The synthesis and characterisation of 4,1,2-MC₂B₁₀ metallacarboranes

Reduction of the tethered carborane 1,2-(CH₂) ₃-1,2-closo-C₂B₁₀H₁₀ followed by treatment with CoCl₂/NaCp, [(p-cymene)RuCl₂]₂ (p-cymene = C₆H₄MeⁱPr-1,4), (PMe ₂Ph)₂PtCl₂ or (dppe)NiCl₂ (dppe = Ph₂PCH₂CH₂PPh₂) affords reasonable yields of the new 13-vertex metallacarboranes 1,2-(CH₂) _3-4-Cp-4,1,2-closo-CoC₂B₁₀H₁₀ (1), 1,2-(CH₂)_3-4-(p-cymene)-4)1,2-closo-RuC₂B ₁₀H₁₀ (2), 1,2-(CH₂)_3-4,4-(PMe ₂Ph)_2-4,1,2-closo-PtC₂B₁₀H ₁₀ (3) and 1,2-(CH₂)_3-4,4-(dppe)-4,1,2-closo- NiC₂B₁₀H₁₀ (4), respectively. All compounds were characterised spectroscopically and crystallographically. The cobalt and ruthenium species 1 and 2 have C_S symmetry in both solution and the solid state, having henicosahedral cage structures featuring a trapezoidal C1C2B9B5 face. The platinum and nickel compounds 3 and 4 have asymmetric docosahedral cage structures in the crystal (the more so for 4 than for 3) although both appear, by ¹¹B and ³¹P NMR spectroscopy, to have C_S symmetry in solution. Low-temperature experiments on the more soluble platinacarborane could not freeze out the diamond-trapezium-diamond fluctional process that we assume is operating in solution, and we therefore conclude that this process has a relatively low activation barrier, probably <35 kJ mol^-1. © The Royal Society of Chemistry 2005.