Boron, aluminum, gallium, and indium complexes of 1,3-bis(2-pyridylimino)isoindoline (BPI)

Numerous metal complexes of 1,3-bis(2-pyridylimino)isoindoline (BPI) are known, but coordination to this ligand has been limited to transition metals. Herein, we report on the synthesis of group 13 (boron, aluminum, gallium, and indium) complexes of BPI and their basic spectroscopic properties. In its deprotonated monoanionic form, the BPI ligand chelates to boron via a bidentate N^N interaction, forming a non-symmetric molecule. Coordination to aluminum, gallium, and indium occurs via a tridendate N^N^N interaction, forming a symmetric molecule. Absorption spectroscopy shows multiple absorption bands in the UV–visible region for the boron, gallium, and indium complex. A single broad absorption in the UV region was noted for the aluminum complex. Fluorescence emission spectroscopy using an excitation wavelength of 352 nm showed small differences in emission behavior among the complexes. However, with excitation at the λmax and longest λ of absorption, the aluminum complex of BPI was found to be much more emissive than the complexes of boron, gallium and indium; The latter complexes all had emission intensities on the same order of magnitude, each having a low fluorescence quantum yield.