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 1938 1 • 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 + O 2  [(DMSO)Co(Salen)] 2 O 2 – Deoxygenation of Active Co(salen) in CHCl 3 • Co(Salen)O 2  Co(Salen) + O 2

Active State vs. Inactive State

• Active State binds Oxygen readily • Dimeric Form coordinates between Cobalt centers.

2 • Binds Oxygen in polar aprotic solvents • Dimeric Form coordinates Co and O.

3 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 H 2 O added via addition funnel – Stirred and kept in 70 0 C 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 N 2 from literature 5 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 C 13 NMR

IR Spectra

IR Spectra of inactive Co(salen) from Unniversity of Wimona 6 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

Absorbance vs Time at 15 C, CHCl3, 409 nm Trace

0.120000

0.100000

0.080000

0.060000

0.040000

0.020000

0.000000

UV-Vis Kinetics Results pt.1

0 100 200 300 400

Time (s)

500 600 700 y = -7E-06x + 0.0671

R 2 = 0.5286

Absorbance vs Time at 15 C, CHCl3, 409 nm Trace

0.067500

0.067000

0.066500

0.066000

0.065500

0.065000

0.064500

0.064000

0.063500

0.063000

0.062500

0 100 200 300 400 500 600 700

Time (s)

Absorbance vs Time graph of oxygenated Co(salen) in CHCl 3 15 0 C at Absorbance vs. Time graph of oxygenated Co(salen in CHCl 3 at 15 0 C, 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

0.100000

0.080000

0.060000

0.040000

0.020000

0.000000

0 200 400

Time (s)

600 800

Absorbance vs Time, 50 C, CHCl3, 409 nm

y = 2E-05x + 0.0456

R 2 = 0.9616

Trace

0.056000

0.054000

0.052000

0.050000

0.048000

0.046000

0 200 400

Tim e (s)

600 800 Absorbance vs. Time graph of oxygenated Co(salen) in CHCl 3 50 0 C at Absorbance vs. Time graph of oxygenated Co(salen) in CHCl 3 50 0 C without first 8 data points at 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

R 2 = 0.629

Trace in CHCl3

2.780000

2.760000

2.740000

2.720000

2.700000

2.680000

2.660000

2.640000

4.5

104.5 204.5 304.5 404.5 504.5 604.5 704.5

Time -LN Absorbance vs Time, 50 C, 409 nm Trace, in CHCl3

y = -0.0003x + 3.0807

R 2 = 0.9467

3.06

3.04

3.02

3 2.98

2.96

2.94

2.92

2.9

2.88

4.5

204.5

404.5

604.5

804.5

Time

-LN Absorbance vs Time plot for 15 0 C deoxygenation of Inactive Co(salen) -LN Absorbance vs. Time plot for 50 0 C 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, DM SO, 409 nm

y = -2E-05x + 0.2922

R 2 = 0.9792

Trace

0.300000

0.295000

0.290000

0.285000

0.280000

0.275000

0.270000

0.265000

0 200 400 600 800 1000

Time (s) -LN Absorbance vs Time, 15 C, DMSO, 409 nm

y = 0.0498x + 1.1575

R 2 = 0.9733

1.6

Time Trace

1.4

1.2

1 0.8

0.6

0.4

0.2

0 0 2 4 6

Time (s)

8 Absorbance vs. Time plot for Inactive Co(salen) in DMSO at 15 0 C -LN Absorbance vs. Time plot for Inactive Co(salen) in DMSO at 15 0 C No Data points were removed For the DMSO runs, temperature was allowed to equilibrate

UV-Vis Kinetics Results pt. 5

Absorbance vs Time, 50 C, DM SO 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

Time (s)

600 800 Absorbance vs. Time graph of inactive Co(salen) in DMSO at 50 0 C 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 formation 5

Discussion

• k = 0.0002 1/s for oxygenated Active Co(salen) in CHCl 3 – at 15 0 C in atmospheric conditions

Validity in question due to low correlation coefficient

• k = -0.0003 1/s for oxygenated Active Co(salen) in CHCl 15 0 C 3 at 15 0 C in atmospheric conditions • k = 0.05 1/s for inactive Co(salen) in DMSO at • k could not be determined for inactive Co(salen) in DMSO at 50 0 C – –

Possible Reason: Reaction has finished Supported by the lower absorbance compared to the 15 0 C 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 C 13 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, Schaefer, W. P., and Marsh, R. E.,

Acta

B25

, 1675 (1969) 252 (1938).

Crystallogr.,

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.

(2000) 21, 4,

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