Silicon-oxygen-nitrogen rings

When a chain or ring system is composed entirely of alternating silicon and oxygen atoms, the parent name siloxane is used with a multiplying affix to denote the number of silicon atoms present. The parent name silazane implies alternating silicon and nitrogen atoms multiplying affixes denote the number of silicon atoms present. 

Among the reactions applied in the synthesis of fullerene derivatives cycloaddition reactions such as [2 + 1]-, [2 + 2]-, [3 + 2] and [4 + 2] cycloadditions play a dominant role. In these reactions ring-fused fullerene derivatives are obtained, at least with incorporation of heteroatoms such as oxygen, nitrogen, or silicon. In this section photochemical reactions leading to cycloalkyl ring-fused fullerene adducts will be presented. Photocycloaddition reactions leading to C6o-fused heterocycles will be discussed later. 

CARBON-SILICON-SULFUR (or OXYGEN or NITROGEN) RINGS... 

Figure 4. Calculated structure for Si04H4[H3(18-azacrown-6)] with hydrogen bonds shown as open lines (a) viewed in direction within the macrocycle ring, (b) viewed perpendicular to the macrocycle ring. Size of circles indicates atom types ranging from silicon (largest) to oxygen, nitrogen, carbon, and hydrogen (smallest) respectively.

The [5,5]-fused bicyclic ring system with one fusion nitrogen atom and three additional heteroatoms in a 2 1 distribution over both ffve-membered rings (2N1) is the origin of a great number of structures. The additional heteroatoms are mainly nitrogen, oxygen, or sulfur, and less commonly phosphorus or silicon atoms. 

The two five-membered rings of this spirocyclic X. Si-silicon(IV) complex each contain two oxygen atoms, one nitrogen atom, one carbon atom, and one (pentacordinate) silicon atom. As shown in Scheme 8, this compound was prepared by analogy to the synthesis of the related A, Si-silicates 10-16. Thus, treatment of (MeO)3SiCH2NMe2 with two mole equivalents of acetohydroxamic acid in acetonitrile at room temperature yielded 28 in 80 % yield as a crystalline solid [5]. The formation of this compound can be understood in terms of a reaction of (MeO)3SiCH2NMe2 with the 1,2-diol acetohydroximic acid, which is a tautomer of acetohydroxamic acid. 

---