Project: Photocatalytic Chemical Fixation of CO₂

Semiconductor photocatalysis has been successfully applied to organic synthesis,¹ environmental decontamination,² as well as water splitting and nitrogen activation.³ However, very few photoactive semiconductors have sufficiently negative conduction band potentials to effect the one electron reduction of CO₂ to its radical anion, CO₂ ^-. In addition, the photocatalyst should be active to UV-vis radiation (l > 300 nm) in order to use solar radiation and avoid photodecomposition of organic reagents and products. Colloidal cadmium sulfide (Q-CdS) is known to meet these requirements and has shown promise towards CO₂ photofixation, typically with quantum efficiencies around 10% for CO₂ reduction (l > 400 nm).^4-6 In a rare example of artificial CO₂ photofixation in organic substrates, Kanemoto et al. demonstrated that Q-CdS colloids catalyzed the formation of a-hydroxycarboxylic acid by reacting with aromatic ketones.⁴

Amines are known to interact physically, and sometimes chemically, with CO₂. The recovery and removal of CO₂ from industrial process exhaust streams (e.g., flue gases) using a CO₂-amine-H₂O system has been the subject of numerous publications.⁷ Aminoethan-2-ol also is used frequently in industrial applications, and triethanolamine is a common sacrificial electron donor in homogeneous systems containing [Ru(bpy)₃]²⁺ and [Re(bpy)(CO₃)Cl] as photocatalysts for the reduction of CO₂.⁸

We are interested in studying the photolysis of amino-2-alcohols in the presence of CO₂ and suitable photocatalysts (Scheme 1), such as manganese(II) sulfide,^9,10 with the goal of providing a novel route to oxazolidinones (1). One desirable feature of this system is the potential for stereochemical control in the orientation of R' and R'' in oxazolidinone (1). The stereoelectronic environment of the aminoalcohol will be varied systematically to investigate this potential. Note that the amine electron donor is not “sacrificial” in this system, but is incorporated in the product.

References

1)      Fox, M. A.; Dulay, M. T. "Heterogeneous Photocatalysis". Chem. Rev. 1993, 93, 341-357.

2)      Hoffmann, M. R.; Martin, S. T.; Choi, W.; Bahnemann, D. "Environmental Applications of Semiconductor Photocatalysis". Chem. Rev. 1995, 95, 69-96.

3)      Lewis, L. N. "Chemical Catalysis by Colloids and Clusters". Chem. Rev. 1993, 93, 2693-2730.

4)      Kanemoto, M.; Ankyu, H.; Wada, Y.; Yanagida, S. "Visible-light Induced Photofixation of CO₂ into Benzophenone Catalyzed by Colloidal CdS Microcrystallites". Chem. Lett. 1992, 2113-2114.

5)      Kanemoto, M.; Nomura, M.; Wada, Y.; Akano, T.; Yanagida, S. "Effect of In³⁺ in Nano-Scale CdS-catalyzed Photoreduction of CO₂". Chem. Lett. 1993, 1687-1688.

6)      Fujiwara, H.; Kanemoto, M.; Ankyu, H.; Murakoshi, K.; Wada, Y.; Yanagida, S. "Visible-light Induced Photofixation of Carbon Dioxide into Aromatic Ketones and Benzyl Halides Catalysed by CdS Nanocrystallites". J. Chem. Soc., Perkin Trans. 2 1997, 317-321.

7)      Ohno, K.; Inoue, Y.; Yoshida, H.; Matsuura, H. "Reaction of Aqueous 2-(N-Methylamino)ethanol Solutions with Carbon Dioxide. Chemical Species and their Conformations Studied by Vibrational Spectroscopy and ab Initio Theories". J. Phys. Chem. 1999, 103, 4283-4292.

8)      Ziessel, R. Photosensitization and Photocatalysis Using Inorganic and Organometallic Compounds. In; Kalyanasundaram, K. and Grätzel, M., Ed.; Kluwer Academic Publishers: Norwell, 1993, pp 217-245.

9)      Michel, F. M.; Schoonen, M. A. A.; Zhang, X. V.; Martin, S. T.; Parise, J. B. "Hydrothermal Synthesis of Pure Alpha-phase Manganese(II) Sulfide Without the Use of Organic Reagents". Chem. Mat. 2006, 18, 1726-1736.

10)    Zhang, X. V.; Martin, S. T.; Friend, C. M.; Schoonen, M. A. A.; Holland, H. D. "Mineral-assisted Pathways in Prebiotic Synthesis: Photoelectrochemical Reduction of Carbon(+IV) by Manganese Sulfide". J. Am. Chem. Soc. 2004, 126, 11247-11253.