1. Reaction of a
Biomimetic Molybdenum Complex
with Carbon Dioxide
By Michael Yanagisawa
Brown University ‘13

2. • Global levels of carbon dioxide (CO2) are
rising, giving way to global climate
change
• A goal worldwide: reduce CO2 levels
› Less CO2 means less global warming
Ref. 1

3. • The challenge: CO2 is very stable
› CO2 reduction gets rid of favorable linear
structure
› CO2 reduction is a thermodynamic uphill
reaction
• Nature effectively reduces CO2
› Photosynthesis produces sugars from CO2
• Bio-inspired solutions seem promising

4. • The enzyme formate dehydrogenase
(FDH) reversibly converts formate (HCO2-)
to CO2
› CO2 + H+ + 2e- → HCO2-
• Our goal: to mimic the active site of FDH
to convert carbon dioxide into formate
› Formate can be used as a fuel source
• Recycling CO2 from a harmful product
into a useful substrate could solve the
CO2 problem Ref. 2,3

5. • The active site of FDH consists of a
molybdenum center with two pterin
ligands
Ref. 4

6. • Biomimetic complexes have been
synthesized by other groups
• Characteristics
› Mo metal center
› Ditholene ligands
• For our complex,
R = phenyl
Ref. 5

7. • Jun Seo of our group reacted a tungsten
analogue with carbon dioxide
› W and Mo have very similar properties
• The reaction formed a tungsten dimer
Ref. 6

8. Research Question
• Our compound is [MoO(pdt)2]2-
• pdt = phenyl dithiolene
• What is the product of a reaction with CO2?

9. • The dream: our complex reduces CO2 to
formate like its inspiration, FDH
• The hope: CO2 binds onto the metal
center, revealing an intermediate to
forming formate
• Another possibility: a product analogous
to Jun's product i.e. a Mo dimer

10. Ref. 7

11. • 50 mL Schlenk flask filled with
• 20 mg [MoO(pdt)2]2- and
• 2 mL MeCN
• attached to a 100 mL CO2 bulb (2 atm)
• Reaction heated to 90°C and stirred 2
days

12. • After two days, we dried the product
• The crude product was rinsed with diethyl
ether and collected (the “ether layer”)
• The remaining product (the “metal
layer”) was then redried

13. Spectroscopy
 To test the reaction, we used IR, UV-Vis,
EPR, 1H and 13C NMR, GC/MS, and ESI
 We also tried to crystallize the product for
x-ray crystallography, but the product did
not crystallize
 We report IR, EPR, GC/MS, and ESI and
their interesting interpretations

14.  Characteristic Mo=O stretching visible
 Starting material νMoO = 886 cm-1
 After reaction, stretching shifted left to
product νMoO = 924 cm-1
 For [MoVO(pdt)2]-, νMoO = 924 cm-1
 Interpretation:
› Our product has a Mo(V) center
Ref. 5b

15.  No peaks present
 Interpretation:
› Our product has no unpaired electrons
› IR shows evidence of Mo(V)
› Conclusion: antiferromagnetic Mo(V) dimer

16.  GC/MS of ether layer
› Peaks at 51, 77, and 105
› Matches up with diphenyl ethanedione
 Interpretation:
› In the reaction, some dithiolene ligand is
falling off the metal center and is part of the
organic product

17.  ESI of metal layer (still preliminary)
› Peaks at 427 and 757
› Mass of [MoO(pdt)2]2- = 596.66
 Interpretation:
› The 757 peak again suggests some sort of
dimer. The 427 peak suggests a
complementary metal center; 427 and 757
average to around the 596.

18. Conclusion
 Our product is a Mo(V) antiferromagnetic
dimer

19. Conclusion
 Predicted product (MW ~ 757)
 Where R1 + R2 may be:
› A CO2 molecule
› O and S bridging atoms
› Something else?

20. Looking Forward
 We would like to crystallize the product
and identify the final product
 Monoatomic Mo and W complexes have
been known to dimerize
 Example: Jun’s W compound
 Use labelled CO2 to track the oxygen
atoms; start to deduce a mechanism

21. References
1. Crowley, T. J.; Berner, R. A. Science 2001, 292, 870-872.
2. Ha, S.; Dunbar, Z.; Masel, R.I. J. Power Sources 2006, 158, 129-136.
3. From a paper’s press notes: http://www.usu.edu/science/htm/one-
step-closer-usu-biochemists-convert-greenhouse-gas-to-fuel/
4. Boyington, J. C.; Gladyshev, V. N.; Khangulov, S. V.; Stadtman, T. C.;
Sun, P. D. Science 1997, 275, 1305-1308.
5. (a) Lim B. S.; Donahue, J. P.; Holm, R. H. Inorg. Chem. 2000, 39, 263-
273. (b) Lim B. S.; Holm, R. H. J. Am. Chem. Soc. 2001, 123, 1920-
1930.
6. Paper in press.
7. (a) Tate, D. P.; Knipple, W. R.; Augi, J. M. Inorg. Chem. 1962, 1, 433-
434. (b) Schrauzer, G. N.; Mayweg, V. P. J. Am. Chem. Soc. 1965,
87, 1483-1489. (c) Lim, B. S.; Donahue, J. P.; Holm, R. H. Inorg. Chem.
2000, 39, 263-273.

22. Acknowledgements
• Camly Tran
• Dr. Eunsuk Kim
• Jun Seo
• The Kim lab
• Brown University
› Undergraduate Teaching and Research Award
for funding (summer 2012)