Synthesis and structure of new trichloroplatinum π-complexes: Reactivity of nitrogen lone-pair versus C–C double bond π-electrons in ligands, effect of steric hindrance

Two trichloroplatinum π-complexes and a diammonium tetrachloroplatinate (II) salt have been unexpectedly isolated during the attempt to synthesize the corresponding cisplatinum square-planar complexes of tertiary cyclohexane 1,4-diamines. All three compounds have been physically and spectroscopically characterized, including X-ray diffraction analysis in two of the three compounds. The formation of the π-complexes instead of the diamino cis-platinum complexes could be explained as due to the steric hindrance exerted by methyl groups on the tertiary amines. So, the π-electrons of the Cdouble bond; length as m-dashC double bond are more available than the electron lone pair of nitrogen atom from the amino groups. When the π-electrons of the Cdouble bond; length as m-dashC from the molecule of ligand were made unavailable by transforming the cyclohexene subunit into a benzene aromatic ring, no cis-diamino dichloro platinum(II) complex nor trichloroplatinum-complexes were isolated but the corresponding tetrachloroplatinate(II) diammonium salt of the 1,4-diamino ligand.