a white crystalline product, which, after a single recrystallization, affords fine needles of the [12]crown-4 complex
5 . @ ]
Addition of 2,2'-bipyridine (bpy) to the solution of the recrystallized complex 5 gives [Fe(bpy),] (PF6)2 and two molar equivalents of [12]crown-4. The single-crystal X-ray structure determination of 5 (Fig. ) shows a sandwich-like arrangement of the crown ether ligands around the central iron atom. The coordination geometry at iron corresponds to that of a cube twisted by 19", in which the eight ligating oxygen atoms occupy the corner positions. For the [Ag([ 1 2]crown-4),]AsF6 complex formed from ethylene oxide and AgAsF, in SO,:71 the faces of the cube are twisted by 30°, while the analogous manganese['] and sodium complexes['' exhibit the coordination geometry of a regular square antiprism.
When 2,2'-bipyridine is added to a solution of non-recrystallized 5 , 85% [12]crown-4 and 15% [15]crown-5 are obtained. When (q5-cyclopentadienyl-q6-toluene)iron(~~) tetrafluoroborate is used as starting material, the 12-and 15-membered crown ethers are formed in a ratio of 10 : 1 ; for the analogous hexafluoroantimonate complex, the ratio is 3 : 2. The irradiated solution contains, in addition to ferrocene and unreacted ethylene oxide, traces of 1,4-dioxane.