Reaction of [HIr4(CO)10(mu-PPh2)], 1, with [Pt(dppe)(eta(2)-PCBut)] yields four Ir4Pt clusters [Ir4Pt(dppe)(CO)(n){mu-PC(H)Bu-t}(mu-PPh2)] (n = 10, 2, and 9, 3), [HIr4Pt(dppe)(mu-CO)(CO)(7)(mu-PCH2But)(mu-PPh2)], 4, and [Ir4Pt(dppe)(mu-CO)(CO)(8)(mu(5)-P)(mu-PPh2)], 5. These compounds contain fragments arising from hydrometalation and cleavage of the P-C triple bond of the phosphaalkyne. The structures of compounds 2 and 3, isolated as a mixture, were proposed on the basis of multinuclear NMR and mass spectrometry. To our knowledge these are the first examples of clusters containing a phosphido fragment {mu-PC(H)Bu-t} originating from hydrometalation of the phosphaalkyne. Compounds 4 and 5 were characterized in solution by multinuclear NMR spectroscopy, and their solid-state structures were determined by X-ray analyses. A remarkably low (1)J(P-Pt) coupling constant in the Pt(dppe) fragment of the former square-based pyramidal compound is discussed.172554605466