Nucleophilic attack on olefins co-ordinated to platinum. Part 2. Stabilities of 2-ammonioethanide σ adducts and of five-co-ordinate complexes

Abstract

The preparation and characterization is reported of various new 2-ammonioethanideplatinum(II) complexes (i.e. compounds containing amCH₂H₂Pt, am = amine). These have been used to assist in the identification by ¹H n.m.r. spectroscopy of other less stable relatives. The n.m.r. data give no indication of the stability of the complexes. trans-Labilization by the amCH₂H₂ group has been studied; exchange of a trans-positioned amine is slow on an n.m.r. time scale. Equilibrium constants have been measured for the reaction am + Pt^II(η-C₂H₄)⇌σ-amCH₂H₂Pt, and are discussed in terms of the nature of am, the attacking amine. Lack of bulk in am is more important than its basicity, π effects also being relevant. Data are also given on an equilibrium in which five-co-ordinate complexes are produced, e.g. py +[PtCl₂(η-C₂H₄)(py)]⇌[PtCl₂(η-C₂H₄)(py)₂](py = pyridine). The reaction is specific to aromatic amines, which suggests that π interactions are important in associative substitution. The susceptibility of η-C₂H₄ and Pt^II to nucleophilic attack is compared, the former being a harder acid.