Organouranium complexes with phosphinine-based SPS pincer ligands. Variations with the substituent at the phosphorus atom

Article abstract of DOI:10.1021/om8003493

Reaction of [K(Et₂O)] [SPS^Me] with [U(Cp*)(BH₄)₃] or [U(COT)(BH₄) ₂(THF)] in THF gave the expected substitution products [U(Cp*)(BH₄)₂(SPS^Me)] (1) and [U(COT)(BH₄)(SPS^Me)] (2), respectively. Protonolysis of 2 with [NEt₃H][BPh₄] afforded the cationic complex [U(COT)(SPS^Me)(NEt₃)][BPh₄] (3), which was transformed into [U(COT)(SPS_Me)(L)][BPh₄] [L = OPPh ₃ (4) or HMPA (5)]. Changing [K(Et₂O)] [SPS ^OMe1] with [Na][SPS^OMe] in its reaction with [U(COT)(BH₄)₂(THF)] afforded a mixture of complexes, among which [U(COT)(BH₄)(SPS^H)] (6) was deposited as red crystals of a THF solvate. Complex 6 was isolated in 79% yield from the reaction of [U(COT)(BH₄)₂(THF)] and SPS in the presence of a catalytic amount of NaBH₄; the key intermediate of the reaction is [Na(THF)_x] [SPS^H · BH₃], formed by addition of NaBH₄ to SPS, which reacts with [U(COT)(BH ₄)2(THF)] to give 6 and NaBH₄. The X-ray crystal structures of 1 · 4.5C₆H₁₂, 2 ·THF, 5 ?Et₂O, and 6 ? 1.5THF indicate that the central moiety of the SPS ligand can be considered as a classical phosphine, the anionic charge being stabilized by delocalization over the five carbon atoms of the phosphahexadienyl anion and negative hyperconjugation into the two Ph ₂PS pendant arms. TheX-raycrystal structures of [(U(COT)(S ₂PP₂)(μ-OMe)}₂] and [{U(COT)}₄ {U(THF)₃}₂(μ₃-S)₈], which resulted from decomposition of the SPS ligand, are also presented.

Full text of DOI:10.1021/om8003493

4158
Organometallics 2008, 27, 4158–4165
Organouranium Complexes with Phosphinine-Based SPS Pincer
Ligands. Variations with the Substituent at the Phosphorus Atom
The´re`se Arliguie,*,† Matthias Blug,‡ Pascal Le Floch,‡ Nicolas Me´zailles,*,‡ Pierre Thue´ry,†
and Michel Ephritikhine*,†
SerVice de Chimie Mole´culaire, DSM, IRAMIS, CNRS URA 331, CEA/Saclay, 91191 Gif-sur-YVette,
France, and Laboratoire “He´te´roe´le´ments et Coordination”, CNRS UMR 7653, Ecole Polytechnique,
91128, Palaiseau Ce´dex, France
ReceiVed April 18, 2008
Reaction of [K(Et2O)][SPSMe] with [U(Cp*)(BH4)3] or [U(COT)(BH4)2(THF)] in THF gave the expected
substitution products [U(Cp*)(BH4)2(SPSMe)] (1) and [U(COT)(BH4)(SPSMe)] (2), respectively. Proto-
nolysis of 2 with [NEt3H][BPh4] afforded the cationic complex [U(COT)(SPSMe)(NEt3)][BPh4] (3), which
was transformed into [U(COT)(SPSMe)(L)][BPh4] [L ) OPPh3 (4) or HMPA (5)]. Changing
[K(Et2O)][SPSMe] with [Na][SPSOMe] in its reaction with [U(COT)(BH4)2(THF)] afforded a mixture of
complexes, among which [U(COT)(BH4)(SPSH)] (6) was deposited as red crystals of a THF solvate.
Complex 6 was isolated in 79% yield from the reaction of [U(COT)(BH4)2(THF)] and SPS in the presence
of a catalytic amount of NaBH4; the key intermediate of the reaction is [Na(THF)x][SPSH · BH3], formed
by addition of NaBH4 to SPS, which reacts with [U(COT)(BH4)2(THF)] to give 6 and NaBH4. The X-ray
crystal structures of 1 · 4.5C6H12, 2 · THF, 5 · Et2O, and 6 · 1.5THF indicate that the central moiety of the
SPS ligand can be considered as a classical phosphine, the anionic charge being stabilized by delocalization
over the five carbon atoms of the phosphahexadienyl anion and negative hyperconjugation into the two
Ph2PSpendantarms.TheX-raycrystalstructuresof[{U(COT)(S2PPh2)(µ-OMe)}2]and[{U(COT)}4{U(THF)3}2(µ3-
S)8], which resulted from decomposition of the SPS ligand, are also presented.
and sulfur centers of this SPS pincer was not an obstacle to its
coordination to the hard f elements, as shown recently with the
synthesis, from the borohydride precursors [Ln(BH4)3], of the
lanthanide derivatives [Ln(BH4)2(SPSMe)(THF)2] and of the ho-
moleptic complexes [Ln(SPSMe)3] (Ln ) Nd, Ce), the formation
of which was clearly favored by the flexibility of the tridentate
ligand.15 In contrast, reactions of UX4 (X ) Cl, BH4) and the
Introduction
Pincer ligands have gained a prominent position in coordina-
tion chemistry, justified by their structural rigidity, which
provides a significant thermodynamic stability to their com-
plexes, and the easy modification of their steric and electronic
properties through changes to the substituents of the central
and peripheral binding sites.1–4 Besides the number of terdentate
pincer ligands of XCX or XNX type, in which a central aromatic
benzene or pyridine ring is substituted by two chelating pendant
arms with a variety of donor heteroatom combinations (X ) C,
N, O, P, and S),5 the unique SPSR ligand, featuring a central
λ4-phosphinine unit and two lateral phosphinosulfide groups,
was found to endow a series of d transition metals with attractive
structures and reactions.6–14 The softness of both the phosphorus
lithium or potassium salts of the [SPSMe -
] anion afforded the
uranium compounds [UX2(SPSMe)2] as the sole products.15 In
order to extend this work and learn more about the uranium
complexes with SPSR ligands, we turned our investigations
toward the organometallic compounds, considering the most
familiar classes of tris(cyclopentadienyl) [U(Cp)3], mono- and
bis(pentamethylcyclopentadienyl) [U(Cp*)] and [U(Cp*)2], and
mono(cyclooctatetraenyl) [U(COT)] derivatives. A series of
neutral and cationic compounds with the SPSMe ligand were
isolated from [U(Cp*)(BH4)3] and [U(COT)(BH4)2(THF)]. Of
special interest was the reaction of [U(COT)(BH4)2(THF)] and
[Na][SPSOMe], which gave a mixture of products including the
SPSH complex [U(COT)(BH4)(SPSH)] (6). Here we report first
on the preparation and characterization of these compounds.
Second, we propose a mechanism for the formation of 6, which
is supported by a straightforward and clean synthesis of this
complex. Finally, we also describe the X-ray crystal structures
* Corresponding authors. E-mail (N.M.): mezaille@poly.polytechnique.fr.
† Service de Chimie Mole´culaire, DSM, IRAMIS, CNRS URA 331.
‡ Laboratoire “He´te´roe´le´ments et Coordination”, CNRS UMR 7653.
(1) Moulton, C. J.; Shaw, B. L. J. Chem. Soc., Dalton Trans. 1976,
1020.
(2) Albrecht, M.; van Koten, G. Angew. Chem., Int. Ed. 2001, 40, 3750.
(3) Singleton, J. T. Tetrahedron Lett. 2003, 59, 1837.
(4) van der Boom, M. E.; Milstein, D. Chem. ReV. 2003, 103, 1759.
(5) D´ıez-Barra, E.; Guerra, J.; Lo´pez-Solera, I.; Merino, S.; Rodr´ıguez-
Lo´pez, J.; Sa´nchez-Verdu´, P.; Tejeda, J. Organometallics 2004, 23, 5833.
(6) Doux, M.; Bouet, C.; Me´zailles, N.; Ricard, L.; Le Floch, P.
Organometallics 2002, 21, 2785.
(7) Doux, M.; Me´zailles, N.; Ricard, L.; Le Floch, P. Eur. J. Inorg.
Chem. 2003, 3878.
(8) Doux, M.; Me´zailles, N.; Ricard, L.; Le Floch, P. Organometallics
2003, 22, 4624.
(12) Doux, M.; Ricard, L.; Le Floch, P.; Jean, Y. Organometallics 2005,
24, 1608.
(9) Moores, A.; Me´zailles, N.; Ricard, L.; Jean, Y.; Le Floch, P.
Organometallics 2004, 23, 2870.
(10) Doux, M.; Ricard, L.; Le Floch, P.; Me´zailles, N. Dalton Trans.
2004, 2593.
(13) Doux, M.; Me´zailles, N.; Ricard, L.; Le Floch, P.; Vaz, P. D.;
Calhorda, M. J.; Mahabiersing, T.; Hartl, F. Inorg. Chem. 2005, 44, 9213.
(14) Doux, M.; Ricard, L.; Le Floch, P.; Jean, Y. Organometallics 2006,
25, 1101.
(11) Doux, M.; Me´zailles, N.; Ricard, L.; Le Floch, P.; Adkine, P.;
Berclaz, T.; Geoffroy, M. Inorg. Chem. 2005, 44, 1147.
(15) Arliguie, T.; Doux, M.; Me´zailles, N.; Thue´ry, P.; Le Floch, P.;
Ephritikhine, M. Inorg. Chem. 2006, 45, 9907.
10.1021/om8003493 CCC: $40.75
2008 American Chemical Society
Publication on Web 07/29/2008

Organouranium Complexes with Phosphinine-Based Ligands
Organometallics, Vol. 27, No. 16, 2008 4159
of complexes resulting from decomposition of the SPSR ligand
in the coordination sphere of U.
Results and Discussion
Complexes with the SPSMe Ligand. Reactions of the
tris(cyclopentadienyl) and bis(pentamethylcyclopentadienyl)
uranium(IV) compounds [U(Cp)3Cl] and [U(Cp*)2X2] (X ) Cl,
BH4) with the lithium or potassium salt of the [SPSMe -
] anion
were quite sluggish, and no product was identified. This lack
of reactivity can be explained by the steric hindrance of the
reagents and the electron richness of the uranium center
impeding the approach of the anionic tridentate ligand. Treat-
ment of the trivalent uranium metallocene [U(Cp)3(THF)] with
[M(Et2O)][SPSMe] (M ) Li or K) led to the formation of dark
red crystals, which were found to be the bridging sulfide
compound [{U(Cp)3}2(µ-S)] by X-ray diffraction analysis (only
a rough model could be obtained, see Experimental Section).
The crystal structure and formation of this complex are
reminiscent of those of [{U(C5H4Me)3}2(µ-S)], which was
synthesized by oxidation of [U(C5H4Me)3] with Ph3PdS.16
Obviously, electron-rich U(III) centers are efficient reducing
agents for phosphine sulfide derivatives.
Figure 1. View of complex 1. The hydrogen atoms (except those
of the borohydride groups) have been omitted. Displacement
ellipsoids are drawn at the 30% probability level.
plane, at 0.2032(13) Å, and a larger S-U-S angle of
139.53(3)°. The two U-S distances in 1 are identical, 2.8793(19)
and 2.8781(18) Å, and the U-P(1) distance is 2.9853(18) Å,
in line with the corresponding average distances of 2.88(8) and
2.98(2) Å in [UCl2(SPSMe)2]. It has been already noted, after
comparison of the U-P distances with the U-Pphosphido and
U-Pphosphino bond lengths in uranium(IV) complexes, that the
SPSMe ligand is better described as containing a tertiary
phosphine functionality.15 This bonding situation will be
confirmed after consideration of the bond lengths within the
SPS ligands in all the organouranium complexes (Vide infra).
Attempts at the synthesis of derivatives of 1 were disappoint-
ing. Complex 1 was inert in the presence of an excess of
[K(Et2O)][SPSMe], likely reflecting unfavorable steric and
electronic effects, as noted in the tris(Cp) and bis(Cp*) series.
Reduction of 1 with sodium amalgam led to the formation of
[U(Cp*)(BH4)3]- as the sole identified complex, in ca. 40%
yield; it is possible that the latter resulted from ligand redistribu-
tion reaction of the expected anion [U(Cp*)(BH4)2(SPSMe)]-.
Reaction of [U(COT)(BH4)2(THF)] with 1 molar equiv of
[M(Et2O)][SPSMe] in THF at 20 °C readily afforded the expected
substitution product [U(COT)(BH4)(SPSMe)] (2) (eq 2); after
usual workup, 2 was isolated as a microcrystalline brown
powder in 80% or 94% yield for M ) Li or K, respectively.
Brown crystals of the solvate 2 · THF were obtained by
crystallization from THF.
The mono(pentamethylcyclopentadienyl) compound [U(Cp*)-
(BH4)3] readily reacted with 1 molar equiv of [K(Et2O)][SPSMe
]
in THF to give [U(Cp*)(BH4)2(SPSMe)] (1) (eq 1); after filtration
and evaporation, 1 was extracted in cyclohexane and crystallized
from this solvent as an orange solvate in 70% yield. Complex
1 is, after the mixed-ring compound [U(Cp*)(C4Me4P)(BH4)2],
the only other derivative of [U(Cp*)(BH4)3] obtained by
substitution of a BH4 ligand.17 One may note here the stability
of the SPSMe ligand in the presence of a borohydride derivative,
unlike the SPSOMe analogue (Vide infra).
A view of complex 1 is shown in Figure 1, while selected
bond lengths and angles are listed in Table 1. The uranium atom
is in the familiar fac pseudo-octahedral configuration with the
Cp* ligand and the central P(1) atom of the SPS ligand in trans
axial positions and the two B and two S atoms defining the
equatorial plane (rms deviation 0.025 Å). The U atom is
displaced by 0.556(4) Å from this plane toward the Cp* ligand.
The short U · · · B distances of 2.577(8) and 2.575(10) Å are
identical to that of 2.58(3) Å in [U(Cp*)2(BH4)2]17 and indicate
a tridentate ligation mode of the BH4 ligands, in keeping with
the positions found for the hydrogen atoms. The coordination
geometry of the SPSMe ligand in 1 can be compared with that
in [UCl2(SPSMe)2], the other uranium SPS compound to have
been crystallographically characterized.15 The flexible SPSMe
ligand in 1 adopts a facial coordination mode, with the U atom
at a distance of 2.1145(11) Å from the P(1)-S(1)-S(2) plane
and the S(1)-U-S(2) angle equal to 77.95(5)°. This geometry
is similar to that of one of the two SPSMe ligands of
[UCl2(SPSMe)2], the other one being closer to the planar
geometry,withtheUatomlessdisplacedfromtheP(1)-S(1)-S(2)
A view of 2 is shown in Figure 2, while selected bond lengths
and angles are listed in Table 1. The five-coordinate uranium
atom can be seen in a distorted square-pyramidal arrangement
if the COT ligand is considered as monodentate. The U atom
is 1.455(4) Å above the basal plane defined by the B, P(1),
S(1), and S(2) atoms (rms deviation 0.336 Å), which is almost
parallel to the planar C8H8 ring, with a dihedral angle of 1.3(2)°.
(16) Brennan, J. G.; Andersen, R. A.; Zalkin, A. Inorg. Chem. 1986,
25, 1761.
(17) Gradoz, P.; Baudry, D.; Ephritikhine, M.; Lance, M.; Nierlich, M.;
Vigner, J. J. Organomet. Chem. 1994, 466, 107.

4160 Organometallics, Vol. 27, No. 16, 2008
Arliguie et al.
Table 1. Selected Bond Lengths (Å) and Angles (deg) in Complexes 1, 2, 5, and 6
[U(Cp*)(BH4)2(SPSMe)] (1)
[U(COT)(BH4)(SPSMe)] (2)
[U(COT)(SPSMe)(HMPA)][BPh4] (5)
[U(COT)(BH4)(SPSH)] (6)
<U-C>
2.758(9)
2.680(11)
2.919(3)
2.931(3)
2.965(3)
2.571(12)
1.810(10)
1.784(11)
1.854(10)
1.755(11)
1.764(10)
2.023(4)
2.008(4)
65.61(8)
69.80(8)
129.86(8)
2.665(16)
2.7940(6)
2.7986(7)
3.0425(7)
2.2567(16)
1.800(3)
1.805(3)
1.840(3)
1.769(2)
1.760(3)
2.668(13)
2.899(4)
2.873(3)
3.018(3)
2.49(2)
U-S(1)
2.8793(19)
2.8781(18)
2.9853(18)
2.577(8); 2.575(10)
1.794(7)
1.792(7)
1.826(7)
1.753(7)
1.778(7)
2.011(2)
2.011(3)
69.70(5)
70.48(5)
U-S(2)
U-P(1)
U · · · B or U-O
P(1)-C(1)
P(1)-C(5)
P(1)-C(6)
P(2)-C(1)
P(3)-C(5)
P(2)-S(1)
P(3)-S(2)
P(1)-U-S(1)
P(1)-U-S(2)
S(1)-U-S(2)
1.772(13)
1.770(12)
1.788(12)
1.776(12)
2.012(4)
2.013(4)
66.63(9)
68.96(9)
116.42(10)
2.0181(9)
2.0204(10)
71.825(18)
72.15(2)
77.95(5)
95.43(2)
The U · · · B distance of the tridentate BH4 group, 2.571(12) Å,
is quite identical to those in 1 and [{U(COT)(BH4)(µ-OEt)}2]
[2.594(8) Å].18 The U-S and U-P distances in 2 seem to be
respectively 0.05 Å larger and 0.02 Å smaller than the
corresponding distances in 1, but the major difference between
the SPSMe ligands of the two complexes concerns their
coordination geometry, which is closer to planar in 2. This
change in the coordination mode of the SPSMe ligand, which
should be related to the distinct configuration, octahedral and
square pyramidal, of complexes 1 and 2 is shown by the smaller
distance of the U atom from the P(1)-S(1)-S(2) plane, 0.845(3)
Å, and the larger S(1)-U-S(2) angle of 129.86(8)°. However,
the conformation of the SPSMe ligand in 2 is different from
that of the planar ligand in [UCl2(SPSMe)2], where the S(1) and
S(2) atoms are located on the same side of the plane defined by
the five carbon atoms of the central ring, whereas they are on
either side of this plane in 2. The COT ligation in 2, as well as
in the other (mono)cyclooctatetraenyl complexes presented
hereafter, is unexceptional.
Protonolysis of M-BH4 bonds by the acidic ammonium salt
[NEt3H][BPh4] proved to be a convenient route to cationic
complexes, as shown in particular by the synthesis of
[U(COT)(BH4)(THF)2][BPh4] and [U(COT)(HMPA)3][BPh4]2
[HMPA ) OdP(NMe2)3] from [U(COT)(BH4)2(THF)].19 Com-
plexes 1 and 2 were then considered as precursors of cationic
SPSMe compounds. Treatment of [U(Cp*)(BH4)2(SPSMe)] (1)
with [NEt3H][BPh4] led to a slow protonolysis reaction, as
shown by the formation of free amine NEt3, but no product
could be identified. In contrast, [U(COT)(BH4)(SPSMe)] (2) was
cleanly transformed into [U(COT)(SPSMe)(NEt3)][BPh4] (3),
which, after filtration and evaporation, was isolated as a brown
powder in 94% yield (eq 3).
(3)
Successive evaporations of THF solutions of 3 did not permit
the elimination of the NEt3 ligand, which was however easily
replaced with OPPh3 or HMPA to give the brown adducts
[U(COT)(SPSMe)(L)][BPh4] [L ) OPPh3 (4) or HMPA (5)] in
almost quantitative yield; crystals of 5 · Et2O were obtained by
slow diffusion of diethyl ether into a THF solution of 5. A view
of 5 is shown in Figure 3, and selected bond lengths and angles
are listed in Table 1. By comparison with the structure of 2,
the SPSMe ligand in 5 adopts a more facial conformation, with
a larger distance of the U atom from the P(1)-S(1)-S(2) plane,
1.8521(5) Å, and a smaller S(1)-U-S(2) angle of 95.43(2)°.
The average U-S and the U-P distances of 2.796(2) and
3.0425(7) Å are respectively the smallest and largest ever
observed in uranium SPS compounds. These features can be
tentatively explained by the stronger interaction between the
cationic metal center and the negatively charged sulfur atoms
of the SPSMe ligand, in line with the contribution of the
resonance hybrid structure C shown in Scheme 2 to the real
Figure 2. View of complex 2. The hydrogen atoms (except those
of the borohydride group) have been omitted. Displacement
ellipsoids are drawn at the 30% probability level.
Figure 3. View of the cation of complex 5. The hydrogen atoms
have been omitted. Displacement ellipsoids are drawn at the 30%
probability level.

Organouranium Complexes with Phosphinine-Based Ligands
Organometallics, Vol. 27, No. 16, 2008 4161
structure (Vide infra). The U-O distance of 2.2567(16) Å is
unexceptional; it can be compared with that of 2.27(1) Å in
[U(COT)(BH4)2(OPPh3)]20 and 2.22(1) Å (average value) in
[U(COT)(HMPA)3][BPh4]2.19
Formation of the [SPSH · BH3]- Anion and Synthesis of
[U(COT)(BH4)(SPSH)]. By comparison with the [SPSMe -
]
anion, the [SPSOMe]- analogue has only seldom been studied.21
Changing [M(Et2O)][SPSMe] (M ) Li, K) with [Na][SPSOMe
]
in its reaction with [U(COT)(BH4)2(THF)] led to a complicated
mixture of products, among which [U(COT)(BH4)(SPSH)] (6)
was deposited as red crystals of the THF solvate 6 · 1.5THF.
Complex 6, the first compound with the SPSH ligand, was
isolated in good yield from reaction of [U(COT)(BH4)2(THF)]
with SPS and NaBH4 (Vide infra). The crystal structure of 6,
which revealed the presence of the SPSH ligand resulting from
P-O bond cleavage of the [SPSOMe]- anion, is quite similar to
that of 2; a view of 6 is shown in Figure 4, and selected bond
lengths and angles are listed in Table 1. The most significant
differences seem to concern the U-P(1) and U-B distances,
which are respectively 0.05 Å larger and 0.08 Å smaller in 6.
The U-B bond length in 6 can be compared with those of
2.45(5) Å in [U(Cp)(BH4)3]22 and 2.48 Å in [U(Cp)3(BH4)].23
It is possible that the shorter U-P(1) bond in 2 results from
both the steric and electronic effects of the methyl substituent,
whose interaction with the COT ring brings the SPSMe ligand
closer to the metal center and which increases the Lewis basicity
of the phosphorus atom. As a consequence, the bond between
the anionic BH4 ligand and the more electron-rich metal center
of 2 would be weaker, as reflected by the larger U-B distance.
Figure 4. View of the cation of complex 6. Carbon-bound hydrogen
atoms have been omitted. Displacement ellipsoids are drawn at the
30% probability level.
In one experiment, the reaction mixture of [U(COT)-
(BH4)2(THF)] and [Na][SPSOMe] was heated at 60 °C, leading
to the formation of red crystals, which were found by X-ray
diffraction analysis to be the dithiophosphinate complex [{U-
(COT)(S2PPh2)(µ-OMe)}2], which obviously resulted from
decomposition of the pincer ligand. It is quite striking to observe
here again the facile elimination of the methoxide fragment from
the ligand. A view of the centrosymmetric methoxy-bridged
dimer is presented in Figure 5, together with selected bond
lengths and angles. The uranium atom is in a square-pyramidal
environment, if the COT ligand is considered to occupy a single
coordination site, the basal plane defined by the O and S atoms
with an rms deviation of 0.152 Å forming a dihedral angle of
5.4(2)° with the planar COT ligand. The U-O distances of
2.262(4) and 2.348(4) Å can be compared with those in
[{U(COT)(BH4)(µ-OEt)}2] and [{U(COT)(OiPr)(µ-OiPr)}2],18
which vary from 2.296(5) to 2.317(6) Å, and the U-S distances
of 2.8824(16) and 2.9435(16) Å can be compared with those
of 2.845(3)-2.871(3) Å measured in [{U(S2PMe2)2(OSPMe2)(µ-
O2PMe2)}2], the only other dithiophosphinate complex of
uranium(IV) to have been crystallographically characterized.24
Figure 5. View of the complex [{U(COT)(S2PPh2)(µ-OMe)}2]. The
hydrogen atoms have been omitted. Displacement ellipsoids are
drawn at the 30% probability level. Selected bond lengths (Å) and
angles (deg): <U-C> 2.676(17), U-S(1) 2.8824(16), U-S(2)
2.9435(16), U-O 2.262(4), U-O′ 2.348(4), O-U-O′ 67.00(16),
S(1)-U-S(2) 69.63(4). Symmetry code: ′ ) -x, 1 - y, -z.
1
[Na][SPSOMe] was monitored by H NMR spectroscopy. The
spectra showed the simultaneous formation of three “U(COT)”
complexes, easily noticed by their specific chemical shifts. The
first of these is the known [U(COT)(BH4)3]- complex (47% of
the complexes), characterized by the signals at δ -25.5 and
+60 for the COT and BH4 ligands, respectively. The second
complex (31%), also present at the beginning of the reaction,
is characterized by a COT resonance at δ -30.4 as well as a
signal at δ 155.7 integrating for 3H. This latter signal is
consistent with the low-field resonance corresponding to the
alkoxide ligand in [U(COT)(OR)X] compounds.22 As this
complex also featured a SPSH fragment, it was formulated as
[U(COT)(OMe)(SPSH)], but not isolated from the reaction
mixture. The last complex, 6, is characterized by the signals at
δ -32.7 for the COT ligand and +245 for the BH4 ligand.
Finally, the mixture also contained a SPSH anionic fragment,
not coordinated to a U center. The coexistence of these species
can be explained by the following sequence. The expected
reaction of [U(COT)(BH4)2(THF)] and [Na][SPSOMe] would
give the unstable complex “[U(COT)(BH4)(SPSOMe)]” and
NaBH4. The presence of NaBH4 in solution is the key to the
formation of the other products. Indeed, it may react with
[U(COT)(BH4)2(THF)] to form the observed [U(COT)(BH4)3]-
To have a better insight into the highly unusual behavior of
the SPSOMe ligand, the reaction of [U(COT)(BH4)2(THF)] and
(18) Arliguie, T.; Baudry, D.; Ephritikhine, M.; Nierlich, M.; Lance,
M.; Vigner, J. J. Chem. Soc., Dalton Trans. 1992, 1019.
(19) Cendrowski-Guillaume, S. M.; Lance, M.; Nierlich, M.; Ephri-
tikhine, M. Organometallics 2000, 19, 3257.
(20) Baudry, D.; Bulot, E.; Ephritikhine, M.; Nierlich, M.; Lance, M.;
Vigner, J. J. Organomet. Chem. 1990, 388, 279.
(21) Doux, M. The`se de Doctorat, Ecole Polytechnique, Palaiseau, France,
2005.
(22) Baudry, D.; Bulot, E.; Charpin, P.; Ephritikhine, M.; Lance, M.;
Nierlich, M.; Vigner, J. J. Organomet. Chem. 1989, 371, 163.
(23) Zanella, P.; Brianese, N.; Casellato, U.; Ossola, F.; Porchia, M.;
Rossetto, G.; Graziani, R. Inorg. Chim. Acta 1988, 144, 129.
(24) Greiwing, H.; Krebs, B.; Pinkerton, A. A. Inorg. Chim. Acta 1995,
234, 127.

4162 Organometallics, Vol. 27, No. 16, 2008
Arliguie et al.
complex. In parallel, it also appeared to have reacted with the
SPSOMe fragment to form the SPSH fragment. This substitution
reaction is unprecedented, although it may be rationalized in
light of our recent DFT study on SPSR anionic derivatives.25
Indeed, we showed in this study that the overall anionic charge
is stabilized both by delocalization in the carbon ring and by
negative hyperconjugation in σ* antibonding orbitals of ap-
propriate energy and symmetry (Scheme 1).
Should this be the case, the P-R bond would be longer than
usual, which was verified experimentally with R ) Me. In the
particular case discussed here, the P-OMe derivative lies quite
lower in energy, which leads to an enhanced leaving ability of
the MeO group.
[SPSH · BH3], as a freshly prepared solution of NaBH4 and SPS,
gave a mixture of 6 and [Na(THF)x][U(COT)(BH4)3] in relative
proportions of 10:90; this ratio changed to 25:75 after heating
for 2 h at 80 °C. The formation of the [U(COT)(BH4)3]- anion,
which was also observed in the reaction of
[U(COT)(BH4)2(THF)] and [Na][SPSOMe], was obviously caused
by the presence of NaBH4, which is in equilibrium with
[Na(THF)x][SPSH · BH3] and is produced in the synthesis of 6
by the substitution reaction (eq 4).
Since the quantity of NaBH4, which is necessary for making
[Na(THF)x][SPSH · BH3] from SPS, is recovered during the
synthesis of 6 (eq 4), the latter could be prepared by reaction
of [U(COT)(BH4)2(THF)] and SPS in the presence of a catalytic
amount of NaBH4, thus avoiding the competitive formation of
[Na(THF)x][U(COT)(BH4)3]. The synthesis of 6 is described
by the catalytic cycle shown in Scheme 2. Complex 6 was
obtained in a 70% yield after 2 h at 80 °C, and its formation
was complete when NEt3 was added to the reaction mixture,
for trapping BH3 as the borane adduct Et3N · BH3 (NMR
observations). In a preparative scale synthesis, analytically pure
6 was isolated in 79% yield as a red microcrystalline powder
after evaporation of the solvent and washing with diethyl ether.
An alternative to this mechanism was envisaged. It involves
the reaction of neutral SPS with [U(COT)(BH4)2(THF)], to form
an intermediate species “[U(COT)(BH4)2(SPS)]”, from which
an intramolecular hydride transfer from the BH4 ligand to the
SPS would lead directly to 6 with the concomitant release of
BH3 (eq 5).
Our efforts were then concentrated on the straightforward and
clean synthesis of
6 from [U(COT)(BH4)2(THF)] and
[Na(THF)x][SPSH · BH3]. Addition of 1 molar equiv of NaBH4
to a THF solution of SPS led to the immediate formation of
[Na(THF)x][SPSH · BH3] in ca. 50% yield; total conversion of
SPS into [SPSH · BH3]- was observed upon addition of 18-
crown-6. The 11B and 31P NMR spectra of this compound are
similar to those of the methyl derivative [K(Et2O)]-
[SPSMe · BH3],25 the high-field signal of the central phosphorus
1
atom being here a doublet at δ -18.45 with J(H-P) ) 380
Hz. Not surprisingly, treatment of [Li(THF)x][SPSH]25 with
Me2S · BH3 also afforded the [SPSH · BH3]- anion as its lithium
salt, which was found to be in equilibrium with SPS and LiBH4.
The [SPSH · BH3]- anion was not stable in THF solution and
decomposed progressively into a product resulting from cleavage
of a Ph2PS arm of the pincer ligand and containing two
phosphorus atoms, as shown by the 31P NMR spectra, which
In practice, treatment of [U(COT)(BH4)2(THF)] with SPS in
THF indeed provided the desired complex 6, yet with a low
yield of 10% after 24 h at 20 °C (eq 5). Heating the reaction
2
exhibit a pair of doublets with J(P-P) ) 109 Hz.
(4)
(5)
Attempts at the synthesis of
[U(COT)(BH4)2(THF)] with 1 molar equiv of [Na(THF)x]-
6
by reaction of
mixture led to a number of unidentified products, including a
[U(COT)(BH4)X] compound characterized by its 1H NMR
signals at δ -34.76 (8H) and 273.23 (4H); this product was
not observed in the reaction of [U(COT)(BH4)2(THF)] and
[Na][SPSOMe]. In one experiment, black crystals were deposited
from the reaction mixture and were found by X-ray diffraction
analysistobethehexanuclearcomplex[{U(COT)}4{U(THF)3}2(µ3-
S)8], a view of which is presented in Figure 6 together with
selected bond lengths and angles. The plane defined by the U(2),
U(2′), U(3), and U(3′) atoms is a mirror plane for the
centrosymmetric complex. The structure exhibits an octahedron-
like skeleton of uranium atoms that are held together with triply
bridging sulfur atoms located above each face of the octahedron.
The U6S8 core of the complex is a tetrakis hexahedron, that is,
a cube of S atoms each face of which is covered by a square
pyramid with a uranium atom at the apex. The U-S distances
vary from 2.662(4) to 2.810(3) Å with an average value of
2.74(5) Å, which is similar to those of 2.74(1) and 2.75(2) Å
inthetrinuclearcompounds[U3(µ3-S)(SBut)10]26and[{U(Cp*)I2}3(µ3-
I)(µ3-S)],27 respectively; the average U · · · U distance between
proximal metal centers is 4.25(8) Å. While octahedral thiolato
Scheme 1
Scheme 2

Organouranium Complexes with Phosphinine-Based Ligands
Organometallics, Vol. 27, No. 16, 2008 4163
Scheme 3
orbital) analysis of the [SPSMe -
anion showed that the
]
electronic structure would be better described by the canonical
form C, where the anionic charge is not fully delocalized but is
stabilized by both delocalization over the five carbon atoms of
the phosphahexadienyl anion and negative hyperconjugation into
the two Ph2PS pendant arms.25 As noted before, the short U-S
bonds suggest that form C contributes significantly to the true
structure of the SPSMe ligand in the cationic complex 5.
Figure 6. View of the complex [{U(COT)}4{U(THF)3}2(µ3-S)8].
The hydrogen atoms and carbon atoms of the THF molecules have
been omitted. Displacement ellipsoids are drawn at the 30%
probability level. Selected bond lengths (Å): <U(1)-O> 2.547(16),
<U(2)-C> 2.715(17), <U(3)-C> 2.71(2), U(1)-S(1) 2.662(4),
U(1)-S(2) 2.684(3), U(2)-S(1) 2.810(3), U(2)-S(2) 2.752(4),
U(3)-S(2) 2.756(3), U(3)-S(1′) 2.791(4). Symmetry code: ′ ) 2
- x, 1 - y, 1 - z.
Conclusion
The first organo-f-element compounds with a phosphinine-
based SPS pincer ligand, [U(Cp*)(BH4)2(SPSMe)] and
[U(COT)(BH4)(SPSMe)], were synthesized by reaction of the
uranium borohydride precursors with the lithium or potassium
salt of the [SPSMe]- anion. Treatment of [U(COT)(BH4)2(THF)]
with [Na][SPSOMe] led to the formation of [U(COT)-
(BH4)(SPSH)] (6), the first compound with the SPSH ligand.
Attempts to devise a more rational synthesis of this complex
via the independent formation of a “M[SPSH]” species was
hampered by the existence of an equilibrium between MBH4
and neutral SPS to form M[SPSH · BH3]. Anyhow, the latter
observation pointed to the potential catalytic use of NaBH4 in
the synthesis. Eventually, synthesis of 6 was achieved by the
reaction of [U(COT)(BH4)2(THF)] with SPS in the presence of
a catalytic amount of NaBH4. In terms of geometrical and
electronic properties of the tridentate anionic derivatives [SPSR]-
(R) Me, H), this study once again points up the flexibility of
the ligand, which can be better seen as a central phosphine
moiety with the anionic charge stabilized by both delocalization
over the five carbon atoms of the heterocycle and negative
hyperconjugation into the two Ph2PS pendant arms.
clusters of the type M6S8 are quite common for d transition
metals, especially for M ) Re, Mo, and W,28–30 such com-
pounds of the f elements have, to the best of our knowledge,
not been reported.
Bonding Situation in the Organouranium SPS Complexes.
The bonding mode of the SPS ligand was assessed by
consideration of its geometrical parameters. As previously
observed in the crystal structure of [UCl2(SPSMe)2],15 the internal
P(1)-C(1) and P(1)-C(5) distances of the SPS ligands in
complexes 1, 2, 5, and 6, which vary from 1.770(12) to
1.810(10) Å and average 1.791(14) Å, are larger than those in
the neutral λ3-phosphinine SPS [av 1.743(2) Å]8 and similar to
those in the [SPSMe - and [SPSOMe -
] ] anions [av 1.808(9) and
1.793(2) Å, respectively];8,25 these bond lengths are typical for
classical phosphine ligands. In turn, the external P(2)-C(1) and
P(3)-C(5) distances, which range from 1.753(7) to 1.788(12)
Å and average 1.768(11) Å, are smaller than those in SPS [av
Experimental Section
1.830(6) Å] and are similar to those in [SPSMe]- and [SPSOMe -
]
All reactions were carried out under argon (<5 ppm oxygen or
water) using standard Schlenk-vessel and vacuum-line techniques
or in a glovebox. Solvents were dried by standard methods and
distilled immediately before use. Nuclear magnetic resonance
spectra were recorded on a Bruker DPX 200 instrument operating
[av 1.777(6) and 1.78(1) Å, respectively]. The average P-S
distance of 2.015(5) Å in complexes 1, 2, 5, and 6 is larger
than in SPS [1.954(2) Å], even larger than the mean P-S bond
lengths of 1.977(5) and 1.971(4) Å in [SPSMe]- and [SPSOMe]-,
respectively, and is identical to that of 2.013(9) Å in
[UCl2(SPSMe)2].15 These variations in the bond lengths, together
with the pyramidalization and sp3-type hybridization of the
central P atom, clearly indicate that the central moiety of
the SPSR ligand can be considered as a classical phosphine and
are in agreement with the resonance structure B in Scheme 3,
where the negative charge is delocalized from one sulfur atom
to the other. However, DFT calculations and NBO (natural bond
at 200 MHz for H, 64.2 MHz for 11B, and 81 MHz for 31P. The
1
1H NMR spectra were referenced internally using the residual protio
solvent resonances relative to tetramethylsilane (δ 0); 31P chemical
shifts are relative to a 85% H3PO4 external reference, and 11B
chemical shifts are relative to a BF3 external reference. The spectra
were recorded at 23 °C when not otherwise specified. Elemental
analyses were performed by Analytische Laboratorien at Lindlar
(Germany). The organouranium complexes [U(Cp)3(THF)],31
[U(Cp*)(BH4)3],32 [U(COT)(BH4)2(THF)]20 and SPS,6 [M(Et2O)]-
[SPSMe] (M ) Li, K),15 [Li(THF)x][SPSH],25 and [Na][SPSOMe 8
]
(25) Doux, M.; Thue´ry, P.; Blug, M.; Ricard, L.; Le Floch, P.; Arliguie,
T.; Me´zailles, N. Organometallics 2007, 26, 5643.
(26) Leverd, P. C.; Arliguie, T.; Ephritikhine, M.; Nierlich, M.; Lance,
M.; Vigner, J. New J. Chem. 1993, 17, 769.
(27) Clark, D. L.; Gordon, J. C.; Huffman, J. C.; Watkin, J. G.; Zwick,
B. D. New J. Chem. 1995, 19, 495.
were prepared as previously reported; [NEt3H][BPh4] was made
by mixing NEt3HCl and NaBPh4 in water. IR samples were prepared
as Nujol mulls between KBr round cell windows and the spectra
recorded on a Nicolet Magna-IR 860 spectrometer.
Reaction of [U(Cp)3(THF)] and [Li(Et2O)][SPSMe]. An NMR
tube was charged with the uranium complex (10.0 mg, 0.020 mmol)
(28) Jin, S.; Adamchuk, J.; Xiang, B.; DiSalvo, F. J. J. Am. Chem. Soc.
2002, 124, 9229.
(29) Baudron, S. A.; Deluzet, A.; Boubekeur, K.; Batail, P. Chem.
Commun. 2002, 2124.
(30) Oertel, C. M.; Sweeder, R. D.; Patel, S.; Downie, C. M.; DiSalvo,
F. J. Inorg. Chem. 2005, 44, 2287.
(31) Le Mare´chal, J. F.; Villiers, C.; Charpin, P.; Lance, M.; Nierlich,
M.; Vigner, J.; Ephritikhine, M. J. Chem. Soc., Chem. Commun. 1989, 308.
(32) Baudry, M.; Ephritikhine, M. J. Organomet. Chem. 1988, 349, 123.

4164 Organometallics, Vol. 27, No. 16, 2008
Arliguie et al.
Table 2. Crystal Data and Structure Refinement Details
[{U(COT)(S2PPh2) [{U(COT)}4{U(THF)3}2
1 · 4.5cyclohexane
79H111B2P3S2U
1477.36
triclinic
j
P1
2 · THF
5 · Et2O
6 · 1.5THF
(µ-OMe)}2]
(µ3-S)8]
56H80O6S8U6
2533.86
monoclinic
C2/m
empirical formula
Mr
cryst syst
space group
C
C
54H54BOP3S2U
C
84H90BN3O2P4S2U
1610.43
triclinic
C
55H55BO1.5P3S2U
1145.86
triclinic
C
42H42O2P2S4U2
C
1124.84
monoclinic
P21/c
1245.00
monoclinic
P21/c
j
P1
j
P1
a/Å
b/Å
c/Å
11.4079(7)
13.8663(8)
24.1144(16)
96.727(2)
91.573(3)
100.436(5)
3721.0(4)
2
13.3300(15)
16.0507(10)
22.223(2)
90
97.554(4)
90
4713.4(8)
4
1.585
12.9649(3)
15.8235(4)
19.9331(4)
94.930(2)
104.712(3)
93.076(2)
3928.47(17)
2
12.596(2)
13.3444(19)
17.325(2)
68.359(9)
88.154(9)
66.305(9)
2455.6(6)
2
12.8051(10)
9.1321(7)
17.4375(16)
90
96.989(6)
90
2023.9(3)
2
2.043
15.0680(13)
17.7057(18)
13.0618(13)
90
95.326(6)
90
3469.7(6)
2
2.425
R/deg
ꢀ/deg
γ/deg
V/Å3
Z
Dcalcd/g cm-3
µ(Mo KR)/mm-1
F(000)
1.319
2.343
1528
1.361
2.248
1640
1.550
3.528
1142
3.674
2240
8.313
1176
14.234
2288
no. of rflns collected
no. of indep rflns
no. of obsd rflns (I > 2σ(I)) 10 037
Rint
22 588
12 539
30 900
8716
5084
0.113
560
159 481
14 905
13 435
0.039
16 056
8372
4377
0.135
577
13 311
3801
2989
0.075
236
13 095
3374
2451
0.087
189
0.065
790
no. of params refined
883
R1
wR2
S
0.059
0.137
1.079
-1.22
1.58
0.066
0.138
1.006
-1.12
1.54
0.025
0.065
1.067
-0.94
0.60
0.072
0.159
0.955
-1.22
0.97
0.033
0.073
1.005
-0.91
0.85
0.054
0.123
1.052
-1.54
1.37
∆Fmin/e Å-3
∆Fmax/e Å-3
and the lithium salt (15.4 mg, 0.020 mmol) in THF-d8 (0.35 mL).
After 20 h at 20 °C, dark red crystals of [{U(Cp)3}2(µ-S)] were
deposited.
NMR (THF-d8): δ 2113 (br, w1/2 ) 415 Hz, PMe), -320.5 (br,
w1/2 ) 165 Hz, PPh2). 11B NMR (THF-d8): δ 276 (br s, w1/2 ) 290
Hz, BH4). IR (Nujol): ν(BH4) 2491(s), 2198(s), 2165(s) cm-1
.
Synthesis of [U(Cp*)(BH4)2(SPSMe)] (1). A flask was charged
Method b. A flask was charged with [U(COT)(BH4)2(THF)] (175
mg, 0.394 mmol) and [Li(Et2O)][SPSMe] (306.2 mg, 0.394 mmol),
and THF (50 mL) was condensed in. The reaction mixture was
stirred for 1 h at 20 °C, and THF was evaporated off. The orange-
brown powder of 2 was washed with diethyl ether (2 × 30 mL)
and dried under vacuum. Yield: 330 mg (80%). The absence of
LiBH4 in the product was checked by 11B NMR spectroscopy.
Synthesis of [U(COT)(SPSMe)(NEt3)][BPh4] (3). A flask was
charged with 2 (69 mg, 0.066 mmol) and [NEt3H][BPh4] (30 mg, 0.07
mmol), and THF (100 mL) was condensed in. The reaction mixture
was stirred at 80 °C for 90 min, and after filtration, the solution was
evaporated to dryness, leaving 3 as a light brown powder. Yield: 198.4
mg (94%). Anal. Calcd for C80H77BNP3S2U: C, 65.88; H, 5.28; S,
4.39. Found: C, 64.08; H, 5.33; S, 4.25. 1H NMR (THF-d8): δ 19.75
(br t, w1/2 ) 25 Hz, 4 H, CH of Ph), 12.35 (t, J ) 7.3 Hz, 4 H, CH
of Ph), 11.01 (t, J ) 7.3 Hz, 2 H, CH of Ph), 8.2-6.8 (m, 16 H, CH
of Ph], 6.72 (m, w1/2 ) 16 Hz, 8 H, CH of BPh4), 6.39 (t, J ) 7.3 Hz,
8 H, CH of BPh4), 6.26 (t, J ) 7.3 Hz, 4 H, CH of BPh4), 5.60 (t, J
) 7.3 Hz, 4 H, CH of Ph), 2.68 (q, J ) 7.2 Hz, 6 H, NCH2CH3), 1.11
(t, J ) 7.2 Hz, 9 H, NCH2CH3), -18.51 (s, 3 H, PMe), -35.89 (s, 8
H, COT). 31P NMR (THF-d8): δ 2638 (br, w1/2 ) 390 Hz, Pme),
-242.6 [d, 2J(P-P) ) 127 Hz, PPh2].
with [U(Cp*)(BH4)3] (106 mg, 0.25 mmol) and [K(Et2O)][SPSMe
]
(203 mg, 0.25 mmol), and THF (20 mL) was condensed in. The
reaction mixture was stirred for 12 h at 20 °C; the solvent was
evaporated off and the residue extracted in toluene (20 mL). After
filtration, the volume of the brown solution was reduced to 2 mL,
and addition of pentane led to the precipitation of a brown powder,
which was filtered off and dried under vacuum. The powder was
extracted with THF (10 mL), and after filtration, the solution
was evaporated to dryness, leaving a brown-orange solid, which
was extracted with cyclohexane (10 mL). Filtration and evaporation
to dryness of the orange cyclohexane solution afforded the orange
powder of 1 · C6H12. Yield: 208.6 mg (70%). Anal. Calcd for
C58H69B2P3S2U: C, 58.89; H, 5.88; P, 7.85; S, 5.42. Found: C,
58.62; H, 5.65; P, 7.81; S, 5.56. 1H NMR (THF-d8): δ 41.26 (s, 3
H, Me), 35.3 (br, w1/2 ) 260 Hz, 8 H, BH4), 11.53 (s, 1 H, H4),
10.35 (br, 4 H, CH of Ph), 9.97 (s, 15 H, Cp*), 9.01 (br t, J ) 9.8
Hz, 4 H, CH of Ph), 7.70 (m, 6 H, CH of Ph), 6.20 (t, J ) 7.3 Hz,
4 H, CH of Ph), 5.62 (t, J ) 7.3 Hz, 2 H, CH of Ph), 4.98 (t, J )
7.3 Hz, 2 H, CH of Ph), 4.30 (t, J ) 7.6 Hz, 4 H, CH of Ph), 1.43
(s, 12 H, C6H12), 0.47 (br t, J ) 9.7 Hz, 4 H, CH of Ph). IR (Nujol):
ν(BH4) 2461(s), 2214(s), 2177(s) cm-1
.
Synthesis of [U(COT)(BH4)(SPSMe)] (2). Method a. A flask
was charged with [U(COT)(BH4)2(THF)] (52.9 mg, 0.119 mmol)
and [K(Et2O)][SPSMe] (96.5 mg, 0.119 mmol), and THF (50 mL)
was condensed in. The color of the solution turned from bright red
to brown. After stirring for 1 h at 20 °C, THF was evaporated off
and the orange-brown residue was extracted in THF (30 mL),
leaving a white precipitate of KBH4; the orange-brown solution
was filtered and evaporated to dryness, leaving a brown microc-
rystalline powder of 2. Yield: 118 mg (94%). Anal. Calcd for
Synthesis of [U(COT)(SPSMe)(OPPh3)][BPh4] (4). An NMR
tube was charged with 3 (10.3 mg, 0.007 mmol) and OPPh3 (2.0
mg, 0.007 mmol) in THF-d8 (0.4 mL). The spectrum showed the
1
immediate and quantitative formation of 4. H NMR (THF-d8): δ
13.43 (dt, J ) 7.3 and 4.6 Hz, 4 H, CH of Ph), 12.12 (m, w1/2
)
28 Hz, 6 H, CH of Ph), 11.12 (t, J ) 7.3 Hz, 4 H, CH of Ph),
10.47 (t, J ) 7.3 Hz, 2 H, CH of Ph), 7.7-6.5 (m, 35 H, CH of
OPh3 and BPh4), 5.91 (dt, J ) 7.3 and 4.6 Hz, 4 H, CH of Ph),
5.41 (m, w1/2 ) 26 Hz, 3 H, CH of Ph and H4), 4.28 (t, J ) 7.3
Hz, 4 H, CH of Ph), -2.91 (dt, J ) 7.3 and 4.6 Hz, 4 H, CH of
Ph), -12.42 (s, 3 H, PMe), -33.71 (s, 8 H, COT). 31P NMR (THF-
d8): δ 2216 (br, w1/2 ) 395 Hz, PMe), 61.84 (s, OPPh3), -285.1
C50H46BP3S2U: C, 57.04; H, 4.40; S, 6.09; P, 8.83. Found C, 57.02;
1
H, 4.51; S, 5.83; P, 8.71. H NMR (THF-d8): δ 255 (br s, w1/2
)
240 Hz, 4 H, BH4), 17.54 (br t, w1/2 ) 24 Hz, 4 H, CH of Ph),
15.17 (t, J ) 7.3 Hz, 4 H, CH of Ph), 14.37 (t, J ) 7.3 Hz, 2 H,
2
[d, J(P-P) ) 130 Hz, PPh2].
CH of Ph), 6.33 (t, J ) 7.3 Hz, 2 H, CH of Ph), 6.16 (m, w1/2
)
Synthesis of [U(COT)(SPSMe)(HMPA)][BPh4] (5). A flask was
charged with 3 (77 mg, 0.052 mmol) in THF (25 mL), and HMPA
(9.1 µL, 0.052 mmol) was added via a microsyringe. The solution
was evaporated to dryness, leaving a brown powder of 5. Yield: 80
mg (99%). Anal. Calcd for C80H80BN3OP4S2U: C, 62.44; H, 5.25; S,
30 Hz, 4 H, CH of Ph), 5.78 (t, J ) 7.3 Hz, 4 H, CH of Ph), 4.84
(t, J ) 7.3 Hz, 4 H, CH of Ph), 3.35 (s, 1H, H4), 1.69 (br, masked
by the THF resonance, 2 H, CH of Ph), -0.43 (br t, J ) 9.8 Hz,
4 H, CH of Ph), -21.09 (s, 3 H, Me), -32.31 (s, 8 H, COT). 31P

Organouranium Complexes with Phosphinine-Based Ligands
Organometallics, Vol. 27, No. 16, 2008 4165
1
4.17; P, 8.06. Found: C, 61.98; H, 5.13; S, 3.92; P, 7.85. H NMR
4.8 Hz, 4 H, CH of Ph), -32.73 (s, 8 H, COT), -35 (br d, J )
267 Hz, 1 H, PH). 31P NMR (THF-d8): δ 2139 (br, w1/2 ) 490 Hz,
(THF-d8): δ 9.80 (dt, J ) 7.3 and 5.1 Hz, 4 H, CH of Ph), 9.62 (t, J
) 7.3 Hz, 4 H, CH of Ph), 9.40 (d, J ) 9.5 Hz, 18 H, HMPA), 9.31
(t, J ) 7.3 Hz, 2 H, CH of Ph), 7.45 (br s, w1/2 ) 16 Hz, 8 H, CH of
BPh4), 6.97 (m, 8 H + 6 H, CH of BPh4 + CH of Ph), 6.76 (t, J )
7.3 Hz, 4 H, CH of BPh4), 5.68 (t, J ) 7.3 Hz, 2 H, CH of Ph), 5.37
(t, J ) 7.3 Hz, 2 H, CH of Ph), 4.73 (br, w1/2 ) 28 Hz, 3 H, CH of
Ph and H4), 3.88 (t, J ) 7.3 Hz, 4 H, CH of Ph), -4.50 (dt, J ) 7.3
and 5.1 Hz, 4 H, CH of Ph), -6.41 (s, 3 H, PMe), -32.65 (s, 8 H,
COT). 31P NMR (THF-d8): δ 2064 (br, w1/2 ) 410 Hz, PMe), 142.4
(br, w1/2 ) 20 Hz, HMPA), -286.51 [d, 2J(P-P) ) 132 Hz, PPh2].
Reaction of [U(COT)(BH4)2(THF)] and [Na][SPSOMe]. An
NMR tube was charged with the uranium compound (9.0 mg, 0.020
mmol) and the sodium salt (14.9 mg, 0.020 mmol) in THF-d8 (0.35
mL). After 15 min at 20 °C, the spectrum showed the formation of
three U(COT) complexes: the anionic derivative [U(COT)(BH4)3]-
(47%), complex 3 (21%), and another complex formulated as
2
PH), -325.5 [d, J(P-P) ) 90 Hz, PPh2]. 11B NMR (THF-d8): δ
263 (br, w1/2 ) 240 Hz, BH4). IR (Nujol): ν(BH4) 2454(s), 2199(s),
2156(s) cm-1
.
Reaction of [U(COT)(BH4)2(THF)] and SPS. An NMR tube
was charged with [U(COT)(BH4)2(THF)] (8.5, 0.019 mmol) and
SPS (12.9 mg, 0.019 mmol) in THF-d8 (0.4 mL). After 24 h at 20
°C, the spectrum showed that 10% of [U(COT)(BH4)2(THF)] was
transformed into 6. After heating for 30 min at 80 °C, the spectrum
showed the formation of unidentified products, including a
[U(COT)(BH4)X] compound characterized by two signals at δ
-34.76 (8H) and 273.23 (4H).
Crystallographic Data Collection and Structure Determina-
tion. The data were collected at 100(2) K on a Nonius Kappa-CCD
area detector diffractometer33 with graphite-monochromated Mo KR
radiation (λ ) 0.71073 Å). The crystals were introduced into glass
capillaries with a protective “Paratone-N” oil (Hampton Research)
coating. The unit cell parameters were determined from 10 frames
and then refined on all data. The data were processed with HKL2000.34
The structures were solved by direct methods or by Patterson map
interpretation with SHELXS97, expanded by subsequent Fourier-
difference synthesis, and refined by full-matrix least-squares on F2
with SHELXL97.35 Absorption effects were corrected empirically with
DELABS36 or SCALEPACK.34 All non-hydrogen atoms were refined
with anisotropic displacement parameters. The hydrogen atom bound
to phosphorus in 6 and those of the borohydride groups in 1, 2, and 6
were found on Fourier-difference maps (only two were found for the
borohydride group in 2 and the two others were introduced at calculated
positions), and the carbon-bound hydrogen atoms were introduced at
calculated positions; all were treated as riding atoms with an isotropic
displacement parameter equal to 1.2 (BH4, CH, CH2) or 1.5 (CH3)
times that of the parent atom. Special details are as follows:
[U(COT)(SPSMe)(HMPA)][BPh4] · Et2O (5 · Et2O). Some voids
in the lattice (about 90 Å3 per asymmetric unit) probably contain
very disordered solvent molecules that could not be resolved. The
corresponding electronic density was taken into account with the
program SQUEEZE.36
[U(COT)(OMe)(SPSH)] (31%). H NMR (THF-d8): δ 155.7 (s, 3
1
H, OMe), 9.75 (t, J ) 7.2 Hz, 2 H, CH of Ph), 9.14 (t, J ) 7.2 Hz,
4 H, CH of Ph), 5.58 (t, J ) 7.2 Hz, 4 H, CH of Ph), 3.79 (t, J )
7.2 Hz, 2 H, CH of Ph), 2.93 (t, J ) 7.7 Hz, 4 H, CH of Ph),
-0.57 (d, J ) 7.6 Hz, 4 H, CH of Ph), -4.04 (s, 1 H, H4), -4.87
(dd, J ) 12 and 8 Hz, 4 H, CH of Ph), -30.38 (s, 8 H, COT);
other signals should be masked by solvent and other complexes’
1
resonances. The H NMR spectrum of the reaction mixture also
exhibits the signals of [Na(THF)x][SPSH · BH3].
Formation of the [SPSH · BH3]- Anion. (a) An NMR tube was
charged with SPS (10.8 mg, 0.016 mmol), NaBH4 (0.6 mg, 0.016
mmol), and THF-d8 (0.4 mL). The color of the solution immediately
turned dark pink. The spectrum showed that 50% of SPS was
transformed into the [SPSH · BH3]- anion. H NMR (THF-d8): δ
1
8.0-6.6 (m, 30 H, CH of Ph), 5.44 [hextuplet, 2J(H-B) ) 3J(H-P)
) 6.3 Hz, 0.5 H, PH] (the other half of the signal is masked by
4
either the Ph or the THF resonances), 5.18 [t, J(H-P) ) 4.8 Hz,
1 H, H4], 1.0 (br, w1/2 ) 220 Hz, 3 H, BH3). 31P NMR (THF-d8):
2
1
δ 37.67 [d, J(P-P) ) 23 Hz, PPh2], -18.45 [br d, J(P-H) )
380 Hz, PH]. 11B NMR (THF-d8): -37.3 (br s, w1/2 ) 270 Hz,
BH3). Addition of 18-crown-6 (4.1 mg, 0.06 mmol) to the reaction
mixture led to the complete conversion of SPS into [SPSH · BH3]-.
After 1 h at 20 °C, the spectrum showed that [SPSH · BH3]-
decomposed into a product resulting from cleavage of a Ph2PS arm
of the pincer ligand and containing two phosphorus atoms, as
indicated by the 31P NMR spectrum, which exhibited a pair of
[U(COT)(BH4)(SPSH)] · 1.5THF (6 · 1.5THF). One solvent THF
molecule was found to be disordered around a symmetry center
and could only be modeled with six atoms. Some restraints on
displacement parameters were applied for some badly behaving
atoms, particularly in the solvent molecules.
[{U(COT)}4{U(THF)3}2(µ3-S)8]. Two C atoms of one THF
molecule are disordered around a mirror plane. Some voids in the
lattice (about 64 Å3 per asymmetric unit) probably contain very
disordered solvent molecules that could not be resolved.
[{U(Cp)3}2(µ-S)]. The low quality of the crystals permitted only
a rough model to be determined, which could not be refined. Crystal
data: monoclinic, space group Cc, a ) 8.21 Å, b ) 14.31 Å, c )
43.23 Å, ꢀ ) 91.73°.
2
doublets at δ 228.80 and 40.69 with J(P-P) ) 109 Hz.
(b) An NMR tube was charged with SPS (10.6 mg, 0.016 mmol)
in THF-d8 (0.4 mL), and BuLi (9.6 µL of a 1.7 M solution in
t
pentane, 0.016 mmol) was added via a microsyringe, giving a deep
red solution of [Li(THF)x][SPSH]. After 20 min at 20 °C,
Me2S · BH3 (7.8 µL of a 2 M solution in Et2O, 0.016 mmol) was
introduced into the tube via a microsyringe. The H, 31P, and 11B
1
spectra of the deep pink solution showed the formation of
[Li(THF)x][SPSH · BH3] in equilibrium with SPS and LiBH4.
Synthesis of [U(COT)(BH4)(SPSH)] (6). A flask was charged
with [U(COT)(BH4)2(THF)] (180 mg, 0.405 mmol), NaBH4 (1.0
mg, 0.027 mmol), NEt3 (56 µL, 0.405 mmol), and SPS (276 mg,
0.405 mmol), and THF (50 mL) was condensed in. The red solution
was heated for 1 h at 80 °C. The solvent was evaporated off and
the red precipitate washed with diethyl ether (2 × 30 mL) and dried
under vacuum. Yield: 333 mg (79%). Anal. Calcd for
Crystal data and structure refinement details are given in Table
2. The molecular plots were drawn with SHELXTL.35
Supporting Information Available: Tables of crystal data,
atomic positions and displacement parameters, anisotropic displace-
ment parameters, and bond lengths and bond angles in CIF format.
This material is available free of charge via the Internet at
http://pubs.acs.org.
C49H44BP3S2U: C, 56.66; H, 4.27; S, 6.17; P, 8.94. Found: C, 56.38;
OM8003493
1
H, 4.42; S, 5.98; P, 8.63. H NMR (THF-d8): δ 245 (br, w1/2
)
240 Hz, 8 H, BH4), 14.73 (dt, J ) 7.3 and 4.8 Hz, 4 H, CH of Ph),
13.42 (t, J ) 7.3 Hz, 4 H, CH of Ph), 12.79 (t, J ) 7.3 Hz, 2 H,
CH of Ph), 6.71 (t, J ) 7.3 Hz, 2 H, CH of Ph), 5.88 (t, J ) 7.3
Hz, 2 H, CH of Ph), 5.49 (m, 8 H, CH of Ph), 4.21 (m, 3 H, CH
of Ph + H4), 1.15 (br s, 2 H, CH of Ph), -1.15 (dt, J ) 7.3 and
(33) Hooft, R. W. W. COLLECT; Nonius BV: Delft, The Netherlands,
1998.
(34) Otwinowski, Z.; Minor, W. Methods Enzymol. 1997, 276, 307.
(35) Sheldrick, G. M. Acta Crystallogr., Sect. A 2008, 64, 112.
(36) Spek, A. L. J. Appl. Crystallogr. 2003, 36, 7.