Synthesis of Electron‐Rich, Planarized Silicon(IV) Species and a Theoretical Analysis of Dimerizing Aminosilanes

Abstract

Equipping silicon(IV) with electron-rich, geometrically constrained NNN- and ONO-tridentate substituents leads to aminosilanes with increased Lewis acidity-expressed through the formation of Si N rings by head-to-tail dimerization. Depending on the substituents, the dimerization can be controlled for the first time, yielding monomeric, structurally reversible and dimeric states. The monomeric species display substantial distortions from tetrahedral towards planar geometry at silicon. The dimerization and the Lewis acidity of aminosilanes are rationalized by (conceptual) DFT, NBO, ETS-NOCV and QTAIM methods. The preorganization at silicon, London dispersion between the substituents and resonance phenomena inside the formed Si N tetracycles are identified as driving forces for the dimerization. Comparison with selected aminosilanes permits general conclusions to be reached on the Lewis acidity of silicon species and on the aggregation of amphiphilic compounds.

Hydrostibination

“…s*(Sb À H) hyperconjugation allowed by the large H-Sb-N-Si dihedral angle (143.28 8,F igure 2a), which is known as the b-silicon effect. [15] Thepivotal role of geometric deformation is emphasized by the low electrophilicity of the LUMO (À0.742 eV) in ((TMS)PhN) 2 SbH, which has two free amino groups instead of af used naphthyl substituent and by the calculated HOMO (N lone pairs) of 3a ( Figure 2b). Thus, when an aphthyl-silyl amino substituent is used, 1) the putative hydride is sterically shielded, 2) its LUMO is prominently centered at the metal (Figure 2b)a nd orthogonal to the SbÀHb ond, and 3) the LUMO energy is significantly lower (À1.25 eV) than in Ph 2 SbH.…”

Lewis Superacids: Classifications, Candidates, and Applications

“…The proof-of-principle has been given by pyramidalization of Group 13, [205] or deformation of Group 14 compounds. [206] However,t he distinguished formation of a Lewis superacid upon geometricald eformation has so far only been realized in silico. [138,207] 7.7.…”

Pincer‐Type Ligand‐Assisted Catalysis and Small‐Molecule Activation by non‐VSEPR Main‐Group Compounds

“…The monomeric compounds show significant Lewis acidity at the silicon center due to the substantial distortions from tetrahedral towards planar geometries. The same research group also reported the similar Si(IV) compounds bearing the amido‐diphenolato (ONO) 3− ligands, which were found to only exist as dimers ( 27 a – b ) in solution as well as in the solid‐state (Scheme ) …”

“…The same research group also reported the similar Si(IV) compounds bearing the amido-diphenolato (ONO) 3À ligands, which were found to only exist as dimers (27 a-b) in solution as well as in the solid-state (Scheme 33). [46] The reaction between the lithium salt of bis [2-(di- 29, respectively (Scheme 34). [47] In these reactions, the tin center's oxidation state was unchanged in the final product, unlike the reaction between L 1 and SnCl 4 as described in Scheme 31.…”

“…The dimerization process could not be avoided by employing bulky substituents at silicon atom (Scheme ) . Recently, Greb and co‐workers reported a series of Si(IV) complexes with triamido (NNN) 3− ligands ( L 2 ), which can be isolated in both monomeric and structurally reversible or dimeric form ( 25 – 26 ) (Scheme ) . The monomeric compounds show significant Lewis acidity at the silicon center due to the substantial distortions from tetrahedral towards planar geometries.…”