Dismutational and Global‐Minimum Isomers of Heavier 1,4‐Dimetallatetrasilabenzenes of Group 14

Abstract

Aromatic species with heavier Group 14 elements show remarkable differences in terms of stability, structure, and reactivity. Herein we report our experimental and theoretical investigations regarding isomers of germanium- and tin-containing benzene analogues E2Si4R6 (E=Ge, Sn). The germanium-substituted dismutational isomer with a tricyclic six-membered scaffold is isolable, but unlike the homonuclear Si6 analogue slowly rearranges even at room temperature to give the propellane-type global minimum isomer. In case of E=Sn the dismutational isomer may be an intermediate on the pathway to the propellane-type species obtained, but cannot be detected even at low temperature. Unprecedentedly large chemical shift anisotropies in the (29)Si NMR spectra that increase from the Si6 species through Ge2Si4 to Sn2Si4 are rationalized by progressively larger paramagnetic-term contributions to the chemical shift tensor as a result of diminishing HOMO-LUMO gaps, which are also reflected in the absorption spectra, as well as by appearance and symmetry of these frontier orbitals.

A One‐Step Germole to Silole Transformation and a Stable Isomer of a Disilabenzene

“…Computational studies clearly indicate however that with increasing number of heavy atoms the relative stability of nonplanar structures increases . Experimentally, this was demonstrated by the landmark investigations on Si 6 R 6 isomers by the groups of Sakurai and Scheschkewitz (Figure ) . These studies revealed the clear thermodynamic preference of non‐planar three‐dimensional arrangements such as 1 – 3 over planar, cyclic delocalized structures.…”

Site-selective functionalization of Si6R6siliconoids

“…The surprisingly downeld shied signals (for tetracoordinate silicon atoms) had been rationalized by invoking magnetically induced cluster currents orin a complementary mannerby the strong LUMO contribution at this atom. 49,65,66 The 29 Si NMR chemical shis of the remaining cluster vertices are located in the typical range for saturated silicon atoms and vary only slightly with the introduced functionality. The longest wavelength absorption bands in the UV/Vis are observed at l max ¼ 459 nm (5a) and 477 nm (5b).…”

The planarity of heteroatom analogues of benzene: Energy component analysis and the planarization of hexasilabenzene

“…Because of the brilliant development of synthetic chemistry in recent years, various 6π aromatic compounds containing heavier group 13-15 elements have been synthesized. [16][17][18][19] These developments have enabled opportunities to revisit the concept of aromaticity. Obviously, planarity is supposed to be one of the crucial requirements for aromaticity.…”