Ferrocene-silver complexes

Compound [25] was thus shown to have an unusual affinity for Ag+ cations. X-ray crystallographic determination of the structures of the free ligand, sodium and silver complexes were carried out and are shown in Fig. 17. The Ag-Fe distance in the silver complex of [25] is only 3.37 A, whereas the Na-Fe distance in the sodium complex is 4.39 A. This evidence together with the FAB MS data and UV spectroscopic data suggests that there may be an interaction between the silver cation and the iron present in the ferrocene moiety. 

The X-ray structure of the monoferrocenyl-silver complex is shown in Fig. 7-71 [195]. The cryptand-like cavity of the peripheral tetraoxa-dizazadecane ring is able to accomodate one Ag ion, but it is thought that a direct Fe-Ag interaction also occurs. The cyclopentadienyl rings of the ferrocene portion are tilted by 10°. 

Thia-crown ethers incorporating propan-2-one units and dimeric silver(I) compounds as (176) and other polymeric species have been prepared.1132,1133 Other substituents can be diisopropyl idene groups which form complexes of the type [AgL(PPh3)]OTf (177),1134 pyridazine,1133 phthalazine1136 ligands or even organometallic compounds as ferrocene in (178).1137... 

Interestingly Gokel has demonstrated the existence of a direct coordination coupling pathway between this ferrocene cryptand and a silver cation. Complexation studies were carried out with [24] and [25] (as well as other ferrocene cryptand-type species) by X-ray crystallography, FAB mass spectral analysis, nmr and UV/Vis spectroscopy. 

As illustrated in Fig. 7-72, complexation of silver ions in acetonitrile solution causes the one-electron oxidation of the ferrocene fragment to shift anodically by... 

A minor shift in redox potential is caused by silver ion complexation of the diferrocenyl-monocryptand complex. In fact, the silver-free ferrocene ligand undergoes a single-step two-electron oxidation at E° = -1-0.39 V in MeCN. On incorporation of silver ion, the two-electron redox change occurs at ° = -1-0.50 V. 

P.L. Pauson (1993) Organo-iron compounds in Chemistry of Iron, ed. J. Silver, Blackie Academic, Glasgow, p. 73 -A good summary of ferrocene chemistry and of other organo-iron complexes. 

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