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.