Silanes oxidation

It is postulated that the mechanism of the silane-mediated reaction involves silane oxidative addition to nickel(O) followed by diene hydrometallation to afford the nickel -jr-allyl complex A-16. Insertion of the appendant aldehyde provides the nickel alkoxide B-12, which upon oxygen-silicon reductive elimination affords the silyl protected product 71c along with nickel(O). Silane oxidative addition to nickel(O) closes the catalytic cycle. In contrast, the Bu 2Al(acac)-mediated reaction is believed to involve a pathway initiated by oxidative coupling of the diene and... 

Although detailed mechanistic studies are not reported, the postulated mechanism for the reductive cyclization of allenic carbonyl compounds involves entry into the catalytic cycle via silane oxidative addition. Allene silylrhodation then provides the cr-allylrhodium hydride A-18, which upon carbometallation of the appendant aldehyde gives rise to rhodium alkoxide B-14. Oxygen-hydrogen reductive elimination furnishes the hydrosilylation-cyclization product... 

Table 10 Silane oxidation with aqueous H202/zeolite-Y-supported MTO...

Entry Silane Oxidant Nature Conversion % Selectivity silanol/ disiloxane % Refs. 

Considerable improvements have been made in the field of organorhenium and organomolybdenum oxide catalyst heterogenisation over the last decade. These include, in particular, the application of zeolites and mesoporous materials as supporting systems. Such heterogeneous systems have proven to be, in most cases, efficient and selective catalysts in various reactions, especially olefin epoxidation and (to a lesser extent) silane oxidation, other oxidation... 

Selective polymerization, enantiomers, 185 Semico rrin-copper complexes, 199 Sharpless epoxidation, racemic alcohols, 45 Side-chain units, prostaglandins, 310 Sigmatropic reactions, 222 Silanes, oxidative addition, 126 Silica gel, 285, 352... 

It is interesting to note that the concentration of protonated amino groups decreased as the take-off angle was decreased from 75° to 15° for y-APS films formed on all the polished substrates except aluminum (see Table 1). These results imply that the protonated amino groups were relatively evenly distributed throughout films formed on aluminum, but were concentrated nearer the silane/ oxide interface for the other substrates. The reason for the difference in behavior of films formed on aluminum and those formed on the other substrates may be related to the ease with which aluminum substrates are etched by aqueous solutions of y-APS at pH 10.4. 

This review is concerned with organosilanes and therefore purely inorganic Si/O/H species are not considered. Nevertheless, because of the importance of silane oxidation and of oxidized silicon coatings there is considerable interest and activity in this area. Four theoretical papers25,80-82 have been published concerning stabilities of the potentially important molecules in these processes. Needless to say there are very few experimental data in the area under consideration. 

A number of a,/J-unsaUiraled acyl silanes have been prepared from silyl enol ethers of acyl silanes (Scheme 41)129. Addition of phenyl sulphenyl chloride to the silyl enol ether with subsequent elimination of chlorotrimethylsilane gives the a-(phenylthio)acyl silane. Oxidation to the sulphoxide followed by in situ elimination of benzenesulphenic... 

In addition to modification by silanization, oxide surfaces can also be modified... 

We stress that, when analyzing the data obtained with these systems, attention should be paid to the fact that the necessary intermediate step giving TiOz-sil-NHj apparently causes a decrease in the activity of TiOj. In particular, the silanized oxide becomes a poorer catalyst for the reduction of O2 than the unmodified one (2). 

Figure 20.6. The friction-load relationship for an 18 pm sphere of cellulose in contact with a silanated, oxidized silicon wafer (98). Data from both loading and unloading is shown. The continuous line is a fit relating the frictional force linearly to the area of contact, assuming that the load-area relationship is described by the DMT theory...

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