Water-soluble organometallic compounds. 5. The regio-selective catalytic hydrogenation of unsaturated aldehydes to saturated aldehydes in an aqueous two-phase solvent system using 1,3,5-triaza-7-phosphaadamantane complexes of rhodium

Article abstract of DOI:10.1016/0022-328X(94)00024-7

The water-soluble phosphine complex of Rh(I), Cl (1), has been synthesized from RhCl3 and 1,3,5-triaza-7-phosphaadamantate (PTA) in 96percent ethanol.This complex is an effective catalyst for the regioselective reduction of unsaturated aldehydes to saturated aldehydes.The rate of hydrogenation of trans-cinnamaldehyde with sodium formate as reductnat was studied as a function of catalyst, substrate, and sodium formate concentration.The presence of an excess of PTA was found to inhibit hydrogenations completely.This reaction was also found to be partially inhibited by cyclo-octatetraene and Hg(O), leading to the conclusion that both heterogeneous and homogeneous mechanisms are operating.Recycling experiments show complex 1 to be quite robust, with minimal leaching into the organic phase in a biphasic system.The complex resulting from the addition of an excess of PTA to 1, Cl3 (2), has been prepared and structurally characterized by a single crystal X-ray diffraction study. 31P and 1H NMR, IR, and UV-VIS spectroscopy and pH titrametric measurements were employed to study the reactivity of the various rhodium PTA complexes in aqueous solutions. Keywords: Rhodium; Hydrogenation; Crystal structure