Cyclophanes arene complexes

Jorgensen. W.L. Nguyen, T.B. Structure and Binding for Cyclophane-Arene Complexes in Water from Monte Carlo Simulations. In Supramolecular Chemistn Balzani. V.. De Cola, L., Eds. Kluwer Acad. Pub. Dordrecht, 1992 ... 

Keywords Cyclophanes, arene complexes, alkyne complexes, chirality, photochemistry. 

Structure and binding for cyclophane-arene complexes in water from Monte Carlo simulations... 

Ferguson, S. B., Sanford, E. M., Seward, E. M., Diederich, F., Cyclophane arene inclusion complexation in protic solvents - solvent effects versus electron-donor acceptor interactions. J. Am. Chem. Soc. 1991, 113, 5410-5419. 

Cyclophane ruthenium complexes have been prepared by the methods developed to make arene ruthenium complexes (Section II,A). Treatment of the solvated complexes of type 7, obtained from the dimers 1 and silver tetrafluoroborate in acetone, with 1 equiv of cyclophanes a-j in the presence of trifluoroacetic acid gives the double-layered (i76-arene)-(i76-cyclophane)ruthenium(II) complexes 263 in good yield (Scheme 26, p. 222). When 7 is used in excess, the triple-layered complex 264 is formed (159-162). 

An attempt to achieve the complexation of the cyclophane iron complex 276 by treatment with the solvated (p-cymene)ruthenium derivative 7 results in disruption of the arene-iron bond and formation of the (p-cymene)[[22](l,4)cyclophane]ruthenium(II) salt 277 as the only-product (164) (Scheme 29, p. 224). 

An electrochemical study of the reduction of the double-layered (arene)-(cyclophane)ruthenium complexes 263 and of bis(arene)ruthenium complexes 235c has been reported (160,166). The compounds show in... 

Smithrud DB, Wyman TB, Diederich E. Enthalpically driven cyclophane arene inclusion complexation - Solvent-dependent calorimetric studies. J. Am. Chem. Soc. 1991 113 5420-5426. Gilson MK, Zhou HX. Calculation of protein-ligand binding affinities. Annu. Rev. Biophys. Biomol. Struct. 2007 36 21 2. Karplus M, McCammon JA. Molecular dynamics simulations of biomolecules. Nat Struct Biol 2002 9 646-652. 

Arene complexes with mint metals are rather rare. The arene metal bond is weaker compared to the other transition metals and hapticity is lower. For this reason the stronger rr-donor properties of the cyclophanes compared to open chained arenes [109c] make the preparation in benzene solution possible. The cyclophane is simply heated with silver-I (Fig. 29a) [109a] or copper-I (Fig. 29b) [109b] and yields the respective complex formed in almost quantitative yield. It is noteworthy that the silver ion in 128 shows no interaction with the benzene ring at all the naphthalene unit acts as 7t-donor only [109a]. 

Harrowfield et al. [37-39] have described the structures of several dimethyl sulfoxide adducts of homo bimetallic complexes of rare earth metal cations with p-/e rt-butyl calix[8]arene and i /i-ferrocene derivatives of bridged calix[4]arenes. Ludwing et al. [40] described the solvent extraction behavior of three calixarene-type cyclophanes toward trivalent lanthanides La (Ln = La, Nd, Eu, Er, and Yb). By using p-tert-huty ca-lix[6Jarene hexacarboxylic acid, the lanthanides were extracted from the aqueous phase at pH 2-3.5. The ex-tractability is Nb, Eu > La > Er > Yb. 

The corresponding dependence of cation complex stability on the anion differs profoundly from that of most other cation receptors such as cyclophanes or calix-arenes [16]. For these cation complex stability decreases on changing the anion from picrate through iodide to tosylate, a dependence that has been attributed to ion-pair aggregation in non-polar solvents. Because the interaction of quaternary ammonium ions with tosylate or iodide in chloroform is considerably stronger than with picrate, cation complexes in the presence of the latter anion are usually more stable. Only when iodide or tosylate cooperatively contributes to cation binding, as in 3 or in some recently described calixarene derivatives [17], is reversal of this order observed. 

A more general route to make bis(cyclophane)ruthenium(II) complexes involves a reduction of 263 (arene = benzene) with Red-Al to afford the [ 174-1,3-cyclohexadiene)(tf-cyclophane)]ruthenium(O) derivatives 271 (Scheme 28, p. 224). Treatment of 271 with hydrochloric acid gives the dimeric chloride complexes 272, which lead the desired bis(r)6-[2 ]cyclo-phane)ruthenium(II) complexes 274 via Bennett s procedure (145). Synthesis of the oligomer 275a is also achieved in quantitative yield by heating 274 with the solvated complex 7 (arene = C6Me6) in neat trifluoroacetic acid. 

Monolayered cyclophane complexes of type 263 are also reduced by sodium bis(methoxyethoxy)aluminum hydride (Red-Al) to give (i74-diene)-(i76-cyclophane)ruthenium(0) complexes (Scheme 33). If the benzene ring of 263 (arene = benzene) is converted to the (1,3-cyclohexadiene)-ruthenium(O) derivative 271, however, when the corresponding rj6-hexa-methylbenzene is reduced with Red-Al, the product is the (if-1, 4-cyclohexadiene)ruthenium(0) complex 288. Synthesis of 271 can... 

Calixarenes have also been used as cyclophane hosts for the binding of quinone acceptors via hydrogen bonding. Arimura and Sessler have appended bis-hydroxy-containing calix[4]arenes to zinc(II) porphyrins. Two phenolic OH groups on the calix[4]arene serve as tweezers to complex a quinone via two-point hydrogen... 

The red shifts observed for the etheno-bridged cyclophanes (21 and 22) are much stronger they reach 6500 cm-1 in 21 and the enormous value of 10,500 cm-1 in 22. Fluorescence red shifts of this magnitude usually are observed only in charge-transfer complexes between donor- and acceptor-substituted arenes (46). The spectroscopic difference of 4000 cm-1 between the isomers 21 and 22 corresponds to about 11 kcal/mol (47 kj/mol). Because no phosphorescence could be detected for all the naphthalenopyridino-phanes, the excited triplet states could not be investigated by ODMR techniques (48). 

Of current importance in the chemistry of cyclophanes is their application as complex ligands for metals. Development of new agents which transfer transition metal moieties to arenes is progressing and the number of 7t-complexes of arenes with main group metals [7] is also increasing. 

Interesting electrical properties are to be expected with the stepwise extension of this TT-system. The preparation of multilayered cyclophanes proved to be laborious [6] nevertheless new synthetic methods in transition metal chemistry of arenes have opened up a promising alternative approach via preparation of multidecker sandwich complexes (structure type D in Fig. 3). First row transition metals like chromium, iron and cobalt [51] form strong coordinative bonds with arenes when their oxidation state is low [48a] whereas second and third row elements like ruthenium, rhodium and iridium are strongly bonded towards arenes in higher oxidation states [48a, 51]. Sandwich complexes of cyclophanes can be divided into two groups ... 

The classic method of preparing bis( j -arene)iron complexes by reacting the arene with FeClj/AlClj is not directly transferable to cyclophanes, because they, even in the presence of traces of HAICI4, isomerize [91]. However, after addition of Me3Al2Cl3 (method g) as a proton scavanger the bisiron complex 107 is formed [79] as an orange solid which is sensitive towards oxidation in solution and in the solid state (Fig. 23). Methyl substituted cyclophane ligands provide stabilization to some extent [92]. 

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