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

The title complex cation, [Sb(tbpc)](+) (where tbpc denotes tetra(tert-butyl)phthalocyaninate, C48H48N82-), was gradually bleached under irradiation with visible light (900 >; lambda/nm > 600) in aerated nonaqueous solvents, such as CH2Cl2, CHCl3, 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 beta-carotene in photolyzed solutions, indicating that photosensitization of singlet oxygen (O-1(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 O-1(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 O-1(2) is essential. Peroxides, such as EtOOH and H2O2, generated through nucleophilic attack to the ozonide by EtOH and H2O (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. (c) 2008 Elsevier B.V. All rights reserved.