Interconversion of methyl and acetyl complexes and isomerization of acetyl complexes of ruthenium(II)

Abstract

Complexes [Ru(CO)₂X(Me)L₂][(I), where X = Cl, Br, or I, and L = PMe₂Ph or AsMe₂Ph] react extremely rapidly with ligands L′(L′= CO, PMe₂Ph, and several other ligands with phosphorus donor atoms, and AsMe₂Ph) to form products [Ru(CO)X(COMe)L₂L′], (II). The reactions involve initial intramolecular combination of methyl and carbonyl ligands followed by attack by L′trans to the newly formed acetyl ligand, which has a strong trans-directing effect. The trans-labilizing influence of the acetyl ligand makes the Ru–L′ bond in (II) extremely labile, and hence the reactions are easily reversed, regenerating (I). In many instances the products (II) undergo a slower rearrangement to a different isomer, (III), indicating that the stereochemistry of the initial reaction is kinetically controlled. The final position of equilibrium between (II) and (III) varies widely with the nature of X and L′: increases in either the size or the π-accepting ability of L′ favour (II), whereas an increase in the size of the halide ligand favours (III). Reconversion of isomer (III) of the complexes [Ru(CO)X(COMe)L₂L′] into the methyl complexes (I), which may be either direct or via(II), is much slower than that of (II) into (I).