P(⁶-C₆H₆)₃ does not exist. You have confused C₆H₅ (phenyl) and C₆H₆ (benzene). Phenyl groups form 1 bond to another electron. Phosphorous has 5 valence electrons, s²p³, and can not -bond to 3 benzene rings. Each ring would then supply 6e^- to the phosphorous exceding its lectrons requirements for a full shell.
 

Fe           = 8e- .5-C5H5 = 5e- COT       = 2e- CH3       = 1e- PPh3      = does not exist

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