Mono- and di-nuclear tricarbonyl Re(I) tetraazaporphyrin complexes (Re1 TAP and Re2 TAP) are investigated and compared with Re(I) phthalocyanine complexes (Re1 Pc and Re2 Pc). Although Re2 Pc is unstable in polar solvents, and easily undergoes demetallation reaction, the coordination of the TAP ligand significantly improves the tolerance toward polar solvents, affording more stability to Re2 TAP. Additionally, the incorporation of [Re(CO)3 ]+ unit(s) and the TAP ligand results in remarkable positive shifts in both oxidation and reduction potentials. Consequently, the more positive oxidation potentials of the ReTAP complexes significantly increase the tolerance toward oxidation, while the reduction potential indicates that Re2 TAP is suitable for a soluble electron acceptor. In contrast to Re1 Pc and Re2 Pc, Re1 TAP and Re2 TAP show unique broad Q bands, which can be attributed to the admixture of the π-π* and metal-to-ligand charge transfer characters, owing to the lowered π orbital energy in the TAP complexes. This study is useful for controlling electronic properties and realizing high stability in Pc analogues.
Keywords: carbonyl ligands; electronic structure; phthalocyanines; porphyrinoids; rhenium.
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