COORDINATIVELY UNSATURATED CP-ASTERISK-RU ALKOXO COMPLEXES .16. ADDITION-PRODUCTS CP-ASTERISK-RU(ACAC)L AND SOLUTION EQUILIBRIA

With [CpRu(OMe)](2) (1) as starting material, a number of 2,4-pentane dionato complexes CpRu(2,4-pentanedionate) were prepared. The solid-s tate structure of CpRu(1-phenyl-2,4-pentanedionate) (3) was elucidate d by X-ray crystallography, and the complex was found to be a dimer in the solid state, as previously established for CpRu(2,4-pentanediona te) (2). The molecular weight of 3 in benzene indicates a dimer (3-3) in solution as well. Low-temperature H-1 NMR spectroscopy reveals a pr ocess involving dissociation of the dimer into monomers associated wit h an inversion of the pentanedionate ligand at Ru. The activation ener gy (E-a = 43.5 +/- 0.7 kJ/mol, toluene-d(8)) reflects the enthalpy of dissociation of the dimer. All dimers are easily cleaved with two-elec tron ligands L, resulting in the mononuclear complexes CpRu(2,4-penta nedionate)l. Besides isolable complexes with L = phosphine, phosphite, and CO, labile adducts of the same composition with sigma-S and N don or ligands (L = methyl p-tolyl sulfoxide, ethyl methyl sulfide, tetrah ydrothiophene, diaza[2.2.2]-bicyclooctane, 3-cyanopyridine) were detec ted in solution by the influence of these ligands on the observed inve rsion barrier. With chiral or enantiotopic ligands diastereoselective adduct formation was observed.