Multi-electron reduction of sulfur and carbon disulfide using binuclear uranium(iii) borohydride complexes† †Electronic supplementary information (ESI) available: Full synthetic and structural characterisation data. CCDC 1480072–1480076. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c7sc00382j
The first use of a dinuclear U III /U III complex in the activation of small molecules is reported. The first use of a dinuclear U III /U III complex in the activation of small molecules is reported. The octadentate Schiff-base pyrrole, anthracene-hinged ‘Pacman’ ligand L A combines two strongly red...
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Published in | Chemical science (Cambridge) Vol. 8; no. 5; pp. 3609 - 3617 |
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Main Authors | , , , , , , |
Format | Journal Article |
Language | English |
Published |
Royal Society of Chemistry
10.03.2017
|
Subjects | |
Online Access | Get full text |
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Summary: | The first use of a dinuclear U
III
/U
III
complex in the activation of small molecules is reported.
The first use of a dinuclear U
III
/U
III
complex in the activation of small molecules is reported. The octadentate Schiff-base pyrrole, anthracene-hinged ‘Pacman’ ligand L
A
combines two strongly reducing U
III
centres and three borohydride ligands in [M(THF)
4
][{U(BH
4
)}
2
(μ-BH
4
)(L
A
)(THF)
2
]
1-M
, (M = Li, Na, K). The two borohydride ligands bound to uranium outside the macrocyclic cleft are readily substituted by aryloxide ligands, resulting in a single, weakly-bound, encapsulated
endo
group 1 metal borohydride bridging the two U
III
centres in [{U(OAr)}
2
(μ-MBH
4
)(L
A
)(THF)
2
]
2-M
(OAr = OC
6
H
2
t
Bu
3
-2,4,6, M = Na, K). X-ray crystallographic analysis shows that, for
2-K
, in addition to the
endo
-BH
4
ligand the potassium counter-cation is also incorporated into the cleft through η
5
-interactions with the pyrrolides instead of extraneous donor solvent. As such,
2-K
has a significantly higher solubility in non-polar solvents and a wider U–U separation compared to the ‘ate’ complex
1
. The cooperative reducing capability of the two U
III
centres now enforced by the large and relatively flexible macrocycle is compared for the two complexes, recognising that the borohydrides can provide additional reducing capability, and that the aryloxide-capped
2-K
is constrained to reactions within the cleft. The reaction between
1-Na
and S
8
affords an insoluble, presumably polymeric paramagnetic complex with bridging uranium sulfides, while that with CS
2
results in oxidation of each U
III
to the notably high U
V
oxidation state, forming the unusual trithiocarbonate (CS
3
)
2–
as a ligand in [{U(CS
3
)}
2
(μ-κ
2
:κ
2
-CS
3
)(L
A
)] (
4
). The reaction between
2-K
and S
8
results in quantitative substitution of the
endo
-KBH
4
by a bridging persulfido (S
2
)
2–
group and oxidation of each U
III
to U
IV
, yielding [{U(OAr)}
2
(μ-κ
2
:κ
2
-S
2
)(L
A
)] (
5
). The reaction of
2-K
with CS
2
affords a thermally unstable adduct which is tentatively assigned as containing a carbon disulfido (CS
2
)
2–
ligand bridging the two U centres (
6a
), but only the mono-bridged sulfido (S)
2–
complex [{U(OAr)}
2
(μ-S)(L
A
)] (
6
) is isolated. The persulfido complex (
5
) can also be synthesised from the mono-bridged sulfido complex (
6
) by the addition of another equivalent of sulfur. |
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ISSN: | 2041-6520 2041-6539 |
DOI: | 10.1039/c7sc00382j |