A novel nontransient
acyclic iminosilylene (1), bearing
a bulky super silyl group (−SitBu3) and N-heterocyclic imine ligand
with a methylated backbone, was prepared and isolated. The methylated
backbone is the feature of 1 that distinguishes it from
the previously reported nonisolable iminosilylenes, as it prevents
the intramolecular silylene center insertion into an aromatic C–C
bond of an aryl substituent. Instead, 1 exhibits an intermolecular
Büchner-ring-expansion-type reactivity; the silylene is capable
of dearomatization of benzene and its derivatives, giving the corresponding
silicon analogs of cycloheptatrienes, i.e. silepins,
featuring seven-membered SiC6 rings with nearly planar
geometry. The ring expansion reactions of 1 with benzene
and 1,4-bis(trifluoromethyl)benzene are reversible. Similar reactions
of 1 with N-heteroarenes (pyridine and
DMAP) proceed more rapidly and irreversibly forming the corresponding
azasilepins, also with nearly planar seven-membered SiNC5 rings. DFT calculations reveal an ambiphilic nature of 1 that allows the intermolecular aromatic C–C bond insertion
to occur. Additional computational studies, which elucidate the inherent
reactivity of 1, the role of the substituent effect,
and reaction mechanisms behind the ring expansion transformations,
are presented