Size-determining dependencies in supramolecular organometallic host-guest chemistry

摘要

Treatment of the pentaphosphaferrocene Cp*Fe(η ~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 Cp _2Feat{Cp*Fe(η ~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(η ~5-P _5), although the 90-vertex ball {Cp*Fe(η ~5:η ~1:η ~1: η ~1:η ~1:?· ~1-P _5)} _(12)(CuCl) _(10)(Cu _2Cl _3) _5{Cu(CH _3CN) _2} _5 (2a) containing pentaphosphaferrocene as a guest is also formed as a byproduct. With use of the triple-decker sandwich complex (CpCr) _2(μ, η ~5-As _5) as a template the reaction between Cp*Fe(η ~5-P _5) and CuBr leads to the 90-vertex ball (CpCr) _2(μ,η ~5-As _5) {Cp*Fe(η ~5-P _5)} _(12){CuBr} _(10){Cu _2Br _3} _5{Cu(CH _3CN) _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(η ~5-As _5) {Cp*Fe(η ~5- P _5)} _(12){CuCl} _(20) (5) is obtained. This accommodates as its guest CpCr(η ~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(μ, η ~5-As _5) requires 53.1 kcalmol ~(-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 π...π 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. Cutting the guest: The system formed from Cp*Fe(η ~5-P _5) and CuBr completely encapsulates the triple-decker complex guest (CpCr) _2(μ,η ~5- As _5) to form a spherical fullerene-like supramolecule containing 90 inorganic core atoms (see figure; left). When CuCl is used, however, an 80-vertex C _(80) topological host molecule is formed, in which fragmentation of the template is now observed, with incorporation of the unprecedented complex CpCr(η ~5-As _5) within the spherical supramolecule (see figure, right).