In 1877, Köhler and Michaelis claimed that they synthesized the first isolated diphosphene (PhP=PPh). However, the molecular weight determination and X-ray crystallographic analysis later proved that this "diphosphene" only had a P-P single bond. Then the research to diphosphenes kept silent over almost 120 years until Masaaki Yoshifuji and his coworkers isolated an unprecedented diphosphene, bis(2,4,6-tri-tert-butylphenyl)diphosphene, in 1981. They first synthesized the (2,4,6-tri-tert-butylphenyl)phosphorus dichloride by adding phosphorus trichloride to (2,4,6-tri-butylphenyl)lithium that was the product of the lithium and halogen exchange. The phosphorus dichloride dimerized to a diphosphene after magnesium extracted two chlorine atoms from (2,4,6-tri-tert-butylphenyl)phosphorus dichloride. The P-P bond distance is 2.034 Å, which is much shorter than the average bond length in (CHP) (2.217 Å) and (CHP) (2.237 Å), indicating its double bond character. This research was a milestone in diphosphene studies because the product here was the first reported compound that had the isolated localized P=P bond. Moreover, this bulky structure provided a instructive pathway for the future synthesis of diphosphenes.