Trialkoxysilanes

UsuaHy, trichlorosilane, trialkoxysilane, methyl dichlorosHane, and methyl dialkoxysHane are used. For example, the reaction of trichlorosilane with aHyl methacrylate is as foHows ... 

In comparison to the Si—OR bond, the Si—C bond can be considered essentially unreactive if the organic moiety is a simple unsubstituted hydrocarbon. If the organic moiety is substituted as in the case of a trialkoxysilane, the chemistry is more appropriately considered elsewhere (see Silicon COMPOUNDS, SILANES SILICON COMPOUNDS, SILYLATING AGENTS). 

The attachment of trialkoxysilane functionality to polyolefins (HDPE, LDPE, PP) though grafting of vinylsilanes (e,g. 40, 41) or silane functional acrylates (e.g. 42) has been widely studied. 63 The principal application of these materials is the... 

By analogy with hydroformylation, dicobalt octacarbonyl has been examined as a hydrosilylation catalyst. Various silanes and a-olefins react, often exothermically. Thermal deactivation occurs above 60° C hence, large exotherms and high temperatures must be avoided (56, 57,130). Isomerization is more pronounced than for the bridged olefin complexes of Pt(II) and Rh(I) (see below) it even occurs with trialkoxysilanes (57). Though isomerization is faster than hydrosilylation, little variation in the relative rates of these two processes with the nature of the silane is observed this is in marked contrast to the bridged systems (55). 

Although the titanium-based methods are typically stoichiometric, catalytic turnover was achieved in one isolated example with trialkoxysilane reducing agents with titanocene catalysts (Scheme 28) [74], This example (as part of a broader study of enal cyclizations [74,75]) was indeed the first process to demonstrate catalysis in a silane-based aldehyde/alkyne reductive coupling and provided important guidance in the development of the nickel-catalyzed processes that are generally more tolerant of functionality and broader in scope. 

Organotrialkoxysilanes (ArSi(OR)3) were used as organometallic reagents without fluoride additives (Scheme 56).144,144a ArSi(OR)3 was easy to use because of its higher air and moisture stability. Oi and co-workers believed that hydrolysis of the trialkoxysilanes to generate silanetriols was likely occurring prior to transmetallation of the cationic rhodium complex. 

Alcohols react with surface hydroxyl group to form C-O-Si bonds. Because this type of bond is not very stable, trialkoxysilanes are preferred for anchoring. Exceptions to this rule are polyhydric alcohols, such as tris(hydroxymethyl)phos-phine [86], which forms multiple bonds with the surface. 

Brook has effectively modified a procedure (introduced by Hosomi) which employs a trialkoxysilane as the stoichiometric reducing agent which, in the presence of amino acid anions reduces aryl alkyl ketones or diaryl ketones to the corresponding (A)-secondary alcohols, albeit in modest ee (generally 25 40%). ... 

Consider a trialkoxysilane as co-precursor for an initial 1 1 mixture of alkoxysilane and organoalkoxysilane, and recall that in the case of ORMOSIL condensation takes place only through elimination of water27 and not by alcohol formation. The mechanism involves hydrolysis and condensation reactions ... 

The specific functionalization of the unprotected silica surface with a trialkoxysilane derivative such as CH3Si(OCH3)3 is then carried out in a slightly basic water-ethanol suspension of the snowman-like particles. TEM images (Figure 1.29) of the resulting suspension of latex nanoparticles whose unmodified part was further functionalized with a second trialkoxysilane such as aminopropyltriethoxysilane and then... 

It is possible to modify the matrix hydrophilicity-lipophilicity balance (HLB) by using different alkyl-modified trialkoxysilanes as co-reagents with tetraethylorthosilicate (TEOS), to greatly alter (reduce) the release rate of heparin, as then water access to the entrapped drug is considerably reduced (Figure 2.10).4... 

Reduction of aryl alkyl ketones with moderate to good (ee 30-80%) entantio-selectivity has been achieved using trialkoxysilanes in the presence of chiral quininium fluorides (or hydroxides) [20]. Greater selectivities were noted (ee >65%) when tris(trimethylsiloxy)silane was used. 

The trialkoxysilane (1.5 mmol) is added with stirring at room temperature to the ketone and quininium fluoride (0.02 mmol) in THF (2 ml). When the reaction is complete, as shown by TLC analysis, aqueous sodium hydroxide (3M, 5 ml) is added and the mixture is stirred for a further 12 h at room temperature. The mixture is extracted with Et20 (3 x 15 ml) and the extracts are washed well with H20, dried (MgS04), and evaporated to yield the chiral alcohol. 

Figure 7.8 The proposed reaction of a hydrolysed mono-organo trialkoxysilane with cell wall polymers.

In this synthetic strategy, the macrocyclic antibiotic is covalently bonded to the silica matrix in two steps (1) chemical modification of the selector via reaction between suitable groups of the antibiotic and proper groups of the spacer, reacting also as a di- or trialkoxysilane (2) immobilization of the functionalized selector on unmodified silica particles. 

Among functionalized silanes, trialkoxysilanes are used most often for immobilization purposes (see Fig. 6). 

Fig. 6 Common silanizing trialkoxysilanes that promote covalent DNA immobilization a 3-aminopropyltriethoxysilane (APTES) b 3-aminopropyltrimethoxysilane (APTMS) c 3-glycidoxypropyltrimethoxysUane (GOPS) d 3-mercaptopropyltrimethoxysilane (MPTS)...

Two schemes can be imagined wherein (1) the component forming the anion, e.g., AICI3 is reacted first then followed by the organic cation component (dialkylimidazolium chloride) or (2) the surface is reacted with a derivative of the cation component which shows a reactive tail for the metal oxide surface, such as trialkoxysilane, and then the anion component is reacted with this immobilized component. For example, using conventional chemistry for decorating metal oxide surfaces with reactive compounds, silica has been decorated first with a dialkylimidazolium chloride and then this surface compound was reacted with AICI3 to form an immobilized... 

Type III (no homodimerization) Acrylonitrile," protected 3° allylamines" Vinyl trialkoxysilanes, vinyl siloxanes 1,1-Disubstituted olefins, " non-bulky trisubstituted olefms, vinyl phosphonates, " vinyl phosphine oxides,phenyl vinyl sulfone, acrylonitrile, 4° allylic carbons (all alkyl substituents), protected 3° allylic alcohols, 7,Aolefm of 2-subst. 1.3- butadienes, 7,Aolefin of electronically deactivated 1.3- butadienes ... 

Modifications of monodisperse colloidal silica, of 10 or 500 nm in diameter, were carried out using trialkoxysilane-terminated polymer in a low polar solvent, such as acetone or 1,2-dimethoxyethane. without coagulation during the coupling reaction (35,37-42). In this modification, the hydrophobic polymer can be efficiently bound to hydrophilic colloidal silica surface. The reaction mechanism of the binding... 

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