Regioselective Derivatization of Silylated [20]Silafulleranes

Silafulleranes with endohedral Cl- ionsare aunique, scarcely explored class of structurally well-defined siliconclusters and host-guest complexes. Herein, we report regioselectivederivatization reactions on the siladodecahedrane [nBu(4)N]-[Cl@Si-20(SiCl3)(12)Cl-8] ([nBu(4)N]-[1]), which has its cluster surface decorated with 12 SiCl3 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(SiH3)(12)H-8] ([nBu(4)N]-[2]) in 50% yield;the non-pyrophoric [2](-) is the largeststructurally authenticated (by X-ray diffraction) hydridosilane knownto date. A simple switch from pure oDFB to an oDFB/Et2O solvent mixture suppresses core hydrogenationand results in the formation of [nBu(4)N]-[Cl@Si-20(SiH3)(12)Cl-8] ([nBu(4)N]-[3]). In addition to the exhaustiveCl/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 all8 SiCl vertices along with the conversion of all 12 SiCl3 to SiH3 groups by treating [nBu(4)N]-[1] with Me2AlH/Me(3)Alin oDFB ([nBu(4)N]-[Cl@Si-20(SiH3)(12)Me-8], [nBu(4)N]-[4]; 73%). Quantum-chemical free-energycalculations find an S(N)2-Si-type hydrogenation of the exohedralSiCl(3) moieties in [1](-) (trigonal-bipyramidalintermediate) slightly preferred over metathesis-like S(N)i-Si substitutions (four-membered transition state). Cage hydrogenationlikely occurs via S(N)i-Si processes. The experimentallydemonstrated influence of an Et2O co-solvent, which drasticallyincreases the respective reaction barriers, is attributed to the increasedstability of the resulting iBu(2)AlH-OEt2 adduct and its higher steric bulk compared to free iBu(2)AlH.

Automated summary

Silafulleranes with endohedral Cl- ions are a unique class of silicon clusters and host-guest complexes. In this study, regioselective derivatization reactions were performed on a specific siladodecahedrane, resulting in the formation of perhydrogenated and non-pyrophoric hydridosilanes. The influence of solvent on the reaction outcomes was also investigated.