Rearrangements carbon- silicon bond

This excellent method of oxidative cleavage (/) of carbon-silicon bonds requires that the silane carry an electronegative substituent (2), such as alkoxy or fluoro. Either hydrogen peroxide or mcpba may be used as oxidant, and the alcohol is produced with retention of configuration (3). Fluoride ion is normally a mandatory additive in what is believed to be a fluoride ion-assisted rearrangement of a silyl peroxide, as shown below ... 

A carbon-silicon bond can be cleaved by a process of (3-methyl elimination. Thermolytic rearrangement of platinum(II) complex 76 yields methyl-plati-num(II) complex 78 [93]. Generation of (ri2-silene)platinum intermediate 77by (3-methyl elimination is followed by migration of the other silylmethyl ligand to the silicon terminus of the r)2-silene ligand. 

Under slightly different conditions both disilene extrusion and rearrangement were observed. Evidence was presented that the rearrangement occurred as the result of radical cleavage of a carbon-silicon bond, followed by a 1,2-silyl migration in the resulting allylsilane system87 (equation 54). 

The stabilization of a carbocationic center by an adjacent carbon-silicon bond (sometimes called the f- ect) can be used to control the course of carbocation rearrangement and carbocation-induced cyclizations. 

Ever since their discovery in 1967, there has been interest in the kinds of rearrangements that silenes might undergo and curiosity about the behavior of the silicon-carbon double bond as compared to that of the carbon-carbon double bond. 

Brook et al. 5X1 observed such reactions during the formation of siienes by photolysis. Using radiation with A > 360 nm, they photolyzed acylsi-lanes such as 127, which bears a mesityl group attached to the carbonyl carbon. On prolonged photolysis of the initially formed silene 128, the C—H bond of the ortho methyl group of the mesityl group added to the silicon-carbon double bond to form the benzocyclobutane 129. Alternatively a 1,5-H shift would lead to the species 130, which would also yield the benzocyclobutane on electrocyclic rearrangement. 

Ishikawa71191 has described the thermal rearrangement at 280°C of the silacyclopropene 160 to the silaallene 161. It was suggested that a 1,2-trimethylsilyl rearrangement from silicon to carbon could lead to the sily-lene 162 on insertion into the C—H bond of one of the trimethylsilyl methyl groups 162 would give 163, which was isolated in 49% yield. 

When similar photolysis of 11 in the presence of MeOD was carried out, again the product whose NMR reveals the resonance due to the Si-H proton was observed. The relative ratio of the Si-H and CH3-0 protons was identical with those of the products obtained in the presence of non-deuterated methanol. The formation of the methoxysilyl group can be understood by the addition of methanol across the silicon-carbon double bonds. H NMR spectra of all photoproducts obtained from the photolyses of 11 in the presence of methanol reveal no resonances attributed to the cyclohexadienyl ring protons. This indicates that the photochemical degradation of the polymer 11 gives no rearranged silene intermediates, but produces... 

Compounds with two or more silicon atoms directly attached to one another, subdivided into sections based first on the number of silicon atoms and then on the carbon functionality attached to the silicon atoms. Frequently, but not exclusively, the main photochemical behavior involves homolysis of a silicon-silicon bond yielding silyl radicals, but in some cases silylenes result directly from the photochemistry. The resulting compounds are frequently the products of a molecular rearrangement. 

Decamethylsilicocene (82) can be regarded as an electron-rich silicon(II) compound containing a hypercoordinated silicon atom. The chemistry of 82 is determined by (a) the nucleophilicity of the silicon lone-pair (cr-donor function towards electrophiles, oxidative-addition processes) and (b) the weakness of the silicon-(cyclopentadienyl)carbon jr-bond rearrangement, Si—C bond cleavage). In the following section, the chem-... 

Similarly, when silene 2a is generated in presence of excess tris(trimethylsilyl)silyllithium, the lithium silanide is added across the silicon-carbon double bond to give an organolithiiun intermediate, which undergoes a rearrangement, a l,3-Si,C-trimethylsilyl migration, resulting in formation of a lithium silanide, which is trapped with chlorotrimethylsilane to yield the polysilane 7. The H-silane 8 is obtained as the protonation product after usual hydrolytic work up (Eq. 4-5). 

In other cases where silicon is attached to both ends of the carbon-carbon triple bond, related rearrangements and products are observed, with the intermediate silaallene evidently undergoing head-to-head dimerization51,52. The resulting disilacyclobutene is itself susceptible to further photochemical isomerization (equation 30). Recently... 

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