Arene complexes redox

There is a wider general interest in understanding the oxidation of cysteine thiolates in proteins since they are involved in redox-sensing reactions [99], Therefore, such oxidation reactions of thiols induced by Ru coordination may also play a more general role in the pharmacological activity of Ru-arene complexes by coupling Ru coordinative binding to redox processes both outside and inside cells. 

The most frequently used electron-reservoir complex for stoichiometric singleelectron transfer reactions is (Fe Cp( / -C6Me6)], because of its stability and ease of preparation, and since it has one of the most negative redox potentials in the series. It can reduce most inorganic and organometallic cations [2]. For instance, it is very useful to synthesize neutral 19-electron complexes (C in the equation below) such as other (Fe Cp( / -arene)] complexes and (Fe ( / -C6Me6H)( / -C6Me6)] from the 18-electron cationic precursors C[PF6 ... 

It has been shown that the use of ionic liquids may be beneficial in aromatic fluorinations in protic solvents." Aryl fluorides may also be obtained using a copper-catalysed halide exchange reaction. The evidence suggests a redox Cu(I)/Cu(III) catalytic cycle involving oxidative addition of aryl halide at the copper(I) centre followed by halide exchange and reductive elimination." A mechanistic investigation of the palladium-catalysed conversion of aryl triflates to fluorides has shown that C-F reductive elimination from the palladium—arene complex does not occur when the aryl group is electron rich and requires in situ modification of the catalyst." ... 

Ruthenium complexes are capable of catalyzing halogen atom transfer reactions to olefins. This has been illustrated in the enantioselective atom transfer reactions of alkane and arene-sulfonyl chlorides and bro-motrichloromethanes to olefins using chiral ruthenium complexes. Moderate ee s up to 40% can be achieved for these transformations [74-77]. These specific reactions are believed to follow a radical redox transfer chain process. 

A sub-set of these reactions is provided by the redox rearrangements of several complexes whicdi have been extensively studied by Cormelly and coworkers [140]. Oxidation of the rj -alkyne complexes M(r] -Me3SiC2SiMe3)(CO)2(ri-arene) (M = Cr, Mo) results in formation of the vinylidene cations [M =C=C(SiMe3)2 (CO)2(ri-arene)]. ... 

Astruc has developed the concept of transition metal sandwiches acting as electron reservoir complexes. The characteristic of an electron reservoir is that the reduced form is easily generated and does not decompose to increase stability, the radical center can be sterically protected in the heart of a bulky molecular framework. The [FeCp(arene)] series of complexes, e.g. 7, are prime examples, for which variation of the arene structure modulates the redox potential. 

The Lever s model has also been extended to sandwich and half-sandwich complexes with 7T-cyclopentadienyl or 7r-arene ligands [66, 67, 69]. The parameter for the 7r-ligands has been defined [69] on the basis of the low spin Fe hH redox couple, by Eqs. (21) or (22), for homolep-tic sandwich [Fe( 7r-L)2] or mixed sandwich ]Fe( 7r-Li)( 7r-L2)] complexes, respectively. 

Tab. 1 Redox potentials of sonne bis(arene)vanadium complexes in DME versus SCE...

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