Synthesis and reactivity of uranium(iv) amide complexes supported by a triamidotriazacyclononane ligand

Article abstract of DOI:10.1039/b603000a

Reaction of [U{(SiMe₂NPh)₃-tacn}Cl] with LiNEt ₂ or LiNPh₂ affords the corresponding amide compounds, [U{(SiMe₂NPh)₃-tacn}(NR₂)] (R = Et (1), R = Ph (2)). The complexes have been fully characterized by spectroscopic methods and the solid-state structure of 1 was determined by single-crystal X-ray diffraction analysis. The six nitrogen atoms of the tris(dimethylsilylanilide)triazacyclononane ligand are in a trigonal prismatic configuration with the nitrogen atom of the diethylamide ligand capping one of the trigonal faces of the trigonal prism. Crystallization of 2 from CH ₃CN solution gave crystals of the six-membered heterocycle [U{(SiMe₂NPh)₃-tacn}{κ²-(HNC(Me)) ₂CCN}] (3). The reactivity of the amides was investigated. Both compounds undergo acid-base reactions with protic substrates such as HOC ₆H₂-2,4,6-Me₃, 3,5-Me₂pzH (pz = pyrazolyl) and HSC₅H₄N to give the corresponding [U{(SiMe₂NPh)₃-tacn}X] (X = OC₆H ₂-2,4,6-Me₃ (4), 3,5-Me₂pzH (5), κ ²-SC₅H₄N (6)) complexes. The solid-state structures of 3 and 6 were determined by single-crystal X-ray diffraction and revealed that the compounds are eight-coordinate with dodecahedral geometry. The Royal Society of Chemistry 2006.

Full text of DOI:10.1039/b603000a

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PAPER
www.rsc.org/dalton | Dalton Transactions
Synthesis and reactivity of uranium(IV) amide complexes supported by a
triamidotriazacyclononane ligand†
ˆ
Maria Augusta Antunes, Marta Dias, Bernardo Monteiro, Angela Domingos, Isabel C. Santos and
Noe´mia Marques*
Received 28th February 2006, Accepted 19th April 2006
First published as an Advance Article on the web 2nd May 2006
DOI: 10.1039/b603000a
Reaction of [U{(SiMe2NPh)3-tacn}Cl] with LiNEt2 or LiNPh2 affords the corresponding amide
compounds, [U{(SiMe2NPh)3-tacn}(NR2)] (R = Et (1), R = Ph (2)). The complexes have been fully
characterized by spectroscopic methods and the solid-state structure of 1 was determined by
single-crystal X-ray diffraction analysis. The six nitrogen atoms of the tris(dimethylsilylanilide)-
triazacyclononane ligand are in a trigonal prismatic configuration with the nitrogen atom of the
diethylamide ligand capping one of the trigonal faces of the trigonal prism. Crystallization of
2 from CH3CN solution gave crystals of the six-membered heterocycle [U{(SiMe2NPh)3-tacn}-
{j2-(HNC(Me))2CC≡N}] (3). The reactivity of the amides was investigated. Both compounds undergo
acid–base reactions with protic substrates such as HOC6H2-2,4,6-Me3, 3,5-Me2pzH (pz = pyrazolyl)
and HSC5H4N to give the corresponding [U{(SiMe2NPh)3-tacn}X] (X = OC6H2-2,4,6-Me3 (4),
3,5-Me2pzH (5), j2-SC5H4N (6)) complexes. The solid-state structures of 3 and 6 were determined by
single-crystal X-ray diffraction and revealed that the compounds are eight-coordinate with
dodecahedral geometry.
Here we wish to report that [U{(SiMe2NPh)3-tacn}Cl] is
Introduction
a useful starting material for obtaining the amide uranium
complexes, [U{(SiMe2NPh)3-tacn}(NR2)] (R = Et, Ph). Amine
elimination reactions of these complexes with protic substrates
constitutes an efficient route for the synthesis of U(IV) com-
plexes with U–O, U–N and U–S bonds. This contribution also
describes that [U{(SiMe2NPh)3-tacn}(NPh2)] reacts with ace-
tonitrile to yield [U{(SiMe2NPh)3-tacn}{(HNC(Me))2CC≡N}],
a uranium(IV) complex in which the metal is coordinated to the
anionic ligand [{HNC(Me)}2CC≡N], resulting of a trimerization
of the nitrile.
It seems likely that while C5Me5 will continue to be of predominant
interest in the inorganic and organometallic chemistry of uranium,
the search for other alternative ligand systems that can offer an
opportunity of new and unforeseen reactivity is of current interest.
The 1,4,7-triazacyclononane-based ligands (tacn) are becoming
increasingly popular due to the ease with which this macrocycle
can be derivatized at the nitrogen atoms to give access to ligands
with one or more pendant functionalities.1 Although widely used
and established as an important class for the main group and d-
transition elements, the chemistry of f-elements with these type
of ligands has hardly been investigated. Recent successes on this
area include the synthesis of neutral and cationic complexes of
yttrium and lanthanum with monoanionic triazacyclononane-
amide ligands that are active in ethene polymerization and in cis-
selective linear dimerization of phenylacetylene2 and the isolation
of the uranium(III) complex, [U{(ArO)3-tacn}] (Ar = 3,5-di-
tert-butyl-2-hydroxybenzyl), that showed a remarkable reactivity.3
Recently, we reported the synthesis of the uranium(III) complex,
[U{(SiMe2NPh)3-tacn}],4 achieved by reaction of one equivalent
Results and discussion
Metathesis of [U{(SiMe2NPh)3-tacn}Cl] with one equivalent of
either LiNEt2 or LiNPh2 at room temperature resulted in a gradual
color change from green to golden–brown. Standard workup of the
reaction mixture yielded [U{(SiMe2NPh)3-tacn}(NEt2)] (1) and
[U{(SiMe2NPh)3-tacn}(NPh2)] (2), respectively. The complexes
were obtained as golden solids in moderate yield (Scheme 1).
Both compounds were soluble in THF and aromatic sol-
vents and moderately soluble in aliphatic solvents. The room-
5
of Na3[(SiMe2NPh)3-tacn](THF)2 with uranium triiodide. Also
we have shown that the U(IV) derivatives, [U{(SiMe2NPh)3-
tacn}X] (X = Cl, I), could be prepared via oxidation of
[U{(SiMe2NPh)3-tacn}] with benzyl chloride or I2.4
1
temperature H NMR spectra of 1 and 2 exhibited only one set
of proton signals associated with the {(SiMe2NPh)3-tacn} ligand,
indicating that the compounds are fluxional on the NMR time
scale. The spectra presented one single peak accounting for the 18
protons of the SiMe2 groups, one set of resonances associated with
the aniline groups and two resonances assigned to the methylenic
protons of the cyclic amine. In addition the spectra showed the
resonances due to the amide ligands, two for the diethylamide
and three for the diphenylamide, with the expected intensities.
Departamento de Qu´ımica, ITN, Estrada Nacional 10, P-2686-953,
Sacave´m, Portugal. E-mail: nmarques@itn.mces.pt
† Electronic supplementary information (ESI) available: 1H NMR data,
selected bond lengths and angles, crystallographic data and ORTEP
diagram. See DOI: 10.1039/b603000a
3368 | Dalton Trans., 2006, 3368–3374
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the resulting compound was shown to be [U{(SiMe2NPh)3-
tacn}{(HNC(Me))2CC≡N}] (3), a uranium complex in which the
metal is coordinated to the anionic ligand [{HNC(Me)}2CC≡N],
resulting of a trimerization of the nitrile (Scheme 2).
Scheme 2
Reactivity of U{(SiMe2NPh)3-tacn}(NR2)] (2)
Scheme 1
Protonolysis of compounds [U{(SiMe2NPh)3-tacn}(NR2)] with
reagents containing acidic protons such as 2,4,6-trimethylphenol,
3,5-dimethylpyrazole and mercaptopyridine in THF, at room
temperature, gave the corresponding [U{(SiMe2NPh)3-tacn}X]
complexes (X = OC6H2-2,4,6-Me3 (4), 3,5-Me2pz (5) or SC5H4N
(6), eqn (1)). The reactions were faster for the diphenylamide
compound (NMR experiments).
Although complexes 1 and 2 are fluxional in solution and exhibited
resonances strongly shifted from the diamagnetic position, the 1H
NMR spectra indicated that their coordination geometries may
be different. In the spectrum of 1 the 18 protons of the SiMe2
groups gave rise to one sharp resonance at high field, while for
2 they appeared as a broad resonance at low field. In addition
the protons of the amide ligands were at low and high field for
complexes 1 and 2, respectively. These differences may be due to
the anisotropy of the magnetic susceptibility, and to the position
of the protons inside the dipolar cone,6 as they have been observed
consistently in seven-coordinate complexes displaying capped
trigonal prismatic or bicapped trigonal bipyramidal geometries.
The 1H NMR spectrum of 1 was similar to that observed in
the seven-coordinate [U{(SiMe2NPh)3-tacn}(OPPh3)] (ESI†), a
complex that displays a capped trigonal prismatic geometry,
suggesting a similar geometry for complex 1. This was confirmed
by a X-ray structural determination (vide infra).
[U{(SiMe2NPh)3-tacn}(NPh2)] + HX
→ [U{(SiMe2NPh)3-tacn}X] + HNPh2
(1)
Compound 6 could be prepared by an alternative route by
using the reducing properties of [U{(SiMe2NPh)3-tacn}]. Addition
of 1/2 equivalent of (C5H4N)SS(C5H4N) to one equivalent of
[U{(SiMe2NPh)3-tacn}] in toluene yielded the yellowish-green
complex 6 in high yield.
In order to get some insight in the formation of 3 the 1H
NMR spectrum of [U{(SiMe2NPh)3-tacn}(NPh2)] in CD3CN was
recorded. In 2–3 h the resonances due to 2 have disappeared
to give rise to several resonances strongly shifted from the
diamagnetic position and diphenylamine. In addition resonances
assigned to methylic and aromatic protons in the diamagnetic
position indicated that attack on the [(SiMe2NPh)3-tacn] ligand
had occurred. In order to minimize the degradation of the ligand,
acetonitrile was added to a benzene-d6 solution of 2 in the
stoichiometric ratio 3 : 1. The reaction proceeded very slowly and
only after several days underwent completion. However, if a large
excess of acetonitrile was added to a benzene-d6 solution of 2 the
reaction was complete after a few hours with minor decomposition
of the [(SiMe2NPh)3-tacn] ligand.
Compound 3 was obtained in a macroscopic scale, as a dark
yellow solid, by reaction of an excess of acetonitrile with 2 in
THF solution. The reaction was complete after stirring overnight.
The diphenylamine formed in the reaction could be removed
by washing the solid with hexane, but all our attempts to
separate 3 from the species resulting from decomposition of the
[(SiMe2NPh)3-tacn] ligand were unfruitful. The IR spectrum of the
solid showed a band located at 2183 cm−1 assigned to the m(N≡C)
stretching vibration and one at 3278 cm−1 in the region where the
m(NH) stretching vibrations are usually observed.8
In contrast, the room-temperature 1H NMR spectrum of 2
was similar to those found for [U{(SiMe2NPh)3-tacn}Cl]4 and
[U{(SiMe2NPh)3-tacn}(g -N2Ph2)],7 two compounds in which the
2
arrangement of the atoms around the uranium displays a bicapped
1
trigonal bipyramidal geometry. Variable-temperature H NMR
studies confirmed this assumption. On cooling a sample of 2
in toluene-d8 the resonances broadened into the baseline and
by −80 ◦C had resolved into six broad peaks assigned to the
methylenic protons of the cyclic amine and three resonances due
to the methyl protons of the SiMe3 groups. Although the slow
exchange limit could not be reached before the solvent froze, this
pattern is consistent with a Cs symmetric coordination sphere and
has been observed in low-temperature 1H NMR studies performed
in the complexes [U{(SiMe2NPh)3-tacn}X] (X = I,4 N2Ph2 ).
7
1
Although without X-ray structural confirmation, the H NMR
spectrum of 2 points for a similar geometry for this complex.
All our attempts to obtain crystals of 2 suitable for X-
ray diffraction analysis from THF or toluene solutions were
unsuccessful. Dissolution of 2 in CH3CN resulted in the formation
of dark yellow crystals in a few hours. However, unexpectedly
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◦
˚
Compounds 4–6 were soluble in aromatic and ethereal solvents
and slightly soluble in hexane.
Table 1 Selected bond lengths (A) and angles ( ) for complexes 1, 3
and 6
The 1H NMR spectrum of 4 was consistent with a capped
trigonal prismatic geometry, while that of 5 indicated a bicapped
trigonal bipyramidal geometry4,7 (see Experimental section). Al-
though complex 5 is formally eight-coordinate, the small bite of the
dimethylpyrazolide ligand allows to consider that the midpoint of
the N–N distance is occupying one single site of the coordination
polyhedron.
1
3
6
U–N(1)
U–N(2)
U–N(3)
U–N(4)
U–N(5)
U–N(6)
U–N7
2.322(11)
2.435(11)
2.327(13)
2.744(11)
2.853(12)
2.765(13)
2.146(12)
2.296(15)
2. 254(16)
2.340(17)
2.719(16)
2.724(16)
2.767(14)
2.433(15)
2.47(2)
2.328(7)
2.332(6)
2.309(7)
2.619(7)
2.689(7)
2.775(6)
2.536(7)
2.880(2)
1
The room-temperature H NMR spectrum of 3 and 6 were
U–N8(S)
similar but quite different of those found for complexes with
capped trigonal prismatic or bicapped trigonal bipyramidal ge-
ometries. The spectra featured six resonances for the protons of
the cyclic amine, three resonances of equal intensity for the protons
of the SiMe2 groups, and two sets of resonances for the aromatic
protons of the aniline groups in a ratio 2 : 1. This pattern is
consistent with a Cs-symmetric coordination sphere. In the solid,
the eight-coordinate complexes 3 and 6 have C1 symmetry (vide
infra), but in solution, if inversion of the ethylenic backbone
is fast in the NMR time scale, the symmetry is raised to Cs
with the [{HNC(Me)}2CC≡N] and SC5H4N ligands contained
in the mirror plane, as could be inferred from the presence of
two resonances due to the methylic protons of the heterocycle
[{HNC(Me)}2CC≡N]. These were assigned by comparison with
the spectrum obtained by dissolution of 2 in CD3CN, where these
resonances were absent. Obviously the increased coordination
number of these complexes increases the steric constraints around
uranium and causes the dynamic process responsible for the
fluxionality of the molecules to slow down.
N(1)–U–N(2)
N(1)–U–N(3)
N(2)–U–N(3)
N(7)–U–N(1)
N(7)–U–N(2)
N(7)–U–N(3)
115.7(4)
111.0(4)
132.2(4)
88.2(4)
83.8(4)
88.0(4)
101.6(6)
158.8(6)
94.7(6)
95.4(2)
163.1(2)
92.3(2)
At the present stage of our investigation we are unable to
rationalize definitively the formation of 3. Trimerization of
acetonitrile has been observed in f-element chemistry. Marks
and co-workers9 reported that reaction of the heterobimetal-
lic compound Cp*2Th(Cl)Ru(Cp)(CO)2 with acetonitrile gives
the four-membered chelate diazathoracyclobutene Cp*2(Cl)Th-
[N(H)C(Me)N(R)] where R is a cyanopropenyl fragment and re-
=
cently, a neutral bis(imino)amine ligand, [(HN CMe)2MeCNH2],
has been reported to be formed in the reactions of DyI2 and
TmI2 with an excess of acetonitrile.10 However, to the best of our
knowledge, this is the first time that trimerization of acetonitrile
to yield the anionic heterocycle [{HNC(Me)}2CC≡N], has been
observed in f-element chemistry.8
Fig. 1 ORTEP diagram of [U{(SiMe2NPh)3-tacn}(NEt)2] (1) with 20%
probability ellipsoids.
Molecular structures of 1, 3 and 6
[U{(SiMe2NPh)3-tacn}(NEt2)] crystallizes from a toluene solution
The average U–N amido and U–N amine distances are
¯
˚
as golden crystals in the triclinic space group P1. The molecular
2.361(12) and 2.787(13) A, respectively, and are in the range
structure is shown in Fig. 1 and comparative bond distances and
angles are shown in Table 1.
found for other [U{(SiMe2NPh)3-tacn}X] complexes.4,7 The
˚
U–N(7) distance of 2.146(12) A is similar to the corre-
11
sponding distance in [U(TpMe2)Cl2(NEt2)] (2.148(10) A) and
[U(OC6H3-2,6-tBu2)3(NEt2)] (2.162(5) A), but significantly
˚
The uranium ion is seven-coordinate by the six nitrogen atoms
of the tacn ligand and the nitrogen atom of the NEt2 group in a
distorted trigonal prismatic configuration. The two trigonal planes
are defined by the two sets of nitrogen donor amido (N123) and
amine (N456) atoms and the pendant amido arms are oriented
around the C3 symmetry axis. The two planes are nearly parallel
and the nitrogen atom of the NEt2 group is capping the trigonal
face defined by the three nitrogen atoms of the amido groups (the
angle between the axis U–N(7) and the perpendicular to the plane
defined by N1N2N3 is 3◦).
12
˚
shorter than those usually found in other structurally char-
acterized uranium(IV) amide complexes. In the triamidoamine
complex [U{(Me3SiNCH2CH2)3N}(NEt2)] the U–N distance
13
˚
to the nitrogen of the NEt2 group is 2.220(5) A, and in
[{Me2Si(C5Me4)(tBuN)}U(NMe2)2] the corresponding distances
14
˚
to the NMe2 groups average 2.210(4) A.
The molecular structure of 1 also features one short con-
tact to the a-carbon (C40) of the NEt2 ligand (U · · · C
3370 | Dalton Trans., 2006, 3368–3374
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˚
3.025(15) A). This distance may be compared with those of
contacts to the methyl groups within the bis(trimethylsilylamide)
ligands in [U(S-2,6-Me2-C6H3){N(SiMe3)2}3]15 (3.158 A) and
˚
Th{N(SiMe3)2}2(NMePh)2]16 (3.073(10) and 3.064(10) A, respec-
˚
tively). The interaction present in the structure of 1 is responsible
for the distortion observed in the trigonal prismatic environment
of the uranium centre: the N(2)–U–N(3) angle increases to
132.2(4) vs. 111.0(4)◦ for N(1)–U–N(3) and 115.7(4)◦ for N(1)–
U–N(2). Although the interaction makes the angle U–N(7)–C(40)
decrease to 109(1)◦, the sum of the angles about the nitrogen
atom N(7) is 360◦ (U–N(7)–C(38) 139(1)◦ and C(40)–N(7)–C(38)
112(1)◦) indicating the planarity of the substituents.
This interaction is weak and a static structure could not be
observed in solution via low-temperature NMR techniques.
Dark yellow crystals of 3 were grown from a solution of 2 in
acetonitrile. Green crystals of 6 were obtained by slow diffusion
of pentane in a saturated solution of the complex in toluene.
The molecular structures are shown in Fig. 2 and 3, respectively.
Selected bond distances and angles are given in Table 1.
Fig. 3 ORTEP diagram of [U{(SiMe2NPh)3-tacn}(SC5H4N)] (6) with
20% probability ellipsoids.
Fig. 4 View of the dodecahedral coordination polyhedron of 3.
Fig. 2 ORTEP diagram of [U{(SiMe2NPh)3-tacn}{(HNC(Me))2CC≡N}]
(3) with 20% probability ellipsoids.
˚
2.787(13) A). The U–S and U–N(7) bond distances in 6 (2.880(2)
and 2.536(7) A) and the average U–N bond distance of 2.45(2)
Both structures consist of isolated molecules with no significant
intermolecular contacts. In both molecules the metal centre is
eight-coordinate with the uranium atom bound to the six nitrogen
atoms of the {(SiMe2NPh)3-tacn} ligand, and to the bidentate
ligand (two nitrogen atoms in 3 and sulfur and nitrogen atoms
in 6). The coordination geometry around the uranium atom can
be described as being dodecahedral, the trapezoids being defined
by the atoms N(1)N(3)N(5)N(6) and N(2)N(4)XN(7) (X = N(8)
for 3 and S for 6) (Fig. 4).17 Distortions from the DD geometries
are defined by the dihedral angle of the intersecting trapezoids
(90.0◦ for 3 and 89.7◦ for 6). The trapezoids are slightly distorted
with normalized u angles of 7.4 and 6.5◦, for 3 and 5.2 and 9.1◦
for 6.
˚
˚
A to the bidentate ligand in 3 compare with the corresponding
distances in [Sm(TpMe2)2(j2-SC5H4N)]18 (Sm–S 2.862(4) and Sm–N
2.523(9) A) and in Sm(TpMe2)2(j2-3,5-Me2pz)]19 (2.374(5) A) after
˚
˚
adjustment for the difference in ionic radii of U(III) and Sm(III).20
˚
˚
The N(7)–C(70) (1.28(2) A), N(8)–C(71) (1.28(3) A), C(70)–C(72)
˚
˚
(1.43(3) A), C(71)–C(72) (1.39(3) A) bond distances compare with
the corresponding distances in [Me2Ga{(HNC(Me))2CC≡N}].8
Conclusions
It is clear that the pocket afforded by the “[U{(SiMe2NPh)3-
tacn}]” fragment is effective for the binding of anionic lig-
ands allowing an entry into uranium(IV) chemistry. Metathe-
sis of [U{(SiMe2NPh)3-tacn}Cl] yields the amide complexes
[U{(SiMe2NPh)3-tacn}(NR2)] (R = Et, Ph). Amine elimination
reactions of these compounds with protic substrates provides a
The U–N amido and the U–N amine bond distances average
˚
˚
2.297(17) and 2.737(16) A in 3 and 2.323(7) and 2.694(7) A in 6.
These are reasonable values compared to data found in the seven-
coordinate complexes [U{(SiMe2NPh)3-tacn}Cl]4 (2.300(13) and
˚
2.636(13) A) and [U{(SiMe2NPh)3-tacn}(NEt2)] (2.361(12) and
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synthetic route for uranium(IV) compounds containing U–O, U–N
and U–S bonds. Therefore, [U{(SiMe2NPh)3-tacn}(NPh2)] reacts
with acetonitrile to yield a U(IV) heterocycle complex in which the
[U{(SiMe2NPh)3-tacn}{(HNC(Me))2CC≡N}] (3). An excess
of acetonitrile (60 mmol) was added to
a solution of
[U{(SiMe2NPh)3-tacn}(NPh2)] (112 mg, 0.11 mmol) in THF. After
stirring overnight, the solvent was removed under vacuum.
The oily product obtained was stirred with hexane resulting in
formation of a light-brown solid. mmax(film)/cm−1 2183 (C≡N);
3278 (NH). dH (300 MHz; C6D6; Me4Si; 20 ◦C) 63.4 (br, 4H, H-o),
52.82 (6H, SiMe2), 27.78 (4H, H-m), 18.61 (2H, H-o), 16.41 (2H,
H-m), 12.41 (6H, SiMe2), 3.19 (2H, CH2), −6.23 (2H, H-p), −8.34
(1H, H-p), −9.36 (2H, CH2), −20.49 (6H, SiMe2), −36.48 (3H,
CH3), −38.22 (3H, CH3), −42.60 (2H, CH2), −53.08 (2H, CH2),
−53.74 (2H, CH2), −77.97 (2H, CH2).
2
anionic ligand [{HNC(Me)}2CC≡N] is g -bonded to the metallic
centre. Some of the complexes were characterized by means of X-
ray diffraction analysis, but solution studies show that the tacn
ligand provides a convenient NMR handle, as the 1H NMR
spectra of the complexes are diagnostic of their coordination
geometries.
Experimental
General procedures
[U{(SiMe2NPh)3-tacn}(OC6H2-2,4,6-Me3)] (4). To a solution
of [U{(SiMe2NPh)3-tacn}(NPh2)] (133 mg, 0.14 mmol) in THF
was added dropwise a solution of HOC6H2-2,4,6-Me3 (19 mg,
0.14 mmol) in the same solvent. Stirring overnight resulted in a
dark brown solution. Removal of the solvent yielded a brown oil,
that after being stirred with hexane, resulted in formation of a
golden solid. The modest isolated yield (25%, 0.035 mmol) was a
result of the high solubility of the compound in hexane (Found: C,
49.31; H, 5.85; N, 8.55. USi3C39H56N6O requires C, 49.45; H, 5.96;
N, 8.87%). dH (300 MHz; C6D6; Me4Si; 20 ◦C) 25.07 (6H, CH3-o),
18.85 (2H, H-m); 10.86 (3H, CH3-p), 8.79 (6H, CH2), 7.95 (6H,
t; H-m), 6.59 (3H, t, H-p) −4.27 (6H, d, H-o), −5.85 (6H, CH2),
−12.47 (18H, SiMe2).
All preparations and subsequent manipulations were carried out
using standard Schlenk-line and dry-box techniques in an atmo-
sphere of dinitrogen. THF, toluene, acetonitrile and n-hexane were
dried by standard methods and degassed prior to use. Toluene-
d8 and benzene-d6 were dried over Na and distilled. HOC6H2-
2,4,6-Me3, 3,5-Me2pzH, S2(C5H4N)2 and HNPh2 were sublimed
prior to use. HNEt2 was dried over BaO and distilled. Mer-
captopyridine, HSC5H4N, was purchased from Aldrich and used
without further purification. LiNPh2 and LiNEt2 were synthesized
by addition of n-BuLi to solutions of the amines in n-hexane,
at 0 ◦C. Na3[(SiMe2NPh)3-tacn](THF)2,5 [U{(SiMe2NPh)3-tacn}]4
and [U{(SiMe2NPh)3-tacn}Cl]4 were prepared by published pro-
1
cedures. H NMR spectra were recorded on a Varian INOVA-
300 spectrometer at 300 MHz. Spectra were referenced internally
using the residual proton resonances relative to tetramethylsilane
(benzene-d6, 7.15 ppm; toluene-d8, 2.09 ppm). Carbon, hydrogen
and nitrogen analyses were performed in-house using a EA110 CE
Instruments automatic analyser.
[U{(SiMe2NPh)3-tacn}(3,5-Me2pz)] (5). The compound was
obtained as described for 4 by using 151 mg of [U{(SiMe2NPh)3-
tacn}(NPh2)] (0.15 mmol) and 15 mg (0.15 mmol) of 3,5-
Me2pzH. The light-green compound was obtained with a yield
of 40% (55 mg, 0.06 mmol) (Found: C, 46.45; H, 5.53; N, 11.99.
USi3C35H52N8 requires C, 46.34;H, 5.78; N, 12.35%). dH (300 MHz;
C6D6; Me4Si; 40 ◦C) 13.96 (6H, br, H-o), 12.21 (18H, SiMe2), 11.14
(6H, H-m); 5.83 (3H, H-p), −7.23 (1H, H-4 (3,5-Me2pz)), −11.7
(6H, CH2), −31.81 (6H, CH3 (3,5-Me2pz)), −40.80 (6H, CH2).
Synthetic procedures
[U{(SiMe2NPh)3-tacn}(NEt2)] (1). Addition of a solution
of LiNEt2 (16 mg, 0.20 mmol) in THF to a solution of
[U{(SiMe2NPh)3-tacn}Cl] (171 mg, 0.20 mmol) in the same
solvent resulted in a gradual colour change of the solution from
green to golden over 3 h. Removal of the solvent followed by
extraction with toluene and separation of the LiCl gave a golden
solid, that was washed with hexane and dried under vacuum.
Washing with hexane results in a lower yield due to the solubility of
the compound in hexane. Yield: 55% (95 mg, 0.11 mmol) (Found:
C, 45.92; H, 6.10; N, 10.54. USi3C34H55N7 requires C, 46.19; H,
[U{(SiMe2NPh)3-tacn}(SC5H4N)] (6). (a) The compound was
obtained as described for 4 by using 115 mg of [U{(SiMe2NPh)3-
tacn}(NPh2)] (0.12 mmol) and 14 mg (0.13 mmol) of
HSC5H4N. The yellowish-green compound was obtained with a
yield of 72% (79 mg, 0.09 mmol).
(b) To
a
solution of [U{(SiMe2NPh)3-tacn}] (123 mg,
◦
6.27; N, 11.09%). dH (300 MHz; C6D6; Me4Si; 20 C) 46.59 (4H,
0.15 mmol) in toluene was slowly added a solution of S2(C5H4N)2
(17 mg, 0.077 mmol) in the same solvent. The brown solution
turns almost immediately to green. Stirring was continued for an
additional 1–2 h. The solution was centrifuged. Removal of the
solvent gave a yellowish-green solid that was further washed with
hexane. Yield 90% (124 mg, 0.13 mmol) (Found: C, 45.79; H, 5.69;
N, 10.74. USi3C35H49N7S requires C, 45.59; H, 5.36; N, 10.63%).
CH2(NEt2)); 23.41 (6H, CH2); 18.79 (6H, CH3(NEt2)); 11.66 (6H,
CH2); 6.02 (6H, t, H-m); 5.67 (3H, t, H-p); −9.37 (6H, d, H-o);
−13.91 (18H, SiMe2).
[U{(SiMe2NPh)3-tacn}(NPh2)] (2). The compound was ob-
tained as described above by reaction of a solution of LiNPh2
(125 mg, 0.71 mmol) in THF with a solution of [U{(SiMe2NPh)3-
tacn}Cl] (604 mg, 0.71 mmol) in the same solvent. The golden solid
was obtained with a yield of 69% (481 mg, 0.49 mmol) (Found C,
51.43; H, 5.45; N 9.79. USi3C42H55N7 requires C, 51.46; H, 5.66;
◦
dH (300 MHz; C6D6; Me4Si; 20 C) 56.30 (4H, H-o), 53.08 (6H,
SiMe2), 23.54 (4H, H-m), 20.79 (2H, d, H-o), 15.75 (6H, SiMe2),
15.02 (2H, t, H-m), 3.52 (2H, CH2), −6.74 (2H, H-p), −6.96 (1H,
H-p), −12.70 (2H, CH2), −12.96 (1H, t, SC5H4N), −15.72 (6H,
SiMe2), −17.84 (1H, t, SC5H4N), −23.40 (1H, d, SC5H4N), −44.67
(2H, CH2), −51.68 (2H, CH2), −58.03 (2H, CH2), −78.26 (2H,
CH2), −78.44 (1H, t, SC5H4N).
◦
N, 10.0%). dH (300 MHz; C6D6; Me4Si; 60 C) 30.9 (6H, br, H-
o), 13.45 (6H, H-m), 9.79 (18H, SiMe2), 8.81 (3H, H-p), −5.89
(2H, H-p (NPh2)), −9. 21 (4H, H-m (NPh2)), −12.3 (4H, br, H-o
(NPh2)), −33.94 (6H, CH2), −46.70 (6H, CH2).
3372 | Dalton Trans., 2006, 3368–3374
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View Article Online
Table 2 Crystallographic data
1
3
6
Formula
Mr
Crystal system
C34H55N7Si3U
884.15
Triclinic
¯
P1
12.8662(17)
10.7009(10)
16.9568(19)
100.262(9)
98.029(10)
119.404(9)
1929.8(4)
2
C36H53N9Si3U
934.17
Triclinic
¯
P1
11.1504(15)
11.274(3)
19.834(4)
77.114(19)
83.551(13)
62.636(15)
2158.5(7)
2
C35H49N7SSi3U
922.17
Monoclinic
Space group
P21/n
˚
a/A
14.213(3)
17.6693(17)
15.321(3)
˚
b/A
˚
c/A
a/◦
b/◦
c /◦
94.273(15)
3
˚
V/A
3837.1(11)
4
1.596
Z
Dc/g cm−3
1.522
1.437
Crystal size/mm
l(Mo-Ka)/mm−1
h Range/◦
Measured reflections
Independent reflections (Rint
Observed reflections [I > 2r(I)]
0.34 × 0.22 × 0.10
0.35 × 0.10 × 0.08
0.45 × 0.25 × 0.15
4.331
3.878
4.413
1.88–24.99
7011
6758 (0.0716)
4017
0.0865
0.1140
2.07–24.99
7742
7509 (0.1231)
3381
0.1035
0.1809
1.84–24.98
6975
6689 (0.0453)
4637
0.0509
0.0995
)
R1
wR2
X-Ray crystallographic analysis
3 (a) I. Castro-Rodriguez, K. Olsen, P. Gantzel and K. Meyer, Chem.
Commun., 2002, 2764–2765; (b) I. Castro-Rodriguez, K. Olsen, P.
Gantzel and K. Meyer, J. Am. Chem. Soc., 2003, 125, 4565–4571;
(c) I. Castro-Rodriguez, H. Nakai, P. Gantzel, L. N. Zacharov, A. L.
Rheingold and K. Meyer, J. Am. Chem. Soc., 2003, 125, 15734–15735;
(d) H. Nakai, X. Hu, L. N. Zakharov, A. L. Rheingold and K. Meyer,
Inorg. Chem., 2004, 43, 855–857; (e) I. Castro-Rodriguez, H. Nakai,
L. N. Zacharov, A. L. Rheingold and K. Meyer, Science, 2004, 305,
1757–1759; (f) I. Castro-Rodriguez and K. Meyer, J. Am. Chem. Soc.,
2005, 127, 11242–11243.
Crystals were mounted in thin-walled glass capillaries in a
nitrogen-filled glove-box. Data were collected at r.t. on an Enraf-
Nonius CAD4-diffractometer with graphite-monochromated
˚
Mo-Ka radiation (k = 0.71069 A) in the x–2h scan mode. Data
were corrected21 for Lorentz and polarization effects, and for
absorption by empirical corrections based on W scans.
The structure of 1 was solved using Patterson methods22 and
successive difference Fourier techniques and refined by full-
matrix least-squares refinements on F2 using SHELXL-97.23 The
structures of 3 and 6 were solved by direct methods using SIR9724
and refined by full-matrix least-squares refinements on F2 using
SHELXL-9723 and the WinGX software package.25 All non-
hydrogen atoms were refined with anisotropic thermal motion
parameters, and the hydrogen atoms were assigned idealized
positions based on the geometries of their attached carbon atoms.
The drawings were made with ORTEP3.26 The poor quality of
data/refinement for 3 was due to the low quality of the crystal. A
summary of the crystallographic data is given in Table 2.
CCDC reference numbers 269724 (1), 269726 (3), 269725 (6).
For crystallographic data in CIF or other electronic format see
DOI: 10.1039/b603000a
4 B. Monteiro, D. Roitershtein, H. Ferreira, J. R. Ascenso, A. M.
ˆ
Martins, A. Domingos and N. Marques, Inorg. Chem., 2003, 42, 4223–
4231.
5 A. R. Dias, A. M. Martins, J. R. Ascenso, H. Ferreira, M. T. Duarte
and R. T. Henriques, Inorg. Chem., 2003, 42, 2675–2682.
6 W. D. Horrocks, Jr., NMR of Paramagnetic Molecules. Principles and
Applications, ed. G. N. La Mar, W. D. Horrocks, Jr. and R. H. Holm,
Academic Press, New York, 1973, ch. 4.
ˆ
7 M. A. Antunes, B. Monteiro, A. Carvalho, J. P. Leal, A. Domingos,
I. C. Santos, N. Marques, presented in part at the 19th Portuguese
Chemical Society Meeting, Coimbra, Portugal, April, 2004. Due to the
small byte of the azobenzene the midpoint of the N–N bond can be
considered as occupying the seventh coordination site of the bicapped
trigonal bipyramid.
8 It has been reported that reaction of Al, In and GaMe3 in refluxing ace-
tonitrile gives [Me2M{HNC(Me)}2C(CN)] (M. K. Kopp, T. Kra¨uter,
A. Dashti-Mommertz and B. Neumu¨ller, Organometallics, 1998, 17,
4226–4231). Formation of this anion has also been observed during the
electrochemical synthesis of a Co compound with tosylamide ligands
in which the solvent used was acetonitrile (; M. L. Dura´n, J. A. Garc´ıa-
Vasquez, C. Go´mez, A. Sousa-Pedrares, J. Romero and A. Sousa,
Eur. J. Inorg. Chem., 2002, 2348).
Acknowledgements
9 R. S. Sternal, M. Sabat and T. J. Marks, J. Am. Chem. Soc., 1987, 109,
7920–7921.
Financial support from Fundac¸a˜o para a Cieˆncia e Tecnologia
(POCTI/QUI/36015/2000, POCTI/QUI/46179/2002) is grate-
fully acknowledged. MAA thanks FCT for a PhD grant
(SFRH/BD/4827/2001).
10 M. N. Bochkarev, G. V. Khoroshenkov, H. Schumann and S. Dechert,
J. Am. Chem. Soc., 2003, 125, 2894–2895.
ˆ
11 M. Silva, M. A. Antunes, A. Domingos, I. Cordeiro dos San-
tos, J. Marc¸alo and N. Marques, Dalton Trans., 2005, 3353–
3358.
12 P. B. Hitchcock, M. F. Lappert, A. Singh, R. G. Taylor and D. Brown,
J. Chem. Soc., Chem. Commun., 1983, 561–562.
13 P. Roussel, N. W. Alcock, R. Boaretto, A. J. Kingsley, I. J. Mun-
slow, C. J. Sanders and P. Scott, Inorg. Chem., 1999, 38, 3651–
3656.
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3374 | Dalton Trans., 2006, 3368–3374
This journal is
The Royal Society of Chemistry 2006
©