Disiliranes reactions

The photochemical addition of some cyclic oligosilanes to Ceo has also been found interesting. Scheme 8.8 shows some examples of such a transformation. Irradiation (X > 300 nm) of a toluene solution of disilirane 36 with Ceo afforded the fullerene derivative 37 in a 82% yield [37]. The reaction mechanism is still unknown. When toluene is replaced by benzonitrile the bis-silylated product of the solvent was obtained in good yields. In these experiments a photoinduced electron transfer between 36 and Ceo is demonstrated, indicating the role of Ceo as sensitizer [38]. The photoinduced reactions of disilirane 36 with higher fullerenes such as C70, Cv8(C2v)and CuiDi) have also been reported... 

Photochemical reaction with disiliranes leads to a [3-i-2]-cycloaddition (Section 4.3.9). Disilylcyclobutanes [67, 68] and cyclotetrasilanes [68, 69] react in a similar fashion. In both cases the four-membered ring is photolytically cleaved and a diradical is formed. This diradical adds in a formal cycloaddition to the [6,6] double bond of CgQ. The cycloadduct 20 (R = 4-MeCgH4) can be obtained from 19 in 13% yield, but it is not the major product (Scheme 6.12). Rearrangement of an H atom leads to 21 in 46% yield. The product distribution depends strongly on R. Changing R from 4-MeCgH4 to phenyl leads to an exclusive formation of 21. 

Compounds with a Si=Si or Ge=Ge bond (i.e., disilenes and digermenes) can be isolated when the double bond contains bulky substituents. Only a few cycloaddition reactions with diazo compounds are known, and two reaction modes have been observed. One of the paths leads to the formation of disiliranes 184 (242) and digermiranes 185 (243) (Scheme 8.42), probably by ring contraction of an initially formed [3 + 2] cycloaddition product. The other path involves a 1,1-cycloaddition of the diazoalkane to give disilaaziridine 186 (244) and digermaazir-idine 187 (245). This nitrene-like reactivity is rather uncommon although some intramolecular examples are known (see Section 8.6.1). 

Irradiation of a toluene solution of l,l,2,2-tetramesityl-l,2-disilirane 116 resulted in the formation of the [6,6]-closed l,l,3,3-tetramesityl-l,3-disilolane 117 with Cs symmetry (Scheme 49) [274a], The reaction is surpressed by addition of DABCO and 1,2,4,5-tetramethoxybenzene and completely inhibited by addition of rubrene. As rubrene is known to be an effective triplet quencher, there is... 

One of the most fascinating reaction modes of disilenes is the ready formation of disiliranes, three-membered ring systems containing two silicon atoms and one heteroatom in the ring, which are hardly accessible by other routes. They are mostly formed by [2 + 1] cycloadditions of atoms or molecular fragments to the Si=Si double bond. One of the few examples of other accesses to this ring system is the reaction of AMithio-2,4,6-trimethylanilide 53 with the disilane 52, which affords the azadisilacyclopropane 54 in modest yield (equation 8)75. 

The reactions of disilenes with diazomethane derivatives are similarly inhomogeneous. While the reaction of diazomethane with the disilene 10 provides the disilirane 6886, that between p-tolyldiazomethane and 9 yields the compound 6987. 

As part of their studies of reactions between fullerenes and dimetalliranes (Section 1.17.4.5), Ando eta/, determined oxidation potentials for disilirane 34b (-1-0.81 V vs. saturated calomel electrode (SCE)) <19930M1514> and diger-mirane 38a (0.72 V vs. SCE) <19900M2061>. 

As shown in Equation (48), the bicyclic compound converts to disilirane 75 upon brief photolysis with low-energy light. The authors report this conversion pair may be cycled repeatedly without side reactions <19850M1487>. 

Strained Si-Si a bonds are also known to act as good electron donors [263-265]. Photoinduced electron transfer from strained disiliranes such as 1,1,2,2-tetramesityl-1,2-disilirane to Ceo occurs in benzonitrile to give a transient absorption spectrum at 1080 nm due to Ceo obtained by 532 nm laser flash photolysis of Ceo in the presence of disilirane [266]. The photochemical reaction of Cso with the disilirane in benzonitrile afforded the 1 1 and 1 2 adducts of disilirane and benzonitrile in good yields. The structures of the corresponding adducts were determined by X-ray crystallographic analysis [266]. These adducts were also obtained in good yields in the presence of catalytic amounts of Ceo- Thus, Ceo acts as a photoinduced electron-transfer catalyst as shown in Scheme 9. 

In a related manner, disilacyclopropane (disilirane) derivatives can be synthesized by the reaction of disilene (322) with other reactive compounds. Thus, via diazomethane one can add a methylene component to 322 to form the corresponding 1,2-disilacyclopropanes (323). These are versatile intermediates which give rise to a large variety of compounds (vide infra). One type of application, the conversion of 323 with m-CPBA to a l,3-disila-2-oxacyclobutane (disilaoxetane) derivative (324), is shown in equation 147171. 

Akasaka et al. reported that the photoexcited Ceo generates [2 + 3] cycloadducts with the disiUranes, such as 1,1,2,2-tetramesityl-l,2-disilirane via the electron-transfer process (Scheme 2) [61]. It is interesting to note that the adduct formation was not observed by the thermal reactions in the dark. The photoadduct formation occurs in the nonpolar toluene, suggesting that the exciplex is a plausible intermediate. When the reaction proceeds in benzonitrile, the generated radical cation of the disiUrane forms 1 1 or 1 2 adducts with benzonitrile in this case, Cgg acts as a photocatalyst... 

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