Metallaaromatics have attracted continuing interest of both theoretical and experimental chemists since the first metallabenzene was predicted by Hoffmann and isolated by Roper. In sharp contrast to metallabenzenes, metallaphosphabenzene (MPB) is much less developed and has not been synthesized so far. Thus, developing synthetic approaches is urgent. Here we present thorough density functional theory (DFT) calculations on the thermodynamics and kinetics of the rearrangement between MPBs and the corresponding η5-phosphacyclopentadiene (η5-PCp) complexes.