Cycloaddition Reactions of (Di)tetrelenes

This thesis examines a variety of cycloaddition reactions of multiply-bonded heavy analogues of carbon. With the aid of a mechanistic probe, the mechanism of the addition of alkynes to a germene and a digermyne was examined. In both cases, the addition does not involve the itermediacy of an vinyl radicals or cations. The addition of a variety of nitro compounds to tetramesityldisilene and tetramesityldigermene was examined. The facile formation of the novel 1,3,2,4,5-dioxazadisil- and digermolidine ring systems, respectively, was observed. In general, 1,3,2,4,5-dioxazadisilolidines and -digermolidines isomerize under thermal conditions to the 1,4,2,3,5-dioxazadisilolidines and -digermolidines ring system. The 1,3,2,4,5-dioxazadisilolidine and digermolidine systems were found also to undergo ring opening to the isomeric oximes. The addition of nitro compounds to ditetrelenes is a general reaction; the variability of products obtained from the reaction can be understood based on the nature of the substituents on the nitrogen in the nitro compound. For most part, the chemistry of ditetrelenes and the Si and Ge(100)- 2 × 1 surfaces were quite comparable although the apparent relative stabilities of the adducts varied. The addition of sulfonyl chloride compounds to tetramesityldisilene (or tetramesityldigermene) lead to the facile formation of a 1,2 addition product, a ß-disilyl (or digermyl) halosulfinate. The formation of the sulfinate compounds revealed an interesting, 2-electron reduction of the sulfur centre using a ditetrelene. The addition reactions of sulfonyl compounds with ditetrelenes illustrates the potential of ditetrelenes to serve as effective reducing agents which react rapidly, at room temperature and under mild conditions. The addition of isocyanide to tetramesityldisilene differs greatly from the addition of isocyanide to tetramesityldigermene. A C-N bond activation product was obtained from the addition of benzyl isocyanide to tetramesityldigermene. In the presence of the bulkier 2,6-dimethylphenyl- or t-butyl isocyanide, the conversion of the digermene to the cyclotrigermane is accelerated. While one equivalent of 2,6-dimethylphenyl- or t-butyl isocyanide add to tetramesityldisilene forming [2+1] cycloaddition products, the addition of two equivalent of t-butyl isocyanide yields a novel double enamine cycloadduct. The reaction was examined computationally to provide an understanding on the reaction pathway and the intermediates involved