Design of simple salophen chromium complexes for a two-steps oxidative carboxylation of styrene with CO2 and O2

Matthieu Balas (1, 2, 3, 4, 5) , Richard Villanneau (1, 2, 4, 5) , Franck Launay (1, 2, 3)

1 SU - Sorbonne Université
2 SU FSI - Sorbonne université - Faculté des Sciences et Ingénierie
3 LRS - Laboratoire de Réactivité de Surface
4 IPCM - Institut Parisien de Chimie Moléculaire
5 E-POM - Edifices PolyMétalliques

In this work, chromium(III) Salophen complexes bearing tertiary dimethyl or diethyl amino substituents were synthesized and tested as homogeneous co-catalysts associated with n-Bu 4 NBr for the cycloaddition of CO 2 on styrene epoxide under 11 bar of CO 2. Full conversion of styrene oxide into styrene carbonate was obtained after 23 h reaction at 50°C using Salophen-Me 2 N-Cr. These results emphasized that tertiary amine groups born by the aromatic cycles of Salophen clearly enhanced the co-catalytic activity of the corresponding Cr(III) complex. The direct conversion of styrene into styrene carbonate was then conducted at 80°C with O 2 and CO 2 either under a single set of conditions (reactants and catalysts together) or using a two-steps transformation. The latter was based on the prior epoxidation of styrene in the presence of isobutyraldehyde and O 2 (3.5 bar) with a delayed addition of the cycloaddition catalysts (n-Bu 4 NBr and Salophen-Me 2 N-Cr) and CO 2 (11 bar). Using these conditions, the maximum yield of styrene carbonate, obtained after 3 h of epoxidation and 20 h of cycloaddition (with Salophen-Me 2 N-Cr), was 31% at 80°C. This work demonstrates that the key-point to afford a high styrene carbonate global yield with that system was related to the implementation of a two-step protocol, since it allowed to minimize the amounts of undesired by-products.

Domaines: Chimie

Matthieu Balas, Richard Villanneau, Franck Launay. Design of simple salophen chromium complexes for a two-steps oxidative carboxylation of styrene with CO2 and O2. Journal of CO2 Utilization, 2023, 72, pp.102497. ⟨10.1016/j.jcou.2023.102497⟩. ⟨hal-04200038⟩