Study on Novel Group-14-Element π-Electron Species Based on Cyclic Silylenes and Carbenes

概要

Since the advent of isolable singlet carbenes, the utility of two-coordinate group-14-element
species, namely tetrylenes (L2E:, tetrylenes, E = C, Si, Ge, Sn, Pb) have seen tremendous development
especially in the field of coordination chemistry and catalysis. The tetrylenic center of a tetrylene has a
formal oxidation state of +II and possesses both a lone pair orbital (LP(σ)) and a vacant p orbital, which
gives tetrylenes a bifunctional reactivity as a Lewis base and a Lewis acid. The electronic properties of a
tetrylene highly depend on the bent angle around the tetrylenic center and the electronic (mesomeric and
inductive) effects involving the adjacent substituents. Thus, careful design of the substituents has allowed
fine tuning of the reactivity as well as electron donating and electron accepting ability of tetrylenes.
Compounds with the general formula of L2E could also be conceivable for species which possess a
two-coordinate element center in the formal oxidation state of 0. Such species have become to be recognized
as “tetrylones” and are known to formally possess symmetric [LP(σ)] and antisymmetric [LP(π)] lone pair
(LP) electron orbitals with respect to the L–E–L plane, which provides them with high electron donating
ability and highly polarized L–E bonds. Although tetrylenes and tetrylones are generally considered as
transient species, a considerable number of such species in isolable forms have been reported by introducing
adequate substituents on the two-coordinate atom. Gaining access to two-coordinate species of group-14
elements in stable forms enable us to not only explore their reactivity but also apply them as reagents for
organic synthesis as well as building blocks to access novel π-electron species with unique functions and
electronic properties. In this dissertation, the author mainly focused on utilizing two compounds, namely,
cyclic (alkyl)(amino)silylene (CAASi) and bis(diisopropylamino)cyclopropenylidene (DAC) for the
aforementioned purposes. ...