Zeise's salt is synthesized by reaction between K2PtCl4 and ethene, with a SnCl2 catalyst. It was one of the very first organometallic compounds to be prepared. The bonding of π-ligands to a transition metal is thought to be a synergic process involving donation of electrons from the filled π-orbital of the ligand into an empty d-orbital of the metal (a donor-acceptor bond), together with release (back donation) of electrons from an occupied d-orbital of the metal into the empty π*-antibonding orbital of the ligand. As a result, the bond order of the ligand is decreased, leading to an elongated C-C distance. This interaction also causes carbon atoms to "rehybridise" from sp2 towards sp3, which bends the hydrogen atoms on the ethylene away from the metal. An illustration of such bonding interactions is shown below.
The above model is a Pt(II) complex of acetylene. A dimethylamine ligand occupies the fourth site of the square planar platinum complex. The bonding of π-ligands to a transition metal is thought to be a synergic process involving donation of electrons from the filled π-orbital of the ligand into an empty d-orbital of the metal (a donor-acceptor bond), together with release (back donation) of electrons from an occupied d-orbital of the metal into the empty π*-antibonding orbital of the ligand. As a result, the bond order of the ligand is decreased, leading to an elongated C-C distance. This interaction also causes carbon atoms to "rehybridise" from sp towards sp2, which bends the hydrogen atoms on the acetylene away from the metal. An illustration of such bonding interactions is shown below.