Chloride‐Induced Aufbau of Perchlorinated Cyclohexasilanes from Si₂Cl₆: A Mechanistic Scenario

Abstract

A surprisingly simple preparative procedure, addition of Si2Cl6 to a solution of [nBu4N]Cl in CH2Cl2, leads to the formation of the chloride-complexed cyclic dianions [Si6Cl12⋅2Cl](2-), [(SiCl3)Si6Cl11⋅2Cl](2-), or [1,y-(SiCl3)2Si6Cl10⋅2Cl](2-) (y = 1, 3, 4), depending on the stoichiometric ratio of the reactants and the reaction temperature (25-85 °C). Below -40 °C the open-chain oligosilane chloride adducts [Si3Cl9](-), [Si3Cl10](2-), [Si4Cl11](-), and [Si6Cl15](-) are formed, again depending on the reaction conditions chosen. All species were characterized by X-ray crystallography. The underlying reaction mechanism is elucidated by DFT calculations. It incorporates all experimental findings and involves a few key elementary steps: 1) chloride-induced liberation of SiCl3(-) or higher silanides, 2) their addition to neutral silanes yielding larger oligosilane chloride adducts, 3) dimerization of larger silanides to (substituted) cyclohexasilane dichloride adducts with inverse sandwich structure.

Synthesis of a Dichlorodigermasilane: Double Si–Cl Activation by a Ge=Ge Unit

“…While the two Ge-Cl bond lengths are almost the same (Ge1-Cl1: 2.2094(14) Å, Ge2-Cl4: 2.2011(15) Å) within a range of standard deviations, the orientation of the two Cl atoms are slightly different to each other. That is, one of the Cl atom (Cl4) is oriented to outside of the five-membered ring skeleton, but another one (Cl1) is approaching to the central Si atom with the Cl1···Si distance of 3.25 Å, which is far from the other one (Cl4···Si = 3.66 Å) [27]. In addition, the two Cl-Ge-Si angles are considerably different from each other, (Cl1-Ge1-Si = 90.20 (8), Cl4-Ge2-Si = 105.40 (8)).…”

Ionic SNi‐Si Nucleophilic Substitution in N‐Methylaniline‐Induced Si−Si Bond Cleavages of Si2Cl6

“…Several years later,i tw as reported that 1 should disproportionate into SiCl 4 and Si 5 Cl 12 under the catalytici nfluence of trimethylamine. [2] For the next 40 years,the mechanism remained ambiguous because no concrete evidencea boutt he intermediates was obtained.…”

“…[2] For the next 40 years,the mechanism remained ambiguous because no concrete evidencea boutt he intermediates was obtained. Recently,s ingle crystals of Si 5 Cl 12 and amine-complexed dichlorosilylene (SiCl 2 ·NR 3 )w ere obtained as key intermediates through low-temperaturet wo-dimensional HETCOR NMR spectroscopy measurements and calculations. [3] In 2012, the reactiono fa nother tertiarya mine, tetramethylethylenediamine (TMEDA), with 1 was reported.…”

“…[3] In 2012, the reactiono fa nother tertiarya mine, tetramethylethylenediamine (TMEDA), with 1 was reported. [4] Neopentasilane Si 5 Cl 12 was synthesized by heating 1 in the presence of 10 mol % 1·TMEDA. Accordingt ot he results, the reactionp roceedsv ia ad ichlorosilylene intermediate.…”

S–H Bond Activation in Hydrogen Sulfide by NHC-Stabilized Silyliumylidene Ions

“…Key to these developments have been the usage of suitable synthetic methodologies in combination with thermodynamic and kinetic stabilization by appropriately chosen ligands. In particular, for the heavier carbon analogue silicon, a plethora of studies reported new low-valent compounds in recent years [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25] and the chemistry of silylene base adducts has already been carefully developed [14,[26][27][28][29][30][31][32][33][34][35][36]. Before these findings, silyliumylidene ions, cationic Si(II) species were found to be promising as similar versatile Lewis amphiphiles [37,38].…”