Electron transfer reactions

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Electron transfer reactions
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The chelate effect

• Chelate from Greek meaning claw or to grab on
  to. Very important in organometallic chemistry
• Thermodynamic by tethering two donor ligands
  together, one removes the entropic driving force
  for dissociating a ligand and thus making more
  particles in solution (more disorder)

• Kinetic if one of the ligands dissociates, it
  will remain close enough to the metal center to
  have a high probability of re-coordinating before
  another ligand can get in and bind

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Redox-catalyzed substitution
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Electron transfer (ET) reactions

• Types of mechanisms
• Inner-sphere the two metals share a ligand
  during electron transfer substitution processes
  are important.
• Outer-sphere
• Barriers to ET between metal sites
• distance the electron has to travel
• solvent reorganization
• coordination sphere reorganization
• different metal-ligand distances for different
  oxidation states
• atom movements are slower than electron
  movements intermediate with intermediate
  distances

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d7 HS
d6 HS
d7 HS
d6 HS
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The inner-sphere mechanism
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(No Transcript)
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Elementary steps
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Role of the bridge

• There are 2 possible mechanisms
• Resonance transfer the electron is transferred
  by a tunneling mechanism (quantum)
• Chemical transfer the electron is transferred to
  the bridge first and then to the oxidant
• Chemical transfer is favored
• The radicals detected by EPR spectroscopy are
  organic radicals

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Remote attack in ET
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Rate-limiting postcursor dissociation
inert