Boron and Phosphorus Containing Heterosiliconoids: Stable p- and n‑Doped Unsaturated Silicon Clusters

Unsaturated silicon clusters (siliconoids) are short-lived
intermediates
during the transition from molecules to the elemental bulk; stable
representatives reiterate surface features of silicon materials. The
incorporation of suitable heteroatoms into the cluster scaffold of
stable siliconoids extends this analogy to the technological process
of silicon doping. Here, we report boron- and phosphorus-containing
heterosiliconoids with BSi5 and PSi5 core based
on the global minimum Si6R6 platform (dubbed
benzpolarene for its relationship to benzene). The reductive cleavage
of an SiR2 moiety (R = 2,4,6-iPr3C6H2) from Si6R6 selectively yields
a dianionic Si5R42– cluster
as its lithium salt. Treatment with Me3SiCl affords the
corresponding trimethylsilyl-substituted (Me3Si)2Si5R4. Reaction of Si5R42– with iPr2NECl2 (E = B,
P) yields the unprecedented p- and n-doped heterosiliconoids iPr2NESi5R4. Their peculiar electronic features
are compared to those of the hexasilabenzpolarene starting material
on grounds of NMR spectroscopy, X-ray diffraction, and DFT calculations.