New photocatalytic materials for carbon dioxide valorisation in carbonylation chemistry

Abstract

The replacement of hazardous carbon monoxide with more benign surrogates is highly desirable and recent ideas focus on the valorization of carbon dioxide as an abundant, non-toxic and renewable carbon source. To achieve this, the high thermodynamic and kinetic barrier for the reduction of carbon dioxide to carbon monoxide needs to be overcome. Photocatalytic systems consisting of a photosensitizer and a photocatalyst such as Ru and Re showed high selectivity for carbon monoxide formation with a turnover number above 50, allowing for visible light photocatalyzed reduction of carbon dioxide. Ionic liquids show considerable potential as cooperative media as they can solubilize large concentrations of carbon dioxide, and are also able to activate carbon dioxide. Materials that combine both photocatalyst and ionic liquid are thus highly desirable for a photocatalytic carbon dioxide reduction to generate carbon monoxide and the in situ conversion into carbonyl compounds. Immobilization of the photocatalyst is favourable, facilitating catalyst handling and recovery, and enable the use in continuous processes. Consequently, we have developed different ionic liquid-photocatalyst polymers by copolymerization of the ionic liquid 1-butyl-3-vinylimidazolium chloride and photocatalytically active Re- and Ru-complexes bearing vinyl groups. The synthesis of the polymer systems was conducted via radical polymerization utilizing varying ratios of photocatalytic materials with vinyl functionalized ligand system and ionic liquids affording high yields of the desired material. Analysis of the synthesized materials with UV-Vis spectroscopy showed high correlation with reported values for vinyl group monomers; the spectra were minimally shifted from 455 nm for the vinyl modified Ru monomer to 480 nm for the Ru-IL-polymer. The obtained novel polymers synthesized from the copolymerisation ionic liquids and photocatalysts, will be further studied for the visible-light photoreduction of carbon dioxide, aiming for a continuous production of carbon monoxide under benign conditions.