Multi-Electron Redox Processes in Tetrakis(imino)pyracene(TIP) Complexes


Alan H. Cowley*, Kalyan V. Vasudevan, Ignacio Vargas-Baca††, and Michael Findlater.

* Department of Chemistry and Biochemistry, The University of Texas at Austin,

† Chemistry Division, Los Alamos National Laboratory,

†† Department of Chemistry and Chemical Biology, McMaster University,

‡ Department of Chemistry and Biochemistry, Texas Tech University,


Recently, we developed the tetrakis(imino)pyracene ligand as a bifunctional analogue of the bis(imino)acenaphthene (BIAN) ligand class. In initial experiments the 2,6-diisopropylphenyl-substituted TIP ligand was shown to undergo single-electron reduction at both diimine functionalities, resulting in electron pairing over the pyracene backbone. We have now discovered that the reaction of PI3 with the TIP ligand results in a four-electron reduction process, thereby generating the first example of a bis(phosphenium) cation. The reaction of TeI2 with the TIP ligand also involves a four-electron reduction process. However, in this case the reduction takes place at the Te centers. The difference in the outcomes of the PI3 and TeI2 reactions can be explained on the basis of electronic structure (DFT) calculations. Interestingly, treatment of the TIP ligand with BI3 results in the three-electron reduction and formation of the pentaiodide salt of the bis-BI substituted radical cation.