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; X1A1g) 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.