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Pentasubstituted Ferrocene and Dirhodium(II) Tetracarboxylate as Building Blocks for Discrete Fullerene-Like and Extended Supramolecular Structures

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journal contribution
posted on 21.03.2011, 00:00 by Lok H. Tong, Laure Guénée, Alan F. Williams
The synthesis of a penta(1-methylpyrazole)ferrocenyl phosphine oxide ligand (1) [Fe(C5(C3H2N2CH3)5)(C5H4PO(t-C4H9)2)] is reported together with its X-ray crystal structure. Its self-assembly behavior with a dirhodium(II) tetraoctanoate linker (2) [Rh2(O2CC7H15)4] was investigated for construction of fullerene-like assemblies of composition [(ligand)12(linker)30]. Reaction between 1 and 2 in acetonitrile resulted in the formation of a light purple precipitate (3). Evidence for the ligand-to-linker ratio of 1:2.5 expected for a fullerene-like structure [Fe(C5(C3H2N2CH3)5)(C5H4PO(t-C4H9)2)]12[Rh2(O2CC7H15)4]30 was obtained from 1H NMR and elemental analysis. IR and Raman studies confirmed the diaxially bound coordination environment of the dirhodium linker by comparing the stretching frequencies of the carboxylate group and the rhodium−rhodium bond with those in model compound (5), [Rh2(O2CC7H15)4](C3H3N2CH3)2, the bis-adduct of linker 2 with 1-methylpyrazole. X-ray powder diffraction and molecular modeling studies provide additional support for the formation of a spherical molecule topologically identical to fullerene with a diameter of approximately 38 Å and a molecular formula of [(1)12(2)30]. Dissolution of 3 in tetrahydrofuran (THF) followed by layering with acetonitrile afforded purple crystals of [(1)(2)2] (6) [Fe(C5(C3H2N2CH3)5)(C5H4PO(t-C4H9)2)][Rh2(O2CC7H15)4]2 with a two-dimensional polymeric structure determined by X-ray crystallography. The dirhodium linkers link ferrocenyl units by coordination to the pyrazoles but only four of the five pyrazole moieties of the pentapyrazole ligand are coordinated. The ligand-to-linker ratio of 1:2 in 6 was confirmed by 1H NMR spectroscopy and elemental analyis, while results from IR and Raman are in agreement with the diaxially coordinated environment of the linker observed in the solid state.