Exploration of bis(Nickelation) of 1,1^′-bis(o-carborane)

The metalation of [Tl]₂ [1-(1^′-3^′,1^′,2^′-closo-TlC₂B₉H₁₀)-3,1,2-closo-TlC₂B₉H₁₀ ], with the smaller {Ni(dmpe)} fragment sourced from [Ni(dmpe)Cl₂ ], is explored. The bis(metalated) products are obtained as a diastereoisomeric mixture. These isomers were separated, fully characterised spec-troscopically and crystallographically and identified as rac-[1-(1^′-3^′-(dmpe)-3^′,1^′,2^′-closo-NiC₂B₉H₁₀)-3-(dmpe)-3,1,2-closo-NiC₂B₉H₁₀ ] (1) and meso-[1-(1^′-3^′-(dmpe)-3^′,1^′,2^′-closo-NiC₂B₉H₁₀)-3-(dmpe)-3,1,2-closo-NiC₂B₉H₁₀ ] (2). Previously, these 3,1,2-NiC₂B₉-3^′,1^′,2^′-NiC₂B₉ architectures (where both cages are not isomerised), were inaccessible, and thus new structures can be achieved during bis(nickelation) with {Ni(dmpe)}. Further, the metalation of the tetra-thallium salt with the bulky {Ni(dppe)} fragment sourced from [Ni(dppe)Cl₂ ] was also studied. These bis(nickelated) products were also fully characterised and are afforded as the stereospecific species rac-[1-(1^′-3^′-(dppe)-3^′,1^′,2^′-closo-NiC₂B₉H₁₀)-3-(dppe)-3,1,2-closo-NiC₂B₉H₁₀ ] (3) and [1-(2^′-4^′-(dppe)-4^′,1^′,2^′-closo-NiC₂B₉H₁₀)-3-(dppe)-3,1,2-closo-NiC₂B₉H₁₀ ] (4α). In the latter metalation, compound 3 shows intramolecular dihydrogen bonding, contributing to the stereospecificity, whereas isomerisation from 3,1,2 to 4,1,2-in the 4α is related to steric relief.