Crystalline salts of anionic free-base tetrapyrazinoporphyrazines with alkyl-substituents or an extended π-electron system

Abstract

Free-base octamethyltetrapyrazinoporphyrazine (H₂TPyzPzMe₈), octaethyltetrapyrazonoporphyrazine (H₂TPyzPzEt₈), and tetra-2,3-[5,6-(9,10-phenanthro)pyrazino]porphyrazine (H₂T(PhnPyz)Pz) have been synthesized by cyclic tetramerization of corresponding dinitriles followed by demetallation of the obtained magnesium complexes. Reduction or deprotonation of these macrocycles in different experimental conditions yield crystalline {PPN⁺}₂[H₂TPyzPzMe₈²⁻]·7.4C₆H₄Cl₂ (1), {PPN⁺}₂[H₂TPyzPzEt₈²⁻]·8C₆H₄Cl₂ (2), and {cryptand(K⁺)}[HT(PhnPyz)Pz⁻]·5C₆H₄Cl₂ (3) complexes, which were precipitated by n-hexane. This allows us to study crystal structures and optical and magnetic properties of 1–3 based on anionic H_nTPyzPzR₈ⁿ⁻ (n = 2 for 1, 2; n = 1 for 3) macrocycles. Formation of 1 and 2 is accompanied by two-electron reduction of macrocycles, providing a blue shift of the Q-bands in the spectra of 1 and 2. Partial disruption of macrocycle aromaticity is observed in 1 and 2, which is accompanied by the alternation of the C–N_meso bonds because of the formation of a 20 π-electron system in the dianions. Contrarily, salt 3 was obtained at the monodeprotonation of H₂T(PhnPyz)Pz macrocycle, and as a result, this macrocycle shows no alternation of bonds observed in 1 and 2. Salt 3 also preserves the position of the bands in the visible-NIR range in contrast to the reduced macrocycles. All these facts indicate the preservation of an 18 π-electron system characteristic of a starting macrocycle. Salts are diamagnetic and EPR silent supporting the formation of H_nTPyzPzR₈ⁿ⁻ (n = 2 for 1, 2; n = 1 for 3) anions.