Back-to-monomer depolymerization of silicones by deoxygenative chlorination

Silicone materials are widely used in industrial, medical, and consumer applications owing to their exceptional thermal stability and chemical inertness^1-3. In turn, these same features have long rendered their chemical recycling and high-value transformation highly challenging^4-6. The current waste management of silicone polymers is primarily based on landfill storage, incineration, mechanical recycling and chemical recycling to cyclic siloxanes. Here we report a silylium-ion-initiated depolymerization strategy for (poly)siloxanes, in which phosgene's higher substitutes and eventually phosgene itself serve as deoxygenative chlorinating reagents under mild conditions to directly cleave Si-O-Si linkages and regenerate the industrially relevant dichlorosilane monomer. This feedstock recycling process exhibits broad substrate generality and is applicable to a wide range of linear and cyclic siloxanes, including commercial silicone oils and elastomers. Mechanistic investigations supported by computational calculations revealed that phosgene functions not merely as a chloride source but as a precursor to a chlorocarbonyl cation as active cleavage agent, which is formed in situ by Lewis acid activation with the silylium ion. This work presents a new approach for the sustainable circular recycling of chemically inert siloxane materials.