Reactions of stable [PtCl2(η2-olefin)(α-di-imine)] complexes. Retention of the five-co-ordinate structure upon halogen exchange and ligand substitution with olefins, α-di-imines, and N,N′-disubstituted 1,2-diaminoethanes

Abstract

The axial halogen atoms as well as the equatorial η²-C₂H₄ and σ,σ-N,N′ chelate-bonded R–NCH–CHN–R or R–N(H)CH₂CH₂N(H)–R ligands (L–L) in five-co-ordinate [PtCl₂(η²-C₂H₄)(σ,σ-N,N′–L–L)] can be replaced with retention of the trigonal-bipyramidal structure. Halogen exchange is initiated by formation of an ionic intermediate [PtCl(η²-C₂H₄)(L–L)]Cl. The reversible exchange of the equatorial ligands with olefins, α-di-imines, or 1,2-diamine ligands is proposed to proceed via five-co-ordinate intermediates. The selectivity observed in these exchange reactions is explained on the basis of the difference in steric constraints of the various olefins and bidentate ligands used.