Silanes and germanes

The metathesis of alkenylsilanes is represented by eqn. (15). Conversions of 4-15% have been reported for the metathesis of vinyltrimethylsilane (n = 0, R = Me) on 

RuCl2(PPh3)3 is also an efficient catalyst for the metathesis of vinyltri(phenyl, methyl)silanes reaction (16). A yield of 75% is obtained after 48 h (for n = 1) or 96 h (n = 2) at 120°C in air. RhCl(PPh3)3 is less active (Marciniec 1991). 

The metathesis of vinyltri(alkoxy,methyl)silanes, reaction (17), proceeds smoothly at 60-130°C in the presence of ruthenium chloride complexes such as RuCl2(PPh3)3, or in some cases rhodium chloride complexes such as RhCl(PPh3)3, 

The complex Ru(SiMe3)(Cl)(CO)(PPh3)2 brings about the conversion of the vinyltrisubstituted silanes CH2=CHSiMe2Ph and CH2=CHSi(OEt)3 to a mixture of two isomers, viz. /ra/Ji-l,2-bis(silyl)ethene and l,l-bis(silyl)ethene, similar to the reaction of vinyltrimethylsilane with this catalyst (Marciniec 1995b). 

With certain ruthenium complexes sueh a [RuCl2(p-eymene)]2, allyltrisubstituted silanes (allyltrimethylsilane, allyltriethoxysilane) undergo isomerization to the corresponding 1-propenyltrisubstituted silane followed by cross-metathesis between the two isomers (Marciniec 1994a). 

---

A number of features of the silane and germane polymerization reactions show unequivocally that there are at least two independant mechanisms operating. This dichotomy is most evident in situations where the products of reaction can be compared for the induction period that precedes the formation of compound J, and the products that are produced after the formation of 1 (12,15,20). 

As with the halogens, the thiols, phosphines, silanes, and germanes undergo photoaddition to olefins via homolytic cleavage. Representative examples follow a24 130) ... 

The solid solution observed between silane and germane and the very close X-ray powder diffraction of both compounds are the evidence of isostery, i.e. of the same structure. 

The use of free radicals allows great versatility and tolerance. Usually, the primary free radicals are generated by reaction of halides as well as phenyl-thio and phenylselenium compounds with stanna-nes such as nBu3SnH, silanes and germanes. Redox processes e.g. using Mnffl oxidation may also be employed. Since tin compounds are quite toxic there was a search going to use other methods for the generation of radicals. 

In theoretical work, the initial steps in the polymerization of 1,1-dicyano-, 1,1-difluoro-, and 1,1-dimethyl-cyclopropanes by reaction with H, OH, and Me have been modelled by ab initio methods. " Other ab initio MO calculations for the reactions of H, Me, Ft, j-Pr, and r-Bu with a variety of silanes and germanes have been carried out. The results indicate that the attacking and leaving radicals adopt an almost co-linear arrangement. Bond distances and energy barriers were predicted for the reactions studied. 

Some simple organometallics have been studied. Poly(silanes) and germanes exhibit very interesting behavior, since they are photochromic and appear to possess excitonic, charge delocalized excited states involving the sigma electrons of the organometallic backbone. 112) THG measured susceptibilities of up to 1 x... 

Compounds of carbon with hydrogen and other elements form the vast area of organic chemistry. Silanes and germanes are Si and Ge analogous of methane and short-chain saturated hydrocarbons, and can be prepared by various methods, such as reduction of halides with LiAlH4 ... 

All halides EX4 form tetrahedral molecules. Mixed halides are known, as well as fully or partially halogen-substituted catenated alkanes, silanes and germanes (e.g., Ge2Cl6). Unlike the carbon... 

Spanier, E. J., and A. G. MacDiarmid The Synthesis of Germylsilane from Silane and Germane in a Silent Electric Discharge. Inorg. Chem. 2, 215-216 (1963). 

This article starts with a discussion of the parent hydrides, MH (M = C, Si, and Ge, n = 2-4), highlighting the major differences between the methane series and the silane and germane series. Some attention is paid to substituent effects on bond energies and geometries, and we introduce the important notion of the divalent state stabilization energy (DSSE). After laying this foundation, Si=C and Ge=C compounds are reviewed. This is followed by Si=Si, Ge=Ge, and Ge=Si doubly bonded structures and their isomers. Finally, triply bonded Si==C, Si=Si, and Ge=Ge compounds are briefly considered. 

Minimization of electrostatic interactions as defined by the various parameters described above, was done in order to calculate bond angles in halomethanes, -silanes and -germanes, as well as one-centre compounds that contain lone pairs and double bonds. The comparison with experimental values is such as to leave no doubt about the power of the VSEPR model. 

Biological Recognition of Enantiomeric Silanes and Germanes Syntheses and Antimuscarinic Properties of the Enantiomers of the Si/Ge Analogues Cyclohexyl(hydroxymethyl)phenyl(2-piperidinoethyl)silane and -Germane and Their Methiodides... 

Since hydroalumination by neutral aluminum hydrides is an electrophilic attack on a C= or C=C linkage, the reaction can be accelerated by Lewis acids such as aluminum halides, and be retarded by Lewis bases like R3N, R2O or even unsaturated R3AI cf. equation 38). Such reagents also exert an effect on the syn or anti character of the A1—H adduct. Evidence suggests that Lewis acids or bases principally affect the rate of isomerization of the initial syn adduct into the generally more stable anti adduct Lewis bases retard such isomerizations, while Lewis acids promote them. The presence of ethers or tertiary amines stabilize the syn adducts of alkynyl-silanes and -germanes (47) and permit such adducts to be formed in >95% geometrical purity (Scheme 12). ... 

Trifluoroacetylation of trialkyl(2-furyl)silanes and -germanes and their carbon analog was realized under Friedel-Crafts conditions using trifluroacetic anhydride. 

Molecular Structure and Vibrational IR Spectra of Fluoro, Chloro and Bromo-substituted Methanes, Silanes and Germanes An Ab Anitio Approach (J. S. Kwiatkowski J. Leszczynski)... 

In connection with hypercoordination in molecules that are not as congested, triaryl-silanes and -germanes are particularly interesting. Corriu et found by X-ray... 

Silanes and germanes are less stable than hydrocarbons. Double bonds involving Si and Ge are very much weaker than with C. 

All halides EX4 form tetrahedral molecules (point group Td). Mixed halides are known, as well as fully or partially halogen-substituted catenated alkanes, silanes and germanes (e.g. Ge2Cl6). Unlike the carbon compounds, halides of Si and Ge are Lewis acids and readily form complexes such as [SiF6]. Attack by Lewis bases often leads to decomposition, and thus rapid hydrolysis in water,... 

---