Ferrocene-Based Ureas as Multisignaling Receptors for Anions

Abstract

The synthesis of structurally new types of ferrocene-based ureas, in which the ferrocene moiety is simultaneously attached to two urea groups, have been prepared directly from 1,1'-bis(isocyanato)ferrocene 1. Homoditopic receptors 2a-e show spectral and electrochemical anion-sensing action: they display a selective downfield shift of the urea protons and a cathodic shift of the ferrocene/ferrocinium redox couple with hydrogen phosphate and fluoride anions. In addition, receptor 2d based on an unprecedent tetraaza[9]ferrocenophane architecture, shows spectral, electrochemical, and selective fluorescent responses to fluoride anion.

Ferrocene‐Based Small Molecules for Multichannel Molecular Recognition of Cations and Anions

“…Another important group of ferrocene-functionalized ureas are the receptors 18, 19, 20, [28] 21 and 22, [29] in which the ferrocene moiety is simultaneously attached to two urea groups.…”

“…[49] The presence of this structural motif, in which two signalling subunits are directly attached by two putative anion-binding sites, yields a combined fluorescence-and redox-based sensor for F -and H 2 PO 4 -anions in a single molecule. Thus, the reversible one-electron wave, corresponding to the free receptor (E 1/2 = -0.350 V vs. Fe/ Fe + ), is shifted upon stepwise addition of F -(∆E 1/2 = -0.190 V) and H 2 PO 4 -(∆E 1/2 = -0.125 V) anions, the BEF being 1628 for F -and 130 for H 2 PO 4 -.…”

Amide and Urea Ferrocene‐Containing Macrocycles Capable of the Electrochemical Sensing of Anions

“…An alternative N-H hydrogen-bond donor is urea: examples of two 1,1Ј-ferrocene bis-urea motifs are depicted in Figure 1 (c and d). [8,9] Of these, the latter has yet to be included in a macrocycle for anion sensing. Here in this paper we report the synthesis of novel ferrocenecontaining macrocycles that incorporate the motifs depicted in Figure 1 (b and d), and the subsequent investigations into their anion recognition and electrochemical sensing properties.…”

Electrochemically Controlled H‐Bonding

“…28 In addition, a significantly larger shift of À240 mV is observed with 18 and H 2 PO 4 À , due to the greater H-bonding capability of this anion compared to simple halides. 29 which shows a significant redox-dependent response to F À (DE 1/2 ¼ À208 mV) and H 2 PO 4 À (DE 1/2 ¼ À90 mV) in DMSO, but not to Cl À , Br À , AcO À , NO 3 À , and HSO 4 À . This is an example of a receptor where strong binding is observed in both oxidation states, resulting in two CV waves being observed at less than 1 equivalent of guest.…”