Patterns of nucleophilic attack on ethene complexes of ruthenium(II)

Abstract

Although reaction of [Ru(CO)(η-C₂H₄)Cl₂(PMe₂Ph)₂] with the nucleophile PMe₂Ph at 308 K simply results in substitution of the ethene ligand, studies at lower temperatures reveal that the kinetically favoured product is the cation [Ru(CO)(CH₂CH₂PMe₂Ph)Cl(PMe₂Ph)₃]⁺. Similarly the complexes [Ru(CO)(η-C₂H₄)X₂(AsMe₂Ph)₂](X = Cl or Br) react with PMe₂Ph to yield [Ru(CO)(CH₂CH₂PMe₂Ph)X(AsMe₂Ph)₂(PMe₂Ph)]⁺ and [Ru(CO)(η-C₂H₄)Cl₂(PMe₂Ph)₂] reacts with PMePh₂ to form [Ru(CO)(CH₂CH₂PMePh₂)Cl(PMe₂Ph)₂(PMePh₂)]⁺. It appears probable that the first step in these reactions involves nucleophilic attack on the ethene, with subsequent substitution of the halide ion trans to the newly formed alkyl ligand. In the case of the nucleophiles L′= AsMe₂Ph, NH₂CH₂Ph, P(OMe)₂Ph, 4-methylpyridine, and SMe₂, there is no evidence of low-temperature attack on the ethene ligand in [Ru(CO)(η-C₂H₄)Cl₂(PMe₂Ph)₂]: on raising the temperature, only the ethene substitution products [Ru(CO)Cl₂L′(PMe₂Ph)₂] are obtained.