The bimetallic compound [{CpRu(PPh3)(2)}(2)(mu,eta(1:1)-P-4)][CF3SO3](2), in which the tetrahedral P-4 is bound to two CpRu(PPh3)2 fragments, slowly reacts under mild conditions with a moderate excess of water (1:20) to yield a mixture of compounds. Among the hydrolysis products, the new, remarkably stable complexes [{CpRu(PPh3)}{CpRu(PPh3)(2)} {mu(1,4:3),eta(2:1)-P(OH)(2)PHPHPH(OH)}](CF3SO3)(2) (2) and [{CpRu(PPh3)(2)}{CpRu(PPh3)}{P(OH)(3)}(mu,eta(1:1)-P2H4)]-(CF3SO3)(2) (3) have been isolated. In the former, the previously unknown 1,1,4-tris(hydroxy)tetraphosphane molecule, P(OH)(2)PHPHPH(OH), is 1,4-and, respectively, 3-coordinated to the CpRu(PPh3) and the CpRu(PPh3)(2) moieties; in the latter, the diphosphane P2H4 is stabilized through coordination to two different metal fragments. All of the compounds were characterized by elemental analyses and IR and NMR spectroscopy. The crystal structure of 2 was determined by X-ray analysis. The formation of the hydroxytetraphosphane, containing the tetraphosphorus entity, provides a clue to the hydrolytic activation of the P-4 molecule.