Biisoquinolines differ from biquinolines in the position of the nitrogen atom relative to the adjacent fused benzene ring. Again, there are six possible biisoquinoline isomers; however, the two symmetric molecules, 1,1'-(52) and 3,3'-(53), are most commonly employed as transition metal ligands.
Like biquinolines, biisoquinolines are typically prepared by Ni0-catalyzed homocoupling of iso-quinolyl halides.293 The 1,1' isomer has also been prepared in moderate yield from simple isoquinoline by reacting it with LDA in hexamethylphosphoramide and ether.295 This isomer is nonplanar when bound to metal ions due to the steric repulsion between protons at the 8 and 8 positions and thus, is chiral. The interconversion of the conformational isomers (known as atropisomers) of this ligand when bound to ruthenium has been reported.296 The 3,3' isomer has also been studied as a transition metal ligand and more recently as a ligand for lanthanide metals.297 Luminescence studies on ruthenium complexes298 of (53) and the ligand itself299 have been reported.
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