Selective Electrochemical Detection of Hydrogen Fluoride by Ambiphilic Ferrocene Derivatives

Abstract

Appropriate linking of Lewis acidic and Lewis basic components—in this case boronic acid and tertiary amine functionalities—allows the construction of a robust organometallic receptor capable of selectively binding hydrogen fluoride. This system can differentiate between exposure to HF and to related acids, such as HCl, by providing opposing electrochemical responses (see picture).

Coordination Chemistry of Neutral (Ln)–Z Amphoteric and Ambiphilic Ligands

“…[20] According to the mechanistic evidence, the dissociation of the aggregate is imperative for the Lewis acid moiety to interact with a transition-metalcarbonyl species, such as [CpFe(CO) 2 Me], [CpMo(CO) 3 Me] and [MeMn(CO) 5 ], [20][21] to yield adducts such as 1-Me in Scheme 1. As it has been observed with the addition of various Lewis acids to carbonyl species, [22] the aluminium-oxygen adduct weakens the metal-ligand bond and makes the carbonyl moiety more electrophilic, leading to the 1,1 insertion to give η 2 -acyl complex 2.…”

“…They have been shown to act as catalysts, [2] as precursors to semiconductors, [3] as fluorescent and conductive materials, [4] as sensors, [5] as small-molecule activators [6] and finally as ligands for transition metals. Although all of these applications are worth discussing thoroughly, this microreview will focus on the coordination chemistry of ambiphilic and amphoteric ligands binding transition metals via neutral moieties.…”

Synthesis and oxidation of hexafluoroisopropoxyborylferrocenes

“…The main advantage of the ferrocene backbone can be assigned to its electrochemical properties paired with the chemical and thermal inertness. Thus, ferrocenylboranes function, for example, as anion sensors for selective fluoride or hydrogen fluoride detection [1][2][3][4]. Owing to the relatively weak Lewis acidity of dialkoxyborylferrocenes, their fluoride binding is weak and recognition by NMR or electrochemical monitoring is possible even in the presence of other potentially competing anions.…”

“…The charge-transfer interaction occurs between the ferrocene donor and the electronpoor B-N adduct bridge. In 1,3-dibora [3]ferrocenophanes, the two Cp rings of ferrocene are connected by a B-E-B (E = O, S, Se, Te, or NMe) fragment [12]. In these compounds, the Cp rings bent to the hetero elements and are exactly staggered, which is unusual for ferrocenophanes.…”

“…To combine a decent stability with sufficient Lewis acidity, we chose the fluorinated alkoxide 1,1,1,3,3,3-hexafluoro-2-propoxy ligand (Ohfip) for the boryl residue. The Ohfip-ligand was proven to provide suitable Lewis acidity to an electron-deficient central atom, e.g., in the related B(Ohfip) 3 , as well as in monomeric Al[OC(CF 3 ) 3 ] 3 or dimeric Al 2 (Ohfip) 6 [30][31][32][33][34]. Carpenter and coworkers suggested that oxidation enhances the Lewis acidity of ferrocenylboranes, so that the B center in certain borylferrocinium compounds abstracts a fluoride from a [BF 4 ] -counteranion [35].…”