A preparatively facile, highly selective synthesis of bifunctional monosilanes R SiHCl, RSiHCl and RSiH Cl is reported. By chlorination of R SiH and RSiH with concentrated HCl/ether solutions, the stepwise introduction of Si-Cl bonds is readily controlled by temperature and reaction time for a broad range of substrates. In a combined experimental and computational study, we establish a new mode of Si-H bond activation assisted by Lewis bases such as ethers, amines, phosphines, and chloride ions. Elucidation of the underlying reaction mechanisms shows that alcohol assistance through hydrogen-bond networks is equally efficient and selective. Remarkably, formation of alkoxysilanes or siloxanes is not observed under moderate reaction conditions.

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.

The industry-scalep roduction of methylchloromonosilanes in the Müller-Rochow Direct Process is accompanied by the formation of ar esidue,t he direct process residue (DPR), comprised of disilanes Me n Si 2 Cl 6-n (n = 1-6). Great research efforts have been devoted to the recycling of these disilanes into monosilanes to allow reintroduction into the siloxane production chain. In this work, disilanec leavage by using alkali and alkaline earth metal salts is reported. The reaction with metal hydrides, in particular lithium hydride (LiH), leads to efficient reduction of chlorine containing disilanes but also induces disproportionation into mono-a nd oligosilanes. Alkali and alkaline earth chlorides, formed in the courseo ft he reduction, specifically induce disproportionation of highly chlorinatedd isilanes, whereas highly methylated disilanes (n > 3) remain unreacted. Nearly quantitative DPR conversion into monosilanes was achieved by using concentrated HCl/ether solutions in the presence of lithium chloride.[a] T.

The Müller–Rochow direct process (DP) for the large‐scale production of methylchlorosilanes MenSiCl4−n (n=1–3) generates a disilane residue (MenSi2Cl6−n, n=1–6, DPR) in thousands of tons annually. This report is on methylchlorodisilane cleavage reactions with use of phosphonium chlorides as the cleavage catalysts and reaction partners to preferably obtain bifunctional monosilanes MexSiHyClz (x=2, y=z=1; x,y=1, z=2; x=z=1, y=2). Product formation is controlled by the reaction temperature, the amount of phosphonium chloride employed, the choice of substituents at the phosphorus atom, and optionally by the presence of hydrogen chloride, dissolved in ethers, in the reaction mixture. Replacement of chloro by hydrido substituents at the disilane backbone strongly increases the overall efficiency of disilane cleavage, which allows nearly quantitative silane monomer formation under comparably moderate conditions. This efficient workup of the DPR thus not only increases the economic value of the DP, but also minimizes environmental pollution.

A convenient single-step process is reported that provides efficient access to the most valuable bifunctional hydridochlorosilane Me 2 SiHCl from the crude Muller−Rochow product mixture. Conceptually, the unavailability of routes to the selective partial reduction of chlorosilanes has been circumvented by using in situ H/Cl exchange, employing substoichiometric amounts of LiH to produce fully reduced hydridosilanes that undergo immediate redistribution with the remaining chlorosilanes in a single step. The reaction is autocatalyzed by LiCl, but reaction temperatures are efficiently reduced in the presence of redistribution catalysts such as simple onium chlorides. Onium chlorides also act as efficient cleavage catalysts for disilanes and carbodisilanes present in the Muller−Rochow product mixture, conversion of which increases the hydridochlorosilane yield up to 58%. Making use of additional post-processing steps for the remaining byproducts, bifunctional monosilane yields exceeding 90% are possible.