Disilene addition

Finally, the chemical properties of the new structures available from disilene addition reactions have hardly been touched. In future developments, theoretical and experimental studies are likely to proceed together and complement one another, as they have from the beginning days of this research. 

Silylene and Disilene Additions to the Double Bonds of Alkenes, 1,3-Dienes, and Hetero-l,3-dienes... 

Silylene and Disilene Additions to Double Bond Systems 311... 

These recent observations suggest that thermal dissociation of disilenes into silylenes may be a more general phenomenon than has previously been thought. Additional examples are likely to be reported in the future. 

Recently, however, Sekiguchi et al. reported that the transient disilene ( )- and (Z)-PhMeSi=SiMePh reacted with alcohols in a syn fashion with high diastereoselectivity, the extent of which depended on the concentration and steric bulk of alcohols used.31 These facts suggest that in the reaction with a sterically hindered disilene like (Z)-3, the addition of alcohols might also proceed diastereoselectively under appropriate reaction conditions. 

At this time, although details remain to be elucidated, it seems that most of the main kinds of reactions of disilenes, have been discovered. These have led to numerous new classes of cyclic compounds, some with unprecedented and beautiful structures. In addition, the chemical bonding in disilenes has received serious study and is at least partially understood. 

Regarding this proposal, it should be noted that while 1,1-eliminations on Si-Si-C units to generate silylenes are well known thermal processes (54) the photochemical variant seems not to have been described. The rearrangement of silylsilylenes (4) to disilenes is known to be rapid (55), and silyl radical addition at the least hindered site would produce the observed persistent radical. Preliminary evidence for the operation of 1,1-photoelimination processes in the polysilane high polymers has been obtained, in that the exhaustive irradiation at 248 nm of poly(cyclohexylmethylsilane) (PCHMS) produces —10-15% volatile products which contain trialkylsilyl terminal groups. For example, the following products were produced and identified by GC— MS (R=cyclohexyl,R = methyl) H(RR Si)2H (49%), H(RR Si)3H (19%), R2R SiH (2%), R 2RSiRR SiH (5%) and R2R SiRR SiH (7%). 

However, at elevated temperatures, the disilene (/-Uu (Si)(k)SiSi( R)(Si/-Bu () 721 undergoes isomerization to give the 1,2-disilyl benzene derivative 730, which can be rationalized in terms of a C-H addition to the Si-Si double bond (Scheme 97). 

The chalcogenolysis of the disilene 721 with N20, S, Se, and Te results in formation of the three- and four-membered heterocyles 748-752 (Scheme 98). The addition of the isonitrile /-BuNC to the disilene 721 affords... 

This disilene undergoes Diels. Alder reaction with 1, 3 diene addition to acetylene and a single example of reaction with a carbonyl system. 

Figure 8.2b corresponds to the superimposition of signals from at least two persistent paramagnetic species. The nature of these species is still unclear even if the g factors are consistent only with silyl radicals carrying three silyl groups as in 6. Mechanistic schemes for their formation could be suggested based on the addition of transient silyl radicals to the transient disilenes generated photolytically [14]. 

The first 1,2-disilacyclobutene (82) was prepared in 1973 by the gas phase reaction of dimethylsilylene and 2-butyne (73JOM(52)C21). It probably results through silylene insertion into the intermediate silacyclopropene (Section 1.20.3.4), but silylene dimerization followed by addition to the alkyne is also suggested (76JA7746), since (82) is formed in good yield if the disilene is generated directly (Scheme 127) (78JOM(162)C43). 

Mechanism and structures in alcohol addition reactions of disilenes and silenes... 

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