The past few years have witnessed a milestone in low valent silicon chemistry - the isolation of the first room temperature stable, two-coordinate acyclic silylenes I-IV by the groups of Power and Jones. In contrast to conventional NHSis, acyclic silylenes are ideal candidates for selective small-molecule activation and lead structures for potential metal-free catalysts. Structures I and II have been reported to cleave dihydrogen at ambient temperatures, the prime example demonstrating their enhanced reactivity. Furthermore, silylene III shows remarkable behavior toward ethylene by reversibly binding the olefin in a dissociation equilibrium with its corresponding silirane ring at ambient conditions. The proposed extended reactivity with the chance to use acyclic silylenes as molecular catalysts in macromolecular chemistry inspired our group to enter this research field. The reaction of the only known room-temperature stable acyclic silylsilylene I toward ethylene was investigated. A full conversion to the silirane product 1 was observed at ambient temperature. However, heating of the benzene solution under an ethylene atmosphere led to an exceptional Si-Si bond insertion to give the modified silirane 2a. With respect to the mechanism, an NMR experiment using C2D4 revealed this reaction to proceed via a migratory insertion of the coordinated ethylene of 1 into the Si-Si bond of the ligand framework and subsequent addition of a second ethylene molecule to form silirane 2b.

Reactivity of an acyclic silylsilylene toward ethylene: Migratory insertion into the Si-Si bond

253rd National Meeting (2017)

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