Toward unidirectional rotary motion in nickelacarboranes: characterization of diastereomeric nickel bis(dicarbollide) complexes derived from the [nido-7-CH3-7,8-C2B9H11]- anion.

Two diastereomeric pairs of nickel bis(C-monomethyldicarbollide) complexes, derived from the racemic [nido-7-CH(3)-7,8-C(2)B(9)H(11)](-) anion, have been synthesized and characterized by NMR spectroscopy and single-crystal X-ray diffraction analysis. Neutral (dd/ll) [1(2),1'(2')-Me(2)-closo-3,1,2-Ni(IV)C(2)B(9)H(10)-{3:3'}-closo-3',1',2'-Ni(IV)C(2)B(9)H(10)] 1 and (meso) [1,2'-Me(2)-closo-3,1,2-Ni(IV)C(2)B(9)H(10)-{3:3'}-closo-3',1',2'-Ni(IV)C(2)B(9)H(10)] 2 adopt typical cisoid conformations in the solid state. The temperature-dependent (11)B and (1)H 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 [NMe(4)](+) salts of the (dd/ll) [1(2),1'(2')-Me(2)-closo-3,1,2-Ni(III)C(2)B(9)H(10)-{3:3'}-closo-3',1',2'-Ni(III)C(2)B(9)H(10)](-) anion NMe(4) x 3 and the (meso) [1,2'-Me(2)-closo-3,1,2-Ni(III)C(2)B(9)H(10)-{3:3'}-closo-3',1',2'-Ni(III)C(2)B(9)H(10)](-) anion NMe(4) x 4 adopt gauche and transoid configurations, respectively, with transoid methyl substituents in both cases.