Fullerenes and diamondoids are at the core of nanoscience. Comparable monodisperse silicon analogues are scarce. Herein, we report the synthesis of the parent siladodecahedrane, which represents the largest Platonic solid. It shares its pattern of pentagonal faces with the smallest fullerene, C 20 , and its saturated, H-terminated skeleton with diamondoids. Similar to endofullerenes, the silicon cage encapsulates a chloride ion ([Cl@Si 20 H 20 ] − ); similar to diamondoids, its Si−H termini offer a wealth of opportunities for further functionalization. Mere treatment with chloromethanes leads to the perchlorinated cluster [Cl@ Si 20 Cl 20 ] − . Both compounds were characterized by mass spectrometry, X-ray crystallography, NMR spectroscopy, and quantumchemical calculations. The experimentally determined 35 Cl resonances of the endohedral chloride ions are particularly diagnostic to probe the Cl − → Si 20 interaction strength as a function of the different surface substituents, as we have proven by high-level computational analyses.

Depending on the solvent, a brominated arylborane gave the multiple helicene B2-TBPA (pyridine) or the oxadiborepin ODBE (THF) after intramolecular Yamamoto coupling.

Silafulleranes with endohedral Cl − ions are a unique, scarcely explored class of structurally well-defined silicon clusters and host-guest complexes. Herein, we report regioselective derivatization reactions on the siladodecahedrane [nBu 4 N][Cl@ Si 20 (SiCl 3 ) 12 Cl 8 ] ([nBu 4 N][1]), which has its cluster surface decorated with 12 SiCl 3 and 8 Cl substituents in perfect T h symmetry. The room-temperature reaction of [nBu 4 N][1] with excess iBu 2 AlH in ortho-difluorobenzene (oDFB) furnishes perhydrogenated [nBu 4 N][Cl@Si 20 (SiH 3 ) 12 H 8 ] ([nBu 4 N][2]) in 50% yield; the non-pyrophoric [2] − is the largest structurally authenticated (by X-ray diffraction) hydridosilane known to date. A simple switch from pure oDFB to an oDFB/Et 2 O solvent mixture suppresses core hydrogenation and results in the formation of [nBu 4 N][Cl@Si 20 (SiH 3 ) 12 Cl 8 ] ([nBu 4 N][3]). In addition to the exhaustive Cl/H exchange at all 44 Si−Cl bonds of [1] − and the regioselective 36-fold silyl group hydrogenation, we achieved the simultaneous introduction of Me substituents at all 8 SiCl vertices along with the conversion of all 12 SiCl 3 to SiH 3 groups by treating [nBu 4 N][1] with Me 2 AlH/Me 3 Al in oDFB ([nBu 4 N][Cl@ Si 20 (SiH 3 ) 12 Me 8 ], [nBu 4 N][4]; 73%). Quantum-chemical free-energy calculations find an S N 2-Si-type hydrogenation of the exohedral SiCl 3 moieties in [1] − (trigonal-bipyramidal intermediate) slightly preferred over metathesis-like S N i-Si substitutions (four-membered transition state). Cage hydrogenation likely occurs via S N i-Si processes. The experimentally demonstrated influence of an Et 2 O co-solvent, which drastically increases the respective reaction barriers, is attributed to the increased stability of the resulting iBu 2 AlH-OEt 2 adduct and its higher steric bulk compared to free iBu 2 AlH.

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) and [nBu4N][Cl@Si20(SiBr3)12Br8] (300 eq. BBr3, 130 °C). Perbromination...