Coordinatively Unsaturated Cp*Ru Alkoxo Complexes. 16.1Addition Products Cp*Ru(acac)L and Solution Equilibria1

With [Cp*Ru(OMe)] 2 ( 1 ) as starting material, a number of 2,4-pentanedionato complexes Cp*Ru(2,4-pentanedionate) were prepared. The solid-state structure of Cp*Ru(1-phenyl-2,4-pentanedionate) ( 3 ) was elucidated by X-ray crystallography, and the complex was found to be a dimer in the solid state, as previously established for Cp*Ru(2,4-pentanedionate) ( 2 ). The molecular weight of 3 in benzene indicates a dimer ( 3 - 3 ) in solution as well. Low-temperature 1 H NMR spectroscopy reveals a process involving dissociation of the dimer into monomers associated with an inversion of the pentanedionate ligand at Ru. The activation energy ( 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-electron ligands L, resulting in the mononuclear complexes Cp*Ru(2,4-pentanedionate)L. Besides isolable complexes with L = phosphine, phosphite, and CO, labile adducts of the same composition with σ-S and N donor ligands (L = methyl p -tolyl sulfoxide, ethyl methyl sulfide, tetrahydrothiophene, diaza[2.2.2]bicyclooctane, 3-cyanopyridine) were detected in solution by the influence of these ligands on the observed inversion barrier. With chiral or enantiotopic ligands diastereoselective adduct formation was observed.