COMPLEXATION OF NA-ACTIVE FERROCENE CROWN-ETHERS, A STRUCTURAL INVESTIGATION, AND AN UNEXPECTED CASE OF LI+ SELECTIVITY( IN REDOX)

The synthesis of several ferrocene crown ethers is described, which we re designed tb selectively coordinate and recognize electrochemically small group I ions sandwiched between two 12-membered crown ether ring s. The reactions of the [1,1'-ferrocenediylbis(methylene)]bis[pyridini um] salt [Fcdiyl(py)(2)(2+)] with diaza-12-crown-4 [H(N-2-12-C-4)H], a za-12-crown-4 [H(N-12-C-4)], and 2-ethanediylbis(1,7-dioxa-4,10-diazac yclododecane) [C(2)H(4)diyl-((N-2-12-C-4)H)(2)] yielded the respective ferrocene crown ethers 1,1 bis(methylene)-1,7-dioxa-4,10-diazacyclodo decane)] 10-diazacyclododecane)] Fcdiyl(N-2-12-C-4)(2)Fcdiyl] (3), [Fc diyl(N-12-C-4)(2)] (2), and [Fcdiyl(N-2-12-C-4)(2)(C(2)H(4)diyl)] (4). Complexation of group 1 ions was evidenced by NMR, cyclic voltammetry , FAB mass spectrometry, and picrate extraction experiments. This last techniques was used to determine a complexation selectivity of 4 for Li+/Na+ approximate to 20:1. The redox potentials of the ligands 2, 3, and 4 were determined by cyclic voltammetry; addition of Li+ or Na+ r esults in anodic shifts of the redox potentials of up to 100 mV for (4 Na+ and 140 mV for(4Li+. The X-ray crystal structures of [(2)NaClO4](2 ), [(2)NaBPh(4)](2), 3, 3 . 2HClO(4), 4, and (4)NaI were determined to understand the coordination behavior of these ligands and the metal i on selectivities displayed. The determining factor for the stability o f the metal complexes is the orientation of the plane of the cyclopent adienyl (Cp) ring with respect to the CpCH(2)-N vector. In metal ion o r proton complexes torsion angles of close to 90 degrees are preferred , which allow the equal participation of all donor atoms in the coordi nation of a cation. This property, however, prevents the complexation of Na+ or Li+ within the cavity formed by 3. Replacing one 1,1'-ferroc enediylbis(methylene) group in 3 by a sterically more suitable C2H4 br idge results in 4 and allows formation of the Na+-sandwich (4)NaI. In this complex strain is apparent, which leads to the preferential coord ination of Li+ by 4. The results obtained in this study make it possib le to set up a correlation of the anodic shifts Delta E of the iron re dox potentials upon complexation of Na+ by ferrocene crown ethers and the inverse distance Fe-Na+ as determined by crystal structure analysi s Delta E congruent to 1/(Fe-Na+). This indicates that crystal structu res of metal complexes of ferrocene crown ethers can serve as reasonab le models for the corresponding species in solution.