Disilenes stable

Similar photolysis of trisilanes may be used to generate other stable disilenes. Stable disilenes can also be synthesized by photoinduced fragmentation of cyclotrisilanes, and, in some cases, by dehalogenation of dihalo-diorganosilanes. ... 

Disilenes, containing the grouping >Si=Si<, can be isolated as thermally stable yellow or orange crystalline compounds provided that the substituents are sufficiently large to prevent... 

Rarely has any research area so continuously been in the focus of scientific interest as organosilicon chemistry. A rapidly increasing number of publications, review articles, and scientific conferences reflects this development. The initiating factor was the spectacular discovery of stable molecules with SiSi double bonds, disilaethenes (disilenes) by R. West and S. Masamune in 1981 and 1982 [1-7]. 

Recently, a variety of silylenes were generated and characterized by matrix isolation techniques. The observed loose donor adducts between silylenes and the matrix molecules (THF, CO) are only stable at very low temperatures. Melting of the matrix induces polymerization of the silylenes which proceeds through disilenes. However, 0->Si transfer reactions do not occur only in the case of 1-methyl-THF has an insertion of the silylene into the C —O bond been observed [155-158],... 

The chemistry of the disilenes (disilaethenes) has developed very rapidly since the discovery of stable compounds. It was an obvious challenge to explore also the possibility of a n-coordination of disilenes to transition metals. According to the Dewar-Chatt-Duncason bonding model, a high stability for a disilene complex should result. 

However, it was about 8 years after the first synthesis of tetramesityldisilene before stable coordination compounds became known. The main reason for this is the kinetic stabilization of the known disilenes by bulky substituents, which effectively prevents the coordination of the double bond to a metal fragment. Thus, a direct coordination of stable disilenes appeared to be reasonable only if metals with very low coordination numbers were used. 

Evidence for a 7t-coordination was obtained through the reaction of various disilenes with Hg(OCOCF3)2, a reaction which leads regioselectively to bis(tri-fluoracetyl)disilanes. A disilene n-complex (79), which is stable up to — 50 °C, could be identified as an intermediate by spectroscopic methods. 

A particularly elegant pathway to stable coordination compounds of disilenes has been found with the reaction of the Pt-phosphine complex 80 with 81 ab, which... 

Kira, Mitsuo, Progress in the Chemistry of Stable Disilenes. 

After decades of unsuccessful attempted syntheses, Gusel nikov and Flowers in 1967 reported the first compelling evidence for the existence of silenes, compounds containing a double bond between silicon and carbon. This initiated a renewed interest in the synthesis and behavior of stable silenes,8 disilenes,b iminosilanes,c phosphasilenesd and their heavier homologs. 

The classic problem of the silicon-silicon double bond dates back at least to the early part of this century, when F. S. Kipping and his students attempted unsuccessfully to synthesize disilenes. Evidence for the probable transient existence of disilenes began to appear in the 1970s, but it was the isolation of the stable disilene 1 in 19811 that opened up modem disilene chemistry. The early history of this discovery has been recounted in a review2 several other reviews covering Si=Si double bonds have been published.2 5... 

The method employed for the first synthesis of stable disilene l,1 the photolysis of linear trisilanes, has been the most widely used synthetic method for disilenes. However, photolysis of cyclic trisilanes and dehalo-genation of dihalosilanes and 1,2-dihalodisilanes are also good routes in some cases (Table I). 

The first synthesis of a disilene by photolysis of the corresponding cyclic trisilane was reported by Masamune et al. in 1982.14 This method has been adapted for the synthesis of a variety of stable and marginally stable disilenes (Eq. 6).15-20 More recently, Kira et al. synthesized the first example of a stable tetrakis(trialkylsilyl)disilene 22 by this method.21... 

Photolytic [4+2] cycloreversion of a disilabicyclo[2.2.2]octadiene precursor is considered to be a general method for the synthesis of disilenes of varying stability. Several examples of this method have been reported (Eq. 9).27-31 First used in reactions producing an unstable disilene, Me2 Si=SiMe2,27 this method is also successful for synthesizing the marginally stable -Bu2Si=Si(t-Bu)2,28 However, it has not yet been applied to the synthesis of disilenes that are fully stable at room temperature, probably because the appropriate precursors are inaccessible. 

In general, an increase in steric demand of the substituents on silicon atoms appears to lead to the formation of more stable disilenes. For example, 3, which has two f-butyl groups, is more stable than 1 while 4, which has two 1-adamantyl groups, is more stable than 3.9 Disilene 4... 

The stable disilenes are pale yellow to orange-red in the solid state and have electronic absorption maxima in solution between 390 and 480 nm (Table I). The longest wavelength absorptions have been assigned to the ir-ir transition.28... 

Thermochromism was already noted for the first stable disilene l.2a In dialkyl- or bis(trimethylsilyl)diaryldisilenes, the size of the aryl groups affects the thermochromism Tip-substituted ones (9,10) are thermochro-mic,10 while Mes-substituted ones (3,4) are not.9 Interestingly, tetrakisftri-alkylsilyl)disilanes 22 and 23 are highly thermochromic hexane solutions of 22 and 23 are light yellow below 0°C but dark red above 50°C.21 These observations were interpreted in terms of a thermal equilibrium between the bent and twisted conformations. Compound 24, having an absorption band at 480 nm, is dark red in solution even at room temperature. 

CH=CH2)2, which was taken as a model for tetraaryldisilenes.47 While these values are all higher than those for tetraccordinate silicon, they are scattered and not very close to the experimental values for stable disilenes, as shown in Table II. 

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