Size-Determining Dependencies in Supramolecular Organometallic Host-Guest Chemistry

Treatment of the pentaphosphaferrocene [Cp*Fe(eta(5)-P-5)] with Cu-I halides in the presence of different templates leads to novel fullerene-like spherical molecules that serve as hosts for the templates. If ferrocene is used as the template the 80-vertex ball [Cp2Fe]@[{Cp*Fe(eta(5)-P-5)}(12){CuCl}(20)] (4), with an overall icosahedral C-80 topological symmetry, is obtained. This result shows the ability of ferrocene to compete successfully with the internal template of the reaction system [Cp*Fe(eta(5)-P-5)], although the 90-vertex ball [{Cp*Fe(eta(5):eta(1):eta(1):eta(1):eta(1):eta(1)-P-5)}(12)(CuCl)(10-)(Cu2Cl3)(5){Cu(CH3CN)(2)}(5)] (2a) containing pentaphosphaferrocene as a guest is also formed as a byproduct. With use of the triple-decker sandwich complex [(CpCr)(2)(mu,eta(5)-As-5)] as a template the reaction between [Cp*Fe(eta(5)-P-5)] and CuBr leads to the 90-vertex ball [(CpCr)(2)(mu,eta(5)-As-5)]@[{Cp*Fe(eta(5)-P-5)}(12){CuBr}(10){Cu2Br3}(5){Cu(CH3CN)(2)}(5)] (6), in which the complete molecule acts as a template. However, if the corresponding reaction is instead carried out with CuCl, cleavage of the triple-decker complex is found and the 80-vertex ball [CpCr(eta(5)-As-5)]@[{Cp*Fe(eta(5)-P-5)}(12){CuCl}(20)] (5) is obtained. This accommodates as its guest [CpCr(eta(5)-As-5)], which has only 16 valence electrons in a triplet ground state and is not known as a free molecule. The triple-decker sandwich complex [(CpCr)(2)(mu,eta(5)-As-5)] requires 53.1 kcal mol(-1) to undergo cleavage (as calculated by DFT methods) and therefore this reaction is clearly endothermic. All new products have been characterized by single-crystal X-ray crystallography. A favoured orientation of the guest molecules inside the host cages has been identified, which shows pi center dot center dot center dot pi stacking of the five-membered rings (Cp and cyclo-As-5) of the guests and the cyclo-P-5 rings of the nanoballs of the hosts.