Unexpected photo-initiated oxidation of antimony in (tetra- tert-butyl)phthalocyaninatoantimony(III) complex in the presence of singlet oxygen acceptors

Abstract

The title complex cation, [Sb(tbpc)] + (where tbpc denotes tetra( tert-butyl)phthalocyaninate, C 48H 48N 8 2−), was gradually bleached under irradiation with visible light (900 > λ/nm > 600) in aerated nonaqueous solvents, such as CH 2Cl 2, CHCl 3, benzene, chlorobenzene. On the other hand, irradiation under the same conditions but in the presence of 1,3-diphenylisobenzofuran (DPBF) caused slow oxidation of [Sb(tbpc)] + to the corresponding antimony(V) derivatives, [Sb(tbpc)LL′] +, (L and L′ denote monoanionic axial ligands containing oxygen as the donor atom), which was monitored by optical absorption and ESI-MS spectra of the photolyzed solutions. Both the photobleaching and oxidation have efficiently been inhibited by preliminary addition of β-carotene in photolyzed solutions, indicating that photosensitization of singlet oxygen ( 1O 2) by [Sb(tbpc)] + itself is involved. The use of furans (except dibenzofuran) or oxazoles instead of DPBF gave rise to similar oxidation but not in the case of the other type 1O 2-acceptors, such as 9,10-diphenylanthracene, tetraphenylcyclopentadienone, or 2,3-dimethyl-2-butene, indicating that formation of ozonide-type endo-peroxide through 1,4-cycloaddition with 1O 2 is essential. Peroxides, such as EtOOH and H 2O 2, generated through nucleophilic attack to the ozonide by EtOH and H 2O (present in the solvent) respectively, are considered to oxidize [Sb(tbpc)] + to the antimony(V) species. Photochemistry of antimony–phthalocyanine complex has been studied for the first time of pnicogen derivatives of phthalocyanine.