INOR 209 |
| Aqueous solutions of rhodium (III) tetra 3,5-disulfonatomesityl porphyrin ((TMPS)Rh(III)) complexes react with dihydrogen to produce equilibrium distributions with rhodium hydride and rhodium(I) complexes. Steric demands of the porphyrin ligand prohibit formation of a Rh(II)-Rh(II) bonded dimer and species that arise from binding of Rh(I) with Rh(III) complexes . Equilibrium thermodynamic studies (298 K) for this system establish the quantitative relationships that define the distribution of species in aqueous solution as a function of the dihydrogen and hydrogen ion concentrations through direct measurement of equilibrium constants in water. The hydride complex ([(TMPS)Rh-D(D2O)]-8) is a weak acid (K(298 K) = 4.3 ± 0.3 x 10-8) and reacts in water with CO, and series of aldehydes and olefin substrates to produce rhodium formyl, a-hydroxy alkyl and alkyl complexes. Relatively fast substrate reactions in water compared to organic media are ascribed to water promoting and supporting ionic reaction pathways. Equilibrium constants and free energy changes for a series of reactions in water are derived from the directly measured equilibria. Near cancellation of solvation energies of reactants and products is illustrated by the close similarity of the equilibrium thermodynamic values for analogous reactions of porphyrin rhodium hydrides in water and organic media. |
|
Organometallic General and Catalysis
7:00 PM-9:00 PM, Sunday, 13 March 2005 Convention Center -- Hall D, Poster
Division of Inorganic Chemistry |