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

Abstract

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 BSi 5 and PSi 5 core based on the global minimum Si 6 R 6 platform (dubbed benzpolarene for its relationship to benzene). The reductive cleavage of an SiR 2 moiety (R = 2,4,6-iPr 3 C 6 H 2 ) from Si 6 R 6 selectively yields a dianionic Si 5 R 4 2− cluster as its lithium salt. Treatment with Me 3 SiCl affords the corresponding trimethylsilyl-substituted (Me 3 Si) 2 Si 5 R 4 . Reaction of Si 5 R 4 2− with iPr 2 NECl 2 (E = B, P) yields the unprecedented p-and n-doped heterosiliconoids iPr 2 NESi 5 R 4 . Their peculiar electronic features are compared to those of the hexasilabenzpolarene starting material on grounds of NMR spectroscopy, X-ray diffraction, and DFT calculations.

A highly unsaturated six-vertex amido-substituted silicon cluster

“… 15 Furthermore, functionalization of the benzpolarene-type cluster D at different positions 6 , 18 and the introduction of boron- and phosphorous-based groups, which corresponds to n- and p-type doping of elemental silicon, was achieved. 19 …”

Chalcogen‐Expanded Unsaturated Silicon Clusters: Thia‐, Selena‐, and Tellurasiliconoids

“…The resonances at 33.5 ( 2 a ), 26.6 ( 2 b ) and 2.3 ppm ( 2 c ) are assigned to the silicon vertex of the former N‐heterocyclic silylene moiety. While siliconoids Si 7 Tip 5 Cp * and Si 8 Tip 5 Cp* [13d] still exhibit a similarly wide 29 Si NMR shift distribution as the Si 6 benzpolarenes, [13c,e] the chemical shifts of 2 a – c for Si7 may seem quite ordinary at first, but are in fact extraordinarily deshielded considering the pentacoordination of Si7. Pentacoordinate silicon atoms containing the same amidinato ligand typically give rise to signals between −124.9 and −82.9 ppm [26] .…”

Boranyl‐Functionalized [Ge9] Clusters: Providing the Idea of Intramolecular Ge/B Frustrated Lewis Pairs

“…We have shown that ligands with free electron lone pairs such as phosphanyl groups (Scheme 1, A ) allow for the attachment of Lewis acidic organometallic fragments, [5, 10, 20] and now focused on the introduction of electron acceptor functions to the sphere of the [Ge 9 ] cluster (Scheme 1, B ). Scheschkewitz and co ‐workers recently reported on the grafting of silicoinoids of general composition Si 6 R 6 with [BH 3 ] − fragments, [21] as well as p‐doping such clusters by a formal exchange of one Si vertex by a boranyl group [22] . These clusters exhibit unsubstituted vertices and thus are conceptually related to Zintl ions [21b] .…”

“…Scheschkewitz and co-workers recently reported on the grafting of silicoinoids of general composition Si 6 R 6 with [BH 3 ] À fragments, [21] as well as p-doping such clusters by a formal exchange of one Si vertex by a boranyl group. [22] These clusters exhibit unsubstituted vertices and thus are conceptually related to Zintl ions. [21b] For several reasons we particularly suspected halo-boranes, 1,3,2-diazaborolidines (DABs), as promising candidates for this venture.…”