Silicon atoms generation

C3H4Si manifold, none of which proved to be the silacyclobutadiene. Silicon atoms, generated thermally, were co-condensed in an argon matrix with HCN. The initial product CH—N=Si is rapidly converted into (133) and SiH—C = The silylene... 

Co-condensation of silicon atoms, generated from a resistively heated, doped silicon rod (1350 -1380 °C) with very diluted ammonia/argon gas mixtures (1 1000) at 10 K leads to the formation of a primary Si,NH3 n-adduct 1, which is stable under these conditions[2]. This compound can be identified by three prominent IR absorptions ( >013 3387.3, 1599.1, and 1185.6 cm ). The silicon-nitrogen stretching band is too low in intensity to be observed. These bands show the expected shifts when the co-deposition is repeated with isotopically labeled ammonia ( ND3 2525.4,1171.5, and 912.5 cm 3 3378.8, 1596.1, and 1180.0 cm ). 

Figure B3.3.14. Template molecule in a zeolite cage. The CFIA stmcture (periodic in the calculation but only a fragment shown here) is drawn by omitting the oxygens which are positioned approximately halfway along the lines shown coimecting the tetrahedral silicon atoms. The molecule shown is 4-piperidinopiperidine, which was generated from the dicyclohexane motif suggested by computer. Thanks are due to D W Lewis and C R A Catlow for this figure. For fiirther details see [225].

Dihydro-lH-l,5,2-azasilaboroles derive from the 2,5-dihydro-lH-l,2-aza-boroles ( 6.5.3.3) by substitution of the carbon neighboring N by a silicon atom. They may act as four-electron donors using electron density from the C=C double bond and the N atom. The B atom behaves as an acceptor center. Two pathways are known for complex synthesis reaction with a generated transition-metal complex fragment and reaction with metal atoms by the metal-vapor synthesis method. 

Disilenes are generally unstable with respect to polymerization. However, if very bulky groups are attached to the silicon atoms then they can be obtained as stable compounds.54 Such disilenes react with in situ generated [PL(PR3)2] to give disilene complexes analogous to alkene complexes.50... 

If Nu is sufficiently nucleophilic toward the silicon atom in BENA (434), intermediate (511) (a conjugated nitroso alkene) is generated, and the latter reacts... 

The effects of silyl groups on the chemical behavior of the anion radicals generated by cathodic reduction is also noteworthy. It is well known that silyl groups stabilize a negative charge at the a position. Therefore, it seems to be reasonable to consider that the anion radicals of re-systems are stabilized by a-silyl substitution. The interaction of the half-filled re orbital of the anion radical with the empty low-lying orbital of the silicon (such as dx-pK interaction) results in partial electron donation from the re-system to the silicon atom which eventually stabilizes the anion radical. 

The fourth neighbor is generated when the prisms are connected. Since each aluminum is connected to a silicon according to Lowenstein s rule, there are Qs - QA silicon atoms available for connecting to another silicon, where Qs = number of silicon atoms and QA = number of aluminum atoms. 

Thermally generated silicon atoms react in an argon matrix with acetylene to give silacyclopropenylidene and in a similar way with ethylene to give silacyclopropylidene... 

It was proposed that an initially generated silyl radical 3, by reaction of i-BuO radical and polysilane 2, attacks another silicon atom in the same backbone to give a cyclic polysilane that contains an acyclic chain and another silyl radical (Scheme 8.1) [12]. The last silyl radical can either cyclize or abstract a hydrogen atom from another macromolecule, thus propagating the chain degradation. The reaction in Scheme 8.1 is an example of intramolecular homolytic substitution (ShO, a class of reactions discussed in Chapter 6. 

Silylium ions, which are not protected sterically or are not stabilized either electronically or by intramolecular interaction with a remote substituent do interact strongly with the solvent and/or the counteranion. The reaction of the transient silylium ion with solvents like ethers, nitriles and even aromatic hydrocarbons lead to oxonium, nitrilium and arenium ions with a tetrahedral environment for the silicon atom. These new cationic species can be clearly identified by their characteristic Si NMR chemical shifts. That is, the oxonium salt [Me3SiOEt2] TFPB is characterized by S Si = 66.9 in CD2CI2 solution at —70°C. " Similar chemical shifts are found for related silylated oxonium ions. Nitrilium ions formed by the reaction of intermediate trialkyl silylium ions with nitriles are identified by Si NMR chemical shifts S Si = 30—40 (see also Table VI for some examples). Trialkyl-substituted silylium ions generated in benzene solution yield silylated benzenium ions, which can be easily detected by a silicon NMR resonance at 8 Si = 90—100 (see Table VI). ... 

Aldol reactions of silyl enolates are promoted by a catalytic amount of transition metals through transmetallation generating transition metal enolates. In 1995, Shibasaki and Sodeoka reported an enantioselective aldol reaction of enol silyl ethers to aldehydes using a Pd-BINAP complex in wet DMF. Later, this finding was extended to a catalytic enantioselective Mannich-type reaction to a-imino esters by Sodeoka s group [Eq. (13.21)]. Detailed mechanistic studies revealed that the binuclear p-hydroxo complex 34 is the active catalyst, and the reaction proceeds through a palladium enolate. The transmetallation step would be facilitated by the hydroxo ligand transfer onto the silicon atom of enol silyl ethers ... 

Figure 5.7. Proposed mechanism for surface hydrosilylation. The initial loss of silicon hydride generates a silicon dangling bond. Reaction between the silicon and an alkene molecule leads to an attached alkyl radical, which may abstract a hydrogen atom from a neighboring silicon.

Plasma etching is a well-established technology for microchip fabrication, involving the removal of silicon with a beam of fluorine atoms generated by high energy electrical excitation of simple fluorocarbons, notahly carbon tetrafluoridc, chlorotrifluoromethanc. trifluorometh-... 

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