Easy access to uranium nucleophilic carbene complexes

Article abstract of DOI:10.1039/b926718m

Metathesis reactions of UCl₄ with Li₂C(Ph ₂PS)₂ in Et₂O only afforded the tris-carbene complex [{Li(OEt₂)}₂U{C(Ph₂PS) ₂}₃] (1), while the bis- and mono-carbene compounds [U{C(Ph₂PS)₂}₂(THF)₂] (2) and [{Li(THF)₂}₂U{C(Ph₂PS)₂}Cl ₄] (3) were obtained by treatment of UCl₄ with Li ₂C(Ph₂PS)₂ in a mixture of THF and toluene. The bis-carbene complex 2 was also obtained either from the comproportionation reaction of 1 and UCl₄ or protonolysis reaction of U(NEt ₂)₄ with H₂C(Ph₂PS)₂ and was transformed into the mono-carbene complex [U{C(Ph₂PS) ₂}Cl₂(THF)₂] (4) by further reaction with UCl₄. The utility of these complexes as precursors is illustrated by the synthesis of the biscyclopentadienyl derivative [Cp₂U{C(Ph ₂PS)₂}] (5) by treatment of 3 with TlCp. The crystal structures of [U{C(Ph₂PS)₂}₂(py) ₂]·1.5py·0.5THF and 5·toluene are reported. The Royal Society of Chemistry 2010.

Full text of DOI:10.1039/b926718m

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Easy access to uranium nucleophilic carbene complexes†
Jean-Christophe Tourneux,a Jean-Claude Berthet,*a Pierre Thue´ry,a Nicolas Me´zailles,*b Pascal Le Flochb and
Michel Ephritikhine*a
Received 30th October 2009, Accepted 15th January 2010
First published as an Advance Article on the web 26th January 2010
DOI: 10.1039/b926718m
Metathesis reactions of UCl4 with Li2C(Ph2PS)2 in Et2O
starting material in uranium chemistry, (b) the utility of these com-
=
plexes as precursors with the synthesis of [Cp2U{ C(Ph2PS)2}]
only afforded the tris-carbene complex [{Li(OEt2)}2-
=
(5), (c) the crystal structures of solvates of 2¢ and 5, first examples of
uranium bis-carbene and bis(cyclopentadienyl) uranium carbene
compounds, and (d) the reaction of U(NEt2)4 and H2C(Ph2PS)2
which afforded a mixture of 2 and the mono-carbene complex
U{ C(Ph2PS)2}3] (1), while the bis- and mono-carbene com-
=
=
pounds [U{ C(Ph2PS)2}2(THF)2] (2) and [{Li(THF)2}2U{
C(Ph2PS)2}Cl4] (3) were obtained by treatment of UCl4
with Li2C(Ph2PS)2 in a mixture of THF and toluene. The
bis-carbene complex 2 was also obtained either from the
comproportionation reaction of 1 and UCl4 or protonolysis
reaction of U(NEt2)4 with H2C(Ph2PS)2 and was transformed
=
[U{ C(Ph2PS)2}(NEt2)2] (6).
The syntheses are summarized in Scheme 1.‡ The geminal
dianionic reagent Li2C(Ph2PS)2 was so far used in diethyl ether
or toluene, but not in THF where it is converted into the corre-
sponding monoanion [HC(Ph2PS)2]-.4 Despite its poor solubility
in Et2O, the green solid of UCl4 was reacted with 3 mol equivalents
of Li2C(Ph2PS)2 and after stirring for 2 days at 20 ◦C, was
transformed into the yellow powder of 1.2 After evaporation of
the solvent, extraction with toluene in which it is more soluble,
complex 1 was isolated in 84% yield. Mono- and bis-carbene
complexes were not obtained by treating UCl4 with 1 or 2 mol
equivalents of Li2C(Ph2PS)2 in Et2O as these reactions led to the
sole formation of 1. However, the desired mono- and bis-carbene
compounds could be synthesized by addition of a toluene solution
of Li2C(Ph2PS)2 to a concentrated solution of UCl4 in THF, in a
volume ratio of 5 : 1. Under these conditions, the reactions were
immediate and much faster than the detrimental conversion of
[C(Ph2PS)2]2- into [HC(Ph2PS)2]-. Thus, the bis-carbene complex
2 was readily synthesized from UCl4 and Li2C(Ph2PS)2 in the
molar ratio of 1 : 2; following usual work-up, the dark orange
powder of 2 was obtained in 95% yield. Similar treatment of
UCl4 with 1 mol equivalent of Li2C(Ph2PS)2 afforded a unique
=
into the mono-carbene complex [U{ C(Ph2PS)2}Cl2(THF)2]
(4) by further reaction with UCl4. The utility of these
complexes as precursors is illustrated by the synthesis of
=
the biscyclopentadienyl derivative [Cp2U{ C(Ph2PS)2}] (5)
by treatment of 3 with TlCp. The crystal structures of
=
[U{ C(Ph2PS)2}2(py)2]·1.5py·0.5THF and 5·toluene are re-
ported.
Actinide carbene complexes with significant metal–carbon mul-
tiple bond character are very rare. These were limited to
the tris(cyclopentadienyl) uranium phosphoylide compounds
=
[Cp3U CHP(Me)RR¢] (Cp = h-C5H5), discovered by Gilje
et al. in 1981 and prepared by treatment of [Cp3UCl]
with Li(CH2)(CH2)PRR¢,1 until we recently reported on
the synthesis of the bis(thiophosphinoyl)methanediide com-
=
plexes [M2U{ C(Ph2PS)2}3] [M = U(BH4)3 or Li(OEt2)] and
2
=
[U{ C(Ph2PS)2}(BH4)2(THF)2]. These nucleophilic carbene
complexes were isolated from U(BH4)4 and the geminal dian-
ionic reagent Li2C(Ph2PS)2. However, this synthetic route suf-
fers from a major drawback, that is the use of the uranium
borohydride as the starting material, whose preparation by
the solvent-free reaction of finely powdered UCl4 and LiBH4
in a vacuum vibration ball mill, followed by sublimation, is
somewhat tedious and skill-demanding.3 As such, these uranium
carbene complexes have a limited utility and more practical
precursors for the development of this class of compounds
were clearly desirable. Here we report on (a) the easy and
efficient syntheses of the tris-, bis- and mono-carbene complexes
=
=
[{Li(OEt2)}2U{ C(Ph2PS)2}3] (1), [U{ C(Ph2PS)2}2(L)2] (L =
=
THF, 2 or L = py, 2¢), [{Li(THF)2}2U{ C(Ph2PS)2}Cl4] (3) and
=
[U{ C(Ph2PS)2}Cl2(THF)2] (4) from UCl4, the most familiar
aCEA, IRAMIS, SIS2M, CNRS UMR 3299, 91191, Gif-sur-Yvette, France.
E-mail: jean-claude.berthet@cea.fr, michel.ephritikhine@cea.fr; Fax: +33
169 08 66 40; Tel: +33 169 08 60 42
Scheme 1 Synthesis of the complexes: (i) 3 Li2C(Ph2P)2, Et2O; (ii) 2
Li2C(Ph2P)2, THF–toluene 1 : 5; (iii) 1 Li2C(Ph2P)2, THF–toluene 1 : 5; (iv)
0.5 UCl4, THF; (v) 1 UCl4, THF; (vi) 2 LiCl, THF; (vii) 2 H2C(Ph2PS)2,
THF; (viii) 2 TlCp, THF. X = Cl except for (vii) X = NEt2. The phenyl
rings on the phosphorus atoms are omitted.
bLaboratoire “He´te´roe´le´ments et Coordination”, Ecole Polytechnique,
CNRS, 91128, Palaiseau Ce´dex, France. E-mail: nicolas.mezailles@
polytechnique.edu; Fax: +33 169 33 44 40; Tel: +33 169 33 44 02
† CCDC reference numbers 753015 and 753016. For crystallographic data
in CIF or other electronic format see DOI: 10.1039/b926718m
2494 | Dalton Trans., 2010, 39, 2494–2496
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brown compound which was formulated as the mono-carbene
“ate” complex 3 because of the failure to eliminate LiCl and in
view of the reactions described hereafter.
˚
=
those of 2.323(3) and 2.47(2) A (average) in the seven- and
nine-coordinate complexes [U{ C(Ph2PS)2}(BH4)2(THF)2] and
1, respectively.2 The average U–S distance of 2.91(3) A can
˚
The bis-carbene complex 2 was also obtained from a 1 : 2
mixture of UCl4 and 1 in THF; after 4 h at 20 ◦C, the solvent
was evaporated off and 2 was separated from LiCl by extraction
in toluene; the yield was almost quantitative. Under the same
conditions, the comproportionation reaction between 2 and UCl4
in the 1 : 1 molar ratio quantitatively yielded the mono-carbene
compound 4 which was isolated as an orange powder after
evaporation of THF. Complex 4 was readily transformed into
the “ate” derivative 3 upon addition of 2 mol equivalents of LiCl
(NMR experiment). The structure of 4 is likely to be similar to
that of the borohydride analogue;2 a plausible structure of 3 is
presented in Scheme 1.
be compared with those of 2.88(2) and 3.08(4) in the above
compounds. The U–S–P–C–P–S cores are planar (rms deviations
˚
0.081 and 0.062 A). The planarity at the carbene carbon atoms,
also demonstrated by the sums of the P–C–P and U–C–P angles
being equal to 360◦, shows the donation of both lone pairs from
the dianionic fragment to the metal centre.
That these complexes are useful precursors was indicated by the
synthesis of 5 by reaction of 3 or 4 with two mol equivalents
of TlCp in THF. After 6 h at 20 ◦C and usual work-up, the
orange powder of 5 was isolated in 79% yield and pale orange
crystals of 5·toluene were deposited from a toluene solution.
A view of 5 is shown in Fig. 2 together with selected bond
distances and angles.§ The bis(cyclopentadienyl) complex adopts
the familiar bent-sandwich configuration with the planar U–S–P–
An alternative preparation of
the reaction of the tetraamide precursor U(NEt2)4 with
2
was attempted with
5
2
mol equivalents of H2C(Ph2PS)2 in THF. Such syn-
˚
C–P–S core (rms deviation 0.086 A) lying in the equatorial girdle
thetic route involving protonolysis of [U]–NR2 bonds with
of the Cp2U fragment. The short U–C1 and mean U–S distances
an acidic proton molecule would be similar to that em-
˚
of 2.336(4) and 2.868(2) A are identical to those measured in
6
2
=
ployed for the preparation of [Hf{ C(Ph2PNSiMe3)2}Cl2] and
=
[U{ C(Ph2PS)2}(BH4)2(THF)2].
7
=
[Sm{ C(Ph2PNSiMe3)2}(NCy2)(THF)]. This reaction afforded
after 5 h at 60 ◦C a mixture of 2 and the mono-carbene
=
derivative [U{ C(Ph2PS)2}(NEt2)2] (6) in relative proportions of
73 : 27 (NMR experiments). Although this procedure cannot be
considered as a convenient synthesis of 2, efforts are currently
being made to isolate 6 in a pure form.
Single crystals of 2¢·1.5py·0.5THF were formed by crystal-
lization of 2 from a mixture of pyridine and THF. A view of
2¢ is presented in Fig. 1 together with selected bond distances
and angles.§ The eight-coordinate uranium atom is in a slightly
distorted square antiprismatic environment, the square bases
defined by the N1–S2–N2–S4 and C1–S1–C26–S3 atoms (rms
◦
˚
deviations 0.435 and 0.511 A) forming a dihedral angle of 2.80(5) .
The line passing through the metal centre and perpendicular to
the square bases is a two-fold axis of pseudo-symmetry. The U–C
˚
distances of 2.399(7) and 2.390(8) A are intermediate between
=
Fig. 2 View of [Cp2U{ C(Ph2PS)2}] (5) with displacement ellipsoids
drawn at the 50% probability level. The hydrogen atoms have been
◦
˚
omitted. Selected bond lengths (A) and angles ( ): U–S1 2.8656(11), U–S2
2.8694(12), U–C1 2.336(4), S1–U–C1 68.29(11), S2–U–C1 67.90(11).
In conclusion, we have demonstrated that either mono-, bis
or even tris-carbene complexes of uranium can be conveniently
prepared in good yields from UCl4 either by substitution of the
Cl groups with the methandiide compound Li2C(Ph2PS)2 or by
comproportionation reactions between UCl4 and the tris- or bis-
carbene complexes. These syntheses are straightforward and the
complexes, which are soluble in toluene, are easily separated from
the LiCl by-product. These complexes are valuable precursors for
the enlargement of the family of uranium nucleophilic carbene
compounds, thus permitting further studies of their chemical
=
properties and the nature of the U C bond.
=
Fig. 1 View of [U{ C(Ph2PS)2}2(py)2] (2¢) with displacement ellipsoids
Notes and references
drawn at the 40% probability level. The hydrogen atoms have been
◦
˚
omitted. Selected bond lengths (A) and angles ( ): U–S1 2.892(2), U–S2
2.940(2), U–C1 2.399(7), U–S3 2.876(2), U–S4 2.951(2), U–C26 2.390(8),
U–N1 2.670(7), U–N2 2.683(6), S1–U–C1 66.44(18), S2–U–C1 66.49(19),
S3–U–C26 67.24(19), S4–U–C26 65.79(19), N1–U–N2 83.5(2).
‡ Synthesis and characterization data. All manipulations were carried out
under argon. The 1H and 31P NMR spectra were recorded at 23 ◦C in
THF-d8 on a Bruker DPX 200 spectrometer operating at 200.0 MHz for
1H and 81.0 MHz for 31P; the 1H NMR spectra are referenced internally
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The Royal Society of Chemistry 2010
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using the residual proton solvent resonances relative to tetramethylsilane
(d 0), the 31P NMR chemical shifts are given relative to an 85% H3PO4
external reference.
in THF (10 mL) and Li2C(Ph2PS)2 (30.9 mg, 0.53 mmol) in toluene
(50 mL). After 6 h at 20 ◦C, the solvents were evaporated off and 5 was
extracted with toluene (50 mL) and isolated as a pale orange powder after
evaporation under vacuum (339 mg, 79%). Found: C, 51.17; H, 4.94; P,
7.25. C35H30P2S2U (M = 814.72) requires C, 51.60; H, 3.71; P, 7.60%. 1H
NMR: d 20.63 (t, J = 7.2 Hz, 8H, o-Ph), 11.14 (t, J = 7.2 Hz, 8H, m-Ph),
=
[{Li(OEt2)}2U{ C(Ph2PS)2}3] (1): A flask was charged with UCl4
(282.3 mg, 0.74 mmol) and a Et2O solution (50 mL) of Li2C(Ph2PS)2
prepared in situ from H2C(Ph2PS)2 (1000 mg, 2.23 mmol) and MeLi
(2.79 mL of a 1.6 M solution in Et2O, 4.46 mmol). The reaction mixture 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
1
9.94 (t, J = 7.2 Hz, 4H, p-Ph), -13.60 (s, 10H, Cp). 31P { H} NMR: d
-361.4.
§ Crystal data for 2¢: C69.5H61.5N3.5O0.5P4S4U, M = 1443.87, monoclinic,
1
vacuum (1086 mg, 84%). Complex 1 was characterized by its H and 31P
space group P21/c, a = 13.8488(4), b = 28.6755(15), c = 17.9735(10) A,
˚
◦
NMR spectra and its X-ray crystal structure.2
b = 96.481(3) , V = 7092.1(6) A , Z = 4. Refinement of 847 parameters
3
˚
=
[U{ C(Ph2PS)2}2(THF)2] (2): (a) A solution of Li2C(Ph2PS)2 (120 mg,
on 13 350 independent reflections out of 157 915 measured reflections
0.26 mmol) in toluene (20 mL) was poured with stirring into a solution
of UCl4 (50.0 mg, 0.13 mmol) in THF (4 mL). After 5 min at 20 ◦C, the
solvents were evaporated off, 2 was extracted with toluene (20 mL) and
isolated as a dark orange powder after evaporation under vacuum (159 mg,
95%). Found: C, 55.16; H, 4.53; S, 9.94. C58H56O2P4S4U (M = 1275.25)
(Rint = 0.075) led to R1 = 0.061, wR2 = 0.162, S = 1.047, Drmin
=
-3
˚
-1.49, Drmax = 1.61 e A . Crystal data for 5: C42H38P2S2U, M = 906.81,
monoclinic, space group P21/c, a = 13.0722(6), b = 16.8709(9), c =
◦
3
˚
˚
16.7480(8) A, b = 90.816(3) , V = 3693.2(3) A , Z = 4. Refinement of
425 parameters on 6980 independent reflections out of 108 095 measured
reflections (Rint = 0.043) led to R1 = 0.032, wR2 = 0.074, S = 1.031,
1
requires C, 54.63; H, 4.43; S, 10.06%. H NMR: d 25.72 (s, 16H, o-Ph),
1
12.77 (s, 16H, m-Ph), 11.41 (s, 8H, p-Ph).31P { H} NMR: d -324 (w1/2
=
-3
˚
Drmin = -1.21, Drmax = 0.91 e A . Data were collected at 150(2) K
290 Hz). (b) A flask was charged with 1 (500 mg, 0.29 mmol) and UCl4
(54.6 mg, 0.14 mmol) in THF (30 mL). After 4 h at 20 ◦C, the solvent was
evaporated off, 2 was extracted in toluene (3 ¥ 20 mL) and isolated as a
brown powder after evaporation to dryness (534 mg, 97%). (c) An NMR
tube was charged with U(NEt2)4 (10.8 mg, 0.020 mmol) and H2C(Ph2PS)2
(18.4 mg, 0.041 mmol) in THF (0.35 mL). After 5 h at 60 ◦C, the 1H NMR
on a Nonius Kappa-CCD area-detector diffractometer and processed
with HKL2000.8 Absorption effects were corrected with SCALEPACK.8
The structures were solved by direct methods and refined by full-matrix
least-squares on F2 with SHELXTL.9 All non-hydrogen atoms were
refined with anisotropic displacement parameters. The hydrogen atoms
were introduced at calculated positions. The solvent molecules are badly
resolved in 2¢ and some of them were given 0.5 occupancy factors in order
to retain acceptable displacement parameters.
=
spectrum showed the presence of 2 and [U{ C(Ph2PS)2}(NEt2)2] (6) in
the ratio 73 : 27. 1H NMR of 6: d 49.00 (s, 12H, Me), 18.17 (s, 8H, o-Ph),
14.32 (s, 8H, m-Ph), 12.58 (s, 4H, p-Ph), -17.53 (s, 8H, CH2).
=
[{Li(THF)2}2U{ C(Ph2PS)2}Cl4] (3): A solution of Li2C(Ph2PS)2 (60 mg,
1 R. E. Cramer, R. B. Maynard, J. C. Paw and J. W. Gilje, J. Am. Chem.
Soc., 1981, 103, 3589.
2 T. Cantat, T. Arliguie, A. Noe¨l, P. Thue´ry, M. Ephritikhine, P. Le Floch
and N. Me´zailles, J. Am. Chem. Soc., 2009, 131, 963.
3 V. V. Volkov and K. G. Myakishev, Radiokhimiya, 1980, 22, 745.
4 T. Cantat, L. Ricard, P. Le Floch and N. Me´zailles, Organometallics,
2006, 25, 4965.
5 J. G. Reynolds, A. Zalkin, D. H. Templeton, N. M. Edelstein and L. K.
Templeton, Inorg. Chem., 1976, 15, 2498.
6 R. P. K. Babu, R. McDonald and R. G. Cavell, Chem. Commun., 2000,
481.
7 K. Aparna, M. Ferguson and R. G. Cavell, J. Am. Chem. Soc., 2000,
122, 726.
8 Z. Otwinowski and W. Minor, Methods Enzymol., 1997, 276, 307.
9 G. M. Sheldrick, Acta Crystallogr., Sect. A: Found. Crystallogr., 2008,
64, 112.
0.13 mmol) in toluene (20 mL) was poured with stirring into a solution
of UCl4 (50 mg, 0.13 mmol) in THF (4 mL). After 5 min at 20 ◦C, the
solvents were evaporated off, leaving the dark brown powder of 3 (143 mg,
1
98%). H NMR: d 21.3 (br s, w1/2 = 215 Hz, 8H, o-Ph), 11.68 (s, w1/2
=
30 Hz, 8H, m-Ph), 10.50 (s, w1/2 = 30 Hz, 4H, p-Ph). 31P { H} NMR: the
1
signal was not detected.
=
[U{ C(Ph2PS)2}Cl2(THF)2] (4): A flask was charged with 2 (100 mg,
0.078 mmol) and UCl4 (29.78 mg, 0.078 mmol) in THF (15 mL). After 3 h
at 20 ◦C, the solvent was evaporated off, leaving 4 as an orange powder
(137 mg, 98%). Found: C, 43.94; H, 4.17; S, 6.95. C33H36Cl2O2P2S2U (M =
899.67) requires C, 44.05; H, 4.03; S, 7.13%. 1H NMR: d 17.04 (s, 8H,
o-Ph), 10.87 (t, J = 7 Hz, 8H, m-Ph), 9.88 (t, J = 7 Hz, 4H, p-Ph). 31P
1
{ H} NMR: d -600.1.
=
[Cp2U{ C(Ph2PS)2}] (5): TlCp (283.8 mg, 1.06 mmol) was added to a
solution of 3 prepared as described before from UCl4 (200 mg, 0.53 mmol)
2496 | Dalton Trans., 2010, 39, 2494–2496
This journal is
The Royal Society of Chemistry 2010
©