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

Starting from the perhydrogenated silafullerane [ n Bu 4 N][Cl@Si 20 (SiH 3 ) 12 H 8 ], treatment with BBr 3 leads to partially and exhaustively brominated clusters, [ n Bu 4 N][Cl@Si 20 (SiBr 2 H) 12 Br 8 ] (120 eq. BBr 3 , room temperature, 30 min) and [ n Bu 4 N][Cl@Si 20 (SiBr 3 ) 12 Br 8 ] (300 eq. BBr 3 , 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 Si 32 framework when mild conditions are maintained. Partial Br/H exchange on [ n Bu 4 N][Cl@Si 20 (SiBr 2 H) 12 Br 8 ] (30 eq. iBu 2 AlH, room temperature, 16 h) affords [ n Bu 4 N][Cl@Si 20 (SiH 3 ) 12 Br 8 ].