Synthesis and f-element ligation properties of NCMPO-decorated pyridine N-oxide platforms

Abstract

Stepwise syntheses of 2-{[2-(diphenylphosphoryl)acetamido]methyl}pyridine 1-oxide, 2-[Ph₂P(O)CH₂C(O)N(H)CH₂]C₅H₄NO (6), 2-{[2-(diphenylphosphoryl)acetamido]methyl}-6-[(diphenylphosphoryl)methyl]pyridine 1-oxide, 2-[Ph₂P(O)CH₂C(O)N(H)CH₂]-6-[Ph₂P(O)CH₂]C₅H₃NO (7) and 2,6-bis{[2-(diphenylphosphoryl)acetamido]methyl}pyridine 1-oxide, 2,6-[Ph₂P(O)CH₂C(O)N(H)CH₂]₂C₅H₃NO (8), are reported along with spectroscopic characterization data and single crystal X-ray diffraction structure determination for 6·2H₂O, 7 and 2,6-[Ph₂P(O)CH₂C(O)N(H)CH₂]₂C₅H₃N·MeOH 18·MeOH, the pyridine precursor of 8. Molecular mechanics computations indicate that 6, 7 and 8 should experience minimal steric hindrance to donor group reorganization that would permit tridentate, tetradentate and pentadentate docking structures for the respective ligands on lanthanide cations. However, crystal structure determination for the lanthanide complexes, {[Yb(6)(NO₃)₃]·(MeOH)}_n, {[Lu(6)(NO₃)₃]·(MeOH)}_n, [Er(6)₂(H₂O)₂](NO₃)₃·(H₂O)₄}_n, {[La(13)(NO₃)₃(MeOH)]·(MeOH)}_n, {[Eu(7)(NO₃)₂(EtOAc)_0.5(H₂O)_0.5](NO₃)}₂·MeOH and [Dy₃(7)₄(NO₃)₄(H₂O)₂](NO₃)₅·(MeOH)₅·(H₂O)₂ reveal solid-state structures with mixed chelating/bridging ligand : Ln(III) interactions that employ lower than the maximal denticity. The binding of 6 and 7 with Eu(III) in the solid state and in MeOH solutions is also accessed by emission spectroscopy. The acid dependence for solvent extractions with 6 and 7 in 1,2-dichloroethane for Eu(III) and Am(III) in nitric acid solutions is described and compared with the behavior of n-octyl(phenyl)-N,N-diisobutylcarbamoylmethylphosphine oxide (OPhDiBCMPO, 1b) and 2-[(diphenyl)phosphinoylmethyl]pyridine N-oxide (DPhNOPO, 4a).