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Reactivity and equilibrium thermodynamic studies of rhodium tetrakis(3,5-disulfonatomesityl)porphyrin species with H2, CO, and olefins in water
Fu, Xuefeng,Li, Shan,Wayland, Bradford B.
, p. 9884 - 9889 (2008/10/09)
Aqueous (D2O) solutions of tetrakis(3,5-disulfonatomesityl) porphyrin rhodium(III) aquo/hydroxo complexes ([(TMPS)RhIII(D 2O)2]-7 (1), [(TMPS)RhIII(OD)(D 2O)]-8 (2), and [(TMPS)RhIII(OD) 2]-9 (3)) react with hydrogen (D2) to form an equilibrium distribution with a rhodium hydride ([(TMPS)Rh-D(D 2O)]-8 (4)) and a rhodium(I) complex ([(TMPS)Rh I(D2O)]-9 (5)). Equilibrium constants (298 K) are measured that define the distribution for all five of these (TMPS)Rh species in this system as a function of the dihydrogen (D2) and hydrogen ion (D+) concentrations. The hydride complex [(TMPS)Rh-D(D 2O)]-8 is a weak acid in D2O (Ka(298 K) = 4.3 × 10-8). Steric demands of the TMPS porphyrin ligand prohibit formation of a Rh(II)-Rh(II)-bonded complex, related rhodium(I)-rhodium(III) adducts, and intermolecular association of alkyl complexes which are prominent features of the rhodium tetra(p-sulfonatophenyl) porphyrin ((TSPP)Rh) system. The rhodium(II) complex ([(TMPS)Rh II(D2O)]-8) reacts with water to form hydride and hydroxide complexes and is not observed in D2O. The (TMPS)Rh-OD and (TMPS)Rh-D bond dissociation free energies (BDFE) are virtually equal and have a value of approximately 60 kcal mol-1. Reactions of [(TMPS)Rh-D(D2O)]-8 in water with CO and olefins produce rhodium formyl and alkyl complexes which have equilibrium thermodynamic values comparable to the values for the corresponding substrate reactions of [(TSPP)-Rh-D(D2O)]-4.
