Tetrakis trimethylsilyl tetrahedrane

Tetrakis(trimethylsilyl)tetrahedrane (12) is a colorless crystalline solid, mp 202°. Unlike tetra-7-butyltetrahedrane (5), wliich melts at 135° with isomerization to the... 

Tetralithiotetrahedrane is apparently unknown. The synthesis of a fully-characterized monolithio tetrahedrane, tris(trimethylsilyl)tetrahedraityllithimn (13), was reported in 2003 by Sekiguchi and Tanaka [41], who prepared it by reacting tetrakis(trimethylsilyl)tetrahedrane 12 [32, 33] with methyllithium. 

Let ns apply these principles to tetra-i-butyltetrahedrane, tetrakis(trimethylsilyl) tetrahedrane, and tetrahedrane itself. Unreferenced calcrrlations are by the author, and some of these results are strmmarized in Table 6.1. Note that calcrrlations designed to address kinetic stability directly, by examining transition states for interconversion of diradicals (below), seem to be limited to the parent molecule. 

Table 6.1 Energies from B3LYP/6-31G calculations on tetrahedranes and cyclobutadienes (by the author, using Gaussian 03). Note that for the tetra-t-buty and the tetrakis(trimethylsilyl) systems the tetrahedrane is calculated to lie below the cyclobutadiene in energy, but for the parent molecules the tetrahedrane is calculated to lie above the eyelobutadiene...

As stated above, B3LYP/6-31G calculations place tetrakis(trimethylsilyl)tetra-hedrane about 37kJ mol below the cyclobutadiene [33]. This calculated energy difference would have made one reasonably confident of the greater thermodynamic stability of the tetrahedrane. 

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