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Chemistry

New organocatalysts for CO2 conversion and studies of the mechanism of CO2 activation


The research project is under the co-supervision of
Alexandre MARTINEZ                                    GAO Guohua
(Chemistry, ENS Lyon)                                  (Chemistry, ECNU)
alexandre.martinez@ens-lyon.fr                   ghgao@chem.ecnu.edu.cn

SUMMARY
This project brings together researchers from ECNU and ENS de Lyon to produce highly engineered molecular and supramolecular environments to catalyze the addition of carbon dioxide to substituted epoxides. The catalytic reaction was chosen for its environmental interest as well as for the potential development of high-value added reaction pathways for fine chemical synthesis. The study itself is fundamental in nature but could result insignificant departures from current technology for catalytic site and nanoreactors design.
The two partners have been already involved in common research project, and a fruitful collaboration has been established between Pr Gao and Dr Martinez as highlighted by the two common papers dealing with fluorescent sensor for the recognition of the biologicall relevant anion phosphate.1,2 Thus, the efficiently of this collaboration is now well established. We now aim to extend this collaboration through a JoRISS proposal in order to reinforce the links between the two groups. We also wish to tackle an important problem environmental and economical issue, namely: the conversion of CO2 using new efficient organocatalyst. Indeed, both teams are interested in the crucial issue as emphasizes by their related publications: Pr Gao has focused on imidazolium ionic liquids catalytic activation of CO2 and carbonates.3 Whereas Dr Martinez has recently focused on this thematic in paper in the Journal of American Chemical Society.4 This project gathers two groups of researchers internationally recognized in their research fields, possessing all the competences to bring new insight into this field where competition and the aroused interests are strongly growing.

CONTEXT, POSITION OF THE PROPOSAL
This project has environmental and economic concerns as it will lead to green catalysts, with expected recyclability, high selectivity and reactivity. Indeed, the development of environmentally friendly catalysts for the production of fine chemicals is becoming an area of growing interest. Efficient catalysts avoiding heating and side reactions could improve the development of green chemistry.
Azaphosphatrane and imidazolium presents, a cationic charge associated with a high robustness, an easy and modulable synthesis and adequate solubility both in aqueous or organic phases. Such catalysts are metal-free, thus their use has less environmental impact than metallic catalysts. They could replace advantageously other metal-free alternatives, in numerous catalytic or stabilizing processes. In particular, we will study their activity as ORCO2OOOR+cat organocatalysts for the synthesis of cyclic carbonates, a reaction which involves carbon dioxide as a carbon source.
Indeed, the development of catalytic processes for utilization of CO2, a global-warming gas, is of growing interest for carbon management and sustainable development.5 Carbon dioxide is a potentially inexpensive and abundant renewable C1 building block and is recognized to be environmentally benign (non toxic, non corrosive and nonflammable). In this regard, the efficient transformation of CO2 under mild conditions into useful chemical compounds is very attractive from both industrial and academic viewpoint.6 CO2 is thermodynamically very stable and its activation requires the use of high energy substrates or electro reductive processes;6b,7 however the synthesis of low energy target molecules such as organic carbonates represents a promising alternative to overcome the thermodynamics. The cycloaddition of CO2 to epoxides to produce five membered cyclic carbonates is one of the few industrial synthetic processes that efficiently utilize CO2 as a raw material. Cyclic carbonates are widely used as electrolytes components in lithium batteries, polar aprotic solvents and intermediates in the production of pharmaceuticals and fine chemicals.8 In terms of “green chemistry” and “atom economy” this process is very attractive because CO2 can be incorporated into epoxides with no formation of side products.9

OBJECTIVES, ORIGINALITY AND NOVELTY OF THE PROJECT
The overall objective of the project is the study of unconventional aspects of the chemistry of azaphosphatranes and imidazolium, in confined media. The synthetic schemes to be used are highly modular, and thus one can easily probe the effects of changes in a) the structure catalytic site, b) the supramolecular cage. The synthetic technologies for each of the separameters are mature, economical and well mastered by our groups, and many of the parameters mentioned can be varied independently of the others. Given this powerful toolkit available to our partnership, we can confidently propose a very ambitious goal: the synthesis of cyclic carbonates using CO2 as a reactant and an efficient supramolecular organocatalyst. Thus, the overall goals of the present project are to explore azaphosphatranes and imidazolium and their supramolecular parents as a new class of tunable organocatalysts for the cycloaddition of CO2 to epoxides. The use of these organocatalysts are in and of itself interesting and novel, but the project consortium will be incorporating these catalysts into different confined and engineered cavities. This constitutes the most original aspect of this project, since to our knowledge supramolecular chemistry and organocatalysis have never been combine to tackle the problem of CO2 conversion.
The catalytically active site is based on the azaphosphatrane unit, the conjugate acid of the Verkade’s superbase or an imidazolium moiety. This cationic species is to be augmented with a hemicryptophane supramolecular cage and/or incorporated into various macrocycles. The synthetic schemes to be used are highly modular, and thus one can easily probe the effects of changes in a) the structure catalytic site, b) the supramolecular cage.

BIBLIOGRAPHY

1. D. Zhang, X. Jiang, H. Yang, Z. Su, E. Gao, A. Martinez and G. Gao. Novel benzimidazolium–urea-based macrocyclic fluorescent sensors: synthesis, ratiometric sensing of H2PO4- and improvement of the anion binding performance via a synergistic binding strategy. Chem. Commun., 2013, 49, 6149.
2. D. Zhang, X. Jiang, H. Yang, A. Martinez, M. Feng, Z. Dong and G. Gao. Acridine-based macrocyclic fluorescent sensors: self assembly behavior characterized by crystal structures and a tunable athochromic-shift in emission induced by H2PO4- via adjusting the ring size and rigidity. Org. Biomol. Chem., 2013, 11, 3375.
3. L. Zhang., X. Fu, G. Gao. Anion–cation cooperative catalysis by ionic liquids, ChemCatChem, 2011, 3, 1359-1364.
4. B. Chatelet, L. Joucla , J.-P.Dutasta , A. Martinez , K. C. Szeto, V. Dufaud J. Am. Chem. Soc., 2013, 135, 5348
5. (a) C. Song, Catalysis Today 2006, 115, 2. (b) I. Omae, Catalysis Today 2006, 115, 33.
6. (a) Chemical fixation of carbon dioxide: methods for recycling CO2 into useful products, M.Halmann, Ed.; CRC Press: Boca Raton, 1993. (b) T.Sakakura, J. C. Choi, H. Yasuda, Chem.Rev. 2007, 107, 2365. (c) Carbon Dioxide as Chemical Feedstock, M. Aresta, Ed.; WileyVCH, Weinheim, 2010. (d) R.Martin, A. W. Kleij, ChemSusChem2011, 4, 1259.
7. P. Jessop, T. Ikariya, R. Noyori, Chem. Rev. 1995, 95, 259.
8. (a) B. Schäffner, F. Schäffner, S. P. Verevkin, A. Börner, Chem. Rev. 2010, 110, 4554. (b) A.
A. G. Shaikh, S. Sivaram, Chem. Rev. 1996, 96, 951. (c) J. H. Clements, Ind. Eng. Chem.Res. 2003, 42, 663.
9. Y. Du, F. Cai, , D. L. Kong, L. N. He, Green Chem. 2005, 7, 518.
 

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