| Abstract
| - Tetra(p-sulfonato-phenyl) porphyrin rhodium hydride ([(TSPP)Rh−D(D2O)]-4) (1) reacts in water(D2O) with carbon monoxide, aldehydes, and olefins to produce metallo formyl, α-hydroxyalkyl, and alkylcomplexes, respectively. The hydride complex (1) functions as a weak acid in D2O and partially dissociatesinto a rhodium(I) complex ([(TSPP)RhI(D2O)]-5) and a proton (D+). Fast substrate reactions of 1 in D2Ocompared to reactions of rhodium porphyrin hydride ((por)Rh−H) in benzene are ascribed to aqueousmedia promoting formation of ions and supporting ionic reaction pathways. The regioselectivity for additionof 1 to olefins is predominantly anti-Markovnikov in acidic D2O and exclusively anti-Markovnikov in basicD2O. The range of accessible equilibrium thermodynamic measurements for rhodium hydride substratereactions is substantially increased in water compared to that in organic media through exploiting thehydrogen ion dependence for the equilibrium distribution of species in aqueous media. Thermodynamicmeasurements are reported for reactions of a rhodium porphyrin hydride in water with each of the substrates,including CO, H2CO, CH3CHO, CH2CH2, and sets of aldehydes and olefins. Reactions of rhodium porphyrinhydrides with CO and aldehydes have nearly equal free-energy changes in water and benzene, but alkenereactions that form hydrophobic alkyl groups are substantially less favorable in water than in benzene.Bond dissociation free energies in water are derived from thermodynamic results for (TSPP)Rh-organocomplexes in aqueous solution for Rh−CDO, Rh−CH(R)OD, and Rh−CH2CH(D)R units and are comparedwith related values determined in benzene.
|
