cyclo-P4 Building Blocks: Achieving Non-Classical Fullerene Topology and Beyond

Abstract

The cyclo-P₄ complexes [Cp^R Ta(CO)₂ (η⁴ -P₄ )] (Cp^R : Cp''=1,3-C₅ H₃ tBu₂ , Cp'''=1,2,4-C₅ H₂ tBu₃ ) turned out to be predestined for the formation of hollow spherical supramolecules with non-classical fullerene-like topology. The resulting assemblies constructed with CuX (X=Cl, Br) showed a highly symmetric 32-vertex core of solely four- and six-membered rings. In some supramolecules, the inner cavity was occupied by an additional CuX unit. On the other hand, using CuI, two different supramolecules with either peanut- or pear-like shapes and outer diameters in the range of 2-2.5 nm were isolated. Furthermore, the spherical supramolecules containing Cp''' ligands at tantalum are soluble in CH₂ Cl₂ . NMR spectroscopic investigations in solution revealed the formation of isomeric supramolecules owing to the steric hindrance caused by the third tBu group on the Cp''' ligand. In addition, a 2D coordination polymer was obtained and structurally characterized.

Keywords: copper; fullerenes; phosphorus; self-assembly; supramolecular chemistry.

Figure 1

a) Supramolecule with 80 vertices based on [Cp*Fe(η⁵‐P₅)] and CuX (X=Cl, Br). b) The molecular scaffold illustrating the I _h‐C₈₀ fullerene topology.

Figure 2

Reactions of [Cp^RTa(CO)₂(η⁴‐P₄)] (1 a: Cp^R=Cp′′; 1 b: Cp^R=Cp′′′) with copper(I) halides yield the supramolecules 2–4 and the coordination polymer 5 (yields in parentheses).

Figure 3

a–c) Molecular structures of 2 c (a), 3 (b), and 4 a (c). d) Section of the 2D polymeric network in 5. Hydrogen atoms omitted for clarity. e–g) Scaffolds of the supramolecules 2 a–d (e), 3 (f), and 4 a (g). h) Repeating unit of 5.