The compounds 1 -Ph-3-(cod)-3,1,2-PdC,B,HlO l a , 1 ,2-Ph2-3-(cod)-3,1 ,2-PdC,BgH, 2a. 1 -Ph-3-(cod)-3.1 ,2-PtC,B,H1, 3a, and 1 ,I 1 -Ph2-3-(cod)-3,1 ,I 1 -PtC,B,H, 4, have been prepared from the reactions between Tl,[7 -Ph-nido -7.8-C,B,H ,,I or TI, [7,8-Ph,-nido -7,8-C,B,H,] and [ PdCI,( cod)] or [ PtCl,(cod)] as appropriate (cod = cycloocta-I ,5-diene). The platinum reactions are considerably cleaner than the palladium ones. Compound 2a was subjected to a crystallographic study which reveals severe intramolecular overcrowding; the palladium atom is slipped by 0.56 A away from the C-bound phenyl groups, the co-ordination of the cod ligand to the metal is distorted and the cage is deformed with extended C-B distances in the ligand face. Although l a and 3a are structural analogues, 2a and 4 are not. Rather, compound 4 is only isolated as the C-separated species defined by a 3,l ,I 1 -PtC,B, architecture, thus illustrating that the nature of the metal atom can influence the ease with which carbametallaboranes undergo polyhedral rearrangement. Compound 1 a was recovered unchanged from refluxing toluene, but under the same conditions 2a was converted into 2a'. tentatively identified as the rearranged isomer 1,11 -PhZ-3-(cod)-3,1 ,I 1 -PdC,B,H,.