1,1-Organoboration of tri-1-alkynyltin compounds: novel triorganotin cations, stannoles, 3-stannolenes and 1-stanna-4-bora-2,5-cyclohexadienes |
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Authors: | Bernd Wrackmeyer Gerald Kehr Dagmar Wettinger |
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Affiliation: | Laboratorium für Anorganische Chemie der Universität Bayreuth, D-95440 Bayreuth Germany |
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Abstract: | Tri-1-alkynyltin compounds [R2Sn(CCR1)3 (1), R2 = Me, R1 = Me (a), nBu (b), tBu (c), Me3Si (d), 1-(1-cyclohexenyl) (e); R2 = Et, R1 = Me (a(Et)), nBu (b(Et)), tBu (c(Et)), SiMe3 (d(Et)); R2 = nBu, R1 = Me (a(Bu)), nBu (b(Bu))] were prepared, and their reactivity towards trialkylboranes Et3B (2) and iPr3B (3) in 1,1-organoboration reactions was studied. The first step in each reaction is an intermolecular 1,1-alkytoboration. Afterwards, intramolecular 1,1-vinyloboration or 1,1-alkyloboration compete with further intermolecular 1,1-alkyloboration. Various triorganotin cations (4-7), stabilized by intramolecular side-on coordination to the CC bond of an alkynylborate moiety, were detected as highly fluxional intermediates prior to rearrangement into heterocyclic systems such as stannoles (9-11), 1-stanna-4-bora-2, 5-cyclohexadienes (8, 12). The reactions between 1a or 1a(Bu) and an excess of Et3B (2) afford the tris(alkenyl)tin compounds 13 via threefold intermolecular 1, 1-ethyloboration. 13 rearrange to the 3-stannolenes (14a or 14a(Bu)). The intermediates and final products were characterized by multinuclear one- and two-dimensional 1H, 11B, 13C, 29Si and 119Sn NMR. |
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Keywords: | Organoboration Tin complexes Zwitterion alkynyl complexes NMR multinuclear |
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