Stereochemistry silicon

Silicon, Stereochemistry at (Corriu, Guerin, Mauman, and Carreira). 11 97... 

V. Bazant, V. Chvalovskj), and J. Rathousky Chemistry of Organosilicon Compounds. Publishing house of the Czechoslovak Academy of Sciences, Prague, and Academic Press, New York. Volumes 1 and 2 (two parts) (1965) 3 and 4 (three parts) (1973). Volume 1 summarizes the chemistry of organosilicon compounds and documents the literature to September 1961 (616 pp.). Volume 2 is a formula register with the same cut-off date. Volume 3 reviews selected topics (NMR, IR and Raman spectroscopy w-bonding penta- and hexa-co-ordinate silicon stereochemistry) up to December 1969 (761 pp.) and Volume 4 is a formula index for the period October 1961-December 1969 (2349 pp.). 

R. J P. Corriu, C. Guerin, Nucleophilic Displacement at Silicon. Stereochemistry and Mechanistic Implications", J. Organomet. Chem. 1980,198, 231. 

The assignment of configuration and the measurement of enantiomeric purity is a necessary step in any stereochemical study. Both the physical and chemical techniques used have been described in detail in the case of carbon compounds (92, 93). In this section we give a brief overview of their application to organo-silicon stereochemistry. 

The second chapter, by Robert J. P. Corriu, Christian Guerin, and Joel J. E. Moreau, constitutes a monumental review of stereochemistry at silicon. This subject was last discussed comprehensively in a pioneering book by L. H. Sommer in 1965, with a brief 1973 update. In the present chapter the authors bring the literature up to date, discussing silicon stereochemistry in all of its aspects, especially with a view to reaction mechanism, in which area they have made a number of original contributions. This chapter will no doubt become required (and welcome) reading for anyone involved in any way with silicon stereochemistry. 

The chemistry and stereochemistry of aminoboranes containing the siLicon—nitrogen—boron linkage have been the subject of numerous studies. Many of these compounds are useful precursors to other B—N systems including diboryl-amines (45) and B—H substituted aminoboranes (46). A series of... 

L. H. Sommer, Stereochemistry, Mechanism and Silicon An Introduction to the Dynamic Stereochemistry and Reaction Mechanisms of Silicon Centers, McGraw-Hill, New York, 1965, p. 126. 

Another strategy to control the regio- and stereochemistry of cycloaddidon is a silicon-tethered reacdon, as discussed in the secdon of nitronates fSecdon 8.2.3 fEq. 8.65. ... 

The silicon- and sulfur-substituted 9-allyl-9-borabicyclo[3.3.1]nonane 2 is similarly prepared via the hydroboration of l-phenylthio-l-trimethylsilyl-l,2-propadiene with 9-borabicy-clo[3.3.1]nonane36. The stereochemistry indicated for the allylborane is most likely the result of thermodynamic control, since this reagent should be unstable with respect to reversible 1,3-borotropic shifts. Products of the reactions of 2 and aldehydes are easily converted inlo 2-phenylthio-l,3-butadienes via acid- or base-catalyzed Peterson eliminations. 

Vinylsilanes react readily with a range of electrophiles to give products of substitution (1). The overall stereochemistry of such substitution will depend on a number of factors, including the stereochemistry of addition and subsequent elimination when 1,2-adducts are discrete species. However, the regiochemistry of substitution is normally unambiguous, the -effect ensuring that carbonium-ion development on attack by the electrophile will occur at the carbon terminus remote, i.e. /3, to silicon ... 

Although the allylation reaction is formally analogous to the addition of allylic boranes to carbonyl derivatives, it does not normally occur through a cyclic TS. This is because, in contrast to the boranes, the silicon in allylic silanes has little Lewis acid character and does not coordinate at the carbonyl oxygen. The stereochemistry of addition of allylic silanes to carbonyl compounds is consistent with an acyclic TS. The -stereoisomer of 2-butenyl(trimethyl)silane gives nearly exclusively the product in... 

The 29Si resonance is therefore a single narrow line. However for dialkylpolysilanes with two different alkyl groups on each silicon, (RR Si)n, each silicon atom is a chiral center and the resonance for a particular silicon will depend upon the relative stereochemistry of other nearby silicon atoms. For such polymers, a rather symmetrical cluster of peaks is observed (Figure 5). These results are consistent with atactic structures, having a statistical (Bernoullian) distribution of relative configurations.(32,33)... 

Most optically active polysilanes owe their optical activity to induced main-chain chirality, as outlined above. However, backbone silicon atoms with two different side-chain substituents are chiral. Long-chain catenates, however, are effectively internally racemized by the random stereochemistry at silicon, and inherent main-chain chirality is not observed. For oligosilanes, however, inherent main-chain chirality has been demonstrated. A series of 2,3-disubstituted tetrasilanes, H3Si[Si(H)X]2SiH3 (where X = Ph, Cl, or Br), were obtained from octaphenylcyclote-trasilane and contain two chiral main-chain silicon atoms, 6.16 These give rise to four diastereoisomers the optically active S,S and R,R forms, the activity of which is equal but opposite, resulting in a racemic (and consequently optically inactive) mixture and the two meso-forms, S,R and R,S, which are optically inactive by internal compensation. It is reported that the diastereoisomers could be distinguished in NMR and GC/MS experiments. For the case of 2-phenyltetrasilane, a racemic mixture of (R)- and (A)-enantiomers was obtained. 

The ability of silicon to direct the stereochemistry is a technique just beginning to be appreciated. 

L.H. Sommer, Stereochemistry, Mechanism and Silicon, McGraw-Hill Inc, 1965. 

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