The synthesis, by electrophilic substitution, and characterisation of two new B-substituted nido diphenylcarboranes is described. [HNMe 3 ][7,8-Ph 2 -9-I-7,8-nido-C 2 B 9 H 9 ] (1) and [HNMe 3 ][7,8-Ph 2 -9,11-I 2 -7,8-nido-C 2 B 9 H 8 ] (2) were characterised spectroscopically with the structure of the latter additionally confirmed by a crystallographic study. [7,8-Ph 2 -9,11-I 2 -7,8-nido-C 2 B 9 H 8 ] 2− was treated with a source of {Pt(PMe 2 Ph) 2 } 2+ and three new platinacarboranes isolated. All were characterised by a combination of 1 H, 11 B and 31 P NMR spectroscopies and by single crystal X-ray diffraction, and all were found to have undergone a 1,2→1,7 cage C atom isomerisation, relative to the presumed first product of the metallation. The major product 3 is 1,8-Ph 2 -2,2-(PMe 2 Ph) 2 -6,7-I 2 -2,1,8-closo-PtC 2 B 9 H 7 with both (iodide) substituted boron vertices in the upper part of the icosahedron. The minor products 4 and 5 are, respectively, 1,8-Ph 2 -2,2-(PMe 2 Ph) 2 -6,12-I 2 -2,1,8-closo-PtC 2 B 9 H 7 and 1,8-Ph 2 -2,2-(PMe 2 Ph) 2 -10,12-I 2 -2,1,8-closo-PtC 2 B 9 H 7 , having one and two substituted boron vertices in the lower pentagonal belt. These structural results allow speculation on the mechanism of isomerisation of crowded platinacarboranes.