SI Group

The ( )-vinylsilane 151 was prepared by treatment of the silylstannation product 150 with hydrogen iodide[75] and the silylzincation product with water[70]. The silylstannylation of 1-ethoxyacetylene proceeds at room temperature using Pd(OAc)i and 1,1,3,3-tetramethylbutyl isocyanide regioselec-tively and an Si group is introduced at the ethoxy-bearing carbon. Subsequent Cul- and Pd-catalyzed displacement of the stannyl group in the product 152 with allyl halide, followed by hvdrolvsis, affords the acylsilane 153[79],... 

The view has also existed in the past that the carbon-silicon bond should be similar in behaviour to the carbon-carbon bond and would have a similar average bond energy. There is some measure of truth in the assumption about average bond energy but because silicon is more electropositive than carbon the C—Si bond will be polar and its properties will be very dependent on the nature of groups attached to the carbon and silicon groups. For example, the CH3—Si group is particularly resistant to oxidation but H13—Si is not. 

Nitroethene substituted with the Me-Si group is used in a Diels-Alder reaction fEq 8 8 ji example of the reaction with l-nitro-l-ftrialkylsilyliacetylenes has also been pubhshed... 

The authors propose that this reaction proceeds by initial insertion of the 7t-bond into a Pd - H bond, in contrast to the Pd - Si insertion seen in the reaction between El3SiH and dienes catalyzed by 100 (Scheme 24) [71]. A weak bond between the cationic palladium and the electron-poor C Si group favoring Pd - H formation accounts for the change in mechanism. 

As shown in equation 5, compound 1 may also be treated with two equivalents of n-BuLi and disubstituted in one step by addition of HMe2SiCI. Several attempts have been made to prepare the mono substituted (with the HMe.Si group) product but mixtures of mono and disubstituted derivatives were obtained and could not bie separated by fractional distillation. 

The temperature resistance of the polysiloxane on the samples was tested by stepwise heating up to 500°C. Whereas the pure hydrolysis product undergoes a complete thermal degradation via oxidative conversion of the CH3-Si groups into HO-Si groups, the polysiloxane persists on the silica sample. This stabilization effect most likely results from the covalent attachment of the methyl-polysiloxane. 

The interconnection of two phosphanide substituents by sterically demanding RR Si groups allows the preparation of cage compounds [38], The two-fold lithia-tion of bis(phosphanyl)(alkyl)arylsilane and the dimerization of this bis(phos-phanido)silane leads to the formation of 19 with a strongly distorted Li4P4 hetero-cubane structure according to Eq. (5). 

According to Girgis (1983) the existence field of the electron phases may be especially related to the combinations of d elements with the elements of the Periodic Table columns from 11 to 14 (from the Cu to Si groups). It can also be observed that, for several alloy systems, the dependence of the structures (structure types) on the electron concentration (instead of on the composition) may be clearly illustrated by well-known diagrams such as those shown in Fig. 4.39. 

Scheme 6.21 Homolytic 1,5 transfer of Mes Si group from an enoxy oxygen to alkoxy oxygen...

When Cp ZrMe3 reacts with a silica(sooor8oo), only one single site surface species =SiO-ZrCp Me2 (3) is obtained [6]. However, on Si02(soo). =SiO-ZrCp Me2 is obtained by reaction with both =Si-OH and =Si-0-Si= groups. As a consequence 3 has three different environments (3a, 3b and 3c in Scheme 2.12). Note that these different environments may lead to different catalytic properties since the olefin in catalysis will probably prefer to migrate to the active site via the most hydro-phobic part of the surface (3b). 

The reaction depicted in equation 43 between a nitrile and a lithium amide takes place as a 1,2-addition to the cyano group. The product crystallizes as a dimer (236) in which the lithium atoms are solvated by nitrile molecules and differently bonded to the amidine moieties, as shown by XRD analysis. Low-temperature H NMR spectrum in solution points to uniform chemical environments for both the aryl groups and for the Me—Si groups, and to rapid rearrangement of the Li—N coordination structures. Acidolysis of the dimer in solution yields the corresponding amidine (237) . The crystal structure of the THF-solvated analog of 236 shows dissimilar N—Li bond lengths for the two Li atoms... 

Silylformylation, defined as the addition of RsSi- and -CHO across various types of bonds using a silane R3SiH, CO, and a transition metal catalyst, was discovered by Murai and co-workers, who developed the Co2(CO)8-catalyzed silylformylation of aldehydes, epoxides, and cyclic ethers [26]. More recently, as described in detail in Section 5.3.1, below, alkynes and alkenes have been successfully developed as silylformylation substrates. These reactions represent a powerful variation on hydroformylation, in that a C-Si bond is produced instead of a C-H bond. Given that C-Si groups are subject to, among other reactions, oxidation to C-OH groups, silylformylation could represent an oxidative carbonylation of the type described in Scheme 5.1. 

Along with the highly reactive substituents OH and OR, cyclo- and polycyclosilo-xanes contain Si—O—Si groups which can be readily cleaved The reactivity of the groups involved in the formation of the polyhedral oligosilsesquioxane framework decreases in the following order... 

The Si—O—Si group in oligosilsesquioxanes is more stable toward sulfuric acid than in cyclosiloxanes. 01igo(hydrosilsesquioxanes) are susceptible to attack by... 

Gas chromatogram of cholesterol and other lipids extracted from bones and derivatized with trimethylsilyl ((CH Si—) groups to increase volatility for chromatography. Bone contains 2 to 50 ng cholesterol/gram of dry bone. 

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