End-grafted Cu-NNN pincer complexes on PAMAM dendrimers-SiO2: synthesis and characterization

Abstract

In this paper, the heterogeneous nature of an amorphous SiO₂ support, the exceptional properties of polyamidoamine dendrimers (PAMAM), and the unique properties of pincer ligands (NNN type) were combined for immobilization of a triazine-derived Cu(II)-NNN pincer complex onto the dendritic nanoparticle supports. All of the prepared samples in each step were fully characterized and compared by several techniques, including FTIR, TGA–DTG, elemental analysis (EA), SEM, and TEM. In this regard, two different methods were applied and used for the synthesis and growth of a PAMAM dendrimer onto the SiO₂ support via the divergent synthesis method (without and with the catalyst). In the presence of a tetrabutylammonium bromide (TBAB) catalyst, dendritic supports were prepared in a shorter time with better growth. Subsequently, a symmetric and neutral tridentate NNN-pincer ligand derived from trichloro-1,3,5-triazine/2-aminopyridine was immobilized on each of these dendritic nanoparticle supports. The successful immobilization of a pincer ligand on the nanoparticle dendritic support was also supported by the techniques mentioned above. Finally, the reaction of each prepared support with copper(II) chloride at room temperature resulted in the formation of immobilized Cu(II)-NNN pincer complexes as partially supported by EPR and UV-vis spectroscopy. The loading of the copper ions for each sample was measured by ICP/OES analysis. Among the five final immobilized ligands, the NNN pincer-G′1-SiO₂ (G′1 = the first generation of PAMAM dendrimers prepared via the second method) showed more suitable ability for copper adsorption.