Cationic complexes involving ferrocenes

In organic chemistry this stabilizing effect is well known the stability of carbanions is known to be enhanced by nitro groups. The stability of the cyclopentadienide anion is increased by complexing with a typical Lewis acid so that it becomes less reactive. For example, ferrocene is not ionized in nitromethane solution. Addition of a Lewis acid such as aluminum chloride facilitates the occurrence of intramolecular race-mization (75) a process which is believed to involve ionic intermediates [16). This belief is supported by kinetic evidence and the failure of the reaction to occur in nearly inert solvents like methylene chloride and in those of high donidty. Whereas the former do not support the solvation of the cation formed in the process of ionization, the latter will react preferentially with the Lewis acid, which is then no longer available for the stabilization of the carbanion. 

The mechanism of reoxidation of reduced GO by ferricenium cations suggested by Bourdillon and co-workers 74) involves intermediate complex-formation between GO(red) (designated as FADH2 in Scheme 5) and ferricenium cation (designated as Q which transforms into ferrocene designated as P). Although no evidence for this has been obtained from the electrochemical data, the formation of the GO ferricenium intermediate has been kinetically proven in later... 

Fullerenes C60 and C70 form supramolecular adducts with a variety of molecules, such as crown ethers, ferrocene, calixarene, and hydroquinone. In the solid state, the intermolecular interactions may involve ionic interaction, hydrogen bonding, and van der Waals forces. Figure 14.2.9 shows a part of the structure of [K(18C6)]3-C6o-(C6H5CH3)3, in which Cgg is surrounded by a pair of [K+(18C6)] complexed cations. 

Ferrocene may accelerate the embrittlement of chlorinated polymers (64) This mechanism also involves a charge-transfer complex witE a C-Cl bond in FVC and ferrocene. The formation cation,chloride ion and a polymer macroradical are formed ... 

Irving-Williams stability order. Supporting data indicated a 2 2 (host/guest) complex stoichiometry in solution with a 1 2 stoichiomefiy in the presence of excess Cu ". Recently, rhodamine-based ferrocene derivatives have been used for cation sensing, for example, system 13 that responds to Cr +, which is an ion involved in various biochemical processes at the cellular level.An unusual anodic shift of —140 mV was observed in the Fc/Fc" " redox potential upon complexation of this cation in ethanol. 

These processes are quite rapid with an apparent rate constant which exceeds lO" cm s" [5,6] The only example of electron transfer reaction which has been observed was between the hydrophobic ferro-cinium - ferrocene redox couple in nitrobenzene and the hydrophilic hexacyanoferrate redox couple in water [9]. A more complex mechanism is involved in the case of ion transfer facilitated by an iono-phore[10]. This is the case, for example in the transfer of the alkali and alkaline earth metal cations across a water/nitrobenzene interface facilitated by synthetic neutral cyclic or acyclic iono-phores derived from 3,6-dioxaoctanedicarboxylic acid [11]. 

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