Ferrocene-boronic acid

Many of the receptors synthesised interact with a wide variety of anions however, selectivity has been introduced to these systems. Ferrocene-based systems have been shown to detect aqueous phosphate [99] and sulphate [100] ions. Ferrocene boronic acid has been shown to associate with fluoride ion with much stronger binding than to chloride,bromide and other anions [101]. 

Recognition of fluoride in aqueous media is particularly difficult due to the strongly hydrated nature of the anion. Shinkai and co-workers have demonstrated that ferrocene-boronic acid 27 acts as a selective redox sensor for fluoride which operates in H20 [23]. The favourable interaction between boron and fluoride (a hard acid and hard base, respectively) generates a stability constant of 700 M"1 for the fluoride-ferrocenium complex. Stability constants for both the bromide and chloride complexes are <2 M"1. 

Mercurioferrocenes (290) and (291) are separable by Soxhlet extraction and these may be used to prepare bromoferrocene or dibromoferrocene or the iodo analogs. Alternatively, these halogenated ferrocenes are prepared from the ferrocene boronic acids or from anions (322) or (323). Bromoferrocene is the starting material for cyanoferrocene, azidoferrocene, or aminoferrocenes, generally in the presence of a copper salt. Amtnoferrocene can be acylated to produce an amide, or converted to isocyanoferrocene by a formylation/dehydration sequence (Scheme 96). The 1,T-diisocyanoferrocene is available from the bis(acyl)azide, itself derived from ferrocene dicarboxylic acid. ... 

Ferrocene derivative 74 shows a B-N distance of 1.72A, considerably longer than the B-N distance of 1.625 A for 44, suggesting that the [5,5] ring fusion is less favorable than the [6,5], It has also been found that ferrocene boronic acid derivative 87 does not form an intramolecular B-N bond <2001J(P2)727> in contrast to the observed B-N bonds for 49-53. 

A synthetically interesting synthetic application of flavo enzymes using ferrocene-boronic acid as mediator [134] has been described for the transformation of /7-hydroxy-toluene (p-cresol) to /7-hydroxybenzaldehyde, which is catalyzed by the enzyme p-cresolmethyl hydroxylase (PCMH) from Pseudomonas piitida. This enzyme is a flavocy-tochrome containing two FAD and two cytochrome c prosthetic groups. To develop a continuous process using ultrafiltration membranes to retain the enzyme and the mediator, water-soluble polymer-bound ferrocenes [26-31,135] (Scheme 3) have been applied as redox catalysts for the application in batch electrolyses or in combination with an electrochemical enzyme membrane reactor (see Fig. 24) [26-31,135] with excellent results. 

The analysis of 2- and 4-hydroxyestradiol and 2- and 4-hydroxyestrones is relevant in relation to the development of breast and prostate cancer. These compounds have been analysed in mine after hydrolysis by means of P-glucuronidase/sulfatase and extraction by LLE or SPE. Prior to LC-MS analysis, the hydroxyestiadiols and hydroxyestrones were derivatized with ferrocene boronic acid to form cyclic boronate esters [32], or with p-toluenesulfonhydrazine to form p-toluenesulfonhydrazones [33], respectively. Product-ion MS-MS enables discrimination between two isomers [32]. 

Heinze proposed a convenient synthetic route starting from ferrocene to give 1-aminofer-rocene-1 -carboxylic acid hydrochloride 45.54 Scheme 12.8 summarizes the reaction sequence. The key synthon in this synthesis is 1-aminoferrocene provided by the Gabriel synthesis from IV-ferrocenylphthalimide. However, this route requires the synthesis of 1-haloferrocene or ferrocene boronic acid as precursors of IV-ferrocenylphthalimide. In addition, the reaction is accompanied by the formation of biferrocenes due to a copper-mediated C—C coupling reaction, even in the presence of excess phthalimide.55,56 57... 

A. N. J. Moore, D. D. M. Wayner, Redox switching of carbohydrate binding to ferrocene boronic acid, Canadian Journal of Chemistry - Revue Canadi-enne De Chimie 1999, 77, 681. 

Chiral ferroceneboronic acid derivatives have been synthesized by Ori and tested for chiral electrochemical detection of monosaccharides. The best discrimination was observed for L-sorbitol and L-iditol at pH 7.0 in 0.1 mol dm phosphate buffer solution. Moore and Wayner have explored the redox switching of carbohydrate binding with commercial ferrocene boronic acid. From their detailed investigations, they have determined that binding constants of saccharides with the ferrocenium form are about 2 orders of magnitude greater than those for the ferrocene form. The increased stability is ascribed to the lower pKe of the ferrocenium (5.8) than ferrocene (10.8) boronic acid. 

Tucker has recently employed chiral ferrocene boronic acid 66 to electrochemically determine the enantiomeric excess of the chiral diol (binol), which took its inspiration from the three component systems used to determine enantiomeric excess of amines and diols by NMR developed by Bull and James. ... 

Gamoh K, Sawamoto H, Takatsuto S et al (1990) Ferrocene boronic acid as a derivatization reagent for the determination of brassinosteroids by HPLC with electrochcanical detection. J Chromatogr 515 227-231... 

Although boranes still produce exciting new molecular species like water-stable B(C6Cl5)3 and associated one-electron reduced radical anions, most work in electroanalytical mechanisms is focused on boronie acid derivatives with a more or less strong interaction with a redox active reaction centre. The most literature-abundant redox active boronie acid is ferrocene-boronic acid (as synthesised first by Nesmeyanov ) with a range of selective redox label applications. 

Moore and Wayner have explored the redox switching of saccharide binding with commercial ferrocene boronic acid. From their detailed investigations, they have determined that binding constants of saccharides with the... 

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