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.

Graphical abstractBoron, aluminum, gallium and indium complexes of 1,3-bis(2-pyridylimino)isoindoline (BPI) have been prepared. This image shows the X-ray determined structure of BPI·GaCl2 along with its absorption spectrum relative to the native BPI ligand.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Group 13 metal complexes of 1,3-bis(2-pyridylimino)isoindoline were synthesized. ► X-ray determined structures of boron and gallium derivatives are reported. ► B is bound to the 1,3-bis(2-pyridylimino)isoindoline ligand in a bidentate fashion. ► Al, Ga and In bind to 1,3-bis(2-pyridylimino)isoindoline in a tridentate fashion. ► UV-Vis and fluorescence emission spectra of all complexes are also reported.