Silylation processes

Moreover, in the divided cell the exo.endo ratio of bromosilanes was 91 9 in the anode compartment bnt only 52 48 in the cathode compartment. Thus, the nature of the ultrasonic effect was explained assuming that beside the electrochemical silylation at the cathode, a parallel silylation process occurs at a magnesium anode, namely the silylation by 70 of an intermediate Grignard reagent produced from dibromide 69. It appears as a rare example of the anodic reduction However, the increase in the current density dnring electrolysis cansed a decrease in the apparent current efficiency. This observation indicates a chemical natnre of the anodic process. Of course, the ultrasonic irradiation facihtates the formation of the organomagnesium intermediate at the sacrificial anode and the anthors reported a similar ultrasonic effect for the nonelectrochemical but purely sonochemical... 

Another modification of the double silylation process reported by Tanaka and co-workers involves the use of a bis(hydrosilane) instead of a disilane as the reactant molecule.61 This reaction can be described as a dehydrogenative double silylation, in that two Si-H bonds are activated rather than an Si-Si bond. The system is best catalyzed by Pt(CH2=CH2)(PPh3)2 other Pt, Pd, Ru, and Rh complexes give only very low yields of the double-silylated products. Alkynes, alkenes, and dienes undergo reaction with the bis (hydrosilane) with a range of results. Silicon-oxygen bonds and silicon-nitrogen bonds can also be formed by this method and are discussed in the appropriate sections later. 

Two different mechanisms have been proposed for this dehydrogenative silylation process. The first mechanism proposed by Oro, Esteruelas and coworkers includes the oxidative addition of 1-alkyne to the Ir—Si bond, followed by the reductive elimination of 151 (equation 61)117,118. The proposed mechanism is supported by the identification of [IrH(C=CPh)( j2-( -Pr)2PCH2CH20Me)]BF4 in stoichiometric as well as catalytic conditions by 31P 1H NMR analyses118. The other mechanism proposed by Jun and Crabtree includes the insertion of 1-alkyne into the Ir—Si bond, followed by isomerization and /J-hydride elimination (equation 62)113, which is consistent with the mechanism proposed for the highly selective formation of (Z)-l-silyl-l-alkenes (see Section IILB)115. 

Surfactant extraction and silylation process is performed with a Konik-type liquid-handling robot endowed with a stirring and heating station. 

The DFT study of the 3 + 2-cycloaddition between ketene and TV-silyl-, IV-germyl-, and TV-stannyl-imines shows that the TV-germylimine reaction is a two-step process the TV-stannylimine reaction is a competition between two- and three-step processes whereas the TV-silyl process follows a three-step process44 A new and convenient synthesis of functionalized furans and benzofurans based on 3 + 2-cycloaddition/oxidation has been reported. The cyclization of cyclic 1,3-bis-silyl enol ethers (48) with l-chloro-2,2-dimethoxyethane (49), via a dianion, produced 5,6-bicyclic 2-alkylidenetetrahydrofurans (50), which are readily oxidized with DDQ to 2,3-unsubstituted benzofurans (51) (Scheme 13)45 The Evans bis(oxazoline)-Cu(II) complex catalyses the asymmetric 1,3-dipolar cycloaddition of a -hydroxyenones with nitrones to produce isoxazolidines.46 The... 

A similar study on the deprotonation/silylation process of iV-benzyl acetophenone imine led to similar results. Again n-butyllithium was shown to be regioselective. A second deprotonation-trimethylsilylation sequence leads to the expected BSMA derivative.150... 

A novel chemical functionalization method for MWCNTs through an oxidation and silylation process was reported in 2002. Purified and oxidatively functionalized MWCNTs were reacted with 3-mercaptopropyltrimethoxysilane, the CNT surface being joined to the organosilane moieties through OH groups [143], Similarly, MWCNTs were functionalized by KMn04 oxidation under PTC catalysis and subsequent reaction with the hydrolysis product of 3-methacryloxypropyltri-methoxysilane (3-MPTS) (Scheme 1.13). The O-silyl-functionalized MWCNTs were characterized by FT-IR spectroscopy and energy-dispersive spectroscopy... 

The tetracoordinate silicon cation is a rather common species in solution. It may be generated by heterolytic cleavage of a bond from silicon to a reactive ligand, as a result of interaction of the silicon center with an uncharged nucleophile like amine, imine, phosphine, phosphine oxide, and amide. Since these nucleophiles are also known to be effective catalysts for many displacements at silicon including important silylation processes (86,89,235-238), the cations of tetracoordinate silicon have received attention as possible intermediates in these reactions according to Eq. (40) (78,235,239-243). 

The silylation should be controlled carefully because of cracking occurring when the content of silicon atoms incorporated into the photoresist is large enough and of not sufficient plasma resistance against RIE in O2, when silylation process is stopped earlier than it should be. 

Aldol reaction. TrichlorosiloxyaUcenes are generated in a dehrominative silylation process from a-bromo ketones. Condensation with ArCHO leads to p-aryl enones. In the presence of the Lewis base Ph3PO the reaction is optimized. 

The silylation of a silica surface not only gives rise to a new, silane peak in the 29Si spectrum (—15 ppm in Figure 1, top), but also causes an alteration of the intensities in the =Si(OH)2, =SiOH, and =Si= peaks. These spectral changes permit the use of silylation for studying relative reactivities, as has been demonstrated by Sindorf and Maciel (16, 18, 19). The silylation process also changes the H CRAMPS spectrum (40) new peak(s) due to the surface-attached silane moieties are introduced, and intensities in the silanol peaks are altered. Thus, the silylation process can be used to correlate H and 29Si NMR views of the silica surface. For this purpose, silylation by trimethylchlorosilane (TMCS) was used. 

An important silicon-nitrogen compound is hexamethyldisilazane or HMDS. This reagent is an effective silylating agent and has found wide applicability assisting in the volatilization of temperature-sensitive alcohol. The silylation process is characterized by the following generalized equation (Equation 21) ... 

M.A. Hartney, R.R. Kunz, L.M. Eriksen, and D.C. LaTulipe, Comparison of liquid and vapor phase silylation processes for 193 nm positive tone hthography, Proc. SPIE 1925, 270 (1993). K. H. Baik, L. Van den Hove, and B. Roland, Comparative study between gas and liquid phase silylation for the diffusion enhanced silylated resist process, J. Vac. Set Technol. B 9, 3399 (1991) K. H. Baik, K. Ronse, L. Van den Hove, and B. Roland, Liquid phase silylation for the DESIRE process, Proc. SPIE 1672, 362 (1992). 

M.A. Hartney, R.R. Kunz, L.M. Eriksen, and D.C. LaTulipe, Comparison of liquid and vapor phase silylation processes for 193 nm positive tone lithography, Proc. SPIE 1925, 270 (1993). 

G.N. Taylor, L.E. Stillwagon, and T. Venkatesen, Gas phase functionalized plasma developed resists Initial concepts and results for electron beam exposure, J. Electrochem. Soc. 131, 1658 (1984) M.A. Hartney, R.R. Kunz, D.J. Ehrlich, and D.C. Shaver, Silylation processes for 193 nm excimer laser hthography, Proc. SPIE 1262, 119 (1990) M.A. Hartney and J.W. Thackeray, Sily lation processes for 193 nm lithography using acid catalyzed resists, Proc. SPIE 1672, 486 (1992) ... 

N. Benjamin, B. Chapman, and R. Boswell, Progress of an advanced diffusion source plasma reactor, Proc. SPIE 1392, 95 (1990) M.W. Horn, M.A. Hartney, and R.R. Kunz, Comparison of etching tools for resist pattern transfer, Proc. SPIE 1672, 448 (1992) S.C. Pahnateer, R.R. Kunz, M.W. Horn, A.R. Forte, and M. Rothschild, Optimization of a 193 nm silylation process for sub... 

Protection of Terminal Alkynes. Terminal alkynes can be protected as TMS alkynes by reaction with Butyllithium in THF followed by TMSCl (eq 17). A one-pot -elimination-silylation process (eq 18) can also yield the protected alkyne. 

---