Research under the theme “green chemistry” is challenged by the development of environmentally and economically sustainable processes for industrial applications. While looking for new and renewable raw material resources carbon dioxide is an attempting alternative, because it is cheap, abundant and non-toxic. By being a stable molecule, a high amount of energy or a suitable catalyst is however required to transform carbon dioxide into chemical products. In COST D30 activity the main emphasis has been on chemical activation of CO₂, especially on the synthesis of carbonates via epoxide reactions/1, 2/. In addition the reduction of CO₂  to produce formic acid was studied/3/

1.Carbonates via CO₂ –epoxide reactions

The results obtained in the project show that aliphatic epoxides, eg. 1-hexene-epoxide  and cyclohexene epoxide can be homo-and co-polymerized by using heterogenous Zn-catalyst system/1/. Also new catalyst candidates, especially cobalt(II) complexes bearing tetradentate ligands have been identified for the synthesis of cyclic carbonates.  These complexes were found to be excellent catalysts under mild conditions for the reaction of epoxide and CO₂ when used in conjunction with Lewis base co-catalyst (n-Bu₄NBr) /2/.

2.Reduction of CO₂ to formic acid

Highly water soluble cationic catalyst precursors,  [RuCl2PR3(h6arene)]+ where arene= 1-(2-benzylethyl)-3-methylimidazolium  or 1-(2-benzylethyl)-2,3-dimethylimidazolium and PR3 = PPh3, PCy3, were also prepared and used for CO2 hydrogenation to formic acid /3/.

The  reduction of CO2, bicarbonate and carbonate ions to formic acid/ formate ion in aqueous solution under mild conditions, though with moderate activity. In case of cationic ruthenium(II)-arene

complexes with tethered imidazolium moieties, hydrido-carbonate. The reduction of CO2 takes place via bicarbonate species, with the rate-determining step to be the intramolecular hydride transfer from the metal to the complexed bicarbonate.

Referencies:

1. Heiskanen & al., “Polycarbonates from Carbon Dioxide”(poster), 8th International Conference on Carbon Dioxide Utilization, Oslo, 20-23 June, 2005.;2. Sibaouih & Repo, “Co (II) mep/n-Bu4NBr: efficient catalyst system for the synthesis of cyclic carbonates from CO₂ and epoxides”, in press.;3.G.Laurency, F.Joo: Adv Synth.cataol.345,(2003) 17-174.

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1. High Pressure Hydrogen Generation from Formic Acid
2. New classical and non-classical hydrides of Ru(II) in aqueous solution