Small Rings, 78[1]. ‐ Tri‐tert‐butyl(trimethylsilyl)cyclobutadiene and Tri‐tert‐butyl(trimethylsilyl)tetrahedrane The chemistry of diazo(1,2,3‐tri‐tert‐butylcyclopropenyl)(trimethylsilyl)methane (6) is unexpectedly diverse. Upon irradiation it fragments exclusively into the acetylenes 7 and 8. Flash thermolysis, on the other hand, gives — aside from the two acetylenes — tri‐tert‐butylazete (10) and trimethylsilyl cyanide (11). Upon heating 6 presumably isomerizes via betaine 17 to Dewar‐diazabenzene 13 — which is split into 10 and 11 — and diazabenzvalene 18. This reaction course is supported by the isolation of the carbonyliron complexes 15 and 16, — The CuCl‐catalyzed thermal decomposition again follows a different route. Under these conditions tri‐tert‐butyl(trimethylsilyl)cyclobutadiene (5) is formed, probably as a weak CuCl complex. Only after addition of ethylenebis(diphenylphosphane) free cyclobutadiene 5 can be isolated. Upon irradiation of 5 a quantitative isomerization to tri‐tert‐butyl(trimethylsilyl)tetrahedrane (29) occurs. This second, spectroscopically unequivocally confirmed tetrahedrane melts at 179°C. In solution the isomerization to cyclobutadiene 5 starts at about 160°C. That means, it is thermally even more stable than tetra‐tert‐butyltetrahedrane.
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Maier et al. (1994) studied this question.