Uranium(IV) amide and halide derivatives of two tripodal tris(N-arylamido-dimethylsilyl)methanes

Article abstract of DOI:10.1039/b926018h

Reaction of three equivalents of ArNH₂ (Ar = 3,5-Me ₂C₆H₃) with HC(SiMe₂Br)₃ in the presence of the auxiliary base NEt₃ afforded the tripodal tris(N-arylamine-dimethylsilyl)methane HC{SiMe₂N(H)Ar}₃ (1) in 83% yield. Three-fold deprotonation of 1 with n-butyllithium afforded the corresponding tri-lithium tris(N-arylamido-dimethylsilyl)methane etherate [HC{SiMe₂N(Li)Ar}₃(OEt₂)] (2) in 92% yield. Salt elimination reactions between 2 or the known complex [HC{SiMe ₂N(Li)Ar′}₃(OEt₂)₂] (3) (Ar′ = 4-MeC₆H₄) with one equivalent of uranium(iv) tetrachloride afforded the corresponding tris(N-arylamido-dimethylsilyl)methane uranium(iv) chloride complexes as monomeric [U(Cl){HC(SiMe₂NAr) ₃}(THF)] (4) and dinuclear [{HC(SiMe₂NAr′) ₃}U(Cl)(μ-Cl)U(THF)₂{(Ar′NSiMe₂) ₃CH}] (5) species in 70 and 90% crystalline yields, respectively. Treatment of 4 and 5 with one equivalent of trimethylsilyl iodide resulted in halide exchange and formation of [U(I){HC(SiMe₂NAr) ₃}(THF)₂] (6) and [U(I){HC(SiMe₂NAr′) ₃}(THF)] (7) in 85 and 90% yields, respectively. The heteroleptic amide [U(NCy₂){HC(SiMe₂NAr)₃}(THF)] (8) was prepared from the reaction between 4 and one equivalent of lithium dicyclohexylamide and was isolated in 78% yield. Analogous attempts to prepare [U(NCy₂){HC(SiMe₂NAr′)₃}(THF)] (9) from 5 consistently resulted in intractable mixtures of products. Complexes 1-8 have been characterised by X-ray crystallography, NMR spectroscopy, FTIR spectroscopy, room temperature Evans method solution magnetic moments, and CHN micro-analyses. The Royal Society of Chemistry 2010.

Full text of DOI:10.1039/b926018h

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www.rsc.org/dalton | Dalton Transactions
Uranium(IV) amide and halide derivatives of two tripodal
tris(N-arylamido-dimethylsilyl)methanes†‡
Dipti Patel, William Lewis, Alexander J. Blake and Stephen T. Liddle*
Received 9th December 2009, Accepted 2nd February 2010
First published as an Advance Article on the web 12th March 2010
DOI: 10.1039/b926018h
Reaction of three equivalents of ArNH2 (Ar = 3,5-Me2C6H3) with HC(SiMe2Br)3 in the presence of the
auxiliary base NEt3 afforded the tripodal tris(N-arylamine-dimethylsilyl)methane HC{SiMe2N(H)Ar}3
(1) in 83% yield. Three-fold deprotonation of 1 with n-butyllithium afforded the corresponding
tri-lithium tris(N-arylamido-dimethylsilyl)methane etherate [HC{SiMe2N(Li)Ar}3(OEt2)] (2) in 92%
yield. Salt elimination reactions between 2 or the known complex [HC{SiMe2N(Li)Ar¢}3(OEt2)2] (3)
(Ar¢ = 4-MeC6H4) with one equivalent of uranium(IV) tetrachloride afforded the corresponding
tris(N-arylamido-dimethylsilyl)methane uranium(IV) chloride complexes as monomeric
[U(Cl){HC(SiMe2NAr)3}(THF)] (4) and dinuclear [{HC(SiMe2NAr¢)3}U(Cl)(m-
Cl)U(THF)2{(Ar¢NSiMe2)3CH}] (5) species in 70 and 90% crystalline yields, respectively. Treatment of
4 and 5 with one equivalent of trimethylsilyl iodide resulted in halide exchange and formation of
[U(I){HC(SiMe2NAr)3}(THF)2] (6) and [U(I){HC(SiMe2NAr¢)3}(THF)] (7) in 85 and 90% yields,
respectively. The heteroleptic amide [U(NCy2){HC(SiMe2NAr)3}(THF)] (8) was prepared from the
reaction between 4 and one equivalent of lithium dicyclohexylamide and was isolated in 78% yield.
Analogous attempts to prepare [U(NCy2){HC(SiMe2NAr¢)3}(THF)] (9) from 5 consistently resulted in
intractable mixtures of products. Complexes 1–8 have been characterised by X-ray crystallography,
NMR spectroscopy, FTIR spectroscopy, room temperature Evans method solution magnetic moments,
and CHN micro-analyses.
uranium(IV)–rhenium34 bonds and computational studies showed
they both exhibit s- and p-components in the uranium(IV)–
Introduction
In recent years there has been a drive to develop the non-aqueous
chemistry of uranium1–3 in order to develop a greater understand-
ing of bonding4–6 and applications in catalysis.7,8 In particular,
determining the extent of covalency in uranium-ligand bonds is
important because uranium possesses a unique combination of
chemical and physical properties that distinguish it from tran-
sition, lanthanide, and heavier actinide metals and which might
eventually be exploited in nuclear waste separation processes.1
Although the extent of covalency in uranium complexes lies in
between that of lanthanide and transition metal compounds,
electrostatics still dominate the bonding picture. Consequently,
ligand design is of paramount importance to designing non-
aqueous uranium complexes with well defined coordination sites.
Thus, multi-dentate ligands which employ hard donor centres such
as nitrogen and oxygen are particularly effective at stabilising novel
uranium chemistry,2,9,10 and this is exemplified by the tripodal Tren-
and Tacn-based ligand systems previously employed by Scott,11–21
Burns and Clark,22 and Meyer.23–32
metal bonds. These complexes were stabilised by the Tren ligand
3-
{N(CH2CH2SiMe3)3} (TrenTMS) which has also supported novel
reactivity at uranium,35 but a molecule of THF was coordi-
nated in the gallium complex whereas the rhenium complex
was solvent-free. This indicates that the ethyl linkages of the
Tren ligand are flexible enough to reorganise to shield, or
uncover, a vacant coordination site at uranium depending on
the nature of the coordinated metal anion. Given that ligand
reorganisation energies could be a key factor in the formation,
or not, of uranium–metal linkages,36 and that a flexible ligand
may open up a vacant coordination site leading to otherwise
avoidable decomposition, we targeted more rigid tripodal ligands
as alternative supporting platforms to develop in parallel to our
studies involving Tren–uranium complexes. Our attention was in
particular drawn to the C3 symmetric, tripodal tris(N-arylamido-
dimethylsilyl)methanes developed by Gade,37,38 especially as they,
and closely related trisilylsilanes, were shown to be excellent
platforms for supporting group(IV)-transition metal bonds and
reactivity.39–48 However, these ligands have not yet been applied
to actinide chemistry, indeed there are only two reports of
rare earth tris(N-arylamido-dimethylsilyl)methane complexes,49,50
so we were interested to examine their coordination behaviour
towards uranium, especially as the HC(SiMe2R)3 fragment would
sterically shield one coordination hemisphere of uranium but
the capping group would not directly interact electronically with
uranium as capping amine and arene groups do. Herein, we report
our initial studies on a range of uranium(IV) derivatives of two
tris(N-arylamido-dimethylsilyl)methanes that represent potential
We are interested in the chemistry of uranium–metal bonds
because metal–metal chemistry has historically delivered seminal
developments in our understanding of chemical bonding.6 Re-
cently, we reported the first examples of uranium(IV)–gallium33 and
School of Chemistry, University of Nottingham, University Park, Notting-
ham, UK NG7 2RD. E-mail: stephen.liddle@nottingham.ac.uk
† Dedicated to Professor William Clegg on the occasion of his retirement.
‡ CCDC reference numbers 757624–757630. For crystallographic data in
CIF or other electronic format see DOI: 10.1039/b926018h
6638 | Dalton Trans., 2010, 39, 6638–6647
This journal is
The Royal Society of Chemistry 2010
©

Scheme 1 Synthesis of 1–9 and I.
precursors for the construction of unsupported uranium–metal
the nitrogen-bound hydrogens point outwards to exo positions.
The molecular geometry parameters lie in the expected ranges.
With 1 and I in hand we prepared the tri-lithium salts
as ligand transfer reagents. Accordingly, treatment of 1 with
three equivalents of n-butyllithium in a hexane–diethyl ether
mixture afforded the corresponding tri-lithium tris(N-arylamido-
dimethylsilyl)methane etherate [HC{SiMe2N(Li)Ar}3(OEt2)] (2)
as an off-white solid in 92% yield following work-up, Scheme 1. Al-
though in the solid-state an asymmetric structure of Ci symmetry
is formed (vide infra), the 1H and 13C NMR spectra, which confirm
the presence of one molecule of diethyl ether, are consistent with
a time-averaged C3 symmetric species in solution which is in line
with the highly fluxional nature of many amido-lithium aggregates
in solution.
Colourless crystals of 2 were obtained from hexane. The
asymmetric unit of 2 and the whole molecular structure are shown
in Fig. 2 and selected bond lengths and angles are compiled in
Table 1. The CSi3N3Li3 core of the asymmetric unit adopts a
distorted adamantyl-type structure such that in the solid state
the three lithium centres are in different environments. One
lithium [Li(2)] is coordinated to the three amide centres in a
bonds.
Results and discussion
We selected two tris(N-arylamino-dimethylsilyl)methanes as tar-
gets, namely the new methane HC{SiMe2N(H)Ar}3 (Ar = 3,5-
Me2C6H3, 1), and the known methane HC{SiMe2N(H)Ar¢}3 (Ar =
4-MeC6H4, I) reported by Gade.38 Accordingly, and in line with
published methods,37,38 treatment of HC(SiMe2Br)3 with three
equivalents of ArNH2, in the presence of the auxiliary base
triethylamine, afforded, after work up, 1 in 83% yield as an off-
white powder, Scheme 1. The 1H and 13C NMR spectra of 1
are consistent with the proposed formulation and the N–H and
Si3C–H protons were found to resonate at 3.47 and 0.94 ppm,
respectively.
Colourless crystals of 1 suitable for X-ray diffraction were grown
from hexane; the molecular structure is illustrated in Fig. 1 and
selected bond lengths and angles are listed in Table 1. In the solid
state, 1 forms a bowl-like conformation with the three arylamine
arms arranged ‘up’ with respect to the methane C–H bond, and
This journal is
The Royal Society of Chemistry 2010
Dalton Trans., 2010, 39, 6638–6647 | 6639
©

◦
˚
Table 1 Selected bond lengths (A) and angles ( ) for 1–3
1
C(1)–Si(1)
1.8859(14)
1.8803(14)
1.7468(13)
114.20(7)
114.58(7)
C(1)–Si(2)
Si(1)–N(1)
Si(3)–N(3)
Si(1)–C(1)–Si(3)
1.8925(14)
1.7413(13)
1.7550(14)
114.56(7)
C(1)–Si(3)
Si(2)–N(2)
Si(1)–C(1)–Si(2)
Si(2)–C(1)–Si(3)
2
C(1)–Si(1)
C(1)–Si(3)
Si(2)–N(2)
N(1)–Li(1)
1.898(2)
1.903(2)
1.7323(17)
2.078(4)
2.184(4)
2.112(4)
1.990(4)
2.503(4)
2.460(4)
2.081(4)
2.503(4)
114.65(10)
117.91(10)
101.83(17)
99.21(16)
C(1)–Si(2)
Si(1)–N(1)
Si(3)–N(3)
N(1)–Li(2)
N(2)–Li(1)
N(3)–Li(2)
Li(3)–O(1)
Li(1) ◊ ◊ ◊ C(4)
Li(2) ◊ ◊ ◊ C(19)
N(2)–Li(1A)
Li(1A) ◊ ◊ ◊ C(14)
Si(1)–C(1)–Si(3)
N(1)–Li(2)–N(2)
N(2)–Li(2)–N(3)
N(1)–Li(3)–N(3)
1.909(2)
1.7376(17)
1.7145(18)
2.060(4)
2.102(4)
1.992(4)
1.887(4)
2.592(4)
2.464(4)
2.081(4)
2.503(4)
112.06(11)
99.47(16)
143.5(2)
97.72(17)
N(1)–Li(3)
N(2)–Li(2)
N(3)–Li(3)
Li(1) ◊ ◊ ◊ C(14)
Li(2) ◊ ◊ ◊ C(14)
Li(1)–N(2A)
Li(1) ◊ ◊ ◊ C(14A)
Si(1)–C(1)–Si(2)
Si(2)–C(1)–Si(3)
N(1)–Li(2)–N(3)
N(1)–Li(1)–N(2)
3
C(1)–Si(1)
C(1)–Si(3)
Si(2)–N(2)
N(1)–Li(1)
1.8933(15)
1.9100(16)
1.7151(13)
2.058(3)
C(1)–Si(2)
Si(1)–N(1)
Si(3)–N(3)
N(1)–Li(2)
1.9056(15)
1.7275(12)
1.7131(13)
2.124(3)
N(1)–Li(3)
N(2)–Li(3)
2.081(3)
2.004(3)
N(2)–Li(1)
N(3)–Li(1)
1.953(3)
1.958(3)
N(3)–Li(2)
O(2)–Li(3)
C(4) ◊ ◊ ◊ Li(2)
Si(1)–C(1)–Si(2)
Si(2)–C(1)–Si(3)
N(1)–Li(1)–N(3)
N(1)–Li(2)–N(3)
1.989(3)
1.891(3)
2.693(3)
113.67(8)
117.80(8)
99.43(12)
96.26(12)
O(1)–Li(2)
1.905(3)
2.553(3)
2.583(3)
112.22(7)
100.90(13)
141.41(15)
98.44(13)
C(4) ◊ ◊ ◊ Li(3)
C(22) ◊ ◊ ◊ Li(2)
Si(1)–C(1)–Si(3)
N(1)–Li(1)–N(2)
N(2)–Li(1)–N(3)
N(1)–Li(3)–N(2)
Fig. 1 Molecular structure of 1 with selective atom labelling and
carbon-bound hydrogen atoms omitted for clarity.
derivative 3 was not crystallographically characterised. During
our studies we obtained colourless crystals of 3 suitable for X-ray
diffraction from hexane so we undertook a crystallographic study.
The molecular structure of 3 is depicted in Fig. 3 and selected
bond lengths and angles are tabulated in Table 1. Complex 3 adopts
a distorted adamantyl-type CSi3N3Li3 structure at its core which
is generally very similar to the asymmetric unit of 2 and overall
3 is topologically identical to the closely related trisilylsilane
[{MeSi(SiMe2N(Li)Ar)3}(OEt2)2].51 However, complex 3 contains
an extra molecule of coordinated diethylether compared to 2,
resulting in a monomeric complex, perhaps reflecting the less
sterically demanding nature of the tolyl groups in 3 compared to
the xylyl groups in 2, which imparts to complex 3 approximate
Cs symmetry. In common with 2, the Li–N bond lengths in
3 do not appear to follow any rational trends with respect
to coordination number or environment and instead appear
to result from steric constraints. For example, the Li(1)–N(1),
Li(1)–N(2), Li(1)–N(3), Li(2)–N(1), Li(2)–N(3), Li(3)–N(1), and
Li(3)–N(2) bond lengths are 2.058(3), 1.953(3), 1.958(3), 2.124(3),
trigonal pyramidal manner (R∠ = 344.8◦). The remaining two
lithium centres each bridge two amide centres but one [Li(3)]
is additionally coordinated by a molecule of diethyl ether. The
asymmetric unit then dimerises by edge sharing of the Li(1)–N(2)
rung with the Li(1A)–N(2A) rung of another unit to form a six-
rung intercepted ladder. The termination of the ladder presumably
occurs because the space around the Li(3)–N(3) rung is not
open enough to allow the approach of another unit in an edge-
sharing arrangement but it is large enough for a diethyl ether
molecule to coordinate. The Li–N bond lengths do not appear to
follow any clear-cut trend based on edge versus rung character,
and bond length variations appear instead to be the result of
differing steric constraints. For example, the Li(1)–N(2), Li(2)–
N(1), and Li(3)–N(3) rung bond lengths are 2.102(4), 2.060(4),
˚
and 1.990(4) A, respectively, which compares to Li(3)–N(1), Li(1)–
N(1), Li(1)–N(2A), Li(1A)–N(2), Li(2)–N(2), and Li(2)–N(3)
edge distances of 2.184(4), 2.078(4), 2.081(4), 2.081(4), 2.112(4),
˚
1.989(3), 2.081(3), and 2.004(3) A, respectively. As in 2, short
˚
and 1.992(4) A, respectively. Close Li ◊ ◊ ◊ C contacts between
distances between Li(2) ◊ ◊ ◊ C(4), Li(3) ◊ ◊ ◊ C(4), and Li(2) ◊ ◊ ◊ C(22)
˚
Li(1) ◊ ◊ ◊ C(4), Li(1) ◊ ◊ ◊ C(14), Li(2) ◊ ◊ ◊ C(14), Li(2) ◊ ◊ ◊ C(19) (and
of 2.533(3), 2.693(3), and 2.583(3) A, respectively, are suggestive
symmetry equivalents) are suggested by distances of 2.592(4),
of Li ◊ ◊ ◊ C interactions.
˚
2.503(4), 2.460(4), and 2.464(4) A, respectively, and are consistent
With 2 and 3 in hand, we investigated their utility as
ligand transfer reagents with uranium(IV) tetrachloride.
Accordingly, addition of THF to cold (-78 ◦C) 1 : 1
mixtures of UCl4 with 2 or 3, respectively, afforded dark
green solutions on warming to room temperature. Removal
of volatiles, extraction into toluene, filtration, removal of
volatiles and recrystallisation from hexane afforded crops
with the low-coordinate, electron-deficient nature of the lithium
centres in 2.
The tri-lithium tris(N-arylamido-dimethylsilyl)methane ether-
ate [HC{SiMe2N(Li)Ar¢}3(OEt2)2] (3) (Ar¢ = 4-MeC6H4) was
reported previously by Gade.38 However, although the crystal
structure of I was reported,38 the corresponding tri-lithium
6640 | Dalton Trans., 2010, 39, 6638–6647
This journal is
The Royal Society of Chemistry 2010
©

˚
˚
2.6409(9) A, compares to a U–Cl bond length of 2.6941(10) A
in [U(Cl)(TrenTMS)(THF)] which possesses an additional U–Namine
dative bond rendering the uranium centre more electron-rich.33
The electron deficient nature of the uranium centre in 4 is
underscored by the presence of an U ◊ ◊ ◊ Cipso interaction. This is
˚
evidenced by a U ◊ ◊ ◊ C(24) distance of 2.964(3) A and a deviation
of 6.4(3)◦ of the N–Cipso–Arylcentroid angle from the expected value
of 180◦.
In contrast to 4, complex 5 crystallises as a dinuclear complex.
The molecular structure is illustrated in Fig. 5 and selected
bond lengths can be found in Table 2. Each uranium centre is
ligated by a tris(N-arylamido-dimethylsilyl)methane ligand but
whereas one uranium centre is bound to two chloride ligands (one
terminal, one bridging), the other uranium centre is bound to
the bridging chloride and two molecules of THF. Presumably,
this form is energetically preferred overall to two individual
“[U(Cl){HC(SiMe2NAr¢)3}(THF)]” units, although given the po-
lar nature of the uranium–ligand bonds this is likely to be a delicate
balance intimately dependent on crystallisation conditions. The
U(1)–N(1), U(1)–N(2), U(1)–N(3), U(2)–N(4), U(2)–N(5), and
U(2)–N(6) bond lengths were observed to be 2.276(6), 2.238(6),
˚
2.251(6), 2.224(6), 2.225(6), and 2.243(6) A, respectively. Three
conclusions can be drawn from these metrical parameters. Firstly,
as a group the U–N bond lengths for U(2) appear to be shorter
than those for U(1), reflecting the 5-coordinate versus 6-coordinate
nature of the two uranium centres, respectively. Secondly, those
U–N bonds which lie trans to U–Cl bonds are longer than the
other U–N bonds. Thirdly the U–N bonds trans to coordinated
THF are, correcting for a coordination number of six, shorter than
the other U–N bonds. The terminal U(2)–Cl(2) bond distance of
˚
2.6897(19) A is, unsurprisingly, shorter than the chloride which
asymmetrically bridges the uranium centres with U(1)–Cl(1) and
˚
U(2)–Cl(1) bond lengths of 2.8813(17) and 2.8116(17) A, respec-
Fig. 2 Molecular structure of 2 with selective atom labelling and hydrogen
atoms omitted for clarity: (a) asymmetric unit; (b) complete aggregate. The
Li ◊ ◊ ◊ C interactions are omitted for clarity. Symmetry operation: -x, -y,
-z + 1.
tively. Complex 5 may therefore be regarded as a cation-ate contact
ion pair complex constructed from [U(Cl)2{HC(SiMe2NAr¢)3}]-
and [U{HC(SiMe2NAr¢)3}(THF)2]+ fragments.
Although chloride is
a good leaving group from the
of green crystals of the complexes identified (vide infra) as
monomeric [U(Cl){HC(SiMe2NAr)3}(THF)] (4) and dinuclear
[{HC(SiMe2NAr¢)3}U(Cl)(m-Cl)U(THF)2{(Ar¢NSiMe2)3CH}]
viewpoint of making derivatives by salt elimination, iodide
1
(5) in 70 and 90% yields, respectively, Scheme 1. The H NMR
spectra of 4 and 5 are broad and span the ranges 80 → -65
and 37 → -49 ppm, respectively but are fully consistent with
the proposed formulations. The 1H NMR spectrum of 5 in
particular consists of very broad resonances which suggests that
the dinuclear structure observed in the solid state is maintained
in solution (vide infra), but variation of temperature did not
significantly improve spectral resolution.
The molecular structure of 4 is shown in Fig. 4 and selected bond
lengths are in Table 2. Complex 4 crystallises as a monomeric
species wherein the uranium centre is ligated by the tris(N-
arylamido-dimethylsilyl)methane, a chloride, and a THF molecule
giving a distorted trigonal bipyramidal geometry at uranium such
that the THF oxygen and one amide nitrogen occupy the axial
sites. The U(1)–N(1), U(1)–N(2), and U(1)–N(3) bond lengths
˚
of 2.210(3), 2.239(3), and 2.229(3) A, respectively, are within the
range reported for U(IV)–N bond lengths,52,53 and the N(1) centre
appears to be more closely bound as a consequence of residing
trans to the datively bound THF. The U(1)–Cl(1) bond length of
Fig. 3 Molecular structure of 3 with selective atom labelling and hydrogen
atoms omitted for clarity. The Li ◊ ◊ ◊ C interactions are omitted for clarity.
This journal is
The Royal Society of Chemistry 2010
Dalton Trans., 2010, 39, 6638–6647 | 6641
©

◦
˚
Table 2 Selected bond lengths (A) and angles ( ) for 4-6·2.5C4H8O and
8·0.5C6H14
4
C(1)–Si(1)
1.891(3)
1.903(3)
1.739(3)
2.210(3)
2.229(3)
2.479(2)
111.87(17)
115.84(17)
92.24(10)
84.95(9)
177.07(9)
97.10(7)
131.80(8)
C(1)–Si(2)
Si(1)–N(1)
Si(3)–N(3)
U(1)–N(2)
1.894(3)
1.758(3)
1.733(3)
2.239(3)
2.6409(9)
2.964(3)
113.63(17)
92.51(10)
97.43(10)
88.68(9)
84.20(6)
129.03(7)
C(1)–Si(3)
Si(2)–N(2)
U(1)–N(1)
U(1)–N(3)
U(1)–Cl(1)
U(1)–O(1)
U(1) ◊ ◊ ◊ C(24)
Si(1)–C(1)–Si(3)
N(1)–U(1)–N(2)
N(2)–U(1)–N(3)
O(1)–U(1)–N(2)
O(1)–U(1)–Cl(1)
N(2)–U(1)–Cl(1)
Si(1)–C(1)–Si(2)
Si(2)–C(1)–Si(3)
N(1)–U(1)–N(3)
O(1)–U(1)–N(3)
O(1)–U(1)–N(1)
N(1)–U(1)–Cl(1)
N(3)–U(1)–Cl(1)
5·1.5C6H14
C(1)–Si(1)
C(1)–Si(3)
Si(2)–N(2)
U(1)–N(1)
U(1)–N(3)
U(1)–O(2)
C(37)–Si(4)
C(37)–Si(6)
Si(5)–N(5)
U(2)–N(4)
U(2)–N(6)
U(2)–Cl(2)
1.896(7)
1.900(7)
1.766(6)
2.276(6)
2.251(6)
2.490(4)
1.799(7)
1.963(7)
1.747(6)
2.224(6)
2.243(6)
2.6897(19)
114.0(3)
95.7(2)
C(1)–Si(2)
Si(1)–N(1)
Si(3)–N(3)
U(1)–N(2)
U(1)–O(1)
U(1)–Cl(1)
C(37)–Si(5)
Si(4)–N(4)
1.891(7)
1.756(6)
1.755(6)
2.238(6)
2.530(5)
2.8813(17)
1.927(6)
1.762(7)
1.802(7)
2.225(6)
2.8116(17)
114.9(4)
113.4(3)
92.4(2)
173.32(19)
93.97(19)
101.14(19)
93.97(19)
93.61(15)
85.49(13)
100.2(2)
89.3(2)
Si(6)–N(6)
U(2)–N(5)
U(2)–Cl(1)
Fig. 4 Molecular structure of 4 with selective atom labelling and hydrogen
atoms omitted for clarity. The U ◊ ◊ ◊ Cipso interaction is shown as a dashed
line.
Si(1)–C(1)–Si(2)
Si(2)–C(1)–Si(3)
N(1)–U(1)–N(3)
O(1)–U(1)–N(3)
O(1)–U(1)–N(1)
O(2)–U(1)–N(3)
O(2)–U(1)–N(1)
Cl(1)–U(1)–N(2)
Cl(1)–U(1)–O(1)
N(4)–U(2)–N(5)
N(5)–U(2)–N(6)
Cl(1)–U(2)–N(5)
Cl(2)–U(2)–N(4)
Cl(2)–U(2)–N(6)
Si(1)–C(1)–Si(3)
N(1)–U(1)–N(2)
N(2)–U(1)–N(3)
O(1)–U(1)–N(2)
O(1)–U(1)–O(2)
O(2)–U(1)–N(2)
Cl(1)–U(1)–N(3)
Cl(1)–U(1)–N(1)
Cl(1)–U(1)–O(2)
N(4)–U(2)–N(6)
Cl(1)–U(2)–N(4)
Cl(1)–U(2)–N(6)
Cl(2)–U(2)–N(5)
Cl(1)–U(2)–Cl(2)
6·2.5C4H8O
96.9(2)
83.87(19)
76.99(16)
159.09(19)
87.84(15)
170.55(15)
76.73(12)
90.1(2)
127.79(17)
94.61(15)
88.45(17)
87.41(5)
131.75(16)
89.63(18)
177.63(16)
C(1)–Si(1)
C(1)–Si(3)
Si(2)–N(2)
U(1)–N(1)
U(1)–N(3)
U(1)–O(1)
1.885(3)
1.890(3)
1.739(3)
2.230(3)
2.258(3)
2.554(2)
113.72(15)
113.04(15)
89.58(9)
89.92(8)
108.78(9)
87.07(8)
175.47(8)
97.78(6)
78.40(5)
C(1)–Si(2)
Si(1)–N(1)
Si(3)–N(3)
U(1)–N(2)
U(1)–I(1)
U(1)–O(2)
Si(1)–C(1)–Si(3)
N(1)–U(1)–N(2)
N(2)–U(1)–N(3)
O(1)–U(1)–N(2)
O(1)–U(1)–O(2)
O(2)–U(1)–N(2)
I(1)–U(1)–N(3)
I(1)–U(1)–N(1)
I(1)–U(1)–O(2)
1.880(3)
1.732(3)
1.741(3)
2.241(3)
3.1561(3)
2.484(2)
113.01(15)
95.32(9)
93.50(9)
155.69(8)
74.29(7)
81.85(8)
168.22(7)
92.74(7)
91.15(5)
Si(1)–C(1)–Si(2)
Si(2)–C(1)–Si(3)
N(1)–U(1)–N(3)
O(1)–U(1)–N(3)
O(1)–U(1)–N(1)
O(2)–U(1)–N(3)
O(2)–U(1)–N(1)
I(1)–U(1)–N(2)
I(1)–U(1)–O(1)
8·0.5C6H14
Fig. 5 Molecular structure of 5·1.5C6H14 with selective atom labelling and
hydrogen atoms and hexane lattice solvent molecules omitted for clarity.
C(1)–Si(1)
1.885(4)
C(1)–Si(2)
1.884(4)
or more weakly coordinated groups such as tetra-aryl bo-
rates may sometimes be synthetically preferred. We there-
fore investigated the conversion of 4 and 5 to the cor-
responding iodides [U(I){HC(SiMe2NAr)3}(THF)2] (6) and
[U(I){HC(SiMe2NAr¢)3}(THF)] (7) by halide exchange, Scheme 1.
Accordingly, treatment of 4 and 5 with one equivalent of
trimethylsilyl iodide gave complexes 6 and 7 in 85 and 90% yields,
C(1)–Si(3)
Si(2)–N(2)
U(1)–N(1)
U(1)–N(3)
1.903(4)
1.736(3)
2.269(3)
2.271(3)
Si(1)–N(1)
Si(3)–N(3)
U(1)–N(2)
U(1)–N(4)
U(1) ◊ ◊ ◊ C(38)
Si(1)–C(1)–Si(3)
N(1)–U(1)–N(2)
N(2)–U(1)–N(3)
N(2)–U(1)–N(4)
O(1)–U(1)–N(1)
O(1)– U(1)–N(3)
1.742(3)
1.741(3)
2.262(3)
2.210(3)
U(1)–O(1)
2.557(3)
3.013(4)
Si(1)–C(1)–Si(2)
Si(2)–C(1)–Si(3)
N(1)–U(1)–N(3)
N(1)–U(1)–N(4)
N(3)–U(1)–N(4)
O(1)–U(1)–N(2)
O(1)–U(1)–N(4)
113.77(19)
117.05(19)
92.72(10)
100.53(11)
127.36(11)
81.91(10)
84.03(10)
112.82(18)
94.64(11)
103.38(10)
125.59(11)
175.36(9)
85.11(10)
1
respectively. The H NMR spectra of 6 and 7 are significantly
different to those of 4 and 5, covering the narrower ranges 11
→ -30 and 14 → -21 ppm, respectively, which allows convenient
1
identification. However, the H NMR spectrum of 7 is similar
6642 | Dalton Trans., 2010, 39, 6638–6647
This journal is
The Royal Society of Chemistry 2010
©

to that of 5 in gross terms which suggests that 7, like 5, may be
dinuclear. Although crystals of 7 suitable for X-ray crystallography
were not obtained, green crystals of 6 were obtained from THF
and were subjected to an X-ray diffraction study.
one equivalent of lithium dicyclohexylamide afforded the target
heteroleptic amide complex [U(NCy2){HC(SiMe2NAr)3}(THF)]
(8) in 78% yield, Scheme 1. However, analogous attempts to
prepare [U(NCy2){HC(SiMe2NAr¢)3}(THF)] (9) in a variety of
solvents (toluene, diethyl ether, THF) at different temperatures
(- 78 ◦C, 0 ◦C, room temperature, reflux of respective solvent)
The molecular structure of 6 is depicted in Fig. 6 and selected
bond lengths and angles are listed in Table 2. The structure of 6 is
similar to 4 except that, in addition to coordination by iodide and
the tris(N-arylamido-dimethylsilyl)methane, the uranium centre
is coordinated by not one but two molecules of THF in a distorted
octahedral geometry; an almost topologically identical structure
was reported for [Zr(Cl){HC(SiMe2NAr¢)3}(THF)2].54 In contrast
to 4, no U ◊ ◊ ◊ Cipso contacts are observed in the solid state structure
of 6 which may be a consequence of coordination of the second
molecule of THF rendering the uranium centre less electrophilic.
The U(1)–N(1), U(2)–N(2), and U(1)–N(3) bond lengths are
1
consistently resulted in mixtures of products, as adjudged by H
NMR spectroscopy, and the resulting brown oil could not be
purified. The 1H NMR spectra of 8 spans the range 44 → -34 ppm
and is consistent with the proposed formulation. Crystals of 9
suitable for X-ray crystallography could not be obtained. However,
brown crystals of 8 were obtained from hexane and were subjected
to an X-ray diffraction study.
The molecular structure of 8 is illustrated in Fig. 7 and selected
bond lengths and angles are listed in Table 2. In general terms,
the structure of 8 is similar to those of 4 and 6 except that the
halide ligand is now substituted by a dicyclohexylamide ligand.
The uranium centre adopts a trigonal bipyramidal geometry such
that the THF oxygen and N(1) centres occupy the axial sites. The
U(1)–N(1), U(1)–N(2), and U(1)–N(3) bond lengths of 2.269(3),
˚
2.230(3), 2.241(3), and 2.258(3) A, respectively which are very
similar to the U–N bond distances observed in 4, despite the fact
the uranium centre in 4 is 5-coordinate whereas a 6-coordinate
uranium centre is found in 6. Notably, however, the U(1)–N(3)
bond distance which resides trans to the U(1)–I(1) bond is the
longest but this trans-effect is smaller than in 4 and 5 as would
be expected from consideration of the relatively hard versus soft
natures of chloride versus iodide, respectively. The U(1)–I(1) bond
˚
2.262(3), 2.271(3) A, respectively, are somewhat longer than those
observed in 4 and 6 reflecting the presence of the bulky amide. The
˚
amide exhibits a shorter U(1)–N(4) bond distance of 2.210(3) A
˚
length of 3.1561(3) A is unremarkable.
which befits its harder, more nucleophilic nature as a dialkyl
amide compared to the aryl-silyl amides of the tris(N-arylamido-
dimethylsilyl)methane. The presence of the bulky dialkyl amide is
˚
also reflected in the U(1)–O(1) bond length of 2.557(3) A which
is considerably longer than the U–OTHF bond distances in 4, 5,
and 6. A U ◊ ◊ ◊ C–H agostic-type interaction is suggested by a
˚
U(1) ◊ ◊ ◊ C(38) distance of 3.013(4) A.
Fig. 6 Molecular structure of 6·2.5C4H8O with selective atom labelling
and hydrogen atoms and hexane lattice solvent molecule omitted for clarity.
Although salt elimination represents an effective route to
preparing uranium–metal bonds, an alternative and attractive
strategy is to react uranium-amides with metal hydrides to give
uranium–metal bond formation with concomitant elimination
of amine.55 Additionally, such protonolysis chemistry can easily
be carried out in non-polar solvents, which could be critical to
the successful isolation of uranium–metal bonds, whereas salt
elimination to form uranium–metal bonds tends to work best
in polar media such as THF, which is a solvent vulnerable
to ring opening decomposition and/or oxo-group abstraction.56
We therefore targeted amide derivatives of 4 and 5 as poten-
tial precursors to uranium–metal bonds. Treatment of 4 with
Fig. 7 Molecular structure of 8·0.5C6H14 with selective atom labelling and
hydrogen atoms and hexane lattice solvent molecule omitted for clarity.
The U ◊ ◊ ◊ CH interaction is shown as a dashed line.
This journal is
The Royal Society of Chemistry 2010
Dalton Trans., 2010, 39, 6638–6647 | 6643
©

and Et3N (10.12 ml, 72.56 mmol) in Et2O (150 ml). After the
addition was complete the mixture was allowed to warm to room
temperature and stirred for a further 16 h. The triethylammonium
bromide was removed by filtration through a frit, and washed with
Et2O (2 ¥ 20 ml) and the filtrate and the washings were combined.
Volatiles were removed in vacuo to give a thick yellow oil, which
Summary and conclusions
The new tris(N-arylamine-dimethylsilyl)methane HC{SiMe2-
N(H)Ar}3 (Ar
=
3,5-Me2C6H3, 1) and the previously
reported HC{SiMe2N(H)Ar¢}3 (Ar¢
=
4-MeC6H4, I)
were prepared and converted to the corresponding tri-
lithium derivatives [HC{SiMe2N(Li)Ar}3(OEt2)] (2) and
[HC{SiMe2N(Li)Ar¢}3(OEt2)2] (3). Salt elimination reactions
between 2 and 3 and uranium(IV) tetrachloride afforded the
corresponding uranium(IV) complexes [U(Cl){HC(SiMe2NAr)3}-
(THF)] (4) and [{HC(SiMe2NAr¢)3}U(Cl)(m-Cl)U(THF)2-
◦
was redissolved in Et2O (15 ml) and stored at -30 C to yield 1
as an off-white solid. Yield: 10.67 g, 83%. Colourless hexagonal
crystals of 1 were obtained from the storage of a saturated hexane
solution at room temperature. Anal. Calcd for C31H49N3Si3: C,
67.93; H, 9.03; N 7.67%. Found: C, 68.00; H, 9.06; N, 7.61%.
1H NMR (C6D6): d 6.42 (3H, s, p-CH), 6.26 (6H, s, o-CH), 3.47
(3H, s, NH), 2.14 (18H, s, Ar(CH3)), 0.94, (1H, s, Si–CH), 0.42
{(Ar¢NSiMe2)3CH}]
and
iodides [U(I){HC(SiMe2NAr)3}(THF)2] (6) and [U(I)-
{HC(SiMe2NAr¢)3}(THF)] (7) by treatment with
(5),
respectively.
Complexes
4
5
can easily be converted to the corresponding
1
(18H, s, Si-(CH3)2). 13C{ H} NMR (C6D6): d 146.77 (Ar), 138.70
(Ar), 120.19 (Ar), 114.81 (Ar), 21.33 (Ar-CH3), 5.19 (Si-CH), 2.78
(Si-CH3).29Si NMR (C6D6): d -0.56 (s). IR v/cm-1 (Nujol): 3405
(s), 3394 (s), 3371 (s), 1600 (vs), 1407 (w), 1345 (vs), 1324 (vs),
1251 (vs), 1177 (vs), 1041 (s), 990 (vs), 957 (s), 817 (vs), 770 (s),
742 (s), 728 (s), 691 (vs), 643 (w), 608 (w), 582 (w), 544 (w), 521
(w), 461 (s), 426 (s).
trimethylsilyl iodide. The corresponding dicyclohexylamide
[U(NCy2){HC(SiMe2NAr)3}(THF)] (8) was prepared by reaction
of 4 with lithium dicyclohexylamide but analogous attempts to
prepare the complex [U(NCy2){HC(SiMe2NAr¢)3}(THF)] (9)
consistently gave intractable mixtures of products. Although
the ease of synthesis of 4–8 indicates that the tris(N-arylamine-
dimethylsilyl)methanes are effective supporting ligands for
uranium, and they are clearly more rigid than TrenTMS, the large
size of uranium(IV) allows THF to coordinate. We are currently
investigating the utility of the complexes reported herein in the
synthesis of unsupported uranium–metal bonds.
Preparation of [HC{SiMe2N(Li)Ar}3(OEt2)] (2)
n
A solution of BuLi in hexanes (2.5 M, 10 ml, 25.00 mmol) was
added dropwise to a cold (-78 ◦C) stirred slurry of 1 (4.42 g,
8.06 mmol) in Et2O (5 ml) and hexanes (30 ml). The resultant
yellow slurry was allowed to warm to room temperature with
stirring for 16 h. After this time, volatiles were removed in vacuo to
yield an off-white solid, which was washed with hexanes (2 ¥10 ml)
and dried in vacuo to give 2 as a colourless solid. Yield: 4.76 g,
92%. Colourless rod-shaped crystals of 2 were obtained from the
storage of a saturated hexane solution at room temperature. Anal.
Calcd for C70H112Si6N6Li6O2: C, 65.68; H, 8.84; N, 6.57%. Found:
Experimental
General
All manipulations were carried out using standard Schlenk
techniques, or an MBraun UniLab glovebox, under an at-
mosphere of dry nitrogen. Solvents were dried by passage
through activated alumina towers and degassed before use. All
solvents were stored over potassium mirrors (with the excep-
1
C, 65.58; H, 8.76; N, 6.54%. H NMR (C6D6): d 6.55 (12H, s,
o-CH), 6.38 (6H, s, p-CH), 2.77 (8H, q, CH2), 2.33 (36H, s, Ar–
CH3), 0.67 (12H, t, CH3), 0.60 (36H, s, Si–CH3), -0.72 (2H, s, Si–
˚
tion of THF which was stored over activated 4 A molecular
1
CH). 13C{ H} NMR (C6D6): d 139.19 (Ar), 120.01 (Ar), 118.00
sieves). Deuterated benzene was distilled from potassium, de-
gassed by three freeze-pump-thaw cycles and stored under ni-
trogen. The compounds HC(Me2SiBr)3,37 HC{SiMe2N(H)Ar¢}3,38
[HC{SiMe2N(Li)Ar¢}3(OEt2)2],38 and UCl4,57 were prepared ac-
cording to published procedures. [Li(NCy2)] was isolated as a white
powder which precipitated from the reaction between HNCy2 and
n-butyllithium in hexane and was dried and used without further
purification following filtration. All other reagents were used as
received.
(Ar), 63.42 (Ar), 21.61 (Ar-CH3), 13.66 (Si-CH3), 6.89 (Si-CH).
29Si NMR (C6D6): dSi -6.06 (s). 7Li NMR (C6D6): dLi 1.16 (s). IR
v/cm-1 (Nujol): 1582 (vs), 1314 (br, vs), 1252 (s), 1180 (m), 1057
(br, s), 986 (m), 884 (vs), 838 (br, s), 701 (s), 676 (w), 649 (w), 545
(w), 511 (w).
Preparation of [HC{SiMe2N(Li)Ar¢}3(OEt2)2] (3)
1H, 13C, 29Si, and 7Li NMR spectra were recorded on a Bruker
400 spectrometer operating at 400.2, 100.6, 79.5, and 155.5 MHz
respectively; chemical shifts are quoted in ppm and are relative
to TMS or external 1M LiCl. FTIR spectra were recorded
on a Bruker Tensor 27 spectrometer. Elemental microanalyses
were carried out by Mr Stephen Boyer (London Metropolitan
University) and Medac Microanalysis Service, UK.
Compound 3 was prepared according to the literature procedure.
Colourless block shaped crystals of 3 were obtained by storage of
a saturated hexane solution at -30 C for 15 h. Anal. Calcd for
◦
C36H60Li3N3O2Si3: C, 64.33; H, 9.02; N, 6.25%. Found: C, 64.29;
H, 8.91; N, 6.18%. 1H NMR (C6D6): d 7.05 (d, 6H, m-CH), 6.87
(d, 6H, o-CH), 2.84 (q, 8H, CH2), 2.35 (s, 9H, Ar–CH3), 0.72 (m,
1
12H, CH3), 0.69 (s, 18H, Si–CH3), -0.67 (s, 1H, Si–CH).13C{ H}
NMR (C6D6): d 155.74 (Ar), 130.41 (Ar), 123.51 (Ar), 121.66 (Ar),
63.92 (CH2), 20.41 (Ar-CH3), 13.92 (CH3), 9.70 (Si-CH), 6.71 (Si-
CH3).29Si NMR (C6D6): dSi -4.01 (s).7Li NMR (C6D6): dLi 1.76
(s). IR v/cm-1 (Nujol): 1603 (s), 1494 (vs), 1268 (br, m), 1176 (s),
1151 (w), 1109 (w), 1089 (w), 1053 (s), 997 (w), 976 (w), 937(m),
911 (sh), 822 (br, m), 734 (br), 696 (w), 518 (w).
Synthesis of HC{SiMe2N(H)Ar}3 (1)
A solution of HC(Me2SiBr)3 (10.00 g, 23.41 mmol) in Et2O
(100 ml) was added dropwise over a period of 2 h to a cold
(0 ◦C) stirring solution of 3,5-dimethylaniline (8.51 g, 70.22 mmol)
6644 | Dalton Trans., 2010, 39, 6638–6647
This journal is
The Royal Society of Chemistry 2010
©

-3.25 (18H, s, CH3), -3.94 (18H, s, CH3), -29.91 (1H, br s, Si–
CH). IR v/cm-1 (Nujol): 1581 (s), 1313 (s), 1293 (s), 1252 (s), 1155
(s), 1035 (s), 977 (w), 892 (s), 841 (vs), 722 (w), 649 (w), 594 (w),
Synthesis of [U(Cl){HC(SiMe2NAr)3}(THF)] (4)
THF (30 ml) was added slowly to a cold (-78 ◦C) stirring mixture
of 2 (1.28 g, 2.00 mmol) and UCl4 (0.76 g, 2.00 mmol), the mixture
was allowed to warm to room temperature slowly over 16 h. After
this time the solution was heated to reflux for 2–3 min, then allowed
to cool to room temperature with stirring, after which all the
volatiles were removed in vacuo. The products were extracted into
hot toluene (20 ml) and filtered through a frit to remove the LiCl
precipitate. Volatiles were removed in vacuo, and the residue was
washed with cold hexane (-78 ◦C) to yield the product as an
analytically pure green solid. Yield: 1.25 g, 70%. Green crystals of
4 were obtained by storage of a hexane solution at -30 ◦C for 16 h.
Anal. Calcd for C35H54ClN3OSi3U: C, 47.20; H, 6.11; N, 4.72; Cl,
557 (w). Magnetic moment (Evans method, C6D6, 298 K): meff
2.72 mB.
=
Synthesis of [U(I){HC(SiMe2NAr¢)3}(THF)] (7)
Me3SiI (0.23 ml, 1.00 mmol) was added dropwise to a cold (-78 ◦C)
stirring slurry of 5 (0.91 g, 1.00 mmol) in toluene (25 ml). The
resultant green slurry was allowed to warm to room temperature
over 16 h. After this time the now brown solution was heated to
reflux for 2 min, allowed to cool to room temperature, and then
volatiles were removed in vacuo. The product was isolated after
extraction into hexane (6 ml) and storage at -30 ◦C for 16 h as a
dark green oil. Yield: 0.85 g, 90%. Satisfactory CHN microanalysis
data could not be obtained due to the oily nature of 7. 1H NMR
(C6D6): d 13.52 (4H, v br s, CH2), 10.00 (4H, v br s, CH2), 7.03
(6H, br s, CH), 3.25 (6H, br s, CH), -4.55 (27H, v br s, CH3),
-21.20 (1H, v br s, Si–CH). IR v/cm-1 (Nujol): 1604 (w), 1497
(m), 1444 (w), 1251 (vs), 1172 (s), 1102 (vs), 1015 (s), 973 (vs),
836 (vs m), 709 (s), 697 (s), 546 (w), 499 (vs), 469 (w). Magnetic
moment (Evans method, C6D6, 298 K): meff = 2.48 mB.
1
3.98%. Found: C, 46.48; H, 6.16; N, 4.75; Cl 3.54%. H NMR
(C6D6): d 80.63 (3H, br s, p-CH), 44.02 (4H, br s, CH2), 4.92 (4H,
br s, CH2), -2.71 (18H, s, CH3), -3.33 (18H, s, CH3), -26.67 (6H,
br s, o-CH), -65.25 (1H, br s, Si–CH). IR v/cm-1 (Nujol): 1582 (s),
1314 (s), 1295 (s), 1250 (s), 1179 (s), 1155 (s), 1046 (m), 1009 (w),
974 (s), 892 (s), 869 (br, m), 771 (s), 756 (s), 701 (s), 682 (s), 649
(s), 581 (w), 572 (w), 560 (w), 538 (w), 509 (w). Magnetic moment
(Evans method, C6D6, 298 K): meff = 2.88 mB.
Synthesis of
[{HC(SiMe2NAr¢)3}U(Cl)(l-Cl)U(THF)2{(Ar¢NSiMe2)3CH}] (5)
Preparation of [U(NCy2){HC(SiMe2NAr)3}(THF)] (8)
THF (30 ml) was added slowly to a cold (-78 ◦C) stirring mixture
of 3 (1.34 g, 2.00 mmol) and UCl4 (0.76 g, 2.00 mmol), the mixture
was allowed to warm to room temperature slowly over 16 h. After
this time the solution was heated to reflux for 2–3 min, then allowed
to cool to room temperature with stirring, after which all the
volatiles were removed in vacuo. The products were extracted into
hot toluene (20 ml) and filtered through a frit to remove the LiCl
precipitate. Volatiles were removed in vacuo, and the residue was
washed with cold hexane (-78 ◦C) to yield the product as an
analytically pure green solid. Yield: 1.53 g, 90%. Green crystals
of 5 were obtained by storage of a hexane solution at -30 ◦C for
16 h. Anal. Calcd for C64H96Cl2N6O2Si6U2: C, 45.30; H, 5.70; N,
4.95%. Found: C, 44.53; H, 5.65; N, 4.82%.1H NMR (C6D6): d
37.01 (8H, v br s, CH2), 18.00 (8H, v br s, CH2), 9.83 (12H, br s,
CH), 5.34 (12H, br s, CH), -4.98 (54H, v br s, CH3), -49.09 (2H,
v br s, Si–CH). IR v/cm-1 (Nujol): 1604, 1497 (vs), 1247 (s), 1216
(vs), 1170 (w), 1103 (w), 1047 (w), 1014 (w), 975 (s), 939 (w), 895
(vs), 845 (m), 812 (vs), 769 (w), 726 (w), 712 (w), 700 (w), 506 (s).
Magnetic moment (Evans method, C6D6, 298 K): meff = 2.79 mB.
THF (20 ml) was added slowly to a cold (-78 ◦C) stirring mixture
of 4 (0.89 g, 1.00 mmol) and [Li(NCy2)] (0.19 g, 1.00 mmol) and the
resultant green slurry was allowed to warm to room temperature
over 16 h. After this time the brown solution was heated to reflux
for 2 min, and then volatiles were removed in vacuo. The product
was extracted into toluene (15 ml) and filtered through a frit
to remove the LiCl precipitate. Volatiles were removed in vacuo,
and the product was recrystallised from hot hexane (5 ml). Yield:
0.81 g, 78%. Brown block shaped crystals of 8 were grown from
◦
a saturated hexane solution at -30 C for 16 h. Anal. Calcd for
C47H76N4OSi3U: C, 54.52; H, 7.40; N, 5.41%. Found: C, 54.47;
H, 7.66; N, 5.34%.1H NMR (C6D6): d 44.24 (3H, s, p-CH), 21.82
(4H, s, THF-CH2), 2.80 (4H, THF-CH2), 1.59 (20H, m, Cy-CH2),
0.96 (2H, m, Cy-CH), 1.50 (36H, s, br, CH3), -8.64 (6H, s, o-CH),
-33.79 (1H, s, Si–CH). IR v/cm-1 (Nujol): 1582 (vs), 1304 (vs),
1247 (vs), 1166 (vs), 1125 (w), 1035 (s), 964 (vs), 889 (vs), 855 (vs),
812 (vs), 768 (w), 703 (w), 680 (w), 650 (s), 561 (w). Magnetic
moment (Evans method, C6D6, 298 K): meff = 3.04 mB.
X-ray crystallography
Preparation of [U(I){HC(SiMe2NAr)3}(THF)2] (6)
Crystal data for compounds 1-6·2.5C4H8O and 8·0.5C6H14 are
given in Table 3, and further details of the structure determinations
are in the ESI.† Bond lengths are listed in Tables 1 and 2.
Crystals were examined variously on Bruker AXS SMART 1000
or SMART APEX CCD area detector diffractometers using
Me3SiI (0.23 ml, 1.00 mmol) was added dropwise to a cold (-78 ◦C)
stirring slurry of 4 (0.89 g, 1.00 mmol) in toluene (25 ml). The
resultant green slurry was allowed to warm to room temperature
over 16 h. After this time the now brown solution was heated to
reflux for 2 min, allowed to cool to room temperature, and then
volatiles were removed in vacuo. The product was isolated after
extraction into hexane (6 ml) and storage at -30 ◦C for 16 h as a
green powder. Yield: 0.56 g, 85%. Green block shaped crystals of 6
were grown from a saturated THF solution at room temperature.
Anal. Calcd for C39H62IN3O2Si3U: C, 44.44; H, 5.93; N, 3.98%.
˚
graphite-monochromated Mo-Ka radiation (l = 0.71073 A).
Intensities were integrated from a sphere of data recorded on
narrow (0.3◦) frames by w rotation. Cell parameters were refined
from the observed positions of all strong reflections in each data
set. Semi-empirical absorption corrections based on symmetry-
equivalent and repeat reflections were applied. The structures were
solved by direct methods and were refined by full-matrix least-
squares on all unique F2 values, with anisotropic displacement
1
Found: C, 40.61; H, 5.71; N, 3.62%. H NMR (C6D6): d 11.21
(16H, v br s, CH2), 3.88 (6H, br s, o-CH), 0.99 (3H, br s, p-CH),
This journal is
The Royal Society of Chemistry 2010
Dalton Trans., 2010, 39, 6638–6647 | 6645
©

Table 3 Crystallographic data for 1-6·2.5C4H8O and 8·0.5C6H14
1
2
3
4
5·1.5C6H14
6·2.5C4H8O
8·0.5C6H14
Formula
C31H49N3Si3
C70H112Li6N6- C36H60Li3N3- C35H54ClN3OSi3U C73H117Cl2N6O2Si6U2 C49H82IN3O4.50Si3U C50H83N4OSi3U
O2Si6
O2Si3
Fw
548.00
0.38 ¥ 0.26 ¥
0.22
1279.84
0.63 ¥ 0.13 ¥
0.12
671.96
0.55 ¥ 0.30 ¥
0.16
890.56
1826.23
1234.38
1078.50
cryst size/mm
0.41 ¥ 0.31 ¥ 0.10 0.26 ¥ 0.14 ¥ 0.09
0.76 ¥ 0.47 ¥ 0.24 0.30 ¥ 0.26 ¥ 0.23
cryst syst
Monoclinic
P21/c
18.2572(15)
8.9742(8)
20.6548(17)
Monoclinic
P21/n
10.5806(11)
25.054(3)
14.7926(15)
Triclinic
P1
Monoclinic
P21/c
13.5913(3)
13.2334(3)
21.9614(5)
Triclinic
P1
Triclinic
P1
Monoclinic
P21/n
12.7504(3)
21.2641(6)
19.8990(6)
¯
¯
¯
Space group
˚
a/A
9.8635(8)
12.6161(10)
17.7573(14)
110.4560(20)
96.7570(20)
96.8310(20)
2025.3(3)
2
14.2778(15)
16.5243(17)
17.9252(19)
98.985(2)
94.570(2)
104.373(2)
4015.3(7)
2
12.7867(7)
12.9462(7)
18.9711(10)
104.553(2)
94.333(2)
114.813(2)
2699.9(3)
2
˚
b/A
˚
c/A
a, ◦
b (◦)
g , ◦
110.523(2)
102.997(2)
92.054(2)
98.515(2)
3
˚
V/A
3169.4(5)
4
1.148
0.174
3820.9(7)
2
1.112
0.153
23692
3947.42(15)
4
1.499
4.300
37076
5335.7(3)
4
1.343
3.146
52857
Z
rc/g cm-3
1.102
0.149
17759
1.510
4.229
35028
1.518
3.688
23847
m/mm-1
no. of reflections 27443
measd
no. of unique
reflns, Rint
7324, 0.0221
8648, 0.0347
5915
8960, 0.0170
7246
8878, 0.0320
6260
18075, 0.0424
10575
12016, 0.0225
10661
12052, 0.0433
9854
no. of reflns with 6725
F2 > 2s(F2)
transmn coeff
range
0.94–0.96
0.67–0.75
0.92–0.98
0.12–0.21
0.40–0.70
0.17–0.47
0.36–0.43
R, Rw a(F2>2s)
0.0418, 0.1073 0.0484, 0.1136 0.0423, 0.1126 0.0252, 0.0531
0.0491, 0.1055
0.0988, 0.1159
0.957
0.0274, 0.0687
0.0333, 0.0707
1.074
0.0314, 0.0763
0.0415, 0.0795
1.050
R, Rw a(all data) 0.0455, 0.1099 0.0855, 0.1339 0.0545, 0.1220 0.0469, 0.0600
Sa
1.072
358
1.023
440
1.023
437
1.026
409
Parameters
796
544
568
max., min. diff
map/e A )
0.43, -0.22
0.41, -0.32
0.39, -0.23
1.09, -0.49
1.57, -1.82
1.38, -0.68
1.40, -0.57
-3
˚
a Conventional R = RꢀFo| - |Fcꢀ/R|Fo|; Rw = [Rw(Fo - Fc2)2/Rw(Fo2)2]1/2; S = [Rw(Fo - Fc2)2/no. data - no. params)]1/2 for all data.
2
2
parameters for all non-hydrogen atoms, and with constrained
riding hydrogen geometries; Uiso(H) was set at 1.2 (1.5 for methyl
groups) times Ueq of the parent atom. The largest features in
final difference syntheses were close to heavy atoms and were of
no chemical significance. Highly disordered solvent molecules of
crystallisation in 5·1.5C6H14, 6·2.5C4H8O, and 8·0.5C6H14could
not be modelled and were treated with the PLATON SQUEEZE
procedure.58 Programs were Bruker AXS SMART (control) and
SAINT (integration),59 and SHELXTL was employed for struc-
ture solution and refinement and for molecular graphics.60
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Acknowledgements
We thank the Royal Society for the award of a University
Research Fellowship (S.T.L.) and the EPSRC, the University
of Nottingham, and the UK National Nuclear Laboratory for
generously supporting this work.
21 P. Roussel, R. Boaretto, A. J. Kingsley, N. W. Alcock and P. Scott,
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This journal is
The Royal Society of Chemistry 2010
Dalton Trans., 2010, 39, 6638–6647 | 6647
©