CS2 activation at uranium(iii) siloxide ate complexes: The effect of a Lewis acidic site

Article abstract of DOI:10.1039/c4dt02585g

Multimetallic cooperative binding of heteroallenes provides an attractive route to their activation, but the reduction of CS₂ at heterobimetallic sites, associating an electron-rich metal with a main group Lewis acid has not been explored. Here we show that the presence of a heterometallic U, K site plays an important role in the CS₂ reduction by uranium(iii) complexes of the electron-rich and the sterically demanding tris(tert-butoxy)siloxide ligand. Specifically, the ion-pair complex [K(18c6)][U(OSi(O^tBu)₃)₄], 1, leads preferentially to the reductive disproportionation of CS₂ to K₂CS₃ and CS. The crystal structure of the thiocarbonate intermediate complex [U(OSi(O^tBu)₃)₄ (μ_3-κ²:κ²:κ^2-CS₃)K₂(18c6)₂], 3, isolated from the toluene reaction mixture has been determined. In contrast, the heterobimetallic complex [U(OSi(O^tBu)₃)₄K], 2, promotes preferentially the reductive dimerization of CS₂ to K₂C₂S₄ and K₂C₃S₅. The [K₂C₂S₄(DMSO)₃]_n, 5, and [U(OSi(O^tBu)₃)₄K₂(C₃S₅)]_n, 6, polymeric compounds were isolated from this reaction and structurally characterized.

Full text of DOI:10.1039/c4dt02585g

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CS2 activation at uranium(III) siloxide ate
complexes: the effect of a Lewis acidic site†
Cite this: Dalton Trans., 2015, 44,
2650
Clément Camp,a,b Oliver Cooper,a,b Julie Andrez,a,b Jacques Pécauta,b and
Marinella Mazzanti*c
Multimetallic cooperative binding of heteroallenes provides an attractive route to their activation, but the
reduction of CS2 at heterobimetallic sites, associating an electron-rich metal with a main group Lewis
acid has not been explored. Here we show that the presence of a heterometallic U, K site plays an impor-
tant role in the CS2 reduction by uranium(III) complexes of the electron-rich and the sterically demanding
tris(tert-butoxy)siloxide ligand. Specifically, the ion-pair complex [K(18c6)][U(OSi(OtBu)3)4], 1, leads prefer-
entially to the reductive disproportionation of CS2 to K2CS3 and CS. The crystal structure of the thiocarbo-
nate intermediate complex [U(OSi(OtBu)3)4 (μ3−κ2:κ2:κ2−CS3)K2(18c6)2], 3, isolated from the toluene
reaction mixture has been determined. In contrast, the heterobimetallic complex [U(OSi(OtBu)3)4K], 2,
promotes preferentially the reductive dimerization of CS2 to K2C2S4 and K2C3S5. The [K2C2S4(DMSO)3]n, 5,
and [U(OSi(OtBu)3)4K2(C3S5)]n, 6, polymeric compounds were isolated from this reaction and structurally
characterized.
Received 26th August 2014,
Accepted 10th November 2014
DOI: 10.1039/c4dt02585g
www.rsc.org/dalton
reductive disproportionation of CS2 affording two different
Introduction
2−
products (80% C2S4 and 20% CS32−)7b. In contrast the reac-
The metal-mediated activation of heteroallenes (CO2, CS2) is tion of the U(III) complex [(RC5H4)3U] (R = Me; SiMe3) with CS2
an area of growing interest due to the potential use of CO2 as a was found to afford the U(IV)–U(IV) dimer [(RC5H4)3U]2-
low cost renewable C1 source.1 Due to the higher reactivity of [µ-κ1:κ2-CS2].7a
CS2 compared to the thermodynamically stable CO2 molecule,
We have recently reported an analogous behaviour for the
the chemistry of d-block transition metals with CS2 has attracted dinuclear homoleptic siloxide complex [U(OSi(OtBu)3)2(µ-OSi-
a significant number of studies as a pertinent model for CO2 (OtBu)3)]2 (Scheme 1), which also reduces CS2 yielding a
2−
reactivity.2 Depending on the nature of the metal ion and the uranium(IV) dimer that features a reduced CS2
bridging
ancillary ligand, metal complexes have been shown to promote group.7d Bulky siloxide ligands such as tris(tert-butoxy)siloxide
CS2 disproportionation to CS3 and CS,3 reductive dimerization have proven to be attractive ancillary ligands in the chemistry
2−
to afford tetrathioxalate4 or CS2 reduction to sulphido complexes5 of trivalent uranium7d,8,9 and in particular in the controlled
with CS or thiocarbonate complexes as by-products.
reduction of heteroallenes.7d,10 Notably, the electronic pro-
A few examples of insertion6 and reduction reactions of perties and steric demand of the uranium center can be tuned
CS2 promoted by f element complexes have been reported by changing the number of the siloxides and their denticity.9a
so far.5b,7
Notably reduction of CS2 has been observed only for three
U(III) systems.7a–d An unusual behaviour was reported for the
reduction of CS2 by the U(III) complex [((AdArO)3N)U(DME)]
which promotes both the reductive dimerization and the
aUniv. Grenoble Alpes, INAC-SCIB, RICC, F-38000 Grenoble, France
bCEA, INAC-SCIB, F-38000 Grenoble, France
cInstitut des Sciences et Ingénierie Chimique, Ecole Polytechnique Fédérale de
Lausanne (EPFL), CH-1015 Lausanne, Switzerland.
E-mail: marinella.mazzanti@epfl.ch
†Electronic supplementary information (ESI) available: 1H and 13C NMR spectra,
and crystallographic data. CCDC 1012567–1012569. For ESI and crystallographic
Scheme 1 Reaction of [UIII(OSi(OtBu)3)2(µ-OSi(OtBu)3)]2 with CO2
data in CIF or other electronic format see DOI: 10.1039/c4dt02585g
and CS2.
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Moreover, tris(tert-butoxy)siloxides due to their multiple
Results and discussion
binding modes provide a route to heterobimetallic U, K com-
plexes.10 In particular we have recently shown that the neutral The reaction of the bulky and electron-rich tetrasiloxide
homodimetallic
complex
[U(OSi(OtBu)3)2(µ-OSi(OtBu)3)]2 complex [K(18c6)][U(OSi(OtBu)3)4], 1, with CS2 (Scheme 3)
(Scheme 1),7d the “ate” complex [K(18c6)][U(OSi(OtBu)3)4], 1, leads to the reductive cleavage of CS2 affording trithiocarbo-
and the heterodimetallic U, K complex [U(OSi(OtBu)3)4K], 2 nate as the major product. The tetrathioxalate is also formed
(Scheme 2) reduce CO2 leading to different reaction products. as a by-product of this reaction. [K(18c6)]2C2S4 can be isolated
2−
Particularly remarkable is the observed effect of the presence from the reaction mixture after 30 minutes, but all C2S4 is
of the potassium site on the reactivity of 2 which highlights transformed into the C3S5 dianion (dmit2− = 1,3-dithiole-
2−
the multimetallic cooperativity taking place in the reduction 2-thione-4,5-dithiolate) after 48 hours.
of CO2 by such heterodimetallic complex.10 Cooperative
The 1H NMR and 13C NMR spectra of the toluene crude
binding of heteroallenes at polymetallic complexes provides mixture from the reaction of 1 with one to four equivalents of
an attractive route for promoting their activation and 13CS2 for two days shows the presence of the U(IV) complex
reduction.3b,4b,11,12
[U(OSi(OtBu)3)4] as the major product (65%). The 13C NMR
However, while the seminal work by Bianchini and co- spectra in deuterated pyridine or in DMSO of this reaction
workers indicated that the presence of Lewis acid is important mixture after toluene evaporation reveal the presence of free
to achieve CS2 dimerization,13 the effect of cooperative binding 13CS32− as the major species (resonance at +267.7 ppm14). This
of CS2 at heterobimetallic sites, associating an electron-rich suggests that the thiocarbonate is released from uranium(IV)
metal with a main group Lewis acid has not been explored.
intermediates in the presence of coordinating solvents. The
In view of the multimetallic cooperative effect observed in formation of 13CS3 indicates that complex 1 promotes the
CO2 reduction for the U, K complex [U(OSi(OtBu)3)4K], 2 we disproportionation of 13CS2 to 13CS32− and 13CS, but the high reac-
have now explored its reactivity with CS2 and compared it with tivity of CS15 prevents its direct characterization. The 13C NMR
that of the “ate” complex 1. Here we show that complex 1 spectrum of the reaction mixture shows also resonances at
2−
favors the reductive disproportionation pathway compared to roughly +146 and +203 ppm assigned to the 13C3S5
2−
the reductive dimerization yielding trithiocarbonate as the dianion.16 The presence of dmit2− is probably the result of the
major product, while for the heterodimetallic complex 2 the reaction of the dimerization product 13C2S4 with CS. The
2−
dimerization of CS2 is the favored pathway affording the tetra- reaction of 13C2S4 with excess 13CS2 could also contribute to
2−
2−
2−
2−
thioxalate as the major product. We were able to isolate inter- the formation of the 13C3S5 dianion.16,17
A
13CS3
:
13C3S5
mediates presenting the CS2 reaction products coordinated to ratio of 10 : 1 was determined by quantitative carbon NMR
the resulting uranium(IV) centres but these products quickly spectroscopy. The 13CS3
:
13C3S5
ratio is independent of
2
2−
dissociate, laying the basis for kinetically accessible exchange complex concentration, but varies with the number of equiva-
of substrates and products required in catalytic processes.
lents of 13CS2 added. Thus, complex 1 promotes both the
2−
reductive disproportionation of CS2 to CS3 and CS and the
2−
reductive coupling of CS2 to C2S4 with the reductive dispro-
portionation being the favoured pathway.
When the reaction of 1 with one equivalent of CS2 in
toluene is followed over time by 1H NMR spectroscopy (see
ESI†) it is evident that several uranium(IV) intermediate
species, in addition to the [U(OSi(OtBu)3)4] complex, are
present in solution after 2 hours. After 48 hours only the
Scheme 2 Reaction of [K(18c6)][U(OSi(OtBu)3)4], 1 (top) and of [U(OSi-
(OtBu)3)4K], 2 (bottom) with CO2.
Scheme 3 Reaction of [K(18c6)][U(OSi(OtBu)3)4] 1 with CS2.
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signals assigned to the [U(OSi(OtBu)3)4] complex are present in
1
the H NMR spectrum. The presence of multiple reaction pro-
ducts and the labile coordination of the reduction products to
the uranium center (observed during the reactions work up)
renders the isolation of uranium complexes containing CS2
reduction products very difficult.
Thus, in order to isolate intermediate reaction species we
worked up the reaction mixture shortly after reacting 1
with CS2. Evaporation of the reaction mixture after reacting 1
with CS2 for 30 minutes in toluene and extraction of the
residue with hexane allows the separation of the hexane
soluble species from an insoluble residue. The 13C NMR spec-
trum of this residue in deuterated pyridine before recrystalliza-
tion shows only the presence of one peak assigned to
[K(18c6)]213C2S4. The presence of the tetrathioxalate was con-
firmed by recrystallization from pyridine/hexane which pro-
duced dark-green crystals of {[K(18c6)]2C2S4}·Py, 4·Py, suitable
for X-ray diffraction studies. (The 13C NMR spectrum of the
isolated crystals is shown in Fig. S3.†)
Fig. 2 Ellipsoid plot for [U(OSi(OtBu)3)4 (μ3−κ2:κ2:κ2CS3)K2(18c6)2]
crystallized from toluene; probability 50%. Hydrogen atoms, methyl
groups and solvent molecules are omitted for clarity.
3
In spite of the fact that the major component of the hexane
extract even after 30 minutes is [U(OSi(OtBu)3)4], recrystalliza-
tion from toluene at −40 °C of the hexane extract afforded few
yellow crystals of the tetravalent uranium trithiocarbonate siloxide ligands. The trithiocarbonate unit bridges in a μ3-κ2:κ2:κ2
species [U(OSi(OtBu)3)4(μ3-κ2:κ2:κ2-CS3)K2(18c6)2], 3.
fashion the uranium and two [K(18c6)]+ cations. Overall, the
The 13C NMR spectrum of the hexane extract (after solvent metrical parameters for 3 and its neutral charge are in agreement
evaporation) in deuterated DMSO shows the presence of with a tetravalent oxidation state for uranium. Notably, the
[K(18c6)]213CS3 confirming that the latter is released from average U–O bond distance (2.199(14) Å) falls in the range of
complex 3 in DMSO.
The crystal structure of {[K(18c6)]2C2S4}·Py, 4·Py is presented lengths are comparable (1.727(8), 1.709(9) and 1.706(8) Å), and
those typically found for U(IV) siloxy systems.7d,9a,b The C–S bond
2−
2−
in Fig. 1. The C2S4 unit lies on a crystallographically imposed are in agreement with an electronic delocalisation over the CS3
centre of symmetry and is coordinated to two [K(18c6)]+ unit. These values are also similar to those found in other trithio-
cations in a bridging κ3:κ3 mode which, to our knowledge, has carbonate complexes.3a,b,7b Unfortunately, attempts to isolate
2−
not been reported before for this ligand. The C2S4 moiety cleanly compound 3 failed in preventing further characterization.
adopts a non-planar structure, with a torsion S2–C1S–C1SA–
Complex 3 is only the second example of an f-element
S2A angle of 83.8(3)°. A similar feature is found in the related complex containing a coordinated trithiocarbonate ligand. In
[PPh4]2[C2S4]18 and [NEt4]2[C2S4]19 structures. The central C–C complex 3, the thiocarbonate adopts a very different binding
bond length and the C–S bond distances (C1S–C1SA 1.511(6) mode from that found in the crystal structure of the previously
Å, S1–C1S 1.670(3) Å and S2–C1S 1.679(3) Å) are also in agree- reported diuranium(IV) complex of a tripodal tris-aryloxide
ment with the presence of a dianionic tetrathioxalate.18
ligand, where the trithiocarbonate bridges the two U(IV) ions in
The structure of 3, set out in Fig. 2, shows the presence of a a μ-κ2:κ2 mode.7b The terminal binding of the trithiocarbonate
uranium(IV) six-coordinated by the two S atoms of a trithio- to the U(IV) ion in complex 3 is probably the result of the sterical
carbonate unit and the four oxygen atoms of four terminal demand of the four siloxide ligands combined in the presence
of potassium counterions stabilizing the mononuclear complex.
The reactivity of the “ate” tetrasiloxide complex [K(18c6)]-
[U(OSi(OtBu)3)4], 1 with CS2 differs from the one reported for
the less bulky, neutral analogue [U(OSi(OtBu)3)2(µ-OSi-
(OtBu)3)]2 where a CS2 bridged diuranium(IV) complex was
2−
obtained as a sole product. This shows the versatility of sil-
oxide ligands in tuning the reactivity of U(III) complexes with
heteroallenes and the important effect of sterical demand and
charge on the outcome of the reaction.
In view of the presence of the K(18c6)+ cation binding the
uranium-bound trithiocarbonate in complex 3 and of its
potential role in stabilizing the thiocarbonate complex, we
Fig. 1 Ellipsoid plot for {[K(18c6)]2C2S4} crystallized from pyridine;
decided to investigate the reactivity of the heterometallic U, K
complex 2 with CS2 (Scheme 4).
probability 50%. Hydrogen atoms and solvent molecules are omitted for
clarity.
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Scheme 4 Reaction of [U(OSi(OtBu)3)4K], 2 with CS2.
Fig. 3 Ellipsoid plot of the coordination environment of the uranium
center in the [U(OSi(OtBu)3)4K2(C3S5)]n, 6 polymer crystallized from
hexane; probability 50%. Hydrogen atoms, methyl groups and solvent
molecules are omitted for clarity.
The 1H NMR spectrum immediately after the addition of
1 equivalent of 13CS2 to a toluene solution of 2 reveals the for-
mation of a new paramagnetic species and [U(OSi(OtBu)3)4].
Following the reaction over time shows a decreasing amount
in the new paramagnetic species and after 48 hours the only
product observed in solution is [U(OSi(OtBu)3)4]. The 13C NMR
spectrum of the reaction mixture (reacted for 30 minutes or
48 hours) measured in deuterated DMSO after the removal of
sented in Fig. 3, the uranium center is hexacoordinated by the
four oxygens of the siloxide ligands and the two sulfur atoms
2−
of the C3S5 ligand. Two potassium cations are bound in the
pockets formed by five oxygen atoms from the siloxide ligands.
The thione sulfur of the C3S52− ligand binds one of the potass-
ium cations of the adjacent complex yielding a 1-D chain. The
structure of 4 shows that the coordination environment pro-
vided by the siloxide ligands can adapt allowing the coordi-
nation of the dmit dianion to the uranium center. Dmit
complexes of transition metals have attracted considerable
attention due to their electrical conductivities.20,21 However, to
the best of our knowledge dmit complexes of f-elements have
not so far been structurally characterized.
Moreover complex 6 provides the first example of a dmit
complex formed from the reduction of CS2 by a metal
complex. The mechanism of formation of 6 remains unclear
although it should involve reductive dimerization of CS2 as a
first step.
Thus, the presence of the bound potassium cation in the
heterometallic complex 2 leads to a different reduction
pathway being preferred in the reaction of the U(III) tetrasil-
oxide with CS2 in toluene. Notably, the reaction affords prefer-
entially the reductive CS2 coupling product tetrathiooxalate
rather than the reductive cleavage product, the trithiocarbo-
nate, found to be the major reaction product in the reaction of
1 with CS2. Future DFT studies should be performed to investi-
gate the mechanism of CS2 reduction by complexes 1 and 2.
Several examples of U(III) mediated C–C coupling are
known7c,22 but only one example of the mediated U(III) reduc-
tive coupling of CS2 has been reported to date.7c
all volatiles shows the presence of free 13CS3
,
13C2S4 and
2−
2−
C3S52− in the ratio 1 : 1.2 : 1. However, when the reaction is carried
out in the presence of excess CS2 (4 equiv.) the 13CS3
,
13C2S4
2−
2−
and 13C3S52− compounds are formed in ratio 1 : 5.9 : 1.
When the reaction mixture obtained from the reaction of 1
equivalent of CS2 with 2 in toluene is evaporated, the recrys-
tallization of the residue from THF, after separation of the
soluble by-products, affords the tetrathiooxalate potassium salt
in 65% yield. Recrystallization of this solid in DMSO layered
with toluene affords yellow crystals of [K2C2S4(DMSO)3]n, 5.
X-ray diffraction studies (Fig. S9 in ESI†) show the presence of
2−
a 2D polymeric structure. Each C2S4 ligand bridges three
potassium cations yielding a 1-D polymer chain. Two DMSO
molecules bridge two potassium cations from adjacent chains
to afford the 2-D polymeric structure. The central C–C bond
length and the C–S bond distances (C1–C3 1.496(3) Å, S1–C1
1.700(2) Å and S2–C1 1.671(2) Å, S3–C3 1.678(3) Å and S4–C3
1.686(2) Å) are in agreement with the presence of a dianionic
tetrathioxalate.18
Attempts to isolate a uranium(IV) complex of the tetrathioxal-
ate ligand from the toluene reaction mixture were not success-
ful. However, evaporation to dryness of the toluene reaction
mixture 30 minutes after the addition of CS2 to 2, and extrac-
tion with hexane of the residue resulted in the isolation of few
crystals of the U(IV) complex [U(OSi(OtBu)3)4K2(C3S5)]n, 6 which
crystallizes as an infinite 1D polymer.‡ While the quality of the
structure is not sufficient to discuss the metrical parameter, it
clearly shows the atom connectivity. In the structure of 6, pre-
Concluding remarks
‡Unit cell parameters for 6·hexane: a, 24.370(4) Å; b, 13.958(5) Å; c, 25.659(5) Å;
α, 90°; β, 107.035(16)°; γ, 90°; unit cell volume 8345(4) Å3; formula,
C57H122K2O16S5Si4U.
In summary the “ate” complex [K(18c6)][U(OSi(OtBu)3)4], 1,
and the heterodimetallic U, K complex [U(OSi(OtBu)3)4K],
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2 both engage in the parallel reductive dimerization and reduc- added to a 2 mL suspension of 1 (25.0 mg, 0.015 mmol, 1 eq.)
tive disproportionation of CS2. In these bulky systems the in toluene to afford a red/pink solution. After 30 min stirring,
reduction products are easily displaced from the uranium the solvent was removed in vacuo. The residue was extracted
coordination sphere by coordinating ligands, suggesting that with hexane to give a pink/red solution (A) and an insoluble
these systems might be well poised for the development of cat- brown solid. The solid was recovered by centrifugation and
alytic cycles. This reactivity differs significantly from that pre- then dissolved in pyridine to give a brown solution; slow
viously observed for the analogous homoleptic tris-siloxide diffusion of hexane into this pyridine solution produced deep
complex [U(OSi(OtBu)3)2(µ-OSi(OtBu)3)]2 which reduces CS2 to green needles of {[K(18c6)]2C2S4}·Py, 4·Py suitable for X-ray
a CS2 group that remains tightly bound to two U(IV) centers diffraction (13% yield). 1H NMR (200 MHz, pyridine-d5, 298 K):
2−
in a bridging mode. Moreover, the presence of the bound δ 3.58 (s, 24H, CH2-18c6). 13C{1H} NMR (200 MHz, pyridine-d5,
Lewis acidic potassium cation in the heterodimetallic U, K 298 K): δ 70.57 (s, CH2-18c6), 248.45 (s, C2S4). 13C{1H} NMR
complex leads preferentially to the reductive dimerization of (200 MHz, water-d2, 298 K): δ 70.00 (s, CH2-18c6), 251.03
CS2 while the reductive disproportionation pathway is favoured (s, C2S4).
by the “ate” complex [K(18c6)][U(OSi(OtBu)3)4]. The coordi-
After removing all volatiles from the pink/red hexane extract
nation of K+ and [K(18c6)]+ in the structure of the isolated A the solid was dissolved in toluene and left standing at
complexes [U(OSi(OtBu)3)4(μ3−CS3)K2(18c6)2] and [U(OSi- −40 °C to afford crystals of [K(18c6)]2[U(μ-κ1:κ2:κ2CS3)(OSi-
(OtBu)3)4K2(C3S5)]n suggest that in both systems the alkali ion (OtBu)3)4] (3) suitable for X-ray diffraction. Unfortunately,
plays an important, if different, role. Future studies will be attempts to separate 3 from [U(OSi(OtBu)3)4] were unsuccess-
directed to elucidate the mechanism of CS2 reduction in these ful, preventing further characterization of this species.
1
systems.
The quantitative H NMR spectrum recorded on a toluene
solution of 1 reacted with one equivalent of CS2 for 30 minutes
after addition of an internal standard (naphthalene) shows the
formation of [U(OSi(OtBu)3)4] in 50% yield.
Experimental
General experimental procedures
1
The quantitative H NMR spectrum of the toluene reaction
mixture after two days shows the presence of the U(IV) complex
All manipulations were carried out at ambient temperature [U(OSi(OtBu)3)4] as the major product (65%).
under an inert argon atmosphere using Schlenk techniques
Quantitative 13C NMR: 10.4 μL of a 0.64 M toluene solution
and an MBraun glovebox equipped with a purifier unit. The of 13CS2 (0.006 mmol, 1 eq.) were added to a 0.5 mL suspen-
water and oxygen level were always kept at less than 0.1 ppm.
Glassware was systematically dried in an oven overnight at
130 °C followed by 3 vacuum/argon cycles before use. Unless
otherwise noted, reagents were purchased from commercial
suppliers and used without further purification. The solvents
were purchased from Aldrich in their anhydrous form, con-
ditioned under argon and vacuum distilled from K/benzophe-
none (toluene and pyridine) or sodium dispersion (hexane)
and degassed by three freeze–pump–thaw cycles. DMSO was
dried over activated molecular sieves for one week. The deuter-
ated solvents were purchased from Eurisotop and prepared
identically. CS2 was degassed by three freeze–pump–thaw
cycles and stored over molecular sieves. Depleted uranium turn-
ings were purchased from the “Société Industrielle du Com-
bustible Nucléaire” of Annecy (France). Complexes [K(18c6)]-
[U(OSi(OtBu)3)4], 19a and [U(OSi(OtBu)3)4K], 210 were prepared
according to the published procedures. 1H and 13C NMR experi-
ments were carried out using NMR tubes adapted with J. Young
valves and the spectra were recorded on Bruker 200 MHz and
Bruker 400 MHz spectrometers. NMR chemical shifts are
reported in ppm with a solvent as an internal reference.
sion of 1 (9.5 mg, 0.006 mmol, 1 eq.) in toluene to afford a
red/pink solution. 13C NMR spectra in deuterated DMSO of the
reaction mixture after toluene evaporation show the presence
of free 13CS32− as the major species, compared to 13C3S52− in a
10 : 1 ratio. Quantitative 13C NMR using naphthalene as an
internal standard shows the quantitative transformation of CS2
2−
into the reduction products 13CS32−, and 13C3S5
.
Reaction of [U{OSi(OtBu)3}4K] (2) with CS2
A – short reaction times. 30 µL (0.038 mmol) of a 1.25 M
toluene-d8 solution of 13CS2 were added to a solution of 2
(25.4 mg, 0.019 mmol, 2 eq.) in toluene-d8 (0.5 mL) and stirred
for 30 minutes. All volatiles were then removed in vacuo. The
residue was suspended in hexane and the undissolved solid
was discarded. Pink/red crystals of [U(OSi(OtBu)3)4K2(C3S5)]n,
6 suitable for X-ray diffraction were isolated by letting this
hexane solution to stand for few days at room temperature.
Attempts to separate 6 from the other reaction products were
unsuccessful, preventing further characterization of this
species.
B – long reaction times. 30 µL (0.038 mmol) of a 1.25 M
toluene-d8 solution of 13CS2 were added to a solution of 2
Caution: Depleted uranium (primary isotope 238U) is a (50.8 mg, 0.038 mmol, 1 eq.) in toluene-d8 (0.5 mL) to afford
weak α-emitter (4.197 MeV) with a half-life of 4.47 × 109 years. an orange solution. After letting the solution stand at room
Manipulations and reactions should be carried out in moni- temperature for 2 days a few red crystals formed which were
tored fume hoods or under an inert atmosphere glovebox in a identified by 13C NMR as K2CS3. The H NMR spectrum of the
1
radiation laboratory equipped with α- and β-counting equipment. toluene reaction mixture shows the presence of the U(IV)
Reaction of [K(18c6)][U(OSi(OtBu)3)4] (1) with CS2. 100 μL of complex [U(OSi(OtBu)3)4] as the major product (66%). All the
a 0.15 M toluene solution of CS2 (0.015 mmol, 1 eq.) were volatiles were then removed in vacuo to afford a brown solid.
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Paper
Recrystallization of this residue by slow diffusion of toluene sphere with ISOR instruction. The thermal coefficients of the
(4 mL) into DMSO (0.5 mL) affords [K2C2S4(DMSO)3]n, 5, as carbon atoms of the toluene C251 were constrained to be
yellow crystals suitable for X-ray diffraction. 13C{1H} NMR equal. The thermal coefficients of the following atoms of the
(200 MHz, DMSO-d5, 298 K): δ = 264.46 (s, C2S4).
silanol ligands were restrained to be closer to a sphere with
An analogous reaction performed with a 1 : 2 ratio complex ISOR instruction: O21B C30 C10B O1B O41 C10 C24 C27B
2:CS2 allows the isolation of the insoluble K2C2S4·5THF salt C30B C31B C46 C48 C50 C50B C52B C67 C70B C69B C71 C72
(5 THFs confirmed from the 1H NMR spectrum in dmso-d6) as C72B C87 C88 O1 O21 O43 O43B C5B C6B C7B C8B C9 C9B
yellow crystals in 65% yield (a yield consistent with the C11B C12 C12B C29B.
1 : 3.7 : 1 13CS32− : C2S4
:
13C3S5
ratio obtained from the
The C9–C10 bonds of the tert-butyl group of a silanol
ligand were restrained to be symmetric with DELU instruction.
For structure 5 at position 000 a 169 Å3 empty space was
2−
2−
quantitative 13C NMR spectra as indicated below).
The quantitative 13C NMR spectrum recorded in deuterated
pyridine or in DMSO immediately after solvent evaporation of found where 30 electrons were modeled by SQUEEZE.26 The
a toluene solution of 2 reacted with one equivalent of CS2 quality of structure 6 is not sufficient for publication in
shows the presence of free 13CS32−, C2S4 and 13C3S5 in a Cambridge Structural Database due to the poor quality of the
2
2−
1 : 1.2 : 1 ratio. The quantitative 13C NMR spectrum recorded in crystals.
deuterated pyridine or in DMSO immediately after solvent
evaporation of toluene solutions of 2 reacted with two or four
equivalents of CS2, showing the presence of an increasingly
Experimental details for X-ray data are given in Table S2.†
higher amount of free C2S4
13C3S52−. (A 1 : 3.7 : 1 13CS32− : C2S4
compared to 13CS3
and
13C3S5 ratio was found
2−
2−
Acknowledgements
2−
2−
:
This work benefited from COST Action CM1006 – EUFEN:
European F-Element Network. We acknowledge support from
the Labex Arcane, ANR-11-LABX-003-01.
for 2 equiv. CS2 and a 1 : 5.9 : 1 for 4 equivalents.)
X-Ray crystallography
Diffraction data were taken using an Oxford-Diffraction XCalli-
bur S kappa geometry diffractometer (Mo-Kα radiation, graph-
ite monochromator, λ = 0.71073 Å). To prevent evaporation of
the co-crystallised solvent molecules, the crystals were coated
with light hydrocarbon oil and the data were collected at
150 K. The cell parameters were obtained with intensities
detected on three batches of 5 frames. The crystal–detector dis-
tance was 4.5 cm. The number of settings and frames has
been established taking into consideration the Laue symmetry
of the cell using CrysAlisPro Oxford-diffraction software.23 503
for 4·Py, 508 for 3, 495 for 5 and 266 for 6 were collected for 1°
increments in ω with 150 s, 10 s, 50 s and 300 s, respectively,
exposure times. Unique intensities detected on all frames
using the Oxford-diffraction Red program were used to refine
the values of the cell parameters. Modelisation of the crystal
shape in CrysAlisPro software allows analytical absorption cor-
rection for 4·Py and 5. In the case of imprecise shape modeli-
sation, substantially redundancy in measured intensities
allows empirical multi-scan absorption correction for 3·4
toluene and 5. Space groups were determined from systematic
absences, and they were confirmed by the successful solution
of the structure. The structures were solved using Superflip
software,24 and refined with the Olex package.25 All non-hydro-
gen atoms were found by difference Fourier syntheses and
refined on F2. Hydrogen atoms were fixed in an ideal position
for 3·4 toluene, 4·Py and 5 and refined using a riding model.
In complex 3·4 toluene 835 restraints were applied: The methyl
distances, and all thermal coefficients of the toluene mole-
cules were restrained with SIMU instruction. The carbon
atoms of three toluene molecules (C151, C251 and C241) were
restrained to be planar with FLAT instruction. The thermal
coefficients of the carbon atoms of three toluene molecules
(C121, C151, and C251) were restrained to be closer to a
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