Synthesis and characterization of polyamidoamine dendrimers surface-functionalized with bromotricarbonylpyridyliminerhenium(I) units

A novel type of rhenium-containing dendrimers has been prepared and characterized. A series of Schiff base-terminated PAMAM dendrimers were prepared by condensing the terminal amine groups of PAMAM dendrimers with pyridine-2-carboxaldehyde. Complete condensation of the terminal amines was confirmed by 1H NMR spectroscopy. Bromotricarbonylrhenium(I) moieties were introduced onto the surface of these modified PAMAM derivatives by refluxing with bromopentacarbonylrhenium(I). These complexes had been characterized by a variety of analytical and spectroscopic techniques and their IR, NMR, and mass spectra discussed. The crystal structure of the model compound [(CH3CONHCH2CH2NCHPy)ReBr(CO)3] confirms a facial configuration of the three carbonyl ligands. UV–Vis absorption spectroscopy suggests that the {Re(CO)3} moieties are quite far apart even in the second generation PAMAM dendrimers and do not interact with one another. In fact, the intensity of the metal-to-ligand (dπ–pπ∗) charge-transfer is a linear function of the number of {Re(CO)3} chromophores.

Graphical abstractFirst and second generation PAMAM dendrimers were modified through condensation reactions to give pyridylimine Schiff base ligands. G0, G1 and G2 pyridylimine PAMAM dendrimers were reacted with [ReBr(CO)5] to give terminally modified dendrimers having four, eight and 16 rhenium tricarbonyl moieties at the terminals, respectively.Figure optionsDownload full-size imageDownload as PowerPoint slide