Selective Oxidations in Green Chemistry

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Selective Oxidations in Green Chemistry
Why are oxidation reactions important?
Why use molecular oxygen?
Why do we need new catalysts?
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Oxidations with O2

• Autoxidations
• Heterogeneous catalytsts
• Wacker oxidations

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Oxidations with O2

• V, Mo Complexes
• Fe, Ru, Os Complexes
• Co, Ir, Pd Complexes

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Pd and Oxidation with O2

• Pd/Cu in hydroformylation
• Pd(OAc)2/py or NR3
• PdX2/(-)sparteine
• Pd(OAc)2/bathophenanthroline

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Molecular Oxygen Activation by Metal Complexes

• Catalytic alcohol oxidation
• Catalytic hydrocarbon oxidation

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Oxidation Reactions
No Reaction
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(No Transcript)
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Mechanism of Benzyl Alcohol Oxidation
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Synthesis of M2M Clusters
M Ni, Pd, Pt L COD, dppe
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Comparison of M2M Complexes

• All three complexes oxidize alcohols with O2
• All oxidize cyclohexene with O2
• All oxidize Me2S with O2 (without other
  substrate)
• Pd gt Ni, Pt
• Ru gtgt Os

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Catalysis in Supercritical CO2
Jesse Kuiper and Chris Rayner (U. Leeds)

• scCO2 behaves as a non-polar organic solvent
• Comparison of toluene and scCO2
• Similar rate and TON
• Lower solubility of metal complex in CO2
• Oxygen partial pressures were important
• Higher reaction rate
• Lower solubility of metal complex
• Ease of product separation
• Characterization by NMR

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Sulfido-Bridged Heterometallics

• Alcohol oxidation
• Alkene oxidation depending on the metal
• In general, rates were low
• Slow catalyst decomposition under O2
• Formation of SOx ?

Where do we go from here?
oxo-bridged complexes nitrogen ligands
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New Route to Bimetallic Complexes
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N(n-Bu)4Ru(N)Me2(µ-O)2Pd(sparteine)

• Kinetics
• First order in alcohol
• Second order in catalyst
• For benzyl alcohols
• p-OMe gt p-Me gt p-H gt p-CF3 gt p-NO2
• Isomerization of allyl alcohol
• Inhibition by pyridine

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New Pd-M Complexes
Pd(bpy)(OSiMe3)2
- H2O, (Me3Si)2O
PdL2(OSiMe3)2
- H2O, (Me3Si)2O
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New Substrates for Synthesis
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Stoichiometric Oxidation of Butanoic Acid
heat
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Oxidations with K2FeO4
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Catalytic Fatty Acid Oxidation
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Bioactive Natural Products

• a-Methoxy and a-hydroxy fatty acids
• anti-bacterial action (TB)
• activity in leukemia
• Isolation from
• marine cyanobacterium
• red algae Schizymenia dubyi
• Helicobacter pylori (gastric mucosae)
• phospholipids of marine sponges

Extracts from the native North American prairie
plant Ipomoea leptophylla (a morning glory)
showed activity in TB. K.P. Manfredi et al. J.
Nat Prod. 2003
Prof. Nestor Carballeira, UPR
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Tuberculosis

• OSHA
• Nearly 1/3 of the world's population is infected
  with Tuberculosis (TB)
• TB causes more deaths than any other infectious
  agent in the world.
• Isoniazid (INH) is the most widely prescribed
  antibiotic used to treat TB.
• Multiple-drug resistant strains of TB hamper
  control.

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Traditional Organic Synthesis

• Can we synthesize molecules like this by the
  direct a-oxidation of fatty acids from
  agricultural sources?
• Better atom economy
• Stereoselectivity

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Fatty Acids from Soy
Solubility of oxidant/catalyst Selectivity Seconda
ry oxidant
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New Route to Bimetallic Complexes
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Chiral Chromate Complex
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Chiral Os-chiraphos Complexes
2 isomers

• Isomer A
• reversible loss of Cl-
• 31P NMR 41.5, 23.3 ppm
• Isomer B
• no dissociation of Cl-
• 31P NMR 31.9, 31.8 ppm
• Isomers dont interconvert.

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Resolution of Diastereomers
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Complexes of (R)-NH2CHMePh
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Supported Catalysts
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Heterometallic Oxidation Catalystsfor Greener
Chemical Synthesis
Continuing Research and New Directions

• Catalysis in water
• Chiral-at-metal catalysts
• Selective fatty acid oxidation
• Selective carbohydrate oxidation
• Supported catalysts

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Michael Gustavson Jesse Kuiper Adam
Kiefer Chris Lutz Karina Paprocki Adeline
Fournier John Giles