Catalytic conversions in aqueous media: A novel and efficient hydrogenation of polybutadiene-1,4-block-poly(ethylene oxide) catalyzed by Rh/TPPTS complexes in mixed micellar nanoreactors

Exceptionally high catalytic activities (TOF > 840 h^-1) were achieved in the aqueous phase hydrogenation of polybutadiene-1,4-block- poly(ethylene oxide) (PB-b-PEO) catalyzed by water-soluble Rh/TPPTS complexes [TPPTS = P(C₆H₄-m-SO₃Na)₃] in mixed micellar nanoreactors formed by dodecyltrimethylammonium chloride along with PB-b-PEO especially when n-hexane was added to the reaction system. This is the first example of a catalytic hydrogenation of an unsaturated polymer using water-soluble transition metal TPPTS complexes in aqueous media. Using Rh/TPPTS catalysts high activities were observed in the hydrogenation of PB-b-PEO in mixed micelles whereas in single micelles the activities were lower. Dynamic light scattering experiments showed the presence of mixed nanomicelles with smaller hydrodynamic radii compared to the radii of single micelles. A model of a mixed micellar nanoreactor was proposed to rationalize the observed results. The hydrogenation reaction was shown to be homogeneously catalyzed by Rh/TPPTS complexes generated in situ from RhCl₃·3H₂O and TPPTS under the reaction conditions. A recycling experiment showed that the catalytic activity remained high in a consecutive run even at a rhodium concentration of only 1 ppm in water.