Reactivity of an Acyclic Silylsilylene toward Ethylene: Migratory Insertion into the Si–Si Bond

The
reaction of the only known room-temperature-stable, acyclic
silylsilylene, Si­{NDipp­(SiMe3)}­{Si­(SiMe3)3}, toward ethylene was investigated. A full conversion to
the silirane product Si­{CH2–CH2}­{NDipp­(SiMe3)}­{Si­(SiMe3)3} (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 Si­{CH2–CH2}­{NDipp­(SiMe3)}­{CH2–CH2–Si­(SiMe3)3} (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. Moreover, [4+1] cycloaddition
with 2,3-dimethyl-1,3-butadiene to give the corresponding silacyclopent-3-ene
ring Si­{CH2–CH3CCCH3–CH2}­{NDipp­(SiMe3)}­{Si­(SiMe3)3} (3) is reported. All structures were
fully characterized by single-crystal X-ray analysis and 1H, 13C, and 29Si NMR spectroscopy.