Cobaltocenium-Containing Polysiloxanes: Catalytic Synthesis, Structure, and Properties

Two different catalytic approaches to synthesize non-cross-linked and cross-linked cobaltocenium-containing polysiloxanes (Cc-polysiloxanes) were proposed and represent copper-catalyzed azide–alkyne cycloaddition (CuAAC) and platinum-catalyzed hydrosilylation reactions. CuAAC of ethynylcobaltocenium hexafluorophosphate with azide-substituted oligo/polysiloxanes leads to obtain Cc-oligo/polysiloxanes with the highest Cc-substituted unit content up to 91 mol % compared to the hydrosilylation reaction with polymethylhydrosiloxane (53 mol %). The structure of the obtained Cc-oligo/polysiloxanes was confirmed by ¹H, ¹³C{¹H}, ²⁹Si{¹H} NMR, and UV–vis spectroscopies. The non-cross-linked Cc-oligo/polysiloxanes are predominantly soluble in polar solvents (acetone, CH₃OH, CH₃CN, and H₂O) due to hydrophilic cobaltocenium cationic moieties attached to the polysiloxane chain, making them different from typical polydimethylsiloxane and ferrocenyl-containing polysiloxanes. All the obtained Cc-oligo/polysiloxanes exhibit redox properties. Cyclic voltammograms of the Cc-oligo/polysiloxanes contain two pairs of redox peaks corresponding to Co^II/Co^III (E_1/2 ≈ –1.4 V) and Co^I/Co^II (E_1/2 ≈ –2.3 V). The cross-linked Cc-polysiloxanes are thermally stable to approx. 230 °C both in the air and argon.