Small rings, 93 - 1,2,3,4-tetra-tert-butyl-4-trimethylsilyl-4-sila-2-cyclobuten-1-yl: A quantum mechanical and ESR study

Trisilane 7 has been synthesized as a potential photochemical precursor of tetra-tert-butylsilatetrahedrane (5) and/or tetra-tert-butylsilacyclobutadi ene (6), Astonishingly, only one Si,Si bond is broken upon irradiation of 7 and the silacy- clobutenyl radical 9 can be identified as the reaction pro duct. The structure of radical 9, which in the absence of oxygen is persist ent even at room temperature, has been elucidated by comparison of its expe rimental and calculated ESR spectra.