Recyclable Pt-Catalyzed Biphase Hydrosilylation on Water: From Functionalized Monomers to Polymer Materials

Ways to resolve the main challenges of the important industrial hydrosilylation process are proposed. Recyclable biphasic Pt/H₂O- and Pt/KBr/H₂O-catalysts are developed. They are prepared by dissolving K₂PtCl₄ with or without KBr in H₂O at r.t. for 2 min. Mechanistic studies revealed that previously unknown highly catalytically active single-atom (Pt/H₂O) or cluster (Pt/KBr/H₂O) [Pt⁰]-complexes are generated. H₂O, Cl^-/Br^-, and alkenes/alkynes coordinate such [Pt⁰]-species, "tuning" their stability, catalytic activity, and structure (single-atom or cluster). The cooperation of [Pt⁰]-species and "on water" effect enabled high efficiency in hydrosilylation. Using Pt/H₂O and Pt/KBr/H₂O, a wide range of hydrosilanes, including oligomeric and polymeric ones, as well as aliphatic and aromatic alkenes and alkynes with functional groups, were employed to prepare anti-Markovnikov products. Pt/KBr/H₂O made it possible to obtain cured monoliths and thin films from PDMS derivatives with Si-H-groups, and vinylsiloxanes, dienes, including gaseous acetylene or butadiene. Pt-free products, including cross-linked materials can be isolated from the biphasic catalytic system by decantation. The recyclability (≥15 cycles), low Pt-loadings and high yields enable a low E-factor (≤0.07) and a high TON (>10⁴). Furthermore, a constructed tube-in-tube flow reactor allows for effective scale-up, automatic separation and recycling of the catalytic system with continuous product synthesis.