Gas-Phase Synthesis of 1-Silacyclopenta-2,4-diene

Silole (1-silacyclopenta-2,4-diene) was synthesized for the first time by the bimolecular reaction of the simplest silicon-bearing radical, silylidyne (SiH), with 1,3-butadiene (C₄H₆) in the gas phase under single-collision conditions. The absence of consecutive collisions of the primary reaction product prevents successive reactions of the silole by Diels–Alder dimerization, thus enabling the clean gas-phase synthesis of this hitherto elusive cyclic species from acyclic precursors in a single-collision event. Our method opens up a versatile and unconventional path to access a previously rather obscure class of organosilicon molecules (substituted siloles), which have been difficult to access through classical synthetic methods.