Noncovalent Assembly and Catalytic Activity of Hybrid Materials Based on Pd Complexes Adsorbed on Multiwalled Carbon Nanotubes, Graphene, and Graphene Nanoplatelets

Abstract

Green catalysts with excellent performance in Cu-free Sonogashira coupling reactions can be prepared by the supramolecular decoration of graphene surfaces with Pd(II) complexes. Here we report the synthesis, characterization, and catalytic properties of new catalysts obtained by the surface decoration of multiwalled carbon nanotubes (MWCNTs), graphene (G), and graphene nanoplatelets (GNPTs) with Pd(II) complexes of tetraaza-macrocyclic ligands bearing one or two anchor functionalities. The decoration of these carbon surfaces takes place under environmentally friendly conditions (water, room temperature, aerobic) in two steps: (i) π–π stacking attachment of the ligand via electron-poor anchor group 6-amino-3,4-dihydro-3-methyl-5-nitroso-4-oxo-pyrimidine and (ii) Pd(II) coordination from PdCl 4 2– . Ligands are more efficiently adsorbed on the flat surfaces of G and GNPTs than on the curved surfaces of MWCNTs. All catalysts work very efficiently under mild conditions (50 °C, aerobic, 7 h), giving a similar high yield (90% or greater) in the coupling of iodobenzene with phenylacetylene to form diphenylacetylene in one catalytic cycle, but catalysts based on G and GNPTs (especially on GNPTs) provide greater catalytic efficiency in reuse (four cycles). The study also revealed that the active centers of the ligand-Pd type decorating the support surfaces are much more efficient than the Pd(0) and PdCl 4 2– centers sharing the same surfaces. All of the results allow a better understanding of the structural factors to be controlled in order to obtain an optimal efficiency from similar catalysts based on graphene supports.

Ye Olde supramolecular chemistry, its modern rebranding and overarching trends in chemistry

“…35 Yet, we do identify as strongly in the inorganic and coordination chemistry community, having long dealt with solution equilibria, 36 metal complexes 37 and catalysis topics. 38,39 Being saddened by current situation, we will try our best to present a brief and impartial account of most coexisting stances on the current supramolecular chaos, from σ-hole to secondary bonding, passing from popular VB concepts (hybridization, resonance), outer/inner sphere complexes, VSEPR models, etc. Impartial means, here, giving due space to ideas other than currently mainstream ones.…”

“…35 Yet, we do identify as strongly in the inorganic and coordination chemistry community, having long dealt with solution equilibria, 36 metal complexes 37 and catalysis topics. 38,39…”