Trisilyl-substituted vinyl cations.
A series of beta,beta-disilyl-substituted vinyl cations were prepared by intramolecular addition of transient silylium ions to C[triple bond]C triple bonds. The vinyl cations were isolated from hydrocarbon solutions as tetrakis(pentafluorophenyl) borates at room temperature. The substituents directly attached to the positively charged carbon atom were varied from tert-butyl- to trialkylsilyl- to trialkylgermyl groups. The cations were identified by their characteristic (13)C and (29)Si NMR data. The NMR investigations revealed for beta,beta-disilyl-alpha-germyl- and trisilyl-substituted vinyl cations a highly dynamic structure in which both vinylic carbon atoms undergo an intramolecular exchange process which is fast on the NMR time scale at room temperature. NMR studies using a doubly (13)C-labeled vinyl cation suggest as mechanism for this exchange process a rotation of the dicarbyne C[triple bond]C(2-) unit within the triangle defined by the three cationic silyl fragments. Therefore the dynamic structure indicated for trisilyl- or disilylgermyl-substituted vinyl cations parallels the situation found for the parent vinyl cation, the protonated acetylene.
Klaer
Andrea
A
Institut für Reine und Angewandte Chemie, Carl von Ossietzky Universität Oldenburg, Carl von Ossietzky Strasse 9-11, 26211 Oldenburg (Germany).
Syha
Yvonne
Y
Institut für Anorganische und Analytische Chemie, Johann Wolfgang Goethe-Universität Frankfurt/Main, Marie-Curie-Strasse 11, 60439 Frankfurt (Germany).
Nasiri
Hamid Reza
HR
Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge, CB2 1EW (UK).
Müller
Thomas
T
Institut für Reine und Angewandte Chemie, Carl von Ossietzky Universität Oldenburg, Carl von Ossietzky Strasse 9-11, 26211 Oldenburg (Germany).