NEW SYNTHETIC ROUTES TO [M3(CO)9(MU-3-ETA-2-ETA-2-ETA-2-C6H6)] (M = RU OR OS)

A new, more convenient route to the benzene cluster [Ru3(CO)9(mu3-eta2:eta2:eta2-C6H6)] directly from [Ru3(CO)12] has been established. Triruthenium dodecacarbonyl, [Ru3(CO)12]. undergoes reaction with Me3NO-CH2Cl2 in the presence of cyclohexa-1,3-diene to give the clusters [Ru3H(CO)9(C6H7)] and [Ru3(CO)9(mu3-eta2:eta2:eta2-C6H6)] in moderate yield. Triosmium dodecacarbonyl does not react similarly, but from the reaction of [Os3(CO)10(MeCN)2] with cyclohexa-1,3-diene a key intermediate compound [Os3(CO)10(eta4-C6H8)] has been isolated and the solid-state structure of its acetonitrile solvate established by single crystal X-ray diffraction analysis at 150 K. The structure is monoclinic, space group P2(1)/n, with a = 8.932(8), b = 17.387(13), c = 14.833(15) angstrom, beta = 105.69(6)degrees and Z = 4. The three osmium atoms form a regular triangle with a mean Os-Os distance of 2.877(12) angstrom. Two osmium atoms, Os(1) and Os(2), are co-ordinated to four carbonyl ligands and one, Os(3), co-ordinates to two carbonyl ligands. All carbonyl ligands are terminal and approximately linear. The cyclohexadiene ligand is eta4 co-ordinated to Os(3) via the 1,3-diene moiety, donating four electrons in total. On thermolysis, this compound is converted to [Os3H(CO)9(C6H7)] and then eventually to [Os3(CO)9(mu3-eta2:eta2:eta2-C6H6)] by established means,