The chemistry of the hexaborane(10) analogue (PPh(3))(2)(CO)IrB5H8 (4) has been investigated. The two standard reactions in which metal-containing moieties may be incorporated into the B6H10 cage find success when applied to the iridahexaborane (4). The reaction of Fe-2(CO)(9) with (PPh(3))(2)(CO)IrB5H8 in C6H6 solution affords 1,1,1(CO)(3)-2,2-(CO)(2)-2,4-(PPh(3))(2)-closo- 1,2-FeIrB5H4 (1) in moderate (28.5%) yield. Except for carborane derivatives, 1 is the first pentagonal bipyramidal metallaheptaborane to be structurally characterized Compound 1 was identified by NMR, IR, and high-resolution mass spectroscopy and by a single-crystal X-ray diffraction study. Crystal data : triclinic, space group , a = 10.675(5) Angstrom, b = 10.736(3) Angstrom, c = 19.221(7) Angstrom, alpha = 88.90(2)degrees, beta = 78.26(4)degrees, gamma = 71.69(3)degrees, Z = 2, V = 2045.2(13) Angstrom(3). Treatment of a THF solution of the sodium anion salt of 4, Na[(PPh(3))(2)(CO)IrB5H7], with [Pt(PMe(2)Ph)Cl-2](2) in CH2Cl2 affords yellow solid 2-(CO)-2, 2-(PPh(3))(2)-7-Cl-7-(PMe(2)Ph)-nido-2,7-IrPtB5H7 (2) in 5% yield. 2 is identified similarily. It exists as a nido seven-vertex cluster formally derived by removal of a vertex of connectivity 5 from a closed triangulated dodecahedral polyhedron. Crystal data : monoclinic, space group P2(1)/n, a = 15.434(2) Angstrom, b = 18.597(1) Angstrom, c = 17.200(1) Angstrom, beta = 92.73(1)degrees, Z = 4, V = 4931.1(7) Angstrom(3). 2 is two skeletal electrons short of the electron count for a classical nido cluster, and it is compared to systems with related structures and also to other systems containing the Pt moiety functioning as a two-orbital two-electon donor.