Cyclic CO trimer formed directly

The metal-mediated cyclotrimerization of carbon monoxide to form C₃O₃^2- has been accomplished for the first time by a team of U.K. chemists (Science 2006, 311, 829). Cyclic aromatic oxocarbon dianions, C_nO_n^2- (n = 3 to 6), are being explored as potential building blocks to make fuels and commodity chemicals. The three-membered homolog has been prepared from the four-membered species, but unlike the other members of the series the direct synthesis of C₃O₃^2- from CO remained elusive until now. Geoff Cloke of the University of Sussex and his colleagues used a strongly reducing U(III) complex to crack the strong CO triple bond at room temperature and pressure in pentane; the C₃O₃^2- species formed as a ligand sandwiched between two of the uranium complex molecules (shown, R = triisopropylsilyl). The synthesis could become an industrially important method of C-C bond formation using coal- and biomass-derived CO as petroleum supplies dwindle, the researchers note.