NEUTRAL MOLECULE RECEPTOR SYSTEMS USING FERROCENES ATOMIC BALL-BEARING CHARACTER AS THE FLEXIBLE ELEMENT

Fourteen novel ferrocene derivatives have been designed to serve as re ceptors for low molecular weight diamines. The compounds that have bee n prepared and fully characterized possess two ferrocenedicarboxylic a cid residues bridged by amide formation in their respective 1'-positio ns by 4,4'-benzidinyl (15), 3,3'-dimethoxy-4,4'-benzidinyl (16), 2,7-f luorenyl (17), 3-methoxy-2,7-fluorenyl (18), 4-N-piperazinoanilinyl (1 9), N,N-4,4'-bipiperdinyl (20), and 4,13-diaza-18-crown-6 (21). In two cases, ferrocenecarboxylic acid was bridged by spacers attached using l-methylene groups. The bridges in these cases were 4,13-diaza-18-cro wn-6 (22) and 1,5-diaminoanthraquinone (24). In a single case, ferroce necarboxylic acid was bridged by 1,5-dicarbonylnaphthalene (25). In on e additional case, the bridge was created by formation of an imine fol lowed by hydrogenation, but both compounds (26, 27) proved to be relat ively unstable. Attempts to increase solubility afforded the N-ethylat ed derivative 28 of 15 and the derivative 29 of 27 having carboxamides in the 1'-positions. A solid state structure of the diethyl ester of 20 confirms the design criteria. Complexation constants were determine d in THF-d(8) or CDCl3 for combinations of receptors 18, 19, and 20 wi th 4-aminopyridine, N,N,N',N'-tetramethylethylenediamine, N,N,N',N'-te tramethylpropylenediamine, DABCO, 3-propyladenine, and benzimidazole a nd were in the range 10(2)-10(4). The anticipated complexation mechani sm for 20 with N,N,N',N'-tetramethylpropylenediamine was confirmed by observation of an NOE between host and guest.