Thermal Synthesis of Perchlorinated Oligosilanes: A Fresh Look at an Old Reaction

Abstract

DedicatedtoProf. Nino Russo on theoccasiono fhis 70th birthday.Abstract: Ac ombined experimentala nd theoretical study of the high-temperature reactiono fS iCl 4 and elemental silicon is presented. The nature and reactivity of the product formed upon rapid coolingo ft he gaseous reactionm ixture is investigated by comparison with the defined model compounds cyclo-Si 5 Cl 10 , n-Si 5 Cl 12 and n-Si 4 Cl 10 .ADFT assessment provides mechanistic insight into the oligosilane formation. Experimental 29Si NMR investigations, supported by quantum-chemical 29 Si NMR calculations, consistently show that the reactionp roduct is composed of discrete molecular perchlorinated oligosilanes. Low-temperature chlorination is an unexpectedly selective means for the transformation of cyclosilanes to acyclic speciesb ye ndocyclic SiÀSi bond cleavage, and we provide am echanistic rationalization for this observation. In contrast to the raw material, the product obtained after low-temperature chlorination represents an efficient source of neo-Si 5 Cl 12 or the amine-stabilizedd isilene EtMe 2 N·SiCl 2 Si(SiCl 3 ) 2 through reactionwith aliphatic amines.

Making Use of the Direct Process Residue: Synthesis of Bifunctional Monosilanes

“…Along the reaction path the calculations indicate the intermediate formation of an unstable contact ion‐pair comprising a proton‐bridged cationic silicon species [Me 2 HSi−H−SiMe 3 ]Cl, which bifurcates into the two possible product channels (for details, see the Supporting Information). Overall, the reaction path shown in Scheme closely resembles the corresponding Cl 2 ‐induced Si−Si bond cleavage reported earlier . The competing chlorination of 3 proceeds through concerted H 2 elimination and HCl addition across the Si−H bond ( TS2 ).…”

“…Overall, the reactionp ath shown in Scheme2 closely resembles the corresponding Cl 2 -induced SiÀSi bond cleavage reported earlier. [13] Cleavage/chlorination ratio [b] (Me 2 HSi) 2 (1)5.5 40 6M e 2 SiHCl (37) The competing chlorination of 3 proceeds through concerted H 2 elimination and HCl addition across the SiÀHb ond (TS2). As detailede arlier for the corresponding reaction of monosilanes [10] the activationbarrieriss ubstantially lowered by coordination of an ether molecule,w hichc ompensates the developing positive chargea tt he silicon center.…”

Why Do Five Ga+ Cations Form a Ligand‐Stabilized [Ga5]5+ Pentagon and How Does a 5:1 Salt Pack in the Solid State?

“…The cation structure is undistorted and shows only very few weak contacts to the anions as shown by the Hirshfeld plot in Figure S10. The pentacation structure of 1 is related to the known (SiX 2 ) 5 pentamers (X=Cl, Br, I), which, in contrast, hold a folded Si 5 ring . However, it was shown that this ring may easily flatten .…”

“…Thep entacation structure of 1 is related to the known (SiX 2 ) 5 pentamers (X = Cl, Br, I), which, in contrast, hold afolded Si 5 ring. [21] However, it was shown that this ring may easily flatten. [22] Related phenomena were observed for the puckered (SiCl 2 ) 6 hexamer and its planar [Si 6 Cl 14 ] 2À chloride adduct.…”

Identifying the mechanism of formation of chlorinated silane polymer by‐products during chemical vapor infiltration of SiC from CH3SiCl3/H2

“…With respect to elementary reactions involving SiCl 2 , there have been many reports regarding molecules containing one or two SiCl 2 units, [11][12][13][14][15][16][17] but only two reports of molecules with more than two SiCl 2 units. 18,19 Mosecatteli et al evaluated the reaction rate constants of SiCl 2 forming cyclic-(SiCl 2 ) 4 via quantum chemical calculation using the B3LYP method with several basis functions: the amount of chlorinated silane polymers was negligibly small at 800 • C. 18 Neumeyer et al 19 studied the reaction mechanism for the formation of chlorinated silane polymers with up to eight SiCl 2 units using quantum chemical calculations with the RI-M06-L/6-311++G(2d,2p)//RI-M06-L/6-31+G(dp) method. The calculations for all SiCl 2 oligomer structures and their transition states revealed that the cyclic chlorinated silane polymer was produced by the oligomerization of SiCl 2 .…”