Ferrocenyl iron as a donor group for complexed silver in ferrocenyldimethyl[2.2]cryptand: a redox-switched receptor effective in water

• Published in: Journal of the American Chemical Society Vol. 114; no. 26; pp. 10583 - 10595
• Main Authors: Medina, Julio C., Goodnow, Timothy T., Rojas, Maria T., Atwood, Jerry L., Lynn, Bert C., Kaifer, Angel E., Gokel, George W.
• Format: Journal Article
• Language: English
• Published: WASHINGTON American Chemical Society 01.12.1992; Amer Chemical Soc
• Subjects: Chemistry; Chemistry, Multidisciplinary; Condensed matter: structure, mechanical and thermal properties; Exact sciences and technology; Organic chemistry; Organic compounds; Organometalloidal and organometallic compounds; Physical Sciences; Physics; Preparations and properties; Science & Technology; Structure of solids and liquids; crystallography; Structure of specific crystalline solids; Transition metals derivatives; FAST-ATOM-BOMBARDMENT; UNIT; CATION BINDING; METAL-CATIONS; DATIVE BOND; CROWN-ETHER; BOND FORMATION; METALLOCENE-CONTAINING CRYPTANDS; STABILITY-CONSTANTS; MASS-SPECTROMETRY; Complexation; Nitrogen crown compound; FAB mass spectrum; Stability constant; Silver Ions; Calcium Ions; Metallocene; Macrocycle; Cyclic voltammetry; Iron Organic compounds; Electrochemical properties; Sandwich compound; Alkali metal Ions; Cryptand; Ultraviolet visible spectrum; Cyclophane; NMR spectrum; Hydrates; Oxygen nitrogen heterocycle
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja00052a064

Three novel ferrocene-crown derivatives have been prepared along with their previously known amide precursors. The new compounds include 1,1'-(1,4,10,13-tetraoxa-7,16-diazacyclooctadecane-7,16-dimethyl)ferrocene (2), N,N'-bis(ferrocenylmethyl)diaza-18-crown-6 (4), mp 114-116-degrees-C, and bis[N,N'-bis(cyclopentadienidylmethyl)-4,13-diaza-18-crown-6]diiron (6), mp 104-106-degrees-C. Solid-state structures have been obtained for 2.H2O (mp 101-104-degrees-C) and for the Na+ClO4- (mp 208-215-degrees-C dec) and Ag+ClO4- (MP 209-210-degrees-C dec) complexes of 2. Comparison of these structures shows that the iron atom of ferrocene is a donor ligand for Ag+ but not Na+ (the Fe-Ag+ distance is almost-equal-to 1 angstrom shorter than for Fe-Na+). Stability constants have been obtained in either CH3OH or CH3CN with Li+, Na+, K+, Ca2+, and Ag+ cations. Complexation properties for these compounds have also been assessed by use of fast atom bombardment mass spectrometry. This technique reveals interactions that were not apparent when other analytical methods were applied to these compounds. When the system was studied by electrochemical methods, a new redox couple at more positive potential was observed in the presence of certain alkali, alkaline earth, and transition metal cations. Evidence is presented that cation binding by 2 involves coordination of the cation within the cryptand cavity in contrast to related amides such as 1. Thus alkali metal redox switching, previously unknown in ferrocenyl amides, is apparent. Evidence is presented for the first example of redox switching of silver ion binding. Determination of the stability constant for the complexation of 2 with the metal cations studied shows a direct correlation with the cyclic voltammetry. The large Ag+ binding constant and electrochemistry both confirm a direct, stabilizing Ag-Fe interaction. This interaction, previously unknown for kinetically dynamic systems, is confirmed by both H-1 NMR and UV-visible spectroscopy. Na-23 NMR studies of compound 2 in the presence of Na+ show two peaks in the NMR spectrum, corresponding to free and bound Na+. This behavior is usually associated with cryptands having oxygen donors and suggests that even sodium ions, when bound, are largely encapsulated by compound 2. This strong interaction permits the first observation of redox switching involving Ag+ in aqueous solution.