Disilene, elimination product

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%). 

It was assumed that an a-fluorosilyl potassium species was formed initially, and that this subsequently underwent a self-condensation reaction. The eventual product (1) displayed both nucleophilic as well as electrophilic character, which was demonstrated in various derivatization reactions. Although it contains fluorine and potassium atoms in close proximity, the compound displayed a remarkable thermal stability. Even at 80 °C, potassium fluoride elimination occurred only sluggishly. Attempted transmetalation reactions with various metal halides, though, caused an immediate elimination of metal fluoride and the formation of tetrakis(trimethylsilyl)disilene. The latter can be trapped in cycloaddition reactions [5] or, in the absence of trapping reagents, it dimerizes to a cyclotetrasilane (Scheme 2) [6]. 

Solely the photolysis of 1 with the heterocyclic, five-membered ring compounds fliran, thiophene and selenophene furnished other products instead of the respective siliranes (see below). The reactions of tetra-t-butyldisilene 3 with alkenes gave rise to a more complex palette of products. In the cases of cyclopentene and cyclohexene, no reactions with the alkene were observed. Instead, compounds 24, 25, 27, and 28 were formed these results can be rationalized in terms of a dimerization of the disilene with / elimination of isobutene 26 and subsequent reactions of the disilene and the silylene with 26 [7, 8],... 

Hydrido-disilanyl complexes L M(H)(SiR2-SiR2H) are interesting because H2 elimination could support a possible 3-Si-H elimination and result in disilene complexes or products derived thereof Analogous to the synthesis of the well-known hydrido-silyl complexes... 

Certainly, the product yields depend on the relative rates of the insertion and elimination processes. For X = Br or 1, only rran -configurated disilenes are formed which may further react with NaR into 1. For X = Cl, in addition to a disilene 9, a cyclotri- and -tetrasilane 10 and 11 may be isolated. Obviously, they react with NaR to give a cyclotrisilene 10a or the silatetrahedrane 1. 

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