In situ generation of uranium alkyl complexes

Article abstract of DOI:10.1039/b927264j

A new method for generating uranium alkyl complexes is described. Although homoleptic uranium alkyl complexes are notoriously unstable and difficult to work with, by generating such species in situ, a wide range of alkyl complexes can be accessed from UI₃(THF)₄.

Full text of DOI:10.1039/b927264j

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In situ generation of uranium alkyl complexesw
´
Selma Duhovic, Saeed Khan and Paula L. Diaconescu*
Received (in Berkeley, CA, USA) 24th December 2009, Accepted 12th March 2010
First published as an Advance Article on the web 6th April 2010
DOI: 10.1039/b927264j
A new method for generating uranium alkyl complexes is
described. Although homoleptic uranium alkyl complexes are
notoriously unstable and difficult to work with, by generating
such species in situ, a wide range of alkyl complexes can be
accessed from UI3(THF)4.
obtained directly from UI3(THF)436–38 and [K(OEt2)2]2[NNfc].18
36–38
Since UI3(THF)4
is a readily available starting material
and U–I bonds are weaker and, therefore, easier to involve in
salt-metathesis reactions than U–Cl bonds, we decided to
follow the same reaction protocol for the synthesis of a
(NNpy)UI2 starting material, even though the formation of
the uranium(IV) complex would require the disproportionation
of the uranium(III) complex UI3(THF)4.1,2,18,39
The reaction between [K(OEt2)2]2[NNpy] and UI3(THF)4
gave a mixture of products that proved intractable. However,
the reaction between [Li(OEt2)2]2[NNpy] and UI3(THF)4
(eqn (1)) led to the isolation of 1py2-U.z Although 1py2-U
was too insoluble in hydrocarbons or diethyl ether to allow
its purification, a single-crystal X-ray diffraction study (see the
ESIw for details) confirmed the solid-state structure of 1py2-U.
The reactivity of uranium complexes can be substantially
modulated by tuning the electronic and steric properties of
their ancillary-ligand framework.1–9 We have been interested
in the reactivity of d0fn metal centers supported by ferrocene
ligands10–17 and proposed that
a weak interaction, of
donor–acceptor type, takes place between iron and the metal
when ferrocene diamides (NNfc = fc(NSitBuMe2)2, fc = 1,10-
ferrocenylene, Chart 1) are used.18,19 For uranium complexes,
we recently reported novel C–H activation reactions by
(NNfc)U(CH2Ph)2, 1fc-U(CH2Ph)2, with both benzyl ligands
of 1fc-U(CH2Ph)2 engaging an sp2-C–H bond of
1-methylimidazole.10,20 We have also shown that, after the
C–H activation events, a unique cascade of functionalization
reactions can be thermally induced.10
In order to probe whether the reactivity of 1fc-U(CH2Ph)2 is
unique,21 we decided to synthesize analogous dibenzyl
complexes of a tridentate, dianionic supporting ligand, 2,6-
bis(2,6-diisopropylanilidomethyl)pyridine (NNpy, Chart 1),
because its geometry mimics that of NNfc. Complexes of
Ti(IV),22–24 Zr(IV),25–28 Ta(V),29,30 and lanthanides31–33
supported by pyridine–diamide ligands are known.
Dialkyl complexes of Th(IV) supported by NNpy have also
been reported.34,35 Those complexes were synthesized from
KCH2Ph or LiCH2SiMe3 and the respective thorium dichloride,
(NNpy)ThCl2(DME), which, in turn, was produced in
the salt-metathesis reaction between ThCl4(DME)2 and
Li2(NNpy).34,35 The complex 1fc-U(CH2Ph)2 was also synthesized
by the salt-metathesis reaction of KCH2Ph and 1fc-I2(THF),
ð1Þ
The analogous 1fc2-U is a by-product of the reaction between
36
UI3(THF)4
and [K(OEt2)2]2[NNfc] that also gives
1fc-I2(THF).18 However, our attempts to modify the conditions
for the reaction shown in eqn (1) have not yielded a (NNpy)UI2
complex. Inspired by a report from the Hayton group on the
synthesis of homoleptic uranium alkyl complexes40 and
encouraged by the fact that (NNpy)Th(CH2SiMe3)2 was
accessible from an in situ reaction between ‘‘Cl2Th(CH2SiMe3)2’’
and H2(NNpy), we decided to pursue the synthesis of uranium
alkyl complexes supported by NNpy by generating and not
isolating their alkyl precursors.
ð2Þ
The reaction of UI3(THF)436 and three equivalents of KCH2Ph,
followed by the addition of 0.75 equivalents of H2(NNpy) at low
temperatures, led to the formation of the uranium(IV) dibenzyl
complex (NNpy)U(CH2Ph)2, 1py-U(CH2Ph)2 (eqn (2)). The
reaction was reproducible and allowed the isolation of
1py-U(CH2Ph)2 in 54–62% yield consistently. The complex
1py-U(CH2Ph)2 was characterized by elemental analysis,
1H NMR spectroscopy, and X-ray crystallography (Fig. 1).
Interestingly, by changing the stoichiometry and employing
two equivalents of KCH2Ph in a reaction with UI3(THF)436 and
0.75 equivalents of H2(NNpy), a new product, 1py-UI(CH2Ph)
(Fig. 1), was obtained (eqn (3)). The reaction was also
reproducible and occurred consistently in 68–76% yield.
Chart 1 Pro-ligands used in the present study.
Department of Chemistry & Biochemistry, University of California,
Los Angeles, CA 90095, USA. E-mail: pld@chem.ucla.edu;
Fax: +1 310 206 4038; Tel: +1 310 794 4809
w EElectronic supplementary information (ESI) available: Detailed
syntheses, NMR spectra, and crystallographic information. CCDC for
1py2-U, 1py-U(CH2Ph)2, and 1py-UI(CH2Ph) are 756840, 756841, and
756842, respectively. For ESI and crystallographic data in CIF or
other electronic format see DOI: 10.1039/b927264j
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Fig.
1
Thermal-ellipsoid (50% probability) representation of
1py-U(CH2Ph)2 (left) and 1py-UI(CH2Ph) (right). Hydrogen atoms
were removed for clarity.
We propose that U(CH2Ph)3(THF)x or UI(CH2Ph)2(THF)y,
generated in situ in the reactions shown in eqn (2) and (3),
respectively, reacts with H2(NNpy) when the disproportionation
to the uranium(IV) product occurs; the disproportionation of
either species to uranium(IV) complexes and uranium(0) before
the reaction with H2(NNpy) is also possible. The formation of
1py-UI(CH2Ph) is especially noteworthy since our attempts to
generate the analogous 1fc-UI(CH2Ph) from 1fc-I2(THF) and
one equivalent of KCH2Ph or by comproportionation from
1fc-I2(THF) and 1fc-U(CH2Ph)2 led to equilibrium mixtures
containing all three uranium complexes.
Scheme 1 Formation of uranium dialkyl complexes supported by
ferrocene–diamide ligands.
aliquots from crude reaction mixtures, they were not the sole
products and could not be separated from the dialkyl and
diiodide complexes also present.
In conclusion, a general method for the synthesis of
uranium(IV) alkyl complexes has been presented. This one-pot
procedure starts from a readily available uranium precursor,
UI3(THF)4, and bypasses the need to isolate halide or homoleptic-
alkyl uranium starting materials. The products of all reactions
were uranium(IV) complexes, presumably formed by the dis-
proportionation of uranium(III) intermediates. Both potassium
benzyl and lithium alkyl reagents were employed and the
ancillary ligands targeted included pyridine and ferrocene-
based diamides. We are currently in the process of extending
the present procedure to the formation of other uranium alkyl
complexes.
ð3Þ
Encouraged by the formation of 1py-U(CH2Ph)2 and
1py-UI(CH2Ph), we decided to explore the reaction scope of
the in situ generation of uranium alkyl complexes. To that end,
similar reaction conditions as those presented in eqn (2) were
used in order to generate (NNfc0)U(CH2Ph)2, 1fc0-U(CH2Ph)2,
where NNfc0 = fc(NSiMe3)2 (Chart 1). Although we had
36
observed the formation of 1fc0-I2(THF) from UI3(THF)4
and [K(OEt2)2]2[NNfc0] previously, the reaction was not
reproducible thus prompting us to employ the tert-
butyldimethyl variant, NNfc = fc(NSitBuMe2)2.
Financial support of this work by the UCLA, Sloan
Foundation, and DOE (Grant ER15984) is gratefully
acknowledged. SD thanks Dr Suyun Jie for a gift of H2(NNpy).
The reaction between UI3(THF)436 and three equivalents of
KCH2Ph, followed by the addition of 0.75 equivalents
of H2(NNfc0) at low temperatures, led to the formation of
(NNfc0)U(CH2Ph)2, 1fc0-U(CH2Ph)2 (Scheme 1), in 51–77%
yield, obtained again consistently and reproducibly. Furthermore,
the same reaction conditions could be applied to the synthesis
of (NNfc0)U(CH2SiMe3)2, 1fc0-U(CH2SiMe3)2, in 60–80% yield
(Scheme 1), circumventing the need to isolate a halide starting
Notes and references
z Characterization data for 1py2-U. 1H NMR (C6D6, 500 MHz, 25 1C),
d (ppm): 97.97 (s, 2H, aromatic-CH), 35.22 (s, 4H, aromatic-CH,
NCH2, or CH(CH3)2), 25.57 (s, 4H, aromatic-CH, NCH2, or
CH(CH3)2), 21.53 (s, 24H, CH(CH3)2), 3.47 (s, 2H, aromatic-CH),
ꢁ5.27 (s, 1H, C5H3N), ꢁ11.30 (s, 4H, aromatic-CH, NCH2, or
CH(CH3)2). Because of its limited solubility, 1py2-U could not be
obtained analytically pure.
t
material. The complexes 1fc-U(CH2Ph)2 and 1fc-U(CH2 Bu)2,
Characterization data for 1py-U(CH2Ph)2. Yield: 54–62%. 1H NMR
(500 MHz, C6D6), d (ppm): 70.91 (s, 2H, aromatic-CH or CH2), 63.29
(s, 2H, aromatic-CH or CH2), 43.18 (s, 2H, aromatic-CH or CH2),
25.82 (s, 2H, aromatic-CH or CH2), 19.26 (s, 6H, CH(CH3)2), 16.72
(s, 2H, aromatic-CH or CH2), 13.12 (s, 6H, CH(CH3)2), 3.38 (s, 6H,
CH(CH3)2), 1.34 (s, 2H, aromatic-CH or CH2), ꢁ3.67 (s, 6H,
CH(CH3)2), ꢁ6.91 (s, 2H, aromatic-CH or CH2), ꢁ9.97 (s, 2H,
aromatic-CH or CH2), ꢁ11.38 (s, 1H, p-NC5H3 or p-C6H5), ꢁ21.00
(s, 2H, aromatic-CH or CH2), ꢁ66.24 (s, 2H, aromatic-CH or CH2),
ꢁ111.21 (s, 2H, aromatic-CH or CH2). Anal. (%): calcd for
C45H55N3U: C, 61.70; H, 6.33; N, 4.80. Found: C, 61.89; H, 6.15;
N, 4.79.
previously reported,18 and 1fc-U(CH2SiMe3)2 were also
synthesized by the present method (Scheme 1) in better yields
than those recorded for their syntheses from 1fc-I2(THF)
(84% vs. 52% for 1fc-U(CH2Ph)2, 54% vs. 27% for
t
1fc-U(CH2 Bu)2,18 and 87% for 1fc-U(CH2SiMe3)2).
Attempts to isolate the mixed alkyl-iodide uranium
complexes supported by ferrocene-diamide ligands have met
with little success by using the present method. Although these
1
species formed, as assessed by inspecting H NMR spectra of
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Characterization data for 1py-UI(CH2Ph). Yield: 68–76%. 1H NMR
(500 MHz, C6D6), d (ppm): 100.68 (s, 2H, aromatic-CH or CH2), 96.38
(s, 2H, aromatic-CH or CH2), 71.58 (s, 2H, aromatic-CH or CH2),
37.91 (s, 2H, aromatic-CH or CH2), 28.61 (s, 6H, CH(CH3)2), 21.92
(s, 1H, p-NC5H3, p-C6H3, or p-C6H5), 21.68 (s, 1H, p-NC5H3, p-C6H3,
or p-C6H5), 16.17 (s, 6H, CH(CH3)2), 1.38 (s, 2H, aromatic-CH or
CH2), 0.79 (s, 6H, CH(CH3)2), ꢁ1.54 (s, 1H, p-NC5H3, p-C6H3, or
p-C6H5), ꢁ5.98 (s, 2H, aromatic-CH or CH2), ꢁ6.54 (s, 2H, aromatic-
CH or CH2), ꢁ8.58 (s, 2H, aromatic-CH or CH2), ꢁ16.13 (s, 1H,
p-NC5H3, p-C6H3, or p-C6H5), ꢁ16.76 (s, 6H, CH(CH3)2), ꢁ41.88
(s, 2H, aromatic-CH or CH2). Anal. (%): calcd for C38H48IN3U:
C, 50.06; H, 5.31; N, 4.61. Found: C, 50.96; H, 5.42; N, 4.27.
Characterization data for 1fc0-U(CH2Ph)2. Yield: 51–77%. 1H NMR
(300 MHz, C6D6), d (ppm): 47.86 (s, 18H, Si(CH3)3), ꢁ8.21 (s, 4H,
C5H4 or C6H5), ꢁ11.92 (s, 2H, p-C6H5), ꢁ17.19 (s, 4H, C5H4 or
C6H5), ꢁ17.75 (s, 4H, C5H4 or C6H5), ꢁ34.49 (s, 4H, C5H4 or C6H5).
Anal. (%): calcd for C30H40FeN2Si2U: C, 46.27; H, 5.18; N, 3.60.
Found: C, 45.92; H, 5.19; N, 3.50.
10 M. J. Monreal, S. Khan and P. L. Diaconescu, Angew. Chem., Int.
Ed., 2009, 48, 8352–8355.
11 C. T. Carver and P. L. Diaconescu, J. Alloys Compd., 2009, 488,
518–523.
12 E. M. Broderick and P. L. Diaconescu, Inorg. Chem., 2009, 48,
4701–4706.
13 C. T. Carver, D. Benitez, K. L. Miller, B. N. Williams,
E. Tkatchouk, W. A. Goddard and P. L. Diaconescu, J. Am.
Chem. Soc., 2009, 131, 10269–10278.
14 C. T. Carver and P. L. Diaconescu, J. Am. Chem. Soc., 2008, 130,
7558–7559.
15 M. J. Monreal, C. T. Carver and P. L. Diaconescu, Inorg. Chem.,
2007, 46, 7226–7228.
16 K. L. Miller, B. N. Williams, D. Benitez, C. T. Carver,
K. R. Ogilby, E. Tkatchouk, W. A. Goddard and
P. L. Diaconescu, J. Am. Chem. Soc., 2010, 132, 342–355.
17 C. T. Carver, B. N. Williams, K. R. Ogilby and P. L. Diaconescu,
Organometallics, 2010, 29, 835–846.
18 M. J. Monreal and P. L. Diaconescu, Organometallics, 2008, 27,
1702–1706.
19 C. T. Carver, M. J. Monreal and P. L. Diaconescu, Organo-
metallics, 2008, 27, 363–370.
20 M. J. Monreal and P. L. Diaconescu, J. Am. Chem. Soc., 2010, in
press.
21 P. L. Diaconescu, Curr. Org. Chem., 2008, 12, 1388–1405.
22 F. Guerin, D. H. McConville and N. C. Payne, Organometallics,
1996, 15, 5085–5089.
23 F. Guerin, D. H. McConville and J. J. Vittal, Organometallics,
1997, 16, 1491–1496.
24 K. K. Kang, S.-P. Hong, Y.-T. Jeong, T. Shiono and T. Ikeda,
J. Polym. Sci., Part A: Polym. Chem., 1999, 37, 3756–3762.
25 F. Guerin, D. H. McConville and J. J. Vittal, Organometallics,
1996, 15, 5586–5590.
26 F. Guerin, D. H. McConville, J. J. Vittal and G. A. P. Yap,
Organometallics, 1998, 17, 5172–5177.
´
27 F. Guerin, O. Del Vecchio and D. H. McConville, Polyhedron,
1998, 17, 917–923.
28 Z. Ziniuk, I. Goldberg and M. Kol, Inorg. Chem. Commun., 1999,
2, 549–551.
Characterization data for 1fc0-U(CH2SiMe3)2. Yield: 60–80%.
1H NMR (300 MHz, C6D6), d (ppm): 64.04 (s, 18H, SiC(CH3)3),
ꢁ21.84 (s, 4H, C5H4), ꢁ30.40 (s, 18H, Si(CH3)3), ꢁ43.38 (s, 4H,
C5H4). Anal. (%): calcd for C24H48FeN2Si4U: C, 37.39; H, 6.28; N,
3.63. Found: C, 37.28; H, 6.10; N, 3.16.
Characterization data for 1fc-U(CH2SiMe3)2. Yield: 87%. 1H NMR
(300 MHz, C6D6), d (ppm): 64.53 (s, 12H, Si(CH3)2), 40.27 (s, 18H,
SiC(CH3)3), ꢁ22.22 (s, 4H, C5H4), ꢁ32.83 (s, 18H, Si(CH3)3), ꢁ44.34
(s, 4H, C5H4). Anal. (%): calcd for C30H60FeN2Si4U: C, 42.14; H,
7.07; N, 3.28. Found: C, 42.22; H, 6.92; N, 3.16.
Crystal data for 1py2-U: C62H82N6Uꢂ0.8(C6H14), monoclinic, space
group C2/c, a = 19.828(2) A, b = 22.158(2) A, c = 14.7466(16) A,
,
b = 108.964(1)1, V = 6127.3(11) A3, Z = 4, m = 2.693 mmꢁ1
F(000) = 2496, T = 100(2) K, 30 847 measured reflections, 9054
unique (Rint = 0.0281), R1 = 0.0255, wR2 = 0.0651 for I > 2s(I).
Crystal data for 1py-U(CH2Ph)2: C45H55N3UꢂOC4H10, triclinic,
ꢀ
space group P1,
a = 10.5281(10) A, b = 12.7043(12) A,
c = 17.9213(16) A, b = 105.205(1)1, V = 2213.0(4) A3, Z = 2,
m = 3.705 mmꢁ1, F(000) = 960, T = 100(2) K, 22 255 measured
reflections, 12 383 unique (Rint = 0.0196), R1 = 0.0313, wR2
0.0806 for I > 2s(I).
=
Crystal data for
1
py-UI(CH2Ph): C38H48N3IUꢂ0.5(C14H12),
29 F. Guerin, D. H. McConville and J. J. Vittal, Organometallics,
1995, 14, 3154–3156.
30 F. Guerin, D. H. McConville, J. J. Vittal and G. A. P. Yap,
Organometallics, 1998, 17, 1290–1296.
monoclinic, space group P21/c, a = 11.3927(15) A, b = 13.9847(19) A,
c = 25.077(3) A, b = 95.235(2)1, V = 3978.7(9) A3, Z = 4,
m = 4.890 mmꢁ1, F(000) = 1956, T = 100(2) K, 26 600 measured
reflections, 6513 unique (Rint = 0.0829), R1 = 0.0397, wR2 = 0.0769
for I > 2s(I).
31 F. Estler, G. Eickerling, E. Herdtweck and R. Anwander, Organo-
metallics, 2003, 22, 1212–1222.
32 M. Zimmermann, F. Estler, E. Herdtweck, K. W. Tornroos
and R. Anwander, Organometallics, 2007, 26, 6029–6041.
33 M. Zimmermann, K. W. Tornroos, R. M. Waymouth and
¨
R. Anwander, Organometallics, 2008, 27, 4310–4317.
34 C. A. Cruz, D. J. H. Emslie, L. E. Harrington, J. F. Britten and
C. M. Robertson, Organometallics, 2007, 26, 692–701.
35 C. A. Cruz, D. J. H. Emslie, C. M. Robertson, L. E. Harrington,
H. A. Jenkins and J. F. Britten, Organometallics, 2009, 28,
1891–1899.
36 L. R. Avens, S. G. Bott, D. L. Clark, A. P. Sattelberger,
J. G. Watkin and B. D. Zwick, Inorg. Chem., 1994, 33, 2248–2256.
37 D. L. Clark, A. P. Sattelberger, S. G. Bott and R. N. Vrtis, Inorg.
Chem., 1989, 28, 1771–1773.
38 D. L. Clark and A. P. Sattelberger, Inorg. Synth., 1997, 31, 307–315.
39 A. L. Odom, P. L. Arnold and C. C. Cummins, J. Am. Chem. Soc.,
1998, 120, 5836–5837.
1 P. L. Diaconescu, P. L. Arnold, T. A. Baker, D. J. Mindiola and
C. C. Cummins, J. Am. Chem. Soc., 2000, 122, 6108–6109.
2 P. L. Diaconescu and C. C. Cummins, J. Am. Chem. Soc., 2002,
124, 7660–7661.
3 I. Castro-Rodriguez, H. Nakai, L. N. Zakharov, A. L. Rheingold
and K. Meyer, Science, 2004, 305, 1757–1759.
4 O. P. Lam, C. Anthon and K. Meyer, Dalton Trans., 2009,
9677–9691.
5 T. Cantat, C. R. Graves, B. L. Scott and J. L. Kiplinger, Angew.
Chem., Int. Ed., 2009, 48, 3681–3684.
6 T. Cantat, B. L. Scott, D. E. Morris and J. L. Kiplinger, Inorg.
Chem., 2009, 48, 2114–2127.
7 O. T. Summerscales, F. G. N. Cloke, P. B. Hitchcock, J. C. Green
and N. Hazari, Science, 2006, 311, 829–831.
8 P. L. Arnold, D. Patel, C. Wilson and J. B. Love, Nature, 2008,
451, 315–317.
40 S. Fortier, B. C. Melot, G. Wu and T. W. Hayton, J. Am. Chem.
Soc., 2009, 131, 15512–15521.
9 W. J. Evans, S. A. Kozimor and J. W. Ziller, Science, 2005, 309,
1835–1838.
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3392 | Chem. Commun., 2010, 46, 3390–3392