Regioselective Derivatization of Silylated [20]Silafulleranes.

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 [BuN][Cl@Si(SiCl)Cl] ([BuN][]), which has its cluster surface decorated with 12 SiCl and 8 Cl substituents in perfect symmetry. The room-temperature reaction of [BuN][] with excess BuAlH in -difluorobenzene (DFB) furnishes perhydrogenated [BuN][Cl@Si(SiH)H] ([BuN][]) in 50% yield; the non-pyrophoric [] is the largest structurally authenticated (by X-ray diffraction) hydridosilane known to date. A simple switch from pure DFB to an DFB/EtO solvent mixture suppresses core hydrogenation and results in the formation of [BuN][Cl@Si(SiH)Cl] ([BuN][]). In addition to the exhaustive Cl/H exchange at all 44 Si-Cl bonds of [] 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 to SiH groups by treating [BuN][] with MeAlH/MeAl in DFB ([BuN][Cl@Si(SiH)Me], [BuN][]; 73%). Quantum-chemical free-energy calculations find an S2-Si-type hydrogenation of the exohedral SiCl moieties in [] (trigonal-bipyramidal intermediate) slightly preferred over metathesis-like Si-Si substitutions (four-membered transition state). Cage hydrogenation likely occurs via Si-Si processes. The experimentally demonstrated influence of an EtO co-solvent, which drastically increases the respective reaction barriers, is attributed to the increased stability of the resulting BuAlH-OEt adduct and its higher steric bulk compared to free BuAlH.