Henry Gilman

The analysis of organolithium compounds

Abstract A large number of organic halides was used in the double titration method of analysis for organolithium compounds. I,2-Dibromoethane has been found to give a satisfactory analysis for alkyllithium compounds and phenyllithium. Titration employing the dibromoethane is recommended for general analytical use, although I,I,2-tribromoethane probably gives a slightly more accurate analysis for fresh preparations of phenyl- and methyllithium. The use of allyl bromide in titrations of n -butyllithium in diethyl ether and hexane was also found to afford reliable results.

Tris(trimethylsilyl)silyllithium

An investigation has been made of the relative reactivity of tris(trimethylsilyl)silyllithium (I) in an attempt to estimate the importance of (dπ-pπ) bonding involving two contiguous silicon atoms. The procedure used were: (1) a comparative metalation reaction; (2) a kinetic study; and (3) a cleavage reaction of a silicon—silicon bond. The results are not definitive; although they seem to imply that the reactivity of I is comparable to or less than that of triphenylsilyllithium. The reactivity of I, together with its ultraviolet and NMR spectra, has been explained in terms of dative π-bonding.

Hexasubstituted disilanes from chlorosilanes and lithium in tetrahydrofuran

Abstract General procedures are provided for the preparation in satisfactory yields of hexamethyl-, hexaethyl- and 1,2-dibenzyl-1,1,2,2-tetramethyldisilane from the corresponding R 3 SiCl compounds with lithium metal in THF. Optimal conditions for the preparation of hexamethyldisilane by this procedure were studied. Dimethylphenyl- and diethylphenylchlorosilanes gave the corresponding disilanes when treated with one equivalent of lithium in THF; no secondary cleavage of the SiSi bond occurred under these conditions. Diethylphenylsilyllithium was obtained by lithium cleavage of the corresponding disilane and characterized by reaction with chlorotriphenylsilane to give 1,1-diethyl-1,2,2,2-tetraphenyldisilane.

Hexakis(trimethylsilyl)disilane: A highly branched and symmetrical organopolysilane

Abstract Hexakis(trimethylsilyl)disilane (1), a novel, highly branched and symmetrical polysilane, was synthesized by a number of procedures. Many of these gave (I) in only 5–9% yield. The reaction of tris(trimethylsilyl)silyllithium (II) with 1,2-dibromoethane ( ca .-70°) gave (I) in 45–50% yields, and proved to be the most satisfactory method of synthesis. The physical and spectral properties of (I) are discussed. Lithium and methyllithium reacted with (I) to cause cleavage of the symmetrical Si Si bond, while (II), triphenylsilyllithium and halogens effected cleavage of peripheral trimethylsilyl groups.

Thermal decomposition of some perfluoroalkyl grignard reagents. Synthesis of trans-1-halo and trans-1-alkylperfluorovinyl compounds

Abstract The thermal decomposition of perfluoroalkyl Grignard reagents (R f MgX), formed from halogen-metal exchange with alkyl Grignard reagents, provides a good synthetic route to trans -1-haloperfluorovinyl compounds. The decomposition of R f MgX (where X = Cl, Br, I) in the presence of RMgX generally leads to a mixture of trans -1-alkylperfluorovinyl and trans -1-haloperfluorovinyl compounds. However, the choice of RMgX with respect to both the alkyl group and halogen is critical as regards the formation of the trans -1-alkylperfluorovinyl compounds. Several possible mechanisms are suggested to account for the experimental observations.

Organic Substituted Cyclosilanes

Publisher Summary This chapter discusses the structure, properties, preparation, and reactions of cyclosilanes in the light of recent investigations of phenyl and methyl series and corrects some misconceptions concerning the perphenylated cyclosilanes. Representative organic substituted cyclosilanes, as illustrated by octaphenylcyclotetrasilane, decaphenylcyclopentasilane, and their p-tolyl analogs and dodecamethylcyclohexasilane have been characterized and shown to undergo reactions that are generally common to compounds containing the disilane linkage. The relative reactivities of these cyclosilanes has been attributed mainly to steric factors and substituent groups on silicon, with the consideration that the silicon atom involved in reaction can attain a pentacovalent state. The extreme reactivity of octaphenylcyclotetrasilane with a variety of reagents, some of which are not considered capable of silicon bond cleavage, had previously been described as being due to the presence of a silyl radical species or due to ring strain, which is then responsible for the homolytic scission of the silicon–silicon bond. Homolytic cleavage is not necessarily important in the reactions of octaphenylcyclotetrasilane, but the molecular geometry of the compound greatly facilitates the formation of apentacovalent complex that undergoes easy cleavage to give the observed products. The products of the reactions of cyclosilanes are organic-substituted polysilanes, which can be considered to be the shorter chain members of a new class of compounds. Further research in preparation and chemical behavior of materials is necessary for establishing the structures of these compounds and explanation of their special properties.

Reactions of some (polyhaloaryl)copper compounds with acid chlorides and chlorosilanes

Abstract (Polyhaloaryl)copper compounds or their complexes, where the aryl group is pentafluorophenyl, pentachlorophenyl, or 2,3,5,6-tetrachloro-4-pyridyl, have been prepared by three methods: ( i ) via a polyhaloaryllithium compound; ( ii ) via a polyhaloaryl Grignard reagent; and ( iii ) via addition of polyhaloarene to lithium dimethylcopper. The copper compounds react readily with acid chlorides but slowly or not at all with chlorosilanes.

Hexakis(trimethylsilyl)-2-butyne by trimethylsilylation of hexachloro-1,3-butadiene

Abstract Lithium (or sodium) chlorotrimethylsilane and hexachlorobutadiene in THF give hexakis(trimethylsilyl)-2-butyne in good yields. Some chemical properties of this sterically hindered compound are described. In contrast, magnesium under similar conditions gives bis(trimethylsilyl)butadiyne; whereas barium fails to react.

The analysis of organic-substituted group IVB lithium compounds

Abstract A method for the quantitative analysis of triorganosilyl-, -germyl-, and -tinlithium compounds, involving a double titration using allyl bromide, has been investigated and compared with other methods of analysis. The new procedure is considered to be more accurate and convenient than previous methods.

Reactions of (polyhaloaryl)copper compounds with aryl, alkyl and allyl halides

Abstract (Polyhaloaryl)copper complexes in solution were reacted with some aryl and alkyl iodides and allyl halides to give the coupled products. The composition of some isolated complexes is reported.