Olefin Metathesis

1
Olefin Metathesis

• 1950s In the presence of various organometallo
  compounds, olefin metathesis (where the R groups
  of olefins were swapped with the other) occurred
• 1970s Chauvin and colleagues proposed mechanism
  that seemed to fit
• Like a dance
• 1980s Schrock and Grubbs synthesized the first
  metallo-carbene compounds that were air sensitive
  and shown to catalyze olefin metathesis
• Three types of olefin metathesis
• Ring closing metathesis (RCM)
• Ring opening metathesis (ROM)
• Cross metathesis (CM)

Image from Greco, G.E. Nobel Chemistry in the
Laboratory. J. Chem. Ed. 2007,84(12), 1996
2
Selectivity Model for CM

• Experiments done by Chatterjee et al showed that
  the various olefin metathesis substrates could be
  classified by their relative reactivity
• Type I formed homodimers rapidly
• Type II formed homodimers slowly
• Type III didnt form homodimers, participate in
  CM
• Type IV spectator olefin, no CM reaction
• Reacting two olefins from different groups could
  yield stereospecific, easily predictable products
  in good yield
• Reactivity of olefins depended on things such as
  sterics as well as deactivating
  electron-withdrawing groups

Chatterjee, A. K. A General Model for Selectivity
in Olefin Metathesis. J. Am. Chem. Soc. 2003,
125, 11360-11370.
3
Hypothesis

• In testing out the selectivity model, by reacting
  a type I (allyl chloride) and type II olefin
  (4-fluoro-ß-nitrostyrene), a predictable product
  can be obtained.

4
Olefin Metathesis Catalysts

• Schrock and Grubbs
• Air sensitive
• Initially were molybdenum and ruthenium based,
  respectively
• Both won 2005 Nobel Prize in Chemistry for work
  in olefin metathesis, along with Chauvin

Images from Pappenfus, T. M. Synthesis and
Catalytic Activity of Ruthenium-Indenylidene
Complexes for Olefin Metathesis, J. Chem. Ed.
2007, 84 (12), 1998-2000.
5
Ruthenium Catalysts, continued

• Ruthenium indenylidene complexes
• Can be synthesized from commercially available
  diphenyl propargyl alcohol, synthetic precursors
  are all relatively air stable, when not in
  solution
• Catalytic properties similar to classic Grubbs,
  if not superior
• Synthesis methods are also relatively simple

Images from Pappenfus, T. M. Synthesis and
Catalytic Activity of Ruthenium-Indenylidene
Complexes for Olefin Metathesis, J. Chem. Ed.
2007, 84 (12), 1998-2000.
6
Methods

• Synthesis of RuCl2(PPh3)3
• Reflux RuCl33H2O with triphenylphosphine under
  argon in a 16 molar ratio for 3 hours, filter
  out black crystals, wash with anhydrous ether.
• Synthesis of 1a and 1b
• 1a
• Reflux diphenyl propargyl alcohol with
  RuCl2(PPh3)3 (21 equivalents) in a positive
  argon atmosphere for 2.5 hours, with THF as the
  solvent. Remove solvent via rotary evaporation,
  redissolve dark red residue in CH2Cl2,
  recrystallize with hexanes, slowly. Filter out
  solid, store in desiccator.
• 1b
• Stir 1a and tricyclohexane in a 13.3 equivalent
  ratio under a positive argon atmosphere for 1.5
  hours, with dichloromethane as the solvent.
  Remove solvent via rotary evaporation, added
  hexanes and stir for another 30 minutes. Filter
  out brown-orange solid, store in desiccator.
• CM reaction
• Reflux styrene, allyl chloride and 1b in a
  110.01 ratio overnight.
• Characterization methods
• NMR IR, as well as TM for the RuCl2(PPh3)3

Synthesis methods taken from Parry, R. W.
Tris(triphenylphospine)dichlororuthenium(II)
Inorganic Syntheses. 1970, XII, 238-239 as well
as Pappenfus, T. M. Synthesis and Catalytic
Activity of Ruthenium-Indenylidene Complexes for
Olefin Metathesis, J. Chem. Ed. 2007, 84 (12),
1998-2000.
7
Data NMR spectra for 1a and 1b, literature
1a in chloroform-d
1b in chloroform-d
All reference spectra obtained from Pappenfus, T.
M. Synthesis and Catalytic Activity of
Ruthenium-Indenylidene Complexes for Olefin
Metathesis, J. Chem. Ed. 2007, 84 (12), 1998-2000.
8
Results NMR spectra of 1a and 1b, experimental
1a in benzene-d
1b in benzene-d
9
Data Literature IR spectra of 1a and 1b
10
Result Experimental IR spectra of 1a and 1b
1a with nujol
1b with nujol
11
Data Allyl Chloride impurities
Used allyl chloride in benzene-d
Allyl chloride without impurities, benzene-d
12
Results Product vs 1b reagents
Product in benzene-d
1b reagents in benzene-d
13
Results Yields

• RuCl2(PPh3)3 (Yield 0.5059 g)
• RuCl3H2O used 0.1658 g (0.641 mmoles, limiting
  reagent)
• triphenylphosphine used 0.9986 g (3.807 mmoles)
• yield 82.3
• TM 130-134C, literature indicates 132-134C
• 1a (Yield 0.1944 g)
• RuCl2(PPh3)3 used 0.3621 g (0.378 mmoles,
  limiting reagent)
• Diphenyl propargyl alcohol used 0.1513 g (0.727
  mmoles)
• yield 58.0
• 1b (Yield 0.1315 g)
• 1a used 0.1524 g (0.172 mmoles, limiting
  reagent)
• Tricyclohexylphosphine used 0.1672 g (0.596
  mmoles)
• yield 89.9

Literature value of Tm obtained from Parry, R. W.
Tris(triphenylphospine)dichlororuthenium(II)
Inorganic Syntheses. 1970, XII, 238-239.
14
Discussion

• The ruthenium indenylidene complexes synthesized,
  based on the NMRs, seem to be the desired
  complexes
• The IRs are less conclusive
• Nujol absorptions seem to drown out any
  characteristic absorptions (peaks at 2950-2800,
  1465-1450 and 1380-1370 cm-1)

Nujol peaks referenced from http//en.wikipedia.or
g/wiki/Nujol
15
Did a reaction occur?

• NMR seems to indicate it did
• However, its also possible that the difference
  in NMRs is due to the presence of liquid allyl
  chloride in the pre-reaction NMR taken
• Theoretically, the allyl chloride is highly
  reactive and should have reacted with the styrene
• Normally, styrenes are part of the Type II group,
  and is also reactive in CM reactions. However,
  its possible that the presence of the nitro
  group directly attached to the CC bond highly
  reduced its reactivity

16
Other possible reasons for no reaction

• Many of the intermediates, though fairly air
  stable, will react with air in the presence of
  water.
• The purity of the catalyst is unknown, possible
  that it was much less than 1 molar of the
  reagents
• Even if the catalyst were pure, its possible
  that 1 molar is insufficient to catalyze the
  reaction overnight.
• When the CM reaction beaker was refluxed, the
  solvent evaporated very quickly, had to turn off
  the heating mantle
• Its possible that since allyl chloride is fairly
  volatile, it evaporated before the reaction could
  take place.
• The effectiveness of the ruthenium indenylidene
  complexes has only been shown in RCM and ROM.

17
Conclusions

• Chatterjee et als model of CM selectivity is
  still valid
• Although the results of this experiment are not
  conclusive, the model is also not disproven
• This model of CM selectivity could open paths to
  new synthetic routes to important organic
  compounds, such as various drugs (i.e.
  epothilones, antitumor agents)

18
Conclusions ways to improve

• Find olefins of different reactivities that are
  both solid
• Also, olefins that are not deactivated by
  electron withdrawing groups
• Product of CM should have distinctive properties
  from the reagents, either physical or spectral
• Possibly work with different catalysts which are
  known to have high reactivity in CM reactions
• Procure correct NMR solvent, to compare with
  literature

19
References

• Casey, C. P. 2005 Nobel Prize in Chemistry
  Development of the Olefin Metathesis Method in
  Organic Synthesis. J. Chem. Ed. 2006, 82 (2),
  192-195.
• Chatterjee, A. K. A General Model for Selectivity
  in Olefin Metathesis. J. Am. Chem. Soc. 2003,
  125, 11360-11370.
• Fürstner, A. Indenylidene Complexes of Ruthenium
  Optimized Synthesis, Structure Elucidation, and
  Performance as Catalysts for Olefin Metathesis
  Application to the Synthesis of the ADE- Ring
  System of Nakadomarin A. Chem. Eur. J. 2001, 7
  (22), 4811- 4820.
• Pappenfus, T. M. Synthesis and Catalytic Activity
  of Ruthenium- Indenylidene Complexes for Olefin
  Metathesis, J. Chem. Ed. 2007, 84 (12),
  1998-2000.
• Parry, R. W. Tris(triphenylphospine)dichlororuthen
  ium(II) Inorganic Syntheses. 1970, XII, 238-239.