Construction of green nanostructured heterogeneous catalysts via non-covalent surface decoration of multi-walled carbon nanotubes with Pd(II) complexes of azamacrocycles

- Efficient and environmentally friendly catalysts were assembled on carbon nanotubes.
- Supramolecular forces are the glue that sticks the active complexes on carbon nanotubes.
- The catalysts were tested toward a Sonogashira cross coupling reaction.
- The heterogeneous Pd(II) catalysts can be reused.

Green nanostructured heterogeneous catalysts were prepared via a bottom-up strategy. Designed ligands were synthesized joining covalently an electrondeficient pyrimidine residue and a scorpiand azamacrocycle. The desired molecular properties were easily transferred to nanostructured materials in two steps: first, exploiting their spontaneous chemisorption onto multi-walled carbon nanotubes (MWCNTs) via the pyrimidinic moiety in water at room temperature, then, taking advantage of the easy coordination of Pd(II) to the azamacrocycle in the same conditions. An evenly distribution of catalytic centres was obtained on the MWCNTs surface. Catalytic properties of these materials were assessed toward the Cu-free Sonogashira cross-coupling, leading to significant improvements in terms of yields and reaction conditions, especially when considering the possibility to maintain yields of 90%, or above, in a feasible amount of time (2 h), while working under green conditions (water, 50 °C, aerobic atmosphere). The catalysts proved to be reusable for several cycles with good yields.

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