Inorganic Calvin Cycle – ICC

We employ a two-steps cascade strategy consisting in a first reduction step followed by a coupling second step mediated by a carbene.

We could prove that the strategy used indeed gives rise to a C3 carbohydrate with CO2 as the only source of carbon. A complete mechanitic experimental and theoretical study was conducted to properly understand and describe each elementary steps occuring in this complex process.

The perspectives concerns the application of this new strategy in order to i) modify the chain lenght, ii) develop a catalytic version of the coupling step and iii) control the chirality of the chiral centers generated.

3 publications have been produced:
1. Béthegnies , A et al. Reductive CO2 Homocoupling: Synthesis of a Borylated C3 Carbohydrate. ChemCatChem 2019, 11, 760-765.
2. Desmons S, et al. Versatile CO2 Transformations into Complex Products: a One-pot Two-step Strategy, JoVE 2019, in press,
3. Desmons, S. et al. Formaldehyde as a Promising C1 Source: The Instrumental Role of Biocatalysis for Stereocontrolled Reactions. ACS Catal. 2019, DOI : 10.1021/acscatal.9b03128

Nature’s ability to transform CO2 into complex molecules is fascinating. Each second, 6000 t of CO2 are naturally transformed under atmospheric conditions into carbohydrates mainly via the Calvin cycle also called C3 cycle. Carbohydrates are considered new chemical platforms for the chemical industry and are currently produced via biomass extraction or biosynthesis. These methods are unfortunately presenting drawbacks.
In the context of finding alternative source of carbon to fossil resources, the reduction of CO2 is attracting a massive attention. However, the compounds formed from CO2 chemical transformation, although obtained with high efficiency, are low value-added products.
What if we could combine both systems and transform CO2 with a good control of the catalytic conditions, a good selectivity while generating molecules of high complexity? In other words can we develop a bio-inspired bench transformation of CO2 and disclose an inorganic Calvin cycle?
The objective of the present proposal is thus to develop a bench transformation of CO2 into carbohydrate with a perfect control of i) the length of the chain and ii) the stereochemistry of the generated stereogenic carbon atoms using earth abundant catalysts. Hydroboranes will enable to reduce CO2 under mild conditions (T < 100 °C, P < 5 atm) and to control each elementary step of the process.
Ground breaking nature of the proposal:
i) Addressing the fundamental challenge of producing carbohydrates.
ii) Forming highly complex molecules which are considered as new feedstock for the chemical industry.
iii) Using mild conditions (T < 100 °C, P < 5 atm) and earth abundant catalysts (first row metal-based complexes and organic compounds) despite the challenging transformations.
How:
i) Tandem reactions and synergy between experiment and theoretical calculations in homogeneous catalysis.
ii) Boron reagent as reductant, but also as key controlling moiety for both the reduction and coupling steps.