Gemini-Porphyrazines: The synthesis and characterization of metal-capped cis- and trans-porphyrazine tetrathiolates

Peripherally-functionalized porphyrazines of the form M[pz(A(n):B(4-n))] (inset 1), where A and B symbolize functional moieties (e.g., a-d in Table 1) fused directly to the β-positions of the pyrroles, have the potential to serve in a wide range of applications. Previously, we reported the synthesis of porphyrazine di- and octathiolate ligands, M[pz(b₃:c₁)] and M[pz(c₄)], respectively, where b is a fused benzo ring and c represents two thiolates fused at the β-pyrrole positions to form a dithiolene capable of the peripheral chelation of a metal ion. We describe here a general strategy that solves the more difficult problem of preparing and isolating the porphyrazinetetra- and hexathioethers and the porphyrazinetetra- and hexathiolates, with the focus being the trinuclear metal complexes of the trans- and cis-porphyrazinetetrathiolate isomers (trans- and cis-M[pz(b₂:d₂)]), denoted as gemini porphyrazines. Spectroscopic and electrochemical studies reveal that the physical properties of the cis- and trans-tetrathioether porphyrazines exhibit intriguing differences associated with their distinct molecular symmetries. These functionalized macrocycles have been used to prepare the trans- and cis-gemini porphyrazines 14 and 16, the two isomeric porphyrazinetetrathiolate macrocycles that are peripherally-metalated with two bis(triethylphosphine)platinum(II) moieties. The X-ray structure of the trans isomer, 14, is presented; it is the first structure of a porphyrazine or phthalocyanine having a trans-type substitution pattern.