Recyclable Pt-catalyzed biphase hydrosilylation on water: from functionalized monomers to polymer materials

This study proposes ways to resolve the main challenges of the important industrial hydrosilylation process using biphase “on water” catalytic systems. The Pt/H2O-catalytic system consists of a commercially available Pt-precatalyst, K2PtCl4, and the most naturally abundant and environmentally benign solvent, H2O. It is easily prepared by mixing them without the use of ligands or an inert atmosphere, at r.t. for 2 min. The use of affordable KBr as an additive significantly increases the efficiency of the method for a range of substrates. Mechanistic studies revealed that during hydrosilylation, single-atom complexes (mainly in Pt/H2O) and cluster (mainly, in Pt/KBr/H2O) Pt0-complexes are generated, which are responsible for the high catalytic activity of these systems. Pt/H2O- and Pt/KBr/H2O-catalytic systems are highly efficient in the hydrosilylation of a wide range of hydrosilanes, including oligomeric and polymeric ones, as well as aliphatic and aromatic alkenes and alkynes containing N-, O-, S-, Si-, and Hal-containing functional groups. The method allows for the synthesis of products in high yields with anti-Markovnikov selectivity, in air at r.t. Using the Pt/KBr/H₂O-catalytic system, cured silicone materials were obtained both as monoliths and thin films, from PDMS derivatives with Si–H-groups with linear and cyclic vinylsiloxanes, various dienes, and, more importantly, by gaseous acetylene and butadiene. Pt-free (monomer, polymer, and cured) products can be isolated from the biphasic catalytic system by simple decantation. The possibility of multiple catalyst recycling (demonstrated over 15 cycles), combined with low Pt-loadings (0.01–0.1 mol%) and high product yields (up to 99%), allows for achieving low E-factor (≤0.07) and high TON (>104). We also constructed a tube-in-tube flow reactor, which enables reaction scale-up with greater efficiency than in batch and the automatic separation of products and the catalytic system.