SYNTHESIS, REACTIVITY, AND LIGAND DYNAMICS OF RU3(CO)9(MU-CO)(MU-3-ETA-2-ALKYNE) COMPOUNDS

Acetylene, terminal HC2R (R = COOH, CHO), and nonterminal RC2R (R = Et, CH2OH, Ph) alkynes react at room temperature with Ru3(CO)10(MeCN)2 to give almost quantitatively Ru3(CO)9(mu-CO)(mu-3-eta-2-alkyne) compounds, which are shown to be the precursors of the acetylides Ru3(CO)9(mu-H)(C2R) in the case of acetylene and of terminal alkynes or of the allenic Ru3(CO)9(mu-H)(RC = C = CR'R'') complexes in the case of internal alkynes. Ru3(CO)9(mu-CO)(C2H2) at room temperature adds H-2 to give Ru3(CO)9(mu-H)2(HC = CH), which is further hydrogenated at 3 atm to give Ru3(CO)9(mu-H)3CCH3. Ru3(CO)9(mu-CO)(C2H2) is stereochemically nonrigid: a low-energy process averages, on the NMR time scale, the semibridging CO with two pairs of terminal carbonyls at the bridged Ru atoms, and it is coupled to an alternate lengthening of one of the Ru-C sigma-bonds at the same metal atoms. At high temperature, all the carbonyls are equivalent.