1. Properties and synthetic methods concerning Co(II) derivatives and CO2 activation
Angelique Amado l Feifei Li, Chao Dong l Department of Chemistry and Biochemistry, Las Cruces, NM 88003
Background
results
Macrocyclic ligands containing metal centers play vital roles in many biological processes, however, the mechanistic properties and interactions of these complexes are not fully understood. *
Cobalt containing macrocyclic complexes are being explored as they can be used to effectively model CO2 activation as well as illustrate catalytic properties and mechanisms undergone in a variety of bio- inorganic based processes.
Spectroscopic X-ray emission analysis will be preformed in order to gain a deeper understanding of how metal coordinated complexes interact; especially in biological systems.
Tetraphenyl borate Triflate Perchlorate
(Bph4) (OTF) (ClO4)
Co[trans(14 diene)] or Co[HMD]
Figure 1: H NMR spectra of HMD ligand
Table 2: UV-Vis data comparisons of Co(II)[HMD] in CH3CN
ʎ max (nm)
Literature Values
Experimental Values
1981
Szalda
N-rac
N-meso
1991 Creutz
1390
N/A
440
442
310
322
209
208
218
Objective
Interest lies in determining the factors that mark the effectiveness of this catalyst in the CO2 activation process using counter-ions as possible sources of variance.
experiment
H¹ NMR
Approximately 10 mg of the sample ligand was dissolved in 0.7 mL of deuterium oxide.
Integration and peak values correspond to according hydrogens labeled in the figure.
Preparation of metal-ligand complexes were done using methods with reference to literature descriptions.¹
Future Directions
Elemental Analysis
Approximately 10 mg samples of both Co[HMD] (CoCl4) and Co[HMD] (ClO4)2 were sent to Altantic Microlabs Inc.
Two scans were done for each sample in order to determine the amount of C, H, and N in the samples.
In the near future, Co(II) will be reduced to Co(I) under oxygen free and moisture free conditions. This reduced species will then be employed to activate CO2.
These samples will be analyzed using X-ray emission spectroscopy to further our understanding of catalytic mechanisms
(1)
(2)
(3)
(4)
Table 1: Elemental analysis by percent composition
Sample
Calculated
Scan 1
Scan 2
Co(trans[14] diene)(CoCl4)
C: 35.58%
H: 5.97%
N: 10.37%
34.18%
5.81%
9.98%
34.04%
5.86%
10.07%
Co(trans[14] diene)(ClO4)2
C: 35.81%
H: 5.64%
N: 10.45%
35.37%
6.02%
10.21%
35.48%
5.97%
10.23%
Conclusion
Initial synthesis of HMD ligand took many trials and the literature did not reflect observations made experimentally.
UV-Vis data clearly shows that the compound containing two separate cobalt centers used as a starting material (Co[HMD](CoCl4)) was fully reduced to a single cobalt center with the according counter-ion.
Elemental analysis as well as H¹ NMR data confirm purity and structure of samples, respectively. The structure of the Co[HMD] was most closely related to the meso orientation.
UV-Vis Spectroscopy
All samples shown in the figure were dissolved in 2-3 mL of acetonitrile.
UV-Vis data was taken using Chemstation software and standard operating procedures at 25°C.
+ CoCl2
For the synthesis of Co(trans[14] diene)(CoCl4)2, the heat was slightly lowered that the recorded literature value. After multiple failed attempts the reaction was eventually done under nitrogen protection using Schlenk like techniques.
In order to form Co(trans[14] diene)(ClO4)2, the starting material was dissolved in less water than initially calculated. An ice bath was also employed to precipitate product.
Co(trans[14] diene)(OTF)2 synthesis had a similar procedure to the perchlorate counter-ion procedure.
Co(trans[14] diene)(BPh4)2 also had a similar procedure to that above, however, methanol is used as a solvent in place of water.
--Co[HMD]CoCl4
--Co[HMD](BPh4)2
--Co[HMD](OTF)2
--Co[HMD](ClO4)2
References
Dixon, N. E., Jackson, W. G., Lancaster, M. J., Lawrance, G. A., & Sargeson, A. M. (1981). Labile (Trifluoromethanesulfonato)cobalt(III) Amine Complexes. Inorganic Chemistry, 20(2),
* Fujita, E., Creutz, C., Sutin, N., & Szalda, D. J. (1991). Carbon Dioxide Activation by Cobalt( I) Macrocycles: Factors Affecting C02 and CO Binding. American Chemical Society, 1-11.
¹ Merrell, P. H., Urbach, F. L., & Arnold, M. (1977). Synthesis and Characterization of Macrocyclic Nickel Complex. Journal of Chemical Education, 54(9),
Rillema, D. P., Endicott, J. F., & Papaconstantinou, E. (1971). Oxidation-Reduction Behavior of Complexes Containing Macrocyclic Ligands. An Electrochemical Comparison of Complexes with the Metals Iron through Zinc. Inorganic Chemistry, 10(8), 1-8.
Szalda, D. J., Schwarz, C., Endicott, J., Fujita, E., & Creutz, C. (1989). Solution Studies of the Cobalt(I1) N-rac - and N-meso -CoL2+ Isomers and Molecular and Crystal Structures of the Low-Spin, Five-Coordinate Cobalt(I1) Macrocyclic Complexes. American Chemical Society, 28(16),
Figure 2: UV-Vis data collected for varying counter-ions in CH3CN
Acknowledgements: Discovery Scholars Program for the opportunity to continue this research; Dr. Li and Dr. Dong for their support and help with these experiments; MARC program (GM ) for their support in printing.