Arene site exchange

Stratakis, M., Rabalakos, C., Mpourmpakis, G. and Froudakis, G.E. (2003). Ene hydroperoxidation of isobutenylarenes within dye-exchanged zeolite Na-Y control of site selectivity by cation-arene interactions. J. Org. Chem. 68, 2839-2843... 

A tentative structure for 44, incorporating one chemical defect and possessing exchange coupling of a symmetric spin trimer, was proposed.105 It was speculated that the annelation of calix[4]arene-based macrocycles leads to substantial strain, especially in the center macrocycle.105 Such strain could have two consequences (1) increased basicity of the arylmethyl carbanion sites, which would facilitate deuterium abstraction from the deuterated solvent, and (2) increased out-of-plane twisting of the 7r-system, which would weaken the exchange coupling.105... 

Cp LuCHj is in equilibrium with its dimer in solution. The monomer and one site in the dimer must therefore possess room for coordination of another molecule— they are sterically unsaturated . Cp LuCHj and CpJLuH effect metallation (p. 40) viz. C—H bond activation (p. 224) for weakly acidic hydrocarbons such as alkynes or arenes. Like RLi(TMEDA) these complexes possess sites of high Lewis acidity and basicity in the same molecule. The lutetium centre appears to be even more fiercely electrophilic and can interact even with methane. The exchange... 

The treatment of 6 with CH30Na in methanol selectively affords a neutral pentahydrido cluster 7 (Equation (2)), which undergoes an intermolecular H/D exchange with C6De as the result of arene C-H bond activation via an 7 -arene intermediate. The two kinds of hydrido ligands, /it-H and /it3-H, mutually exchange coordination sites in solution. Pentahydrido cluster 7 displays remarkable activity in reactions with non-activated hydrocarbons such as alkanes. 

In addition, there are several investigations on proton exchange polymers, whose phosphonic acid sites are linked to aromatic ring directly or by means of alkylene spacers. These polymers can be prepared by polycondensation of phosphonic acid functionalized monomers or phosphorylation of existing aromatic condensation polymers. There are several methods reported for the preparation of arene phosphonates from aryl bromides [38-40]. The classical Arbuzow reaction [41,42] is commoifly used, in which triethylphos-phite and nickel dichloride are employed as catalysts. The reaction often requires harsh conditions (160 °C) and suffers from low yields. Alternative paUadiiun-catalyzed reaction [43-45] useful for phosphonation proceeds more smoothly. 

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