Heterobimetallic
complexes containing short uranium–group
10 metal bonds have been prepared from monometallic IUIV(OArP-κ2O,P)3 (2) {[ArPO]− = 2-tert-butyl-4-methyl-6-(diphenylphosphino)phenolate}.
The U–M bond in IUIV(μ-OArP-1κ1O,2κ1P)3M0, M = Ni (3–Ni), Pd (3–Pd), and Pt (3–Pt), has been
investigated by experimental and DFT computational methods. Comparisons
of 3–Ni with two further U–Ni complexes
XUIV(μ-OArP-1κ1O,2κ1P)3Ni0, X = Me3SiO (4) and F (5), was also possible via iodide substitution. All complexes were
characterized by variable-temperature NMR spectroscopy, electrochemistry,
and single crystal X-ray diffraction. The U–M bonds are significantly
shorter than any other crystallographically characterized d–f-block
bimetallic, even though the ligand flexes to allow a variable U–M
separation. Excellent agreement is found between the experimental
and computed structures for 3–Ni and 3–Pd. Natural population analysis and natural localized molecular orbital
(NLMO) compositions indicate that U employs both 5f and 6d orbitals
in covalent bonding to a significant extent. Quantum theory of atoms-in-molecules
analysis reveals U–M bond critical point properties typical
of metallic bonding and a larger delocalization index (bond order)
for the less polar U–Ni bond than U–Pd. Electrochemical
studies agree with the computational analyses and the X-ray structural
data for the U–X adducts 3–Ni, 4, and 5. The data show a trend in uranium–metal
bond strength that decreases from 3–Ni down to 3–Pt and suggest that exchanging the iodide for a fluoride
strengthens the metal–metal bond. Despite short U–TM
(transition metal) distances, four other computational approaches
also suggest low U–TM bond orders, reflecting highly transition
metal localized valence NLMOs. These are more so for 3–Pd than 3–Ni, consistent with slightly larger U–TM
bond orders in the latter. Computational studies of the model systems
(PH3)3MU(OH)3I (M = Ni, Pd) reveal
longer and weaker unsupported U–TM bonds vs 3.