Reactivity and Equilibrium Thermodynamic Studies of Rhodium Tetrakis(3,5-disulfonatomesityl)porphyrin Species with H2, CO, and Olefins in Water

Xuefeng Fu, Shan Li, and Bradford B. Wayland*
Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6323
Inorg. Chem., 2006, 45 (24), pp 9884–9889
DOI: 10.1021/ic0615022
Publication Date (Web): October 26, 2006
Copyright © 2006 American Chemical Society
*

 To whom correspondence should be addressed. E-mail:  wayland@sas.upenn.edu.

Abstract

Abstract Image

Aqueous (D2O) solutions of tetrakis(3,5-disulfonatomesityl)porphyrin rhodium(III) aquo/hydroxo complexes ([(TMPS)RhIII(D2O)2]-7 (1), [(TMPS)RhIII(OD)(D2O)]-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(D2O)]-8 (4)) and a rhodium(I) complex ([(TMPS)RhI(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(D2O)]-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)RhII(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.

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History

  • Published In Issue November 27, 2006
  • Received August 9, 2006

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