Cryptands Containing the Ferrocene Unit

The first synthesis of molecules of this kind was reported independently by Vogtle [52] and Hall [51] and both involved condensation of 34 with a range of diazamacrocycles 37 under high dilution conditions to form the corresponding amide cryptands 38 together with dimeric analogues 39 and some polymers. The compounds were easily separated by column chromatography on alumina and were fully characterised by mass spectrometry, elemental analysis, and multinuclear NMR 

The first confirmation of cis-binding of cations by the amide functions came from an X-ray crystal structure of the complex between 38 (m, n = 2) and yttrium perchlorate [65]. The stoichiometry was 1 2 1 ligand H2O) and the seven- 

The electrochemistry associated with these redox-active cryptands is quite intriguing. As pointed out earlier, anodic shifts of the ferrocene redox potential may be used via the Nernst equation to estimate the decrease in binding capacity (Xj/Ki) on coordination with a cation. Beyond this, however, if Kj is determined independently as is the case for 38 (m, n = 2) [63] then Xj may be calculated and correlated with the ratio of cationic radius/charge (Fig. 6-7) — data that reveal that increasing charge density on the cation destabilizes the complex between the oxidised cryptand and the cation, presumably by charge repulsion [68]. Alkali metal cations gave only small ( 20 mV) anodic shifts with this cryptand. 

Laser flash photolysis has also been used to study the photophysics and photochemistry of metallocene-containing cryptands and their complexes with rare earth eations [69]. The metallocene moiety was shown to act as an efficient centre for the radiationless deactivation of the lanthanide excited state. Detailed time-resolved studies permitted the characterisation of the coordination chemistry about Dy within the cryptate and showed, once again, that the functions within the host cryptand primarily responsible for coordination of the guest cation were the amide carbonyl groups. 

Reduction of the carbonyl groups of 38 to 48 had to await the development of an elegant method by Gokel using LiAlH4 in a mixture of CH2CI2 and THF [70]. 

Ca and Ag , together with an assessment of complexation by mass spectrometry. The evidence suggests that, in contrast to the amide ligands 38, complexation by 

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In general, there are two types of macrocycles or cryptands containing the ferrocene unit. The first is that in which the ferrocene is appended to either a macrocycle — represented schematically by Fig. 6-1, or to a cryptand, spherand or cavitand (Fig. 6-2). The second class of compounds has ferrocene incorporated... 

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