Synthesis, Lanthanide Coordination Chemistry, and Liquid–Liquid Extraction Performance of CMPO-Decorated Pyridine and Pyridine N-Oxide Platforms

Abstract

Syntheses for a set of new ligands containing one or two carbamoylmethylphosphine oxide (CMPO) fragments appended to pyridine and pyridine N-oxide platforms are described. Molecular mechanics analyses for gas phase lanthanide-ligand interactions for the pyridine N-oxides indicate that the trifunctional NOPOCO molecules, 2-{[Ph2P(O)][C(O)NEt2]C(H)}C5H4NO (7) and 2-{[Ph2P(O)][C(O)NEt2]CHCH2}C5H4NO (8), and pentafunctional NOPOP'O'COC'O' molecules, 2,6-{[Ph2P(O)][C(O)NEt2]C(H)}2C5H3NO (9) and 2,6-{[Ph2P(O)][C(O)NEt2]CHCH2}2C5H3NO (10), should be able to adopt, with minimal strain, tridentate and pentadentate chelate structures, respectively. As a test of these predictions, selected lanthanide coordination chemistry of the N-oxide derivatives was explored. Crystal structure analyses reveal the formation of a tridentate NOPOCO chelate structure for a 1:1 Pr(III) complex containing 7 while 8 adopts a mixed bidentate/bridging monodentate POCO/NO binding mode with Pr(III). Tridentate and tetradentate chelate structures are obtained for several 1:1 complexes of 9 while a pentadentate chelate structure is observed with 10. Emission spectroscopy for one complex, [Eu(9)(NO3)3], in methanol, shows that the Eu(III) ion resides in a low-symmetry site. Lifetime measurements for methanol and deuterated methanol solutions indicate the presence of four methanol molecules in the inner coordination sphere of the metal ion, in addition to the ligand, with the nitrate anions most likely dissociated. The solvent extraction performance of 7-10 in 1,2-dichloroethane for Eu(III) and Am(III) in nitric acid solutions was analyzed and compared with the performance of 2,6-bis(di-n-octylphosphinoylmethyl)pyridine N-oxide (TONOPOP'O') and n-octyl(phenyl)-N,N-diisobutylcarbamoylmethylphosphine oxide (OPhDiBCMPO) measured under identical conditions.

Synthesis and selected lanthanide coordination chemistry of new ((1H-pyrazol-1-yl)methyl)pyridine and -pyridine 1-oxide ligands

“…Subsequent formation of the complex [Eu(4) 3+ ] with a tridentate coordination mode occurs with (G) = 4.78 kcal/mole or 1.59 kcal/mol/donor group. Although the ligand reorganization energy is significantly higher for 4 compared to 2, it is still lower than the value computed for the NOPOPO ligand, I (R = Ph), 8.8 kcal/mol or 2.93 kcal/mol/donor group[45], and it is well known that ligands of type I readily form strong lanthanide complexes utilizing the tridentate binding mode[22][23][24][45][46][47][48][49]. Interestingly, addition of the N-oxide group back into the ligand framework and subsequent formation of the tridentate chelate structure [ Eu(5) 3+ ], as shown inFigure 7b, leads to a decrease in strain free energy, (G) = 3.78 kcal/mol or 1.26 kcal/mol/donor.…”

“…The resulting calculated relative strain free energies (G) per donor group were then compared with data for similar ligand types. The method has been used in the evaluation of a number of other ligand systems[43] including studies of several related NOPO and NOPOPO ligands[22][23][24][44][45][46][47][48]. The energy minimized free ligand conformers for 2, 4 and 5 are shown in Figures 5a, 6a and 7a, respectively.…”

Synthesis and lanthanide coordination chemistry of CMPO-decorated dibenzothiophene and dibenzothiophene sulfone platforms

“…Americium and europium distribution ratios were calculated as the ratio of the volumetric count rates of the 241 Am and 152/154 Eu isotopes in each phase at equilibrium. Hz (meso) [41].…”

“…Since carbamoylmethyl phosphine oxides, CMPOs, G, are also known to be effective ligands and extractants for f-element ions [38,39], several approaches for the assembly of multiple CMPO fragments on a single platform have been explored and that work has been reviewed [ 27,40]. In this regard, Fand G-ligand types have recently been combined through C-atom attachment to provide examples of potential pentadenate chelators, H and I [41]. A family of N-attached ligands has also been reported [42].…”

Synthesis, Structural Characterisation and Solution Behaviour of High‐Symmetry Lanthanide Triflate Complexes with the Sterically Demanding Phosphine Oxides Cy3PO and tBu3PO

“…Lanthanide complexes of phosphine oxides, R 3 PO, continue to attract interest due to their various potential applications. The chemically robust nature of phosphine oxides and the availability of synthetic routes to fine‐tune the nature of the R groups has allowed development of extractants suitable for reprocessing nuclear fuels , . Judicious selection of R groups can also enhance the light‐harvesting properties of complexes and facilitate ligand‐to‐metal energy transfer in potential photoluminescent devices , .…”