Silicon-Sulfur Syntheses

The methods available for synthesis have advanced dramatically in the past half-century. Improvements have been made in selectivity of conditions, versatility of transformations, stereochemical control, and the efficiency of synthetic processes. The range of available reagents has expanded. Many reactions involve compounds of boron, silicon, sulfur, selenium, phosphorus, and tin. Catalysis, particularly by transition metal complexes, has also become a key part of organic synthesis. The mechanisms of catalytic reactions are characterized by catalytic cycles and require an understanding not only of the ultimate bond-forming and bond-breaking steps, but also of the mechanism for regeneration of the active catalytic species and the effect of products, by-products, and other reaction components in the catalytic cycle. 

As mentioned in this chapter, in recent years much progress has been made in the chemistry of silicon-chalcogen multiple bonds. For silicon-sulfur doubly-bonded compounds, we have now several isolated examples, both kinetically stabilized and thermodynamically stabilized. Furthermore, there have been reports of the synthesis and characterization of stable compounds with silicon-nitrogen double bonds (i.e. silanimines or iminosilanes) as well as their heavier group 15 element analogues such as phosphasilenes and arsasilenes. 

This study was complemented by a selective synthesis of the tautomeric enethiols [77]. Aliphatic thioketones were deprotonated by LDA, silylated, and the resulting silyl vinyl sulfides were smoothly converted to enethiols by simple addition of methanol. These are stable compounds which do not equilibrate with thioketones, this behaviour probably related to the extremely mild conditions of the (easy) cleavage of the silicon-sulfur bond. 

A new method allowing the prediction of many important physical properties of polymers prior to synthesis was presented in this book. Our quantitative structure-property relationships based on this method enable the prediction of the properties of uncrosslinked isotropic amorphous polymers constructed from nine key elements (carbon, nitrogen, oxygen, hydrogen, fluorine, silicon, sulfur, chlorine and bromine) from which most technologically important synthetic polymers are built. Some properties of crosslinked polymers can also be predicted. 

Olefin synthesis starts usually from carbonyl compounds and carbanions with relatively electropositive, redox-active substituents mostly containing phosphorus, sulfur, or silicon. The carbanions add to the carbonyl group and the oxy anion attacks the oxidizable atom Y in-tramolecularly. The oxide Y—O" is then eliminated and a new C—C bond is formed. Such reactions take place because the formation of a Y—0 bond is thermodynamically favored and because Y is able to expand its coordination sphere and to raise its oxidation number. 

J. D. Morrison and J. W. ScoXt, Asymmetric Synthesis, Vol. 4, The Chiral Carbon Pool and Chiral Sulfur, Nitrogen, Phosphorus, and Silicon Centers, Academic Press, Inc., Odando, Fla., 1984. 

In spite of the hazardous nature of Sc4N4, this binary selenium nitride has been used for the synthesis of other Se-N compounds, all of which have sulfur analogues (Scheme 5.2). " However, safer alternatives to the use of Sc4N4, e.g., selenium-nitrogen halides and silicon-nitrogen-selenium reagents, are available for the development of Se-N chemistry. ... 

The synthetic approach to silylene complexes (Eq. (2)) is versatile and allows a high variability of both the metals and the substituents at the silicon. A whole series of compounds with bulky substituents like 1 -adamantyloxy, 2-adamantyloxy, neopentyloxy, triphenylmethoxy or f-butylthio could be prepared (Table 1). Compounds with sulfur at silicon are particularly interesting however, their synthesis proved to be very difficult. 

Cairns J., Dunne C., Franczyk T. S., Hamilton R., Hardacre C., Stern M. K., Treacy A, Walker BJ The Synthesis and Chemistry of Formylphosphonate Phosphorus, Sulfur Silicon Relat. Elem. 1999 144-146 385-388... 

Aminolysis of the corresponding halides is the preferred method for the synthesis of dialkylamino derivatives of boron,1 silicon,2 germanium,3 phosphorus,4 arsenic,5 and sulfur.6 (Dialkylamino) chlorosilanes are prepared stepwise by the reaction of silicon tetrachloride with dialkylamines. This method may be utilized equally well for the conversion of alkyl- or aryl-substituted halides [e.g., (CH3) SiCl4. ] or of oxide and sulfide halides (e.g., POCl3 or PSC13) to the corresponding dialkylamino compounds. 

PSS(161)181 A.R. Hajipour M. Hantehzadeh Phosphorus, Sulfur Silicon Relat. Elem. 2000,161,181-189. 00S273 E.M. Brun S. Gil R. Mestres M. Parra Synthesis 2000,273-280. 

The present volume comprises 17 chapters, written by 27 authors from 11 countries, and deals with theoretical aspects and structural chemistry of peroxy compounds, with their thermochemistry, O NMR spectra and analysis, extensively with synthesis of cyclic peroxides and with the uses of peroxides in synthesis, and with peroxides in biological systems. Heterocyclic peroxides, containing silicon, germanium, sulfur and phosphorus, as well as transition metal peroxides are treated in several chapters. Special chapters deal with allylic peroxides, advances in the chemistry of dioxiranes and dioxetanes, and chemiluminescence of peroxide and with polar effects of their decomposition. A chapter on anti-malarial and anti-tumor peroxides, a hot topic in recent research of peroxides, closes the book. 

H.J. Cristau, C. Garcia, J. Kadoura u. E. Torreilles, Phosphorus, Sulfur, Silicon Relat. Elem. 49/50,151-154 (1990). Phosphonium Diaza-diylids and Aza-yldiid as New and Efficient Reagents for Primary and Secondary Amine Synthesis". 

Replacement of the carbonyl oxygen atom by sulfur may be effected by heating with phosphorus pentasulfide (49JCS2142), boron sulfide or silicon disulfide which gives high yields under mild conditions, as, for example, in the synthesis of 7-methoxy-2-methylchromene-4-thione (438) (69JCS(C)2192). Such compounds are more easily converted into their oximes or hydrazones than the oxygen compounds. 

Dandia, A., Saha, M. and Taneja, H., Improved one-pot synthesis of 3-spiro indolines under microwave irradiation, Phosphorus, Sulfur Silicon, 1998, 139, 77-85. 

The synthesis of heterocycles containing both silicon and sulfur in the ring from linear thiols have recently been described by Kirpichenko and coworkers190 (Scheme 66). 

Demethylation by sulfuric acid can be successfully extended to certain organofunctional methyldisilanes. For instance, (chloromethyl)penta-methyldisilane easily undergoes demethylation under similar conditions to give l-(chloromethyl)-2-chloro(or fluoro)tetramethyldisilane upon treatment with an ammonium halide, in good yield (120). Moreover, this method is still satisfactory for synthesis of l,3-dichloro(or difluoro-)hexamethyl-trisilane (III), which is obtainable in 40% (or 55%) yield from octamethyl-trisilane (in this case, demethylation occurs concurrently at both the 1- and 3-silicon atoms, unlike the demethylation of hexamethyldisilane) (102,106, 107). 

However, the method is no longer satisfactorily applicable to synthesis of higher polysilane derivatives because extensive cleavage of the silicon-silicon bond occurs and a mixture of isomeric halopolysilane derivatives that are inseparable by distillation is formed. For example, the reaction of decamethyltetrasilane with sulfuric acid and treatment with ammonium hydrogen fluoride leads to the formation of several fluoro derivatives of... 

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