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 pK_s1 = −0.45 for Ar = Ph; pK_s1 = 0.68 for Ar = ^tBuPh), while two consequent protonation stages are observed for the more basic corrolazine complex (Pr₃SiO)SiCzPh₈ (pK_s1 = 0.93, pK_s2 = 0.45). Both types of Si(IV) complexes are poorly fluorescent (Φ_F < 0.07). The porphyrazine complexes have low ability to generate singlet oxygen (Φ_Δ < 0.15), whereas the corrolazine derivative (Pr₃SiO)SiCzPh₈ is a very efficient photosensitizer (Φ_Δ = 0.76).