Organometallic chemistry in unusual media : water and supercritical carbon dioxide as solvents for organometallic chemistry

Abstract

A series of water soluble transition metal complexes, utilizing the water soluble phosphine 1,3,5,-triaza-7-phosphaadamantane (PTA), were synthesized and studied. The water-soluble phosphine complex of Rh(I), (Rh(PTAH)(PTA)$sb2$Cl) Cl is an effective catalyst precursor for the regioselective reduction of unsaturated aldehydes to saturated aldehydes. The rate of hydrogenation of trans-cinnamaldehyde in a biphasic system with sodium formate as reductant was studied as a function of catalyst, substrate, sodium formate concentration, and temperature. The addition of excess PTA was found to completely inhibit hydrogenation. This reaction was also found to be partially inhibited by cyclooctatetraene and Hg(0). Recycling experiments show this complex to be quite robust with minimal leaching into the organic phase. $rmlbrack Rh(PTAH)sb2Clsb2rbrack Cl, lbrack Rh(PTAH)sb3(PTA)Clrbrack Clsb3, lbrack Pt(PTAH)sb2Clsb2rbrack Clsb2,$ and $rmlbrack Pd(PTAH)sb4rbracklbrack NOsb3rbracksb4$ have all been structurally characterized by single crystal x-ray diffraction studies. NMR, infrared and uv-visible spectroscopies and pH titrametric measurements were employed to study the reactivity of these transition metal complexes in aqueous solutions. The palladium, rhodium, and platinum complexes are catalysts for the hydrodehalogenation of aryl halides. In an aqueous solution, another water soluble phosphine ligand, meta-sulfonatophenyldiphenylphosphine (TPPMS), reacts instantaneously with aldehydes to afford 1-hydroxyalkylphosphonium salts. An x-ray diffraction study of a crystal of the TPPMS-benzaldehyde adduct, which underwent methanolysis, was performed. Maleic and fumaric acid also react with TPPMS to give phosphonium salts. The rate dependence on excess TPPMS of the hydrogenation of several unsaturated carboxylic acids by RhCl(TPPMS)$sb3$ in aqueous solutions was determined. Adduct formation is used to explain an unusual lack of inhibition of excess phosphine in the reduction of maleic acid. Phosphonium salt formation was not observed between PTA and aldehydes. The copolymerization of carbon dioxide and propylene oxide utilizing a heterogeneous zinc catalyst was investigated. The effect of gaseous versus supercritical carbon dioxide as solvent on the yield of polymer, fraction of polycarbonate linkages, and cyclic carbonate production was determined. However, there is some undetermined variable that is causing some irreproducibility in this system.