Five-co-ordinate ethylene complexes of platinum(II). Part 2. Synthesis and reactivity of some five-co-ordinate complexes of platinum with bis(hydrazones) and X-ray crystal structure of [butane-2,3-dione bis(methylhydrazone)]dichloro(η-ethylene)platinum(II)

Abstract

The reaction of bis(hydrazones) with Zeise's salt, K[Pt(C₂H₄)Cl₃], to give stable five-co-ordinate complexes of general formula [Pt(C₂H₁)Cl₂(L)] is reported [L = Ph(H)N·N:[graphic omitted]:N·N(H)Ph (L¹), Ph(H)N·N:C(Me)·C(Me):N·N(H)Ph (L₂), Ph(Me)N·N:C(Me)·C(Me):N·N(Me)Ph (L³), Me(H)N·N:C(Me)·C(Me):N·N(H)Me (L⁴), or Me₂N·N:C(Me)·C(Me):N·NMe₂(L⁵)]. These have a trigonal bipyramidal structure with the chlorine atoms in the apical positions, and the bidentate ligand (which co-ordinates through its α-di-imine unit) and the ethylene in the equatorial plane. The five-co-ordinate species decompose in solution releasing ethylene and giving four-co-ordinate complexes of formula [PtCl₂(L)]. The rate of decomposition in 1,2-dichloroethane has been measured and its relationship to ¹H n.m.r. data is discussed.

The crystal and molecular structure of the five-co-ordinate [Pt(C₂H₄)Cl₂(L⁴)] has been determined at room temperature from three-dimensional X-ray data collected by counter methods. The structure has been refined by full-matrix least-squares techniques to a final R(on F) of 0.035 based on 712 reflections. The title compound crystallizes in the orthorhombic space group Cmcm, with four molecules in a cell of dimensions a= 7.912(7). b= 15.821 (9), and c= 10.718(8)Å. The co-ordination of the platinum atom is trigonal bipyramidal, assuming the ethylene molecule acts as a umdintate ligand. One symmetry plane contains the Cl–Pt–Cl group and bisects the bis(hydrazone) and the ethylene molecules, whilst the other contains the platinum atom and all the non-hydrogen atoms of the equatorial ligands. Significant bond distances are Pt–Cl = 2 304(3). Pt–N = 2.221(10), and Pt–C = 2.073(12)Å. The results suggest that the equatorial and axial covalent radii of five-co-ordinate platinum(II) resemble those of three-co-ordinate platinum(0) and four-co ordinate platinum(II) respectively.