Structural and mechanistic studies on ion insertion into the molecular box {[CpCo(CN)3]4[Cp*Ru]4}

The molecular box [CpCo(CN)3]4[Cp*Ru]4 (Co4Ru4) reacts readily with a variety of monocations to form M Co4Ru4 (M1⁄4Kþ, Csþ, Rbþ). Ion competition experiments, monitored by ESI-MS, show that the molecular box binds the smaller Kþ more rapidly than Csþ, but that thermodynamically Co4Ru4 prefers the larger ion. The rates of ion-insertion for K þ and Csþ into Co4Ru4 were found to qualitatively follow second order kinetics with Kþ, 300 M 1 s 1 and Csþ, 36 M 1 s . The ratio kK/kCs qualitatively matched the ESI-MS results from ion competition experiments. The rates of ion-insertion into Co4Ru4 were found to depend on the counter anions. In particular, RbBF4 reacted with Co4Ru4 more slowly than did RbOTf. The slower rates allowed us to establish second order kinetics. H NMR studies reveal that the Cp signal for Co4Ru4 is very sensitive to the presence of entering ions, e.g., Rbþ, whereas the corresponding Cp signal for Rb Co4Ru4 was insensitive to the presence of Rbþ. The molecular structures of [Co4Ru4] 6MeCN, [K Co4Ru4]BF4 7MeCN, [Cs Co4Ru4]BF4 6MeCN and [Tl Co4Ru4]BF4 6MeCN, determined by X-ray diffraction, showed that although the compounds crystallized in the same space group I23, a correlation exists between the Ru–N/ Co–C bond distances and the size of the interstitial ion. 2004 Elsevier B.V. All rights reserved.