Regioselective Derivatization of Silylated [20]Silafulleranes

Autor: Marcel Bamberg, Thomas Gasevic, Michael Bolte, Alexander Virovets, Hans-Wolfram Lerner, Stefan Grimme, Markus Bursch, Matthias Wagner
Rok vydání: 2023
Předmět:
Zdroj: Journal of the American Chemical Society 145(20), 11440-11448 (2023). doi:10.1021/jacs.3c03270
ISSN: 1520-5126
0002-7863
Popis: Journal of the American Chemical Society 145(20), 11440 - 11448 (2023). doi:10.1021/jacs.3c03270
Silafulleranes with endohedral Cl$^−$ ions are a unique,scarcely explored class of structurally well-defined silicon clustersand host-guest complexes. Herein, we report regioselectivederivatization reactions on the siladodecahedrane [nBu$_4$N][Cl@Si$_{20}$(SiCl$_3$)$_{12}$Cl$_8$] ([nBu$_4$N][1]), which has its cluster surfacedecorated with 12 SiCl$_3$ and 8 Cl substituents in perfect T$_h$ symmetry. The room-temperature reaction of [nBu$_4$N][1] withexcess iBu$_2$AlH in ortho-difluorobenzene (oDFB) furnishesperhydrogenated [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 structurallyauthenticated (by X-ray diffraction) hydridosilane known to date. Asimple switch from pure oDFB to an oDFB/Et$_2$O solvent mixturesuppresses 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 theregioselective 36-fold silyl group hydrogenation, we achieved the simultaneous introduction of Me substituents at all 8 SiCl verticesalong 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 SN$_2$-Si-type hydrogenation of theexohedral SiCl$_3$ moieties in [1]$^−$ (trigonal-bipyramidal intermediate) slightly preferred over metathesis-like SNi-Si substitutions (four-membered transition state). Cage hydrogenation likely occurs via SNi-Si processes. The experimentally demonstrated influenceof an Et$_2$O co-solvent, which drastically increases the respective reaction barriers, is attributed to the increased stability of theresulting iBu$_2$AlH-OEt$_2$ adduct and its higher steric bulk compared to free iBu$_2$AlH.
Published by ACS Publications, Washington, DC
Databáze: OpenAIRE
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