Dendrimers with a Copper(I) Bis(phenanthroline) Core: Synthesis, Electronic Properties, and Kinetics

The copper(I) bis(chelate) complex Cu(L0)2 has been prepared from 2,9-diphenethyl-1,10-phenanthroline and
Cu(CH3CN)4BF4. Derivative Cu(L0)2 has been characterized by NMR, UV−vis spectroscopy, and X-ray crystallography.
Interestingly, owing to the presence of the ethylene linker, the interligand π−π stacking interactions between the
phenyl rings and the phenanthroline subunits in Cu(L0)2 do not induce significant distortions of the pseudotetrahedral
symmetry around the Cu(I) center in the solid state or in solution. Following the synthesis of Cu(L0)2, dendrimers
Cu(L1-4)2 with a Cu(I) bis(2,9-diphenethyl-1,10-phenanthroline) core surrounded by Fréchet type dendritic branches
have been prepared and the kinetics of their cyanide-assisted demetalation studied. Importantly, the surrounding
dendritic wedges have no significant influence on the coordination geometry of the Cu(I) center, as deduced from
their absorption spectra. Therefore, the variations of the rate constants only reflect changes resulting from the
presence of the dendritic branches. The kinetics of the cyanide-mediated demetalation reaction indeed revealed
that cyanide diffusion through the dendritic shell is slightly influenced by the size of the branches. Significant
effects were observed in the kinetics when going from the third to the fourth generation and have been ascribed
to changes in the lipophilicity around the metallic core as a result of dendritic encapsulation.