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. In the present context, a stable α-free ligand 2 has been developed and complexation of ligands 1 and 2 with diamagnetic Co3+, Ga3+, and In3+ has been 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−vis spectroscopy, and X-ray crystallography. Again, the 1H NMR analysis showed that both the triple-stranded helicates and mesocates were generated in this metal-directed assembly. Consistent with our previous finding on coordinatively inert Co3+ complexes, variable-temperature NMR spectroscopy indicated that the triple-stranded helicate and mesocate of labile In3+ did not interconvert in solution, either. However, the diastereoselectivity of the M223 complexes was found to improve with an increase in the reaction te...