Though the first metal olefin complex dates back a long time to the beginning of 19^th century, its formulation was established only a century later in the 1950s. While reacting K₂PtCl₄ with EtOH in 1827, the Danish chemist Zeise synthesized the famous Zeise’s salt K[PtCl₃(C₂H₄)]•H₂O containing a Pt bound ethylene moiety and which incidentally represented the first metal−olefin complex (Figure 1).