Room Temperature Intermolecular Dearomatization of Arenes by an Acyclic Iminosilylene
Huaiyuan Zhu, Arseni Kostenko, Daniel Franz, Franziska Hanusch, Shigeyoshi Inoue
Abstract
A novel nontransient acyclic iminosilylene ( 1 ), bearing a bulky super silyl group (−Si t Bu 3 ) 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 SiC 6 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 SiNC 5 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.