The cycloaddition of CO₂ with various epoxides to afford cyclic carbonates was investigated via the catalysis of ruthenium 2,2 -bipyridine complex RuCl₃(2,2 -bipy)(CH₃OH) and hexadecyl trimethyl ammonium chloride (CTAC). The cyclic carbonate formation mechanism was studied by using electrospray ionization mass spectrometry (ESI-MS) in the case of cycloaddition of CO₂ with propylene oxide (PO). Two intermediate complexes, RuCl₃(2,2 -bipy)(PO) and RuCl₃(2,2 -bipy)(PC), in the proposed reaction mechanism were successfully detected via ESI-MS measurement. Experimental results suggested that the initial coordination of epoxide is likely to occur first through the methanol ligand replacement in RuCl₃(2,2 -bipy)(CH₃OH). A nucleophilic attack of the chloride anion in CTAC on the less sterically hindered β-carbon atom of the coordinated epoxide is responsible for the epoxide ring-opening, CO₂ succeedingly inserts into the Ru—O bond and ring-closure happens subsequently yielding the cyclic carbonate.

Key words: ruthenium 2,2 -bipyridine complex, catalysis, carbon dioxide, epoxides, mechanism