Ferrocenes ligand exchange

Xanthene and 6-thiaxanthene complexes of iron, 102 (X = O, S) are prepared by the ligand exchange reaction between the heterocycle and ferrocene (86JOM(305)199). Chemical oxidation using potassium permanganate leads to the ketones 103 (X = O, S). In the case of X = S, sulfone 104 is also obtained. 

The yellow CpFe1 (//6-arene) salts (most commonly BF4 or PF6 ) are usually stable up to at least 200 °C, are stable in concentrated sulfuric acid, and are very resistant towards oxidation (until recently, it was believed that they could not be oxidized [23] vide infra). They are not easy to reduce either [23] (vide infra). The chloride salts [CpFe+( f -arene) Cl- are water-soluble they are formed upon hydrolysis following ligand-exchange reactions between ferrocene and the arene in the presence of aluminum chloride [21]. Such aqueous solutions may sometimes be directly used for nucleophilic reactions [22] (vide infra). The BF4- salts are also sometimes quite soluble in water, but the PF6- salts are much less so. Electrophilic reactions that are readily undergone by the free arenes, such as Friedel-Crafts reactions, are no longer possible on the CpFe+( /6-arene) complexes [19, 23]. On the other hand, a range of nucleophilic reactions that are impossible or very difficult to carry out with free arenes become possible under ambient or mild conditions with the CpFe+()/6-arene) complexes (Scheme 2) [16-20]. 

XV. Ligand Exchange in Ferrocene. Arene Cyclopentadienyl Derivatives... 

The first indication of an electronic effect in the ring migration studies was demonstrated when l,T-diethylferrocene was observed to undergo ligand exchange with mesitylene much more readily than did ferrocene... 

Dyson PJ, Grossel MC, Srinivasan N, Vine T, Welton T, Williruns DJ, White AJP, Zigras T (1997) OrganometaUic synthesis in ambient temperature chloroeiluminate(III) ionic liquids. Ligand exchange reactions of ferrocene. J Chem Soc Dtilton Trans 3465—3469... 

The most favorable compound for non-natural amino acid requires the following 1) stability to air, moisture, acid, base and heat, 2) complex inert to ligand exchange reaction, 3) electrochemical stability and 4) synthetic facility. Consequently, we selected ruthenium-polypyridine compounds and ferrocene derivatives shown in Fig. 3.33(b). Palladium compounds were prepared for spectroscopic comparisons and investigation. 

The complexation of 1 with CpFe+ was performed by ligand exchange with a Cp group of ferrocene [47]. The reaction proceeded in the presence of aluminum powder and aluminum chloride without a solvent under argon at 120 °C for 19 h. The counteranion of the crude complex was replaced by hexafluorophosphate, giving [CpFe(sumanene)]PFg (15) as an orange solid. The use of excess ferrocene and aluminum chloride selectively afforded the desired monometallated complex in 91% yield (Scheme 35.2). However, the reaction in decahydronaphthalene as a solvent did not yield 15 [47]. The complex 15 was fully characterized by fast atom bombardment (FAB) mass spectrometry, and C NMR spectroscopy, and X-ray crystallography. 

Gold. and P NMR spectroscopy has been used to show that there is rapid ligand exchange in [(AuSPh)(p-trans-dpen)(AuCl)] and [(AuSPh)(p-dppfe)(AuCl)]. NMR spectroscopy has been used to show that cyclodextrin-modified gold nanoparticles bind ferrocene. " ... 

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