Reactivity of (C5Me5)2UMe2 and (C5Me5)2 UMeCl toward group 13 Alkyls

Article abstract of DOI:10.1021/om800914w

The reactions of group 13 alkyl reagents (ATMe₃, AlEt ₃, GaMet₃, InMet₃) with the uranium metallocene complexes Cp*₂UCl₂, Cp*₂UMe ₂, and Cp*₂UClMe (Cp* = C<

Full text of DOI:10.1021/om800914w

Organometallics 2009, 28, 1173–1179
1173
Reactivity of (C5Me5)2UMe2 and (C5Me5)2UMeCl toward Group 13
Alkyls
H. Martin Dietrich,† Joseph W. Ziller,‡ Reiner Anwander,*,† and William J. Evans*,‡
Department of Chemistry, UniVersity of Bergen, Alle´gaten 41, N-5007, Bergen, Norway, and Department
of Chemistry, UniVersity of California, IrVine, California 92697-2025
ReceiVed September 19, 2008
The reactions of group 13 alkyl reagents (AlMe3, AlEt3, GaMe3, InMe3) with the uranium metallocene
complexes Cp*2UCl2, Cp*2UMe2, and Cp*2UClMe (Cp* ) C5Me5) were studied, and similarities to
pertinent group 4 and lanthanide chemistry were considered. The methyl derivative Cp*2UMe2 exhibits
high reactivity toward the alkylaluminum reagents involving C-H bond activation, in contrast to Cp*2UCl2,
which did not react under similar conditions. The orange-red C-H bond activation product of the AlMe3
reaction, Cp*2MeU(µ-Me)AlMe2(µ3-CH2)Al2(µ-Me)Me4, was identified by X-ray crystallography. It
contains a trinuclear aluminum-methyl-methylene moiety, [Al3Me8(CH2)]-, linked to [Cp*2UMe]+ via
a bridging methyl group. The reaction of triethylaluminum with the orange-red chloro-methyl derivative
Cp*2UClMe gives reduction to the dark green uranium(III) complex Cp*2U[(µ-CH2CH3)AlEt2(µ-
Cl)]2UCp*2 as evidenced by an X-ray structural analysis. Reactions of the less Lewis acidic gallium and
indium alkyls were not observable by NMR spectroscopy, but the heterobimetallic complex Cp*2U[(µ-
Me)(InMe3)]2 was obtained by crystallization of a 1:2 mixture of Cp*2UMe2 and InMe3 from hexane. As
indicated by a rather long (U-CH3) · · · In distances in the range of 2.846-2.922 Å, the InMe3 molecules
interact only weakly with the dimethyl metallocene unit (no tetramethylindate coordination), which is
further substantiated by facile removal of the group 13 alkyl under vacuum.
organometallics have appeared in the literature.7-17 In fact,
tetrachloroaluminate complexes constitute the only well-
examined organouranium-aluminum(III) derivatives reported
to date.7-10 Already more than 35 years ago, the π-arene
complex (η6-C6H6)UIII(AlCl4)3, A (Chart 1), was crystallographi-
Introduction
Alkylaluminum reagents interact synergistically with a wide
range of transition metals and lanthanide metals to make
combinations active in Ziegler-Natta-type polymerization
catalysis.1,2 Investigations into structure-reactivity relationships
have revealed not only the beneficial alkylating and reducing
power of the organoaluminum compounds, but also their crucial
role as chain transfer reagents and catalyst deactivators.1,2,4,5
Uranium-based catalyst mixtures also were found to be highly
active and efficient polymerization initiators (e.g., [U(OMe)4-
EtAlCl2], >99% cis-polybutadiene), but their applicability is
limited due to their radioactive nature.6 It is therefore not
surprising that only a few reports on discrete actinide/aluminum
(7) Cesari, M.; Pedretti, U.; Zazzetta, A.; Lugli, G.; Marconi, W. Inorg.
Chim. Acta 1971, 5, 439.
(8) (a) Cotton, F. A.; Schwotzer, W.; Simpson, C. Q., II Angew. Chem.,
Int. Ed. Engl. 1986, 25, 637. (b) Cotton, F. A.; Schwotzer, W. Organome-
tallics 1985, 4, 942. (c) Cotton, F. A.; Schwotzer, W. Organometallics 1987,
6, 1275.
(9) Garbar, A. V.; Leonov, M. R.; Zakharov, L. N.; Struchkov, Yu. T.
IzV. Akad. Nauk, Ser. Khim. (Russ. Chem. Bull.) 1996, (2), 469.
(10) For the synthesis of complex [Cp3UIV(AlCl4)(THF)], see: Chang,
C. C.; Sung-Yu, N. K.; Kang, C. W.; Chang, C. T. Inorg. Chim. Acta 1987,
129, 119.
(11) Despite the rich structural chemistry of rare-earth12 and group 4
metal tetrahydroaluminate complexes,13 uranium(actinide) derivatives re-
mained scarce. Complexes Cp2UIV(AlH4)2, Cp3UIV(AlH4), and UIII(AlH4)3
were described but not structurally characterized.14 The latter homoleptic
complex was suggested as an active species in hydroalumination reactions.15
(12) For a review article, see: Soloveichik, G. L. New J. Chem. 1995,
19, 597.
* To whom correspondence should be addressed. E-mail: reiner.anwander@
kj.uib.no.
† University of Bergen.
‡ University of California, Irvine.
(1) Ziegler Catalysts; Fink, G., Mülhaupt, R., Brintzinger, H.-H., Eds.;
Springer-Verlag: Berlin, 1995.
(2) For reviews, see: (a) Thiele, H.-K.; Wilson, D. R. J. Macromol. Sci.,
Polym. ReV. 2003, C43, 581. (b) Fischbach, A.; Anwander, R. AdV. Polym.
Sci. 2006, 204, 155.
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1978, 100, 3611. (b) Howard, T. R.; Lee, J. B.; Grubbs, R. H. J. Am. Chem.
Soc. 1980, 102, 6878.
(13) For recent examples, see: (a) Khan, K.; Raston, C. L.; McGrady,
J. E.; Skelton, B. W.; White, A. H. Organometallics 1997, 16, 3252. (b)
Etkin, N.; Stephan, D. W. Organometallics 1998, 17, 763.
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J. Organomet. Chem. 1986, 310, C1-C4. (b) Ossola, F.; Brianese, N.;
Porchia, M.; Rossetto, G.; Zanella, P. J. Chem. Soc., Dalton Trans. 1990,
877. (c) Brianese, N.; Casellato, U.; Ossola, F.; Porchia, M.; Rossetto, G.;
Zanella, P.; Graziani, R. J. Organomet. Chem. 1989, 365, 223.
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Chem. 1986, 309, C1-C3.
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R. Organometallics 2002, 21, 4021.
(5) For reviews, see: (a) Brintzinger, H.-H.; Fischer, D.; Mu¨lhaupt, R.;
Rieger, B.; Waymouth, R. M. Angew. Chem., Int. Ed. Engl. 1995, 34, 1143.
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(16) UVI(OiPr)6 was reported to form the 6:1 adduct UVI(OiPr)6(AlMe3)6
with trimethylaluminum: Sigurdson, E. R.; Wilkinson, G. J. Chem. Soc., Dalton
Trans. 1977, 822.
(17) The U(III)-Al(I) heterobimetallic complex [C5H4(SiMe3)]3UAlCp*
was described recently: Minasian, S. G.; Krinsky, J. l.; Williams, V. A.;
Arnold, J. J. Am. Chem. Soc. 2008, 130, 10086.
10.1021/om800914w CCC: $40.75
2009 American Chemical Society
Publication on Web 01/21/2009

1174 Organometallics, Vol. 28, No. 4, 2009
Dietrich et al.
example.3,24-28 To the best of our knowledge, well-characterized
alkylated heterobimetallic complexes of uranium and group 13
metals have not been reported so far.17 Herein we present the
initial results of a study aiming at the reactivity of known
metallocenes Cp*2UCl2,29 Cp*2UMe2,30 and Cp*2UMeCl31
toward organoaluminum reagents, as well as trimethylgallium
and -indium.
Chart 1
Results and Discussion
The orange-red precursor compounds Cp*2UCl2 (1a),29
Cp*2UMe2 (1b),30 and Cp*2UMeCl (1c)31 were synthesized
according to literature procedures. Such discrete organoactini-
de(IV) complexes have been subjected to a number of X-ray
crystallographic investigations with bulky cyclopentadienyl
ligands C5R5 stabilizing mononuclear complexes with terminally
bonded methyl and chloro ligands (Table 1),32-35 but surpris-
ingly Cp*2UMeCl (1c) has never been structurally characterized
by X-ray diffraction. Compound 1c crystallizes from toluene
in space group P21 with unit cell parameters that are very close
to those of crystals of 1a obtained in this study from toluene/
hexane solution in the monoclinic space group P21/n (Figure
1). Previously, single crystals of 1a obtained by sublimation
were reported to crystallize in a different crystal system
(orthorhombic Fmm2).29 Although the structure of 1c had
disorder between the Me and Cl ligands, the crystal data suggest
that this is Cp*2UMeCl and not a cocrystallization of 1a and
1b, the latter of which crystallizes in I1/a. Metrical parameters
cannot be discussed for 1c due to the disorder. A model in which
the Me and Cl ligands were 50% disordered at each position
gave the best results. The overall rigidity and chemical robust-
ness of the well-shielded metallocene environment is anticipated
to facilitate reactivity studies involving U-X moieties and group
13 reagents. Additionally, comparisons to the corresponding
well-investigated metallocene chemistry of the group 4 and rare-
earth metals can be drawn.
cally characterized and found to contain three η2-coordinated
tetrachloroaluminate ligands.7
Later on, closely related complexes with hexamethylbenzene8
and toluene π-donors9 were investigated with uranium, and a
pronounced similarity to group 3 and 4 transition metals and
lanthanides was found. While the synthesis conditions for such
tetrachloroaluminate complexes, that is, Fischer’s reductive
Friedel-Crafts reaction,18 routinely involved UIV/UIII redox
couples (cf., ZrIV/ZrII yielding (η6-C6H6)2ZrII(AlCl4)2),19 struc-
tural similarities were found with redox-stable lanthanide
metal(III) congeners (e.g., isostructural (η6-C6Me6)U(AlCl4)3 and
(η6-C6Me6)Sm(AlCl4)3).8c,20 Higher agglomerated complexes
[UIV2(η6-C6Me6)2Cl4(µ-Cl)3]+[AlCl4]8b and [UIII2(η6-C6Me6)3(µ3-
Cl)2(µ2-Cl)3(µ1,η2-AlCl4)]+[AlCl4]- ([B]+[AlCl4]-, Chart 1)8a
were shown to form separated ion pairs.
Rather distinct reactivity patterns have been discovered with
lanthanide and group 4 metal complexes with organoaluminum
reagents and in particular with trimethylaluminum. While the
lanthanides form a variety of thermally stable homo- and
heteroleptic tetraalkylaluminate complexes,2b,21 the isolation of
corresponding group 4 derivatives seems to be hampered by
their intrinsic instability.22 The complex [Ti(NtBu)(Me3[9]-
aneN3)(µ-Me)2AlMe2][BArF ] appears to be the only crystallo-
Reactivity of Cp*2UCl2. The metallocene bis(chloride)
complex 1a did not react with any of the group 13 reagents
under study (trimethylaluminum, triethylaluminum, trimethyl-
gallium, and trimethylindium) in hexane at ambient temperature.
After 2 d, only unreacted 1a was recovered. Neither chloro/
alkyl ligand exchange occurred, nor did adduct complexes of
type [Cp*2UCl2(MR3)x] (M ) Al, Ga, In) form upon crystal-
lization. For comparison, in group 4 chemistry, AlR3 addition
and chloro/alkyl ligand exchange is commonly observed when
complexes Cp′2MCl2 (M ) Ti, Zr, Hf) are treated with
4
graphically authenticated tetraalkylaluminate derivative.23 It is
noteworthy that C-H bond activation is a common reaction
pathway in such heterobimetallic complexes, with the “Tebbe
reagent”, Cp2Ti(µ-Cl)(µ-CH2)AlMe2, being the most prominent
(18) Fischer, E. O.; Ro¨hrschied, F. J. Organomet. Chem. 1966, 6, 53.
(19) Calderazzo, F.; Pallavicini, P.; Pampaloni, G. J. Chem. Soc., Dalton
Trans. 1990, 1813.
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(21) (a) Evans, W. J.; Anwander, R.; Ziller, J. W. Organometallics 1995,
14, 1107. (b) Zimmermann, M.; Frøystein, N. Å.; Fischbach, A.; Sirsch,
P.; Dietrich, H. M.; To¨rnroos, K. W.; Herdtweck, E.; Anwander, R.
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33, 1634.
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(24) (a) Kaminsky, W.; Kopf, J.; Thirase, G. Liebigs Ann. Chem. 1974,
1531. (b) Kaminsky, W.; Sinn, H. Liebigs Ann. Chem. 1975, 424. (c)
Kaminsky, W.; Kopf, J.; Sinn, H.; Vollmer, H. J. Angew. Chem., Int. Ed.
Engl. 1976, 15, 629. (d) Kopf, J.; Kaminsky, W.; Vollmer, H. J. Cryst.
Struct. Commun. 1980, 9, 197. (e) Kopf, J.; Vollmer, H. J.; Kaminsky, W.
Cryst. Struct. Commun. 1980, 9, 271. (f) Kopf, J.; Vollmer, H. J.; Kaminsky,
W. Cryst. Struct. Commun. 1980, 9, 985. (g) Kaminsky, W.; Steiger, R.
Polyhedron 1988, 7, 2375.
(25) Siedle, A. R.; Newmark, R. A.; Schroepfer, J. N.; Lyon, P. A.
Organometallics 1991, 10, 400.
(26) Kickham, J. E.; Gue´rin, F.; Stephan, D. W. J. Am. Chem. Soc. 2002,
124, 11486.
(29) (a) Manriquez, J. M.; Fagan, P. J.; Marks, T. J. J. Am. Chem. Soc.
1978, 100, 3939. (b) Spirlet, M. R.; Rebizant, J.; Apostolidis, C.;
Kanellakopulos, B. Acta Crystallogr. 1992, C48, 2135.
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Golden, J. T.; Morris, D. E.; Scott, B. L.; Taw, F. L.; Kiplinger, J. L.
Organometallics 2004, 23, 4682. (b) Barnea, E.; Andrea, T.; Kapon, M.;
Berthet, J.-C.; Ephritikhine, M.; Eisen, M. S. J. Am. Chem. Soc. 2004, 126,
10860.
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Marks, T. J. J. Am. Chem. Soc. 1981, 103, 6650. (b) Morris, D. E.; Da Re,
R. E.; Jantunen, K. C.; Castro-Rodriguez, I.; Kiplinger, J. L. Organometallics
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M.; Eisen, M. S. Organometallics 2001, 20, 5017. (b) Evans, W. J.;
Kozimor, S. A.; Ziller, J. W.; Fagin, A. A.; Bochkarev, M. N. Inorg. Chem.
2005, 44, 3993. (c) Evans, W. J.; Kozimor, S. A.; Hillmann, W. R.; Ziller,
J. W. Organometallics 2005, 24, 4676.
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Andersen, R. A. Organometallics 1999, 18, 1235.
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W. E.; Zhang, H. J. Chem. Soc., Dalton Trans. 1995, 3335.
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Chem.sEur. J. 2008, 14, 9555.

ReactiVity of (C5Me5)2UMe2 and (C5Me5)2UMeCl
Organometallics, Vol. 28, No. 4, 2009 1175
Table 1. Selected Metrical Parameters of Uranium Metallocenes (C5R5)2UX2 (X ) Me, Cl)
compound
(C5Me5)2UMe2
[1,3-(Me3Si)2C5H3]2UMe2
(C5Me4H)2UMe2
(C5Me4H)2UMeCl
(C5Me5)2UMeCl (1c)
(C5Me4H)2UCl2
(C5Me5)2UCl2 (1a)
(C5Me5)2UCl2 (1a)
[1,3-(Me3Si)2C5H3]2UCl2
[1,3-tBu2C5H3]2UCl2
[1,2-tBu2C5H3]2UCl2
U-X (Å)
2.424(7), 2.414(7)
2.42(2)
2.426(2)
C, 2.653(6); Cl, 2.38(2)
C, 2.34(2), 2.35(2); Cl, 2.679(4), 2.650(4)
2.5909(7)
2.583(6)
2.953(8)
2.579(2)
U-Cnt (Å)
X-U-X (deg)
Cnt-U-Cnt (deg)
ref
2.456
2.44
2.444
2.429
2.393, 2.501
2.42
2.47
2.44
2.44
2.49
94.5(3)
140.5
130.8
134.3
133.6
139.2
133.1
132
30a,b
33
32c
32c
105.0(7)
100.76(13)
101.5(15)
98.0(4), 98.4(5)
99.79(3)
97.9(4)
98.31(3)
95.3(1)
91.0(2)
this work, 31a
32b
29b
138
this work
33, 34
33
124.7
128.1
123
2.577(4)
2.591(4), 2.576(4)
2.43
97.66(14)
35
trimethyl(alkyl)aluminum.1,5,25 Moreover, subsequent reaction
of these M-methyl(alkyl) moieties with an excess of the
organoaluminum compound can lead to C-H bond activation
(cf., Tebbe reagent).3 Mixtures of [Cp*2LnCl]x/AlR3 (R ) Me,
Et, iBu) neither undergo a fast chloride exchange, nor is C-H
bond activation a common reaction pathway. Instead the
formation of adducts with the alkylaluminum reagents seems
to be favored as shown recently for complexes Cp*2Y(µ-Cl)(µ-
Variation of the Cp*2UMe2/AlR3 ratios gave different mixtures
of products as determined by NMR spectroscopy, but the
paramagnetism of the uranium precluded a more detailed
interpretation of these reactions. Moreover, a highly fluxional
nature of the alkylaluminum groups is anticipated to contribute
to signal broadening.21 For comparison, Cp2ZrMe2 undergoes
facile methyl exchange with AlMe3 in toluene solution,25 while
complexes [Cp*2LnMe]x and [Cp*LnMe2]3 add AlMe3 to form
36
4
Me)AlMe2 and [Cp*2Sm(µ-Et)(µ-Cl)AlEt2]2.37
tetramethylaluminate complexes [Cp*2Ln(AlMe4)]n and
Reactivity of Cp*2UMe2. Instant reaction of the dimethyl
complex Cp*2UMe2 (1b) with trialkyl aluminum reagents
(AlMe3, AlEt3) was observed at ambient temperature in deu-
terated benzene as indicated by methane/alkane evolution and
a considerable chemical shift of the C5Me5 proton resonance to
higher field (Figures S1 and S2, Supporting Information).
Cp*Ln(AlMe4)2, respectively.27a
Fortunately, we were able to identify the product of the
reaction of 1b with an excess (8 equiv) of AlMe3 in hexane by
X-ray crystallography (Scheme 1). At -35 °C, the reaction
mixture produced red single crystals of Cp*2UAl3(µ3-CH2)(µ2-
CH3)2(CH3)7, 2. The molecular structure of the UAl3 heterobi-
metallic complex provides the first structural evidence of an
alkylaluminum induced C-H bond activation in actinide
chemistry. Single-crystalline 2 showed a rather complicated 1H
NMR spectrum (benzene-d6; >20 signals at 25 °C; Figure S2,
Supporting Information). For group 4 organometallics, such
hydrogen abstraction from alkyl ligands is a well-documented
reaction pathway with several reaction products fully defined
by X-ray crystallography.24-26,38 Also, in the organolanthanide
area, several examples of organoaluminum-assisted transforma-
tions of methyl ligands into cluster-embedded methylene
(CH22-), methine (CH3-), and carbide (C4-) moieties have been
observed.27,28 The latter monocyclopentadienyl complexes,
2-
however, involve direct Ln3+-CH2 interaction. Heating
complex 2 with an excess of trimethylaluminum led to further
C-H bond activation as indicated by methane formation, but
the attempted crystallization of these products was unsuccessful.
The molecular structure of complex 2 is shown in Figure 2,
and selected bond lengths and angles are listed in Table 2. The
most striking structural feature is the negatively charged
trimetallic aluminum ligand [Al3(CH3)6(µ3-CH2)(µ2-CH3)2]-,
which is linked to the [Cp*2UMe]1+ entity via one of the
bridging methyl groups. The U-CMe bond length of 2.658(5)
Å of the latter bridging methyl group is markedly elongated
compared with the terminally bonded one (2.395(6) Å). For
comparison, complexes (C5R5)2UMe2 show U-CMe bond lengths
Figure 1. Molecular structure of Cp*2UCl2 (1a, left) and partial
ball-and-stick figure of Cp*2UMeCl (1c, right) with the atomic
displacement parameters set at the 50% level; for clarity, only
hydrogen atoms are shown for the methyl ligands of 1c.
(36) Evans, W. J.; Champagne, T. M.; Giarikos, D. G.; Ziller, J. W.
Organometallics 2005, 24, 570.
(37) Evans, W. J.; Champagne, T. M.; Ziller, J. W. Organometallics
2005, 24, 4882.
(38) (a) Herzog, A.; Roesky, H. W.; Zak, Z.; Noltemeyer, M. Angew.
Chem., Int. Ed. Engl. 1994, 33, 967. (b) Herzog, A.; Roesky, H. W.; Ja¨ger,
F.; Steiner, A.; Noltemeyer, M. Organometallics 1996, 15, 909. (c) Kickham,
J. E.; Gue´rin, F.; Stewart, J. C.; Stephan, D. W. Angew. Chem., Int. Ed.
2000, 39, 3263. (d) Yue, N.; Hollink, E.; Gue´rin, F.; Stephan, D. W.
Organometallics 2001, 20, 4424. (e) Kickham, J. E.; Gue´rin, F.; Stewart,
J. C.; Urbanska, E.; Stephan, D. W. Organometallics 2001, 20, 1175. (f)
Kickham, J. E.; Gue´rin, F.; Stephan, D. W. J. Am. Chem. Soc. 2002, 124,
11486. (g) Wei, P.; Stephan, D. W. Organometallics 2003, 22, 1992. (h)
Gue´rin, F.; Stephan, D. W. Angew. Chem., Int. Ed. 1999, 38, 3698.
Figure 2. Molecular structure of Cp*2UAl3(µ3-CH2)(µ2-CH3)2-
(CH3)7 (2) with the atomic displacement parameter drawn at the
50% probability level. Hydrogen atoms of the Cp* ligands have
been omitted for clarity.

1176 Organometallics, Vol. 28, No. 4, 2009
Dietrich et al.
Table 2. Selected Bond Lengths (Å) and Bond Angles (deg) for
Scheme 1. Reaction of Cp*2UMe2 (1b) with Trimethyl-
aluminum and Trimethyindium
[Cp*2UAl3(µ3-CH2)(µ2-CH3)2(CH3)7] (2)
Bond Distances (Å)
U-C21
2.395(6)
2.658(5)
2.431
2.429
2.099(5)
2.076(6)
Al1-C23
Al2-C25
Al2-C26
Al3-C25
Al3-C26
1.983(6)
2.018(6)
2.219(8)
2.104(6)
2.219(8)
U-C22
U-Cp(Cnt1)
U-Cp(Cnt2)
Al1-C22
Al1-C25
Bond Angles (deg)
C21-U-C22
Al1-C22-U
C22-Al1-C25
Al1-C25-Al3
Al1-C25-Al2
93.4(2)
C25-Al3-C26
C25-Al2-C26
C25-Al3-C28
C26-Al3-C28
C27-Al3-C28
103.6(3)
170.3(3)
107.5(2)
166.3(3)
98.4(3)
102.2(3)
114.8(3)
103.1(3)
123.0(4)
in the range of 2.404(5)-2.426(2) Å (Table 1).30,32 The angle
CMe-U-CMe of 93.4(2)o is only slightly more acute than the
one found in Cp*2UMe2 (94.5(3)°) consistent with no interaction
of the “Al3” ligand with the terminal methyl group (C21). Each
aluminum atom is surrounded by four carbon atoms in a
distorted tetrahedral fashion and is attached to two terminally
bonded methyl groups (Al-C, 1.968(7)-1.986(6) Å). Although
one has to be careful with the localization of hydrogen atoms
on the basis of X-ray structure data only, the Al3 coordination
of carbon atom C25 is very supportive of a five-coordinated
methylene unit in this position.28
The Al-CH2 bond distances average 2.066 Å being compa-
rable to those found for the Al3-CH2 moiety in complexes
(Cp*M)3Al6(CH3)8(µ3-CH2)2(µ4-CH)4(µ3-CH) (M ) Zr, Hf)
(2.047(8)-2.071(8) Å).38a,b The Al1 atom is linked to the
Cp*2UMe2 entity via a bridging methyl group (Al1-C22,
2.099(5) Å), whereas the other two aluminum atoms complete
their coordination sphere by sharing an asymmetrically bridging
methyl group (Al2-C26, 2.219(8); Al3-C26, 2.094(7) Å). The
distinct coordination chemistry of Al2 and Al3 is also revealed
by almost linear and rather acute Al1-C25-Al3 (166.3(3)°)
and Al1-C25-Al2 (98.4(3)°) bonding angles, respectively. Due
to the significantly longer Al-C bond lengths of the linear
Al1-C25-Al3 array (2.076(6) and 2.104(6) Å) compared with
the 2.018(6) Å of Al2-C25 at right angles, one might postulate
an inverse trans influence.
No visible reaction occurred when Cp*2UMe2 (1b) was
treated with less Lewis acidic trimethylgallium or trimethylin-
dium, and the unreacted uranium compound 1b could be
recovered upon evaporation of the solvent and the group 13
alkyl reagent. However, from mixtures of 1b and 2 equiv of
InMe3 in toluene/hexane, the complex Cp*2U[(µ-Me)(InMe3)]2
(3) could be obtained as red crystals (Scheme 1, Figure 3). The
weakly coordinated InMe3 molecules dissociate and sublime
under vacuum, and the proton NMR spectrum of complex 3
only shows the unshifted signals of 1b and InMe3.
The solid-state structure of complex 3 revealed an unusual
interaction of two InMe3 molecules with the Cp*2UMe2 unit
(Figure 3; selected bond lengths and angles are listed in Table
3; two independent molecules in the unit cell). The U-C(methyl)
bond distances average 2.451 Å and appear only slightly
elongated compared with those in 1b (2.404(5) and 2.414(7)
Å), whereas the CMe-U-CMe angle of average 98.8° is
marginally wider (1b, 94.5(3)°).27 The coordination geometry
of the indium metal centers is close to trigonal planar with In-C
distances of 2.158(5)-2.184(6) Å and the In atoms displaced
0.164-0.221 Å out of the ligand plane in the direction toward
the bridging methyl group and the uranium center.
Figure 3. Molecular structure of Cp*2U(µ-Me)2(InMe3)2 (3) with
the atomic displacement parameter drawn at the 50% level.
Hydrogen atoms have been excluded for clarity.
the In atoms located only 0.0701(2) Å above the ligand plane.39
Interestingly, the In · · · C(µ-Me) distances of the U-CH3 · · · In
linkages average 2.890 Å, which is considerably shorter than
the intermolecular In · · · C contacts in pure InMe3 (3.028(3)-
3.409(4) Å).39 This shorter contact might indeed be the driving
force for the formation and crystallization of compound 1b.
Homoleptic tetramethylaluminate complexes Ln(AlMe4)3 tend
to cocrystallize with trimethylaluminum forming 2:1 inclusion
compounds [Ln(AlMe4)3]2[Al2Me6] with no additional close
Ln · · · C or Al · · · C contact.21a However, it is clear from the
Al-C distances of the η1-coordinated tetramethylaluminate
ligand in [2,6-{(2,6-iPr2C6H3)NCMe2}2C5H3N]Ln[(µ-Me)-
(AlMe3)](THF) (Al-Cµ-Me, 2.024(7); Al-CMe, avg 1.974 Å),40
that the In-methyl coordination in 3 does not make up a
tetramethylindate ligand. For indium, only the alkali metal
tetramethylindates MInMe4 (M ) Li, Na, K, Cs) have been
structurally investigated by X-ray diffraction, each showing four
equal In-C bond lenghts (Li, 2.223(4); Na, 2.195(4); K,
2.239(3); Cs, 2.26(2) Å).41 The two trimethylindium molecules
(39) (a) Amma, E. L.; Rundle, R. E. J. Am. Chem. Soc. 1958, 80, 4141.
(b) Lewinski, J.; Zachara, J.; Starowieyski, K. B.; Justyniak, I.; Lipkowski,
J.; Bury, W.; Kruk, P.; Wozniak, R. Organometallics 2005, 24, 4832.
(40) Zimmermann, M.; To¨rnroos, K. W.; Anwander, R. Angew. Chem.,
Int. Ed. 2007, 46, 3126.
(41) (a) Hoffmann, K.; Weiss, E. J. Organomet. Chem. 1972, 37, 1. (b)
Hoffmann, K.; Weiss, E. J. Organomet. Chem. 1973, 50, 17.
For comparison, the In-C distances in the two different
polymorphs of InMe3 range from 2.149(5) to 2.173(3) Å with

ReactiVity of (C5Me5)2UMe2 and (C5Me5)2UMeCl
Organometallics, Vol. 28, No. 4, 2009 1177
Table 3. Selected Bond Lengths (Å) and Bond Angles (deg) for
Scheme 2. Reaction of Triethylaluminum with Cp*2UMeCl
(1c)
Cp*2U(µ-Me)2(InMe3)2 (3)
molecule 1
molecule 2
Bond Distances (Å)
U1-Cp(Cnt1)
2.455
2.455
2.448(4)
2.448(4)
2.876
U2-Cp(Cnt3)
U2-Cp(Cnt4)
2.458
2.459
2.448(4)
2.458(4)
2.922
U1-Cp(Cnt2)
U1-C21
U2-C49
U2-C50
In3 · · · C49
In4 · · · C50
In3-C51
In3-C52
In3-C53
In4-C54
In4-C55
In4-C56
U1-C22
In1 · · · C21
In2 · · · C22
In1-C23
In1-C24
In1-C25
In2-C26
In2-C27
In2-C28
2.915
2.846
2.164(5)
2.152(5)
2.161(6)
2.160(5)
2.167(5)
2.167(5)
2.184(6)
2.158(5)
2.158(5)
2.176(6)
2.164(6)
2.164(5)
catalysts, and the enhanced reducing capability of AlEt3 toward
chlorinated hydrocarbons has been first reported 45 years ago.43
Complex 4 crystallizes in the space group P21/c showing a
centrosymmetric dinuclear metallocene structure with two
[Cp*2U]1+ units connected by µ2-η1(Et):η1(Cl) heterobridging
[AlEt3Cl]1- ligands to form an eight-membered metallacycle.
The solid-state structure is isomorphous to that of the samari-
um(III) complex Cp*2Sm[(µ-CH2CH3)AlEt2(µ-Cl)]2SmCp*2,
which was obtained by addition of AlEt3 to [Cp*2Sm(µ-Cl)]3.37
Bond Angles (deg)
97.32(16)
169.3
C21-U1-C22
U1-C21-In1
U1-C22-In2
C23-In1-C24
C25-In1-C23
C24-In1-C25
C26-In2-C27
C26-In2-C28
C27-In2-C28
C49-U2-C50
U2-C49-In3
U2-C50-In4
C51-In3-C52
C51-In3-C53
C52-In3-C53
C54-In4-C55
C54-In4-C56
C55-In4-C56
100.33(16)
162.5
175.8
121.3(3)
117.3(3)
119.2(3)
115.7(3)
120.7(3)
120.6(2)
164.7
117.5(3)
119.9(3)
119.5(3)
118.6(2)
122.0(2)
117.7(2)
Conclusion
Reactions of the known uranium(IV) metallocene complexes
Cp*2UMe2 and Cp*2UClMe with organoaluminum compounds
AlR3 (R ) Me, Et) reveal similarities to both group 4 and
lanthanide metal complexes. Comparable to well-established
zirconocene chemistry, the dimethyl complex engages in C-H
bond activation reactions and aluminum-methyl-methylene
clustering as evidenced by the formation of Cp*2UIVAl3(µ3-
CH2)(µ2-CH3)2(CH3)7. Under the same conditions, the less Lewis
acidic GaMe3 and InMe3 interact only weakly with these
cyclopentadienyl-supported UIV-CH3 moieties. The approach
of two group 13 metal alkyls as structurally identified in adduct
Cp*2U[(µ-Me)2InMe3]2 can be seen as the first possible reaction
intermediate prior to C-H bond activation and formation of
the UAl3 cluster. In contrast, mixed chloride/methyl coordination
as in Cp*2UClMe favors an AlEt3-promoted reduction and
formation of [Cp*2UIIIAl(µ-CH2CH3)(Et)2(µ-Cl)]2. Such dimer-
ization via µ2-η1(Et):η1(Cl) heterobridging [AlEt3Cl]1- ligands
involving the larger uranium(III) is a known structural motif in
trivalent lanthanide chemistry.
Figure 4. Ball-and-stick figure of Cp*2U[(µ-CH2CH3)AlEt2(µ-
Cl)]2UCp*2 (4).
in 3 are bent away from each other in such a way that they
form obtuse U-Cµ-Me-In angles ranging from 162.5° to 175.8°.
Reactivity of Cp*2UMeCl. As with Cp*2UMe2 (1b), treat-
ment of Cp*2UClMe (1c) with trimethylgallium and trimeth-
ylindium in hexane for 48 h led to the isolation of unreacted 1c
after evaporation of the solvent (and group 13 alkyls). Surpris-
ingly, also trimethylaluminum did not show any reactivity
toward 1c within 3 d at ambient temperature in deuterated
benzene or hexane. On the other hand, triethylaluminum reacted
instantly with 1c in aliphatic solvents (pentane, hexane) as
indicated by a color change from red to dark green. Upon
crystallization from hexane solution at -35 °C, dark green single
crystals of complex 4 could be obtained in reasonable yields
(59%; thicker crystals appear black). The crystals could be
redissolved in a hexane/toluene mixture. The overall structure
of 4 was determined by X-ray crystallography as Cp*2U[(µ-
CH2CH3)AlEt2(µ-Cl)]2UCp*2 (Figure 4); however, the quality
of the crystals (examined from different batches and reactions)
precluded a detailed discussion of metrical parameters. The
formation of a UIII compound, 4, with this molecular composi-
tion/connectivity (Scheme 2) is consistent with the observed
color changes, microanalytical data, mass spectrum (peak
Experimental Procedures
General Remarks. This chemistry was performed under argon
with rigorous exclusion of air and water using Schlenk, vacuum
line, and glovebox techniques. Solvents were sparged with UHP
argon (airgas) and dried over columns containing Q-5 and molecular
sieves. NMR solvents (Cambridge Isotopes) were dried over
benzophenone-ketyl, degassed, and vacuum transferred before use.
Cp*2UCl2 (1a) and Cp*2UMe2 (1b) were prepared according to
the literature procedures.29,30 The synthesis of Cp*2UMeCl (1c)
was slightly modified31 by stirring an equimolar mixture of 1a and
1b overnight at ambient temperature. HCp* (Aldrich) was distilled
before use. Trimethylaluminum, triethylaluminum, trimethylgallium,
1
and trimethylindium were used as received from Aldrich. H and
13C NMR spectra were recorded on Bruker 500 and 600 MHz
spectrometers. Infrared spectra were recorded as Nujol mulls
between CsI plates on a NICOLET Impact 410 FTIR spectrometer.
Elemental analyses were performed on an Elementar Vario EL III.
(42) (a) Manriquez, J. M.; Fagan, P. J.; Marks, T. J.; Vollmer, S. H.;
Day, C. S.; Day, V. W. J. Am. Chem. Soc. 1979, 101, 5075. (b) Fagan,
P. J.; Manriquez, J. M.; Marks, S. H.; Day, C. S.; Vollmer, T. J.; Day,
V. W. Organometallics 1982, 1, 170.
assignable to [Cp*2UCl]3),42 and H NMR data (Figure S3,
1
Supporting Information). Moreover, the reducing action of
organoaluminum compounds is well-established in Ziegler-Natta
(43) Reinheckel, H. Angew. Chem. 1963, 75, 1206.

1178 Organometallics, Vol. 28, No. 4, 2009
Dietrich et al.
Table 4. X-ray Data Collection Parameters for Cp*2UCl2 (1a),
Cp*2UClMe (1c), [Cp*2UAl3(µ3-CH2)(µ2-CH3)2(CH3)7] (2), and
Cp*2U[(µ-Me)(InMe3)]2 (3)
X-ray Data Collection, Structure Determinations, and
Refinement. A typical procedure is given for 2. All other structures
were done similarly except as noted. Table 4 presents the crystal-
lographic data.
compound
1a
1c
2
3
empirical formula C20H30Cl2U C21H33ClU C30H59Al3U C28H54In2U
Cp*2UAl3(µ3-CH2)(µ2-CH3)2(CH3)7, 2. A red plate of ap-
proximate dimensions 0.06 × 0.18 × 0.21 mm3 was mounted on
a glass fiber and transferred to a Bruker CCD platform diffracto-
meter. The SMART44 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 SAINT45 and SADABS46 to yield the reflection data file.
Subsequent calculations were carried out using the SHELXTL47
program. The diffraction symmetry was mmm, and the systematic
absences were consistent with the orthorhombic space group
P212121, 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
factors48 for neutral atoms were used throughout the analysis.
Hydrogen atoms were included using a riding model. At conver-
gence, wR2 ) 0.0689 and GOF ) 1.121 for 352 variables refined
against 7678 data (0.78 Å), and R1 ) 0.0294 for those 7231 data
with I > 2.0σ(I) (GOF ) S ) [∑[w(Fo2 - Fc2)2]/(n - p)]1/2 where
n is the number of reflections and p is the total number of parameters
refined). The structure was refined using the SHELXTL47 TWIN
command, BASF ) 0.328(7).
Cp*2UCl2, 1a. A red crystal of approximate dimensions 0.04 ×
0.13 × 0.23 mm3 was mounted on a glass fiber and transferred to
a Bruker CCD platform diffractometer. The diffraction symmetry
was 2/m, and the systematic absences were consistent with the
centrosymmetric monoclinic space group P21/n, which was later
determined to be correct. Hydrogen atoms were located from a
difference-Fourier map and refined (x, y, z, and Uiso). At conver-
gence, wR2 ) 0.0477 and GOF ) 1.071 for 328 variables refined
against 5004 data (0.75Å); R1 ) 0.0201 for those 4095 data with
I > 2.0σ(I).
FW
579.37
148(2)
558.95
163(2)
738.74
163(2)
858.38
163(2)
temp (K)
cryst syst
space group
a (Å)
monoclinic monoclinic orthorhombic triclinic
P21/n
8.6224(12) 8.1602(13) 9.5861(14)
j
P21
P212121
P1
10.5446(16)
b (Å)
c (Å)
16.960(2)
13.919(2)
90
91.340(2)
90
2034.9(5)
4
1.891
17.039(3) 12.0189(17) 16.071(3)
8.3283(13) 30.141(4)
90 90
116.735(3) 90
90 90
1034.2(3) 3472.7(9)
18.994(3)
88.303(2)
89.779(2)
83.912(2)
3199.1(8)
4
R (deg)
ꢀ (deg)
γ (deg)
vol (Å3)
Z
2
4
Fcalcd (mg/mm3)
1.795
7.976
0.0226
0.0355
1.413
4.765
0.0308
0.0438
1.782
6.491
0.0262
0.3568
µ (mm-1
)
8.237
R1a (I > 2.0σ(I)) 0.0288
wR2b (all data)
0.0349
b
a R1 ) ∑||Fo| - |Fc||/∑|Fo|. wR2 ) [∑[w(Fo - Fc2)2]/∑[w(Fo )2]]1/2
.
2
2
Cp*2UAl3(µ3-CH2)(µ2-CH3)2(CH3)7, 2. Cp*2UMe2 (150 mg,
0.279 mmol) was dissolved in 5 mL of hexane, and AlMe3 (161
mg, 2.236 mmol) dissolved in 3 mL of hexane was added under
stirring. The solution was filtered after 1 h and transferred into a
vial, and the solvent was reduced by evaporation at ambient
temperature for several hours. Overnight crystallization at -35 °C
afforded red crystalline 2 in 49% yield (104 mg). The synthesis of
2 is also possible in pentane. Anal. Calcd for C30H59Al3U (741.796
g/mol): C, 48.58; H, 8.42. Found: C, 50.16; H, 7.80. 1H NMR (500
MHz, toluene-d8, 25 °C): δ ) 9.17, 7.09, 6.21, -1.33, -2.09,
-3.06, -3.75, -5.00, -7.38, -7.94, -9.58, -14.07 ppm (see
Figures S1 and S2 of Supporting Information). IR (Nujol): 1308 m,
1152 w, 971 w, 919 w, 888 w, 842 w cm-1
.
Cp*2U[(µ-Me)InMe3]2, 3. Cp*2UMe2 (100 mg, 0.19 mmol) was
dissolved in 10 mL of pentane. InMe3 (2.5 eq., 74 mg, 0.46 mmol)
was added, and the reaction mixture was stirred for 2 h. The solvent
was reduced to ca. 4 mL under vacuum. Cooling the red solution
to -35 °C produced colorless crystals of InMe3 overnight. The red
supernatant was decanted and filtered, producing orange crystals
(thicker crystals appear red) of 3 overnight at -35 °C. The X-ray
crystal structure was confirmed by checking the cell constants of a
second crystal. The InMe3 was easily removed under vacuum,
making follow-up characterization difficult. After drying under
vacuum, only Cp*2UMe2 (1b) could be recovered in quantitative
yield. A 1H NMR spectroscopic examination of a solution of
Cp*2UMe2 and InMe3 in C6D6 did not reveal any significant
chemical shifts of the adduct signals.
Cp*2UCl(CH3), 1c. A red crystal of approximate dimensions
0.07 × 0.10 × 0.23 mm3 was mounted on a glass fiber and
transferred to a Bruker SMART1K diffractometer. For data
collection, 40 s/frame scan time was used for a hemisphere of
diffraction data. The diffraction symmetry was 2/m, and the
systematic absences were consistent with the monoclinic space
groups P21 and P21/m. It was later determined that the noncen-
trosymmetric space group P21 was the better choice. The structure
was solved in space groups P21 and P21/m and was disordered in
both. Refinement in space group P21/m was not satisfactory and
resulted in the pentamethylcyclopentadienyl rings adopting an
eclipsed orientation due to the mirror plane. The chloro and methyl
ligands were also disordered. Space group P21 yielded a better
refinement, and a reasonable disorder for the chlorine and methyl
ligands was observed (each was included as two components with
site-occupancy factors ) 0.50, Cl1/Cl2 and C21/C22). It was
necessary to refine all carbon atoms with isotropic thermal
parameters. While neither space group gave an entirely satisfactory
refinement, it was determined that refinement using the noncen-
trosymmetric space group P21 resulted in the best model. Least-
squares analysis yielded wR2 ) 0.0719 and GOF ) 1.070 for 129
variables refined against 4425 data (0.78Å); R1 ) 0.0286 for those
4068 data with I > 2.0σ(I). The structure was refined as a twin
with BASF ) 0.514(14).
[Cp*2UAl(µ-CH2CH3)(Et)2(µ-Cl)]2, 4. Cp*2UClMe (200 mg,
0.36 mmol) was dissolved in 15 mL of hexane, and AlEt3 (200
mg, 1.75 mmol) in 5 mL of hexane was added under stirring. After
the color had changed from red to dark green within 1 h, the mixture
was reduced to ca. 2 mL. The dark green solid, which crystallized
upon evaporation of the solvent under vacuum, was redissolved
by addition of 1 mL of toluene to the mixture. After filtration, the
product was recovered by crystallization at -35 °C as dark green
almost black crystals. Three crystallization steps within 3 days
yielded 138 mg (59%) of a single-crystalline product. The crystals
could be stored in glass ampules at ambient temperature over weeks
without decomposition. Anal. Calcd for C52H88Al2Cl2U2 (1314.198
g/mol): C, 46.90; H, 6.56. Found: C, 47.52; H, 6.75. 1H NMR (500
MHz, toluene-d8, 25 °C): δ ) -2.77, -9.90, -11.83 ppm (see
Figure S3 of Supporting Information). IR (Nujol): 1303 m, 1240 w,
1194 m, 1168 m, 1152 m, 1080 w, 1023 w, 971 w, 935 w, 888 w,
Cp*2[(µ-Me)InMe3]2, 3. A red crystal of approximate dimen-
sions 0.20 × 0.23 × 0.25 mm3 was mounted on a glass fiber and
transferred to a Bruker CCD platform diffractometer. For data
collection, 25 s/frame scan time was used for a sphere of diffraction
(44) SMART Software Users Guide, version 5.1, Bruker Analytical
X-Ray Systems, Inc.; Madison, WI, 1999.
(45) SAINT Software Users Guide, version 6.0, Bruker Analytical X-Ray
Systems, Inc.; Madison, WI, 1999.
847 w, 811 w, 681 s, 547 m cm-1
.

ReactiVity of (C5Me5)2UMe2 and (C5Me5)2UMeCl
Organometallics, Vol. 28, No. 4, 2009 1179
data. There were no systematic absences nor any diffraction
symmetry other than the Friedel condition. The centrosymmetric
triclinic space group P1 was assigned and later determined to be
Supporting Information Available: 1H NMR spectra showing
the progress of the reaction of 1b with trimethylaluminum, 1H NMR
spectrum of single-crystalline 2, VT H NMR spectra of complex
1
j
correct. The pentamethylcyclopentadienyl ring defined by atoms
C39-C48 was disordered and included using multiple components,
partial site-occupancy factors, and isotropic thermal parameters. At
convergence, wR2 ) 0.0661 and GOF ) 1.085 for 591 variables
refined against 15540 data (0.75Å), R1 ) 0.0280 for those 13853
data with I > 2.0σ(I).
4, and full crystallographic data for complexes 1a, 1c, 2, 3, and 4
(CIF). This material is available free of charge via the Internet at
http://pubs.acs.org.
OM800914W
(46) Sheldrick, G. M. SADABS, version 2.10, Bruker Analytical X-Ray
Systems, Inc.; Madison, WI, 2002.
(47) Sheldrick, G. M. SHELXTL, version 6.12, Bruker Analytical X-Ray
Systems, Inc.; Madison, WI, 2001.
(48) International Tables for X-Ray Crystallography; Kluwer Academic
Publisher: Dordrecht, The Netherlands, 1992; Vol. C.
Acknowledgment. We thank the program Nanoscience@
UiB and the Chemical Sciences, Geosciences, and Bio-
sciences Division of the Office of Basic Energy Sciences of
the U.S. Department of Energy for financial support.