C-H bond activation at antimony(III): synthesis and reactivity of Sb(III)-oxyaryl species

We report on the synthesis, structure and reactivity of [{NCN^Me4}Sb(C₆H₂-Bu₂-3,5-O-4)] (3), an organoantimony(III)-oxyaryl species obtained upon C_sp-H bond activation in a phenolate ligand and stabilised by the monoanionic pincer {NCN^Me4}^-. The mechanism leading to the formation of 3 is highly sensitive to steric considerations. It was probed experimentally and by DFT calculations, and a number of intermediates and related complexes were identified. All data agree with successive heterolytic bond cleaving and bond forming processes involving charged species, rather than a pathway involving free radicals as previously exemplified with congeneric bismuth species. The nucleophilic behaviour of the oxyaryl ligand in 3, a complex that features both zwitterionic and quinoidal attributes, was illustrated in derivatisation reactions. In particular, insertion of CS₂ in the Sb-C_oxyaryl bond generates [{NCN^Me4}Sb(S₂C-C₆H₂-Bu₂-3,5-O-4)].