In 1983, Philip P. Power synthesized a transition-metal complex containing P=P double bond (trans&ndash;{[2}) via a simple one-step procedure. They mixed Na[Fe(CO)] and dichlorobis(trimethylsilyl)methylphosphine and got dark red-brown crystals, which was the first complex that contained an unbridged P-P double bond. Each phosphorus exhibited terminal coordination nature and the P-P distance was essentially unchanged. Later in 1983, A. H. Cowley reported ArP=PArFe(CO) (with Ar=2,4,6-tri-tert-butylphenyl) by treating diphosephene with Fe(CO) or NaFe(CO). In this synthesis procedure, there was only one terminal P-coordination and P-P double bond had Z configuration. Apart from iron, other similar transition metal complexes by reacting diphosphenes with transition metal carbonyls of nickel, tungsten, and chromium were discovered and they all exhibited Z configuration. M. Yoshifuji proved E/Z isomerization can take place under lighting, probably via migration of the metal moiety from one side to the other.