The reaction of white phosphorus with the coordinatively unsaturated [M(CO)3(PR3)2] complexes (M = Mo, W; R = Cy, Pri) yields the compounds [M(CO)3(PR3)2(η1-P4)] in which the P4-tetrahedron is end-on bonded to the metal. In the same manner reacts Ar‘CP (Ar‘ = C6H2But3-2,4,6) with this complex to give [W(CO)3(PCy3)2(η1-PCAr‘)]. The X-ray structures of the products are discussed, and for the P4-unit in [W(CO)3(PCy3)2(η1-P4)] the librational analysis was performed to correct their translational and rotational motions.