Electronic Communication in a Novel Five-Step Redox System

Abstract

Chemical systems containing electronically communicating redox-active termini have attracted recent attention due to their potential applications in the construction of electronic devices and electron storage media. 1-8 Our group has recently suggested a novel concept for the generation of charge transfer polymers 9-11 and highly efficient electron sponges 12 exploiting the spontaneous formation of boron-nitrogen and boronoxygen bonds. Following this strategy, we have synthesized cations [1] + -[3] 4+ , in which up to four 2,2′-bipyridylboronium substituents, [B(Me)bipy] + , are attached to a ferrocene core ( Figure 1). 12 Similar to the well-known Diquat, 2,2′-bipyridylboronium ions [4] + were found to be perfectly reversible two-step redox systems. 13 Consequently, [1] + -[3] 4+ behave as highly redox-active species capable of storing three, five, and nine electrons, respectively. According to cyclic voltammetric measurements, however, there is only negligible electronic communication between the individual [B(Me)bipy] + fragments in [2a] 2+ (comproportionation constant K com ) 10). 12 Chalcogen atoms are known to be efficient transmitters of electronic and magnetic interactions. Thus, linking the 2,2′-bipyridylboronium substituents of 2 by an oxygen bridge might be helpful to attain the desired electronic communication. We report herein the facile synthesis, structural characterization, and electrochemical properties of the ansa-ferrocene [1,1′-fc(Bbipy) 2 O]-(PF 6 ) 2 , [5](PF 6 ) 2 . While [2a]Br 2 and [3]Br 4 can be dissolved in water without decomposition, [2b]Br 2 is rapidly hydrolyzed with liberation of ferrocene under similar conditions. However, the reaction of an acetonitrile solution of blue [2b]Br 2 with a trace amount of water in the presence of triethylamine gave [5]Br 2 in almost quantitative yield. In contrast to [2b]Br 2 , [5]Br 2 is no longer sensitive to air and moisture and can be transformed into the corresponding PF 6 salt, [5](PF 6 ) 2 , upon treatment of its aqueous solution with excess NH 4 PF 6 (Scheme 1). 14 The 11 B NMR spectrum of [5](PF 6 ) 2 shows a signal at δ ) 9.1, which lies in a range typical of tetracoordinate * Corresponding (1) Balzani, V.; Juris, A.; Venturi, M.; Campagna, S.; Serroni, S. Chem. Rev. 1996, 96, 759. (2) Gallo, E.; Solari, E.; Re, N.; Floriani, C.; Chiesi-Villa, A.; Rizzoli, C.

An Approach Towards Functional Dendrimers Based on the Hydroboration Reaction and Spontaneous Boron–Nitrogen Bond Formation

“…In our second approach, we tried to link ferrocene‐1,1′‐diylbis(2,2′‐bipyridylboronium) cations via their boron atoms by introducing oxygen bridges between them. In contrast to our expectations, no polymeric species were formed but ansa ‐bridged complexes E (Figure 1) were obtained as the result of an intramolecular reaction 12…”

Recent Progress on Synthesis of N,N′-Chelate Organoboron Derivatives

“…In 2002, Matthias Wagner’s group studied the synthesis of ferrocene complexes {Fc(Bbipy) 2 O}(PF 6 ) 2 ( 11 ) and {Fc(Bbipy) 2 (OH) 2 }(PF 6 ) 2 ( 12 ) [ 39 , 40 ], as shown in Scheme 3 . They successfully synthesized tetracoordinated organoboron compounds with two boron centers.…”

“…The data presented in this study are openly available in references [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 , 54 , 55 , 56 , …”

Synthesis and oxidation of hexafluoroisopropoxyborylferrocenes

“…In these compounds, the Cp rings bent to the hetero elements and are exactly staggered, which is unusual for ferrocenophanes. The spontaneous formation of B-N bonds was amongst others exploited in electron sponges [13][14][15], which are composed of ferrocene and up to four 2,2'-bipyridylboronium moieties. Those stable multi-step redox systems are able to store up to nine electrons and the ligands are electronically communicating.…”