Triamidotriazacyclononane complexes of group 3 metals. Synthesis and crystal structures

Article abstract of DOI:10.1021/ic034090v

Reaction of yttrium and lanthanide trichlorides (Ln = La, Eu, Yb) with 1 equiv of the trisodium salt of 1,4,7-tris(dimethylsilylaniline)-1,4,7-triazacyclononane (Na₃[(SiMe₂NPh)₃-tacn](THF)₂) gives good yields of the compounds [M{(SiMe₂NPh)₃-tacn}] (M = Y (1), Eu (3), Yb (4)) and [La{(SiMe₂NPh)₃-tacn}(THF)] (2). Reduction of 3 with Na/Hg followed by recrystallization in the presence of diglyme yielded crystals of [Eu{(SiMe₂NPh)₃-tacn}][Na(diglyme)₂] (5). Synthesis of the uranium(III) complex [U{(SiMe₂NPh)₃-tacn}] (6) is achieved by reaction of 1 equiv of Na₃[(SiMe₂NPh)₃-tacn](THF)₂ with uranium triiodide. The U(IV) complexes, [U{(SiMe₂NPh)₃-tacn}X] (X = Cl (7); I (8)), were prepared via oxidation of 6 with benzyl chloride or I₂, but salt metathesis from UCl₄ provided a higher yield route for 7. The solid-state structures of 1-7 were determined by single-crystal x-ray diffraction. The ligand [(SiMe₂NPh)₃-tacn] generates a trigonal prismatic coordination environment for the metal center in the neutral complexes 1, 3, 4, and 6 and the ionic 5. In 2 the six nitrogen atoms of the ligand are in a trigonal prismatic configuration with the oxygen atom of the THF capping one of the triangular faces of the trigonal prism. In 7 the coordination geometry around the uranium atom is best described as bicapped trigonal bipyramidal.

Full text of DOI:10.1021/ic034090v

Inorg. Chem. 2003, 42, 4223−4231
Triamidotriazacyclononane Complexes of Group 3 Metals. Synthesis and
Crystal Structures
Bernardo Monteiro,† Dmitrii Roitershtein,† Humberto Ferreira,‡ Jose´ R. Ascenso,‡ Ana M. Martins,‡
,†
Aˆngela Domingos,† and Noe´mia Marques*
Departmento de Qu´ımica, ITN, Estrada Nacional 10, P-2686-953, SacaVe´m, Portugal, and Centro
de Qu´ımica Estrutural, Complexo I, Instituto Superior Te´cnico, P-1096 Lisboa Codex, Portugal
Received January 28, 2003
Reaction of yttrium and lanthanide trichlorides (Ln ) La, Eu, Yb) with 1 equiv of the trisodium salt of 1,4,7-tris-
(dimethylsilylaniline)-1,4,7-triazacyclononane (Na3[(SiMe2NPh)3-tacn](THF)2) gives good yields of the compounds
[M{(SiMe2NPh)3-tacn}] (M ) Y (1), Eu (3), Yb (4)) and [La{(SiMe2NPh)3-tacn}(THF)] (2). Reduction of 3 with
Na/Hg followed by recrystallization in the presence of diglyme yielded crystals of [Eu{(SiMe2NPh)3-tacn}][Na-
(diglyme)2] (5). Synthesis of the uranium(III) complex [U{(SiMe2NPh)3-tacn}] (6) is achieved by reaction of 1 equiv
of Na3[(SiMe2NPh)3-tacn](THF)2 with uranium triiodide. The U(IV) complexes, [U{(SiMe2NPh)3-tacn}X] (X ) Cl (7);
I (8)), were prepared via oxidation of 6 with benzyl chloride or I2, but salt metathesis from UCl4 provided a higher
yield route for 7. The solid-state structures of 1−7 were determined by single-crystal X-ray diffraction. The ligand
[(SiMe2NPh)3-tacn] generates a trigonal prismatic coordination environment for the metal center in the neutral
complexes 1, 3, 4, and 6 and the ionic 5. In 2 the six nitrogen atoms of the ligand are in a trigonal prismatic
configuration with the oxygen atom of the THF capping one of the triangular faces of the trigonal prism. In 7 the
coordination geometry around the uranium atom is best described as bicapped trigonal bipyramidal.
Introduction
separation of the lanthanides.6
1,4,7-Triazacyclononane-based ligands are becoming in-
creasingly popular due to the ease with which this macrocycle
can be derivatized at the nitrogen atoms to yield C3-
symmetric N,N′,N′′-trisubstituted ligands, which can bind in
a facial fashion to a wide range of metals.7 Although widely
used and established as an important class for the main group
and transition elements, only a few complexes of tacn-based
ligands with group 3 metals have been structurally char-
acterized. Recently, a low-valent uranium(III) complex
supported by an aryloxide functionalized triazacyclononane,
[((ArO)3tacn)U], has been synthesized.8 Attempts to recrys-
tallize this compound from pentane and solutions of Et2O
or THF yielded mono- and dinuclear seven-coordinate
uranium(IV) complexes, [((ArO)3tacn)U(OAr)] and
[{((ArO)3tacn)U}2(µ-O)], that have been structurally char-
acterized.8 Other reports include the synthesis of Sc, Y, and
Lu complexes with neutral 1,4,7-triazacyclononane ligands
During the past decade there has been a renewal of interest
in the coordination chemistry of lanthanides with macrocyclic
ligands. This is due to the diverse array of applications that
their metal complexes have found as contrast-enhancing
agents in nuclear magnetic resonance imaging,1 as lumines-
cent probes in medicine and biology,2 as radiometal-labeled
agents for diagnostic imaging,3 as catalysts4,5 and in the
* Author to whom correspondence should be addressed. E-mail:
nmarques@itn.pt. Fax: 351-219941455.
† ITN.
‡ Instituto Superior Te´cnico.
(1) (a) Parker, D.; Dikins, D. S.; Puschmann, H.; Crossland, C.; Howard,
J. A. K. Chem. ReV. 2002, 102, 1977. (b) To´th, E.; Burai, L.; Merbach,
A. E. Coord. Chem. ReV. 2001, 216, 363. (c) Bianchi, A.; Calabi, L.;
Corana, F.; Fontana, S.; Posi, P.; Maiocchi, A.; Paleari, L.; Baltancoli,
B. Coord. Chem ReV. 2000, 204, 309. (d) Comblin V.; Gilsoul, D.;
Hermann, M.; Humblent, V.; Jacques, V.; Mesbahi, M.; Sauvage, C.;
Desreux, J. F. Coord. Chem. ReV. 1999, 185, 451. (e) Cavalan, P.;
Ellison, J. J.; McMurray, T. J.; Lauffer, R. B. Chem. ReV. 1999, 99,
2293.
(2) Bunzli, J.-C. G. In Lanthanides Probes in Life, Chemical and Earth
Sciences, Theory and Practice; Bunzli, J.-C. G., Choppin, G. R., Eds.;
Elsevier: Amsterdam, The Netherlands, 1989.
(3) Volkert, W. A.; Hoffman, T. J. Chem. ReV. 1999, 99, 2269.
(4) Hajela, S.; Schaefer, W. P.; Bercaw, J. E. J. Organomet. Chem. 1997,
532, 45.
(5) Bambirra, S.; Leuse, D.; Meetsma, A.; Hessen, B.; Teuben, J. H. Chem.
Commun. 2001, 637.
(6) Alexander, V. Chem. ReV. 1995, 95, 273-342 and references therein.
(7) Wainwright, K. P. Coord. Chem. ReV. 1997, 166, 35-90.
(8) Castro-Rodriguez, I.; Olsen, K.; Gantzel, P.; Meyer, K. Chem.
Commun. 2002, 2764.
10.1021/ic034090v CCC: $25.00 © 2003 American Chemical Society
Published on Web 06/06/2003
Inorganic Chemistry, Vol. 42, No. 13, 2003 4223

Monteiro et al.
23
24
(Ln ) Eu, Yb),22 UI3(THF)4 and UCl4 were prepared by
published procedures. The THF content for the yttrium and
lanthanum trichlorides and the uranium triiodide was established
by elemental analysis. 1H and 13C NMR spectra were recorded on
a Varian INOVA-300 spectrometer at 300 and 75 MHz, respec-
tively. Spectra were referenced internally using the residual proton
resonances relative to tetramethylsilane (toluene-d8, 2.09 ppm;
dichloromethane-d2, 5.32 ppm). Carbon, hydrogen, and nitrogen
analyses were performed in-house using a EA110 CE Instruments
automatic analyzer.
(1,4,7-tris(carbamoylmethyl)-1,4,7-triazacyclononane (TMCT),
M ) Y, Lu, and 1,4,7-trimethyl-1,4,7-triazacyclononane
(Me3-tacn), M ) Sc, Y)4,9 and the X-ray structural charac-
terization of [Y(TMCT)(CF3SO3)2(H2O)](CF3SO3)9 and [(Me3-
tacn)ScCl3].4 Two yttrium dialkyl complexes with linked
1,4,7-triazacyclononane-amido monoanionic ancillary ligands,
[{(R)2-tacn-(CH2)2NBut}Y(CH2SiMe3)2] (R ) Me, Pri), have
also been reported.5 In addition, the synthesis and structural
characterization of lanthanide complexes LnL (Ln ) La, Sm,
Yb) of a nonadentate ligand derived from 1,4,7-triazacy-
clononane (L ) [O2CC(Me)N(CH2)2]3tacn) have been de-
scribed.10 The X-ray crystal structure of a Eu complex,
[Eu(HL)]Cl‚10H2O, where L is a tacn unit incorporating
bipyridine arms, with each subunit bearing a negatively
charged carboxylate group, is also known.11 Because of the
interesting photophysical properties of the Eu and Tb
complexes with this ligand, they have been used as the basis
for luminescent probes for bioaffinity assays that rely on TR
luminescence measurements.11
In recent years, a rich chemistry of f elements involving
quadridentate triamidoamine ligands has emerged.12-19 This
stimulated our interest in the use of the somewhat related
trianionic 1,4,7-triazacyclononane-amido ligands as ancil-
laries in the chemistry of group 3 metals. In this paper we
report full details on the synthesis and characterization of a
range of trivalent [M{(SiMe2NPh)3-tacn}(THF)x] complexes
(M ) Y, Eu, Yb, U, x ) 0; La, x ) 1). The synthesis and
characterization of the U(IV) compounds, [U{(SiMe2NPh)3-
tacn}X] (X ) Cl, I) and of the divalent europium compound,
[Eu{(SiMe2NPh)3-tacn}][Na(diglyme)2], are also described.
The solid-state X-ray structures of several members have
been determined, and a detailed structural comparison is
provided.
Synthetic Procedures. [Y{(SiMe2NPh)3-tacn}] (1). Na3[(SiMe2-
NPh)3-tacn](THF)2 (402 mg, 0.51 mmol) in THF solution was
slowly added to a suspension of YCl3(THF)2.5 (192 mg, 0.51 mmol)
in THF. After stirring overnight, the NaCl formed was discharged
and the solution evaporated to dryness. The beige solid obtained
was washed with n-hexane. Yield: 80% (270 mg, 0.41 mmol).
Elemental anal. Calcd for YSi3C30H45N6: C, 54.36; H, 6.84; N
12.68. Found: C, 53.75; H, 6.55; N, 12.19.
1H NMR (toluene-d8, 20 °C): 7.04 (6H, m, H-m), 6.75 (6H, m,
H-o), 6.72 (3H, m, H-p), 2.77 (6H, m, CH2), 2.24 (6H, m, CH2),
0.27 (18H, s, SiMe2).
13C NMR (toluene-d8, 20 °C): 153.3 (Cipso), 129.6 (C-m), 121.8
(C-o), 117.6 (C-p), 48.4 (C-ring), 0.0 (C-SiMe2).
Crystallization from toluene gives colorless crystals of 1‚C6H5-
Me.
[La{(SiMe2NPh)3-tacn}(THF)] (2). The compound was pre-
pared as described for 1, by adding 363 mg (0.46 mmol) of
Na3[(SiMe2NPh)3-tacn](THF)2 to a solution of LaCl3(THF)1.5 (163
mg, 0.46 mmol) in THF. The beige solid was obtained with a yield
of 80% (290 mg, 0.37 mmol). Elemental anal. Calcd for
LaSi3C34H53N6O: C, 52.02; H, 6.81; N, 10.71. Found: C, 51.57;
H, 6.64; N, 10.57.
1H NMR (toluene-d8, 20 °C): 7.15 (6H, m, H-m), 6.88 (6H,
m, H-o), 6.73 (3H, m, H-p), 3.33 (4H, THF), 3.03 (6H, m, CH2),
2.38 (6H, m, CH2), 1.10 (4H, THF), 0.29 (18H, SiMe2).
13C NMR (toluene-d8, 20 °C): 155.7 (Cipso), 129.1 (C-m), 124.0
(C-o), 117.5 (C-p), 68.1 (THF), 48.4 (C-ring), 24.9 (THF), 0.0
(C-SiMe2).
Experimental Section
Crystallization from toluene gives colorless crystals of 2.
[Eu{(SiMe2NPh)3-tacn}] (3). The compound was synthesized
as described for 1 using 101 mg (0.39 mmol) of EuCl3 and 308
mg (0.39 mmol) of Na3[(SiMe2NPh)3-tacn](THF)2. The red com-
pound was isolated in 74% yield (210 mg, 0.29 mmol). Crystal-
lization from toluene gives red-orange crystals of [Eu{(SiMe2NPh)3-
tacn}]‚0.5C6H5Me. Elemental anal. Calcd for EuSi3C30H45N6‚
0.5C7H8: C, 52.62; H, 6.40; N, 10.80. Found: C, 52.19; H, 6.44;
N, 10.89.
1H NMR (toluene-d8, 20 °C): 36 (6H, vbr, CH2), 32.8 (6H, H-o),
15.2 (3H, H-p), 13.8 (6H, d, H-m), -0.2 (6H, br, CH2), -16.1
(18H, SiMe2); -60 °C, 89.3 (3H, CH2), 56.1 (6H, H-o), 29.4 (3H,
CH2), 20.0 (9H, H-p + H-o), 12.7 (3H, CH2), -13.5 (3H, CH2),
-22.5 (9H, SiMe2), -30.5 (9H, SiMe2).
General Procedures. All preparations and subsequent manipula-
tions were carried out using standard Schlenk line and drybox
techniques in an atmosphere of dinitrogen. THF, toluene, and
n-hexane were dried by standard methods and degassed prior to
use. Toluene-d8 was dried over Na and distilled, and dichlo-
romethane-d2 was vacuum distilled from P2O5. Na3[(SiMe2NPh)3-
tacn](THF)2,20 LnCl3(THF)x21 (Y, x ) 2.5; La, x ) 1.5), LnCl3
(9) Amin, S.; Marks, C.; Toomey, L. M.; Churchill, M. R.; Morrow, J.
R. Inorg. Chim. Acta 1996, 246, 99.
(10) Tei, L.; Baum, G.; Blake, A. J.; Fenske, D.; Schro¨der J. Chem. Soc.,
Dalton Trans. 2000, 2793.
(11) Charbonnie`re, L.; Ziessel, R.; Guardigli, M., Roda, A.; Sabbatini, N.;
Cesario, M. J. Am. Chem. Soc. 2001, 123, 2436.
(12) Morton, C.; Alcock, N. W.; Lees, M. R.; Munslow, I. J.; Sanders, C.
J.; Scott, P. J. Am. Chem. Soc. 1999, 121, 11255.
[Yb{(SiMe2NPh)3-tacn}] (4). The compound was prepared as
described above for 1 by using 164 mg (0.59 mmol) of YbCl3 and
462 mg (0.59 mmol) of Na3[(SiMe2NPh)3-tacn](THF)2. The yellow
solid was obtained with a 68% yield (300 mg, 0.40 mmol).
(13) Roussel, P.; Alcock, N. W.; Scott, P. Chem. Commun. 1998, 801.
(14) Odom, A. L.; Arnold, P. L.; Cummins, C. C. J. Am. Chem. Soc. 1998,
120, 5836.
(15) Roussel, P.; Scott, P. Polyhedron 1994, 13, 1651.
(16) Roussel, P.; Scott, P. J. Am. Chem. Soc. 1998, 120, 1070.
(17) Boaretto, R.; Russel, P.; Kingsley, A. J.; Munslow, I. J.; Sanders, C.
J.; Alcock, N. W.; Scott, P. Chem. Commun. 1999, 1701.
(18) Roussel, P.; Alcock, N. W.; Boaretto, R.; Kingsley, A. J.; Munslow,
I. J.; Sanders, C. J.; Scott, P. Inorg. Chem. 1999, 38, 3651.
(19) Roussel, P.; Hitchcock, P. B.; Tinker, N. D.; Scott, P. Inorg. Chem.
1997, 36, 5716.
(21) Hermann, W. A. In Synthetic Methods of Organometallic and
Inorganic Chemistry (Hermann/Brauer). Vol. 6. Lanthanides and
Actinides; Edelmann, F. T., Ed.; Verlag: Stuttgart, 1997; p 34.
(22) Meyer, G. Inorg. Synth. 1989, 25, 146.
(23) Clark, D. L.; Sattelberger, A. P.; Bott, S. G.; Vrtis, R. N. Inorg. Chem.
1989, 28, 1771; Avens, L. R.; Bott, S. G.; Clark, D. L.; Sattelberger,
A. P.; Watkin, J. G.; Zwick, B. D. Inorg. Chem. 1994, 33, 2248.
(24) Hermann, J. A.; Suttle, J. F. Inorg. Synth. 1957, 5, 143.
(20) Dias, A. R.; Martins, A. M.; Ascenso, J. R.; Ferreira, H.; Duarte, M.
T.; Henriques, R. T. Inorg. Chem., accepted.
4224 Inorganic Chemistry, Vol. 42, No. 13, 2003

Triamidotriazacyclononane Complexes of Group 3 Metals
Crystallization from toluene gives yellow crystals of [Yb{(SiMe2-
NPh)3-tacn}]‚C6H5Me. Calcd for YbSi3C30H45N6‚C7H8: C, 52.96;
H, 6.37; N, 10.01. Found: C, 52.32; H, 6.21; N, 9.91.
1H NMR (toluene-d8, 40 °C) 82 (6H, vbr, CH2), 59.6 (6H, H-o),
24.6 (6H, H-m), 19.2 (3H, H-p), 4.5 (6H, vbr, CH2), -34.1 (18H,
SiMe3); -60 °C, 212.0 (3H, br, CH2), 109.8 (6H, H-o), 74.9 (3H,
br, CH2), 66.4 (3H, br, CH2), 39.3 (6H, H-m), 29.2 (3H, H-p), -48.6
(9H, SiMe2), -57.4 (3H, br, CH2) -74.0 (9H, SiMe2).
1H NMR (CD2Cl2, 35 °C): 13.6 (18H, br, SiMe2), 9.6 (6H, br),
6.2 (9H, br), -12 (6H, vbr), -49.5 (6H, CH); -70 °C, 86.5 (6H,
SiMe2), 83.6 (6H, H-o), 32.3 (6H, H-m), 19.2 (3H, H-p), -10.3
(6H, SiMe2), -18.5 (2H, CH2), -28.3 (6H, SiMe2), -29.4 (2H,
CH2), -55.5 (2H, CH2), -77.7 (2H, CH2), -91.1 (2H, CH2),
-143.3 (2H, CH2).
Crystallization from CH2Cl2 gave thin yellowish-green needles
not adequate for X-ray diffraction analysis.
[Eu{(SiMe2NPh)3-tacn}][Na(diglyme)2] (5). [Eu{(SiMe2NPh)3-
tacn} (89 mg) in THF solution was reacted overnight with an
equimolar amount of sodium amalgam 0.5% (564 mg). The reddish-
brown solution turned gradually to brown. After the mercury had
been discharged, the solution was evaporated to dryness and the
dark yellow solid washed with hexane. Crystallization from a
concentrated THF solution with a few drops of diglyme gave yellow
crystals of [Eu{(SiMe2NPh)3-tacn}][Na(diglyme)2]. Calcd for
EuNaSi3C42H73N6O6: C, 49.59; H, 7.23; N, 8.26. Found: C, 49.31;
H, 7.41; N, 8.12.
[U{(SiMe2NPh)3-tacn}] (6). Addition of 298 mg (0.40 mmol)
of Na3[(SiMe2NPh)3-tacn](THF)2 to a solution of UI3(THF)4 (360
mg, 0.40 mmol) in THF resulted in an immediate color change
from blue to purple. The mixture was stirred overnight at room
temperature, and then the solvent was removed under vacuum. The
residue was extracted with toluene and centrifuged to remove the
NaI. Removal of the toluene under vacuum yielded 6 as a brown
powder, which was further washed with hexane and vacuum-dried.
Yield: 70% (250 mg). Crystallization from toluene solution gives
dark brown crystals of [U{(SiMe2NPh)3-tacn}]‚0.5C6H5Me. Calcd
for USi3C30H45N6‚0.5C7H8: C, 46.80; H, 5.71; N, 9.79. Found: C,
46.04; H, 5.44; N, 9.45.
1H NMR (toluene-d8, 20 °C): 7.3 (18H, SiMe2), 3.0 (6H, H-m),
1.3 (3H, H-p), -0.5 (6H, CH2), -6.7 (6H, H-o), -29.1 (6H, CH2);
-70 °C, 15.1 (9H, SiMe2), 10.8 (9H, SiMe2), -0.8 (3H, CH2),
-1.3 (6H, H-m), -3.00 (3H, H-p), -3.4 (3H, CH2), -21.1 (6H,
H-o), -43.0 (3H, CH2), -52.1 (3H, CH2).
[U{(SiMe2NPh)3-tacn}Cl] (7). [U{(SiMe2NPh)3-tacn}Cl] was
prepared by adding a stoichiometric amount of benzyl chloride (26
mg, 0.20 mmol) to a solution of 180 mg (0.20 mmol) of 6 in
toluene. The reaction was immediate with formation of a green
precipitate. Stirring was continued for an additional 4 h. The green
precipitate was washed twice with toluene and vacuum-dried.
Yield: 30% (55 mg, 0.06 mmol)).
Alternatively 7 could be prepared by adding 320 mg (0.39 mmol)
of Na3[(SiMe2NPh)3-tacn](THF)2 to a solution of UCl4 (150 mg,
0.39 mmol) in THF. The mixture immediately turned from green
to green-brownish. Stirring was continued for 4 h. The NaCl was
discharged and the solvent removed under vacuum. The solid
obtained was washed twice with toluene and extracted in CH2Cl2.
Yield: 65% (200 mg, 0.23 mmol). Calcd for UClSi3C30H45N6‚CH2-
Cl2: C, 42.52; H, 5.35; N, 9.92. Found: C, 42.44; H, 5.46; N,
9.92.
1H NMR (CD2Cl2, 20 °C): 11.6 (18H, SiMe2), 9.1 (6H, H-m),
6.5 (6H, br), 5.6 (3H, t, H-p), -11.1 (6H, br), -49.0 (6H, CH2).
Green crystals of 7 were obtained by slow concentration of a
dichloromethane solution.
[U{(SiMe2NPh)3-tacn}I] (8). Iodine (26 mg, 0.10 mmol) in
toluene was added dropwise to a solution of 180 mg (0.19 mmol)
of 6 in toluene. There was an immediate color change from reddish-
brown to green. After 2 h of stirring, the mixture was centrifuged.
The brown supernatant solution was discharged and the light green
solid washed twice with toluene and vacuum-dried. Calcd for
USi3C30H48N6I: C, 38.38; H, 4.83; N, 8.95. Found: C, 37.62; H,
4.79; N, 8.67.
X-ray Crystallographic Analysis. Colorless crystals of [Y{-
(SiMe2NPh)3-tacn}]‚C6H5Me (1‚C6H5Me) and [La{(SiMe2NPh)3-
tacn}(THF)] (2), red-orange crystals of [Eu{(SiMe2NPh)3-tacn}]‚
0.5C6H5Me (3‚0.5C6H5Me), and dark brown crystals of [U{(SiMe2-
NPh)3-tacn}]‚0.5C6H5Me (6‚0.5C6H5Me) were grown by slow
concentration of toluene solutions. Crystals of [Yb{(SiMe2NPh)3-
tacn}]‚C6H5Me (4‚C6H5Me) (yellow) were grown from toluene/
hexane mixtures and crystals of [Eu{(SiMe2NPh)3-tacn}][Na-
(diglyme)2] (5) (yellow) from a THF/diglyme mixture. Green
crystals of [U{(SiMe2NPh)3-tacn}Cl] (7) were obtained by slow
concentration of a dichloromethane solution. Crystals were mounted
in thin-walled glass capillaries in a nitrogen-filled glovebox (crystals
of 4‚C6H5Me and 6‚0.5C6H5Me were immersed in Nujol before
mounting). Data were collected at room temperature on an Enraf-
Nonius CAD4-diffractometer with graphite-monochromatized Mo
KR radiation. Data were corrected25 for Lorentz and polarization
effects, for linear decay, and for absorption by empirical corrections
based on Ψ scans. A summary of the crystallographic data is given
in Table 1.26
The structures were solved using Patterson methods27 and
successive difference Fourier techniques and refined by full-matrix
least squares refinements on F2 using SHELXL-97.28 Compounds
1‚C6H5Me and 4‚C6H5Me are isomorphous, and in their lattice there
is one disordered toluene solvent molecule per formula unit. 3‚
0.5C6H5Me and 6‚0.5C6H5Me are isomorphous, with half-toluene
solvent molecule per formula unit, disordered about an inversion
center. Examination of the crystal structure of 7 with the VOID
routine of PLATON29 showed 60.6% of filled space and 14.8% of
potential solvent area (∼557.3 Å3), which was an indication of
solvent present in the lattice. The five strongest peaks in the
difference Fourier map, in the range 5.1-2.1 e Å-3, were introduced
as full-occupancy atoms (one oxygen and four carbon atoms), but
no chemical identity could be assigned to these solvent peaks. So,
they were excluded from the formula, from the molecular weight,
and from the calculation of the density in Table 1. 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 solvent atoms
in 3‚0.5C6H5Me were refined isotropically, with geometric restraints
and H atoms omitted). Atomic scattering factors and anomalous
(25) Fair, C. K. MOLEN; Enraf-Nonius: Delft, The Netherlands, 1990.
(26) Crystal data for 1‚C6H5Me: C37H53N6Si3Y, fw ) 755.03, monoclinic,
space group P21/n, a ) 10.9430 (8) Å, b ) 16.3749(14) Å, c ) 22.582-
(3) Å, â ) 91.195(7)°, V ) 4045.7(7) Å3, Z ) 4, Dcalc ) 1.240 Mg/
m3. 7084 unique reflections were used in the structure solution and
refinement of 425 parameters. Final refinement converged at R1 )
0.109 and wR2 ) 0.123 for 2614 reflections with I > 2σ(I). Crystal
data for 6‚0.5C6H5Me: C33.5H49N6Si3U, fw ) 858.09, monoclinic,
space group P21/n, a ) 11.0783(11) Å, b ) 15.7081(17) Å, c )
21.187(2) Å, â ) 97.246(10)°, V ) 3657.4(6) Å3, Z ) 4, Dcalc
)
1.558 Mg/m3. 6395 unique reflections were used in the structure
solution and refinement of 377 parameters. The refinement converged
at R1 ) 0.101 and wR2 ) 0.167 for 2807 reflections with I > 2σ(I).
(27) Sheldrick, G. M. SHELXS-97: Program for the Solution of Crystal
Structure; University of Go¨ttingen: Go¨ttingen, Germany, 1997.
(28) Sheldrick, G. M. SHELXS-97: Program for the Refinement of Crystal
Structure; University of Go¨ttingen: Go¨ttingen, Germany, 1997.
(29) Speck, A. L. Acta Crystallogr. 1990, A46, C34.
Inorganic Chemistry, Vol. 42, No. 13, 2003 4225

Monteiro et al.
Table 1. Crystallographic Data
2
3‚0.5C6H5Me
4‚C6H5Me
5
7
formula
fw
cryst syst
space group
a, Å
C34H53N6Si3OLa
785.00
monoclinic
P21/n
11.752(2)
18.536(2)
18.301(2)
105.082(10)
3849.5(9)
4
C33.5H49N6Si3Eu
772.02
monoclinic
P21/n
11.0803(12)
15.772(2)
21.081(2)
97.039(9)
3656.2(7)
4
C37H53N6Si3Yb
839.16
monoclinic
P21/n
10.9131(10)
16.355(2)
22.560(3)
91.150(9)
4025.9(9)
4
C42H73N6O6NaSi3Eu
1017.28
monoclinic
Cc
21.763(2)
12.6630(13)
19.082(2)
100.240(9)
5175.0(10)
4
C30H45N6Si3ClU
847.47
orthorhombic
P212121
13.267(2)
16.472(2)
17.285(4)
b, Å
c, Å
â, deg
V, Å3
Z
3777.5(11)
4
1.490
4.490
0.0671
0.1184
F
calc, g cm-3
1.354
1.237
0.0545
0.1098
1.403
1.845
0.0738
0.1288
1.385
2.445
0.0897
0.1383
1.306
1.336
0.0542
0.0649
µ(Mo KR), mm-1
R1
wR2
Scheme 1
Compounds 1-6 were soluble in common aromatic and
ethereal solvents and slightly soluble in hexane, with the
exception of 6, which was moderately soluble in this solvent.
Although the NMR spectra showed no evidence for
significant impurities, analytically pure samples of 3-5 were
difficult to obtain probably due to variable amounts of solvent
retained in the lattice.
Since the new ligand has been demonstrated to support
the trivalent oxidation state of uranium(III), it was of obvious
interest to explore the redox chemistry of uranium(III) in
this coordination environment. Compound 6 is readily
oxidized by benzyl chloride and iodine in toluene to yield
the insoluble chloride [U{(SiMe2NPh)3-tacn}Cl] (7) and
iodide [U{(SiMe2NPh)3-tacn}I] (8) compounds, respectively.
However, salt metathesis provides a higher yield route to 7.
Thus, stirring UCl4 with Na3[(SiMe2NPh)3-tacn](THF)2 in
THF results in formation of a white precipitate and a green
brownish solution. Removal of the THF followed by addition
of toluene yielded a green precipitate and a brown solution
(eq 3).
dispersion terms were taken as in ref 28. The drawings were made
with ORTEP 3.30 Because of the low quality of crystals 1 and 6
and, consequently, poor quality of data/refinement, relevant geo-
metrical parameters will be given, but details regarding structure
solution and refinement are available as Supporting Information.
Results and Discussion
Addition of a THF solution of the sodium salt of 1,4,7-
tris(dimethylsilylphenylamine)-1,4,7-triazacyclononane (Na3-
[(SiMe2NPh)3-tacn](THF)2) (Scheme 1) to a suspension of
the trivalent lanthanide chlorides (Ln ) Y, La, Eu, Yb) in
the same solvent affords the corresponding [M{(SiMe2NPh)3-
tacn}] (M ) Y (1), Eu (3), Yb (4)) and [La{(SiMe2NPh)3-
tacn}(THF)] (2) complexes (eq 1).
UCl4 + Na3[(SiMe2NPh)3-tacn(THF)2] f
[U{(SiMe2NPh)3-tacn}Cl] + 3NaCl (3)
MCl3 + Na3[(SiMe2NPh)3-tacn](THF)2 f
[M{(SiMe2NPh)3-tacn}(THF)x] + 3NaCl
M ) Y (1), Eu (3), Yb (4)
x ) 0
The green precipitate was further extracted with CH2Cl2
to separate some unreacted uranium tetrachloride.
Both compounds are insoluble in aromatic solvents,
suggesting the presence of ionic compounds. However,
determination of the X-ray structure of 7 showed that this
was not the case.
The new complexes have been characterized by standard
analytical and spectroscopic techniques. Because complexes
1-8 represent a complete series of new complexes, single
crystals were grown for X-ray diffraction studies.
M ) La (2)
x ) 1
(1)
With the objective of synthesizing a Eu(II)-tacn com-
pound, 3 was treated in THF with a stoichiometric amount
of 0.5% Na/Hg. The initial red-brown solution gradually
changed to brown. The dark yellow solid isolated from the
reaction mixture was crystallized from a concentrated THF
solution with a few drops of diglyme to give yellow crystals
of [Eu{(SiMe2NPh)3-tacn}][Na(diglyme)2] (5).
Solid-State Structures of the Six-Coordinate
[Y{(SiMe2NPh)3-tacn}]‚C6H5Me (1‚C6H5Me), [Eu-
{(SiMe2NPh)3-tacn}]‚0.5C6H5Me (3‚0.5C6H5Me), [Yb-
{(SiMe2NPh)3-tacn}]‚C6H5Me (4‚C6H5Me),[Eu{(SiMe2-
NPh)3-tacn}][Na(diglyme)2] (5), and [U{(SiMe2NPh)3-
tacn}]‚0.5C6H5Me (6‚0.5C6H5Me) Complexes. Complexes
1 and 4 are isomorphous and crystallize in the monoclinic
space group P21/n31 with a molecule of toluene contained
within the lattice. Complexes 3 and 6 are isomorphous and
crystallize in the monoclinic space group P21/n with a half-
Addition of 1 equiv of Na3[(SiMe2NPh)3-tacn](THF)2 in
THF to a solution of uranium triiodide in the same solvent
resulted in formation of a brown-greenish solution. [U{-
(SiMe2NPh)3-tacn}] (6) was separated from the NaI formed
in the reaction by extraction in toluene.
UI3(THF)4 + Na3[(SiMe2NPh)3-tacn(THF)2] f
[U{(SiMe2NPh)3-tacn}] + 3NaI (2)
(30) Farrugia, L. J. ORTEP-3, J. Appl. Crystallogr. 1997, 30, 565.
4226 Inorganic Chemistry, Vol. 42, No. 13, 2003

Triamidotriazacyclononane Complexes of Group 3 Metals
distances, 1 (2.279(9) Å), 3 (2.313(11) Å), 4 (2.216(14) Å),
are slightly longer than those observed in [M{N(SiMe3)2}3]
(2.226(6), 2.259(9), and 2.158(13) Å for Y, Eu, and Yb,
respectively),35-37 which is not surprising in view of the
higher coordination number of the metal center in the
triazacyclononane environment. Thus, the Y-N(amido)
distance in 1 is better compared with that of the five-
coordinate [Y{N(SiMe2H)3(THF)2]38 (2.26 Å). 1 can also be
compared with the five-coordinate [Y{N(CH2CH2NSiMe2-
But)3}ClLi(thf)3],12 a compound with both Y-N(amido) and
Y-N(amine) bonds. In 1 the Y-N(amido) bond distance
(2.279(9) Å) is 0.05 Å longer than that observed in [Y{N-
(CH2CH2NSiMe2But)3}ClLi(thf)3] (2.231 (2) Å), while the
average Y-N(amine) bond length of 2.517(15) Å is some
0.07 Å shorter than the corresponding distance of 2.588(4)
Å in that compound.12 This is a consequence of the position
of the metal in the two coordination polyhedra. In [Y{N-
(CH2CH2NSiMe2But)3}ClLi(thf)3] the yttrium sits 0.67 Å out
of the plane defined by the three amido nitrogen atoms, while
in 1 the metal atom is 0.69 Å below the corresponding plane
approaching the three nitrogen amine atoms. The average
M-N(amine) distances in 3 and 4 (2.563(10) and 2.50(3)
Å, respectively) are consistent with those reported in the
literature.39 In 5 the average Eu-N(amido) distance of 2.522-
(9) Å is slightly longer than the average Eu-N distance of
2.448(4) Å in the ionic NaEu[N(SiMe3)2]3,40 and the average
Eu-N(amine) distance of 2.746(12) Å compares with those
reported in the literature.41 In 6 the average U-N(amido)
distance of 2.35(2) Å is similar to those of 2.320(4), 2.339-
(3), and 2.320 Å observed in the uranium(III) complexes
U[N(SiMe3)2]3,42 [(SiMe3)2N]4U2[-N(H)(mesityl)]2,43 and
U(N(R)Ar)3(THF) (R ) tert-butylanilide, Ar ) Ph-2,6-Me2)44
and to the longer U-N bond distance of 2.358(19) Å in (η-
C5Me5)U[N(SiMe3)2]245 (the other U-N distance is 2.23(3)
Å). The U-N(amine) distance of 2.66(2) Å is slightly shorter
than the corresponding distance of 2.697(4) Å in the ionic
[U(tbpa)I2]Ipy (tbpa ) tris[(2,2′-bipyridin-6-yl)methyl]-
amine).46
Figure 1. ORTEP diagram of [Eu{(SiMe2NPh)3-tacn}]‚0.5C6H5Me, (3‚
0.5C6H5Me), using 20% probability ellipsoids.
molecule of toluene included in the crystal lattice. The
structure of 5 consists of [Eu{(SiMe2NPh)3-tacn}]- anions
and well-separated sodium cations coordinated to two
molecules of diglyme, and they crystallize in the monoclinic
space group Cc. As a representative, the molecular structure
of 3 is shown in Figure 1 (1 and 4-6 are not illustrated, but
analogous atomic numbering schemes are used for all the
molecular structures).
Table 2 summarizes important bond distances and angles.
For all the complexes the metal center is six-coordinate
by the three amine nitrogen donors of the 1,4,7-triazacy-
clononane ring and three amido nitrogen donor atoms of the
pendant arms. The resulting N6M polyhedron is best de-
scribed as a slightly distorted trigonal prism, the two trigonal
planes defined by the two sets of nitrogen donor atoms being
nearly parallel (interplanar angles N123/N456 in Table 3).
In all compounds the pendant amido groups are oriented
around the C3 symmetry axis in the same direction (∆ or Λ
conformation)32 with average twist angles (æ)33 of 4.3°, 1.7°,
4.6°, 0.6°, and 0.8° for 1, 3, 4, 5, and 6, respectively. The
coordinated 1,4,7-triazacyclononane backbone of the amine
forms three five-membered chelate rings M-N-C-C-N
which adopt a (δδδ)5 or (λλλ)5 conformation. In crystals of
1 and 4, the enantiomeric pair of the complexes (∆(δδδ)5/
Λ(λλλ)5) is present in the centric unit cell of the space group
P21/n, while complexes 3 and 6 exhibit the ∆(λλλ)5/Λ(δδδ)5
pair.
Solid-State Structures of the Seven-Coordinate [La-
{(SiMe2NPh)3-tacn}(THF)] (2) and [U{(SiMe2NPh)3-
(35) Westerhausen, M.; Hartmann, M.; Pfitzner, A.; Schwarz, W. Z. Anorg.
Allg. Chem. 1995, 621, 837.
(36) Ghotra, J. S.; Hursthouse, M. B., Welch, A. J. J. Chem. Soc., Chem.
Commun. 1973, 669.
(37) Eller, P. G.; Bradley, D. C.; Hursthouse, M. B.; Meek, D. W. Coord.
Chem. ReV. 1977, 24, 1.
(38) Herrmann, W. A.; Anwander, R.; Munck, F. C.; Scherer, W.; Dufaud,
V.; Huber, N. W.; Artus, G. R. J. Z. Naturfosch 1994, B49, 1789.
(39) (a) Wietzke, R.; Mazzanti, M.; Latour, J. M.; Pe´caut, J.; Cordier, P.
Y.; Madic, C. Inorg. Chem. 1998, 37, 6690. (b) Wietzke, R.; Mazzanti,
M.; Latour, J. M.; Pe´caut, J. Chem. Commun. 1999, 209. (c) Batsanov,
A. S.; Beeby, A.; Bruce, J. I.; Howard, J. A. K.; Kenwright, A. M.;
Parker, D. Chem. Commun. 1999, 1011.
(40) Tilley, T. D.; Andersen, R. A.; Zalkin, A. Inorg. Chem. 1984, 23,
2271.
(41) Evans, W. J., Greci, M. A.; Ziller, J. W. J. Chem. Soc., Dalton Trans.
1997, 3035.
(42) Stewart, J. L.; Andersen, R. A. Polyhedron 1998, 17, 95.
(43) Andersen, R. A. New J. Chem. 1995, 19, 587.
(44) Odom, A. L.; Arnold, P. L.; Cummins, C. C. J. Am. Chem. Soc. 1998,
120, 5836.
(45) Avens, L. R.; Burns, C. J.; Butcher, R. J.; Clark, D. L.; Gordon, J. C.;
Schake, A. R.; Scott, B. L.; Watkin, J. G.; Zwick, B. D. Organome-
tallics 2000, 19, 451.
The metal nitrogen distances reflect the difference in the
ionic radii of the metal.34 The average M-N(amido)
(31) Crystals of 1 and 4 in another crystalline form were isolated during
another crystallization process: trigonal space group R3, with two
molecules per asymmetric unit, one lying on a crystallographic 3-fold
axis. 1‚1.5C6H5Me: a ) 29.733(4) Å, c ) 18.204(3) Å, V ) 13937-
(4) Å3, Z ) 12, Dcalc ) 1.145 Mg/m3. 4‚1.5C6H5Me: a ) 29.643(4)
Å, c ) 18.147(3) Å, V ) 13809(3) Å3, Z ) 12, Dcalc ) 1.277 Mg/m3.
(32) The convention adopted assigns ∆ and Λ to a structure where the
trigonal plane defined by the nitrogen amine atoms is twisted to the
right and left, respectively, by reference to the trigonal plane defined
by the nitrogen amido atoms when viewed down the C3 axis.
(33) The twist angles were calculated by taking the average of the angles
made by the projections of the vertices of the top and bottom faces
along the direction of the two centroids of the trigonal faces. For a
regular trigonal prism æ ) 0°.
(34) Shannon, R. D. Acta Crystallogr. 1976, A32, 751.
Inorganic Chemistry, Vol. 42, No. 13, 2003 4227

Monteiro et al.
Table 2. Selected Bond Lengths (Å) and Angles (deg) for Six-Coordinate Complexes
1‚C6H5Me
3‚0.5C6H5Me
4‚C6H5Me
5
6‚0.5C6H5Me
M-N(1)
M-N(2)
M-N(3)
M-N(4)
M-N(5)
M-N(6)
2.283(9)
2.283(9)
2.271(8)
2.504(8)
2.513(9)
2.533(8)
2.321(9)
2.318(8)
2.301(8)
2.574(9)
2.556(8)
2.558(8)
2.205(14)
2.227(13)
2.216(13)
2.473(13)
2.520(12)
2.517(13)
2.515(9)
2.530(9)
2.522(9)
2.739(8)
2.740(8)
2.760(9)
2.326(19)
2.367(15)
2.360(16)
2.677(19)
2.640(18)
2.653(19)
N(1)-M-N(2)
N(1)-M-N(3)
N(2)-M-N(3)
N(4)-M-N(5)
N(4)-M-N(6)
N(5)-M-N(6)
110.6(3)
111.6(3)
111.6(3)
71.5(3)
70.8(3)
71.8(3)
111.6(3)
111.0(3)
115.5(3)
70.1(3)
69.2(3)
70.4(3)
110.7(5)
110.5(5)
109.7(5)
72.7(4)
71.1(4)
72.6(5)
117.2(3)
114.2(3)
117.8(3)
67.8(3)
67.5(3)
67.0(3)
115.1(7)
112.3(6)
118.4(6)
68.4(6)
68.8(6)
67.5(6)
Table 3. Interplanar Angles (deg) between the Amido(N1,2,3)/Amine(N4,5,6) Trigonal Planes, Dihedral Angles (deg) between the Amido(N1,2,3) and the
Phenyl Planes, Average Twist Angles (æ) (deg), and Distances (Å) of the Metal to the Trigonal Planes
1‚C6H5Me
2
3‚0.5C6H5Me
4‚C6H5Me
5
6‚0.5C6H5Me
N1,2,3/N4,5,6
0.63
1.83
0.81
1.56
0.48
0.26
N1,2,3/Ph1
N1,2,3/Ph2
N1,2,3/Ph3
78.03
73.09
78.40
50.04
43.29
60.26
81.59
88.57
74.26
77.67
72.32
77.69
88.84
79.89
77.44
85.01
88.48
76.28
æ
4.3
12.5
1.7
4.6
0.6
0.8
d(M/N1,2,3
d(M/N4,5,6
)
)
0.69
1.86
0.31
2.16
0.64
1.92
0.71
1.84
0.48
2.11
0.52
2.02
(Table 3). The enantiomorphous pair identified as ∆(δδδ)5/
Λ(λλλ)5 is observed in the crystals of 2. The average La-
N(amido) bond length of 2.45(3) Å is slightly longer than
the corresponding distance in the four-coordinate [La-
{N(SiMe3)2}3(PPh3O)]47 (2.41(2) Å) and in the five-
coordinate [La{N(SiHMe2)2}3(THF)2]48 (2.402(5) Å). The
average La-N(amine) of 2.75(2) Å compares with the
distance of 2.728(4) Å in [La(tbpa)(H2O)(ClO4)][ClO4]2‚
2CHCl3‚MeOH (tbpa ) tris[(2,2′-bipyridin-6-yl)methyl]-
amine),46 and the La-O distance of 2.598(4) Å is very
similar to that of 2.573(4) Å in [La{N(SiHMe2)2}3(THF)2].48
Complex 7 crystallized from a CH2Cl2 solution in the
orthorhombic space group P212121. The uranium ion is seven-
coordinate by the six nitrogen donor atoms and the chlorine
atom. Selected bond distances and angles are summarized
in Tables 3 and 4. An analysis of the metal geometry showed
that the structure could not be assigned to the usual
polyhedral forms for seven-coordinate complexes. The best
way to visualize the structure is to consider the geometry
around the metal as a bicapped trigonal bipyramid (Figure
3).
Figure 2. ORTEP diagram of [La{(SiMe2NPh)3-tacn}(THF)] (2), using
20% probability ellipsoids.
tacn}Cl] (7) Complexes. Complex 2 crystallizes in the
monoclinic space group P21/n. The lanthanum ion is seven-
coordinate by the six nitrogen atoms of the ligand and the
oxygen atom of the THF molecule, which is capping the
trigonal face defined by the three nitrogen atoms of the amido
groups (Figure 2).
Relevant metrical parameters are collected in Tables 3 and
4.
The nitrogen atoms N(2), N(5), and N(6) define the
equatorial plane, while the chlorine atom and N(4) define
the apexes (Cl-U-N(4) ) 170.5(3)°). The two nitrogen
atoms N(1) and N(3) cap two of the triangular faces of the
bipyramid making N-U-Cl angles of 79.5 (4)° and 78.8
(3)°, respectively. The U-N(2) distance of 2.249(13) Å is
within the range (2.20-2.28 Å) of amido U-N distances in
[UN{CH2CH2N(SiMe3)}3Cl]2,15 [UN(CH2CH2NSiMe2But)3],19
The coordination of the THF molecule results in a higher
distortion from the trigonal prismatic geometry. The phenyl
rings are pushed away from the trigonal plane N123 as shown
by the dihedral angles between the trigonal plane N123 and
the planes of the phenyl rings (N123/Ph) that average 51.2°
to be compared with the values of approximate 80° in the
six-coordinate complexes. Also, the nitrogen amine atoms
are much twisted by reference to the nitrogen amido atoms
(47) Bradley, D. C.; Ghotra, J. S.; Hart, F. A.; Hursthouse, M. B., Raithby,
P. R. J. Chem. Soc., Dalton Trans. 1977, 1166.
(46) Wietzke, R.; Mazzanti, M.; Latour, J. M.; Pe´caut, J. J. Chem. Soc.,
Dalton Trans. 1998, 4087.
(48) Anwander, R.; Runte, O.; Eppinger, J.; Gerstberger, G.; Herdtweck,
E.; Spiegler, M. J. Chem. Soc., Dalton Trans. 1998, 847.
4228 Inorganic Chemistry, Vol. 42, No. 13, 2003

Triamidotriazacyclononane Complexes of Group 3 Metals
Table 4. Selected Bond Lengths (Å) and Angles (deg) for Seven-Coordinate Complexes (X ) O (2), Cl (7))
2
7
2
7
M-X
2.598(4)
2.475(5)
2.460(4)
2.423(5)
2.668(4)
M-N(4)
M-N(5)
M-N(6)
2.739(4)
2.773(5)
2.741(4)
2.632(11)
2.626(13)
2.651(12)
M-N(1)
M-N(2)
M-N(3)
2.324(13)
2.249(13)
2.327(13)
N(1)-M-N(2)
N(1)-M-N(3)
N(2)-M-N(3)
N(4)-M-N(5)
118.90(15)
124.70(17)
111.62(16)
65.13(14)
97.5(5)
158.3(5)
93.7(5)
67.7(4)
N(4)-M-N(6)
N(5)-M-N(6)
N(2)-M-N(5)
N(2)-M-N(6)
64.58(13)
64.77(13)
105.03(15)
121.67(14)
67.4(4)
65.7(4)
124.2(5)
119.7(5)
X-M-N(1)
X-M-N(2)
X-M-N(3)
78.10(14)
89.52(14)
81.42(15)
79.5(4)
121.8(4)
78.8(3)
X-M-N(4)
X-M-N(5)
X-M-N(6)
146.97(13)
142.11(13)
135.30(13)
170.5(3)
102.8(3)
109.3(3)
Figure 4. ORTEP diagram of [U{(SiMe2NPh)3-tacn}Cl] (7), using 20%
probability ellipsoids.
trigonal prismatic geometry are seen in the lanthanum
complex, and it is is not surprising that greater distortions
have to occur in 7 since the U(IV) has an ionic radius 0.05
Å smaller than La. It is noteworthy that the U(III) ion, with
an ionic radius only 0.007 Å smaller than La, has no room
to accommodate a THF ligand. In order to minimize severe
Cl‚‚‚N contacts, the N(1) and N(3) atoms are pulled away
from the chlorine as shown by the increase in the N(1)-
U-N(3) angle to 158.3° vs 97.5° for N(1)-U-N(2) and
93.7° for N(2)-U-N(3). N(1) and N(3) are twisted in
opposite directions by reference to N(6) and N(5), while N(2)
is slightly twisted by reference to N(4) (Figure 4).
Dynamic Behavior of Complexes 1-8 in Solution. As
pointed out above, complexes 1-6 have approximate C3
symmetry. This symmetry should give rise to four signals
for the diastereotopic methylene protons of the amine ligand
(two equatorial and two axial) and two signals for the
diastereotopic methyl protons of the SiMe3 groups in the 1H
NMR spectra. In accordance two signals should be expected
for the six carbons of the amine backbone in the 13C spectra.
The 1H NMR spectra of the diamagnetic complexes of Y
(1) and La (2) showed one single signal for the methyl
protons of the SiMe2 groups and three peaks for the ortho,
meta, and para protons of the phenyl groups with the
expected integration and peak multiplicities. Two resonances
due to the ethylenic protons of the cyclic amine ligand
appeared as AA′BB′ spin systems. In addition there were
two resonances due to the THF protons in the spectrum of
2. This pattern is consistent with a C3V symmetry in solution,
Figure 3. View of the bicapped triangular bypiramidal coordination
polyhedron of 7.
and cis-UCl2[N(SiMe3)2]2‚DME.49 The distances of the
capping nitrogen atoms to uranium (U-N(1) ) 2.324(13)
Å and U-N(3) ) 2.327(13) Å) are about 0.08 Å longer than
the corresponding distance of the nitrogen amido atom lying
in the equatorial plane. The U-N amine bond distances are
similar and average 2.636(13) Å, a value that is in line with
those found in the trisamidoamine uranium(IV) complexes
[UN{CH2CH2N(SiMe3)}3Cl]215 (2.567(9) Å) and [UN(CH2-
CH2NSiMe2But)3X]18 (2.67(2) Å, X ) Cl; 2.67(1) Å, X )
Br; 2.685(6) Å, X ) I) and the tacn-based ligands,
[((ArO)3tacn)U(OAr)] (2.703(15) Å) and [{((ArO)3tacn)U}2-
(µ-O)] (2.75(2) Å).8 The U-Cl distance of 2.668(4) Å is
similar to the corresponding distance in [U(N(CH2CH2-
NSiMe2But)3)Cl]18 (2.641(5) Å) and in other tetravalent
systems with nitrogen chelating ligands.50
A noteworthy feature of the structure of 7 is the presence
of the two short Cl‚‚‚N(1) and Cl‚‚‚N(3) contacts of 3.20
and 3.18 Å, respectively. We believe that the unusual
coordination geometry adopted by the ligands in 7 is not
electronic in origin but caused by the crowded environment
of the small U(IV) ion. As noted above, distortions of the
(49) McCullogh, L. G.; Turner, H. W.; Andersen, R. A.; Zalkin, A.;
Templeton, D. H. Inorg. Chem. 1981, 20, 2869.
(50) Ball, R. G.; Edelmann, F.; Matisons, G. J.; Takats, J.; Marques, N.;
Marc¸alo, J.; Pires de Matos, A.; Bagnall, K. W. Inorg. Chim. Acta
1987, 132, 137.
Inorganic Chemistry, Vol. 42, No. 13, 2003 4229

Monteiro et al.
Scheme 2
which is not in accordance with the symmetry found in the
solid. The 13C NMR spectra at room temperature gave
analogous information: one single signal for the ethylene
carbon atoms of the 1,4,7-triazacyclononane backbone, four
signals for the carbon atoms of the phenyl rings, and one
signal for the methyls of the SiMe3 groups was consistent
with a C3V symmetrical structure. Cooling the samples to
-80 °C resulted in broadening and collapsing of the 1H NMR
signals associated with the CH2 and SiMe2 groups, but a static
spectrum was not reached before the solvent froze. The
resonances due to the protons on the phenyl ring suffered
only minimal line broadening, indicating fast rotation of the
phenyl groups.
explain the increase in the symmetry observed in solution.
An illustrative diagram of this process is presented in Scheme
2.
At room temperature the 1H NMR spectrum of 7 in CD2-
Cl2 displayed one resonance at 11.6 ppm for the protons of
the SiMe2 groups and two resonances assigned to the H-m
and H-p of the phenyl rings at 9.1 and 5.6 ppm, respectively.
In addition, the spectrum exhibited three resonances ac-
counting for six protons each at 6.5, -11.1, and -49.0 ppm.
Assignment of these resonances to the H-o protons of the
phenyl rings and to the ethylenic protons of the amine
backbone was not possible. A 2D COSY spectrum was run,
but cross peaks were only observed for the H-m and H-p
protons. It has been noticed by others that, presumably due
to effective transverse relaxation, cross peaks were not
observed in the COSY spectra of other heavy paramagnetic
chelates.52d Homonuclear decoupling experiments were also
Spectra were also recorded for the paramagnetic Eu (3),
Yb (4), and U (5) complexes. One single resonance for the
18 protons of the SiMe2 groups and two resonances for the
six H-m and three H-p protons of the anilide could be
immediately assigned. In addition there were three resonances
accounting for six protons each. Because these resonances
were broadened and very shifted from the diamagnetic
position, it was not possible to assign them to the H-o protons
and to the ethylenic protons the cyclic amine.51 This
ambiguity could be solved by variable-temperature NMR
experiments. When the samples were cooled, the resonances
assigned to the SiMe2 groups and to the methylenic protons
shifted due to the temperature dependence of the magnetic
susceptibility, broadened, and collapsed. By -60 °C the
spectra of 3-5 had begun to sharpen, and four broad
resonances in a 1:1:1:1 intensity ratio assigned to the CH2
groups and two in a 9:9 intensity ratio owing to the methyl
protons of the SiMe2 groups appeared, consistent with C3
symmetrical structures. While these changes occurred, the
resonances of the aromatic protons of the amido groups
shifted and broadened, especially that of the ortho protons,
but they did not collapsed, indicating that rotation of the
phenyl groups is still fast at -80 °C.
Exchange processes are common in macrocyclic lanthanide
compounds and have been studied in detail for Ln(DOTA)-
complexes. Exchange between isomers which reflects arm
rotation and/or exchange between enantiomers which reflects
ethylene ring inversion plus arm rotation have been invoked
to explain the NMR data.52 As mentioned above, the
complexes exhist as pairs of enantiomers. An intramolecular
isomerization (∆(δδδ)5 S Λ(δδδ)5) or ring inversion
(∆(δδδ)5 S ∆(λλλ)5) would not lead to an increase in
symmetry from C3 to C3V, but a ∆ S Λ interconversion of
the MN6 polyhedra and simultaneous concerted inversion of
the five-membered chelate rings ((λλλ)5 S (δδδ)5) can
1
unsuccessful. Variable-temperature H NMR spectra were
obtained for the compound. Cooling of the sample resulted
in progressive broadening and shifting of the H NMR
signals, and by -80 °C all the resonances had disappeared
into the baseline. Thus, the 1H NMR spectrum of 7 is rather
structurally uninformative and is suggestive of a complex
with a fluxional coordination sphere.
1
The room temperature 1H NMR spectrum of 8 in CD2Cl2
displayed several broad overlapping resonances between 14
and 6 ppm and one resonance at -52.0 ppm. Warming of
the sample to 35 °C resulted in sharpening of the resonances.
At this temperature the spectrum displayed one resonance
centered at 13.6 ppm for the methyl protons of the SiMe2
groups, two broad resonances centered at 9.7 and 6.2 ppm,
one almost collapsed into the baseline at -12 ppm, and one
at -49.5 ppm. Hence, the spectrum is similar to that of 7,
suggesting that 8 is a molecular compound with a structure
similar to that of 7, with the larger iodide ligand giving rise
to a more rigid structure in solution. In fact the broadness
of the signals indicated that in the case of 8 the process
responsible for the fluxionality of the molecule was slower
on the NMR time scale. Cooling of the sample results in
progressive broadening and shifting of the signals, and by
-30 °C all the resonances had collapsed. By -70 °C the
spectrum had began to sharpen again: five resonances
accounting for six protons at 86.6, 83.0, 32.3, -10.3, and
-28.3 ppm, one at 19.2 ppm accounting for three protons,
and six at -18.5, -29.4, -55.5, -77.7, -91.1, and -143.3
ppm integrating for two protons were observed (Figure 5).
These last six resonances are certainly due to the ethylenic
protons of the amine, but the assignment of the other
resonances remains speculative. Since there is only one
resonance accounting for the para protons of the phenyl
(51) In the spectrum of 4 only one broad resonance assigned to the protons
of the cyclic amine was observed at room temperature. Upon warming
of the sample to 40 °C the second resonance appeared as a broad
signal centered at 4.5 ppm.
(52) (a) Aime, S.; Botta, M.; Fasano, M.; Marques, M. P. M.; Geraldes, C.
F. G. C.; Pubanz, D.; Merbach, A. E. Inorg. Chem. 1997, 36, 2059.
(b) Zhang, S.; Kovacs, Z.; Burgess, S.; Aime, S.; Terreno, E.; Sherry,
A. D. Chem. Eur. J. 2001, 7, 288. (c) Pittet, P. A.; Fru¨h, D.; Tissie`res,
V.; Bu¨nzli, J. C. J. Chem. Soc., Dalton Trans. 1997, 895. (d) Forsberg,
J. H.; Delaney, R. M.; Zhao, Q.; Harakas, G.; Chandran, R. Inorg.
Chem. 1995, 34, 3705.
4230 Inorganic Chemistry, Vol. 42, No. 13, 2003

Triamidotriazacyclononane Complexes of Group 3 Metals
Figure 5. 1H NMR spectrum of [U{(SiMe2NPh)3-tacn}Cl] (7), recorded in CD2Cl2 at -70 °C.
groups, two of the five resonances accounting for six protons
may be due to the H-o and H-m of the phenyl rings, the
three remaining resonances being due to the split of the
methyl protons of the SiMe2 groups.
At -80 °C the resonances due to the ethylenic protons
begin to broad again, indicating that inversion of the ethylenic
chain might be slowing. However, the slow exchange limit
was not reached before the solvent froze.
In the low-temperature spectrum of 8 the presence of three
resonances with an intensity ratio 6:6:6 due to the methylic
protons of the SiMe2 groups and six resonances with an
intensity ratio 2:2:2:2:2:2 assigned to the ethylenic protons
of the amine is reminiscent of a Cs symmetry. In the solid 7
has C1 symmetry (Figure 4), but in solution, if inversion of
the ethylenic backbone of the amine is fast in the NMR time
scale, the symmetry raises to Cs, with U, Cl, N2, and N4
contained in the mirror plane. This symmetry is consistent
with the low-temperature NMR spectrum of 8.
the THF is capping a trigonal face of the prism. The
compounds are fluxional at room temperature, but variable-
1
temperature H NMR studies sustain a dynamic process
involving a change in conformation of the ethylenic units in
concert with movement of the pendant arms. Tetravalent
uranium halides can be prepared either by redox methods
or in the case of the chloride by metathesis. The uranium-
(IV) halides are seven-coordinate molecular complexes, but
contrary to the La compound, the coordination geometry is
better described as bicapped trigonal bipyramidal. Both
compounds are fluxional, but a different dynamics than that
observed for the six-coordinate complexes seems to be
responsible for the fluxionality of these molecules. Work to
develop this chemistry continues, namely, replacement of
the halide by other ligands with different electronic and steric
properties in order to get a better insight into the molecular
structure and the dynamic behavior of these compounds.
Acknowledgment. Financial support from Fundac¸a˜o para
a Cieˆncia e Tecnologia, Portugal (POCTI/36015/QUI/ 1999)
(N.M.) and POCTI/39734/QUI/221 (A.M.M.)) is gratefully
acknowledged. B.M. thanks FCT for a BIC grant (SFRH/
BD/10066/2002) and H.F. for a Ph.D. grant (PRAXIS XXI/
BD/16128/98). We are grateful to NATO for the postdoctoral
grant of D.R.
Conclusions
A series of group 3 metal complexes with the hexadentate
(SiMe2NPh)3-tacn)3- ligand has been prepared. The yttrium,
europium, ytterbium, and uranium(III) complexes are six-
coordinate by the tacn ligand with identical coordination
geometries. The compounds display trigonal prismatic struc-
tures with the six nitrogen atoms of the ligand defining
parallel planes. The higher ionic radius of La allows
coordination of a THF ligand, with the metallic center
retaining a C3 coordination sphere since the oxygen atom of
Supporting Information Available: Crystallographic data in
CIF format. This material is available free of charge via the Internet
at http://pubs.acs.org.
IC034090V
Inorganic Chemistry, Vol. 42, No. 13, 2003 4231