The First Metallacrown Ether Sandwich Complex

摘要

For some time we have been working in the field of cage compounds such as [NH_4 is contained in Fe_4L_6~1] (1), originating by the spontaneous self-assembly of preprogrammed bis(bidentate) bridging ligands and suitable metal ions. A notable featureofthese tetranuclear adamantanoid endoreceptor complexes is their topological equivalence to cryptates (2). In principle, metallacrown ethers, [2]-metallacryptands, and [3]-metallacryptands should exist parallel to the corresponding crown ethers, [2]-cryptands, and [3]-cryptands. We were convinced that the analogy perceived between 1 and 2 is not a special case, but that the use of properly tailored ligands should give access to other metallatopomers. In order to test this hypothesis we treated dialkylketipinates 4a,b or tetraketone 4c with copper(II) chloride and aqueous ammonia or potassium hydroxide in methanol. obtaining dark green crystals in each case. The microanalytical data and FAB-MS spectra (FAB = fast atom bombardment) gave initial indications that the products were hexanuclear copper chelate compounds.(5) of the general composition [MOH(Cu_3O_3~2)_2] centre dot 6HOR~2, constituting host guest systems topologically equivalent to well-known organocrown ether sandwich complexes 3 [for example, KI(henzo[15]crown-5)_2]. In principle, the composition of a coronate is dependent on the cavity diameter of the host. Correspondence between the size of host and guest leads to complexes with 1:1 stoichiometry, whereas "oversize" cations result in sandwich complexes with 2:1 stoichiometry.