Synthesis of Triple-Stranded Complexes Using Bis(dipyrromethene) Ligands.

The reaction of an α-free, β,β’-linked bis(dipyrromethene) ligand with Fe3+ or Co3+ led to noninterconvertible triple-stranded helicates and mesocates (Z. Zhang and D. Dolphin, 2009). In the present context, complexation of bis(dipyrromethene) ligands I·2HBr (1-H2·2HBr) and newly developed stable α-free ligand II (2-H2) with diamagnetic Co3+, Ga3+, and In3+ was studied. The triple-stranded M213 (M = Ga, In) and M223 (M = Co, Ga, In) complexes were characterized using matrix-assisted laser desorption ionization time-of-flight spectrometry, 1H NMR and UV-visible spectroscopy, and x-ray crystallog. Again, the 1H NMR anal. showed that both the triple-stranded helicates and mesocates were generated in this metal-directed assembly. Consistent with the authors’ previous finding on coordinatively inert Co3+ complexes, variable-temp. NMR spectroscopy indicated that the triple-stranded helicate and mesocate of labile In3+ did not interconvert in soln., either. However, the diastereoselectivity of the M223 complexes was found to improve with an increase in the reaction temp. Taken together, this study complements the coordination chem. of poly(dipyrromethene) ligands and provides further insight into the formation of helicates vs. mesocates. [on SciFinder(R)]