Computational Insights into Enhanced Uranium(IV/III/II)–Metal (Ni, Pt, and Pd) Bonding Interactions Aroused by Planar d ¹⁰ of Transition Metals

Analyses of the series RMUL(thf)nCl2-n complexes (where M = group 10 transition metals, R = PPh₃ and L stands for [CH₂O(CH₂)₂NP(iPr)₂]₂²⁻ ligands; n = 0, 1, or 2 denote species 1, 2, or 3, respectively) were carried out with the means of quantum chemical calculations to understand the inherent difference and trends in stability and bonding features. Electronic structure analysis reveals that the oxidation states are M⁰/UIV, M⁰/UIII, and M⁰/UII in species 1, 2, and 3, respectively, which thus exhibits a unique M d¹⁰ configuration with dz2 being the highest occupied molecular orbital. The covalent single bond formed between U and M via the 6dx2-y2-ndx2-y2 interaction shows a slight increase in U-M bond strength from Pd to Ni or Pt within the same formula, being nearly independent of the residence of uranium. Further study on 1-Ni-based model compounds shows that the U-Ni bond strength significantly reduced when Ni was transferred from Ni⁰ 3d¹⁰ to Ni¹⁺ 3d⁹. Thus, the stability of the M-U direct bond corresponds to the planar M d¹⁰ configuration and short length for achieving orbital interaction. This notion explains the experimental findings in RPdUCl₂L and presents fundamental insight for future endeavors for isolable complexes with U-M bonds.