The synthesis and systematic study of the reaction chemistry of a bifunctional phosphinidene cluster, Fe-3(CO)(9)(mu(3)-PH)(2) (3) is reported. Reaction chemistry at one P-H functional site is effectively communicated through the Fe-3(CO)(9) core, and impacts on the reactivity of the second P-H site. Deprotonation of the acidic protons in 3 allows access to a lone electron pair on phosphorus, The first proton is readily removed with NEt3/[PPN]Cl ([PPN](+) = (Ph3P)(2)N+) to produce the [PPN](+) salt of [Fe-3(CO)(9)(mu(3)-PH)(mu(3)-P)(-) ([4](-)) Removal of both phosphorus-bound hydrogen atoms in 3 requires the use of 2 equiv of n-BuLi, to produce Li-2[Fe-3(CO)(9)(mu(3)-P)(2)] (Li-2[5]). Quenching of Li-2[5] with MeOH-d(4) generates [Fe-3(CO)(9)(mu(3)-PD)(mu(3)-P)](-). The lone electron pairs on the cluster-bound phosphorus atoms undergo analogous reaction chemistry to organophosphines. Alkylation at the phosphorus site is carried out by reaction of [Et3NH][4] with MeOSO2CF3 generating the monosubstituted cluster, Fe-3(CO)(9)(mu(3)-PMe)(mu(3)-PH) (6) as the primary product, The cluster anions [4](-) and [8](-), containing a phosphorus lone pair, are oxidized by elemental sulfur to produce the phosphine sulfide complexes, [Et3NH][Fe-3(CO)(9)(mu(3)-PH)(mu(3)-P=S)] ([Et3NH][10]) and [Et3NH][Fe-3(CO)(9)(mu(3)-PMe)(mu(3)-P=S)] ([Et-3-NH][11]). Treatment of [10](-) with an additional equivalent of NEt3 and S-8 yields the dianionic cluster, [Et-3-NH](2)[Fe-3(Co)(9)(mu(3)-P=S)(2)] ([Et3NH](2)[12]). Without added base, reaction of the neutral clusters, 3 and 6, with S-8 in THF solution yield the clusters Fe-3(CO)(9)(mu(3)-PH)(mu(3)-PSCH2CH2CH2CH2OH) (13), Fe-3(CO)(9)(mu(3)-PSCH2-CH2CH2CH2OH)(2) (14), and Fe-3(CO)(9)(mu(3)-PMe)(mu(3)-PSCH2CH2CH2CH2OH) (15), with a ring-opened THF molecule appended to sulfur. Reaction of 3 with Ss in THF solution in the presence of ClAuPPh3 produces the gold derivative, Fe-3(CO)(9)(mu(3)-PSAuPPh3)(2) (17). Like PH groups in phosphines, the mu(3)-PH moieties in 3 react with activated alkenes to yield single- and double-insertion products, Fe-3(CO)(9)(mu(3)-PH)(mu(3)-PCH2CH2R) (R = CN (18a), CO2Me (19a)) and Fe-3(CO)(9)(mu(3)-PCH2CH2R)(2) (R = CN (18b), Co2Me (19b)). The solid-state structures of 3, 17, and 18b were determined by single-crystal X-ray diffraction.