Tetrameric arrays of the [Re₆(μ₃-Se) ₈]²⁺ clusters supported by a porphyrin core: Synthesis, characterization, and electrochemical studies

A tetracluster array {[Re₆(μ₃-Se)₈ (PEt₃)₅]₄ [5,10,15,20-tetra(4-pyridyl)-21H,23H-porphine]}(SbF₆) ₈ (R₄) featuring a central porphyrin core and four circumjacent [Re₆(μ₃-Se)₈] ²⁺ units was synthesized by reacting the previously reported cluster solvate [Re₆(μ₃-Se)₈ (PEt₃)₅(MeCN)](SbF₆)₂ (R) with 5,10,15,20-tetra(4-pyridyl)-21H,23H-porphine. Metallation of R₄ with metal (Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺) salts afforded the corresponding cluster-studded metalloporphyrins (R₄-Co, R₄-Ni, R₄-Cu, and R₄-Zn). All compounds were characterized by ¹H and ³¹P NMR spectroscopy and elemental analysis (CHN). Electrochemical studies revealed one chemically reversible oxidation event attributable to the simultaneous removal of four electrons, one from each of the four cluster units. The uncoupled redox event suggests minimal electrical communication between the cluster sites. The cluster arrays were also studied by UV-vis spectroscopy. The electronic spectra of R₄-Co, R₄ -Ni, and R₄-Cu each showed the absorptions of the metalloporphyrins and the cluster complex. For R₄-Zn, solvatochromism was observed. Its electronic absorptions in a variety of solvents of different dielectric constants were studied.