Temperature Controlled Rate
Studies of Co(salen)
Reversible Oxygen Binding
By Philip Chuang
Background Information
• Co(salen) is Cobalt N,N’-bis (salicylaldehyde)
ethylenediamine
• Ability to reversibly bind oxygen discovered by
Tsumaki in 19381
• A square planar dioxygen carrier
• Exists in both an Active and Inactive state
• Interested in Effect of Temperaturee on Rate in:
– Oxygenation of Inactive Co(Salen) in DMSO
• [(DMSO)Co(Salen)]2 + O2  [(DMSO)Co(Salen)]2O2
– Deoxygenation of Active Co(salen) in CHCl3
• Co(Salen)O2  Co(Salen) + O2
Active State vs. Inactive State
• Active State binds
• Binds Oxygen in polar
Oxygen readily
aprotic solvents
• Dimeric Form
• Dimeric Form
coordinates between
coordinates Co and O.3
Cobalt centers.2
Diagram from Reference 2
Diagram from Reference 3
Hypothesis
• The Rate of Oxygen Binding and
Dissociation increases with Higher Temp.
More specifically:
– The Rate of Inactive Co(salen) Oxygenation
will Increase with Temperature in DMSO.
– Rate of Active Co(salen) Deoxygenation will
Increase with Temperature in chloroform.
Synthetic Method
• Synthesis of Inactive Co(salen)
– 1 eq. ethylenediamine added to 2 eq.
Salicylaldehyde in boiling ethanol, for 4 min.
– 1 eq. Salen product (from above) refluxed in
ethanol under Argon, 1 eq. Cobalt Acetate in
H2O added via addition funnel
– Stirred and kept in 700C Water bath for 1
hour
• Synthesis of Active Co(salen)
– Same methods as Inactive, but no hot water
bath
Procedure derived from Reference 4
UV-Vis
UV-VIS of Inactive Co(salen) in
DMSO in atmosphere
UV-Vis of Inactive Co(salen) in
DMSO in N2 from literature5
The UV spectra indicates that the Inactive product was
obtained.
Differences between UV spectra likely due to availability
of Oxygen in the DMSO solution
H-NMR
H-NMR of Active Product in dDMSO H-NMR of Inactive Product in dDMSO
-The H-NMRs did not correspond to predicted H-NMRs
-Conclusive Identification from H-NMR unobtainable
-Future improvement: prepare H-NMR in inert atmosphere, include
C13 NMR
IR Spectra
IR Spectra of inactive Co(salen) from
Unniversity of Wimona6
IR spectra of Inactive Co(salen)
With the exception of the C-H peak at 3000, and the nujol
peaks at 1500, 1400 and 700 cm-1 look similar
Further reinforces likelihood of obtaining Inactive Product
UV-Vis Kinetics Results pt.1
y = -7E-06x + 0.0671
Absorbance vs Time at 15 C, CHCl3, 409 nm
R2 = 0.5286
Absorbance vs Time at 15 C, CHCl3, 409 nm
Trace
Absorbance (AU)
Absorbance (AU)
0.120000
0.100000
0.080000
0.060000
0.040000
0.020000
0.000000
0
100
200
300
400
500
600
700
0
Time (s)
Absorbance vs Time graph of
oxygenated Co(salen) in CHCl3 at
150C
Trace
0.067500
0.067000
0.066500
0.066000
0.065500
0.065000
0.064500
0.064000
0.063500
0.063000
0.062500
100
200
300
400
500
600
700
Time (s)
Absorbance vs. Time graph of
oxygenated Co(salen in CHCl3 at
150C, excluding first 8 data points
The first 8 data points were removed
Not enough time given to allow temperature to equilibrate
UV-Vis Kinetics Results pt. 2
Absorbance vs Time, 50 C, CHCl3, 409 nm Trace
Absorbance vs Time, 50 C, CHCl3, 409 nm
Trace
y = 2E-05x + 0.0456
R2 = 0.9616
0.056000
0.080000
Absorbance (AU)
Absorbance (AU)
0.100000
0.060000
0.040000
0.020000
0.000000
0
200
400
600
800
0.054000
0.052000
0.050000
0.048000
0.046000
0
200
Time (s)
400
600
800
Tim e (s)
Absorbance vs. Time graph of
Absorbance vs. Time graph of
oxygenated Co(salen) in CHCl3 at oxygenated Co(salen) in CHCl3 at
500C
500C without first 8 data points
Again, the first 8 data points were discarded.
Not enough time was given for temperature to equilibrate
UV-Vis Spectra Results pt. 3
-LN Absorbance vs Time, 15 C, 409 nm Time
y = 0.0002x + 2.6812
Trace in CHCl3
2
y = -0.0003x + 3.0807
R2 = 0.9467
3.06
3.04
3.02
3
2.98
2.96
2.94
2.92
2.9
2.88
R = 0.629
2.780000
2.760000
2.740000
2.720000
2.700000
2.680000
2.660000
2.640000
-LN Absorbance
-LN Absorbance
-LN Absorbance vs Time, 50 C, 409 nm
Trace, in CHCl3
4.5
104.5 204.5 304.5 404.5 504.5 604.5 704.5
Time
-LN Absorbance vs Time plot for
150C deoxygenation of Inactive
Co(salen)
4.5
204.5
404.5
604.5
804.5
Time
-LN Absorbance vs. Time plot
for 500C deoxygenation of
Inactive Co(salen)
The slope of the –LN Absorbance vs. Time plot yields the rate
constant of a first order reaction.
UV-Vis Kinetics Results pt. 4
Absorbance vs Time, 15 C, DMSO, 409 nm
Trace
y = -2E-05x + 0.2922
2
-LN Absorbance vs Time, 15 C, DMSO, 409 nm
Time Trace
y = 0.0498x + 1.1575
R = 0.9792
0.295000
-LN Absorbance
Absorbance (AU)
0.300000
0.290000
0.285000
0.280000
0.275000
0.270000
0.265000
0
200
400
600
800
1000
Time (s)
Absorbance vs. Time plot for
Inactive Co(salen) in DMSO at
150C
R2 = 0.9733
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0
0
2
4
6
Time (s)
-LN Absorbance vs. Time plot for
Inactive Co(salen) in DMSO at
150C
No Data points were removed
For the DMSO runs, temperature was allowed to
equilibrate
8
UV-Vis Kinetics Results pt. 5
Absorbance (AU)
Absorbance vs Time, 50 C, DMSO 409 nm
Time Trace
0.18
0.179
0.178
0.177
0.176
0.175
0.174
0.173
0.172
0
200
400
600
800
Time (s)
Absorbance vs. Time graph of inactive
Co(salen) in DMSO at 500C
Result was not workable, rate could not be calculated
Possible explanations in Discussion Section
Discussion
• When LN Absorbance vs. LN Time plotted
(not pictured), linearity observed
• Indicated a first order reaction:
– R = k[A]  -d[A]/dt = k[A]
– -d[A]/[A] = k Integrate to get LN [A] = -kt
– Thus k = -LN [A] /t
• This method used to attain reaction rates
from results
• Decreasing absorbance indicative of
oxygen complex formation5
Discussion
• k = 0.0002 1/s for oxygenated Active Co(salen)
in CHCl3 at 150C in atmospheric conditions
– Validity in question due to low correlation coefficient
• k = -0.0003 1/s for oxygenated Active Co(salen)
in CHCl3 at 150C in atmospheric conditions
• k = 0.05 1/s for inactive Co(salen) in DMSO at
150C
• k could not be determined for inactive Co(salen)
in DMSO at 500C
– Possible Reason: Reaction has finished
– Supported by the lower absorbance compared to the 150C
sample.
Conclusions
• Data supports hypothesis for increased rate of
Oxygen Dissociation for Oxygenated Co Active
Co(salen) at increased temperatures
• Not enough data to support or disprove
hypothesis for increased rate of Oxygen uptake
in Active form of Co(salen at increased
temperatures.
• Future Considerations:
– Prepare NMRs and UV-Vis solutions in an inert
glovebox using a sealable cuvette
– Take the C13 NMR to better characterize products
– Run more samples at different temperatures to give
better overall picture
References
1.
2.
3.
4.
5.
T. Tsumaki, Bull. Chem. Soc. Jpn., 13,
252 (1938).
Schaefer, W. P., and Marsh, R. E., Acta
Crystallogr.,
B25, 1675 (1969)
Bruckner, S.,Calligaris, M., Nardin, G., and Randaccio,
L., Acta Crystallogr., B25, 167 (1969)
Bailes, R. H., and Calvin, M., J. Amer. Chem. Soc., 69,
1886 (1947)
B. Ortiz, and Park, S., Bull. Korean Chem. Soc. 21, 4,
(2000)
Acknowledgements
• I’d like to thank Ankur for always being available
to help me at all hours of the day
• Simone for being a big help during the lab
sessions and being ridiculously funny
• Professor Roth for allowing me to use her
temperature controlled UV-Vis and giving us a
cool, albeit hard final project that taught us to
make use of the journal articles available to us
• Finally my fellow students for being ever
supportive and cheery