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

Abstract

The gas phase reaction of the simplest silicon-bearing radical silylidyne (SiH; X 2 Π) with disilane (Si 2 H 6 ; X 1 A 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 (Si 3 H 5 )the isovalent counterpart of the cyclopropyl radical (C 3 H 5 )along with molecular hydrogen via indirect scattering dynamics through long-lived, acyclic trisilapropyl (i-Si 3 H 7 ) 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 (C 2 H 6 ) reaction, which leads to propylene (C 3 H 6 ) radical plus atomic hydrogen but not to cyclopropyl (C 3 H 5 ) radical plus molecular hydrogen. The identification of the trisilacyclopropyl radical (Si 3 H 5 ) 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.