Gas Phase Synthesis of the Elusive Trisilacyclopropyl Radical (Si₃H₅) via Unimolecular Decomposition of Chemically Activated Doublet Trisilapropyl Radicals (Si₃H₇)

The gas phase reaction of the simplest silicon-bearing radical silylidyne (SiH; X²Π) with disilane (Si₂H₆; X¹A_1g) was investigated in a crossed molecular beams machine. Combined with electronic structure calculations, our data reveal the synthesis of the previously elusive trisilacyclopropyl radical (Si₃H₅)the isovalent counterpart of the cyclopropyl radical (C₃H₅)along with molecular hydrogen via indirect scattering dynamics through long-lived, acyclic trisilapropyl (i-Si₃H₇) collision complex­(es). Possible hydrogen-atom roaming on the doublet surface proceeds to molecular hydrogen loss accompanied by ring closure. The chemical dynamics are quite distinct from the isovalent methylidyne (CH)–ethane (C₂H₆) reaction, which leads to propylene (C₃H₆) radical plus atomic hydrogen but not to cyclopropyl (C₃H₅) radical plus molecular hydrogen. The identification of the trisilacyclopropyl radical (Si₃H₅) opens up preparative pathways for an unusual gas phase chemistry of previously inaccessible ring-strained (inorgano)silicon molecules as a result of single-collision events.