Homo arenes

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. 

Another recent development in the field of palladium-catalyzed reactions with alkynes is a novel multicomponent approach devised by the Lee group. Starting from a-bromovinyl arenes and propargyl bromides, the assembly ofeight-membered car-bocycles can be realized via a cross-coupling/[4+4] cycloaddition reaction. The authors also presented the combination of a cross-coupling and homo [4+2], hetero [4+2], hetero [4+4] or [4+4+1] annulation leading to various cyclic products [147]. 

Very recently, Ishirihara et al. [237] reported the application of a chiral iodine atom throngh the reaction of NSI and a chiral nucleophilic phosphoramidite for the halocyclization of homo(polyprenyl)arenes. 

The preference for bridging at the meso positions is dictated by HOMO-LUMO coefficients in the exciplex. At high arene concentrations, the stereochemical preference is diminished. In general, however, the local symmetry of the frontier orbitals determines implicitly the favorable pathway for cycloadditions involving significant charge transfer but without the intervention of radical ions (55). 

Superacid-catalysed intramolecular reactions of some dicationic electrophiles have been investigated.36 The positively charged centres migrate apart and this chemistry gives a new synthetic route to aza-polycyclic compounds. The polycyclic compound (26) can, for example, be formed from reaction of 2-phenyl-3-(l-hydroxy-2-phenyl-ethyl)quinoline (25) with CF3SO3H at 25 °C, loss of water and benzene being involved. Highly diastereoselective polycyclization of homo(polyprenyl)arenes [e.g. (27)... 

The 1,2 and 3,4 regioselectivity of the ortho addition of an alkene to an arene substituted with a strong donor substituent is, according to Houk, dominated by interaction of the benzene S orbital with the alkene -tt HOMO, because the A -tt interaction would result in a 2,3 ortho adduct. For an arene substituted with a strong donor, the donor substituent, rather than the approaching alkene, will determine the symmetry of the orbitals [188],... 

The metal-bound carbon atom in organopalladium(II) complexes can formally react either as an electrophile or as a nucleophile. Treatment of arylpalladium(II) complexes with alkyl halides, for example, yields products of homo- or cross-coupling, possibly via intermediate formation of hexacoordinated Pd(IV) complexes [31,33] (Scheme8.1). Treatment of the same type of complex with alkyl Grignard reagents or other carbon nucleophiles, on the other hand, also yields the corresponding alkyl arenes via nucleophilic displacement of a ligand followed by reductive elimination (Scheme 8.1). 

Partial quantum yields3 of Nd111 and quantum yields of Yb111 luminescence upon ligand excitation (300 nm) in homo-and hetero-bimetallic complexes with p>-fert-butylcalix[8]arene in dmf, at room temperature (Korovin et al., 2000)... 

Homo- and heterobimetallic complexes of the lanthanides are routinely observed with the large calix[8]arene [191]. However, this extended highly functionalized cavity can also accommodate just one lanthanide ion as shown in [Eu(H6L)(N03XDMF)4] 3DMF (H8L = p-tert-butylcalix[8]arene, Table 13) [192]. Only two adjacent phenolic OH groups were deprotonated according to... 

Figure 5.5 Survey of the symmetry properties for selected types of homo- and heterodimers of tetra-urea calix[4]arenes, represented by squares with the phenolic units (A, B) on the corners. Symmetry elements and symmetry classes (with and without directionality of the hydrogen bonds, shown by arrows) are indicated.

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