Synthesis and Characterisation of Uranium(IV) Complexes with Tridentate NNS Ligands

Hybrid ligands combining hard and soft donor groups can potentially enable new reactivity patterns for low valent uranium complexes. We therefore investigated the coordination chemistry of the NNS pincer ligands N-[2-(ethylthio)ethyl]-2-pyridinemethaneamine (PyNHSEt) and N-[2-(phenylthio)ethyl]-2-pyridinemethaneamine (PyNHSPh) with uranium(IV). Analogous complexes were obtained for both ligands, with two equivalents of the ligand coordinating to uranium via the pyridine and amine nitrogen atoms. The complexes were characterised by NMR, IR and UV-Vis-NIR spectroscopies, DOSY NMR and in the case of [UCl4(PyNHSPh)2] single crystal x-ray diffraction. The deprotonation of the neutral pro-ligand was not successful and deprotonation of the coordinated ligand led to decomposition of the complex and protonation of the amine in the ligand.