Redox-active systems

The outer sphere mechanism may take place in all redox active systems while inner sphere mechanism requires substitutionally labile reactants and products. 

True porphyrin complexes also exist for molybdenum, and their chemistry has been explored by Collman and coworkers (equation 39). Oxidation of these complexes has been shown to increase the bond order ft om 2.0 to 3.0 for these redox-active systems. ... 

Tetrathiafulvalene-containing systems have also been reported. One such pseudorotaxane represents a redox-active system in which a similar molecular motion can be controlled by two different inputs. Reversible dethreading-rethread-ing cycles involving this product can be performed by either oxidation and consecutive reduction of the linear component or reduction and consecutive oxidation of the electron-accepting cyclophane tetracation. As such, the system corresponds to a further level of sophistication in systems of this type. Formally, the input (elec-trochemical)/output (absorption spectrum) characteristics of this assembly correspond to those of an XNOR logic gate. 

Later on, they investigated the bis(iron) derivative Fe2 and showed that the presence of the ferrocenyl substituent makes possible a quantitative thermal reopening upon partial or complete oxidation of the redox active system without oxidizing the photochromic core [85, 86]. This process is catalytic in electrons in the case of the perhydro-DTE compound. The thermal reopening of neutral DTE unit is facilitated by electron-withdrawing substituent as gew-dicyanovinyl (Fig. 12). 

The above examples demonstrate that metal centres can conveniently be used to link redox active fragments in order to generate multi-electron redox active systems. If a stable system is desired, a metal ion that forms inert complexes should be chosen. This is the case of the cis-[Pt (Fcpy)2Cl2] system. On the contrary, the [Fe (Fcsal2-)3]3- species possesses a labile metal centre and the redox active ligand can be removed, for instance on addition of a strong add. It should be noted that the two considered metal centres (Pt, Fel ) do not present individual redox activity in the coordinative environments examined and play a purely 2irchitectviral role. 

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