Complexes of hydrazones with dichloro(η-ethylene)platinum(II): stereo-chemical and conformational analysis of the co-ordinated ligand

Abstract

By reaction of the hydrazones (Me₂C:N·NMePh. L¹; MeHC:N·NMe₂, L²; MeHC:N·NMePh. L³; EtHC:N·NMe₂. L⁴; EtHC:N·NMePh. L⁵: and Me₂C:N·NHPh, L⁶) with Zeise's salt, complexes of formula trans-[Pt(C₂H₄)Cl₂-(hydrazone)] have been prepared in which the imino-nitrogen acts as donor atom. Of the hydrazones derived from aldehydes, which in the free state are present as pure syn isomers, L² and L⁴ retain their configuration on co-ordination to the metal, while L³ and L⁵ give two isomeric complexes, in one of which the ligand keeps the syn configuration, whereas in the other isomerization to the anti form occurs (with respect to the C:N double bond). Evidence of rotational isomerism about the N·N bond has been found in the case of L⁶. The coupling of the ligand protons with the ¹⁹⁵Pt nucleus has been measured and correlated with their relative cis or trans position about the C:N double bond. A coupling of ca. 74 and 27 Hz has been found for the aldehydic proton, trans and cis to platinum respectively. For the methyl substituents at the carbonylic carbon, a higher coupling constant (11–13 Hz) is observed when the methyl group is cis to platinum and a lower one (6–8 Hz) when it is trans. This result is discussed in connection with other literature data.