“…In the first type of {P 4 } complexes (82 in Scheme 30) the P 4 ring is completely planar, the originally antiaromatic {P 4 } species is stabilized by the coordination toward the ligand sphere of the metal ion, such as Nb [116], W [117], Ta [118], Co [119][120][121], Rh [122], V [123], and Cu [124,125]. In these {P 4 } systems, the number of electrons participating in the conjugation decreases, in analogy with the cyclobutadiene metal complexes, exhibiting 88.4% aromaticity for the bare compound 82 with Co atom as a metal core [88].…”