Anionic intermediates in the reductive coupling of 1-chloro-2-phenyltetramethyldisilane with lithium and subsequent redistribution processes

Abstract

Oligosilyl anions have been found to participate in the reaction of 1-chloro-2-phenyltetramethyldisilane with excess lithium in THF at room temperature. The overall reaction was monitored by lH NMR, HPLC, and UV spectroscopy. The reaction proceeds in four steps. In the first slow stage, the disilyl chloride reacts with lithium to form a disilyllithium anion, which immediately reacts with the remaining disilyl chloride to yield 1,4-diphenyloctamethyltetrasilane. In a second faster stage, the tetrasilane accepts an electron from lithium to form a radical anion and subsequently mono-, di-, and trisilyl anions, which react with the disilyl chloride to form a,w-diphenyltrisilanes, -tetrasilanes, and -pentasilanes. The third stage begins when all of the silyl chloride has been consumed and the cleavage of Si-Si bonds in a,w-diphenyloligosilanes by silyl anions produces dodecamethylcyclohexasilane. A thermodynamic product distribution is formed in this scrambling process. During the final stage more electrons are being added to the system from lithium and an equilibrium mixture of (2-phenyltetramethyldisilyl)lithium, (phenyldimethylsilyl)lithium, and dodecamethylcyclohexasilane is established. The silyl anions formed in the process are characterized by various methods (lH NMR, 13C

Regioselective Synthesis of Polyfunctionalized Alkyltrisilanes and -tetrasilanes via Reductive Cross-Coupling Reaction of Aminoalkylsilyl Chlorides with Lithium

“…Of course, the idea has long been used for the synthesis of permethylated linear oligosilanes and branched oligosilanes . In the present cases, the electronic and steric effects of the amino group(s) should be considered additionally.…”

Selective Synthesis of Functional Alkynylmono‐ and ‐trisilanes

“…Thus, the product of the reaction of dimethyl(phenyl)silyllithium (PhMe 2 SiLi) and Et 2 NMe 2 Si-SiMe 2 Cl was identified by 29 Si NMR spectroscopy as the anticipated 1-(diethylamino)-1,1,2,2,3,3-hexamethyl-3-phenyltrisilane (Et 2 NMe 2 Si-SiMe 2 -SiMe 2 Ph, 18) (Scheme 6). Subsequent reaction with methanol afforded 1-methoxy-1,1,2,2,3,3-hexamethyl-3-phenyltrisilane (MeOMe 2 Si-SiMe 2 -SiMe 2 Ph, 19), which reacted with CH 3 COCl to 1-chloro-1,1,2,2,3,3-hexamethyl-3-phenyltrisilane (ClMe 2 Si-SiMe 2 -SiMe 2 Ph, 20) [53,54] Table 3. Both depend on the substituents of the silicon atom and on the organic substituent R. As expected the carbon atom neighboring the silicon atom is more shielded than the other carbon atom (assignment proved by 29 Si satellites).…”

Low Temperature Wurtz-Type Polymerization of Substituted Dichlorosilanes

“…14 • 53 This process is also accompanied by the formation of various colors said to be characteristic of silyl anions. 54 The role of silyl anions in end-biting cyclization reactions and under certain reaction conditions in backbiting to produce cyclosilanes from polysilane polymers seems based on ample precedent. Such is not the case for silyl radical intermediates which would require either energetically unfavorable chain transfer from an w-chlorooligosilyl radical or the statistically improbable cyclication of an a,w-polysilyldiyl biradical in the absence of an intramolecular homolytic backbiting route to cyclics.…”

“…Indeed, a detailed structural analysis might be complicated by the known tendency of silicon catenates to undergo equilibration and redistribution in the presence of anionic reagents. 54 Our attempts to terminate anionic chain ends by the inclusion of an alkylating agent such as dimethyl sulfate into the polymerization media were unsuccessful. Although no visible reaction of dimethyl sulfate with sodium occurred upon mixing, subsequent addition of PhEtSiC1 2 produced no color change or the formation of any high polymer (Table II, entry I 0).…”