Acid hydrolysis of [Ru(5)(CO)(15)(mu(4)-PN(i)Pr(2))] (2) or protonation of the anionic PO cluster [Ru(5)(CO)(15)(mu(4)-PO)](-) (3) affords the hydroxyphosphinidene complex [Ru(5)(CO)(15)(mu(4)-POH)].1.[H(2)N(i)()Pr(2)][CF(3)SO(3)], which cocrystallizes with a hydrogen-bonded ammonium triflate salt. Reaction of [Ru(5)(CO)(15)(mu(4)-PN(i)Pr(2))] (2) with bis(diphenylphosphino)methane (dppm) leads to [Ru(5)(CO)(13)(mu-dppm)(mu(4)-PN(i)Pr(2))] (4). Acid hydrolysis of 4 leads to the dppm-substituted hydroxyphosphinidene [Ru(5)(CO)(13)(mu-dppm)(mu(4)-POH)] (5), which is analogous to 1, but unlike 1, can be readily isolated as the free hydroxyphosphinidene acid. Compound 5 can also be formed by reaction of 3 with dppm and acid. The cationic hydride cluster [Ru(5)(CO)(13)(mu-dppm)(mu(3)-H)(mu(4)-POH)][CF(3)SO(3)] (6) can be isolated from the same reaction if chromatography is not used. Compound 4 also reacts with HBF(4) to form the fluorophosphinidene cluster [Ru(5)(CO)(13)(mu-dppm)(mu(4)-PF)] (7), while reaction with HCl leads to the mu-chloro, mu(5)-phosphide cluster [Ru(5)(CO)(13)(mu-dppm)(mu-Cl)(mu(5)-P)] (8).