Well-defined hydrogen and organofunctional polysiloxanes with spiro-fused siloxane backbones

Organofunctional polysiloxanes with functionalized substituents on their silicon atoms form a class of silicone material with widespread applications. A well-established synthetic route to an organofunctional polysiloxane involves the post-functional hydrosilylation of a functionalized olefin with a ready-made polysiloxane bearing a Si–H group. In this paper, structurally well-defined macrocyclic polysiloxanes with unique spirosiloxane units and regularly arranged Si–H groups along the main chain are selectively synthesized by the B(C6F5)3-catalyzed dehydrocarbonative cross-couplings of spirosiloxane monomers bearing two isopropoxysilane moieties with trihydrosilanes (the Piers–Rubinsztajn reaction). Macrocyclic polysiloxanes bearing Si–H groups prepared in this manner are successfully transformed into novel organofunctional polysiloxanes without degrading their well-defined macrocyclic and spiro structures by the Pt-catalyzed hydrosilylations of functionalized olefins.