Complete Isocyanide Triple Bond Scission by a Silylene Yields an Optoelectronic 1,3-Disilacyclobutene

Abstract

The complete scission of strong triple bonds is a definitive hallmark of transition metals, typically remaining beyond the reach of main-group elements. Despite the success of silylenes in activating various inert linkages, the full fragmentation of the isocyanide C≡N moiety by a low-valent silicon center has yet to be realized. Herein, we report that the hypersilyl-stabilized amidinato-silylene, [PhC(NtBu)2SiSi(SiMe3)3] (1), accomplishes the complete cleavage of the C≡N triple bond in xylyl and mesityl isocyanides, providing a new benchmark for silicon-mediated small-molecule activation. We also demonstrate remarkably divergent reactivity where the isocyanide substituent dictates the product formation: aryl isocyanides undergo a complex multistep rearrangement and simultaneous C≡N and Si–Si bond scission to yield novel cyclic silenes (2 and 3) in high yield, whereas cyclohexyl isocyanide leads to a stable insertion product (4) keeping the oxidation state of silicon intact. Such an insertion reaction contrasts with common reports on the reactivity of low-valent silicon compounds, which are regularly oxidized to a more stable higher oxidation state. Finally, we reveal the successful integration of the cyclic silene 2 as a hole-injection layer in a functional light-emitting diode device.