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Metal ions can be separated from one another by complexation with organic ligands–the chelating agent– to form uncharged chelates. Here, the chelating agent must contain hydrophobic groups and behave as a weak acid, losing a proton to bind with the metal. Since most organic ligands used in this process are insoluble or undergo oxidation in the aqueous phase, the chelating agent is initially added to the organic phase and extracted into the aqueous phase. The metal-ligand complex is...
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Mixed amidophenolate-catecholates of molybdenum(VI).

Sukesh Shekar1, Seth N Brown

  • 1Department of Chemistry and Biochemistry, 251 Nieuwland Science Hall, University of Notre Dame, Notre Dame, IN 46556-5670, USA. Seth.N.Brown.114@nd.edu.

Dalton Transactions (Cambridge, England : 2003)
|January 11, 2014
PubMed
Summary

Molybdenum complexes with bulky ligands react with catechol to form new mono- and dimolybdenum structures. These complexes exhibit fluxional behavior and varying Lewis acidity, offering insights into molybdenum coordination chemistry.

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Area of Science:

  • Coordination Chemistry
  • Organometallic Chemistry
  • Molybdenum Chemistry

Background:

  • Dioxomolybdenum(VI) complexes are key intermediates in various catalytic processes.
  • The synthesis and characterization of novel molybdenum complexes with bulky ligands are crucial for understanding their reactivity and properties.
  • Catecholate ligands play a significant role in stabilizing different oxidation states and coordination geometries of metal ions.

Purpose of the Study:

  • To synthesize and characterize novel oxo-free and oxo-bridged molybdenum complexes derived from a dioxomolybdenum(VI) precursor and 3,5-di-tert-butylcatechol.
  • To investigate the structural features, fluxional behavior, and Lewis acidity of the newly formed mono- and dimolybdenum complexes.
  • To explore the electronic properties, including π-donation from amidophenoxide ligands, and their influence on complex reactivity.

Main Methods:

  • Synthesis of molybdenum complexes using a (t)BuClipH2)MoO2 precursor and 3,5-di-tert-butylcatechol.
  • Structural characterization using X-ray crystallography and variable-temperature Nuclear Magnetic Resonance (NMR) spectroscopy.
  • Investigation of Lewis acidity through pyridine binding kinetics studies.

Main Results:

  • Formation of an oxo-free monomeric bis(amidophenoxide)-monocatecholate complex, ((t)BuClip)Mo(3,5-(t)Bu2Cat), with cis-β geometry.
  • Observation of two distinct fluxional processes in the mono- and dimolybdenum complexes: geometric isomer interconversion and ligand end-interchange.
  • Synthesis of a dimolybdenum mono-oxo complex, ((t)BuClip)Mo(μ-3,5-(t)Bu2Cat)2Mo(O)(3,5-(t)Bu2Cat), a structural hybrid of known molybdenum complexes.
  • The mixed amidophenoxide-catecholate complex exhibits lower Lewis acidity compared to related complexes, evidenced by slower pyridine binding kinetics.

Conclusions:

  • The bulky (t)BuClip ligand facilitates the formation of unique mono- and dimolybdenum catecholate complexes with interesting structural and dynamic properties.
  • Fluxional processes, including Bailar twists and atropisomerization, are key to the observed dynamic behavior of these molybdenum complexes.
  • The electronic structure, influenced by π-donation from amidophenolates, impacts the Lewis acidity and reactivity of the molybdenum centers.