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 CoII/CoIII (E1/2 ≈ –1.4 V) and CoI/CoII (E1/2 ≈ –2.3 V). The cross-linked Cc-polysiloxanes are thermally stable to approx. 230 °C both in the air and argon.