Abstract
On reaction of BiBr~3~ with Li(thf)~3~SiPh~2~__t__Bu (1) in the corresponding ratios redox/metathesis reactions were observed, yielding dibismuthane (__t__BuPh~2~Si)~4~Bi~2~ (2) and disilylbismuth halide (__t__BuPh~2~Si)~2~BiBr (3). The latter is a reaction intermediate in the formation of the dark‐red 2. The X‐ray crystal structures of 1–3 were determined by low‐temperature X‐ray diffraction. The Si~2~Bi–BiSi~2~ core of 2 is in the semi‐eclipsed conformation. No oligomerization of “nonthermochromic” 2 was observed. Compound 3 is a mixed substituted monomer with a pyramidal environment around the bismuth center. On the basis of quantum chemical calculations, the formation of tertiary bismuthane (__t__BuPh~2~Si)~3~Bi is not expected for steric reasons. According to DFT‐optimized geometries of the simplified model systems n[(H~3~Si)~2~Bi]~2~ (n = 1–3), the closed‐shell attraction between intermolecular Bi centers in the chain provides a moderate elongation of the intramolecular Bi–Bi bond in the dibismuthane unit and a shortening of the intermolecular Bi···Bi contacts. According to MP4(SDQ) computations, such oligomerization is carried out by intermolecular interaction of s lone pairs that are bound together and p‐type orbitals of the Bi–Bi bonds in the bismuth chain. An increase in the number of [(H~3~Si)~2~Bi]~2~ molecules per chain results in a decrease in the HOMO–LUMO gap and leads to a bathochromic shift. TD‐PBE0 computations suggest that the lowest energy electron transition in 2 is metal–metal charge transfer. In addition, the attractive contributions in the chain [(H~3~A)~2~Bi]~2~···[Bi(AH~3~)~2~]~2~ with silyl groups (A = Si) outweigh the repulsion of the Bi···Bi centers, whereas for the alkyl‐substituted bismuth chain (A = C) the repulsive van der Waals force dominates. This fact makes the rectangle oligomerization model more preferred for n[(H~3~A)~2~Bi]~2~ (A = C; n = 2), while for A = Si chain formation is favored in the gas phase.