Uranium(IV) nucleophilic carbene complexes

Article abstract of DOI:10.1021/om200006g

The mono-, bis-, and tris-carbene uranium complexes [Li(THF) ₂U(SCS)Cl₃(THF)] (2a), [U(SCS)₂(THF) ₂] (3a), and [{Li(OEt₂)}₂U(SCS)₃] (1) were synthesized in good yields by reactions of UCl₄ and the stoichiometric amount of Li₂(SCS) [(SCS)^2- = [Ph ₂P(=S)]₂C^2-]. Complex 3a was also obtained by comproportionation reaction of 1 and 0.5 molar equiv of UCl₄ and further reacted with 1 molar equiv of UCl₄ to give the neutral mono-carbene [U(SCS)Cl₂(THF)₂] (5a). Treatment of U(NEt₂)₄ with H₂C(Ph₂PS)₂ in THF led to a mixture of 3a and [U(SCS)(NEt₂)₂] (6), while the same reaction in Et₂O gave the mixed alkyl-carbene compound [U(SCS)(SCHS)(NEt₂)] (7) in 85% yield. The cationic uranium carbene complex [U(SCS)(NEt₂)(THF)₃][BPh₄] (9) was isolated in almost quantitative yield from reaction of [U(NEt₂) ₃][BPh₄] and H₂C(Ph₂PS)₂. Mono-carbenes 2a, 5a, and 9 were used as precursors for the synthesis of Cp and COT derivatives (Cp = C₅H₅, COT=C₈H ₈). Treatment of 2a with 1 or 2 molar equiv of TlCp gave [Tl{U(Cp)(SCS)}₂(μ-Cl)₃] (10) and [U(Cp) ₂(SCS)] (11) in 90% and 79% yield, respectively, whereas [U(Cp*)₂(SCS)] (12) (Cp* = C₅Me₅) was obtained only by reaction of [U(Cp*)₂Cl₂] and Li₂(SCS). Reactions of 5a or 9 with K₂COT gave [U(COT)(SCS)(THF)] (13) in 78% and 99% yield, respectively. 2a, [Li(THF)(Et ₂O)U(SCS)(μ-Cl)₃]₂ (2b), [U(SCS) ₂(py)₂] · 1.5py · 0.5THF (3b · 1.5py · 0.5THF), [U(SCS){CS(Ph₂PS)₂}(py)] (4), 7 3 toluene, [Li(THF)₂U(SCS)(NEt₂)(μ-O)]₂ (8), 10 3 2toluene, 11, 12, and 13 3 0.5pentane were characterized by X-ray diffraction. The crystal data revealed that, in contrast to transition metal complexes, changes in the coordination sphere of the U(IV) center have little influence on the UdC bond. This feature was explained by DFT analysis of analogous U(IV) and Zr(IV) compounds [M(SCS')Cl₂(py)₂] and [M(SCS')(Cp)₂] [M = U, Zr; SCS' = C(H₂PS)₂]. Although the 5f orbitals are more radially contracted than the 6d atomic orbitals, the 5f AOs are lower in energy in uranium and can lead to greater angular overlaps in symmetry-constrained systems. As a result, the seven 5f orbitals play a "buffer" role by engaging in covalent interactions with the carbon center to stabilize the nucleophilic carbene lone pairs.

Full text of DOI:10.1021/om200006g

ARTICLE
pubs.acs.org/Organometallics
Uranium(IV) Nucleophilic Carbene Complexes
†
,†
†
†
Jean-Christophe Tourneux, Jean-Claude Berthet,* Thibault Cantat, Pierre Thu ꢀe ry,
,‡
‡,§
,†
Nicolas M ꢀe zailles,* Pascal Le Floch, and Michel Ephritikhine*
†
CEA, IRAMIS, SIS2M, CNRS UMR 3299, 91191 Gif-sur-Yvette, France
‡
Laboratoire “H ꢀe t ꢀe ro ꢀe l ꢀe ments et Coordination”, CNRS UMR 7653, Ecole Polytechnique, 91128 Palaiseau C ꢀe dex,
§
France Deceased March 17, 2010.
S Supporting Information
b
ABSTRACT: The mono-, bis-, and tris-carbene uranium com-
plexes [Li(THF) U(SCS)Cl (THF)] (2a), [U(SCS) (THF) ]
2
3
2
2
(
3a), and [{Li(OEt )} U(SCS) ] (1) were synthesized in good
2 2 3
yields by reactions of UCl and the stoichiometric amount of
Li (SCS) [(SCS) = [Ph P(dS)] C ]. Complex 3a was also
4
2ꢀ
2ꢀ
2
2
2
obtained by comproportionation reaction of 1 and 0.5 molar
equiv of UCl and further reacted with 1 molar equiv of UCl to
4
4
give the neutral mono-carbene [U(SCS)Cl (THF) ] (5a).
2
2
Treatment of U(NEt ) with H C(Ph PS) in THF led to a
2
4
2
2
2
mixture of 3a and [U(SCS)(NEt ) ] (6), while the same
2
2
reaction in Et O gave the mixed alkyl-carbene compound [U(SCS)(SCHS)(NEt )] (7) in 85% yield. The cationic uranium
2
2
carbene complex [U(SCS)(NEt )(THF) ][BPh ] (9) was isolated in almost quantitative yield from reaction of [U(NEt ) ][BPh ]
2
3
4
2 3
4
and H C(Ph PS) . Mono-carbenes 2a, 5a, and 9 were used as precursors for the synthesis of Cp and COT derivatives (Cp = C H ,
2
2
2
5 5
COT = C H ). Treatment of 2a with 1 or 2 molar equiv of TlCp gave [Tl{U(Cp)(SCS)} (μ-Cl) ] (10) and [U(Cp) (SCS)] (11) in
8
8
2
3
2
9
0% and 79% yield, respectively, whereas [U(Cp*) (SCS)] (12) (Cp* = C Me ) was obtained only by reaction of [U(Cp*) Cl ] and
2 5 5 2 2
Li (SCS). Reactions of 5a or 9 with K COT gave [U(COT)(SCS)(THF)] (13) in 78% and 99% yield, respectively. 2a,
2
2
[
(
Li(THF)(Et O)U(SCS)(μ-Cl) ] (2b), [U(SCS) (py) ] 1.5py 0.5THF (3b 1.5py 0.5THF), [U(SCS){CS(Ph PS) }(py)]
2 3 2 2 2 2 2
3
3
3
3
4), 7 toluene, [Li(THF) U(SCS)(NEt )(μ-O)] (8), 10 2toluene, 11, 12, and 13 0.5pentane were characterized by X-ray
3
2
2
2
3
3
diffraction. The crystal data revealed that, in contrast to transition metal complexes, changes in the coordination sphere of the U(IV)
center have little influence on the UdC bond. This feature was explained by DFT analysis of analogous U(IV) and Zr(IV)
0
0
0
compounds [M(SCS )Cl (py) ] and [M(SCS )(Cp) ] [M = U, Zr; SCS = C(H PS) ]. Although the 5f orbitals are more radially
2
2
2
2
2
contracted than the 6d atomic orbitals, the 5f AOs are lower in energy in uranium and can lead to greater angular overlaps in
symmetry-constrained systems. As a result, the seven 5f orbitals play a “buffer” role by engaging in covalent interactions with the
carbon center to stabilize the nucleophilic carbene lone pairs.
’
INTRODUCTION
are provided by the sole ligand, in contrast to the Fischer- and
Schrock-type carbenes. The bis-phosphorus-stabilized carbene
compounds could therefore be constructed from any electron-
1
Carbene complexes of the d-transition metals occupy a
prominent position in coordination chemistry due to their
fundamental aspects and their extensive utility in organic synth-
esis and catalytic processes. In these complexes, classified as
Fischer- or Schrock-type carbenes depending on the electrophilic
or nucleophilic character of the CR moiety, both the carbenic
and metal fragments bring two electrons to the MdC
interaction. In contrast, the carbene complexes that are not
simple adducts of free stable N-heterocyclic carbene (NHC)
ligands are very rare in the f-element series. This situation is
related to the strong ionic character of the metalꢀligand bond-
ing, with poor covalent contribution and unlikely stabilization of
the carbenic center by π-back-donation from the metal fragment.
In recent years, a new class of metal carbene complexes was
designed and developed with the use of geminal carbon dianions
deficient metal center and, most notably, from oxidized f-element
5
1
ions.
Three different types of geminal dianions, namely, bis(imino-
2
ꢀ
phosphoranyl) methanediides ([Ph P(dNR)] C , named
2
2
2
R
2ꢀ
(
NCN)
2
hereafter), bis(thiophosphinoyl)methanediides
2ꢀ
2ꢀ
1
([Ph P(dS)] C , named (SCS)
hereafter), and bis-
2
2
ꢀ
(
phosphonate)methanediides ([(RO) P(dO)] C ) ligands,
2 2
2
3,4
were used as precursors for the synthesis of carbene complexes.
The use of these ligands for the formation of f-element carbene
complexes was first explored for the lanthanide series with the
synthesis by Cavell et al. of the first structurally characterized
samarium(III) alkylidene complex [Sm{C(Ph PNSiMe ) }
2
3 2
5
stabilized by phosphorus(V) substituents (Scheme 1). In these
complexes, the four electrons of the formal MdC double bond
Received: January 5, 2011
Published: May 06, 2011
r 2011 American Chemical Society
2957
dx.doi.org/10.1021/om200006g
|Organometallics 2011, 30, 2957–2971

Organometallics
ARTICLE
Scheme 1. Phosphorus-Stabilized Geminal Dianions
Scheme 2. Syntheses of Carbene Complexes from UCl4
(
NCy )(THF)], by double deprotonation of the methylene
2
backbone of H C(Ph PNSiMe ) with the tris-amide [Sm-
2
2
3 2
6
(
NCy ) (THF)]. This chemistry was then extended to
2 3
samarium(III), thulium(III), and scandium(III) mono- and bis-
7,8
carbene complexes by Le Floch and co-workers, using the
2ꢀ
SCS ligand and, later on, to yttrium(III), erbium(III), and
9ꢀ11
dysprosium(III) alkyl-carbene complexes
and to larger rare
earth (Ln = La, Ce, Pr, Nd, Sm, and Gd) carbene complexes by the
Liddle and Le Floch groups, using the bis(iminophosphoranyl)
1
2ꢀ15
methanediide backbone.
2
ꢀ
Mes
2ꢀ
Recently, the (SCS) and ( NCN) dianions proved to be
excellent precursors to uranium(IV) nucleophilic carbene com-
plexes, a class of coordination compounds then limited to tris-
(
{
1
cyclopentadienyl) uranium phosphoylide compounds [Cp U
3
0
CHP(Me)RR }] (Cp = η-C H ), discovered by Gilje et al in
5
5
3
981. The bis(thiophosphinoyl)- and bis(iminophospho-
2 Mes
ꢀ
2ꢀ
ranyl)methanediides (SCS) and ( NCN) have been co-
ordinated to uranium(IV) by reactions of their dilithium salts
with U(BH4)4 and UI (THF) , which gave [M U(SCS) ]
3
4
2
3
16
[
[
M = U(BH ) or Li(OEt )], [U(SCS)(BH ) (THF) ], and
4 3 2 4 2 2
Mes 17
U( NCN) ] respectively. However, these synthetic routes
2
16
suffer from major drawbacks that are, for the former, the use of
uranium tetraborohydride as the starting material, whose pre-
18
paration is somewhat tedious and skill-demanding, and, for the
latter, the poor yield, which was accounted for by the detrimental
waste of uranium metal following disproportionation of the
THF, the solvent usually employed for reactions with UCl4.
The mono- and tris-carbene complexes [U(SCS)(BH4)2
17
U(III) intermediate. In this context, our first objective was to
find easy and efficient routes to uranium(IV) carbenes, stemming
from practical starting materials. A second objective was to access
functionalized derivatives in order to investigate the influence
of ancillary ligands in the coordination sphere of the metal
(
THF) ] and [M U(SCS) ] [M = U(BH ) or Li(OEt )] were
2 2 3 4 3 2
16
thus obtained from uranium tetraborohydride. Because of the
tedious preparation of U(BH ) , these complexes cannot be
4
4
considered as practical starting materials for the synthesis of
functional derivatives.
IV
ion on the U dC multiple bond. Here we report on the syn-
2
ꢀ
The reaction chemistry between the lithium salt of (SCS)
thesis of neutral, anionic, and cationic mono-, bis-, and tris-
carbene uranium complexes from UCl , U(NEt ) , and
and UCl has been explored, and the syntheses of the corre-
4
4
2 4
sponding carbene compounds are summarized in Scheme 2.
[
U(NEt ) ][BPh ] and their transformation into cyclopentadie-
2 3 4
19
Despite its poor solubility in diethyl ether, UCl was found to
4
nyl and cyclooctatetraenyl derivatives. We describe the crystal
structures of [Li(THF) U(SCS)Cl (THF)], [Li(THF)(Et O)
react with 1 or 2 molar equiv of Li (SCS), prepared in situ from
2
2
3
2
H C(Ph PS) and MeLi in Et O or toluene. After stirring for 2
2
2
2
2
U(SCS)(μ-Cl) ] , [U(SCS) (py) ], [U(SCS){CS(Ph PS) }
3
2
2
2
2
2
days at 20 ꢀC, the tris-carbene complex [{Li(OEt )} U(SCS) ]
2
2
3
(
(
py)], [U(SCS)(SCHS)(NEt )] [SCHS = CH(Ph PS) ], [Li
2 2 2
(
1) was the sole uranium-containing product observed. By using
THF) U(SCS)(NEt )(μ-O)] , [Tl{U(C H )(SCS)} (μ-Cl) ],
2
2
2
5
5
2
3
the correct 1:3 stoichiometry, the yellow powder of 1 was
isolated with a 84% yield after evaporation of the solvent and
extraction in toluene; this yield is identical to that obtained for
the previously reported synthesis of 1 from U(BH ) . In order
to avoid the detrimental conversion of (SCS) into (SCHS) in
[U(C R ) (SCS)] (R = H, Me), and [U(C H )(SCS)(THF)];
5 5 2 8 8
we compare the structure of the bis(cyclopentadienyl) complex
20
with that of the zirconium analogue and analyze the role of the f
electrons in the UdC interaction by relativistic density functional
theory (DFT) calculations.
1
6
4
4
2
ꢀ
ꢀ
15
THF, the synthesis of the mono- and bis-carbene complexes
was attempted by addition of a toluene solution of the lithium
methanediide Li (SCS) to a concentrated THF solution of the
uranium chloride, in a ca. 5:1 volume ratio. The brown solution
’
RESULTS AND DISCUSSION
2
Carbene Complexes from UCl . In contrast to UCl , ura-
obtained from equimolar amounts of UCl4 and Li (SCS)
4
4
2
nium tetraborohydride, U(BH ) , is quite soluble in toluene and
afforded a unique brown product after evaporation to dryness,
which was formulated as the “ate” compound [Li2
(THF) U(SCS)Cl ] (2) because of the failure to eliminate LiCl.
4
4
diethyl ether and was for this reason first considered as a
precursor for the synthesis of bis(thiophosphinoyl)methanediide
4
4
2
ꢀ
complexes. The lithium salt of the dianion (SCS) is indeed
Crystallization of this complex from a mixture of THF and
very stable in these solvents, whereas it is converted into the
pentane gave red-brown crystals of [Li(THF) U(SCS)
Cl (THF)] (2a), while red crystals of the dimeric complex
3
2
ꢀ
ꢀ
corresponding monoanion [CH(Ph PS) ] ((SCHS) ) in
2
2
2
958
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Organometallics
ARTICLE
Figure 2. View of 2b with displacement ellipsoids at the 30% prob-
ability level. The hydrogen atoms have been omitted. Symmetry
0
code: = 1 ꢀ x, 2 ꢀ y, ꢀz.
Figure 1. View of one of the two independent and quite identical
molecules of 2a with displacement ellipsoids at the 30% probability level.
The hydrogen atoms have been omitted.
Table 1. Selected Bond Lengths (Å) and Angles (deg) for
Complexes 2a and 2b
[
Li(THF)(Et O)U(SCS)(μ-Cl) ] (2b) were obtained by crys-
2 3 2
a
tallization from diethyl ether. Similar treatment of UCl with 2
2a
4
molar equiv of Li (SCS) led to the formation of the first actinide
U(1)ꢀC(1A)
U(1)ꢀS(1A)
U(1)ꢀS(2A)
U(1)ꢀCl(1A)
U(1)ꢀCl(2A)
2.344(13) U(1)ꢀCl(3A)
2.612(4)
1.663(15)
1.690(15)
2.012(5)
2.026(5)
2
bis-carbene compound, [U(SCS) (THF) ] (3a), which was
2
2
2.868(4)
2.865(4)
2.718(4)
2.745(4)
P(1A)ꢀC(1A)
P(2A)ꢀC(1A)
P(1A)ꢀS(1A)
P(2A)ꢀS(2A)
isolated after extraction in toluene as a dark orange powder in
5% yield. These syntheses of 2 and 3a in THF were successful
9
2
ꢀ
because the reaction of the in situ generated (SCS) dianion
with UCl is much faster than its protonation into the corre-
4
C(1A)ꢀU(1)ꢀS(1A) 67.7(4)
C(1A)ꢀU(1)ꢀS(2A) 68.4(4)
Cl(2A)ꢀU(1)ꢀCl(3A) 94.24(13)
O(1A)ꢀU(1)ꢀCl(2A) 76.6(3)
sponding methanide monoanion. In order to circumvent the
2
ꢀ
problematic instability of (SCS) in THF and avoid the use of
solvent mixtures, complex 3a was prepared in a more convenient
way and in almost quantitative yield by in situ deprotonation of
H C(Ph PS) , that is, treatment of a 1:2 mixture of UCl and
S(1A)ꢀU(1)ꢀS(2A)
136.02(10) U(1)ꢀC(1A)ꢀP(1A) 106.0(7)
Cl(1A)ꢀU(1)ꢀCl(2A) 142.4(4)
U(1)ꢀC(1A)ꢀP(2A) 105.5(6)
Cl(1A)ꢀU(1)ꢀCl(3A) 171.95(12) P(1A)ꢀC(1A)ꢀP(2A) 148.4(9)
2
2
2
4
H C(Ph PS) with 4 molar equiv of LiCH SiMe in THF.
2
2
2
2
3
2
b
Orange crystals of a solvate of [U(SCS) (py) ] (3b) were
2
2
obtained by crystallization of 3a from a mixture of pyridine
and THF. Interestingly, complex 3a was found to be heat
sensitive and to decompose when heated in THF or pyridine
solution. Dark orange crystals deposited in one experiment and
revealed the formation of [U(SCS){CS(Ph PS) }(py)] (4),
which formally results from the addition of a sulfur atom to the
UdC bond.
UꢀC(1)
UꢀS(1)
2.321(6)
2.809(2)
UꢀCl(2)
UꢀCl(3)
2.6737(19)
2.6841(19)
UꢀS(2)
2.826(2)
P(1)ꢀC(1)
P(2)ꢀC(1)
P(1)ꢀS(1)
1.676(8)
1.682(7)
2.032(3)
2.014(3)
167.92(6)
75.76(6)
104.9(3)
106.0(3)
148.5(4)
UꢀCl(1)
2.8275(18)
2.7924(19)
2
2
0
b
UꢀCl(1 )
P(2)ꢀS(2)
C(1)ꢀUꢀS(1)
C(1)ꢀUꢀS(2)
S(1)ꢀUꢀS(2)
Cl(1)ꢀUꢀCl(2)
Cl(1)ꢀUꢀCl(3)
69.43(19)
68.33(19)
137.46(6)
84.29(6)
87.31(6)
Cl(2)ꢀUꢀCl(3)
The bis-carbene complex 3a was also obtained in almost
0
Cl(1)ꢀUꢀCl(1 )
quantitative yield from a 1:2 mixture of UCl and 1 in THF;
4
UꢀC(1)ꢀP(1)
UꢀC(1)ꢀP(2)
P(1)ꢀC(1)ꢀP(2)
after 4 h at 20 ꢀC, the solvent was evaporated off and 3a was
separated from LiCl by extraction in toluene. Under the same
conditions, the comproportionation reaction between 3a and
a
b
UCl in a 1:1 molar ratio led to the quantitative formation of the
Data for one of the two independent and quite identical molecules.
Symmetry code: = 1 ꢀ x, 2 ꢀ y, ꢀz.
4
0
neutral monocarbene compound [U(SCS)Cl (THF) ] (5a),
2
2
which was isolated as an orange powder after evaporation of
THF. The pyridine adduct [U(SCS)Cl (py) ] (5b) was ob-
the carbene ligand and Cl(2) and O(1) atoms lying in the
equatorial plane (rms deviation 0.14ꢀ0.15 Å) and Cl(1) and
Cl(3) in axial positions. The planarity of the carbenic fragment is
demonstrated by the sum of the PꢀCꢀP and UꢀCꢀP angles,
which is equal to 360ꢀ. The average UꢀC and UꢀS distances of
2.349(5) and 2.857(10) Å, respectively, are similar to those of
2
2
tained by dissolving 5a in this solvent. Complex 5a was readily
transformed into the “ate” derivative 2 upon addition of 2 molar
equiv of LiCl (NMR experiment).
A view of one of the two independent yet similar molecules in
the crystal of 2a and a view of 2b are presented in Figures 1 and 2,
respectively, and selected bond lengths and angles are listed in
Table 1. The uranium environment in 2a is a slightly distorted
pentagonal bipyramid with the S, P, and central C(1) atoms of
1
6
2.323(3) and 2.88(2) Å found in [U(SCS)(BH ) (THF) ].
4
2
2
The uranium atom in the centrosymmetric dimer 2b is also in a
pentagonal bipyramidal environment with the S, P, and central
2
959
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Organometallics
ARTICLE
Figure 4. View of 4 with displacement ellipsoids at the 30% probability
level. The hydrogen atoms have been omitted.
Figure 3. View of 3b 1.5py 0.5THF with displacement ellipsoids at
the 40% probability level. The hydrogen atoms and lattice solvent
3
3
molecules have been omitted.
the planar tridentate carbene ligand are quite identical to those in
2
a, with a UꢀC bond length of 2.321(6) Å. The LiꢀCl bond
Table 2. Selected Bond Lengths (Å) and Angles (deg) for
Complexes 3b 1.5py 0.5THF, 4, and 7 toluene
lengths, which average 2.390(10) Å in 2a and 2.438(8) Å in 2b,
are smaller than those measured in [LiCl(THF) {U-
2
3
3
3
21a
(
C H CH C H )Cl } ] [average 2.7(1) Å] and [{Li(TM-
5 4 2 5 4 2 2
21b
3
b
4
7
EDA)} U(C Me SiMe C Me )Cl ]
[average 2.49(2) Å],
2
5
4
2
5
4
4
UꢀC(1)
2.399(7)
2.390(8)
2.892(2)
2.940(2)
2.876(2)
2.951(2)
2.374(7)
2.636(7)
2.8634(18)
2.865(2)
2.865(2)
2.964(2)
2.7021(19)
2.569(6)
2.395(5)
where the lithium atoms are linked to four and three Cl atoms,
respectively, and are similar to those found in solvated LiCl
UꢀC(26)
2.819(5)
22
structures (2.33ꢀ2.42 Å).
The crystal structure of 3b 1.5py 0.5THF was described in a
UꢀS(1)
2.8533(14)
2.8556(15)
2.8824(14)
2.8994(17)
UꢀS(2)
3
3
1
9
preliminary communication, and only the major geometrical
parameters will be recalled here and compared with those of the
recently reported uranium(IV) bis-carbene compound
UꢀS(3)
UꢀS(4)
UꢀS(5)
Mes
17
[
U( NCN)2]. A view of 3b is presented in Figure 3, and
UꢀN(1)
2.670(7)
2.683(6)
1.658(8)
1.680(8)
1.681(8)
1.663(8)
2.015(3)
2.019(3)
2.031(3)
2.014(3)
66.44(18)
66.49(19)
67.24(19)
65.79(19)
132.88(6)
132.72(6)
147.6(5)
146.5(5)
106.0(3)
106.2(4)
106.1(4)
107.4(4)
2.159(6)
selected bond lengths and angles are listed in Table 2. The UꢀC
distances of 2.399(7) and 2.390(8) Å in this eight-coordinate
compound, which are intermediate between those measured
in the seven- and nine-coordinate complexes [U(SCS)
UꢀN(2)
P(1)ꢀC(1)
P(2)ꢀC(1)
P(3)ꢀC(26)
P(4)ꢀC(26)
P(1)ꢀS(1)
P(2)ꢀS(2)
P(3)ꢀS(3)
P(4)ꢀS(4)
C(1)ꢀUꢀS(1)
C(1)ꢀUꢀS(2)
C(26)ꢀUꢀS(3)
C(26)ꢀUꢀS(4)
S(1)ꢀUꢀS(2)
S(3)ꢀUꢀS(4)
1.679(7)
1.686(7)
1.744(8)
1.753(7)
2.025(3)
2.027(3)
2.008(3)
1.999(3)
67.92(16)
67.79(17)
67.00(17)
65.54(16)
135.71(6)
126.04(6)
148.9(5)
136.9(4)
105.3(3)
105.6(3)
98.5(3)
1.662(6)
1.668(6)
1.751(6)
1.758(6)
2.036(2)
2.038(2)
2.004(2)
2.003(2)
68.06(13)
68.65(13)
65.73(12)
65.80(12)
135.37(4)
85.49(5)
150.0(4)
123.7(3)
104.7(2)
103.7(2)
92.0(2)
16
(BH ) (THF) ] and 1 [2.323(3) and 2.47(2) Å (average),
4
2
2
respectively], are shorter than those of 2.427(8) and 2.448(9) Å
Mes
17
measured in the six-coordinate complex [U( NCN)2].
While the UꢀSꢀPꢀCꢀPꢀS cores are planar in 3b (rms
Mes
deviations 0.081 and 0.062 Å), the two four-membered
CꢀPꢀNꢀU rings in each carbene ligand of [U( NCN)2]
adopt “open book” conformations with a dihedral angle of ca.
4
7ꢀ. These differences likely reflect the much greater steric
constraints imposed by the C(Ph PNMes) vs C(Ph PS)
2
2
2
2
ligand, due to UꢀN and PꢀN bonds much shorter than UꢀS
and PꢀS bonds and to the presence of bulky Mes substituents
(Mes = 2,4,6-Me C H ) on the coordinated N atoms. Even
3
6 2
though the nonplanarity of the bis(iminophosphoranyl) group
suggested that the formation of UdC double bonds was unlikely,
the manifestation of both σ and weak π components in these
P(1)ꢀC(1)ꢀP(2)
P(3)ꢀC(26)ꢀP(4)
UꢀC(1)ꢀP(1)
UꢀC(1)ꢀP(2)
UꢀC(26)ꢀP(3)
UꢀC(26)ꢀP(4)
1
7
bonds was proposed on the basis of DFT calculations.
A view of 4 is shown in Figure 4, while selected bond lengths
and angles are listed in Table 2. The eight-coordinate uranium
atom is in a very distorted square-antiprismatic environment, the
square bases defined by the N(1)ꢀC(1)ꢀS(2)ꢀS(4) and S-
100.6(3)
93.6(2)
(
1)ꢀS(3)ꢀC(26)ꢀS(5) atoms (rms deviations 0.33 and 0.29
C(1) atoms of the carbene ligand and the bridging Cl(1) and
Å), forming a dihedral angle of 17.2(2)ꢀ. The geometry of the
planar carbene ligand is identical to that found in 2a, 2b, and 3b
with a UꢀC(1) distance of 2.374(7) Å. The UꢀC(26) bond
0
Cl(1 ) atoms in the equatorial plane (rms deviation 0.083 Å) and
Cl(2) and Cl(3) in axial positions. The structural parameters of
2
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length of 2.636(7) Å is much larger, at the upper limit of the
U(NEt ) with 2 molar equiv of H C(Ph PS) in toluene or
2
4
2
2
2
range of typical σ UꢀC distances (2.4ꢀ2.6 Å) of uranium(IV)
THF. After 5 h at 60 ꢀC in THF, a mixture of 3a and the
2
3
alkyl compounds, and can be compared with that of 2.44(1) Å
monocarbene complex [U(SCS)(NEt ) ] (6) in relative propor-
2
2
ꢀ
24
in the thiametallacyclopropane [U(C Me ) (SMe)(SCH )] .
tions of 73:27 was obtained (NMR experiments). The structure
of the products appeared to strongly depend on the nature of the
solvent. A similar reaction carried out in diethyl ether gave a
5
5 2
2
The UꢀS distances of the thiophosphinoyl groups average
2
3
.89(5) Å and are quite similar to those found in 2a, 2b, and
b [2.91(3) Å]. The smaller UꢀS(5) distance of 2.702(2) Å is in
yellow microcrystalline powder of [U(SCS)(SCHS)(NEt )] (7)
2
the range of those determined for terminally coordinated thiolate
ligands, which vary from 2.58(1) Å in [U (S)(S Bu) ] to
2
in 85% yield, after 2 days at 20 ꢀC. Recrystallization from a
t
25
toluene/pentane mixture afforded dark yellow crystals of 7 to-
3
10
3
26
.759(3) Å in [NEt H ][U(SPh) ]. The UꢀS(5)ꢀC(26) ring
luene. Complex 7 is a novel example, the first with an actinide
element, of a mixed alkyl-carbene compound with both metha-
nide and methanediide ligands. This compound is not stable in
THF, being readily converted almost quantitatively into the bis-
2
2
6
is very strained, as shown by the CꢀUꢀS and UꢀSꢀC angles of
9.59(14)ꢀ and 68.2(2)ꢀ, respectively, which are similar to the
corresponding angles of 40.0(3)ꢀ and 64.7(3)ꢀ of the U(SCH )
3
2
ꢀ
24
fragment in [U(C Me ) (SMe)(SCH )] , while the planar
carbene 3a, with loss of free HNEt . Attempts to isolate the
5
5 2
2
2
UꢀS(3)ꢀP(3)ꢀC(26) and UꢀS(4)ꢀP(4)ꢀC(26) rings
form a dihedral angle of 28.29(14)ꢀ. The PꢀC(1) and PꢀS
distances in the SCS ligand, with average values of 1.683(4) and
mono-carbene 6 from reactions of U(NEt ) or [U(NEt ) ]
2
4
2 3
[BPh ] with H C(Ph PS) or Li (SCS), respectively, were un-
4
2
2
2
2
successful. In one of these latter experiments, bright red crystals of
the μ-oxo derivative [Li(THF) U(SCS)(NEt )
2
.026(1) Å, are respectively 0.06 Å smaller and 0.02 Å larger than
2
2
the PꢀC(26) and PꢀS distances in the CS(Ph PS) frag-
(μ-O)] (8) were deposited, obviously resulting from the pre-
sence of adventitious water.
2
2
2
ment. Such variations, which were also measured between the
PꢀC and PꢀN bond lengths of the alkyl and carbene
In contrast to the reactions of U(NEt ) and H C(Ph PS) ,
central
ligands in [Ln{C(Ph PNSiMe ) }{CH(Ph PNSiMe ) }] and
2 4
2
2
2
1
1
reaction of the cationic uranium tris-amide [U(NEt ) ][BPh ]
2 3 4
2
3 2
2
3 2
i
2 2 2 2
i
14
[
Nd{C(Ph PN Pr) }{CH(PPh N Pr) }], reflect the stabiliza-
tion of the two anionic charges of the methanediide ligand by
negative hyperconjugation in the vacant antibonding σ* PꢀN,
1
5
PꢀPh, and PꢀS orbitals.
Mixed Amide-Carbene Complexes from U(NEt ) and
2
4
[
U(NEt ) ][BPh ]. Uranium nucleophilic carbene complexes
2
3
4
R
featuring the ( NCN) and (SCS) ligands are limited to date to
mixed halide-carbene or homoleptic carbene complexes. It is
now of interest to access functional derivatives where the
uranium ion is coordinated to nucleophilic carbene ligands and
to other reactive functions such as amides, organometallic
ligands, etc. In this context, the reaction chemistry between
uranium amide complexes (U(NEt ) and [U(NEt ) ][BPh ])
2
4
2 3
4
and the neutral H C(Ph PS) ligand was investigated
2
2
2
2
7
6
(
(
Scheme 3).
In contrast to [Sm{C(Ph PNSiMe ) }
2 3 2
28
NCy )(THF)] and [Hf{C(R PNSiMe ) }Cl ] (R = Cy, Ph),
2
2
3 2
2
which were obtained by protonolysis of the MꢀNR
2
bonds of [Sm(NCy ) (THF)] and [Hf{N(SiMe ) } Cl ] with
2
3
3 2 2
2
Figure 5. View of 7 toluene with displacement ellipsoids at the 30%
probability level. The hydrogen atoms [except on C(26)] and lattice
3
H C(R PNSiMe ) (R = Cy, Ph) in hot toluene, the bis-carbene
2
2
3 2
complex 3a could not be isolated pure from the reaction of
solvent molecules have been omitted.
a
Scheme 3. Syntheses of Carbene Complexes from U(NEt ) and [U(NEt ) ][BPh ]
2
4
2 3
4
a
Complex 6 was formed only in reaction of U(NEt
2
)
4
and H
2
C(Ph
2
2
PS) in THF.
2
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Scheme 4. Syntheses of Cyclopentadienyl Uranium Carbene
Complexes
Figure 6. View of 8 with displacement ellipsoids at the 30% probability
0
level. The hydrogen atoms have been omitted. Symmetry code: = 1 ꢀ x,
2
ꢀ y, 1 ꢀ z.
Table 3. Selected Bond Lengths (Å) and Angles (deg) for
Complex 8
UꢀC(1)
UꢀS(1)
UꢀS(2)
UꢀN(1)
UꢀO(1)
2.544(5)
2.9509(14)
2.9180(13)
2.230(4)
2.177(3)
2.152(3)
67.18(10)
66.75(12)
122.24(3)
80.00(9)
83.20(8)
87.97(12)
P(1)ꢀC(1)
P(2)ꢀC(1)
P(1)ꢀS(1)
P(2)ꢀS(2)
LiꢀO(1)
1.681(5)
1.662(5)
respectively. These features are explained by the stabilization of
the two lone pairs at C(1) by negative hyperconjugation into the
thiophosphoranyl groups and by electron donation to the metal
center, this latter interaction accounting for the double-bond
character of UꢀC(1) and its reduced bond length compared to
2.0349(16)
2.033(2)
1.828(12)
2.890(12)
92.27(11)
106.49(12)
72.28(15)
138.3(2)
0
a
UꢀO(1 )
LiꢀS(1)
15
C(1)ꢀUꢀS(1)
C(1)ꢀUꢀS(2)
S(1)ꢀUꢀS(2)
S(1)ꢀUꢀO(1)
S(2)ꢀUꢀO(1 )
S(1)ꢀUꢀN(1)
S(2)ꢀUꢀN(1)
O(1)ꢀUꢀN(1)
O(1)ꢀUꢀO(1 )
P(1)ꢀC(1)ꢀP(2)
UꢀC(1)ꢀP(1)
UꢀC(1)ꢀP(2)
UꢀC(26).
A view of the centrosymmetric dimer 8 is shown in Figure 6,
and selected bond lengths and angles are listed in Table 3. The
carbene ligand is not planar, the two UꢀSꢀPꢀC(1) rings
adopting an “open book” conformation with an interplanar angle
of 35.71(10)ꢀ, and the UꢀC(1) distance is larger, by ca. 0.15 Å,
than in the other planar U(SCS) complexes. This difference can
be tentatively explained by the greater electron richness of the
metal center, related to the presence of the electron-donating oxo
and amide ligands, with driving of the negative charge onto the
C(1) atom. The average UꢀO distance of 2.165(12) Å can be
0
0
101.28(18)
102.0(2)
a
0
Symmetry code: = 1 ꢀ x, 2 ꢀ y, 1 ꢀ z.
with 1 molar equiv of H C(Ph PS) in THF was straightforward,
leading to the immediate formation of [U(SCS)(NEt )-
2
2
2
2
t
29
(
THF) ][BPh ] (9), which was isolated as a red powder in
compared with those of 2.12(1) Å in [(C H Bu ) U(μ-O)]
5 3 2 2 2
30
3
4
almost quantitative yield. Complex 9 is the first example of a
cationic uranium carbene complex.
and 2.18(2) Å in [{(Ph N) U(μ-O)] . The LiꢀO(1) distance
2
2
2
of 1.828(12) Å is similar to those of 1.932(10) and 2.013(10) Å
A view of 7 is shown in Figure 5, and selected bond lengths and
angles are presented in Table 2. The complex adopts a distorted
pentagonal-bipyramidal configuration; the equatorial plane de-
fined by the C(1), C(26), S(1), S(2), and S(3) atoms also
contains the P(1) and P(2) atoms of the planar carbene ligand,
and the N(1) and S(4) atoms occupy the axial positions, forming
a N(1)ꢀUꢀS(4) angle of 167.15(17)ꢀ. The UꢀC(26) bond of
the alkyl ligand is much longer, by 0.42 Å, than the UꢀC(1) bond
of the carbene ligand, whose length of 2.395(5) Å is quite similar
to those found in the other [U](SCS) compounds. This
difference is comparable to the 0.54 and 0.27 Å differences
between the LnꢀC distances in the lanthanide complexes
in [U(Me calix)(μ-O)LiCl(THF)] [H Me calix = 25,27-di-
2
2
2
2
31
methoxy-5,11,17,23-tetra-tert-butylcalix[4]arene]. The LiꢀS-
(1) bonding interaction distance is very long, at 2.890(12) Å,
being similar to that of 2.894(5) Å found in [Li(12-crown-4)-
32
(NC H S-2)].
5
4
Cyclopentadienyl and Cyclooctatetraenyl Uranium Car-
bene Complexes. The isolation of the mixed alkyl-carbene
complex 7 demonstrated that uranium(IV) carbene complexes
could support σ-bound organometallic ligands. From this result,
we tried to extend the synthesis of mixed uranium carbene
complexes to π-organometallic compounds. Mono-carbenes 2,
5a, and 9 were used as precursors for the synthesis of Cp and
COT derivatives (Cp = η-C H , COT = η-C H ); the syntheses
[
Ln{C(Ph PNSiMe ) }{CH(Ph PNSiMe ) }] (Ln = La, Ce,
2 3 2 2 3 2
11 i i 14
5
5
8 8
Pr, Sm, Gd) and [Nd{C(Ph PN Pr) }{CH(PPh N Pr) }],
are summarized in Schemes 4 and 5. Treatment of the “ate”
complex 2 with 1 molar equiv of freshly sublimed TlCp in THF
gave the trinuclear compound [Tl{U(Cp)(SCS)} (μ-Cl) ]
2
2
2
2
respectively. In analogy with these complexes, the average PꢀS
distance in the monoanionic fragment is measured at 2.0035(5)
vs 2.037(1) Å in the dianionic unit, and the PꢀC(1) distances are
shorter in the methanediide than the PꢀC(26) in the methanide
fragment, with average values of 1.665(3) and 1.755(4) Å,
2
3
(10), which was isolated as a red powder in 90% yield. Red
crystals of 10 2toluene were obtained by slow diffusion of
3
pentane into a toluene solution. Complex 10 can be seen as
2
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Scheme 5. Syntheses of the Monocyclooctatetraenyl Ura-
nium Carbene Complex 13
Figure 8. View of 12 with displacement ellipsoids at the 50% probability
level. The hydrogen atoms have been omitted.
1
1 toluene were deposited from a toluene solution. In contrast,
3
the bis(pentamethylcyclopentadienyl) analogue [U(Cp*)2
(
SCS)] (12) could not be obtained by treatment of 2 with
Figure 7. View of 10 2toluene with displacement ellipsoids at the 30%
3
KCp* or Mg(Cp*)Cl, but was synthesized by reaction of
[U(Cp*) Cl ] and Li (SCS) in diethyl ether and isolated as
red crystals in 87% yield.
probability level. The hydrogen atoms and lattice solvent molecules have
0
been omitted. Symmetry code: = ꢀx, 1 ꢀ y, ꢀz.
2
2
2
A view of 10 is shown in Figure 7, and selected bond lengths
and angles are presented in Table 4. The two U(Cp)(SCS) units
are bridged by the three Cl atoms, and the thallium atom is
attached to Cl(1) and the S(2) and S(4) atoms of the SCS
ligands. The plane defined by Tl, Cl(1), Cl(2), and Cl(3) is a
pseudo plane of symmetry (rms deviation 0.005 Å), which is
perpendicular to the plane defined by U(1), U(2), Cl(1), C(1),
and C(26) (rms deviation 0.029 Å); the latter is another pseudo
plane of symmetry of the complex with the exception of the Tl
atom, which is out of this plane at a distance of 2.978(5) Å and is
Table 4. Selected Bond Lengths (Å) and Angles (deg) for
Complex 10 2toluene
3
U(1)ꢀC(1)
2.359(6)
U(2)ꢀC(26)
U(2)ꢀS(3)
U(2)ꢀS(4)
ÆU(2)ꢀC(Cp)æ
U(2)ꢀCl(1)
U(2)ꢀCl(2)
U(2)ꢀCl(3)
TlꢀS(4)
2.379(6)
U(1)ꢀS(1)
2.8804(17)
2.9237(16)
2.731(5)
2.8908(18)
2.9341(16)
2.737(14)
2.8468(15)
2.8510(16)
2.8440(15)
3.2132(16)
3.4511(16)
1.692(6)
U(1)ꢀS(2)
ÆU(1)ꢀC(Cp)æ
U(1)ꢀCl(1)
2.8565(15)
2.8631(15)
2.8422(15)
3.2576(16)
3.0579(16)
1.673(6)
U(1)ꢀCl(2)
0
U(1)ꢀCl(3)
linked to the S(4 ) atom of an adjacent complex. Such com-
TlꢀS(2)
pounds where thallium(I) coordinates to metal-bound halide
ions to form soluble coordination compounds are quite uncom-
0
a
TlꢀCl(1)
TlꢀS(4 )
33
mon and have been obtained by serendipity. The TlꢀCl(1)
P(1)ꢀC(1)
P(3)ꢀC(26)
distance of 3.0579(16) Å compares with those of 3.0556(11) and
P(2)ꢀC(1)
1.684(6)
P(4)ꢀC(26)
1.667(6)
3
3
3
.0260(11) Å in [TlCr(C Ph )Cl(μ-Cl) ] and 2.9157(13) Å
5 5 2 2
t
P(1)ꢀS(1)
2.018(2)
P(3)ꢀS(3)
2.016(2)
in [Tl{Ru(CtC Bu)(dcypb)} (μ-Cl) ] (dcypb = 1,4-bis-
2
3
P(2)ꢀS(2)
2.030(2)
P(4)ꢀS(4)
2.043(2)
34
(
3
dicyclohexylphosphino)butane). The TlꢀS distances of
35
C(1)ꢀU(1)ꢀS(1)
C(1)ꢀU(1)ꢀS(2)
S(1)ꢀU(1)ꢀS(2)
P(1)ꢀC(1)ꢀP(2)
U(1)ꢀC(1)ꢀP(1)
U(1)ꢀC(1)ꢀP(2)
U(1)ꢀCl(1)ꢀU(2)
U(1)ꢀCl(3)ꢀU(2)
67.15(15)
66.67(15)
132.56(5)
145.4(4)
C(26)ꢀU(2)ꢀS(3)
C(26)ꢀU(2)ꢀS(4)
S(3)ꢀU(2)ꢀS(4)
P(3)ꢀC(26)ꢀP(4)
U(2)ꢀC(26)ꢀP(3)
U(2)ꢀC(26)ꢀP(4)
U(1)ꢀCl(2)ꢀU(2)
S(2)ꢀTlꢀS(4)
Cl(1)ꢀTlꢀS(4)
67.02(16)
66.12(16)
132.46(5)
146.8(4)
.2132(16), 3.2576(16), and 3.4511(16) Å are similar to those
measured in the polysufide Tl (S ), which vary from 3.04(3) to
2
5
3
.47(3) Å. The uranium atoms are heptacoordinate, considering
that the Cp ring occupies a single coordination site, and the
environment geometry is a distorted pentagonal bipyramid, with
Cl(2), Cl(3), and the S and C atoms of their SCS ligand defining
the equatorial basis, and Cl(1) and the ring centroid are in axial
positions. The geometrical parameters of the planar SCS ligands
are identical to those previously observed. The UꢀC(Cp) and
bridging UꢀCl distances, which average 2.734(11) and 2.851(7)
Å, respectively, are unexceptional and can be compared with
those of 2.67(2) and 2.78(3) Å in the hexacoordinate anion
105.9(3)
104.6(3)
107.3(3)
108.5(3)
93.31(5)
93.08(5)
93.68(4)
112.02(4)
75.72(4)
Cl(1)ꢀTlꢀS(2)
74.94(4)
a
0
Symmetry code: = ꢀx, 1 ꢀ y, ꢀz.
ꢀ
the assemblage of the expected monocyclopentadienyl uranium
carbene [U(Cp)(SCS)Cl] with half the quantity of the bypro-
duct TlCl. The same reaction with 2 molar equiv of TlCp gave a
pale orange powder of the biscyclopentadienyl complex
[{U(Cp)Cl } (μ-Cl) ] or those of 2.73(3) and 2.83(6) Å in
the hexacoordinate cation [{U(Cp) (μ-Cl)} (μ -Cl) ].
2
2
3
3
6
2
3
3
2
The crystal structure of 12, shown in Figure 8, is quite
similar to that of 11, which was described in a preliminary
19
[
U(Cp) (SCS)] (11) in 79% yield, and pale orange crystals of
communication, with the planar UꢀSꢀPꢀCꢀPꢀS core
2
2
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ARTICLE
Table 5. Selected Bond Lengths (Å) and Angles (deg) for
Complexes 11 and 12
1
1
12
UꢀC(1)
2.336(4)
2.8656(11)
2.8694(12)
2.73(3)
2.396(4)
UꢀS(1)
2.8637(10)
2.8588(11)
2.79(2)
UꢀS(2)
ÆUꢀC(Cp)æ
P(1)ꢀC(1)
1.684(4)
1.678(5)
2.0344(16)
2.0352(16)
68.29(11)
67.90(11)
135.33(3)
119.7
1.674(4)
P(2)ꢀC(1)
1.681(4)
P(1)ꢀS(1)
2.0235(16)
2.0232(14)
67.49(10)
67.91(10)
135.35(3)
127.3
P(2)ꢀS(2)
C(1)ꢀUꢀS(1)
C(1)ꢀUꢀS(2)
S(1)ꢀUꢀS(2)
centroidꢀUꢀcentroid
P(1)ꢀC(1)ꢀP(2)
UꢀC(1)ꢀP(1)
UꢀC(1)ꢀP(2)
Figure 9. View of 13 0.5pentane with displacement ellipsoids at the
147.1(3)
106.1(2)
106.7(2)
150.7(3)
3
3
0% probability level. The hydrogen atoms and lattice solvent molecules
104.91(19)
104.38(18)
have been omitted.
Table 6. Selected Bond Lengths (Å) and Angles (deg) for
(
rms deviation 0.075 Å) lying in the equatorial girdle of the bent-
sandwich U(Cp*)2 fragment. The geometrical parameters
Table 5) reveal only two significant differences concerning
the UꢀC(carbene) and UꢀC(ring) distances, which are ca.
.05 Å larger in 12; these variations obviously reflect the greater
Complex 13 0.5pentane
3
UꢀC(1)
2.351(8)
2.909(2)
2.906(2)
2.70(2)
P(1)ꢀC(1)
P(2)ꢀC(1)
P(1)ꢀS(1)
P(2)ꢀS(2)
1.686(8)
1.692(8)
2.027(3)
2.017(3)
(
UꢀS(1)
0
UꢀS(2)
ÆUꢀC(COT)æ
UꢀO(1)
C(1)ꢀUꢀS(1)
C(1)ꢀUꢀS(2)
UꢀC(1)ꢀP(1)
steric hindrance and electron-donating capacity of the Cp* ligand
compared to the Cp ring. It is noteworthy that the UꢀC(1)
2.475(6)
67.68(19)
67.80(19)
106.2(3)
(
2.336(4) Å) and UꢀS distances (2.87 Å av) in 11 are
S(1)ꢀUꢀS(2)
P(1)ꢀC(1)ꢀP(2)
UꢀC(1)ꢀP(2)
126.04(6)
139.6(5)
105.8(4)
respectively only 0.08 and 0.11 Å larger than the ZrꢀC(1) and
20
ZrꢀS distances in the isostructural zirconium analogue, while
4þ
4þ 37
the ionic radius of U is 0.26 Å larger than that of Zr
.
A
purely ionic bond model cannot account for such differences and
would predict a UdC bond distance of about 2.52 Å. In addition,
the UdC bond length in 11 is equivalent to that measured in the
other uranium(IV) monocarbene complexes 2a, 2b, 4, 7, 10, and
[Li(THF) U(COT)(SCS)Cl] since it was also formed from
13 upon addition of LiCl.
x
A view of 13 is shown in Figure 9, and selected bond lengths
and angles are listed in Table 6. The uranium atom is in a
distorted square-pyramidal arrangement, considering the C H
1
3 (2.36 Å av), showing that the ligand field around the
uranium(IV) ion has no influence on the UdC bond. In contrast,
a bond elongation of 0.08 Å was observed upon replacing the
chloride ligands in [Zr(SCS)Cl (py) ] (ZrꢀC = 2.172(2) Å)
8
8
ring as a monodentate ligand, a configuration that is classical for
40
2
2
five-coordinate monoCOT uranium compounds. The square
base defined by C(1), O(1), S(1), and S(2) (rms deviation
0.108 Å) forms a dihedral angle of 5.1(4)ꢀ with the planar COT
ligand (rms deviation 0.011 Å). As observed with 8 and in
contrast to the other U(SCS) complexes, the UꢀSꢀPꢀCꢀPꢀS
core in 13 deviates from planarity, with a dihedral angle of
30.62(12)ꢀ between the two UꢀSꢀPꢀC(1) rings of the carbene
ligand. However, the UꢀC(1) and UꢀS distances, as well as the
PꢀC(1) and PꢀS distances, are not significantly different from
those measured in the other planar carbene complexes reported
here and are in favor of the covalent nature of the metalꢀcarbene
interaction. The average UꢀC(COT) and the UꢀO(1) dis-
tances of 2.70(2) and 2.475(6) Å are unexceptional.
by cyclopentadienyl ligands (ZrꢀC = 2.251(2) Å in [Zr-
(
Cp) (SCS)]), pointing to a noticeable influence of the coordi-
2
nation sphere in the transition metal complexes. These findings
prompted us to carry out a theoretical study on the bonding
interactions in analogous uranium(IV) and zirconium(IV) com-
plexes (vide infra).
Although the chemistry of the monocyclooctatetraenyl ura-
nium compounds has been significantly developed during the last
3
8
years, dialkyl complexes of general formula [U(COT)R ]
2
3
9
remain very rare. It was thus of interest to introduce the
carbene ligand in the series of monoCOT uranium complexes.
The monocyclooctatetraenyl compound [U(COT)(SCS)
(
THF)] (13) was synthesized by metathesis reaction of 5a and
Theoretical Investigation. Previous studies have shown that
2
ꢀ
K2COT in THF (Scheme 5); after filtration, evaporation of the
solvent, and extraction in toluene, the red-brown powder of 13
was isolated with a 78% yield, and red-orange crystals of
the geminal dianion (SCS) behaves as a carbene precursor
because of the presence of two lone pairs on the central carbon
atom able to transfer electron density upon coordination to an
electron-deficient metal center (such as zirconium(IV) or
1
3 0.5pentane were obtained from a mixture of THF and
3
5
2
pentane. Complex 13 was alternatively prepared in almost
uranium(IV)). Donation from the sp lone pair to a metal
vacant orbital accounts for the establishment of the MdC σ-
bond, whereas the MdC π-bond results from an electron
transfer from the carbon 2p lone pair (Scheme 6). The
quantitative yield by treatment of 9 with K COT in THF.
Reaction of 2 with 1 molar equiv of K COT in THF led to the
formation of a compound formulated as the “ate” complex
2
2
2
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Organometallics
ARTICLE
2
ꢀ
complexes formed from coordination of the (SCS) ligand to an
oxidized metal center therefore present a metalꢀcarbon multiple
bond. Detailed descriptions of the chemical bonding in geminal
difference in reactivity between the different types of carbene
complexes.
16
In order to gain insight into the bonding scheme between the
5ꢀ20
2ꢀ
dianions and their complexes are available in the literature.
uranium ion and the SCS ligand in the new uranium(IV)
Because the two carbon lone pairs are stabilized by the
phosphorus(V) centers (by electrostatic interactions and negative
complexes 1ꢀ13, the electronic structure of model uranium
complexes was studied computationally, using density functional
theory methods. This investigation is aimed at answering two
fundamental questions: (i) How does the UdC bonding inter-
action in the uranium complexes compare with that in analogous
transition metal complexes? (ii) Why is the UdC left unchanged
upon modification of the coordination sphere around the
metal ion?
For comparing the electronic structure of these new uranium-
(IV) nucleophilic carbene complexes with transition metal
analogues, the electronic structure of complexes IꢀIV, in which
the phenyl rings were replaced by H atoms, was investigated
2ꢀ
hyperconjugation) in the geminal dianion (SCS) and its
complexes, the complexes are better described as carbene com-
plexes rather than alkylidene complexes. Indeed, for carbene
complexes, the carbene center is stabilized by the metal ion and
donation from the substituents on the C atom. In contrast, in
alkylidene complexes stability of the carbene center is completely
ensured by the sole metal ion. Since carbene complexes usually
refer to Fisher-type complexes that are electrophilic, we named
complexes resulting from coordination of geminal dianions,
2ꢀ
such as (SCS) , “nucleophilic carbene complexes” to mark the
(
Scheme 7). This simplification was validated in the past for
16,20
transition metal and actinide complexes.
Two different
Scheme 6. Formation of a MdC Double Bond upon Coor-
dination of the Geminal Dianion (SCS) to an Electron-
Deficient Metal Center
ligand sets were chosen to explore the influence of the coordina-
tion environment around the metal on the UdC double bond,
namely, a bis-cyclopentadienyl backbone (complexes II and IV)
and a dichloro/bis-pyridine set (complexes I and III). The choice
of zirconium(IV) (complexes III and IV) was motivated by an
s/p/d valence electronic distribution similar to uranium(IV)
2
ꢀ
IV
0
0
0
IV
0
0
0
2
(
Zr : 5s /5p /4d vs U : 7s /7p /6d /5f ) and the availability
of experimental (including X-ray structures) and theoretical data
19
for complexes analogous to 5 and 11. Complex 5b was not
characterized by X-ray diffraction analysis; however, we assume
Scheme 7. The Model Compounds IꢀIV
Figure 10. Selected KohnꢀSham HOMOs in I.
Table 7. Selected Structural Parameters for IꢀIV
MꢀC bond
length (Å)
PꢀC bond
length (Å)
PꢀS bond
length (Å)
MꢀS bond
length (Å)
PꢀCꢀP bond
angle (deg)
DFT
X-ray
DFT
X-ray
DFT
X-ray
DFT
X-ray
DFT
X-ray
a
I
2.33
2.36
2.21
2.27
2.344(13)
2.336(4)
2.172(2)
2.251(2)
1.69
1.68
1.69
1.68
1.68(av)
1.68(av)
1.68(av)
1.67(av)
2.04
2.05
2.04
2.04
2.02(av)
2.03(av)
2.02(av)
2.02(av)
2.94
2.93
2.78
2.87(av)
2.87(av)
2.69(av)
2.77(av)
144.9
146.7
145.4
148.4(9)
147.1(3)
145.7(1)
145.7(1)
b
II
c
III
d
IV
aꢀd
2.88
19
143.1
20
The structures of IꢀIV are compared respectively to the X-ray crystal structures of 2a (a), 11 (b), [Zr(SCS)Cl (py) ] (c), and [Zr(Cp) (SCS)]
2
2
2
2
0
(
d).
2
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Organometallics
ARTICLE
Figure 11. Natural bond orbitals of the UdC double bond in I.
that the geometric and electronic structures are very similar to
that of 2a given that the ligand environment was observed to
have little influence on the UdC bond in complexes 2ꢀ5. The
optimized geometries for complexes IꢀIV compare very well
with experimental structures derived from X-ray diffraction
(
Table 7).
The electronic structure of I is closely related to that of
16
[
U(SCS)(BH ) (THF) ], reported previously. The highest
4
2
2
occupied molecular orbitals (HOMO and HOMOꢀ2) are singly
occupied and mostly 5f in character, as expected for a uranium-
0
2
(
IV) complex with a high-spin 6d 5f configuration. The other
HOMOs are all doubly occupied and describe the interaction
between the SCS ligand and the UCl (py)2 fragment:
2
HOMOꢀ7, HOMOꢀ6, and HOMOꢀ5 account for the two
UꢀS and the UꢀC σ-bonds, whereas HOMOꢀ4, HOMOꢀ3,
and HOMOꢀ1 describe the UꢀS and UꢀC π-bonds
(
Figure 10). Overall, the electron donation from the chloride,
IV
pyridine, and SCS ligands to the U metal center results in a
Mulliken charge of þ1.2 for the metal ion (vs ꢀ0.6 for the
0.31
1.75
2.75
carbenic center) with a (7s,7p) (6d) (5f)
electronic
configuration (Table 8). These charges point to a covalent
participation of the uranium ion in the stabilization of the
carbene σ and π lone pairs. As depicted in Figure 10, the
KohnꢀSham orbitals describing the uraniumꢀcarbon interac-
tion show an important admixture of the sulfur lone pairs (see
HOMOꢀ4 for example), making it difficult to clearly investigate
the involvement of the uranium valence orbitals in the UdC
double bond. A natural bond orbital (NBO) analysis was thus
performed so as to provide a more localized and chemically
relevant picture of the UdC interaction and to avoid the over-
estimation of covalency usually encountered in Mulliken popula-
tion analysis. As in [U(SCS)(BH ) (THF) ], the Lewis
4
2
2
structure involving a uraniumꢀcarbon double bond is the closest
structure to the fully delocalized complex. The NBOs describing
the UdC double bond involve the two lone pairs on the carbon
atom and uranium hybrid valence orbitals (Figure 11). Donation
2.34
from a carbon sp lone pair (81.7%) to a uranium vacant orbital
18.3%) having 29.4% 6d character and 52.0% 5f character forms
(
the UdC σ-bond. On the other hand, the UdC π-bond is made
of a carbon pure 2p orbital (84.3%) and a metal hybrid orbital
(
15.7%) of 47.6% 6d and 41.7% 5f character. These data clearly
support the formation of a polarized double bond. Interestingly,
the participation of the metal orbitals is similar in the σ- and the
π-bond, showing that both bonds exhibit the same amount of
covalency. The 5f and 6d uranium orbitals have equal weights in
the π-bond with the carbene center (about 45%), whereas the
involvement of 6d orbitals in the UdC σ-bond is less pro-
nounced (about 28% vs 50% 5f character in the metal hybrid
orbital). On the basis of these results, the four electrons of the
UdC double bond distribute as follows in complex I: 0.68
electron is located on uranium, whereas the other 3.32 electrons
are brought by the carbon atom. As the carbon atom retains most
2
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Organometallics
Scheme 8. Schematic Representation of the MetalꢀCarbon Double Bond in Zirconium and Uranium Complexes IꢀIV
ARTICLE
of the electron density, the carbene center is nucleophilic
cyclopentadienyl ligands that destabilize the vacant orbital
involved in the electron donation from the 2p lone pair on the
(
q = ꢀ1.6 vs q = þ0.9). The Wiberg bond index for the
C
U
2
0
UdC bond of 0.88 confirms that, despite the bond polarization,
the bond order is greater in I than in uranium(IV) alkyl
complexes (for example the UꢀC Wiberg bond index in
carbene center to the zirconium(IV) ion (Scheme 8). The
0
electron transfer from the dianionic carbene ligand to the d
metal ion is responsible for the formation of the metalꢀcarbon
double bond. As such, the strength of the double bond depends
on the electron withdrawing character of the metal fragment. The
experimental study of complexes 1ꢀ13 and the electronic
structure analysis of model complexes IꢀIV clearly show that
this rule applies to zirconium(IV) but not to uranium(IV).
Although the 5f orbitals are more radially contracted than the
6d atomic orbitals, the 5f AOs are lower in energy in uranium and
can lead to greater angular overlaps in symmetry-constrained
systems. As a result, the seven 5f orbitals play a “buffer” role by
engaging covalent interactions with the carbon center to stabilize
the nucleophilic carbene lone pairs (Scheme 8, right-hand side).
[U(Cp) (CH ) ] is 0.70).
2 3 2
The electronic structure of I can be compared with that of its
zirconium(IV) analogue III, which is model for
Zr(SCS)Cl (py) ]. Results from the Mulliken and NBO
a
20
[
2
2
analyses are summarized in Table 8. The ZrdC Wiberg bond
index of 0.89 in III clearly suggests similar bonding schemes in
the two complexes. This is further confirmed by the participation
of the carbon and metal valence orbitals in the MdC (M = Zr, U)
σ and π NBOs. Indeed, the UdC π-bond in I has a similar
polarization to the ZrdC π-bond in III, the absence of f orbitals
in the valence shell of zirconium being balanced by a greater
involvement of the metal 4d, 5s, and 5p orbitals.
The influence of the coordination environment around the
metal ion on the metalꢀcarbene interaction has been investi-
gated by studying the effects of replacing the chloride and
pyridine ligands in I and III by a bis-cyclopentadienyl backbone
’
CONCLUSION
In this contribution, we have described simple routes to new
uranium(IV) nucleophilic carbene complexes, from readily avail-
able UCl . Examples include mixed carbene-halide, carbene-
amide, and carbene-organometallic complexes. Together with
crystal data, theoretical calculations show that the UdC multiple
bond presents a covalent character similar to the bonding
situation in transition metal complexes. In addition, the vacant
4
(
II and IV, respectively). The Mulliken and NBO analyses point
out the resistance of the UdC bonding scheme to changes in the
metal coordination sphere: the UdC Wiberg bond index (0.88 in
I vs 0.86 in II), the bond polarization, and the 5f/6d uranium
participation remain unchanged (Table 8). As a result, the
uranium carbon bond distance is left unchanged from I
5
f atomic orbitals on the actinide ion engage in covalent
interactions with the carbene center, so as to better stabilize
the carbene valence orbitals. As a result, and in contrast with
transition metal complexes, changes in the coordination sphere
of the uranium(IV) center have little influence on the UdC
bond. Having in hand a variety of functional carbene complexes,
future developments will focus on their reactivity, with special
attention to their oxidation.
(
2.33 Å) to II (2.36 Å), in excellent agreement with the data
collected by X-ray diffraction for 2a and 11 (Table 7). In contrast,
the same change in coordination environment at the zirconium
center induces an elongation of the ZrꢀC bond from 2.172(2) Å
in [Zr(SCS)Cl (py) ] to 2.251(2) Å in IV. Computationally, this
2
2
stretch is well reproduced (ZrꢀC = 2.21 Å in III vs 2.27 Å in IV)
and the ZrdC Wiberg bond index drops by 10% from III to IV,
pointing to a significant sensitivity of the ZrdC under coordina-
tion changes. Importantly, this stimulus has no effect on the
ZrdC σ-bond; the σZrdC NBO is even slightly more covalent in
IV than in III with a greater participation of zirconium orbitals
’
EXPERIMENTAL SECTION
All reactions were carried out under argon with the rigorous exclusion
of air and water (<5 ppm oxygen or water) using standard Schlenk-vessel
and vacuum line techniques or in a glovebox. Solvents were thoroughly
dried by standard methods and distilled immediately before use. The H
and P NMR spectra were recorded on a Bruker DPX 200 or DRX 300
(19.2% in IV vs 18.2% in III). However, the ZrdC π-bond is
1
clearly weakened in IV, with 90.4% of the corresponding electron
density localized on the C atom (compared to 83.0% in III). This
decrease in covalency was attributed to the presence of the
3
1
1
instrument; the H NMR spectra are referenced internally using the
2
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Organometallics
ARTICLE
residual protio solvent resonances relative to tetramethylsilane (δ 0),
(29.78 mg, 0.078 mmol) in THF (15 mL). After 3 h at 20 ꢀC, the solvent
was evaporated off, leaving 5a as an orange powder. Yield: 137 mg
31
and the P NMR chemical shifts are given relative to an 85% H PO
3
4
external reference; the spectra were recorded in THF-d
8
at 23 ꢀC when
(98%). Anal. Calcd for C33
Found: C, 43.94; H, 4.17; S, 6.95. H NMR: δ 17.04 (s, 8H, o-Ph), 10.87
2 2 2 2
H36Cl O P S U: C, 44.05; H, 4.03; S, 7.13.
1
not otherwise specified. Elemental analyses were performed by Analy-
4
1
42
31
1
tische Laboratorien at Lindlar (Germany). UCl , U(NEt ) ,
(t, J = 7 Hz, 8H, m-Ph), 9.88 (t, J = 7 Hz, 4H, p-Ph). P{ H} NMR: δ
ꢀ600.1. An NMR tube was charged with 5a (10.5 mg, 0.011 mmol) and
4
2 4
4
3
44
15
[
U(NEt ) ][BPh ], [U(Cp*) UCl ], H C(Ph PS) , and solu-
2
3
4
2
2
2
5
2
2
1
tions of Li
2
(SCS) in diethyl ether or toluene were prepared according
8
LiCl (0.5 mg, 0.023 mmol) in THF-d (0.4 mL), and the NMR spectrum
to published methods.
2 4 4
showed the immediate formation of [Li (THF) U(SCS)Cl ]. (b) An
Synthesis of [{Li(OEt )} U(SCS) ] (1). A flask was charged with
NMR tube was charged with 5a (10 mg, 0.011 mmol) in pyridine
(1 mL), and after 10 min at 20 ꢀC, the solvent was evaporated off. The
2
2
3
UCl (282.3 mg, 0.74 mmol) and an Et O solution (50 mL) of Li (SCS)
4
2
2
prepared in situ from H
2
C(Ph
2
PS)
2
(1000 mg, 2.23 mmol) and LiMe
spectrum of the orange residue in Tol-d
8
showed the quantitative
1
(
2.79 mL of a 1.6 M solution in Et
2
O, 4.46 mmol). The reaction mixture
formation of [U(SCS)Cl
2
(py)
2
] (5b). H NMR (Tol-d ): δ 13.01 (br
8
was stirred for 2 d at 20 ꢀC. After evaporation of the solvent, 1 was
extracted with toluene (50 mL) and isolated as a yellow powder after
drying under vacuum. Yield: 1086 mg (84%). Complex 1 was character-
s, w1/2 = 56 Hz, 8H, o-Ph), 9.71 (t, J = 7.2 Hz, 8H, m-Ph), 8.66 (t, J = 6.6
Hz, 4H, p-Ph), 7.74 (m, 1H, py), 7.41 (m, 2H, py), 7.23 (s, 2H, py).
Reaction of U(NEt
) and H C(Ph PS)
. An NMR tube was
C(Ph PS) (18.4
2 4 2 2 2
1
31
ized by its elemental analyses, H and P NMR spectra, and X-ray
charged with U(NEt (10.8 mg, 0.020 mmol) and H
2
)
4
2
2
2
1
6
1
crystal structure. Anal. Calcd for C H Li O P S U: C, 57.30; H,
4
(
mg, 0.041 mmol) in THF (0.35 mL). After 5 h at 60 ꢀC, the H NMR
spectrum of the brown solution showed the presence of 3a and
83
80
2 2 6 6
1
.63; S, 11.06. Found: C, 57.20; H, 4.51; S, 10.99. H NMR: δ 19.78
s, 12H, o-Ph), 11.89 (t, J = 7 Hz, 12H, m-Ph), 10.59 (t, J = 7 Hz, 8H,
p-Ph), 9.61 (s, 12H, o-Ph), 6.54 (t, J = 7 Hz, 12H, m-Ph), 6.40 (t, J = 7 Hz,
H, p-Ph), 3.42 (q, J = 7 Hz, 8H, Et O), 1.16 (t, J = 7 Hz, 12H, Et O).
P{ H} NMR: δ ꢀ562 (w1/2 = 120 Hz).
Synthesis of [Li (THF) U(SCS)Cl ] and Crystals of
1
[U(SCS)(NEt
2
)
2
] (6) in the ratio 73:27. H NMR of 6: δ 49.00
(s, 12H, Me), 18.17 (s, 8H, o-Ph), 14.32 (s, 8H, m-Ph), 12.58 (s, 4H,
3
1
1
6
p-Ph), ꢀ17.53 (s, 8H, CH
2
). P{ H} NMR: δ ꢀ404.1.
2
2
3
1
1
Synthesis of [U(SCS)(SCHS)(NEt )] (7). A flask was charged with
2
U(NEt
)
4
(17.3 mg, 0.032 mmol) and H
C(Ph PS) (29.2 mg, 0.065
2 2 2
2
4
4
2
[
Li(THF) U(SCS)Cl (THF)] (2a) and [Li(THF)(Et O)U(SCS)(μ-
mmol) in Et
2
O (5 mL). After stirring for 2 h at 20 ꢀC, the volume of the
2
3
2
Cl) ] (2b). A solution of Li
2
(SCS) (60 mg, 0.13 mmol) in toluene
orange solution was reduced to 3 mL. The yellow microcrystalline
powder of 7, which was deposited after 2 d at 20 ꢀC, was filtered off and
dried under vacuum. Yield: 32.7 mg (85%). Anal. Calcd for
3
2
(
20 mL) was poured with stirring into a solution of UCl
mmol) in THF (4 mL). After 5 min at 20 ꢀC, the solvents were
evaporated off, leaving the dark brown powder of [Li (THF) U-
SCS)Cl ]. Yield: 143 mg (98%). Despite several attempts, satisfactory
4
(50 mg, 0.13
54 4 4
C H51NP S
U: C, 53.86; H, 4.27; N, 1.16. Found: C, 53.53; H, 4.51;
N, 1.06. H NMR: δ 63.47 (s, 2H, CH ), 45.12 (s, 2H, CH ), 42.63 (s,
6H, CH ), 20.14 (s, 8H, o-Ph), 12.18 (s, 8H, m-Ph), 11.92 (s, 8H, o-Ph),
2
4
1
(
4
2
2
elemental analyses were not obtained; the low values suggest incomplete
combustion of the sample. Anal. Calcd for C H Li O P S U: C, 43.63;
H, 4.64; S, 5.68. Found: C, 34.75; H, 3.88; S, 5.28. H NMR: δ 21.3 (br s,
3
10.48 (s, 4H, p-Ph), 9.06ꢀ6.11 (m, 12H, m- and o-Ph); the methanide
41 52 2 4 2 2
1
31
1
proton of SCHS was not detected. P{ H} NMR: δ 43.17 (P of SCHS),
w
1/2 = 215 Hz, 8H, o-Ph), 11.68 (s, w1/2 = 30 Hz, 8H, m-Ph), 10.50 (s, w1/
ꢀ495 (w1/2 = 219 Hz, P of SCS). Dark yellow crystals of 7 toluene were
3
31
1
=
30 Hz, 4H, p-Ph). P{ H} NMR: the signal was not detected. Red-
obtained by slow diffusion of pentane into a toluene solution. An NMR
2
brown crystals of 2a were obtained by slow diffusion of pentane into a
THF solution of this powder, and red crystals of 2b were formed by
recystallization from diethyl ether.
8
tube was charged with 7 (10 mg) in THF-d (0.4 mL), and after 48 h at
20 ꢀC, the spectrum showed the almost quantitative formation of 3a
with concomitant elimination of HNEt
Crystals of [Li(THF) U(SCS)(NEt
was charged with [U(NEt ][BPh
(0.3 mL), and a solution of Li (SCS) (6.0 mg, 0.013 mmol) in toluene
2
.
Synthesis of [U(SCS) (THF) ] (3a) and Crystals of
2
2
)(μ-O)] (8). An NMR tube
2 2
2
[
U(SCS) (py) ] 1.5py 0.5THF (3b 1.5py 0.5THF). (a) A solu-
2
)
3
4
] (10.1 mg, 0.013 mmol) in toluene
2
2
3
3
3
3
tion of Li
2
(SCS) (600 mg, 1.3 mmol) in toluene (100 mL) was poured
2
with stirring into a solution of UCl (250 mg, 0.65 mmol) in THF
(0.1 mL) was added. The tube was immersed for 2 h in an ultrasound
bath (70 W, 42 kHz), and a brown precipitate was deposited from
the orange solution. After evaporation to dryness, the residue was
dissolved in THF-d (0.4 mL), and the NMR spectrum showed the
8
formation of unidentified products. Bright red crystals of 8 were formed
after 1 week.
4
(20 mL). After 5 min at 20 ꢀC, the solvents were evaporated off, and 3a
was extracted with toluene (30 mL) and isolated as a dark orange powder
after evaporation under vacuum. Yield: 0.804 g (96%). Anal. Calcd for
C H O P S U: C, 54.63; H, 4.43; S, 10.06. Found: C, 55.16; H, 4.53;
5
8 56 2 4 4
1
S, 9.94. H NMR: δ 25.72 (s, 16H, o-Ph), 12.77 (s, 16H, m-Ph), 11.41 (s,
3
1
1
8
H, p-Ph). P{ H} NMR: δ ꢀ324 (w1/2 = 290 Hz).
Synthesis of [U(SCS)(NEt )(THF) ][BPh ] (9). A flask was
2
3
4
(
b) A flask was charged with UCl (100.0 mg, 0.23 mmol) and
4
charged with [U(NEt ) ][BPh ] (200 mg, 0.25 mmol) and H C-
2 3 4 2
H C(Ph PS) (263.2 mg, 0.46 mmol) in THF (25 mL), and LiCH
2 2
(Ph PS) (115.8 mg, 0.25 mmol) in THF (30 mL). After stirring for
2
2
2
2-
SiMe
3
(104.1 mg, 1.10 mmol) was added to the green solution. After
5 min at 20 ꢀC, the red solution was evaporated to dryness, leaving the
3 2-
red powder of 9. Yield: 330 mg (99%). Anal. Calcd for C H BNO P
stirring for 3 h at 20 ꢀC, the reaction mixture was evaporated to dryness
and the orange residue was extracted in toluene (3 ꢁ 10 mL). The
solvent was evaporated off, leaving the dark orange powder of 3a. Yield:
6
5
74
1
S U: C, 60.42; H, 5.77; S, 4.96. Found: C, 59.70; H, 5.69; S, 4.82. H
2
NMR: δ 137.90 (s, 4H, CH ), 53.80 (s, 6H, CH ), 29.98 (s, 8H, o-Ph),
2
3
3
1
1
5
34 mg (98%).
c) A flask was charged with 1 (500 mg, 0.29 mmol) and UCl
54.6 mg, 0.14 mmol) inTHF (30mL). After 4 h at20 ꢀC, the solvent was
14.03 (s, 8H, m-Ph), 12.14 (s, 4H, p-Ph). P{ H} NMR: δ ꢀ122.4.
(
4
Synthesis of [Tl{U(C H )(SCS)} (μ-Cl) ] (10). An NMR tube
5
5
2
3
(
was charged with UCl (25.1 mg, 0.065 mmol) in THF (0.2 mL), and a
4
evaporated off, and 3a was extracted in toluene (3 ꢁ 20 mL) and isolated
as a brown powder after evaporation to dryness. Yield: 534 mg (97%).
Orange crystals of[U(SCS) (py) ] 1.5py 0.5THF (3b 1.5py 0.5THF)
solution of Li (SCS) (30 mg, 0.065 mmol) in toluene (3 mL) was added.
2
After stirring for 5 min at 20 ꢀC, TlCp (17.7 mg, 0.065 mmol) was added.
The tube was immersed for 1 h in the ultrasound bath, and after 8 h at
20 ꢀC, the solution was filtered and evaporated to dryness, leaving the
2
2
3
3
3
3
were formed by crystallization of 3a from a mixture of pyridine and THF,
while a few dark orange crystals of[U(SCS){CS(Ph PS) }(py)] (4) were
2
2
red powder of 10. Yield: 52.9 mg (90%). Red crystals of 10 2toluene
3
obtained when a pyridine solution of 3a was heated for 4 h at 80 ꢀC.
were obtained by slow diffusion of pentane into a toluene solution. Anal.
Synthesis of [U(SCS)Cl (THF) ] (5a) and [U(SCS)Cl (py) ]
2
5b). (a) A flask was charged with 3a (100 mg, 0.078 mmol) and UCl
4
Calcd for C74
3 4 4 2
H66Cl P S TlU : C, 44.56; H, 3.31; S, 6.42. Found: C,
2
2
2
1
(
45.09; H, 3.69; S, 6.01. H NMR: δ 21.11 (s, 8H, o-Ph), 11.61 (s, 8H, m-
2
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31
1
Ph), 10.47 (s, 4H, p-Ph), ꢀ17.27 (s, 5H, Cp). P{ H} NMR: δ ꢀ375
interpretation, and expanded by subsequent Fourier-difference synth-
esis. All structures were refined by full-matrix least-squares on F with
2
(
w
= 54 Hz).
1/2
Synthesis of [U(Cp) (SCS)] (11). TlCp (283.8 mg, 1.06 mmol)
SHELXL-97. All non-hydrogen atoms were refined with anisotropic
displacement parameters. The hydrogen atoms were introduced at
calculated positions and were treated as riding atoms with an isotropic
2
was added into a flask containing a solution of [Li (THF) U(SCS)Cl ]
2
4
4
prepared from UCl
Li (SCS) (30.9 mg, 0.53 mmol) in toluene (50 mL). After 6 h at
0 ꢀC, the solvents were evaporated off and 11 was extracted with
toluene (50 mL) and isolated as a pale orange powder after evaporation
under vacuum. Yield: 339 mg (79%). Anal. Calcd for C35 U: C,
1.60; H, 3.71; P, 7.60. Found: C, 51.17; H, 3.94; P, 7.25. H NMR: δ
0.63 (t, J = 7.2 Hz, 8H, o-Ph), 11.14 (t, J = 7.2 Hz, 8H, m-Ph), 9.94 (t, J =
4
(200 mg, 0.53 mmol) in THF (10 mL) and
displacement parameter equal to 1.2 (CH, CH
) or 1.5 (CH ) times that
2 3
2
2
of the parent atom. Crystal data and structure refinement parameters are
47
given in Table 9. The molecular plots were drawn with SHELXTL.
Special details are as follows:
30 2 2
H P S
1
5
2
7
Compound 2a. Restraints on bond lengths and/or displacement
parameters were applied for the carbon atoms of one THF in
molecule B.
Compound 2b. Restraints on bond lengths and/or displacement
parameters were applied for some atoms in the THF and diethyl ether
molecules.
Compound 4. One aromatic ring was refined as an idealized hexagon,
and restraints on displacement parameters were applied for some
aromatic carbon atoms.
31
1
.2 Hz, 4H, p-Ph), ꢀ13.60 (s, 10H, Cp). P{ H} NMR: δ ꢀ361.4. Pale
orange crystals of 11 toluene were deposited from a toluene solution.
3
Synthesis of [U(Cp*) (SCS)] (12). A flask was charged with
2
H
(
2
C(Ph
216 μL of a 1.6 M solution in Et
solution of Li (SCS) was added [U(Cp*) Cl ] (100 mg, 0.17 mmol)
2
PS)
2
(77 mg, 0.17 mmol) in Et
2
O (2 mL), and LiMe
2
O, 0.34 mmol) was added. To this
2
2
2
dissolvedinEt
for 20 min, and, after filtration, the volume of the solution was reduced to
0 mL. After 1 d at 20 ꢀC, the red crystals of 12 that were deposited were
filtered off and dried under vacuum. Yield: 141.2 mg (87%). Anal. Calcd
for C45 U: C, 56.60; H, 5.28; S, 6.72. Found: C, 55.85; H, 5.28; S,
.38. H NMR: δ 13.30 (s, 8H, o-Ph), 9.75 (s, 8H, m-Ph), 9.28 (t, J =
2
O (20mL). The flaskwas immersedinthe ultrasound bath
Compound 7 toluene. Restraints on displacement parameters were
3
applied for some atoms in the aromatic rings. Two aromatic rings (one in
a ligand and the solvent toluene molecule) were refined as idealized
hexagons. The hydrogen atom bound to C26 was introduced as found
on a Fourier-difference map.
1
50 2 2
H P S
1
6
7
31
1
Compound 8. One carbon atom in one THF molecule is disordered
over two positions, which were refined with occupancy parameters
constrained to sum to unity.
.2 Hz, 4H, p-Ph), 5.70 (s, 15H, Cp*). P{ H} NMR: δ ꢀ665.6.
Synthesis of [U(COT)(SCS)(THF)] (13). (a) A flask was charged
with 5a (200 mg, 0.22 mmol) in THF (50 mL), and a solution of
COT (40.4 mg, 0.22 mmol) in THF (10 mL) was slowly added. After
Compound 10 2toluene. Some voids in the lattice likely indicate the
K
4
2
3
presence of other, unresolved solvent molecules.
h at 20 ꢀC, the solution was filtered to eliminate a small quantity of
Compound 13 0.5pentane. The pentane solvent molecule was
green [U(COT) ] and evaporated to dryness. The red powder was
3
2
given an occupancy factor of 0.5 in order to retain acceptable displace-
ment parameters. Restraints on bond lengths and displacement para-
meters were applied for the atoms of the THF and pentane molecules.
Computational Details. The B3LYP hybrid density functional
was employed to optimize the equilibrium molecular structure of the
model complex I. The Stuttgart RSC 1997 ECP was employed for
uranium, which incorporates scalar relativistic effects and replaces 60
core electrons (complete shells 1s through 4f). The valence electrons are
represented as [8s/7p/6d/4f]; 6-31G* basis sets were used for carbon,
hydrogen, boron, oxygen, phosphorus, and sulfur. The LANL2DZ basis
extracted with toluene (20 mL). After filtration and evaporation, the red
powder of 13 was washed with diethyl ether (15 mL) and dried under
vacuum. Yield: 152.5 mg (80%). Anal. Calcd for C37
H
36OP
2
S
2
U: C,
1.63; H, 4.22; S, 7.45. Found: C, 49.94; H, 4.39; S, 7.29. H NMR: δ
2.68 (s, 8H, o-Ph), 11.29 (s, 8H, m-Ph), 10.22 (s, 4H, p-Ph), ꢀ32.72
1
5
2
(
31
1
s, 8H, COT). P{ H} NMR: δ ꢀ230.6.
b) A flask was charged with 9 (81.5 mg, 0.064 mmol) in THF
20 mL), and K COT (11.8 mg, 0.064 mmol) was added. After stirring
(
(
2
for 2 h, the solution was filtered to eliminate the released salts KNEt
KBPh and then evaporated to dryness, leaving the red powder of 13.
Yield: 55 mg (99%).
c) To a flask containing a toluene/THF solution of [Li (THF)
2
and
4
4
8
set was used for Zr. Harmonic vibrational analysis was performed to
confirm that the structure was a minimum. All calculations were carried
(
2
4
4
9
out using the Gaussian03 suite of codes. The Mulliken population
U(SCS)Cl
slowly added a solution of K
3 mL). The flask was immersed for 10 min in the ultrasound bath, the
4
] (145 mg, 0.13 mmol), prepared as described above, was
50,51
analysis was performed using the AOMIX suite of programs.
2
COT (23.9 mg, 0.13 mmol) in THF
(
solvents were evaporated off, and the residual red powder was extracted
with toluene (10 mL). The solution was further filtered to eliminate a
small quantity of [U(COT) ] and then evaporated to dryness. The red
2
’
ASSOCIATED CONTENT
Supporting Information. Tables of crystal data, atomic
S
b
powder formulated as [Li(THF) U(COT)(SCS)Cl] was washed with
x
positions and displacement parameters, anisotropic displace-
ment parameters, and bond lengths and bond angles in CIF
format. This information is available free of charge via the
Internet at http://pubs.acs.org.
diethyl ether (15 mL) and dried under vacuum. Yield: 75.6 mg (60%
with x = 2). The same product was formed upon addition of LiCl into a
1
solution of 13 in THF-d . H NMR: δ 24.21 (s, 4H, Ph), 16.61 (s, 4H,
8
Ph), 13.42 (s, 4H, Ph), 11.84 (s, 2H, Ph), 8.32 (s, 4H, Ph), 7.18 (s, 2H,
31
1
Ph), ꢀ30.91 (s, 8H, COT). P{ H} NMR: δ ꢀ352.1.
’
AUTHOR INFORMATION
Crystallography. The data were collected on a Nonius Kappa-
45
CCD area detector diffractometer using graphite-monochromated Mo
KR radiation (λ = 0.71073 Å). The crystals were introduced into glass
capillaries with a protecting “Paratone-N” oil (Hampton Research)
coating. The unit cell parameters were determined from 10 frames, then
refined on all data. The data (combinations of j- and ω-scans giving
complete data sets up to θ = 25.7ꢀ and a minimum redundancy of 4 for
Corresponding Author
*
nicolas.mezailles@polytechnique.edu; michel.ephritikhine@cea.fr.
E-mail: jean-claude.berthet@cea.fr; thibault.cantat@cea.fr;
46
’ ACKNOWLEDGMENT
9
0% of the reflections) were processed with HKL2000. Absorption
4
6
effects were corrected empirically with the program SCALEPACK. All
This work was supported by CEA, CNRS, and the Ecole
Polytechnique. We thank CINES for the allowance of computer
time (Project No. c2010086494).
47
structures were solved by direct methods with SHELXS-97, except for
those of 2b and 7 toluene, which were solved by Patterson map
3
2
970
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Organometallics
DEDICATION
ARTICLE
’
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dx.doi.org/10.1021/om200006g |Organometallics 2011, 30, 2957–2971