Benzoquinonediimine ligands: Synthesis, coordination chemistry and properties

International audienceThis review covers the synthesis and properties of 2,5-diamino-1,4-benzoquinonediimines (DABQDI), and their use as ligand in coordination chemistry. Although reported more than a century ago, these molecules emerged as highly versatile ligands only from 1998, and are so far used for the synthesis of numerous complexes with remarkable properties. This exceptional versatility results from the possible tuning of the N-substituents and the observation of an isomerization process upon coordination depending on the metal center. As such, these DABQDI can be also considered as ligands that combine the structural elements of ortho- and para-benzoquinonediimines (o-BQDI and p-BQDI) which are bidentate monotopic and monodentate ditopic ligands, respectively. These two classes of BQDI ligands are also reviewed in order to parallel their properties to those of the complexes based on DABQDI