The addition of terminal alkynes to dimesitylfluorenylidenegermane

A variety of terminal alkynes were added to dimesitylfluorenylidenegermane, [Mes.sub.2]Ge=[CR.sub.2] (where [CR.sub.2] = fluorenylidene). The addition of phenylacetylene and 1-hexyne to [Mes.sub.2]Ge=[CR.sub.2] gave a germacyclohexene via a cycloaddition where the germene acts as the 4π component and the alkyne as the 2π component. Through the use of a mechanistic probe, trans-(2-phenylcyclopropyl)acetylene, the reaction was postulated to proceed through a concerted [2+4] cycloaddition. The addition of ethoxyacetylene to the germene produced both a [2+2] cycloadduct, a germacyclobutene, and a [2+4] cycloadduct, a germacyclohexene. The results of this study are compared to the results of the addition of alkynes to [Mes.sub.2]Ge=CH[CH.sub.2]-t-Bu. Key words: germene, alkyne, cycloaddition, mechanism. Divers alcynes terminaux ont ete ajoutes au dimesitylfluorenylidenegermane, [Mes.sub.2]Ge=[CR.sub.2] (ou [CR.sub.2] = fluorenylidene). L'addition du phenylacetylene et du hex-1-yne au [Mes.sub.2]Ge=[CR.sub.2] a produit un germacyclohexene par une cycloaddition lors de laquelle le germene agit comme le composant 4π et l'alcyne comme le composant 2π. En utilisant une sonde mecanistique, trans-(2-phenylcyclopropyl)acetylene, on suppose que la reaction s'effectue par l'intermediaire d'une cycloaddition concertee [2+4]. L'addition d'ethoxyacetylene au germene a produit a la fois un cycloadduit [2+2], le germacyclobutene, et un cycloadduit [2+4], le germacyclohexene. Les resultats de la presente etude sont compares a ceux de l'addition d'alcynes au [Mes.sub.2]Ge=CH[CH.sub.2]t-Bu. [Traduit par la Redaction] Mots-cles: germene, alcyne, cycloaddition, mecanisme.
Introduction Cycloaddition reactions of group 14 metallenes have been attracting the interest of chemists for more than 40 years due to the high levels of regio- and stereospecificity. (1) The [...]