Cyclophane complex

The reaction of (cyclobutadiene)metal complexes with X2 results in the oxidative decomplexation to generate either dihalocyclobutenes or tetrahalocyclobutanes. In comparison, substitution of (cyclobutadiene)MLn complexes 223 [MLn = Fe(CO)3, CoCp, and RhCp] with a variety of carbon electrophiles has been observed (equation 34)15. Electrophilic acylation of 1-substituted (cyclobutadiene)Fe(CO)3 complexes gives a mixture of regioisomers predominating in the 1,3-disubstituted product and this has been utilized for the preparation of a cyclobutadiene cyclophane complex 272 (equation 35)246. For (cyclobutadiene)CoCp complexes, in which all of the ring carbons are substituted, electrophilic acylation occurs at the cyclopentadienyl ligand. 

Figure 6. Evidence for the cation-7t. effect in cyclophane complexes (all complexation free energies AG [kJ/mol], in water).

Cyclic Voltammetry and Reduction of Double-Layered Cyclophane Complexes... 

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... 

Fig. 16A-D. Mechanical switching in rotaxanes. A Rotaxanes may exist in isomeric states by the movement of the ring component between dissymmetric sites on the string component. B A redox- or pH-switchable [2]rotaxane. While the cyclophane complexes the native benzidine site (spectrum, curve a), the reduced or protonated benzidine repels the cyclophane, causing it to move to the dioxybiphenylene site (spectrum, curve b). C An azobenzene-based switchable [2]rotaxane. The cyclodextrin ring complexes the azobenzene site in the trans-state, but it is repelled from the ds-azobenzene. The state of the system is measurable by circular dichroism (plot). D A pH-switchable rotaxane. When the amine on the string component is protonated, it complexes the crown ether ring by hydrogen-bonding interactions (40a). When the amine is deprotonated, however, the ring component moves to the bipyridinium unit, where it is complexed by n donor-acceptor interactions (40b). The plots in B and C are adapted from [67] and [69], respectively, with permission...

Atwood [46] obtained the first jy -coordinated transition metal cyclophane complex (41a), reacting 41 with Cr(CO)3(CH3CN)3 in dioxane (Fig 8c). The different complexation behaviour of 40 and 41 reveals, that in case of complexation with the Cr(CO)3-group steric effects are more important than electronic reasons [45]. The Tos-group is placed above the benzene ring to which it is attached and shields it from complexation (Fig 8b) [45]. 

F. 13. Synthesis of cyclophane complexes containing heteroatoms in the bridges with rj -coordinated chromium metal [20,58], Reaction 59 has not been carried out. 

Fig. 31a. Reaction path to a new class of superphanes containing cobalt stabilized orrti-aromatic n-decks and b. 135 as a useful intermediate for the preparation of various cyclophane complexes [112-114]...

A number of interesting compounds is available, when the coordinated metal atom of cyclophane complexes bearing a fi-aromatic tr-decks is removed, because of the resulting cyclophane is instable and subjected to valence isomerism [161]. 

Fig. 2 Ciystal structures of cyclophane complexes 2b.4 (acetic acid) 2H2O (A) and 2b.2 (propionic acid) (B).

This in itself is evidence for a more specific type of interaction in cases where arenes can approach the uncomplexed face of the (arene)Cr(CO)3 complex. Furthermore, direct evidence for face-to-face interactions between free and complexed arenes is available from studies of cyclophane complexes, as in the solid state, the separation between the arene rings of cyclophanes has been shown by X-ray crystallography to decrease when one of the rings is complexed to Cr(CO)3 [54]. 

There are other synthetic methods that are restricted to particular cases such as the catalyzed trimerization of alkynes and the historical reaction of PhMgBr with CrC leading to [Crfri -CeH Xti -diphenyl)]. A useful method is the reaction of arenes with [Rufri -CeH Xacetonels] pioneered by Bennett which allows to make Ru sandwich complexes containing two different arenes. This method has allowed Boekelheide to synthesize cyclophane complexes. 

Also, Fiirstner et al. demonstrated that oxidative addition of C2-C1 imidazolium ions to Pd(PPti3)4] generated mixed phosphine-NHC complexes. Baker described the interesting C-C oxidative addition reaction of diimida-zolium ion 8 to [Pd(PPh3)4] yielding the bis-NHC cyclophane complex 9 (Equation (3.2)). ... 

Guan and coworkers have extended the study of hindered diimine catalysts even further with cyclophane complex 69 (Camacho et al, 2004). Upon activation with MMAO, 69 is highly active for production of branched PEs (66-97 branches/1000 carbons) with relatively narrow polydispersities (M M as low as 1.23 at 50 °C). Most significantly, these catalysts exhibit impressive thermal stability, with good activities even up to 90 °C. However, the polydispersity increases, and the activities decrease somewhat at higher temperatures. Interestingly, a related alkyl cyclophane Ni complex demonstrated almost no activity for ethylene polymerization (Camacho et al., 2005). 

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