Disilanyl

In a similar way, a set of disilanyl and polysilanyl complexes has recently been synthesized and exposed to photochemical deoligomerization reactions [137]. The photolytically obtained reactive silylene complexes have been identified by trapping experiments [138, 139]. 

An unexpected ds,ds to trans,trans isomerization of a disilanyl analog of 1,5-cy-clooctadiene was observed with 1 as the catalyst [241]. 

The TT-electron system-substituted organodisilanes such as aryl-, alkenyl-, and alkynyldisilanes are photoactive under ultraviolet irradiation, and their photochemical behavior has been extensively studied (1). However, much less interest has been shown in the photochemistry of polymers bearing TT-electron substituted disilanyl units (2-4). In this paper, we report the synthesis and photochemical behavior of polysiloxanes involving phenyl(trimethylsilyl)-siloxy units and silicon polymers in which the alternate arrangement of a disilanylene unit and a phenylene group is found regularly in the polymer backbone. We also describe lithographic applications of a double-layer system of the latter polymers. 

The trimeric platinum(O) complex [Pt3(CNBu )6] undergoes a double oxidative addition reaction with 2,2-bis(disilanyl)dithiane to give tetrakis(organosilyl)bis(/-butylisocyanide)platinum(IV) complexes.53 The Si—Ge bonds in bis(silylgermyl)dithiane are also cleaved by [Pt3(CNBu )6] giving analogous platinum(IV) complexes with Pt—Si and Pt—Ge bonds.53... 

In contrast to its organic analog, o-(disilanyl)-phenylene,46 the reaction of 41 with ethanol leads to cleavage of a Si—C bond rather than a Si—Si bond. 

A unique bis-silylation system, in which a bis(silyl)palladium intermediate is generated via recombination of two Si-Si bonds, has been developed.8,97 A bis(disilanyl)dithiane reacts with alkynes in the presence of a palladium/ isocyanide catalyst, giving five-membered ring bis-silylation products in high yield with elimination of hexamethyl-disilane (Scheme 14). The recombination, that is, bond metathesis, is so efficient that no product derived from direct insertion of acetylene into the Si-Si bonds of the bis(silyl)dithiane is formed at all. 

Table 1 Intramolecular bis-silylation of disilanyl ethers of substituted homoallylic alcohols in the presence of a palladium/ f-OcNC catalyst... 

Palladium-catalyzed bis-silylation of a,/ -unsaturated ketones using bis(disilanyl)dithiane affords seven-membered ring silyl enol ethers in high yields via 1,4-addition (Equation (48)).8,97 Application of this reaction to a,/ -unsaturated esters and nitriles gives five-membered ring 1,2-addition products in good yields (Equation (49)). 

In this method, attack by an anionic initiator ( -BuLi, potassium alkoxides/cryptand[2.2.2],62 or silyl anions in benzene)63 occurs regioselectively on the less hindered silicon of 9, resulting in an anionically terminated disilanyl-lithium which then attacks another monomer at the less hindered silicon atom. The process continues rapidly (the reaction is usually complete within a few minutes) in a living polymerization fashion to yield 10 on alcohol workup. 

A novel intramolecular bis-silylation of propargylic disilanyl ethers followed by a Peterson-type syn elimination provides access to a variety of allenylsilanes (Table 9.36) [57]. The elimination is initiated by treatment of the presumed four-membered siloxane intermediate with BuLi. This intermediate could not be isolated, but spectral data were in accord with the assigned structure. The cycloaddition and elimination steps were shown to take place stereospecifically (Eq. 9.48). 

SILICON DIOXIDE HEXACHLORODISILANE HEXAFLUORODISILANE DISILANYL CHLORIDE DISILANE... 

H5CI DISILANYL CHLORIDE 50.2854 -2.4890E+03 -1.8081E+01 2.1374E-02 -1.0671E... 

SCHEME 4. Self-condensation reaction of [(tert-butoxydiphenyl)silyl]lithium (20) to give [2-(tert-butoxy)disilanyl]hthium derivative 21... 

The study also suggests that the reaction proceeds via S/ 2-type displacement with retention of configuration of the silicon in the nncleophilic part bnt with inversion of configuration of the silicon in the electrophihc part. However, the final products, [2-(alkoxy)disilanyl]lithium and lithium methoxide, were in good agreement with experimental results. The verification of the stereochemistry is of future interest. 

Disilanyl enol ethers (22) are the main product of the reaction of alkyl ketones with photochemically generated phenyltrimethylsilylsilylene (Scheme 30) (77JOM(135)C45). They could result from silylene insertion into the enol O—H bond, particularly as many have been isolated from dodecamethylcyclohexasilane and alkyl ketones or aldehydes on photolysis (Scheme 31) (78CL609). 

The photolysis of tris(trimethylsilyl)phenylsilane in the presence of a series of alkynes alforded the silacyclopropene through silylene addition to the triple bond. Those obtained from monosubstituted alkynes underwent photochemical isomerization to the disilanyl-alkyne through a 1,2-hydrogen shift (Scheme 48) (80JOM(190)117). Disubstituted alkynes form silirenes that can be isolated by preparative GLC. 

Reaction of bis(disilanyl)methane gives only trace amounts of the five-membered cyclic product, 2, and higher yield (76%) of a mixture of the insertion products 3 and 4. Substitution at the methylene tether leads to formation of 2 in good yield, with essentially no product from the insertion of two equivalents of phenylacetylene. Only mixtures of 3 and 4 are obtained from reaction of bis(disilanyl)alkanes tethered by longer chains. 

Ito and co-workers have also used the Pd(OAc)2/t-alkyl isocyanide catalyst to affect the double silylation of carbon-carbon multiple bonds in an intramolecular system to yield silacarbocycles.59 Alkenes or alkynes that are tethered to a disilanyl group through a carbon chain, an ether linkage, or an amine functionality undergo intramolecular addition of the disilane moiety to the multiple bond. Activation of the disilane by the presence of electron-withdrawing groups on silicon is not necessary for the reaction to... 

A wide variety of disilanyl-substituted terminal alkenes undergo regio-and stereoselective intramolecular double silylation to yield cyclic bis(silyl) ring closure products [Eq. (16)].59abe... 

Similar results are observed in the intramolecular double silylation of alkynes.59cd Both terminal and internal alkynes lead to exocyclic olefin formation. Interestingly, the reaction is not successful for internal alkynes tethered to a disilanyl functionality by a four atom chain, but is accomplished when four atoms link a disilanyl to a terminal alkyne. Internal alkynes with ester or olefin in conjugation with the C-C triple bond undergo chemoselective double silylation, and alkynes with substituents in the tether are also good substrates for the reaction. 

Silylstannylation is also observed in the Pd(PPh3)4-catalyzed reaction of alkynes with disilanyl stannanes, in which both Si-Si and Si-Sn bonds are present. The alkynes undergo insertion into the Si-Sn bond, to regio-and stereoselectively yield (/8-disilanylalkenyl)stannanes [Eq. (25)].73 With terminal alkynes, the stannyl group adds regioselectively to the internal carbon atom. Aliphatic alkynes are not reactive in this system. 

Double silylation is also observed in the reaction of a,/3-unsaturated ketones with a bis(disilanyl)dithiane, resulting in high yields of cyclic silyl enol ethers [Eq. (65)].58 The catalyst for this reaction is a cyclic bis(silyl)pal-ladium(II) bis(ferf-butyl isocyanide) complex. Analogous reactions of ester... 

LiSi4C21H5, Lithium, tris(tetrahydrofuran) [2,2,2-trimethyl-1,1 -bis(trimethylsilyl) disilanyl]-, (T-4)-, [81859-95-2], 31 163 04C12MoS2C4H12, Molybdenum, dichloro-dioxobis[sulfinylbis[methane]]-, [54183-28-7], 31 246... 

The rate of hydrolysis of the disilanyl benzyl bromide 28 is about 1 x 105 larger than that of 2953. Thus the -effect of 28 is similar in magnitude to 26. 

---