The unexpected reactivity of 9-iodo-nido-carborane: from nucleophilic substitution reactions to the synthesis of tricobalt tris(dicarbollide) Na[4,4′,4′′-(MeOCH2CH2O)3-3,3′,3′′-Co3(μ3-O)(μ3-S)(1,2-C2B9H10)3]

Abstract

An unusual reactivity of 9-iodo-nido-carborane [9-I-7,8-C₂B₉H₁₁]⁻ towards nucleophiles under strong basic conditions was revealed. The nucleophilic substitution of iodine with O- and N-nucleophiles results in [9-RO-7,8-C₂B₉H₁₁]⁻ (R = H, CH₂CH₂OMe) and [9-L-7,8-C₂B₉H₁₁] (L = Py, NEt₃, Me₂NCH₂CH₂NMe₂), respectively. Reaction of [9-I-7,8-C₂B₉H₁₁]⁻ with CoCl₂ in 1,2-dimethoxyethane in the presence of t-BuOK, depending on the order of addition of the reagents, leads either to a diastereomeric mixture of diiodo derivatives cobalt bis(dicarbollide) rac-[4,4′-I₂-3,3′-Co(1,2-C₂B₉H₁₀)₂]⁻ and meso-[4,7′-I₂-3,3′-Co(1,2-C₂B₉H₁₀)₂]⁻ or to the corresponding mixture of 2-methoxyethoxy derivatives rac-[4,4′-(MeOCH₂CH₂O)₂-3,3′-Co(1,2-C₂B₉H₁₀)₂]⁻ and meso-[4,7′-(MeOCH₂CH₂O)₂-3,3′-Co(1,2-C₂B₉H₁₀)₂]⁻. In the presence of accidental admixture of sodium thiosulfate, the reactions of 9-iodo-nido-carborane and 9-(2′-methoxyethoxy)-nido-carborane with CoCl₂ in 1,2-dimethoxyethane were found to produce additionally unprecedented tricobalt tris(dicarbollide) cluster Na[4,4′,4′′-(MeOCH₂CH₂O)₃-3,3′,3′′-Co₃(μ³-O)(μ³-S)(1,2-C₂B₉H₁₀)₃], the central fragment of which is a trigonal bipyramid with apical oxygen and sulfur atoms, and the base is formed by the Co₃ triangle flanked by three dicarbollide ligands. In addition, the 2-methoxyethoxy substituents of the dicarbollide ligands chelate the sodium cation in such a way that they form a helix whose rotation direction depends on the enantiomer of the parent ligand. Thus, in this case, induction of the helical chirality of the complex occurs due to the point chirality of the initial inorganic ligand. It is worth noting that in the case of symmetrically substituted 2-methoxyethoxy derivative of nido-carborane [10-MeOCH₂CH₂O-7,8-C₂B₉H₁₁]⁻ only formation of the corresponding cobalt bis(dicarbollide) complex [8,8′-(MeOCH₂CH₂O)₂-3,3′-Co(1,2-C₂B₉H₁₀)₂]⁻ was observed.