The Redox-Active Chromium Phthalocyanine System: Isolation of Five Oxidation States from Pc4- CrI to Pc2- CrIII.

ABSTRACT

The preparation and structural characterization of a series of chromium phthalocyanine complexes with multiple metal and ring oxidation states were achieved using PcCrII (1) (Pc=phthalocyanine) or PcCrII (THF)2 (1⋅THF2 ) as starting materials. The reaction of soluble 1⋅THF2 with Br2 or I2 gave the PcCrIII 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 [PcCrIII (THF)2 ]SbF6 (6). The reduction of 1 with three sequential equivalents of KEt3 BH resulted in the isolation of [K(DME)4 ][Pc3- CrII ] (7), [K(DME)4 ]2 [Pc4- CrII ] (8) and [K6 (DME)4 ][Pc4- CrI ]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.