Macrocycle catenate

The polyether-diimine macrocycle (108) forms a catenate [Fe(cat)] which proved impossible to oxidize to [Fe(cat)] " but which is readily reducible, electrochemically in dichloromethane solution on a Pt or Hg surface, to [Fe(cat)]+ and to [Fe(cat)]°. " [Fe(bmpphen)2] (bmpphen = (109) can be electroreduced to [Fe(bmpphen)2] and to [Fe(bmpphen)2]. The relatively high stabilities of all three bmpphen complexes may be due to their entwined character. Here and below one should bear in mind the possibility, outlined in Section 5.4.1.3 above, that it is the ligand rather than the metal which is being reduced. 

A second experiment should prove that macromonocycles are actually the intermediate supramolecular templates in the course of catenane formation. Therefore macromonocycle 17 was reacted with 5 and 3, and the first [2]catenane 18 of the amide type consisting of two different macromonocycles was isolated (Figure 8). Unsymmetric catenanes like 18 can be identified unambiguously by mass spectrometry, because the corresponding tetrameric macromonocycle can not be formed in this reaction sequence. This confirms the presumption that catenation here proceeds via a macrocycle rather than via intertwining open chain units. 

A third example where the modification of the building blocks hindered catenation is shown in Figure 11 [16]. When diamine 5 is reacted with 2,5-fiiranedicar-boxylic acid dichloride (23) only macrocycle 24 is obtained, whereas catenane formation seems to be negligible. 

It is clear from comparison of the reactivity towards polycondensation of the difunctionalized [2]catenand 50b and 53 with their corresponding difunctionalized [2]catenates 50a and 54, respectively, that the mobility of the interlocked macrocycles of catenanes plays a fundamental role for the nature of the resulting polycondensates - either cyclic oligo[2]catenanes 52,54 or linear high molecular-weight poly[2]catenanes 51b,56 (Schemes 18-20). 

There are two distinct approaches to catenane synthesis the statistical approach, and approaches relying on self-assembly, so-called directed synthesis . The statistical approach relies on the small chance that macrocyclisation may occur while a linear precursor is threaded through a macrocyclic component. Because this is a rather unlikely eventuality, it naturally results in low yields of interlinked product and is chiefly of historical interest. It was this kind of statistical approach that resulted in the first synthesis of a [2] catenane by Wasserman in 1960 (10.64), from cyclisation of the long-chain diester 10.65 while threaded through the annulus of a deuterated C34 cycloalkane 10.66 (Scheme 10.11), 57 Although the overall yield of the catenation reaction was less than 1 %, the existence of the catenane was firmly established. The relatively polar [2] catenane product, along with other polar macrocyclisation reaction products and... 

The existence of interlocked molecules such as 10.95 can be established by a variety of spectroscopic techniques. Most importantly, mass spectrometry provides very characteristic patterns for catenanes. The mass spectra for catenated species are very different from those of covalently linked precursors (such as 10.94) but are more than the sum of their two individual components. Catenane mass spectra are characterised by the appearance of peaks at high mlz corresponding to the parent species as well as fragments corresponding to the transfer of hydrogen atoms from one macrocycle to the functional... 

In the [2]catenate, the circumrotation of the terpyridine-containing macrocyclic component can be reversibly controlled 21,22 (Figure 5), by altering the redox state of the metal. The absorption spectrum of a red-brown solution of [5 Cu] BF4 in MeCN shows a band, centered on 437 nm, characteristic of a Cu+ ion tetracoordinated to two phenanthroline ligands. Upon oxidative electrolysis, or upon addition of Br2, Cu+ is oxidized (step 1 in Figure 5) to Cu2+ and the solution turns deep green. The absorption spectrum shows a band, centered on 670 nm, typical of a Cu2+ ion tetracoordinated to two phenanthroline ligands. However, this absorption band shifts to... 

When short, flexible diamine a was used as a subcomponent in helicate formation, as shown on the left side of Scheme 1.7, only one topological isomer of product was observed twisted macrocycle 5. This diamine is not long enough to loop around the phenanthroline to form a catenated structure [28]. 

Scheme 1.7 The selection of a macrocyclic (5) or catenated (6) topology based on the rigidity and length of the subcomponents employed.

However, produced a neutral [2]catenane (Scheme 11.5) [lib] bearing a mechanically interlocked bis-NDI macrocycle in 53% yield. This yield is far more attractive for a bis-NDI macrocycle than the 10% yield originally obtained in macrocycles [30a]. This approach involved an oxidative coupling of two acetylenic naphthalene diimides in the presence of crown ether. The efficiency of the catenation can be attributed to the crown ether component acting as a permanent template for the forming cyclophane. 

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