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.