Synthesis and/or molecular structures of some simple 2,1,7- and 2,1,12-ruthena- and cobaltacarboranes

The ruthenacarboranes 2-(p-cymene)-2,1,7-closo-RuC₂B ₉H₁₁ (2) (p-cymene = 1-methyl-4-isopropylbenzene) and 2-(p-cymene)-2,1,12-closo-RuC₂B₉H₁₁ (3) have been synthesised by simple metallation of [7,9-nido-C₂B ₉H₁₁]^2- and [2,9-nido-C₂B ₉H₁₁]^2-, respectively. In preparing the known cobaltacarborane 2-(?-C₅H₅)-2,1,12-closo-CoC ₂B₉H₁₁ (6), the new bis(dicarbollide) [2,2'-Co(1,12-closo-C₂B₉H₁₁)₂] ^- (as its [(?-C₅H₅)₂Co] ⁺ salt; 7) was also formed. Molecular structures of 2, 3, 6 and 7 and that of the known compound 2-(?-C₅H₅)-2,1,7-closo- CoC₂B₉H₁₁ (5) have been determined. Patterns in <d(¹¹B)>, the weighted average ¹¹B NMR chemical shift, of these metallacarboranes, together with those in 3-(p-cymene)-3,1,2-closo-RuC₂B₉H₁₁ (1) and 3-(?-C₅H₅)-3,1,2-closo-CoC₂B ₉H₁₁ (4) are discussed in relation to <d(11B)> in the parent carboranes 1,2-closo-C₂B₁₀H₁₂, 1,7-closo-C₂B₁₀H₁₂ and 1,12-closo-C ₂B₁₀H₁₂. The similarity between the 1H and 11B spectra of 6 and 7 confirm the isolobality of the [C₅H ₅]^- and [C₂B₉H₁₁] ^2- ligands. An electrochemical study of 7 confirms that trends in the potential of the Co^III/Co^II couple for the series of isomers of (?-C₅H₅)CoC₂B₉H ₁₁ are reproduced for the bis(dicarbollides) [Co(C₂B ₉H₁₁)₂]^-. The molecular structures of compounds 1-3 as a family and 4-6 as a family provide a unique opportunity to consider structural patterns in simple isomeric metallacarboranes. © 2010 Institute of Organic Chemistry and Biochemistry.