Silicon(IV) corrolazine with fused camphanopyrazine units and its porphyrazine precursors

Silicon(IV) corrolazine with annulated electron-deficient camphanopyrazine fragments (HO)SiCz was obtained using two approaches based on the contraction of the porphyrazine (Pz) macrocycle in the corresponding silicon complex (HO) 2 SiPz or the macrocyclic ligand H 2 Pz (3). In turn, (HO) 2 SiPz was prepared by template cyclotetramerization or by a complexation reaction. Methods using a free macrocyclic ligand were shown to be more suitable for the preparation of both corrolazine and porphyrazine. Axial modification of (HO) 2 SiPz and (HO)SiCz yielded silicon(IV) complexes bearing F, Pr 3 SiO and Ph 3 SiO ligands. Axial silylation with the bulky Ph 3 SiO group effectively suppresses aggregation in the corrolazine series, resulting in comparatively enhanced fluorescence and high singlet oxygen quantum yield (Φ Δ = 0.70). The reduction of the porphyrazine macrocycle is facilitated by the annulation of pyrazine fragments, and hindered by its contraction to form the corresponding corrolazine. For the Si IV tetra(camphanopyrazino)corrolazines, two sequential protonation stages at the meso- and pyrazine nitrogen atoms are clearly observed in contrast to the competitive character of acid-base interaction in the case of related porphyrazines. Circular dichroism spectra of the corrolazines showed a pronounced axial-ligand dependence, while porphyrazines exhibit exclusively negative Cotton effects independent of the axial ligand.