Here we describe the site-selective functionalization of sila-adamantane, the fundamental silicon diamondoid nanocluster. Sila-adamantane shares the same core structure as the unit cell of crystalline silicon, the semiconductor material at the heart of computer chips and solar cells. Its synthesis was first disclosed by Marschner and coworkers in 2005, who employed a Lewis acid catalyst to isomerize a strained tricyclic oligosilane to its lowest energy sila-diamondoid isomer. Here we provide experimental support that a silylium-like ion is generated at the 2-position at the penultimate isomerization step preceding terminal methylation. The deliberate removal of methyl donors from the reaction medium allows us to hijack the isomerization pathway and functionalize sila-adamantane with halides at the 2-position. Akin to π-directing effects in aromatic substitution reactions, these halide groups induce strong σ-directing effects for functionalization at adjacent silicon centers due to their inductively withdrawing nature. Next, we show that sila-adamantane can be functionalized at its 1-, 3-, 5-, and 7-positions by the selective cleavage of terminal trimethylsilyl groups and reaction with electrophiles. These synthetic approaches enable the regioselective functionalization of sila-adamantane at five distinct silicon centers within the sila-adamantane core. Finally, this functionalization chemistry allows us to append electrode-linking endgroups to sila-adamantane, where we are now interrogating quantum electronic transport through the unit cell of the silicon semiconductor using a scanning tunneling microscopy break-junction (STM-BJ) approach in our laboratory.

Site-selective functionalization of sila-adamantane

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.