Brominated [20]silafulleranes: pushing the limits of steric loading

Abstract

Starting from the perhydrogenated silafullerane [nBu₄N][Cl@Si₂₀(SiH₃)₁₂H₈], treatment with BBr₃ leads to partially and exhaustively brominated clusters, [nBu₄N][Cl@Si₂₀(SiBr₂H)₁₂Br₈] (120 eq. BBr₃, room temperature, 30 min) and [nBu₄N][Cl@Si₂₀(SiBr₃)₁₂Br₈] (300 eq. BBr₃, 130 °C, 3 d). Perbromination is accompanied by a massively increased steric strain on the cluster surface, which explains why our approach achieves regioselective derivatization of the Si₃₂ framework when mild conditions are maintained. Partial Br/H exchange on [nBu₄N][Cl@Si₂₀(SiBr₂H)₁₂Br₈] (30 eq. iBu₂AlH, room temperature, 16 h) affords [nBu₄N][Cl@Si₂₀(SiH₃)₁₂Br₈].