Convenient synthesis, structure, and reactivity of (C5Me5)U(CH2C6H5)3 : A simple strategy for the preparation of monopentamethylcyclopentadienyl uranium(IV) complexes

Article abstract of DOI:10.1021/om0206610

A high-yield one-pot synthesis of (C₅Me₅)U(CH₂C₆H₅)₃ has been developed and applied to the synthesis of a new organouranium complex possessing a (pentamethylcyclopentadienyl)bis(cyclopentadienyl) ligand framework, (C₅Me₅)(C₅H₅)₂U(CH₂ C₆H₅). Both complexes have been structurally characterized. We also report herein an improved and safer synthesis for the popular uranium starting material UCU.

Full text of DOI:10.1021/om0206610

5
978
Organometallics 2002, 21, 5978-5982
Con ven ien t Syn th esis, Str u ctu r e, a n d Rea ctivity of
(
C Me )U(CH C H ) : A Sim p le Str a tegy for th e
5
5
2
6
5 3
P r ep a r a tion of Mon op en ta m eth ylcyclop en ta d ien yl
Ur a n iu m (IV) Com p lexes
J aqueline L. Kiplinger,* David E. Morris, Brian L. Scott, and Carol J . Burns*
Chemistry Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545
Received August 14, 2002
A high-yield one-pot synthesis of (C
the synthesis of a new organouranium complex possessing a (pentamethylcyclopentadienyl)-
bis(cyclopentadienyl) ligand framework, (C Me )(C U(CH ). Both complexes have
been structurally characterized. We also report herein an improved and safer synthesis for
5 5 2 6 5 3
Me )U(CH C H ) has been developed and applied to
5
5
5
H
5
)
2
2 6 5
C H
4
the popular uranium starting material UCl .
In tr od u ction
mediated chemistry due to the inherent steric and
electronic unsaturation of the (C5Me5)U framework
relative to the bulkier systems. Evidence for this has
been provided by Marks and co-workers, who demon-
strated that monopentamethylcyclopentadienyl thorium
complexes supported on dehydroxylated alumina show
enhanced catalytic activity compared with supported
bis(pentamethylcyclopentadienyl) thorium and tris(cy-
Organometallic uranium chemistry has been the
subject of an increasing number of investigations over
the past two decades, with pentamethylcyclopentadi-
1
2
enyl and sterically bulky nitrogen donor ligands
frequently being employed as ancillary ligands to both
enhance solubility and define or limit the reactive sites
in these complexes. Whereas systems such as (C5-
4
clopentadienyl) thorium complexes.
1
2
Me5)2U and (R2N)3U have played a prominent role in
these efforts, reports of uranium compounds containing
a single pentamethylcyclopentadienyl ancillary ligand
A convenient entry into the monopentamethylcyclo-
pentadienyl uranium framework might be envisioned
to be (C5Me5)U(CH2C6H5)3, which has been the subject
of only a single investigation described by Marks and
3
are considerably less common. This is unfortunate since
monopentamethylcyclopentadienyl uranium complexes
offer opportunities for the development of new uranium-
5
co-workers in 1982. The previously reported route to
this compound involves a multistep and variable (24-
6
0%) yield synthesis which may present a barrier to the
(
1) (a) Fagan, P. J .; Manriquez, J . M.; Maatta, E. A.; Sayam, A. M.;
development of new chemistry of (C5Me5)U(CH2C6H5)3.
In our ongoing pursuit to develop synthetic entries
toward uranium complexes containing multiply bonded
Marks, T. J . J . Am. Chem. Soc. 1981, 103, 6650-6667. (b) Duttera,
M. R.; Fagan, P. J .; Marks, T. J . J . Am. Chem. Soc. 1982, 104, 865-
8
67. (c) Fagan, P. J .; Manriquez, J . M.; Marks, T. J .; Day, C. S.;
Vollmer, S. H.; Day, V. M. Organometallics 1982, 1, 170-180. (d)
Smith, G. M.; Suzuki, H.; Sonnenberger, D. C.; Day, V. M.; Marks, T.
J . Organometallics 1986, 5, 549-561. (e) Straub, T.; Frank, W.; Reiss,
G. J .; Eisen, M. S. J . Chem. Soc., Dalton Trans. 1996, 2541-2546. (f)
Haskel, A.; Wang, J . Q.; Straub, T.; Neyroud, T. G.; Eisen, M. S. J .
Am. Chem. Soc. 1999, 121, 3025-3034, and references therein. (g)
Ventelon, L.; Lescop, C.; Arliguie, T.; Leverd, P. C.; Lance, M.; Nierlich,
M.; Ephritikhine, M. Chem. Commun. 1999, 659-660.
6
functional groups, we have devised a high-yield, straight-
forward synthesis of (C5Me5)U(CH2C6H5)3. Since (C5-
Me5)U(CH2C6H5)3 provides an attractive entry into both
homogeneous and heterogeneous organouranium chem-
istry, we report the details of our synthesis herein.
Furthermore, we demonstrate that (C5Me5)U(CH2C6H5)3
can be easily tailored and applied to the synthesis of
new uranium(IV) monopentamethylcyclopentadienyl
mixed-ring compounds such as the mixed-ring uranium-
(2) (a) Andersen, R. A. Inorg. Chem. 1979, 18, 1507-1509. (b) Burns,
C. J .; Smith, W. H.; Huffman, J . C.; Sattelberger, A. P. J . Am. Chem.
Soc. 1990, 112, 3237-3239. (c) Nelson, J . E.; Clark, D. L.; Burns, C.
J .; Sattelberger, A. P. Inorg. Chem. 1992, 31, 1973-1976. (d) Avens,
L. R.; Bott, S. G.; Clark, D. L.; Sattelberger, A. P.; Watkins, J . G.;
Zwick, B. D. Inorg. Chem. 1994, 33, 2248-2256. (e) Stewart, J . L.;
Andersen, R. A. Polyhedron 1998, 17, 953-958. (f) Odom, A. L.; Arnold,
P. L. Cummins, C. C. J . Am. Chem. Soc. 1998, 120, 5836-5837. (g)
Meyer, K.; Mindiola, D. J .; Baker, T. A.; Davis, W. M.; Cummins, C.
C. Angew. Chem., Int. Ed. 2000, 39, 3063-3066. (h) Diaconescu, P. L.;
Odom, A. L.; Agapie, T.; Cummins, C. C. Organometallics 2001, 20,
(IV) metallocene complex (C5Me5)(C5H5)2U(CH2C6H5).
In the course of these studies, we found it desirable to
(4) (a) He, M. Y.; Xiong, G.; Toscano, P. J .; Burwell, R. L., J r.; Marks,
T. J . J . Am. Chem. Soc. 1985, 107, 641-652. (b) Eisen, M. S.; Marks,
T. J . J . Am. Chem. Soc. 1992, 114, 10358-10368. (c) Eisen, M. S.;
Marks, T. J . J . Mol. Catal. 1994, 86, 23-50.
(5) Mintz, E. A.; Moloy, K. G.; Marks, T. J .; Day, V. W. J . Am. Chem.
Soc. 1982, 104, 4692-4695.
4
993-4995.
3) (a) Cymbaluk, T. H.; Ernst, R. D.; Day, V. W. Organometallics
983, 2, 963-969. (b) Cramer, R. E.; Mori, A. L.; Maynard, R. B.; Gilje,
(
1
J . W.; Tatsumi, K.; Nakamura, A. J . Am. Chem. Soc. 1984, 106, 5920-
926. (c) Schake, A. R.; Avens, L. R.; Burns, C. J .; Clark, D. L.;
Sattelberger, A. P.; Smith, W. H. Organometallics 1993, 12, 1497-
498. (d) Ephritikhine, M.; Berthet, J . C.; Boisson, C.; Lance, M.;
Nierlich, M. J . Alloys Comp. 1998, 271-273, 144-149. (e) 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,
(6) (a) Arney, D. S. J .; Burns, C. J . J . Am. Chem. Soc. 1995, 117,
9448-9460, and references therein. (b) Warner, B. P.; Scott, B. L.;
Burns, C. J . Angew. Chem., Int. Ed. 1998, 37, 959-960. (c) Duval, P.
B.; Burns, C. J .; Clark, D. L.; Morris, D. E.; Scott, B. L.; Thompson, J .
D.; Werkema, E. L.; J ia, L.; Andersen, R. A. Angew. Chem., Int. Ed.
2001, 40, 3358-3361. (d) Kiplinger, J . L.; Morris, D. E.; Scott, B. L.;
Burns, C. J . Chem. Commun. 2002, 30-31. (e) Kiplinger, J . L.; Morris,
D. E.; Scott, B. L.; Burns, C. J . Organometallics 2002, 21, 3073-3075.
(f) Kiplinger, J . L.; J ohn, K. D.; Morris, D. E.; Scott, B. L.; Burns, C.
J . Organometallics 2002, 21, 4306-4308.
5
1
4
51-457. (f) Evans, W. J .; Nyce, G. W.; Ziller, J . W. Angew. Chem.,
Int. Ed. 2000, 39, 240-242. (g) Evans, W. J .; Nyce, G. W.; Forrestal,
K. J .; Ziller, J . W. Organometallics 2002, 21, 1050-1055.
1
0.1021/om0206610 CCC: $22.00 © 2002 American Chemical Society
Publication on Web 11/27/2002

Monopentamethylcyclopentadienyl U(IV) Complexes
Organometallics, Vol. 21, No. 26, 2002 5979
Sch em e 1
F igu r e 1. Molecular structure of 3 with thermal ellipsoids
at the 30% probability level. Selected bond distances (Å)
and angles (deg): U(1)-C(1) 2.477(18); U(1)-C(8) 2.51(2);
U(1)-C(15) 2.53(2); U(1)-C(2) 2.814(19); U(1)-C(9) 2.809-
develop an improved and safer route to the common
uranium starting material, UCl4, which we also report
herein.
(19); U(1)-C(16) 2.85(2); U(1)-C(3) 3.37(2); U(1)-C(7)
3
3
1
.42(2); U(1)-C(10) 3.47(2); U(1)-C(14) 3.40(2); U(1)-C(17)
.42(2); U(1)-C(21) 3.50(2); C(1)-C(2) 1.46(3); C(8)-C(9)
.47(3); C(15)-C(16) 1.44(3); U(1)-C(1)-C(2) 87.3(11);
Resu lts a n d Discu ssion
U(1)-C(8)-C(9) 85.5(12); U(1)-C(15)-C(16) 87.0(13); C(1)-
U(1)-C(8) 112.4(6); C(1)-U(1)-C(15) 116.6(6); C(8)-U(1)-
C(15) 114.0(7).
As depicted in Scheme 1, treatment of a toluene slurry
of UCl4 (1) with (C5Me5)MgCl‚THF (1 equiv) and diox-
ane at room temperature generates complex 2 in situ.
Subsequent addition of dioxane (excess) and benzyl-
magnesium chloride (3 equiv) to the solution of 2 affords
eters associated with the uranium-benzyl linkages
(Benzyl ligand #1: U(1)-C(1) ) 2.477(18) Å, U(1)-C(2)
)
)
2.814(19) Å, U(1)-C(1)-C(2) ) 87.3(11)°, U(1)-C(3)
3.37(2) Å, U(1)-C(7) ) 3.42(2) Å. Benzyl ligand #2:
(C5Me5)U(CH2C6H5)3 (3). Following workup, the isolated
yield for complex 3 is typically 80-90%. Although
Marks’ preparation of 3 is effective, our protocol cir-
cumvents the isolation of (C5Me5)UCl3. In addition, the
present synthetic scheme also avoids the use of CH2Cl2
and LiCH2C6H5 and takes advantage of the com-
mercially available reagent benzylmagnesium chloride.
The addition of dioxane permits the facile removal of
precipitated MgCl2(dioxane)x adducts from solution and
allows for the straightforward workup and high-yield
U(1)-C(8) ) 2.51(2) Å, U(1)-C(9) ) 2.809(19) Å, U(1)-
C(8)-C(9) ) 85.5(12)°, U(1)-C(10) ) 3.47(2) Å, U(1)-
C(14) ) 3.40(2) Å. Benzyl ligand #3: U(1)-C(15) )
2
.53(2) Å, U(1)-C(16) ) 2.85(2) Å, U(1)-C(15)-C(16)
87.0(13)°, U(1)-C(17) ) 3.42(2) Å, U(1)-C(21) ) 3.50-
)
4
(
2) Å). The benzyl groups are best described as η , with
the strongest secondary interaction occurring between
the uranium metal center and the ipso carbon of the
coordinated benzyl ligands in addition to weaker un-
symmetrical secondary interactions taking place be-
tween the uranium and the ortho carbons of the benzyl
ligands.
7
synthesis of 3.
Single crystals of 3 suitable for X-ray diffraction were
obtained by slow evaporation of a solution of 3 in
toluene. As shown in Figure 1, the molecular structure
of 3 reveals that the uranium complex is essentially
identical to the previously reported thorium(IV) ana-
4
The proclivity for benzyl ligands to bond in an η -mode
5
with actinide metals has been noted by both Marks and
8
5
Andersen. Two parameters have been defined to quan-
logue, (C5Me5)Th(CH2C6H5)3, with the U(IV) metal
tify the benzyl ligand-to-metal interaction, ∆ and ∆′,
where ∆ ) [MCo - MCH2] - [MCipso - MCH2] and ∆′ )
center bound to the pentamethylcyclopentadienyl ligand
5
in an η -manner and interacting with the three benzyl
[MCo′ - MCH2] - [MCipso - MCH2] and where MCo is
ligands in a decidedly multihapto fashion. The interac-
tion between the uranium metal center and the pen-
tamethylcyclopentadienyl ligand is unexceptional, and
the U-(C5Me5) distances (U-Cav ) 2.83 Å; C-Cav )
the shorter metal-to-ortho carbon contact, MCo′ is the
longer metal-to-ortho contact, MCH2 is the metal-to-
methylene carbon bond length, and MCipso is the metal-
8
to-ipso carbon bond length. For the f-block metals, ∆
1
(
.42 Å) compare well with those found in other uranium-
IV) complexes.3a,b That the three benzyl ligands are
and ∆′ have been shown to have comparable values, as
4
would be expected for an η -benzyl-to-metal bonding
bound to the uranium metal center in a multihapto
fashion is clearly demonstrated by the metrical param-
interaction. Table 1 compares and contrasts the ∆ and
∆
′ values determined for complex 3 with the other
(
7) (a) Handbook of Grignard Reagents; Silverman, G. S., Rakita,
P. E., Eds.; Marcel Dekker: New York, 1996. (b) This metholodogy
has been utilized to prepare a variety of organoactinide complexes,
see: England, A. F.; Burns, C. J .; Buchwald, S. L. Organometallics
(8) Edwards, P. G.; Andersen, R. A.; Zalkin, A. Organometallics
1984, 3, 293-298. In this work, ∆ and ∆′ values for transition metal
benzyl complexes is provided and compared to the actinide benzyl
complexes.
1
994, 13, 3491-3495.

5
980 Organometallics, Vol. 21, No. 26, 2002
Ta ble 1. Bon d Len gth s in Actin id e Ben zyl Com p lexes
Kiplinger et al.
compound
MCipso-MCH2a
MCo-MCH2b
MCo′-MCH2c
∆d
∆′e
reference
(
(
(
(
(
(
(
(
(
(
(
(
C5Me5)Th(CH2Ph)3
0.29
0.77
1.00
0.48
0.71
0.58
0.69
0.61
0.66
0.65
5
shortest contacts)
dmpe)Th(CH2Ph)4f
0.35
0.22
0.34
0.30
0.32
0.78
0.55
0.89
0.89
0.89
0.39
0.91
0.94
0.96
0.97
0.43
0.33
0.56
0.59
0.57
8
shortest contacts)
dmpe)U(CH2Ph)3(Me)f
8
shortest contacts)
C5Me5)U(CH2Ph)3 (3)
benzyl ligand #1, U-CH2 ) U(1)-C(1))
C5Me5)U(CH2Ph)3 (3)
benzyl ligand #2, U-CH2 ) U(1)-C(8))
C5Me5)U(CH2Ph)3 (3)
benzyl ligand #3, U-CH2 ) U(1)-C(15))
this work
this work
this work
a
Metal-to-ipso carbon bond length minus metal-to-methylene carbon bond length. b Metal-to-shorter ortho carbon bond length
c
minus metal-to-methylene carbon bond length. Metal-to-longer ortho carbon bond length minus metal-to-methylene carbon bond length.
d
MCo - MCH2] - [MCipso - MCH2]. [MCo′ - MCH2] - [MCipso - MCH2]. f dmpe ) 1,2-bis(dimethyldiphosphino)ethane.
e
[
known structurally characterized actinide benzyl com-
plexes. The metrical parameters exhibited by complex
3
are comparable with those reported for the other
4
actinide η -benzyl systems, which supports the formula-
tion of the ligands in complex 3 as η -benzyl ligands.
4
The reactivity of complex 3 was probed using cyclo-
pentadiene. As shown in eq 1, reaction of a toluene
solution 3 with excess cyclopentadiene affords the new
mixed-ring metallocene complex 4 as a brown crystalline
solid in 86% isolated yield. Although the reaction is
F igu r e 2. Molecular structure of 4 with thermal ellipsoids
at the 25% probability level. Selected bond distances (Å)
and angles (deg): U(1)-C(21) 2.485(16); U(1)-C(22) 3.70-
(
2
2); C(21)-C(22) 1.51(2); U(1)-X(1A) 2.473; U(1)-X(1B)
.489; U(1)-X(1C) 2.500; U(1)-C(21)-C(22) 134.0(11);
X(1A)-U(1)-X(1B) 113.8; X(1A)-U(1)-X(1C) 119.8; X(1A)-
U(1)-C(21) 100.2; C(21)-U(1)-X(1C) 94.9; C(21)-U(1)-
X(1B) 106.4; X(1C)-U(1)-X(1B) 116.8.
That complex 3 participates in protonolysis chemistry
with relatively weak carbon acids to give the new
1
1
metallocene system is rather interesting. It appears
that the reaction is dictated by steric factors, since only
two C5H5 rings are transferred to the uranium metal
center even in the presence of excess cyclopentadiene.
The driving force for this transformation can be ex-
plained by comparing the pKa’s for toluene (pKa ≈ 41)
1
rather slow and requires days for completion, H NMR
spectroscopy shows that the protonolysis is exceptionally
clean with quantitative formation of complex 4. The H
NMR spectrum of 4 is sharp and paramagnetically
shifted, which suggests that the complex is a U(IV)
1
1
2
and cyclopentadiene (pKa ≈ 16). As a weak acid,
toluene serves as an excellent leaving group for the
stronger carbon acid cyclopentadiene and suggests that
this simple methodology may be readily extended to
other carbon acids with pKa’s less than that of toluene.
Accordingly, complex 3 also reacts with pentamethyl-
cyclopentadiene to give the previously reported (C5-
1
species. A noteworthy feature of the H NMR spectrum
of 4 is the exceptionally large chemical shift observed
for the U-CH2 resonance, which appears as a broad
singlet at δ -229.58 ppm. Significant isotropic chemical
shifts have been reported for tris(cyclopentadienyl)-
uranium(IV) alkyl complexes (e.g., Cp3UCH2Ph, δ -213
1
a
Me5)2U(CH2C6H5)2.
Complex 4 has been structurally characterized (Fig-
ure 2). The molecular structure of 4 reveals a distorted
tetrahedral coordination environment about the ura-
nium metal center, which is common for all compounds
9
9
ppm; Cp3UCH2-p-Tol, δ -214 ppm; Cp3UBu, δ -200
1
0
ppm). Additionally, the room-temperature electronic
absorption spectra for 4, recorded in toluene solution
from 1600 to 300 nm, exhibits several narrow line-
1
3
of the type (C5R5)3MX (R ) H, alkyl). The uranium
metal center is encased by one C5Me5 ring (U-Cav )
-
1
-1
width, low molar absorptivity (<100 M cm ) transi-
2
tions and is consistent with the assignment of an f
U(IV) metal center.6d-f
(11) Little is known about the chemical reactivity of complex 3. It
2
has been noted that 3 reacts with alcohols, formaldehyde, and H to
give alkoxide and hydride complexes. See ref 5.
(12) Lowry, T. H.; Richardson, K. S. Mechanism and Theory in
Organic Chemistry, 3rd ed.; Harper and Row: New York, 1987; pp
297-298.
(
9) Brandi, G.; Brunelli, M.; Lugli, G.; Mazzei, A. Inorg. Chim. Acta
973, 7, 319-322.
10) Marks, T. J .; Seyam, A. M.; Kolb, J . R. J . Am. Chem. Soc. 1973,
5, 5529-5539.
1
(
9

Monopentamethylcyclopentadienyl U(IV) Complexes
Organometallics, Vol. 21, No. 26, 2002 5981
was prepared according to literature procedures.1a (C
H CH )-
5 2
MgCl (1.0 M diethyl ether solution, Aldrich) was used as
received. Deuterated solvents (Cambridge Isotope Laborato-
ries) were purified by storage over activated 4 Å molecular
sieves or sodium metal and then degassed by three freeze-
pump-thaw cycles prior to use. All other reagents were ACS
reagent grade and used as received and obtained as follows:
uranium(VI) oxide dihydrate (Cerac) and hexachloropropene
2
2
.77 Å; C-Cav ) 1.38 Å) and two C5H5 rings (U-Cav )
6
.74, 2.75 Å; C-Cav ) 1.37, 1.42 Å), which all interact
5
with the metal center in an η -manner. These metrical
parameters compare well with those found in other tris-
(
ligand) uranium(IV) metallocene complexes (e.g., Cp3-
1
4
UCl, U-Cav ) 2.74 Å; (C5Me4H)3UCl, U-Cav ) 2.79
1
5
16
Å; (C5Me5)3UCl, U-Cav ) 2.83 Å). The benzyl ligand
1
is bound to the metal center in an η -fashion (U(1)-
(Aldrich) and anhydrous methylene chloride (Aldrich).
C(21) ) 2.485(16) Å, U(1)-C(22) ) 3.70(2) Å, U(1)-
C(21)-C(22) ) 134.0(11)°) and displays no secondary
interactions between the arene ring and the uranium
metal center. However, the larger than tetrahedral
angle about the R-carbon atom is curious and could
Syn th esis of UCl (1). The following synthesis was found
4
2
0
to be a safer and more convenient alternative to the published
procedure.21 On a Schlenk-line, a 250 mL three-neck round-
bottomed flask equipped with a condenser (outfitted with a
nitrogen inlet) and a thermometer was charged with hexachlo-
ropropene (110 mL, 780 mmol, 1.765 g/mL) and a stir bar.
Under a strong nitrogen flow, the flask was heated to 190 °C,
and two small portions (spatula tip, ca. 0.3 g) of uranium(VI)
oxide dihydrate were added. A cloudy yellow mixture was
produced. (Note: This is a radical-initiated reaction; efficient
stirring is critical to smoothly initiate the reaction.) Heating
was continued at 190 °C. Gas evolution was observed and the
mixture changed color from yellow to dark orange. Small
1
7
suggest the presence of an R-agostic interaction.
Similar structural findings have been reported for the
related tris(cyclopentadienyl) complexes Cp3UBu (U-
C(1)-C(2) ) 127.9(19)°) and Cp3U(CH2-p-tol) (U-C(1)-
C(2) ) 128.5(13)°).18
In summary, the synthetic methodology provided in
this contribution offers a convenient one-pot synthesis
of (C5Me5)U(CH2C6H5)3. This new approach affords (C5-
Me5)U(CH2C6H5)3 in high-yield, making it an attractive
starting material readily available in multigram quanti-
ties for uranium metallocene chemistry. Preliminary
reactivity studies show that (C5Me5)U(CH2C6H5)3 can
be readily manipulated for the synthesis of novel
monopentamethylcyclopentadienyl uranium(IV) sys-
tems. We are presently exploring its use in the prepara-
tion of a variety of mixed-ring uranium metallocene
complexes.
portions (spatula tip, ca. 0.3 g) of UO
added to the hot reaction mixture until all of the UO
10.591 g, 32.89 mmol) was exhausted. With each addition of
UO ‚2H O, a vigorous reaction ensues, as evidenced by a
3
‚2H
2
O were carefully
3
‚2H
2
O
(
3
2
significant amount of foaming and smoke which is produced
as the reaction mix changes color from orange to dark red.
Once addition of the UO
mixture was heated at reflux (190 °C) overnight (12 h), during
which time the red dissolved UCl was gradually converted to
3
‚2H
2
O was complete, the reaction
5
insoluble green UCl (1). The reaction mixture was then cooled
4
to room temperature and taken into an inert atmosphere
4
drybox and filtered. The crude UCl was collected and washed
with 160 mL of methylene chloride in 20 mL portions (or until
the washings go from dark red to colorless); this removes
hexachloropropene and other soluble impurities that adhere
Exp er im en ta l Section
Gen er a l Com m en ts. Unless otherwise noted, reactions and
manipulations were performed at 20 °C in a recirculating
4
to the UCl . The crude product was collected and the volatiles
Vacuum Atmospheres Model HE-553-2 inert atmosphere (N
2
were removed under reduced pressure overnight to afford 1
or He) drybox with a MO-40-2 Dri-Train or using standard
Schlenk and high-vacuum-line techniques. Glassware was
dried overnight at 150 °C before use. Reagents were purchased
from commercial suppliers and used without further purifica-
tion unless otherwise noted. Celite (Aldrich) and alumina
as a green solid (12.25 g, 32.23 mmol, 98%).
Syn th esis of (C
5 5 2 6 5 3
Me )U(CH C H ) (3). A 125 mL Erlen-
meyer flask equipped with a stir bar was charged with UCl
(1.558 g, 4.10 mmol), dioxane (4.0 mL, 46.9 mmol, 1.034 g/mL),
and toluene (40 mL). To the resulting green slurry was added
4
(
Brockman I, Aldrich) were dried in vacuo at 250 °C for 48 h
prior to use. Toluene (Fisher), hexanes (Fisher), diethyl ether
Fisher), and tetrahydrofuran (Fisher) were passed through a
column of activated alumina (A2, 12 × 32, Purify) under
nitrogen pressure and sparged with N prior to use. Dioxane
Aldrich) was degassed, passed through a short column (5-6
5 5
(C Me )MgCl‚THF (1.100 g, 4.12 mmol) with additional toluene
(40 mL). The resulting red slurry was stirred at room tem-
perature for 12 h. To the resulting dark brick red mixture was
sequentially added dioxane (5.0 mL, 58.7 mmol, 1.034 g/mL)
(
1
9
2
2
and benzylmagnesium chloride (1.0 M solution in Et O, 15 mL,
(
15 mmol), which afforded a dark brown colored solution that
was stirred at room temperature for 3 h. The mixture was then
filtered through a Celite-padded coarse frit to remove the
insoluble salts. The reddish brown filtrate was collected and
the volatiles were removed under reduced pressure to give a
brown solid. This solid was taken up in toluene/hexane (20
mL/20 mL) and filtered through a Celite-padded coarse frit to
remove the insoluble salts. The filtrate was collected and the
volatiles were removed under reduced pressure. This last step
cm) of activated alumina, and stored over 4 Å molecular sieves
prior to use. Uranium tetrachloride was prepared using a
modification to the literature procedure published by Suttle
2
0
5 5
and Hermann, which is detailed below. (C Me )MgCl‚THF
(13) (a) Marks, T. J . Prog. Inorg. Chem. 1979, 25, 223-333. (b)
Marks, T. J .; Ernst, R. D. In Comprehensive Organometallic Chemistry;
Wilkinson, G., Stone, F. G. A., Abel, E. W., Eds.; Pergamon: Oxford,
1
982; Vol. 3. (c) Edelmann, F. T. In Comprehensive Organometallic
Chemistry II; Lappert, M. F., Ed.; Pergamon: Oxford, 1995; Vol. 4.
14) Wong, C. H.; Yen, T. M.; Lee, T. Y. Acta Crystallogr. 1965, 18,
40-345.
15) Cloke, F. G. N.; Hawkes, S. A.; Hitchcock, P. B.; Scott, P.
Organometallics 1994, 13, 2895-2897.
16) Evans, W. J .; Nyce, G. W.; J ohnston, M. A.; Ziller, J . W. J . Am.
Chem. Soc. 2000, 112, 12019-12020.
17) There is no structural evidence for any nonbonded contacts on
(
(20) We have experienced some safety issues with the published
3
UCl
2H O and hexachloropropene to high temperatures. In our hands,
different lots of UO ‚2H O have initiated at different temperatures
(presumably a consequence of variable surface area and waters of
hydration with different UO O batches), which has led to unex-
4 3
synthesis which involves heating a “one-pot” mixture of UO ‚
(
2
3
2
(
3
‚2H
2
(
pected thermal excursions of reagent from the reaction vessel. We have
found that this can be avoided using the following procedure, which
either side of the benzyl ligand that could lead to a steric increase in
the U-C-C angle.
3 2
entails the portionwise addition of UO ‚2H O to a hot hexachloropro-
pene solution and allows for control of the reaction.
(
18) Perego, G.; Cesari, M.; Farina, F.; Lugli, G. Acta Crystallogr.
1
976, B32, 3034-3039.
(21) (a) Hermann, J . A.; Suttle, J . F.; Hoekstra, H. R. Inorg. Synth.
1957, 5, 143-145. (b) Hermann, J . A.; Suttle, J . F.; Hoekstra, H. R. In
Lanthanides and Actinides; Herrmann, W. A., Edelmann, F. T., Eds.;
Synthetic Methods of Organometallic and Inorganic Chemistry Series;
Thieme: New York, 1997; Vol. 6, pp 156-157.
(
19) (a) Pangborn, A. B.; Giardellop, M. A.; Grubbs, R. H.; Rosen,
R. K.; Timmers, F. J . Organometallics 1996, 15, 1518-1520. (b) Alaimo,
P. J .; Peters, D. W.; Arnold, J .; Bergman, R. G. J . Chem. Ed. 2001, 78,
6
4.

5
982 Organometallics, Vol. 21, No. 26, 2002
Kiplinger et al.
was repeated to afford 3 as a dark brown crystalline solid
absorption coefficient was 6.303 mm-1. The least-squares
1
(
2.364 g, 1.023 mmol, 90%). H NMR (C
δ 6.56 (t, J ) 6.9 Hz, 2H meta), 3.52 (br s, 2H, U-CH
t, J ) 7.5 Hz, 1H, para), -0.49 (s, 15H, Cp*-CH ), -21.33 (br
s, 2H, ortho). UV-vis/NIR (ꢀ, M cm , toluene): 419 (sh)
3250), 594 (sh) (800), 684 (sh) (350), 1107 (113), 1167 (179),
6
D
6
, 300 MHz, 21 °C):
refinement converged normally with residuals of R1 ) 0.1180
2
2
), 0.13
(I > 2σ(I)), wR2 ) 0.1767, and GOF ) 3.331 (F ); C31
H
36
U
(
3
1
(646.63 g/mol), space group P2 /n, monoclinic a ) 9.556(2) Å,
-
1
-1
b ) 30.725(8) Å, c ) 17.877(5) Å, â ) 100.351(5)°, V ) 5163(2)
3
-3
(
Å , Z ) 8, F(000) ) 2512, Fcalcd ) 1.664 g cm . Structure
1
5
430 (26), 1570 (30). Mp ) 119-121 °C. MS (EI, 70 eV): m/z
solution, refinement, graphics, and creation of publication
+
25
56 (M - C
7
H
7
).
materials were performed using SHELXTL NT.
Syn th esis of (C
Erlenmeyer flask equipped with a stir bar was charged with
Me )U(CH (3) (0.689 g, 1.07 mmol) and toluene (60
5 5 5 5 2 2 6 5
Me )(C H ) U(CH C H ) (4). A 125 mL
5 5 5 5 2 2 6 5
Cr ystallogr aph ic Details for (C Me )(C H ) U(CH C H )
(
4). A brown crystal (0.25 × 0.21 × 0.21 mm) grown by slow
(C
5
5
2 6 5 3
C H )
evaporation of a hexane solution of 4 was mounted from
Paratone N oil (Exxon) onto a glass fiber under argon gas flow
and placed on a Bruker P4/CCD diffractometer, equipped with
a Bruker LT-2 temperature device. A hemisphere of data was
collected using æ scans, with 30 s frame exposures and 0.3°
frame widths. A total of 7046 reflections (-9 e h e 9, 0 e k e
mL). To the dark brown solution was added freshly cracked
cyclopentadiene via syringe (0.189 mL, 2.25 mmol, 0.80 g/mL).
The brown solution was stirred at room temperature for 6
days. The reaction mixture was then filtered through a Celite-
padded coarse frit, the filtrate was collected, and the volatiles
were removed under reduced pressure to give crude 4 as a dark
brown solid. Recrystallization from toluene (3 mL) and hexanes
3
2, 0 e l e 19) were collected at T ) 203(2) K in the θ range
of 1.8-23.3°, of which 3237 were unique (Rint ) 0.068); Mo
ΚR radiation (λ ) 0.71073 Å). Data collection and initial
(
15 mL) at -30 °C afforded 4 as a black crystalline solid (0.546
1
g, 0.918 mmol, 86%). H NMR (C
s, 15H, Cp*-CH ), 2.81 (t, J ) 7.5 Hz, 2H, meta), -1.75 (t,
J ) 6.9 Hz, 1H, para), -6.36 (s, 10H, Cp-H), -22.51 (d, J )
6
D
6
, 300 MHz, 21 °C): δ 8.13
22
indexing and cell refinement were handled using SMART
(
3
software. Frame integration and final cell parameter calcula-
23
tions were carried out using SAINT software. The data were
-1
7
.5 Hz, ortho), -229.58 (br s, 2H, U-CH
2
). UV-vis/NIR (ꢀ, M
cm , toluene): 467 (20), 494 (sh) (20), 511 (100), 546 (20), 575
sh), 599 (10), 621 (10), 648 (10), 680 (42), 709 (34), 728 (11),
40 (sh) (5), 768 (3), 796 (3), 810 (3), 939 (45), 1005 (62), 1036
75), 1053 (5), 1078 (107), 1140 (48), 1184 (sh) (30), 1227 (55),
24
corrected for absorption using the DIFABS program. The
-1
structure was solved using direct methods, completed by
subsequent difference Fourier techniques, and refined by full-
matrix least-squares procedures. All non-hydrogen anisotropic
temperature factors were restrained to approximate isotropic
behavior using the ISOR option in SHELXTL, and hydrogen
atoms were treated as idealized contributions. The absorption
(
7
(
1
1
C
336 (95), 1375 (sh) (25), 1481 (11), 1499 (sh) (5). Mp ) 192-
+
94 °C (dec). MS (EI, 70 eV): m/z 594 (M - H ), 529 (M -
+
+
5
H
6
), 504 (M - C
7
H
7
). Anal. Calcd for C27
H
32U (594.58
-1
coefficient was 7.192 mm . The least-squares refinement
g/mol): C, 54.54; H, 5.42. Found: C, 54.70; H, 5.60.
Cr ysta llogr a p h ic Deta ils for (C Me )U(CH
converged normally with residuals of R1 ) 0.0540 (I > 2σ(I)),
5
5
2
C
6
H
5
)
3
(3).
2
wR2 ) 0.1356, and GOF ) 1.027 (F ); C27
H
32U (594.56 g/mol),
A black crystal (0.25 × 0.12 × 0.12 mm) grown by slow
evaporation of a toluene solution of 3 was mounted from
Paratone N oil (Exxon) onto a glass fiber under argon gas flow
and placed on a Bruker P4/CCD diffractometer, equipped with
a Bruker LT-2 temperature device. A hemisphere of data was
collected using æ scans, with 30 s frame exposures and 0.3°
frame widths. A total of 37 913 reflections (-9 e h e 9, 0 e
k e 32, 0 e l e 19) were collected at T ) 203(2) K in the θ
range of 1.3-22.5°, of which 6380 were unique (Rint ) 0.071);
Mo ΚR radiation (λ ) 0.71073 Å). Data collection and initial
indexing and cell refinement were handled using SMART22
software. Frame integration and final cell parameter calcula-
tions were carried out using SAINT23 software. The data were
space group P2 /n, monoclinic a ) 8.099(3) Å, b ) 19.261(6)
1
3
Å, c ) 14.495(5) Å, â ) 92.016(5)°, V ) 2259.7(12) Å , Z ) 4,
-3
F(000) ) 1144, Fcalcd ) 1.748 g cm . Structure solution,
refinement, graphics, and creation of publication materials
25
were performed using SHELXTL NT.
Ack n ow led gm en t. For financial support of this
work, we acknowledge the Division of Chemical Sci-
ences, Office of Basic Energy Sciences, U.S. Department
of Energy (C.J .B.), and the LANL Laboratory Directed
Research and Development Program (D.E.M.). J .L.K. is
the recipient of a Frederick Reines fellowship at Los
Alamos National Laboratory. Finally, we thank Prof.
Paul B. Duval (U Missouri, Columbia) and Drs. J udith
L. Eglin (LANL) and J effery T. Golden (LANL) for
helpful discussions.
2
4
corrected for absorption using the DIFABS program. The
structure was solved using direct methods, completed by
subsequent difference Fourier techniques, and refined by full-
matrix least-squares procedures. All non-hydrogen anisotropic
temperature factors were restrained to approximate isotropic
behavior using the ISOR option in SHELXTL, and hydrogen
atoms were treated as idealized contributions. Difference
Fourier maps revealed the presence of residual electron density
consistent with minor static rotational disorder of the molecule,
but this disorder could not be fit with any realistic model. The
Su p p or tin g In for m a tion Ava ila ble: X-ray crystallo-
graphic information for 3 and 4 (PDF and CIF). The material
is available free of charge via the Internet at http://pubs.acs.org.
OM0206610
(22) SMART-NT 4; Bruker AXS, Inc.: Madison, WI 53719, 1996.
(23) SAINT-NT 5.050; Bruker AXS, Inc.: Madison, WI 53719, 1998.
(24) Walker, N.; Stuart, D. Acta Crystallogr. 1983, A39, 158-166.
(25) SHELXTL NT Version 5.10; Bruker AXS, Inc.: Madison, WI
53719, 1997.