SILICON-COMPOUNDS WITH STRONG INTRAMOLECULAR STERIC INTERACTIONS .43. FORMATION AND MOLECULAR-STRUCTURES OF 2 ISOMERIC DISILACYCLOBUTANEDIIMINES

In the presence of mesityl isocyanide (7) or 2,6-diisopropylphenyl isocyanide (8), photolysis of hexa-tert-butylcyclotrisilane (1) gives dark red crystals of N,N'-dimesityl-2,2,4,4-tetra-tert-butyl-2,4-disilacyclobutane-1,3-diimine (9) and violet crystals of N,N'-bis(2,6-diisopropylphenyl)-2,2,4,4-tetra-tert-butyl-2,4-disilacyclobutane-1,3-diimine (10), respectively. In the latter case small amounts of the isomeric N,N'-bis(2,6-diisopropylphenyl)-3,3,4,4-tetra-tert-butyl-3,4-disilacyclobutane-1,2-diimine (11) are also isolated as green crystals. The X-ray structure analysis of 10 shows that the ring atoms, and the exocyclic nitrogen atoms lie almost exactly in one plane. The two aryl groups are arranged trans to each other. The X-ray structure of the ring 11, however, reveals a folded C2Si2 framework with the exocyclic nitrogen atoms being oriented in opposite directions. The aryl groups adopt the syn, anti conformation.