A water-soluble complex Rh/PPA(Na+)/DPPEA 1 was obtained from poly(4-pentenoic acid) (PPA) and bis[2-(diphenylphosphino)ethyl]amine (DPPEA). Complex 1 is a highly active catalyst for the hydroformylation of olefins. Some selectivity for linear aldehydes was observed in the hydroformylation of aliphatic olefins, while high ratios of branched aldehydes resulted in the case of vinyl ethers. Complex 1 is also the first polymeric water-soluble metal complex which can catalyze the conversion of vinylarenes to 2-arylpropanals in a highly chemoselective and regioselective manner.