Towards the mechanism of heteroborane isomerisation: 1,2 → 1,2 and 1,2 → 1,7 low-temperature isomerisations from metallations of [5-I-7,8-Ph2-7,8-nido-C2B9H8]2−

The reaction between [5-I-7,8-Ph2-7,8-nido-C2B9H8]2− and NiCl2(dppe) affords 1,2-Ph2-4,4-dppe-12-I-4,1,2-closo-NiC2B9H8 (1) and 1,8-Ph2-2,2-dppe-10-I-2,1,8-closo-NiC2B9H8 (2). Reaction between the same carborane ligand and cis-PtCl2(PMe2Ph)2 yields three species, 1,8-Ph2-2,2-(PMe2Ph)2-10-I-2,1,8-closo-PtC2B9H8 (3), 1,8-Ph2-2,2-(PMe2Ph)2-12-I-2,1,8-closo-PtC2B9H8 (4), and 1,8-Ph2-2,2-(PMe2Ph)2-7-I-2,1,8-closo-PtC2B9H8 (5). Compounds 1–5 have been characterised spectroscopically and crystallographically. The 4,1,2-MC2B9 architecture of 1 constitutes a “1,2 → 1,2” cage C atom isomerisation, and the 2,1,8-MC2B9 architectures of 2–5 a 1,2 → 1,7 cage C atom isomerisation, relative to the presumed first product of the metallations, 1,2-Ph2-3,3-L2-9-I-3,1,2-closo-MC2B9H8 [M = Ni, L2 = dppe; M = Pt, L2 = (PMe2Ph)2]. The location of the (iodide) labelled boron vertex in the products allows speculation as to the mechanism of these isomerisations and the possible involvement of triangle face rotation is discussed.