Kleine Ringe, 78. Tri‐ tert ‐butyl(trimethylsilyl)cyclobutadien und Tri‐ tert ‐butyl(trimethylsilyl)tetrahedran

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.