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Homogeneous catalysts based on soluble transition metal complexes exhibit high activities and selectivities under mild reaction conditions, but are not easily recovered from the reaction products. Now, researchers from the Universität Konstanz, Germany, report recoverable rhodium (Rh) homogeneous catalysts electrostatically bound to hyperbranched polymers (E. Schwab and S. Mecking, Organometallics, 2005, 24, (15), 3758–3763 http://dx.doi.org/10.1021/om050266k).

Polyelectrolytes with Ph₂P(C₆H₄-p-SO₃⁻) counterions were prepared by ion exchange from hyperbranched polycations with a polyglycerol-based polyether scaffold and 1,2-dimethylimidazolium end groups. After the polyelectrolytes and [Rh(acac)(CO)₂], in DMSO-d₆, were exposed to 1 atm CO/H₂, most of the Rh precursor converted to [(phosphine)₃Rh(H)(CO)]. Hydroformylation of 1-hexene in methanol proceeded with moderate activity at 80°C and 30 bar CO/H₂. The Rh-polyelectrolyte catalyst could be recovered by ultrafiltration and reused.