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-

Abstract The reaction between [5-I-7,8-Ph 2 -7,8- nido -C 2 B 9 H 8 ] 2− and NiCl 2 (dppe) affords 1,2-Ph 2 -4,4-dppe-12-I-4,1,2- closo -NiC 2 B 9 H 8 ( 1 ) and 1,8-Ph 2 -2,2-dppe-10-I-2,1,8- closo -NiC 2 B 9 H 8 ( 2 ). Reaction between the same carborane ligand and cis -PtCl 2 (PMe 2 Ph) 2 yields three species, 1,8-Ph 2 -2,2-(PMe 2 Ph) 2 -10-I-2,1,8- closo -PtC 2 B 9 H 8 ( 3 ), 1,8-Ph 2 -2,2-(PMe 2 Ph) 2 -12-I-2,1,8- closo -PtC 2 B 9 H 8 ( 4 ), and 1,8-Ph 2 -2,2-(PMe 2 Ph) 2 -7-I-2,1,8- closo -PtC 2 B 9 H 8 ( 5 ). Compounds 1 – 5 have been characterised spectroscopically and crystallographically. The 4,1,2-MC 2 B 9 architecture of 1 constitutes a “1,2 → 1,2” cage C atom isomerisation, and the 2,1,8-MC 2 B 9 architectures of 2 – 5 a 1,2 → 1,7 cage C atom isomerisation, relative to the presumed first product of the metallations, 1,2-Ph 2 -3,3-L 2 -9-I-3,1,2- closo -MC 2 B 9 H 8 [M = Ni, L 2  = dppe; M = Pt, L 2  = (PMe 2 Ph) 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.