Silylation/silylated

Structures that come to mind for assignment to die observed spectra are those that would be expected from an initial disproportionation of two primary silyl radicals to a silene and a hydrosilane, followed by an addition of another silyl radical to the silene, producing a / silylated silyl radical. Repetition of the process would eventually lead to a highly sterically encumbered and undoubtedly persistent silicon-based radical carrying only silicons in its / positions ... 

For an effective measurement of "/(SiH) (1 < n < 4) values in silylated silyl enol ethers, a selective population transfer experiment was modified so that selective decoupling was applied during acquisition. 1H-29Si heteronuclear COSY confirmed the presence of silylated groups in the molecule6. 

The ESR/ENDOR TT-spin populations p in the radical anion of 1.4-di[tris(trimethyl-silyl)silyl]benzene (Scheme 7a) and the corresponding squared HMO coefficients (cjM)2, which allow one to augment the blind centers without a CH bond (Scheme 7b), prove that more than half of the 7r-spin population p7 is located in the [(HjC Si Si half-shell... 

Very recently, Matsumoto and coworkers have been interested in the generation of persistent silyl radicals where the substituents on the silicon centre enforce highly planar architectures11. A series of silylated silyl radicals (6-10) were generated by photolysis of the corresponding silane or disilane, or by oxidation of the silylsodium precursor, and their EPR spectra recorded (equations 2-4). 

E)-AUylsilanes and allenylsilanes. The preparations from allylic and propargylic alcohols via the (silyl)silyl ethers involve bis(organosilyl)Pd(II) complexes to insert into the multiple C-C bonds and a subsequent yyn-elimination of the ensuing oxasilacyclobutanes to afford the products and PhjSi=0. 

Fig. 2. Possible reaction profile of the dyotropic silyl-silyl exchange.

Compounds 28a-c were found to rearrange smoothly at 150°-190° to 29a-c, respectively. The reactions are extremely clean, the yields being greater than 96% in all cases (31, 32). Kinetic data for the rearrangements are summarized in Table V. In striking contrast to the silyl-silyl... 

Rate Data for Dyotropic Silyl-Silyl Exchange in Hydroxylamines... 

Since the activation parameters are quite similar to those of the silyl-silyl exchange in silyl silylmethyl ethers (Section II), the authors suggest that the rearrangements in the hydroxylamine series may also occur via a dyotropic mechanism (51). Furthermore, insensitivity to solvent polarity appears to rule out the intermediacy of ions or zwitterions. The possibility of an asymmetric transition state was discussed (51). 

Although the above evidence points to a dyotropic exchange, it might be mentioned that the thermolysis of 7V-phenyl-iV,0-bis(trimethylsilyl)hydroxylamine (43) at 100°C (16 hours) results in phenylnitrene formation [Eq. (11)], as shown by trapping experiments (53). This is reminiscent of Scheme 4. Possible silyl-silyl exchange in... 

Finally, silyl-silyl valence isomerization has been invoked by Wanna-gat to explain certain transformations in silylated hydrazines (55) in which both stationary atoms are nitrogen [Eq. (12)]. No rate data or... 

C27H63Si4] Me SHSi f-Bu / 3 Reduetion of tris [di -butyl (methyl) silyl] silyl sodium with GeCE-dioxane eomplex / hexane 2.0256 02Sekl... 

Keeping in mind the possible variety of substrates used for silylation, it is not so simple to reliably characterize the differing activity of various silylation reagents. So far the typical form of presentation of such information includes a semiquantitative description (e.g., -I-+ —good silylation + —silylation is possible, —no reaction... 

Silyl-silylation. The Pd(PhCN)2Cl2-catalyzed reaction of l,l,2,2-tetramethyl-3,4-di(prop-2-ylidene)-l,2-disilacyclo-butane with dimethyl acetylenedicarboxylate gave a mixture of disilacyclohexene and disilacyclooctane (eq 125)7 The reaction with phenyl or diphenylacetylene afforded a mixture of disilacyclohexene and tetrasilacyclooctane (eq 126)7 ... 

The preparation and structure of (tert-butylimino)(tris(trimethyl-silyl)silyl)borane have been reported and whilst the molecule does not contain a boron-carbon bond it is of relevance to the subject of this report. 

The chemistry of acylmethylidynetricobalt nonacarbonyl compounds has received attention, especially their reduction to the corresponding alcohols. This conversion may be accomplished in good yield by a hydro-silylation/silyl ether solvolysis sequence (Seyferth et al., 1974b) ... 

The volatility of many compounds can be increased by silanization, so as to improve their amenability to gas chromatographic separation. Trimethylsilyl-imidazole in pyridine is a typical reagent, useful for carbohydrate silylation. Silylating agents also find use... 

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