Iridium-Catalyzed Ring-Expanding Silylene Transfer from Aryldiorganosilanes

Silylene transfer reaction, which allows single-step formation of two silicon-containing -bonds, have attracted much attention in synthetic organosilicon chemistry, whereas its development has been significantly hampered by the lack of synthetically viable, readily accessible silylene precursors. We herein report a new silylene transfer reaction (STR) using aryldiorganosilanes (ArR1R2SiH) as silylene precursors, in which a silylene unit is inserted into the O–C(sp2) bond of unsaturated oxacycles, such as benzofurans, was enabled by iridium catalysts with extrusion of Ar–H as the only byproduct. A variety of silylenes, including diaryl, (aryl)(alkyl), dialkyl, and even (aryl)(alkoxy)silylene units, are transferred to give ring-enlarged oxasilacycles. This protocol is extended to the germylene transfer reaction using Ph3GeH as a source of diphenylgermylene (Ph2Ge:). The new STR is not limited to benzofurans containing various functional groups, but applicable to furans, 1,4-benzodioxin, dihydrofuran, dihydropyran, and even acyclic enol ether. The complete STR process consists of two sequential STRs, i.e., intermolecular STR into the C(sp2)–H bond to the oxygen atom, followed by intramolecular STR into the C–O bond. Formal silicon atom transfer is demonstrated using PhSiH3 as a source of the silicon atom, which in the first step undergoes cyclative double C–H silylation, followed by the present Ir-catalyzed STR with benzofuran. Using a 5-(2-diphenylhydrosilylethyl)benzofuran as a monomer, silylene transfer polymerization has been demonstrated.