchored onto PDA via simple immersion of PDA@PUF in a hydro-alcoholic solution of Pd(NH3)4Cl2·H2O at room temperature under air to afford a Pd@PDA@PUF foam. XPS showed the absence of initial reduction of palladium despite the redox properties of PDA, and HR-SEM and SEM-EDX suggested a coordination of evenly dispersed Pd(II) ions by the catechol moieties of the PDA layer, thus resulting in a single atom-type dispersion of the active phase. The “dip-and-play” catalytic pattern of Pd@PDA@PUF and high dispersion of Pd on the surface guaranteed high activity, selectivity and reusability in alkyne semi-hydrogenation and in Suzuki coupling under air without prior reduction procedures. Self-enhancing properties, observed in recycling and control experiments, were explained by XPS as the chelated Pd(II) ions were gradually reduced to isolated coordinated Pd(0) atoms under hydrogenation or Suzuki coupling reaction conditions.