Axial reactivity of soluble silicon(IV) phthalocyanines

The axial reactivity of peripherally octasubstituted soluble silicon(IV) phthalocyanines (SiPcZ(8), Z = OC(5)H(11) or Z = C(5)H(11)) was studied in order to explore new synthetic routes for preparing axially functionalized SiPc monomers and dimers. Self-exchange of the axial methoxide in methylmethoxy SiPcZ(8) was about 10 times faster for Z = OC(5)H(11) than for Z = C(5)H(11). The Pc rings of these two complexes do not differ in electron-richness; their first oxidation potentials ( -0.880 and -0.875 V, respectively) are the same within experimental error. The axial alkoxide ligand in methylisopropoxy SiPcZ(8) monomer (1c, 2c) could be quantitatively replaced by mercaptoethanol to yield O-bound methylmercaptoethoxy SiPcZ(8) (1h, 2h). Condensation of methylhydroxy SiPcZ(8) monomers yielded mu -oxo-bridged bismethyl SiPcZ(8) dimers (1k, 2k) without formation of oligomeric byproducts. Photolysis of such methyl-capped dimers in the presence of mercaptoethanol yielded mu -oxo-bridged bismercaptoethoxy SiPcZ(8) dimers (1n, 2n) which are of interest as precursors for oriented self-assembled monolayers (SAMs) of oligomeric phthalocyanines.