Electronic spectra and photochemical reactivity of bismuth corrole complexes

Abstract

The first examples of bismuth complexes with meso-substituted corrole ligands are presented. Complexation of 5,10,15-triphenylcorrole with bismuth(III) salts leads to the formation of a neutral low-valent species Bi-tpc, which is characterized by various spectroscopic techniques. In addition to the intense intraligand (IL) absorption bands of the corrole macrocycle, this bismuth(III) complex displays metal-centered (MC) sp-transitions and metal-to-ligand charge transfer (MLCT) transitions which show a substantial mixing with the intraligand absorption bands, thus resulting in an irregular hyper-type electronic spectrum. Excitation of Bi-tpc in the spectral region of the MC-bands under ambient conditions leads to dioxygen activation and concomitant photochemical formation of the high-valent species (O )Bi V(tpc), an unprecedented example of a bismuth(V) tetrapyrrole complex. As a potential reaction intermediate of this photoredox process, a labile hydroperoxo species (HOO)Bi V(tpc) + is also identified. First results on the spectroscopic features and the chemical reactivity of (O )Bi V(tpc) are reported. In solution this neutral bismuth(V) species is in equilibrium with the corresponding protonated form (HO)Bi V(tpc) + carrying an axial hydroxo ligand. Axial ligand exchange processes and the formation of adducts with solvent derived photoproducts are also identified in high-resolution mass spectra of irradiated samples. The molecular and electronic structures of the novel bismuth corrole systems are discussed in terms of supporting density functional theory (DFT) calculations, which suggest an out-of-plane structure of the Bi-tpc and (O )Bi V(tpc) species. Time-dependent DFT results are supporting the proposed assignment of electronic transitions observed in low- and high-valent bismuth tpc derivatives.