Toward Unidirectional Rotary Motion in Nickelacarboranes: Characterization of Diastereomeric Nickel Bis(Dicarbollide) Complexes Derived from the [<i>Nido</i>-7-CH₃-7,8-C₂B₉H₁₁]⁻ Anion

Two diastereomeric pairs of nickel bis(C-monomethyldicarbollide) complexes, derived from the racemic [nido-7-CH3-7,8-C2B9H11]− anion, have been synthesized and characterized by NMR spectroscopy and single-crystal X-ray diffraction analysis. Neutral (dd/ll) [1(2),1′(2′)-Me2-closo-3,1,2-NiIVC2B9H10-{3:3′}-closo-3′,1′,2′-NiIVC2B9H10] 1 and (meso) [1,2′-Me2-closo-3,1,2-NiIVC2B9H10-{3:3′}-closo-3′,1′,2′-NiIVC2B9H10] 2 adopt typical cisoid conformations in the solid state. The temperature-dependent 11B and 1H NMR spectra of 2 indicate that the energy barrier to the interconversion of racemic rotational isomers is 66.5 ± 2 kJ/mol. In the solid state, the [NMe4]+ salts of the (dd/ll) [1(2),1′(2′)-Me2-closo-3,1,2-NiIIIC2B9H10-{3:3′}-closo-3′,1′,2′-NiIIIC2B9H10]− anion NMe4·3 and the (meso) [1,2′-Me2-closo-3,1,2-NiIIIC2B9H10-{3:3′}-closo-3′,1′,2′-NiIIIC2B9H10]− anion NMe4·4 adopt gauche and transoid configurations, respectively, with transoid methyl substituents in both cases.