Synthesis of an Isolable Bis(silylene)-Stabilized Silylone and Its Reactivity Toward Small Gaseous Molecules.

The first bis(N-heterocyclic silylene)-stabilized zero-valent silicon compound, [Si(Xant)Si]Si (, Xant = 9,9-dimethyl-xanthene-4,5-diyl), has been synthesized via the reduction of the corresponding chlorosilyliumylidene chloride precursor {[Si(Xant)Si]SiCl}Cl (). The electronic structure of silylone , whose molecular structure is confirmed spectroscopically and crystallographically, is investigated by DFT calculations and Natural Bond Orbital analysis, showing two perpendicular lone-pairs of electrons on the central Si atom, i.e., an -type lone-pair and a delocalized lone-pair. With the electron-rich and oxophilic Si center, silylone exhibits a striking reactivity toward small gaseous molecules. Remarkably, the oxidation of silylone by NO can be controlled to generate distinct products by regulating the amount of added NO. Exposing to an excess or two molar equivalents of NO yields the unexpected oxidation product , bearing a central six-membered SiO ring. When is mixed with one molar equivalent of NO, the unique compound is obtained, resulting from a rare 1,4-addition of two central silicon atoms to a phenyl ring of an amidinate ligand coordinated to the Si atom. In addition, cleavage of the strong N-H bond in ammonia is also readily accomplished by silylone , representing the first example of NH activation in silylone chemistry. In the presence of the Lewis acid BPh, silylone achieves heterolytic dihydrogen cleavage and ethylene addition to form the corresponding hydridosilyliumylidene hydroborate salt and the zwitterionic compound , respectively, which represent a new type of frustrated Lewis pair based on an electron-rich Si donor and a borane acceptor.