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Metal-Metal Bonding in Uranium-Group 10 Complexes
#MMPMID26942560
Hlina JA
; Pankhurst JR
; Kaltsoyannis N
; Arnold PL
J Am Chem Soc
2016[Mar]; 138
(10
): 3333-45
PMID26942560
show ga
Heterobimetallic complexes containing short uranium-group 10 metal bonds have
been prepared from monometallic IU(IV)(OAr(P)-?(2)O,P)3 (2) {[Ar(P)O](-) =
2-tert-butyl-4-methyl-6-(diphenylphosphino)phenolate}. The U-M bond in
IU(IV)(?-OAr(P)-1?(1)O,2?(1)P)3M(0), 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 XU(IV)(?-OAr(P)-1?(1)O,2?(1)P)3Ni(0), 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.
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