Complexes of hydrazones with dichloro (η-ethylene)platinum(II): stereochemical and conformational analysis of the co-ordinated ligands

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.