Reactions of incompletely-condensed silsesquioxanes with pentamethylantimony: A new synthesis of metallasilsesquioxanes with important implications for the chemistry of silica surfaces

Article abstract of DOI:10.1021/ja00036a038

The reactions of the incompletely condensed polyhedral oligosilsesquioxanes (c-C₆H₁₁)₇Si₇O₉(OH) ₃ (1a), (c-C₆H₁₁)₇Si₇O ₉(OTMS)(OH)₂ (2a), (c-C₆H₁₁)₇Si₇O ₉(OTMS)₂(OH) (3a), (c-C₆H₁₁)₈Si₈O₁₀(OH) ₂ (4a), and (c-C₆H₁₁)₇Si₇O₁₀(OH) (5a) with excess Me₅Sb result in the formation of the corresponding stibonium-substituted silsesquioxanes (c-C₆H₁₁)₇Si₇O ₉(OSbMe₄)₃ (1b), (c-C₆H₁₁)₇Si₇O ₉(OTMS)(OSbMe₄)₂, (2b), (c-C₆H₁₁)₇Si₇O ₉(OTMS)₂(OSbMe₄) (3b), (c-C₆H₁₁)₈Si₈O ₁₀(OSbMe₄)₂ (4b), and (c-C₆H₁₁)₇Si₇O ₁₀(OSbMe₄) (5b) in high yields. These stibonium siloxides show enhanced reactivity toward main-group and transition-metal halide complexes and provide an alternative route for the preparation of metallasilsesquioxanes. The reaction of 1a with 1 equiv of Me₅Sb is much faster than the reactions of Me₅Sb with silanols containing fewer than three mutually hydrogen-bonded siloxy groups. This suggests that multiply hydrogen-bonded surface sites are more reactive toward nucleophilic organometallic reagents than either isolated surface silanols or isolated pairs of geminally or vicinally hydrogen-bonded siloxy groups.