Silicon(IV) complexes of octaaryl-substituted porphyrazines and corrolazines: influence of macrocycle contraction on spectral-luminescence, acid-base, and redox properties.

Abstract

The template cyclomerization of the iminoimide derivatives (obtained by the treatment of diarylfumarodinitriles with NH3 in methanol containing catalytic amounts of dissolved Na) in the presence of SiCl4 in pyridine leads to silicon(IV) octaarylporphyrazine complexes ((HO)2SiPzAr8, Ar = Ph, tBuPh) as a main reaction product. In the case of phenyl-substituted derivative, the formation of a distinctive Si(IV) complex as a byproduct was observed, which according to mass-spectroscopy measurement contains the macrocycle with five diphenylpyrrolic units. The treatment of bishydroxy complexes with tripropylchlorosilane in the presence of magnesium in pyridine leads to the formation of axially siloxylated porphyrazines (Pr3SiO)2SiPzAr8, followed by the reductive contraction of the macrocycle and formation of the corresponding corrolazine complexes (Pr3SiO)SiCzAr8. It is shown that the addition of acid (trifluoroacetic acid, TFA) facilitates the detachment of one siloxy group in (Pr3SiO)2SiPzAr8 and is essential for its Pz → Cz transformation. In the presence of TFA, only one meso-nitrogen is protonated in the porphyrazine complexes (Pr3SiO)2SiPzAr8 (stability constant of the protonated form pKs1 = -0.45 for Ar = Ph; pKs1 = 0.68 for Ar = tBuPh), while two consequent protonation stages are observed for the more basic corrolazine complex (Pr3SiO)SiCzPh8 (pKs1 = 0.93, pKs2 = 0.45). Both types of Si(IV) complexes are poorly fluorescent (ΦF < 0.07). The porphyrazine complexes have low ability to generate singlet oxygen (ΦΔ < 0.15), whereas the corrolazine derivative (Pr3SiO)SiCzPh8 is a very efficient photosensitizer (ΦΔ = 0.76).