Size-determining dependencies in supramolecular organometallic host-guest chemistry

Treatment of the pentaphosphaferrocene Cp*Fe(η⁵‐P₅)] 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(η⁵‐P₅)}₁₂{CuCl}₂₀] ( 4 ), with an overall icosahedral C₈₀ topological symmetry, is obtained. This result shows the ability of ferrocene to compete successfully with the internal template of the reaction system Cp*Fe(η⁵‐P₅)], although the 90‐vertex ball {Cp*Fe(η⁵:η¹:η¹:η¹:η¹:η¹‐P₅)}₁₂(CuCl)₁₀(Cu₂Cl₃)₅{Cu(CH₃CN)₂}₅] ( 2 a ) containing pentaphosphaferrocene as a guest is also formed as a byproduct. With use of the triple‐decker sandwich complex (CpCr)₂(μ,η⁵‐As₅)] as a template the reaction between Cp*Fe(η⁵‐P₅)] and CuBr leads to the 90‐vertex ball (CpCr)₂(μ,η⁵‐As₅)]@{Cp*Fe(η⁵‐P₅)}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(η⁵‐As₅)]@{Cp*Fe(η⁵‐P₅)}₁₂{CuCl}₂₀] ( 5 ) is obtained. This accommodates as its guest CpCr(η⁵‐As₅)], 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,η⁵‐As₅)] 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 π???π stacking of the five‐membered rings (Cp and cyclo‐As₅) of the guests and the cyclo‐P₅ rings of the nanoballs of the hosts.