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The Synthesis, Characterization and Reactivity of a Series of Ruthenium N-triphosPh Complexes
Published on: April 10, 2015
Substituent effects in five oxo-centered trinuclear rhodium(III) clusters
Jacqueline R Houston1, Marilyn M Olmstead, William H Casey
1Departments of Chemistry and Geology, University of California, Davis, Davis, California 95616, USA.
This study investigates water substitution rates in rhodium(III) clusters, finding that alkyl chain variations significantly impact reactivity. These findings suggest a method for predicting water exchange rates using nuclear magnetic resonance (NMR) data.
Area of Science:
- Inorganic Chemistry
- Coordination Chemistry
- Materials Science
Background:
- Oxo-centered trinuclear rhodium(III) clusters are important in catalysis and materials science.
- Understanding ligand substitution kinetics is crucial for designing new functional materials.
Purpose of the Study:
- To report water substitution rates for new rhodium(III) clusters with varying carboxylate ligands.
- To elucidate the mechanism of water substitution and its dependence on ligand structure.
- To explore the correlation between reactivity and 103Rh NMR chemical shifts.
Main Methods:
- Synthesis and characterization of four new oxo-centered trinuclear rhodium(III) clusters.
- Kinetic studies of water substitution by methanol-d(4) at 298 K.
- Determination of activation parameters (enthalpy and entropy).
- 103Rh Nuclear Magnetic Resonance (NMR) spectroscopy.
Main Results:
- Water substitution rates varied by nearly three orders of magnitude based on the R group of the carboxylate ligand.
- Activation parameters indicate a dissociative substitution pathway (DeltaH = 99-115 kJ mol(-1); DeltaS = 48-52 J mol(-1) K(-1)).
- 103Rh NMR chemical shifts correlated with water substitution rates, spanning over 200 ppm.
Conclusions:
- The inductive ability of aliphatic substituents on carboxylate ligands significantly influences the kinetic reactivity of ligated waters.
- The substitution mechanism remains largely dissociative, irrespective of the R group.
- 103Rh NMR chemical shifts can be used to estimate water exchange rates in similar rhodium(III) trimers.
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