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

In this paper, the heterogeneous nature of amorphous SiO2 support, exceptional properties of polyamidoamine dendrimers (PAMAM), and unique properties of pincer ligands (NNN type) were combined for immobilization of triazine-derived Cu(II)-NNN pincer complex onto the dendritic supports. All 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 PAMAM dendrimer onto SiO2 support via the divergent synthesis method (without and with catalyst). In the presence of tetrabutylammonium bromide (TBAB) catalyst, dendritic supports were prepared in a shorter time with better growth. Subsequently, symmetric and neutral tridentate NNN-pincer ligand derived from trichloro-1,3,5-triazine/2-aminopyridine immobilized on each of these dendritic supports. The successful immobilization of pincer ligand on dendritic support also was 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.