The threading of a double-calixarene system (4) with dialkylammonium axles (2 and 3) has been investigated in the presence of the ‘superweak’ tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (TFPB) anion. NMR and ESI(þ)-mass spectrometry analyses showed that singly and doubly threaded pseudorotaxanes can be stepwise formed under appropriate conditions. The directional threading of an alkylbenzylammonium axle with double-calixarene 4 occurs with an endoalkyl preference in accordance with the ‘endo-alkyl rule’. DFT calculations confirmed this preference and evidenced that the pseudorotaxane complexes are characterised by an anti-conformation around the OcalixZCHbridge 2 bonds, which led to a spatial divergence of the two calix-cavities
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