Recently we developed the straightforward synthetic route to silyliumylidene ions bearing bulky substituent from reaction of stable dichlorosilane with three equivalents of N-heterocyclic carbenes (NHCs) (Chem. Commun. 2014, 50, 12619-12622.; Bull. Chem. Soc. Jpn. 2017, 90, 255-277.). This combination of kinetic and thermodynamic stabilization effect and facile synthesis starting from silicon(IV) precursor led to the isolation of novel silyliumylidene ions in a single step. In fact, obtained silyliumylidne ions are stable enough to investigate their reactivity based on the nucleophilic silicon center as well as NHCs. Bulky silyl substituent has also been utilized in this system (Dalton Tran. 2019, 48, 10403-10406). It is of note that the use of NHCs for isolation of reactive low-valent main group compounds including the low-valent silicon compounds, we were able to publish the review article in Chem. Rev. 2018, 118, 9678-9842 which is highest impact factor journal in chemistry (IF = 53.613). The various substituents at central silicon atom has been investigated in order to understand the electronic and steric effect for corresponding silyliumylidene ions. Within this variation, the utilization of N-hetrocyclic imines (NHIs) as ligands for isolation of low-valent silicon species was conducted and these has been outlined and published in Chem. Soc. Rev. 2016, 45, 6327-6344 (IF = 40.182). As an initial investigation on reactivity of silyliumylidene ions, we found that it reacts with phenylacetylenem, affording the C-H bond activation product with concomitant elimination of imidazolium salts (Chem. Commun. 2014, 50, 12619-12622.). The reduction of carbon dioxide CO2 by silyliumylidene ions yielded the silaacylium ions, silicon analogue of acylium ion that is well known as an important intermediate species of Friedel-Crafts reaction (J. Am. Chem. Soc. 2015, 137, 5828-5836). In addition, we found that activation of elemental chalcogens such as sulfur, selenium, and tellurium gave corresponding heavier derivatives of silaacyclium ions, showing intriguing chalcogen transfer reaction as well as chalcogen exchange reaction (Dalton Tran. 2017, 46, 16014-16018). Furthermore, activation of S-H bond of hydrogen sulfide was also investigated and its reaction mechanism has been elucidated by using both experimental as well as computational methods (Inorganics, 2018, 6, 54-67). In addition, we could obtain the silicon analogue of aldehyde from the reaction of silyliumylidene ions with water in the presence of Lewis acid (Chem. Eur. J. 2019, 24, 1198-1202). Moreover, we could found that intriguing coordination behavior of silyliumylidene ions in various reactions towards transition metals (Chem. Commun. 2018, 54, 13658-13661: Chem, Eur, J. 2020, 26, 6271-6278) which would lead to the novel catalytic applications.
