Macrocyclic Ligands: Functional Host Guest Systems.

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Macrocyclic Ligands Functional Host Guest
Systems.

• Post Graduate Lecture Course
• February 2000
• Lecture 6

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More Macrocycles

• Many other types of macrocycles
• Pendant (Lariat) arm Macrocycles
• Cage Ligands
• Cryptands
• Sephulcrates
• Binucleating Macrocycles
• Neutral Molecule/Anion Binding
• Metallamacrocycles
• Cyclodextrins
• Threaded Macrocycles
• Rotaxanes/Catenanes

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Pendant Arm (Lariat) Macrocycles

• Variations
• Arms From Donor Atoms or Backbone
• Arms With or Without Donor Atoms
• Flexible or Rigid Arms
• Different Donor Types
• Redox Active Sites

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Preparations of Pendant Arm Macrocycles
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A Naturally Occurring Pendant- arm Macrocycle

• Enterobactin
• Used by E. Coli to transport FeIII across its
  cell wall
• Consists of a small crown ether with three
  pendants
• 3 catechol groups coordinate iron

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Cage Macrocycles Cryptands

• Bicyclic Species
• Enhanced metal binding

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Preparation
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Cage Macrocycles Sephulchrates

• Particularly used for transition metals
• Give rigid, constrained coordination sphere
• Useful for comparing different metals in same
  ligand environment
• Outer sphere electron transfer.

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Preparation
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Binucleating Macrocycles

• Two metals in the same complex
• Cooperative effects
• magnetic
• redox
• Binucleation can occur via
• two macrocyclic cavities
• linked by a single bridge
• linked by two (or more) bridges
• large ring size, many donor atoms
• pendant arms

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Anion and Neutral molecule Binding

• Anions require positive centres
• ammonium cations (protonation)
• metallacmacrocycles
• Neutral species are often polar
• Use hydrogen bonding

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Threaded Macrocycles Towards Molecular Machines

• Catenane
• Macrocycle with molecule threaded through
• Stopper group on end of thread
• Rotaxane
• macrocycle threaded through a macrocycle

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Bibliography

• L.F.Lindoy, The Chemistry of Macrocyclic Ligand
  Complexes, C.U.P., 1989.
• Comprehensive Supramolecular Chemistry
• Dictionary of Inorganic Chemistry
• etc.