Homoleptic Uranium-Bis(acyl)phosphide Complexes

The first uranium bis(acyl)phosphide (BAP) complexes were synthesized from the reaction between sod i u m bis(mesitoyl)phosphide (Na((mes)BAP)) or sodium bis(2,4,6-triisopropylbenzoyl)phosphide (Na-((tripp)BAP)) and UI3(1,4-dioxane)1.5. Thermally stable, homoleptic BAP complexes were characterized by single-crystal X-ray diffraction and electron paramagnetic resonance (EPR) spectroscopy, when appropriate, for the elucidation of the electronic structure and bonding of these complexes. EPR spectroscopy revealed that the BAP ligands on the uranium center retain a significant amount of electron density. The EPR spectrum of the trivalent U((tripp)BAP)3 has a rhombic signal near g = 2 (g(1) = 2.03; g(2 )= 2.01; and g(3) = 1.98) that is consistent with the EPR-observed unpaired electron being located in a molecula r orbital that appears ligand-derived . However, upon warming the complex to room temperature, no resonance was observed, indicating the presence of uranium character.