Multiple syntheses of (C5Me5)3U

Article abstract of DOI:10.1021/om010831t

Several new synthetic routes to the sterically crowded (C₅Me₅)₃U complex have been developed. (C₅Me₅)₃U can be prepared by (a) reaction of [(C₅Me₅)₂UH₂]₂ with tetramethylfulvene, (b) reduction of (C₅Me₅)₂Pb with (C₅Me₅)₂UH(DMPE), (c) reaction of [(C₅Me₅)₂U(L)]⁺ (L = THF, DMPE) with K(18-crown-6)(C₅Me₅), and (d) reaction of [(C₅Me₅)₂U] [BPh₄] with KC₅Me₃. Reaction of (C₅Me₅)₂UH(DMPE) with C₈H₈ forms the product of the (C₅Me₅)₃U/ C₈H₈ reaction, [(C₈H₈)(C₅Me₅)U]₂(C₈ H₈). The X-ray crystal structures of the (C₅Me₅)₂U[N(SiMe₃)₂] and [(C₅Me₅)₂U] [BPh₄] precursors used in this study are reported, as well as the convenient synthesis of a new trivalent uranium precursor, (C₅Me₅)₂UMe₂K.

Full text of DOI:10.1021/om010831t

1050
Organometallics 2002, 21, 1050-1055
Mu ltip le Syn th eses of (C5Me5)3U
William J . Evans,* Gregory W. Nyce, Kevin J . Forrestal, and J oseph W. Ziller
Department of Chemistry, University of California, Irvine, Irvine, California 92697-2025
Received September 18, 2001
Several new synthetic routes to the sterically crowded (C5Me5)3U complex have been
developed. (C5Me5)3U can be prepared by (a) reaction of [(C5Me5)2UH2]2 with tetramethyl-
fulvene, (b) reduction of (C5Me5)2Pb with (C5Me5)2UH(DMPE), (c) reaction of [(C5Me5)2U-
(L)]+ (L ) THF, DMPE) with K(18-crown-6)(C5Me5), and (d) reaction of [(C5Me5)2U][BPh4]
with KC5Me5. Reaction of (C5Me5)2UH(DMPE) with C8H8 forms the product of the (C5Me5)3U/
C8H8 reaction, [(C8H8)(C5Me5)U]2(C8H8). The X-ray crystal structures of the (C5Me5)2U-
[N(SiMe3)2] and [(C5Me5)2U][BPh4] precursors used in this study are reported, as well as
the convenient synthesis of a new trivalent uranium precursor, (C5Me5)2UMe2K.
In tr od u ction
One of the recent advances in the organometallic
chemistry of the pentamethylcyclopentadienyl ligand
has been the synthesis of (C5Me5)3M complexes contain-
ing three of these large moieties. Previously, it was
thought that such a molecule was too sterically crowded
to exist, since the cone angle of (C5Me5)- was thought
to be much larger than the 120° necessary for a (C5-
Me5)3M complex.1 However, syntheses of (C5Me5)3Sm,2
(C5Me5)3Nd,3 (C5Me5)3U,4 (C5Me5)3UX (X ) Cl, F),5 and
(C5Me4R)3La6 (R ) Me, Et, iPr, SiMe3) have shown that
this class of compounds is accessible. Interestingly, once
the existence of (C5Me5)3Sm was established by one
synthetic method2a (eq 1), several other syntheses were
subsequently found (eqs 2-4).2b,3,4 Similarly, formation
of (C5Me5)3UCl via eq 5 led to four other synthetic
routes5 from either (C5Me5)3U4 or [(C5Me5)2UCl]3.10
The only reported synthetic route to (C5Me5)3U is the
reaction of the 1,2-bis(dimethylphosphinoethane) adduct
of a trivalent uranium hydride, (C5Me5)2UH(DMPE),7
with tetramethylfulvene8 (eq 6),4 which is an analogue
of eq 3. Although this route provides (C5Me5)3U in
reasonable yield, the tetramethylfulvene precursor re-
quires several steps to prepare and slowly decomposes
over time.8 Since the multiple electron reduction reac-
tivity discovered so far for (C5Me5)3U5,9 indicates that
this molecule deserves further study, it was desirable
to develop better synthetic routes.
(1) (a) Tolman, C. A. Chem. Rev. 1977, 77, 313. (b) White, D.;
Taverner, B. C.; Leach, P. G. L.; Coville, N. J . J . Comput. Chem. 1993,
14, 1042. (c) Stahl, L.; Ernst, R. D. J . Am. Chem. Soc. 1987, 109, 5673.
(d) Lubben, T. V.; Wolczanski, P. T. J . Am. Chem. Soc. 1987, 109, 424.
(2) (a) Evans, W. J .; Gonzales, S. G.; Ziller, J . W. J . Am. Chem. Soc.
1991, 113, 7423. (b) Evans, W. J .; Forrestal, K. J .; Leman, J . T.; Ziller,
J . W. Organometallics 1996, 15, 527.
(3) Evans, W. J .; Seibel, C. A.; Ziller, J . W. J . Am. Chem. Soc. 1998,
120, 6745.
(4) Evans, W. J .; Forrestal, K. J .; Ziller, J . W. Angew. Chem., Int.
Ed. Engl. 1997, 36, 774.
(5) Evans, W. J .; Nyce, G. W.; J ohnston, M. A.; Ziller, J . W. J . Am.
Chem. Soc. 2000, 122, 12019.
(6) Evans, W. J .; Davis, B. L.; Ziller, J . W. Inorg. Chem. 2001, 40,
6341-6348.
(7) Duttera, M. R.; Fagan, P. J .; Marks, T. J .; Day, V. W. J . Am.
Chem. Soc. 1982, 104, 865.
(8) J utzi, P.; Heidemann, T.; Neuman, B.; Stammler, H. G. Synthesis
1992, 1096.
(9) Evans, W. J .; Nyce, G. W.; Ziller, J . W. Angew. Chem., Int. Ed.
2000, 39, 240.
Since multiple synthetic routes to (C5Me5)3Sm and
(C5Me5)3UCl had been found, other routes to (C5Me5)3U
10.1021/om010831t CCC: $22.00 © 2002 American Chemical Society
Publication on Web 02/14/2002

Multiple Syntheses of (C5Me5)3U
Organometallics, Vol. 21, No. 6, 2002 1051
vacuum to yield [(C5Me5)(C8H8)U]2(C8H8) (24 mg, 88%), identi-
1
fied by H NMR spectroscopy.9
(C5Me5)2U[N(SiMe3)2] (1).13 In an argon-filled glovebox, a
toluene solution of Na[N(SiMe3)2] (27 mg, 0.147 mmol) was
added to a slurry of (C5Me5)2UCl2K (100 mg, 0.147 mmol) in
ca. 5 mL of toluene. After 1 h, the reaction mixture had turned
from green to black. This mixture was then stirred for an
additional 6 h. A white precipitate was removed from the
reaction mixture by centrifugation to yield a black solution.
Toluene was removed by rotary evaporation to yield 1 as a
1
blue-black solid (74 mg, 75%). H NMR (C6D6): δ -5.7 (s, C5-
were sought. We report here four new syntheses of (C5-
Me5)3U, as well as new synthetic and structural data
on three precursors: [(C5Me5)2U[N(SiMe3)2],10 the un-
solvated metallocene cation complex [(C5Me5)2U][BPh4],
and a new U(III) organometallic precursor, (C5Me5)2-
UMe2K.
Me5); -25.5 (br s, N(SiMe3)2, ∆ν1/2 ) 920 Hz). Crystals suitable
for X-ray diffraction were grown by slowly cooling a saturated
hexane solution of 2 to -30 °C.
(C5Me5)2UMe2K (2). In an argon-filled glovebox, potassium
metal (29 mg, 0.742 mmol) was added to a stirred toluene
solution of (C5Me5)2UMe2 (400 mg, 0.742 mmol). After 8 h, a
green precipitate was observed. The reaction mixture was
stirred for an additional 48 h and then filtered to leave 2 as a
pale green powder (407 mg, 95%). 1H NMR (THF-d8): δ -11.9
(s, C5Me5, ∆ν1/2 ) 15 Hz). Only the ring methyl resonances
were located in the 1H NMR spectrum. [(C5Me5)2UMe2K-
(THF)x]: IR (cm-1) 2957 s, 2903 vs, 2853 vs, 2721 w, 1444 s,
1374 m, 1258 m, 1239 m, 1058 vs, 1031 s, 942 m, 903 s, 826
m, 803 m, 664 s. Anal. Calcd for C22H36UK: C, 45.74; H, 6.28;
U, 41.21; K, 6.77. Found: C, 44.56; H, 6.00; U, 42.55, K, 7.05.
[(C5Me5)2U(THF )2][BP h 4] (3).14 In the glovebox, [Et3NH]-
[BPh4] (219 mg, 0.52 mmol) was dissolved in THF and slowly
added to a dark brown stirred solution of 2 (150 mg, 0.26
mmol). Upon addition, gas evolution was immediately observed
and the solution turned emerald green with formation of a
white precipitate. After the mixture was stirred for an ad-
ditional 30 min, the white precipitate was removed by cen-
trifugation. The solvent was removed by rotary evaporation
to yield 3 as an emerald green powder (240 mg, 95%).
Characterization was consistent with literature values.14
(C5Me5)3U fr om 3 a n d K(18-cr ow n -6)(C5Me5). In an
argon-filled glovebox, a green suspension of 3 (104 mg, 0.107
mmol) in 5 mL of benzene was added to a yellow solution of
KC5Me5 (18 mg, 0.106 mmol) and 18-crown-6 (28 mg, 0.106
mmol) in 5 mL of benzene. Upon addition, the solution
immediately turned brown. The reaction mixture was stirred
for 12 h. Centrifugation removed a white precipitate, and the
solvent was removed by rotary evaporation to yield (C5Me5)3U
Exp er im en ta l Section
The complexes described below are extremely air and
moisture sensitive. Syntheses and manipulations of these
compounds were conducted under nitrogen or argon with
rigorous exclusion of air and water by Schlenk, vacuum line,
and glovebox techniques. The argon glovebox used in these
experiments was free of coordinating solvents. Silylated
glassware was prepared using Silaclad (Gelest). (C5Me5)2-
UMe2,11 (C5Me5)2UCl2K,10 (C5Me5)2UH[dmpe],7 [(C5Me5)2UH2]2,11
and Na[N(SiMe3)2]12 were prepared according to literature
procedures. 1,2-Bis(dimethylphosphino)ethane (DMPE) was
dried over sieves and degassed before use. Although all of the
uranium complexes discussed here are paramagnetic, 1H NMR
spectra were recorded on Bruker DRX 400 and GN 500
spectrometers at 25 °C. Infrared spectra were recorded as thin
films on an AST ReactIR 1000 instrument. The extremely air
sensitive organouranium complexes were sent to Analytische
Laboratorien, Lindlar, Germany, for elemental analysis.
(C5Me5)3U fr om [(C5Me5)2UH2]2 a n d Tetr a m eth ylfu l-
ven e. In an argon-filled glovebox, [(C5Me5)2UH2]2 (213 mg,
0.418 mmol) was dissolved in 5 mL of toluene in a glass vial
equipped with a stirbar. Tetramethylfulvene (112 mg, 0.840
mmol) was dissolved in toluene and was slowly added to the
stirred [(C5Me5)2UH2]2 solution. The solution immediately
turned dark brown, and the reaction mixture was stirred for
5 min. The solvent was removed by rotary evaporation to yield
a dark brown powder. Recrystallization of the powder yielded
(C5Me5)3U (135 mg, 50%), identified by 1H NMR spectroscopy.4
(C5Me5)3U fr om (C5Me5)2UH(DMP E) a n d (C5Me5)2P b. In
an argon-filled glovebox, (C5Me5)2UH(DMPE) (50 mg, 0.076
mmol) and (C5Me5)2Pb (18 mg, 0.038 mmol) were combined in
a glass vial equipped with a stirbar. The vial was then wrapped
with aluminum foil. Hexanes (5 mL) were added to the vial,
and the reaction mixture was stirred for 24 h. The solvent was
removed by rotary evaporation, and the reaction mixture was
redissolved in toluene. Centrifugation of the reaction mixture
removed Pb (7.6 mg), and the solvent was removed by rotary
1
(35 mg, 50%), identified by H NMR spectroscopy.4
[(C5Me5)2U(DMP E)][BP h 4] (4).14 In an argon-filled glove-
box, (C5Me5)2UH(DMPE) (95 mg, 0.144 mmol) was partially
dissolved in 5 mL of toluene to form a black solution. Upon
addition of [Et3NH][BPh4] (60 mg, 0.144 mmol) to the reaction
mixture, immediate gas evolution was observed. The reaction
mixture was stirred for an additional 2 h. A green precipitate
was isolated by centrifugation and dried under vacuum to yield
4 (130 mg, 93%) as a light green powder. Characterization was
consistent with literature values.14
(C5Me5)3U fr om 4 a n d K(18-cr ow n -6)(C5Me5). In an
argon-filled glovebox, a green suspension of 4 (143 mg, 0.146
mmol) in 5 mL of benzene was added to a yellow solution of
KC5Me5 (24 mg, 0.14 mmol) and 18-crown-6 (37 mg, 0.14
mmol) in 5 mL of benzene. Upon addition, the solution
immediately turned brown. The reaction mixture was stirred
for 12 h. Centrifugation removed a white precipitate, and the
solvent was removed by rotary evaporation to yield (C5Me5)3U
1
evaporation to yield (C5Me5)3U (45 mg, 92%), identified by H
NMR spectroscopy.4
[(C5Me5)(C8H8)U]2(C8H8) fr om (C5Me5)2UH(DMP E) a n d
C8H8. Addition of C8H8 (24 mg, 0.23 mmol) in an argon-filled
glovebox to a stirred benzene (5 mL) solution of (C5Me5)2UH-
[DMPE] (38 mg, 0.057 mmol) caused an immediate color
change from black to brown. After 3 h, the solvent was
removed by rotary evaporation to yield a tacky brown solid.
The product was washed with hexanes and dried under
1
(63 mg, 70%), identified by H NMR spectroscopy.4
[(C5Me5)2U][BP h 4] (5). In an argon-filled glovebox, [Et3-
NH][BPh4] (357 mg, 0.848 mmol) was added to a slurry of 2
(245 mg, 0.424 mmol) in ca. 10 mL of benzene. The reaction
(10) Fagan, P. J .; Manriquez, J . M.; Marks, T. J .; Day, C. S.; Vollmer,
S. H.; Day, V. W. Organometallics 1982, 1, 170.
(11) Fagan, P. J .; Manriquez, J . M.; Maatta, E. A.; Seyam, A. M.;
Marks, T. J . J . Am. Chem. Soc. 1981, 103, 6650.
(12) Avens, L. R.; Bott, S. G.; Clark, D. L.; Sattelburger, A. P.;
Watkin, J . G.; Zwick, B. D. Inorg. Chem. 1994, 33, 2248.
(13) This is a modification of an existing procedure.10
(14) For alternative syntheses of 3 and 4 see: Boisson, C.; Berthet,
J . C.; Ephritikhine, M.; Lance, M.; Nierlich, M. J . Organomet. Chem.
1997, 533, 7.

1052 Organometallics, Vol. 21, No. 6, 2002
Evans et al.
Ta ble 1. Da ta Collection P a r a m eter sa for
mixture immediately began to turn brown, and gas evolution
was observed. The mixture was stirred for 6 h. A white
precipitate was removed by centrifugation, and the solvent was
removed by rotary evaporation to yield 5 as a brown powder
(291 mg, 83%). 1H NMR (C6D6): δ 4.7 (s, C5Me5, ∆ν1/2 ) 55
(C5Me5)2U[N(SiMe3)2] (1) a n d
[(C5Me5)2U][BP h 4]‚C6H6 (5‚C6H6)
1
5‚C6H6
formula
fw
temp (K)
cryst syst
space group
a (Å)
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
C26H48NSi2U
668.86
163(2)
rhombohedral
R3h
17.7735(4)
17.7735(4)
47.2029(13)
90
90
120
12913.5(5)
18
1.548
C44H50BU‚C6H6
905.79
163(2)
monoclinic
P21/c
10.9677(5)
27.9202(13)
13.5321(7)
90
98.0130(10)
90
4103.3(3)
4
1.466
3.989
1
Hz). Only the ring methyl resonances were located in the H
NMR spectrum. IR (cm-1): 3057 s, 3038 s, 2961 s, 2910 vs,
2856 s, 1961 w, 1903 w, 1884 w, 1818 w, 1590 s, 1478 s, 1432
s, 1378 s, 1378 s, 1316 m, 1262 vs, 1239 vs, 1185 s, 1154 s,
1092 s, 1069 s, 1031 s, 1019 s, 883 m, 841 m, 803 m, 745 m,
702 vs, 679 vs. Anal. Calcd for C44H50UB: C, 63.85; H, 6.09;
U, 28.76. Found: C, 63.15; H, 5.77; U, 29.60.
(C5Me5)3U fr om [(C5Me5)2U][BP h 4] (5). In an argon-filled
glovebox, 5 (150 mg, 0.18 mmol) was combined with 10 mL of
benzene, in a silylated glass vial equipped with a stir bar, to
form a dark brown solution. KC5Me5 (35 mg, 0.19 mmol) was
added to the stirred solution. The reaction mixture was stirred
for 9 h at room temperature. A white precipitate was removed
by centrifugation, and the solvent was removed by rotary
Z
Fcalcd (Mg/m3)
µ (mm-1
)
5.752
0.0220
0.0519
R1
0.0426
0.0887
1
wR2 (I > 2σ(I))
evaporation to yield (C5Me5)3U (98 mg, 85%), identified by H
a
NMR spectroscopy.
Radiation: Mo KR (µ ) 0.710 73 Å). Monochromator: highly
2
oriented graphite. R1 ) ∑||Fo| - |Fc||/∑|Fc|; wR2 ) [∑[w(Fo
Fc2)2]/∑[w(Fo2)2]]1/2
-
X-r a y Da ta Collection , Str u ctu r e Deter m in a tion , a n d
Refin em en t for (C5Me5)2U[N(SiMe3)2] (1). A black crystal
of approximate dimensions 0.16 × 0.17 × 0.23 mm was
mounted on a glass fiber and transferred to a Bruker CCD
platform diffractometer. The SMART15 program package was
used to determine the unit cell parameters and for data
collection (30 s/frame scan time for a sphere of diffraction data).
The raw frame data were processed using SAINT16 and
SADABS17 to yield the reflection data file. Subsequent calcula-
tions were carried out using the SHELXTL18 program. The
systematic absences were consistent with the rhombohedral
space groups R3 and R3h. It was later determined that the
centrosymmetric space group R3h was correct.
The structure was solved by direct methods and refined on
F2 by full-matrix least-squares techniques. The analytical
scattering factors19 for neutral atoms were used throughout
the analysis. Hydrogen atoms were included using a riding
model. At convergence, wR2 ) 0.0541 and GOF ) 1.052 for
271 variables refined against 7061 data (as comparison for
refinement on F, R1 ) 0.0220 for those 6278 data with I >
2.0σ(I)). Experimental parameters for data collection and
structure refinement for 1 are given in Table 1. Selected bond
distances and angles for 1 are given in Table 2.
.
Ta ble 2. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for (C5Me5)2U[N(SiMe3)2] (1)
U-Cnt1a
U-Cnt2b
U-N(1)
U-C(1)
U-C(2)
U-C(3)
U-C(4)
U-C(5)
U-C(11)
U-C(12)
U-C(13)
U-C(26)
2.532
2.523
N-Si(1)
1.696(3)
1.699(3)
1.871(4)
1.874(4)
1.892(4)
1.868(4)
1.869(4)
1.891(4)
2.806(3)
2.787(3)
3.197(4)
N-Si(2)
2.352(2)
2.826(3)
2.816(3)
2.800(3)
2.788(3)
2.783(3)
2.791(3)
2.781(3)
2.808(3)
3.222(4)
Si(1)-C(21)
Si(1)-C(22)
Si(1)-C(23)
Si(2)-C(24)
Si(2)-C(25)
Si(2)-C(26)
U-C(14)
U-C(15)
U-C(23)
Cnt1-U-N
113.1
132.4
114.12(13)
105.8(1)
Cnt2-U-N
114.6
Cnt1-U-Cnt2
Si(1)-N-U
Si(1)-N-Si(2)
Si(2)-N-U
131.36(16)
114.48(13)
106.1(1)
N-Si(1)-C(23)
N-Si(2)-C(26)
a
b
Cnt1 is the centroid of the C(1)-C(5) ring. Cnt2 is the
centroid of the C(11)-C(15) ring.
Ta ble 3. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for [(C5Me5)2U][BP h 4] (5)
X-r a y Da ta Collection , Str u ctu r e Deter m in a tion , a n d
Refin em en t for [(C5Me5)2U][BP h 4]‚C6H6. A brown crystal
of approximate dimensions 0.03 × 0.07 × 0.23 mm was
handled as described for 1. The diffraction symmetry was 2/m,
and systematic absences were consistent with the centrosym-
metric space group P21/c, which was later determined to be
correct. The structure was solved by direct methods and
refined on F2 by full-matrix least-squares techniques. The
analytical scattering factors19 for neutral atoms were used
throughout the analysis. There was one molecule of benzene
solvent per formula unit. Hydrogen atoms were included using
a riding model. At convergence, wR2 ) 0.0887 and GOF )
1.045 for 469 variables refined against 6980 unique data (as
comparison for refinement on F, R1 ) 0.0426 for those 4862
data with I > 2.0σ(I)). The data were very weak. The final
least-squares refinement was limited to data with 0.85 Å
resolution. Experimental parameters for data collection and
U-Cnt1a
U-Cnt2b
U-C(1)
U-C(2)
U-C(3)
U-C(4)
U-C(5)
U-C(23)
B-C(21)
B-C(27)
2.490
2.516
U-C(11)
U-C(12)
U-C(13)
U-C(14)
U-C(15)
U-C(22)
U-C(28)
U-C(29)
B-C(33)
B-C(39)
2.808(7)
2.755(8)
2.755(7)
2.790(7)
2.830(8)
2.857(7)
2.880(7)
3.166(8)
1.619(11)
1.650(11)
2.787(7)
2.746(7)
2.753(7)
2.745(8)
2.796(8)
3.138(8)
1.637(11)
1.637(11)
Cnt1-U-Cnt2
Cnt1-U-C22
Cnt2-U-C23
132.7
101.9
98.1
C22-U-C23
Cnt2-U-C22
Cnt2-U-C23
65.5(2)
116.3
103.7
a
b
Cnt1 is the centroid of the C(1)-C(5) ring. Cnt2 is the
centroid of the C(11)-C(15) ring.
structure refinement for 5 are given in Table 1. Selected bond
distances and angles for 5 are given in Table 3.
(15) SMART Software Users Guide, Version 5.0; Bruker Analytical
X-ray Systems: Madison, WI, 1999.
(16) SAINT Software Users Guide, Version 6.0; Bruker Analytical
X-ray Systems: Madison, WI, 1999.
(17) Sheldrick, G. M. SADABS; Bruker Analytical X-ray Systems,
Inc.; Madison, WI, 1999.
Resu lts
(18) Sheldrick, G. M. SHELXTL, Version 5.10; Bruker Analytical
X-ray Systems, Inc., Madison, WI 1999.
(19) International Tables for X-ray Crystallography; Kluwer Aca-
demic: Dordrecht, The Netherlands, 1992; Vol. C.
New Syn th eses: Tetr a m eth ylfu lven e Rou tes. Re-
action of (C5Me5)2UH(DMPE) with tetramethylfulvene
(TMF) (eq 6) was the first successful synthesis of (C5-

Multiple Syntheses of (C5Me5)3U
Organometallics, Vol. 21, No. 6, 2002 1053
Me5)3U. This route was originally examined in analogy
to the [(C5Me5)2SmH]2-based synthesis of (C5Me5)3Sm
(eq 3). It has now been found that this tetramethylful-
vene route can also provide (C5Me5)3U, starting from
the U(IV) hydride [(C5Me5)2UH2]2,11 in 50% yield (eq 7).
improved synthesis of [(C8H8)(C5Me5)U]2(C8H8), since
reaction times are shorter and the synthesis does not
require the preparation of (C5Me5)3U.
Rea ction s Ba sed on Ca tion ic P r ecu r sor s. After
successfully mimicking the Sm-based reactions de-
scribed above, attention was turned to developing a
route analogous to eq 4, involving the reaction of a
(C5Me5)- salt with a [(C5Me5)2M]+ cation. This cationic
route was used to make (C5Me5)3Nd3 as well as the (C5-
i
Me4R)3La6 complexes (R ) Me, Et, Pr, SiMe3) and
appears to be the best route if an analogue of divalent
(C5Me5)2Sm is unavailable. In the Sm and Nd cases, it
was essential that the cationic precursor, [(C5Me5)2Ln]-
[BPh4], be THF-free, since (C5Me5)3Ln complexes ring-
open THF to form (C5Me5)2Ln[O(CH2)4C5Me5]24,25 and
KC5Me5 reacts with [(C5Me5)2Ln(THF)2]+ to make the
same ring-opened product. However, (C5Me5)3U does not
ring-open THF as readily as (C5Me5)3Sm. Thus, solvated
and unsolvated cations were examined.
One route to an appropriate solvated cationic precur-
sor involves the protonation of (C5Me5)2U[N(SiMe3)2] (1)
with [NH4][BPh4] to make [(C5Me5)2U(THF)2][BPh4]14
(3). Since high yields of this cation were not readily
obtainable in our hands, we questioned the purity of the
(C5Me5)2U[N(SiMe3)2] precursor that we had prepared.
To definitively confirm the identity of the (C5Me5)2U-
[N(SiMe3)2] precursor, the crystal structure of this
complex was determined and is described below. Con-
comitantly, we developed an alternative synthesis of 3
involving the new trivalent precursor (C5Me5)2UMe2K
(2). This complex has not been reported in the literature,
to our knowledge, and can be synthesized in high yield
by reacting (C5Me5)2UMe2 11 with potassium in toluene
or benzene (eq 10). Although this compound was not
The mechanism of this reaction is unknown, but the
insertion of TMF into one of the UIV-H bonds to form
a (C5Me5)- ring may lead to the reductive elimination
of hydrogen to generate the U(III) product, (C5Me5)3U.
Reductive elimination of hydrogen from U(IV) hydride
complexes to yield U(III) products has been observed
in other systems.11,20-22
(C5Me5)2P b As a Rea gen t. To mimic the reductive
route used in the (C5Me5)2Sm/(C5Me5)2Pb reaction (eq
2), the reduction of (C5Me5)2Pb with (C5Me5)2UH-
(DMPE) was studied. The U(III) reduction of (C5Me5)2-
Pb could form (C5Me5)3UH, in direct analogy to eq 2, or
it could generate hydrogen and (C5Me5)3U directly. No
evidence for the formation of (C5Me5)3UH was observed,
but the (C5Me5)2UH(DMPE)/(C5Me5)2Pb reaction does
produce (C5Me5)3U in 90% yield (eq 8). This constitutes
a third synthetic route to (C5Me5)3U.
(C Me ) UMe K
(C5Me5)2UMe2 + K f
(10)
5
5 2
2
2
characterized by X-ray crystallography, its analytical
data and reactivity are consistent with the formula (C5-
Me5)2UMe2K. Unlike (C5Me5)2UMe2, 2 is insoluble in
arenes and can be easily isolated by filtration or
centrifugation. Protonation of 2 with [Et3NH][BPh4] in
THF afforded 3 in excellent yield.
The reaction of 3 with KC5Me5 in arene solvents does
not yield (C5Me5)3U, perhaps because both reactants are
insoluble. However, addition of 18-crown-6 partially
solubilizes KC5Me5 in arene solvents26 and allows (C5-
Me5)3U to be made by this route in 50% yield (eq 11).
Cycloocta tetr a en e a s a Rea gen t. The original
synthesis of (C5Me5)3Sm involved Sm(II) reduction of
1,3,5,7-cyclooctatetraene (eq 1). The analogous reduction
using (C5Me5)2UH(DMPE) did not form (C5Me5)3U but
instead gave [(C8H8)(C5Me5)U]2(C8H8) (eq 9), the product
obtained by reacting (C5Me5)3U with cyclooctatetraene.23
Although eq 9 is not a new route to (C5Me5)3U, it is an
Interestingly, small amounts of THF do not prevent the
isolation of (C5Me5)3U.
An alternative solvated cation approach involved the
cation formed by the reaction of (C5Me5)2UH(DMPE)
(20) Ossola, F.; Brianese, N.; Porchia, M.; Rossetto, G.; Zanella, P.
J . Chem. Soc., Dalton Trans. 1990, 877.
(21) Marks, T. J .; Seyam, A. M.; Kolb, J . R. J . Am. Chem. Soc. 1973,
95, 5529.

1054 Organometallics, Vol. 21, No. 6, 2002
Evans et al.
with [Et3NH][BPh4] to form [(C5Me5)2U(DMPE)][BPh4]14
(4). Complex 4 also reacts with K(18-crown-6)(C5Me5),
in toluene, to produce (C5Me5)3U in 70% yield (eq 12).
[(C5Me5)2U(DMPE)][BPh4] +
K(18-crown-6)(C5Me5)
8
-K(18-crown-6)(BPh4),
-DMPE
(C5Me5)3U (12)
The synthesis of (C5Me5)3U from an unsolvated cation
required that a synthetic route to the unsolvated cat-
ionic precursor, [(C5Me5)2U][BPh4], be developed. Al-
though 2 and [Et3NH][BPh4] are both insoluble in arene
solvents, they react cleanly to form [(C5Me5)2U][BPh4]
(5) and KBPh4 (eq 13). 5 is soluble in benzene and can
F igu r e 1. Plot of (C5Me5)2U[N(SiMe3)2] (1), with thermal
ellipsoids drawn at the 50% probability level.
U(III) and Sm(III), the only M(III) comparison possible
for these elements in the table of Shannon radii.29
Hence, 1 has U-(C5Me5) ring centroid distances of 2.523
and 2.532 Å compared to 2.470 and 2.479 Å in 6 and
the M-N distances are 2.352(2) and 2.301(3) Å, respec-
tively. Like 6, 1 contains small N-Si-C angles which
are often associated with agostic M-H-CH2-Si or
M-C-Si interactions in N(SiMe3)2 complexes.30-33 The
105.78(14)° N-Si(1)-C(23) and 106.09(15)° N-Si(2)-
C(26) angles are both smaller than the other N-Si-C
angles in 1, which range from 113.16(17) to 115.1(2)°.
However, the U-C(23) and U-C(26) distances,
3.197(4) and 3.222(4) Å, respectively, are not close to
the very short 2.80(2) and 2.86(2) Å U-C distances
noted for two of the silylmethyl carbon atoms in (C5-
Me5)U[N(SiMe3)2]2.34 Hence, the situation is like that
in 6, in which small angles do not correlate with close
Sm-C contacts.
be separated from the insoluble KBPh4 byproduct. As
described below, the X-ray structure of the unsolvated
cation 5 was also determined to see how the anion
approached the metallocene cation.
The cationic complex 5 reacts with KC5Me5 in benzene
to form (C5Me5)3U, but the yield was <20%. Recently,
in investigations of cationic routes to (C5Me4R)3La
complexes, we have found that, for some (C5Me4R)3La
complexes,6 it was beneficial to conduct the reaction in
silylated glassware. When silylated glassware was used,
the (C5Me5)3U yield was improved to 85% (eq 14).
[(C5Me5)2U][BPh4] (5; Figure 2) cocrystallized with
C6H6 as (C5Me5)2U][BPh4]‚C6H6 and hence is not iso-
morphous with the Sm analogue [(C5Me5)2Sm][BPh4]
(7).35 However, the two structures are similar. The
(28) den Haan, K. H.; de Boer, J . L.; Teuben, J . H.; Spek, A. L.;
Kojick-Prodic, B.; Hays, G. R.; Huis, R. Organometallics 1986, 5, 1726.
(29) Shannon, R. D. Acta Crystallogr., Sect. A 1976, 32, 751.
(30) (a) Tilley, T. D.; Andersen, R. A.; Spencer, H.; Ruben, A.; Zalkin,
D. H. Templeton, B. Inorg. Chem. 1980, 2999. (b) Tilley, T. D.;
Andersen, R. A.; Zalkin, A. Inorg. Chem. 1984, 23, 2271. (c) Boncella,
J . M.; Andersen, R. A. Organometallics 1985, 4, 205. (d) Tilley, T. D.;
Andersen, R. A.; Zalkin, A. J . Am. Chem. Soc. 1982, 104, 3725. (e)
Tilley, T. D.; Zalkin, A.; Andersen, R. A.; Templeton, D. H. Inorg. Chem.
1981, 20, 551.
(31) (a) Evans, W. J .; Drummond, D. K.; Zhang, H.; Atwood, J . L.
Inorg. Chem. 1988, 27, 575. (b) Evans, W. J .; J ohnston, M. A.; Clark,
R. D.; Anwander, R.; Ziller, J . W. Polyhedron 2001, 20, 2483-2490.
(32) (a) Van der Sluys, W. G.; Burns, C. J .; Sattelberger, A. P.;
Watkin, J . G.; Zwick, B. D. Inorg. Chem. 1994, 33, 2248. (b) Clark, D.
L.; Miller, M. M.; Watkin, J . G. Inorg. Chem. 1993, 32, 772. (c)
Barnhart, D. M.; Clark, D. L.; Grumbine, S. K.; Watkin, J . G. Inorg.
Chem. 1995, 34, 1695.
(33) (a) Van der Heijden, H.; Schaverien, C. J .; Orpen, A. G.
Organometallics 1989, 8, 255. (b) Schaverien, C. J .; Van der Heijden,
H.; Orpen, A. G. Polyhedron 1989, 8, 1850. (c) Schaverien, C. J .
Organometallics 1994, 13, 69. (d) Schaverien, C. J .; Nesbitt, G. J . J .
Chem. Soc., Dalton Trans. 1992, 157. (e) Klooster, W. T.; Brammer,
L.; Schaverien, C. J .; Budzelaar, P. H. M. J . Am. Chem. Soc. 1999,
121, 1381.
(34) Avens, L. R.; Burns, C. J .; Butcher, R. J .; Clark, D. L.; Gordon,
J . C.; Schake, A. R.; Scott, B. L.; Watkin, J . G.; Zwick, B. D.
Organometallics 2000, 19, 451.
Str u ctu r a l Stu d ies. (C5Me5)2U[N(SiMe3)2] (1; Figure
1) was found to be isomorphous with (C5Me5)2Sm-
[N(SiMe3)2]27 (6), which is similar to but not isomor-
phous with (C5Me5)2Y[N(SiMe3)2].28 All of the distances
in 1 are about 0.05 Å longer than those in 6, which is
close to the 0.067 Å difference between six-coordinate
(22) For stable tris(cyclopentadienyl)uranium(IV) hydride complexes
see: Berthet, J .-C.; Le Mare´chal, J .-F.; Lance, M.; Nierlich, M.; Vigner,
J .; Ephritikhine, M. J . Chem. Soc., Dalton Trans. 1992, 1573.
(23) Evans, W. J .; Nyce, G. W.; Ziller, J . W. Angew. Chem., Int. Ed.
2000, 39, 240-242.
(24) Evans, W. J .; Ulibarri, T. A.; Chamberlin, L. R.; Ziller, J . W.
Organometallics 1990, 9, 2124.
(25) Evans, W. J .; Forrestal, K. J .; Ziller, J . W. J . Am. Chem. Soc.
1998, 120, 9273.
(26) Neander, S.; Tio, F. E.; Buschmann, R.; Behrens, U.; Olbrich,
F. J . Organomet. Chem. 1999, 582, 58.
(27) Evans, W. J .; Keyer, R. A.; Ziller, J . W. Organometallics 1993,
12, 2618.

Multiple Syntheses of (C5Me5)3U
Organometallics, Vol. 21, No. 6, 2002 1055
Direct analogues of the reductive reactions used to make
(C5Me5)3Sm from the Sm(II) precursors (eqs 1 and 2)
were not possible, since U(II) precursors are unavail-
able. However, reductive approaches using U(III) reduc-
ing agents are successful because of the tendency of
U(IV) hydrides to form U(III) complexes. Hence, the
U(III) product, (C5Me5)3U, can be obtained using the
U(III) hydride precursor (C5Me5)2UH(DMPE) to reduce
(C5Me5)2Pb (eq 8) in a reaction with similarities to the
(C5Me5)2Sm(OEt2) reduction in eq 2. The U(IV) hydride
to U(III) conversion can also be used to make trivalent
(C5Me5)3U from the U(IV) hydride [(C5Me5)2UH2]2 and
tetramethylfulvene (eq 7).
The remaining new syntheses are based on the
trivalent cationic precursors [(C5Me5)2U]+, which are
formally similar to the samarium and neodymium
systems.3 Subtle differences arise, since (C5Me5)3U is
more THF tolerant than (C5Me5)3Sm; thus, a THF-
solvated uranium cation is a suitable precursor to the
synthesis of (C5Me5)3U (eq 11). Solubility problems of
the solvated uranium cations can be overcome by using
the 18-crown-6 solubilized K(C5Me5) (eqs 11 and 12).
The reaction of the unsolvated [(C5Me5)2U][BPh4] with
K(C5Me5) (eq 14) is analogous to the samarium case,
except that silylated glassware was needed to obtain
high yields.
The synthesis of [(C5Me5)2U][BPh4] required the
development of a new trivalent uranium compound, (C5-
Me5)2UMe2K. Since (C5Me5)2UMe2K and [(C5Me5)2U]-
[BPh4] are readily synthesized and easily isolated, these
compounds are the most convenient precursors for the
synthesis of (C5Me5)3U. Hence, eq 14 is the preferred
synthesis of all those discovered so far.
F igu r e 2. Plot of [(C5Me5)2U][BPh4] (5), with thermal
ellipsoids drawn at the 50% probability level.
2.77(3) Å U-C(C5Me5) average distance is as expected
compared to the 2.70(2) Å Sm analogue, when the
differences in ionic radii are taken into account. The
132.7° (C5Me5)-U-(C5Me5) ring centroid angle is also
similar to the 134.4° value in 7.
In each of these complexes, the [BPh4]- approaches
the cation through two ortho carbon positions, C(22) and
C(28). For 5, these 2.857(7) and 2.880(7) Å distances are
intermediate between the 2.825(3) and 2.917(3) Å
distances in 7. The next closest U-C(BPh4) distances,
3.138(8) and 3.166(8) Å, for U-C(23) and U-C(29) are
also intermediate between the analogous distances in
7, 3.059(3) and 3.175(3) Å. The 69.3(2)° C(22)-U-C(28)
angle is similar to the 67.8(3)° C(22)-Sm-C(28) angle.
The dihedral angles between the planes defined by U,
C22, C23 and C22, C23, and the C21-C26 arene ring
centroid (128°) and U, C28, C29, and C28, C29, and the
C27-C32 arene ring centroid (122°) show that the arene
rings do not approach the uranium directly via the edge
or face of the ring.
The six C-B-C angles around boron in 5 span a
wider range, 102.2(6)-115.4(6)°, than the 107.5(2)-
110.9(2)° angles in 7. The B-C distances of the inter-
acting rings, B-C(21) and B-C(27), have lengths which
happen to be equivalent, 1.637(11) Å, and are interme-
diate between those of the other rings: B-C(33) )
1.619(11) Å, and B-C(39) ) 1.650(10) Å. Hence, no
effect on the local geometry around the boron is observed
by coordination of the anion to the cation.
Con clu sion
Several synthetic routes to (C5Me5)3U are now avail-
able, just as several have been developed for (C5Me5)3-
Sm and (C5Me5)3UCl. In addition to the new syntheses,
the multiple synthetic connections between uranium
and samarium syntheses shown in this study suggest
that, with the appropriate modifications, analogous
chemistry can be developed between U(III) and Sm(III).
The structural studies on (C5Me5)2U[N(SiMe3)2] and
[(C5Me5)2U][BPh4] also show that similarities exists
between trivalent uranium and trivalent samarium
coordination chemistry.
There are now 13 different reactions that are known
to form (C5Me5)3M complexes, a class of compounds
originally thought to be too crowded to exist. In retro-
spect, most of the routes are quite reasonable, but they
were not attempted most probably due to the expecta-
tion that the products would not be isolable.
Discu ssion
Like (C5Me5)3Sm and (C5Me5)3UCl, (C5Me5)3U can
also be made by several different routes. Syntheses
similar or analogous to three of the four routes to (C5-
Me5)3Sm (eqs 2-4) are available for (C5Me5)3U, even
though Sm(II)/Sm(III) chemistry and U(III)/U(IV) chem-
istry have significant differences. These results suggest
that there may be more connections between samarium
and uranium chemistry, if the appropriate modifications
in procedures and starting materials are made.
Ack n ow led gm en t. We thank the National Science
Foundation for support of this research.
Su p p or tin g In for m a tion Ava ila ble: Tables of crystal-
lographic data and figures giving additional views of com-
pounds 1 and 5. This material is available free of charge via
the Internet at http://pubs.acs.org.
The first synthesis of (C5Me5)3U from a U(III) hydride
and tetramethylfulvene (eq 6) was exactly analogous.
(35) Evans, W. J .; Seibel, C. A.; Ziller, J . W. J . Am. Chem. Soc. 1998,
120, 6745.
OM010831T