Thermal Rearrangement of 1,2-Bis Silyl Derivatives

In this section the thermal behavior of bis(silyl) compounds with respect to reversible degenerate valence isomerization 4 5 is de- 

All three classes of compounds fulfill the above-mentioned requirements concerning empty li-orbitals in both migrating groups. However, 

The observation of a degenerate dyotropic exchange in silyl silylmethyl ethers [Eq. (3)] requires labeled silyl groups. Thus, syntheses were designed with Si = trimethylsilyl and Si = Dg-trimethylsilyl as well as Si - trimethylsilyl and Si = dimethylphenylsilyl (9, 10). 

In order to avoid undesired side reactions, such as silanol elimination, compounds were chosen with R = aryl. Such substituents were also expected to facilitate the rearrangement process, partly owing to electron withdrawing effects as discussed in Section I, and partly owing to the increased reactivity of benzyl bonds in general (//). The synthesis of 6, 8, 10, 12, and 14 required several different methods and has been described in detail 10). 

The thermolysis of 8, 10, and 12 at 140°-175°C in inert solvents (e.g., benzene) does indeed afford the rearrangement products 9, 11, and 13, respectively, the reactions leading to equilibria that are easily detected by H— NMR spectroscopy 10). Equilibrium is reached rapidly, e.g., within 2 hours at 175°C. Heating an independently synthesized sample of 11 leads to the same equilibrium as 10. All reactions are clean, no traces of side products being observed. The fluxional behavior of 8 and 12 is strictly thermoneutral, i.e., the equilibrium constants have the value K = 1.0 within experimental error. The valence isomerization 10 11 is 

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