Aluminum(III) tetraphenylporphine complexes: Synthesis and coordination properties

The stable aluminum(III) complexes (X)AITPhP (X = Cl-, OH-, HSO4-, OAc-, an d Acac(-)) were synthesized. The complexes were characterized by UV, visibl e, and IR spectroscopy, and quantitative analysis for chlorine and aluminum . The forms of existence and the rate of substitution of HSO4- for the acid o ligands in mixed proton-donating solvents containing H2SO4 were determine d at 298 K. The complexes exhibit very high stability of the donor-acceptor Al-N bonds that do not dissociate in concentrated H2SO4 at temperatures of 298-343 K. The complexes slowly oxidize to the corresponding pi-cation rad icals in mixed Solv-H2SO4 solvents upon heating above 323 K. Reaction equil ibria were studied for the complexation of aluminum(III) porphyrins with th e donating imidazole and pyridine molecules (L). The electronic absorption spectra and stabilities of the hexacoordinate mixed-ligand aluminum(III) co mplexes (L)(X)AlTPhP were found to be different. They are discussed in term s of the structural and electronic effects, as well as the trans-effect of the ligands located in the first coordination sphere.