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, kalyan@lanl.gov.

†† 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.