The Redox-Active Chromium Phthalocyanine System: Isolation of Five Oxidation States from Pc^4- Cr^I to Pc^2- Cr^III

The preparation and structural characterization of a series of chromium phthalocyanine complexes with multiple metal and ring oxidation states were achieved using PcCr^II (1) (Pc=phthalocyanine) or PcCr^II (THF)₂ (1⋅THF₂ ) as starting materials. The reaction of soluble 1⋅THF₂ with Br₂ or I₂ gave the PcCr^III halide complexes PcCrX(THF) (X=I/I₃ , Br; 3, 4, respectively). Treatment of 1 with 0.5 equivalent of PhIO or air generated the dinuclear [PcCr(THF)]₂ (μ-O) (5), whereas the addition of one equivalent of AgSbF₆ to 1 resulted in oxidation to THF-solvated octahedral [PcCr^III (THF)₂ ]SbF₆ (6). The reduction of 1 with three sequential equivalents of KEt₃ BH resulted in the isolation of [K(DME)₄ ][Pc^3- Cr^II ] (7), [K(DME)₄ ]₂ [Pc^4- Cr^II ] (8) and [K₆ (DME)₄ ][Pc^4- Cr^I ]₂ (9), respectively. The reduced products are deep purple in colour, with visible absorption maxima between 500-580 nm. The ring-reduced complexes 7 and 8 are monomeric, whereas 9 is a 1D chain of dinuclear [PcCr]₂ units with intercalated K⁺ cations and supported by Cr-Cr interactions of 2.988(2) Å. Addition of four equivalents of KC₈ resulted in the demetallated product PcK₂ (DME)₄ (10), which has a 1D chain structure. The isolation and structural characterization of new PcCr complexes spanning five oxidation states, including rare examples of crystalline reduced Pc-ring species emphasizes the broad redox activity and stability of phthalocyanine-based complexes.