Gas‐Phase Formation of the Disilavinylidene (H2SiSi) Transient

The hitherto elusive disilavinylidene (H₂SiSi) molecule, which is in equilibrium with the mono‐bridged (Si(H)SiH) and di‐bridged (Si(H₂)Si) isomers, was initially formed in the gas‐phase reaction of ground‐state atomic silicon (Si) with silane (SiH₄) under single‐collision conditions in crossed molecular beam experiments. Combined with state‐of‐the‐art electronic structure and statistical calculations, the reaction was found to involve an initial formation of a van der Waals complex in the entrance channel, a submerged barrier to insertion, intersystem crossing (ISC) from the triplet to the singlet manifold, and hydrogen migrations. These studies provide a rare glimpse of silicon chemistry on the molecular level and shed light on the remarkable non‐adiabatic reaction dynamics of silicon, which are quite distinct from those of isovalent carbon systems, providing important insight that reveals an exotic silicon chemistry to form disilavinylidene.     

Gas‐Phase Synthesis of the Elusive Cyclooctatetraenyl Radical (C8H7) via Triplet Aromatic Cyclooctatetraene (C8H8) and Non‐Aromatic Cyclooctatriene (C8H8) Intermediates

The 1,2,4,7‐cyclooctatetraenyl radical (C₈H₇) has been synthesized for the very first time via the bimolecular gas‐phase reaction of ground‐state carbon atoms with 1,3,5‐cycloheptatriene (C₇H₈) on the triplet surface under single‐collision conditions. The barrier‐less route to the cyclic 1,2,4,7‐cyclooctatetraenyl radical accesses exotic reaction intermediates on the triplet surface, which cannot be synthesized via classical organic chemistry methods: the triplet non‐aromatic 2,4,6‐cyclooctatriene (C₈H₈) and the triplet aromatic 1,3,5,7‐cyclooctatetraene (C₈H₈). Our approach provides a clean gas‐phase synthesis of this hitherto elusive cyclic radical species 1,2,4,7‐cyclooctatetraenyl via a single‐collision event and opens up a versatile, unconventional path to access this previously largely obscure class of cyclooctatetraenyl radicals, which have been impossible to access through classical synthetic methods.