6533b7d4fe1ef96bd1261f86

RESEARCH PRODUCT

Rigidified Calixarenes Bearing Four Carbamoylmethylphosphineoxide or Carbamoylmethylphosphoryl Functions at the Wide Rim

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Conformationally rigidified tetraCMPO derivatives have been prepared from calix[4]arene bis(crown ether) 4 a in which adjacent oxygens are bridged at the narrow rim by two diethylene glycol links. Acylation of the tetraamine 4 c with the CMPO-active ester 5 b gave the tetraphosphine oxide 6 a, while the tetraphosphinate 6 b and the tetraphosphonate 6 c were obtained by Arbuzov reaction of tetrabromoacetamido derivative 7 with PhP(OEt)2 or P(OEt)3. The extraction ability of these CMPO derivatives was checked for selected lanthanides and actinides and compared with the analogous compounds 1 b, 10 b and 10 d derived from calix[4]arene tetrapentyl ether. All rigidified bis(crown ether) ligands are more effective extractants than their pentyl ether counterparts and require only 1/10 of the concentration (cL=10−4 M) to obtain the same distribution coefficients, while with CMPO itself a 2000-fold concentration is necessary. This could be a consequence of a better preorganisation of the ligating functions owing to the rigidity which on the other hand did not change the observed selectivity for americium (DAm/DEu=9–19) and for light lanthanides over heavy ones. NMR relaxivity titration curves show that the complex of Gd3+ with ligand 6 a is highly oligomerised in anhydrous acetonitrile over a large range of ligand:metal concentration ratios. Nuclear magnetic relaxation dispersion (NMRD) profiles also showed that large oligomers were formed, and their mean tumbling times were deduced from the Solomon-Bloembergen-Morgan equations. The NMR spectra of dia- and paramagnetic lanthanide complexes with 6 a agreed with the presence of two conformers with an elongated calix[4]arene skeleton in which the distances between opposite methylene groups are different. Contrary to what was observed with ligand 2 a, the addition of nitrate ions does not labilize the metal complexes, presumably because of the rigidification effect of the ether bridges. Single-crystal X-ray structures were obtained for the active ester 5 b and for diphenylphosphorylacetic acid 5 a.