Synthese und NMR-Spektroskopie von 2,5-diborylierten 3-Plumbolenen und 3-Stannolenen / Synthesis and NMR Spectroscopy of 2,5-Diborylated 3-Plumbolenes and 3-Stannolenes

The organoboration of bis(alkynyl)plumbanes (1) leads to intermediates 7 in which a triorganolead cation is stabilized by intramolecular side-on coordination to the C=C triple bond of an alkynylborate function. These compounds decompose rapidly at room temperature or rearrange to give 1,4-plumbabora-2,5-cyclohexadienes (10). If the compounds 7 are treated with an excess of trialkylborane (2) they are converted into bis(alkenyl)lead derivatives (8) as the final products (8c, 8ca) or again as intermediates for the 2,5-bis(dialkylboryl)-3-plumbolenes 9. A mechanism suggested for the formation of 9 is based on the product distribution (9ab/9ba = 2:1) obtained from the reaction of a distinct compound 7a with different trialkylboranes (2a, 2b). All compounds have been fully characterized by multinuclear magnetic resonance data ( H, B, C, Pb), dynamic NMR and two-dimensional (2 D) NMR techniques. In addition, these techniques have been applied to some of the analogous tin compounds (e.g. 4b, 5).