Trisilyl‐Substituted Vinyl Cations

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Abstract
A series of β,β‐disilyl‐substituted vinyl cations were prepared by intramolecular addition of transient silylium ions to C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 13C and 29Si NMR data. The NMR investigations revealed for β,β‐disilyl‐α‐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 13C‐labeled vinyl cation suggest as mechanism for this exchange process a rotation of the dicarbyne CC2− 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.

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