Lanthanide complexes coordinated by a dianionic bis(amidinate) ligand with a rigid naphthalene linker

Article abstract of DOI:10.1002/ejic.201000330

The synthetic pathway to a new bis(amidine) ligand with a conformationally rigid naphthalene linker, 1,8-C₁₀H₆[NHC-(tBu)=N(2,6- Me₂-C₆H₃)][N=C(tBu)NH(2,6-Me₂-C ₆H₃)] (

Full text of DOI:10.1002/ejic.201000330

FULL PAPER
DOI: 10.1002/ejic.201000330
Lanthanide Complexes Coordinated by a Dianionic Bis(amidinate) Ligand with
a Rigid Naphthalene Linker
Marina V. Yakovenko,[a] Anton V. Cherkasov,[a] Georgy K. Fukin,[a] Dongmei Cui,[b] and
Alexander A. Trifonov*[a]
Keywords: Lanthanides / Amidinates / Coordination modes / Ligand design
The synthetic pathway to a new bis(amidine) ligand with a
conformationally rigid naphthalene linker, 1,8-C10H6[NHC-
structures of complexes 4–6 were established by X-ray dif-
fraction studies, which reveal that the new ligand framework
can coordinate to the lanthanide atoms in different fashions
depending on the central atom ion size. Alkylation of com-
plex 6 with equimolar amounts of LiCH2SiMe3 afforded the
unexpected amido–amidinate complex [{1,8-C10H6(NC(tBu)-
N-2,6-Me2–C6H3)2}{1,8-C10H6(NC(tBu)N-2,6-Me2–C6H3)-
(NH)}Sm][Li(dme)3] (7), which obviously results from the
cleavage of one amidinate group during decomposition of
the transient alkyl species and ligand redistribution.
(tBu)=N(2,6-Me2–C6H3)][N=C(tBu)NH(2,6-Me2–C6H3)]
(3)
was elaborated. Deprotonation of this bis(amidine) ligand
with two equivalents of nBuLi and subsequent reaction with
anhydrous LnCl3 (Ln = Y, Nd, Sm) allowed the synthesis
of the chlorido complexes [1,8-C10H6{NC(tBu)N-2,6-Me2–
C6H3}2]YCl(dme)
(4),
[1,8-C10H6{NC(tBu)N-2,6-Me2–
C6H3}2]Nd(dme)(µ-Cl)2Li(dme) (5), and [1,8-C10H6{NC(tBu)-
N-2,6-Me2–C6H3}2]Sm(thf)(µ-Cl)2Li(thf)2 (6), which are coor-
dinated by the linked dianionic bis(amidinate) ligand. The
catalytic potential in reactions of transformation of unsatu-
rated substrates (olefin polymerization,[3d,e;4] isoprene poly-
merization,[5] acetylene dimerization,[3c] olefin hydrobor-
ation,[6] hydrosilylation,[7] and hydroamination[8]). The sta-
bility and reactivity of rare-earth organometallic com-
pounds are known to be largely determined by the degree
of saturation of the coordination sphere of metal atom;
therefore in recent years, the trend was toward the develop-
ment of new ancillary ligands, which would allow greater
flexibility in the design of the metal coordination environ-
ment.[9] Greater stability of rare-earth complexes can be
achieved by use of more sterically hindered ligands or li-
gands that can give additional electronic stabilization to
highly electronically unsaturated metal centers. Thus, em-
ployment of bulky amidinate ligands[3d,e;5;7] and amidinates
containing an additional donor group[10] in the side chain
allows to overcome the limitations inherent to the initially
used N,NЈ-bis(trimethylsilyl)benzamidinate ligand and to
synthesize the formerly inaccessible bis(alkyl) rare-earth
species. Dianionic linked bis(amidinate) ligands[11] are
highly interesting from the point of view of design and con-
trol of the geometry of the metal coordination sphere, and
their use can stimulate progress in lanthanide chemistry
similar to that observed by the transposition from metallo-
cene to ansa-metallocene-type structures. Several examples
of lanthanide complexes coordinated by linked bis(amidin-
ate) ligands with flexible backbones have been reported.[12]
In order to provide control of the geometry of the metal
coordination sphere and control of the selectivity of the
catalytic reactions mediated by metal complexes, we focused
Introduction
The amidinate ligands [RC(NRЈ)2]– belong to the group
of four-electron chelating monoanionic ligands in which the
negative charge is delocalized in the NCN fragment. Amid-
inates have proven to be versatile ligands because of the
fact that their steric and electronic properties can easily be
modified through variations of the organic substituents on
the nitrogen atoms. The combination of flexibility and vari-
ety of coordination modes of amidinate ligands with donor
properties results in their compatibility with a wide number
of metal ions across the periodic table[1] and their suitability
as a supporting ligand framework, which allows control
over the metal atom coordination sphere and metal-medi-
ated chemical processes. Application of amidinate ligands,
which were introduced in the organometallic chemistry of
rare-earth metals by Edelmann[2] and Teuben,[3] greatly in-
fluenced the development of this area and allowed the syn-
thesis and characterization of a new series of isolable, highly
reactive species. Monoalkyl, bis(alkyl), cationic alkyl, and
hydrido rare-earth complexes supported by amidinate li-
gands have been described, and some of them demonstrated
[a] G. A. Razuvaev Institute of Organometallic Chemistry of
Russian Academy of Sciences,
Tropinia 49, 603600 Nizhny Novgorod GSP-445, Russian
Federation
Fax: +7-831-462-74-97
E-mail: trif@iomc.ras.ru
[b] State Key Laboratory of Polymer Physics and Chemistry,
Changchun Institute of Applied Chemistry, Chinese Academy
of Sciences,
Changchun 130022, People’s Republic of China
3290
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Lanthanide Complexes Coordinated by a Dianionic Bis(amidinate) Ligand
on elaboration of a new bulky bis(amidinate) ligand frame-
Pale-yellow crystals of the bis(amidine) 3 suitable for X-
work containing a rigid 1,8-disubstituted naphthalene ray diffraction studies were obtained by slow concentration
linker. Herein, we report on the synthesis of a new linked of its solutions in CH2Cl2/hexane mixture (3) or in acetoni-
bis(amidine) ligand, 1,8-C10H6[NHC(tBu)=N(2,6-Me2– trile [3·(MeCN)] at room temperature. The molecular struc-
C6H3)][N=C(tBu)NH(2,6-Me2–C6H3)], and its application ture of 3 is shown in Figure 1, and the structure refinement
for the preparation of lanthanide bis(amidinate) complexes. data are listed in Table 1 [for the structure of 3·(MeCN),
see Supporting Information].
Results and Discussion
Synthesis of 1,8-C10H6[NHC(tBu)=N(2,6-Me2–C6H3)]-
[N=C(tBu)NH(2,6-Me2–C6H3)] (3)
1,8-Diaminonaphthalene was used as a platform for the
synthesis of bis(amidine) ligand containing a conformation-
ally rigid planar linker between two functional groups. The
general procedure was based on those previously reported
by Arnold[11a] and Hill[11c] that use pivaloyl chloride to give
a tertiary butyl group at the amidine C functionality. The
synthetic route is shown in Scheme 1. Synthesis of bis-
(amide) 1 proceeded easily by reacting 1,8-diaminonaphth-
alene with pivaloyl chloride in the presence of triethylamine
in CH2Cl2; compound 1 was obtained in a 77% yield. Con-
Figure 1. ORTEP diagram (30% probability thermal ellipsoids) of
version of bis(amide) 1 to bis(imidoylchloride) 2 was
achieved by addition of PCl5 to a solution of 1 in chloro-
benzene. In contrast to previously published synthetic pro-
cedures,[11a,11c] at this step, chlorobenzene was used instead
of toluene in order to solubilize 1. By heating the reaction
mixture at 65 °C for 3 d, a yield of 42% was achieved. Ex-
tension of the reaction time to up to 5 d does not result in
an increase in the product yield. The bis(amidine) 3 was
3. Hydrogen atoms (except those of the amidine fragments) are
omitted for clarity. Selected bond lengths [Å] and angles [°]: N(1)–
C(1) 1.404(3), N(1)–C(11) 1.390(3), N(2)–C(3) 1.416(3), N(2)–
C(24) 1.295(3), N(3)–C(11) 1.280(3), N(3)–C(16) 1.402(3), N(4)–
C(24) 1.369(3), N(4)–C(29) 1.425(3), N(1)–C(11)–N(3) 128.3(2),
C(11)–N(3)–C(16) 127.3(2), N(2)–C(24)–N(4) 126.7(2), C(24)–
N(4)–C(29) 128.5(2).
The X-ray diffraction study reveals that bis(amidine) 3
synthesized by reaction of 2,6-dimethylaniline with 2 in can adopt conformations with different mutual arrange-
chlorobenzene (65 °C, 3 d). Recrystallization of 3 from a ments of the amidine groups relative to the naphthalene
CH2Cl2/hexane mixture allowed its isolation in a 70% yield fragment. Thus, in 3, the amidine groups are situated in an
as a pale-yellow crystalline solid, while when acetonitrile anti position, while in 3·(MeCN), they are in a syn position
was used as the solvent, the solvate 3·(MeCN) was obtained with respect to the naphthalene ring. The C(29–34) and
(63% yield). Products 1–3 returned acceptable microanalyt- C(2–7) rings in 3 are located in a “face to face” fashion,
ical results.
with a value of 22.2° for the dihedral angle between their
Scheme 1.
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M. V. Yakovenko, A. V. Cherkasov, G. K. Fukin, D. Cui, A. A. Trifonov
Table 1. Crystallographic data and structure refinement details for 3–7.
FULL PAPER
3
4
5
6
7
Empirical formula
Formula weight
Crystal size [mm]
Space group
C
532.75
36H44N4
C40H52ClN4O2Y
745.22
C52H82Cl2LiN4NdO6 C48H66Cl2LiN4O3Sm C71H97LiN7O6Sm
1081.30
0.26ϫ0.15ϫ0.07
P21/c
975.24
0.28ϫ0.15ϫ0.09
¯
P1
1301.85
0.40ϫ0.12ϫ0.10
P21/c
0.50ϫ0.50ϫ0.450.40ϫ0.40ϫ0.27
Pbca
P21/c
a [Å]
b [Å]
c [Å]
α [°]
15.715(2)
13.885(2)
28.972(4)
90
90
90
6322.1(16)
8
1.119
0.066
14.3924(4)
13.7686(4)
20.4216(6)
90
107.6570(10)
90
3856.16(19)
4
1.284
28.2427(14)
17.7600(9)
22.1877(11)
90
96.0580(10)
90
11067.0(10)
8
1.298
13.1746(3)
14.6174(3)
24.3385(6)
93.4900(10)
92.0370(10)
93.2970(10)
4667.05(18)
4
15.7262(3)
19.3451(4)
22.3292(5)
90
97.1330(10)
90
6740.5(2)
4
1.283
β [°]
γ [°]
V [Å3]
Z
Calculated density [mg/m3]
1.388
1.417
µ [mm–1
]
1.620
1.083
0.926
Tmin/Tmax
F(000)
2θ [°]
0.9679/0.9710 0.5635/0.6689
0.7660/0.9280
4536
53
0.6925/0.8831
2020
55
0.7082/0.9131
2740
52
2304
52
1568
52
Unique reflections collected (Rint
R1 [IϾ2σ(I)]
wR2 (all data)
)
6202 (0.0448) 7541 (0.0281)
22872 (0.0536)
0.0650
0.1692
21191 (0.0175)
0.0331
0.0875
57778 (0.0436)
0.0377
0.0980
0.0649
0.1801
380
0.0331
0.0861
445
Parameters
1111
1063
800
Goodness-of-fit on F2
1.031
–0.612/0.685
1.046
–0.240/1.078
1.046
–1.286/2.472
1.060
–0.825/1.940
1.050
–0.544/1.676
Largest diff. hole and peak /e/Å3
planes. The short distance between the centers of these rings these calculations, the conformation that is realized in com-
(3.473 Å) allows for the realization of π–π interactions[13] in plex 3 is energetically preferable (1.18 kcal/mol) relative to
3.
that of 3·(MeCN). Probably stabilization of the conforma-
Unlike in previously reported linked bis(amidine) tion of 3·(MeCN) is reached because of the presence of
groups,[11a,11c] in both 3 and 3·(MeCN), the hydrogen atoms solvate molecules of MeCN in the crystal. In order to evalu-
in the amidine groups are attached to different nitrogen ate the energy of the intramolecular N···H hydrogen bonds,
atoms. This fact becomes evident from analysis of the geo- the Bader theory[16] and the correlation equation of Espi-
metric parameters of the amidine groups. Within one of the nosa[17] were used. The calculations have shown that the
two NCN fragments, the bond length N(C10H6)–C energy of the bonds N(2)···H(1A) and N(1)···H(2A) in 3
[1.292(2) Å] is comparable to that of a normal double C=N and 3·(MeCN) are 9.68 and 9.93 kcal/mol, respectively.
bond,[14] while the bond between central carbon atom and
the nitrogen atom of the 2,6-dimethylaniline moiety is sub-
stantially longer [1.371(2) Å] and corresponds better to a
single N–C bond. In the second NCN fragment, the bond-
Synthesis of Bis(amidinate)Chlorido Lanthanide Complexes
ing situation is reverse: the bond N(C10H6)–C is long
Bis(amidine) 3 can easily be deprotonated by treatment
[1.414(2) Å] and the C–N(2,6-Me2–C6H3) is short with 2 equiv. of nBuLi in a thf/hexane mixture at 0 °C. The
[1.272(2) Å]. It should be noted that intramolecular N···H dilithium derivative of 3 obtained after metallation with
hydrogen bonds are realized in 3 and 3·(MeCN). The nBuLi was used in situ in the reaction with anhydrous
N(2)···H(1A) and N(1)···H(2A) distances in 3 and LnCl3 (Ln = Y, Nd, Sm; 1:1 molar ratio) in thf at ambient
3·(MeCN) are 2.10(2) and 2.02(2) Å, respectively. The temperature (Scheme 2).
NHN bond angles at the hydrogen atoms are 138.9(3)° in 3
Evaporation of thf, extraction of the solid residue with
and 135.1(4)° in 3·(MeCN). The different locations of the toluene, and subsequent recrystallization of the reaction
hydrogen atoms within the two amidine fragments is proved product from dme/hexane (4), diethyl ether (5), or thf/hex-
also by the solid-state IR spectrum of 3: the NH groups ane (6) mixtures led to the isolation of bis(amidinate)-
give rise to two different absorption bands at 3400 and chlorido lanthanide complexes [1,8-C10H6{NC(tBu)N-2,6-
3278 cm–1. Obviously, the same situation is retained in solu- Me2–C6H3}2]YCl(dme) (4), [1,8-C10H6{NC(tBu)N-2,6-
tion since the protons attached to the nitrogen atoms in the Me2–C6H3}2]Nd(dme)(µ-Cl)2Li(dme) (5), and [1,8-C10H6-
1H NMR spectrum of 3 give rise to a set of two singlets of {NC(tBu)N-2,6-Me2–C6H3}2]Sm(thf)(µ-Cl)2Li(thf)2 (6) in
equal intensity at δ = 6.07 and 8.98 ppm.
reasonable yields (45–61%). Complexes 4–6 were obtained
In order to evaluate the difference in the energies of the as pale-yellow crystalline moisture- and air-sensitive solids.
conformers and the energy of the intramolecular N···H hy- They are soluble in thf, dme, Et2O, and toluene and are
1
drogen bonds, density functional theory (DZVP basis set) slightly soluble in hexane. The H and 13C{1H}NMR spec-
calculations on the isolated molecules 3 and 3·(MeCN) were tra of the diamagnetic yttrium derivative 4 in C6D6 at 20 °C
carried out with the program Firefly 71c.[15] According to show the expected set of signals corresponding to the bis-
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Lanthanide Complexes Coordinated by a Dianionic Bis(amidinate) Ligand
Scheme 2.
(amidinate) ligand and the dme molecule. The protons of atoms of the dme molecule, 6: one oxygen atom of the thf
the tBu groups give rise to a single singlet at δ = 0.88 ppm, molecule). The lithium atom in 5 is coordinated by one dme
and the protons of the xylyl fragments appear as a singlet molecule and in complex 6 by two thf molecules. The four
at δ = 2.46 ppm. Two broad singlets at δ = 2.67 and 2.99 Ln–N distances in compounds 4–6 have rather similar val-
ppm correspond to the methyl and methylene protons of ues [4: 2.331(1)–2.369(1); 5: 2.454(3)–2.573(3); 6: 2.404(2)–
the dme molecules. The variable-temperature 1H and 2.481(2) Å], and the average bond lengths are comparable
13C{1H} NMR spectroscopic data for 4 is indicative of to those reported for related bis(amidinate) complexes
complex dynamic behavior over the temperature range +60 (Y,[3a,12a] Nd,[2c] Sm[18]).
to –60 °C (in C7D8), which results in an apparent mirror
plane within the molecule. Clear pale-yellow crystals of
complexes 4–6 suitable for X-ray diffraction studies were
obtained by slow concentration of their solutions (4: dme/
hexane mixture, 5: diethyl ether, 6: thf/hexane mixture) at
ambient temperature. Complex 5 was isolated as a solvate
5·(2Et2O), while the crystals of 4 and 6 do not contain sol-
vent molecules. Crystals of complexes 5 and 6 contain two
crystallographically independent molecules. The molecular
structures of 4–6 are shown in Figures 2, 3, and 4, respec-
tively; the structure refinement data are listed in Table 1. X-
ray diffraction studies reveal that compound 4 is a mono-
meric salt-free complex, while 5 and 6 are heterobimetallic
complexes. The coordination sphere of the yttrium atom in
4 is made up of four nitrogen atoms of two amidinate frag-
ments, two oxygen atoms of the dme molecule, and one ter-
minal chlorido ligand. In complexes 5 and 6, the coordina-
tion spheres of the metal atoms contain two chlorine atoms
that µ-bridge the lanthanide and lithium atoms, in addition
to four nitrogen atoms of the bis(amidinate) ligand and the
Figure 2. ORTEP diagram (30% probability thermal ellipsoids) of
4. Hydrogen atoms are omitted for clarity. Selected bond lengths
[Å] and angles [°]: Y(1)–N(1) 2.331(1), Y(1)–N(4) 2.348(1), Y(1)–
N(3) 2.354(1), Y(1)–N(2) 2.369(1), Y(1)–O(1) 2.409(1), Y(1)–O(2)
2.421(1), Y(1)–Cl(1) 2.596(4), N(1)–C(11) 1.348(2), N(2)–C(24)
1.341(2), N(3)–C(11) 1.328(2), N(4)–C(24) 1.354(2), N(1)–Y(1)–
oxygen atoms of coordinated Lewis bases (5: two oxygen N(3) 56.17(5), N(4)–Y(1)–N(2) 55.88(4).
Eur. J. Inorg. Chem. 2010, 3290–3298
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M. V. Yakovenko, A. V. Cherkasov, G. K. Fukin, D. Cui, A. A. Trifonov
FULL PAPER
Figure 4. ORTEP diagram (30% probability thermal ellipsoids) of
6. Hydrogen atoms and the methylene groups of the thf molecules
are omitted for clarity. Selected bond lengths [Å] and angles [°]:
Sm(1A)–N(2A) 2.404(2), Sm(1A)–N(4A) 2.415(2), Sm(1A)–N(3A)
2.419(2), Sm(1A)–N(1A) 2.481(2), Sm(1A)–O(1SA) 2.576(2),
Sm(1A)–Cl(2A) 2.7611(7), Sm(1A)–Cl(1A) 2.7675(6), Cl(1A)–
Li(1A) 2.328(5), Cl(2A)–Li(1A) 2.326(5), N(1A)–C(11A)1.327(3),
N(2A)–C(24A)1.358(3), N(3A)–C(11A) 1.359(3), N(4A)–C(24A)
1.338(3), N(2A)–Sm(1A)–N(4A) 54.52(7), N(3A)–Sm(1A)–N(1A)
53.62(7).
Figure 3. ORTEP diagram (30% probability thermal ellipsoids) of
5. Hydrogen atoms and methyl and methylene groups of the dme
molecules are omitted for clarity. Selected bond lengths [Å] and
angles [°]: Nd(1A)–N(2A) 2.454(3), Nd(1A)–N(1A) 2.479(3),
Nd(1A)–N(3A) 2.496(3), Nd(1A)–O(1SA) 2.555(2), Nd(1A)–
N(4A) 2.573(3), Nd(1A)–O(2SA) 2.602(2), Nd(1A)–Cl(2A)
2.8056(9), Nd(1A)–Cl(1A) 2.8869(9), N(1A)–C(11A) 1.320(5),
N(2A)–C(24A) 1.334(5), N(3A)–C(11A) 1.339(5), N(4A)–C(24A)
1.330(4), Cl(1A)–Li(1A) 2.287(7), Cl(2A)–Li(1A) 2.318(7), Li(1A)–
O(4SA) 1.947(8), Li(1A)–O(3SA) 2.015(8), N(1A)–Nd(1A)–N(3A)
52.7(1), N(2A)–Nd(1A)–N(4A)51.8(1).
and 109.6°. Moreover, the coordination of bis(amidine) 3
to lanthanide atoms of different sizes provokes distortions
of different magnitudes in the naphthalene linker. In parent
The bonding situation within the NCN fragments of bis(amidine) 3, the mean deviation of the carbon atoms of
complexes 4–6 indicates a negative charge delocalization. the naphthalene ring from the plane is 0.0483 Å [0.0505 Å
Comparison of the structures of complexes 4–6 reveals ver- for 3·(MeCN)]. However, the same parameter in complexes
satility of the coordination modes of the new bis(amidinate) 4 and 6, which display a trans disposition of the amidinate
ligand framework to the lanthanide atoms, which is depend- groups, has values of 0.1119 Å and 0.1069, 0.1016 Å respec-
ent on ion size of the central atom. Thus, in complexes of tively. In complex 5, where the amidinate groups are located
yttrium and samarium, the amidinate groups are located in on the same side of the naphthalene ring the value of mean
a trans position with respect to the naphthalene fragment, deviation (0.0461, 0.0459 Å) is noticeably lower and is sim-
while in the neodymium derivative with a larger ion,[19] they ilar to that observed for starting bis(amidine) 3. The at-
adopt a cis configuration (Figure 5). At the same time, the tempt to alkylate complex 6 with an equimolar amount of
values of the dihedral angles in these cases differ substan- LiCH2SiMe3 was carried out in toluene at 0 °C. Separation
tially: in complexes 4 and 6 they are in the region 77.6– of the precipitate of LiCl, evaporation of toluene in vacuo,
79.7°, while in complex 5 this value is much larger – 109.4 and subsequent recrystallization of the solid residue from a
Figure 5. Dihedral angles between planes N(3)LnN(1) and N(2)LnN(4) in complexes 4–6 (4: 77.6°; 5: 109.4, 109.6°; 6: 78.5, 79.7°).
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Lanthanide Complexes Coordinated by a Dianionic Bis(amidinate) Ligand
Scheme 3.
dme/hexane mixture led to the isolation of an unexpected seven. The formation of 7 obviously results from the cleav-
product
[{1,8-C10H6(NC(tBu)N-2,6-Me2–C6H3)2}{1,8- age of one amidinate fragment during decomposition of the
C10H6(NC(tBu)N-2,6-Me2–C6H3)(NH)}Sm][Li(dme)3] (7) transient alkyl complex and ligand redistribution. The cat-
(Scheme 3). All attempts to isolate other samarium-con- ionic part consists of the Li cation coordinated to three dme
taining products failed. Complex 7 was obtained as a yellow molecules. The average Sm–N(amidinate) bond length in 7
crystalline moisture- and air-sensitive solid in 24% yield. [2.470(2) Å] is somewhat longer than those in the parent
Complex 7 is soluble in thf, dme, Et2O, and toluene and complex of the seven-coordinate samarium 6 [2.429(2) Å]
insoluble in hexane. Transparent yellow crystals of 7 suit- and ionic bis(guanidinate) complexes [(Me3Si)2NC(N-R)2]2-
able for X-ray single-crystal structure investigation were ob- Sm-(µ-BH4)2Li(thf)2 (R = Cy, 2.424 Å;[20] R = iPr,
tained by slow concentration of the solution in a dme/hex- 2.455 Å[21]). The Sm–N(amido) bond length [2.350(2) Å] in
ane mixture at ambient temperature. The X-ray diffraction 7 is similar to that formerly reported for a related ionic
study reveals that complex 7 is an ionic compound (Fig- amido complex {Li(thf)4}{Sm[(R)-C20H12N2(C10H22)]2}
ure 6) consisting of the complex anion formed by the Sm3+ [2.348(3) Å].[22]
cation coordinated to one dianionic bis(amidinate) ligand
Further studies on the synthesis of alkyl, hydrido,
and one dianionicamido–amidinate ligand {1,8-C10H6 borohydride, alkoxide, and amido species supported by new
(NC(tBu)N-2,6-Me2–C6H3)(NH)}2–. The coordination linked bis(amidinate) ligand systems are currently in pro-
sphere of the samarium atom in 7 is made up of seven nitro- gress.
gen atoms, thus providing a formal coordination number of
Conclusions
A new dianionic bis(amidinate) ligand framework with a
conformationally rigid naphthalene linker was developed
and shown to form a suitable coordination environment for
lanthanide ions. The salt metathesis reactions of dilithium
derivatives of 3 with LnCl3 (Ln = Y, Nd, Sm) for the metals
with a small ion size (Y) results in the synthesis of mono-
meric salt-free bis(amidinate)chlorido complexes, while for
the metals possessing larger ion sizes (Nd, Sm), the forma-
tion of heterobimetallic complexes was observed. The struc-
tures of complexes 4–6 were established by X-ray diffraction
studies, which reveal that a new ligand framework can coor-
dinate to lanthanide atoms in different fashions depending
on the central atom ion size. The attempt to synthesize a
samarium alkyl species that is supported by the linked bis-
(amidinate) ligand by reaction of complex 6 with an equi-
molar amount of LiCH2SiMe3 afforded the unexpected
amido–amidinate complex 7, which obviously was formed
by cleavage of one amidinate group during decomposition
Figure 6. ORTEP diagram (30% probability thermal ellipsoids) of
of the transient alkyl species and ligand redistribution.
the anionic part of 7. Hydrogen atoms (except that of the amido
group) are omitted for clarity. Selected bond lengths [Å] and angles
[°]: Sm(1)–N(7) 2.350(2), Sm(1)–N(6) 2.420(2), Sm(1)–N(5)
2.434(2), Sm(1)–N(3) 2.473(2), Sm(1)–N(1) 2.476(2), Sm(1)–N(4)
2.483(2), Sm(1)–N(2) 2.538(2), N(7)–Sm(1)–N(6) 100.72(7), N(7)–
Experimental Section
All experiments were performed in evacuated tubes by using stan-
dard Schlenk techniques, with the rigorous exclusion of traces of
Sm(1)–N(5) 69.49(7), N(6)–Sm(1)–N(5) 54.50(6), N(1)–Sm(1)–N(2)
52.17(6), N(3)–Sm(1)–N(4) 52.56(7).
Eur. J. Inorg. Chem. 2010, 3290–3298
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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3295

M. V. Yakovenko, A. V. Cherkasov, G. K. Fukin, D. Cui, A. A. Trifonov
FULL PAPER
moisture and air. After drying over KOH, thf was purified by distil-
lation from sodium/benzophenone ketyl and hexane and toluene
by distillation from sodium/triglyme benzophenone ketyl prior to
use. C6D6 was dried with sodium/benzophenone ketyl and con-
densed in vacuo prior to use. CH2Cl2 and C6H5Cl were dried with
P2O5, distilled twice, and degassed by freeze-vacuum-thaw cycles
prior to use. 1,8-diaminonaphthalene and pivaloyl chloride were
purchased from Acros. Anhydrous YCl3, SmCl3, NdCl3,[23] and
Me3SiCH2Li[24] were prepared according to literature procedures.
All other commercially available chemicals were used after appro-
priate purification. NMR spectra were recorded on Bruker Avance
DRX-400 and DPX-200 spectrometers in C6D6 or CDCl3 at 20 °C,
unless otherwise stated. Chemical shifts for 1H and 13C spectra
were referenced internally by using the residual solvent resonances
and are reported relative to tms in parts per million (ppm). IR
spectra were recorded as Nujol mulls on a “Bruker-Vertex 70” in-
strument. Lanthanide metal analyses were carried out by complex-
ometric titration. Mass spectra were recorded on a Polaris Q/Trace
GC Ultra (Ion Trap analyser) chromatography mass spectrometer.
The C, H, N elemental analysis was performed in the microanalyti-
cal laboratory of the G. A. Razuvaev Institute of Organometallic
Chemistry.
was stirred at 65 °C for 3 d, and the volatiles were removed in vacuo
to yield a pale-yellow solid. Et2O (50 mL) and an aqueous solution
of Na2CO3 (50 mL, 0.5 ) were added to the residual solid, and
the mixture was stirred for 30 min. The organic layer was separated,
washed with water (3ϫ 20 mL) and dried with MgSO4. The solvent
was removed in vacuo at room temperature to give a yellow solid.
Recrystallization of the residue from a mixture of hexane/CH2Cl2
(2:1) afforded 3 as pale-yellow crystals (2.94 g, 70%). If 3 was
recrystallized from acetonitrile, pale-yellow crystals of 3·(MeCN)
were obtained (2.65 g, 63%). C36H44N4 (532.8): calcd. C 81.16, H
8.32, N 10.52; found C 81.42, H 8.00, N 10.31. 1H NMR
(200 MHz, CDCl3, 20 °C): δ = 1.45 [s, 9 H, C(CH3)3], 1.55 [s, 9 H,
C(CH3)3], 2.01 (s, 3 H, CH3), 2.05 (s, 9 H, CH3), 6.07 (s, 1 H, NH),
6.24–6.81 (m, 12 H, aryl), 8.99 (s, 1 H, NH) ppm. 13C{1H} NMR
(50 MHz, C6D6, 20 °C): δ = 18.5 (CH3), 29.4 [C(CH3)3], 39.6
[C(CH3)3], 40.4 [C(CH3)3], 113.3, 115.7, 120.0, 121.1, 122.5, 123.7,
124.1, 125.6, 127.6 (aryl, CH), 117.6, 127.4, 135.1, 135.8, 137.8,
147.0 (aryl, C), 159.3 (NCN), 162.4 (NCN) ppm. IR (Nujol, KBr):
ν = 3400 (m), 3278 (m, N–H), 3043 (w), 1638 (m, C=N), 1608 (w),
˜
1570 (w), 1369 (w), 1288 (m), 1209 (w), 1135 (m), 1034 (w), 925
(w), 894 (m), 884 (m), 831 (m), 820 (m), 806 (m), 760 (s) cm–1. MS
(EI): m/z = 532.3 [M+].
1,8-C10H6{NHC(O)tBu}2
(1):
Pivaloyl
chloride
(3.15 g, Synthesis of [1,8-C10H6{NC(tBu)N-2,6-Me2–C6H3}2]YCl(dme) (4):
26.20 mmol) was added slowly to a solution of 1,8-diaminonaphth-
alene (2.00 g, 12.65 mmol) and Et3N (2.65 g, 26.23 mmol) in
CH2Cl2 (30 mL) at room temperature to give an exothermic reac-
tion. The reaction mixture was stirred at 35 °C for 16 h, and the
volatiles were removed in vacuo at room temperature. After tritura-
tion with water (3ϫ 50 mL), the grey solid was washed with hexane
(3ϫ 50 mL) and dried in vacuo at room temperature for 2 h. Yield:
3.16 g (77%). C20H26N2O2 (326.4): calcd. C 73.69, H 8.03, N 8.58;
found C 73.25, H 8.29, N 8.15. 1H NMR (200 MHz, C5D5N,
A solution of nBuLi in hexane (2.18 mL, 0.95 N, 2.07 mmol) was
added to a solution of 3 (0.55 g, 1.03 mmol) in thf (30 mL) at 0 °C;
the reaction mixture was stirred for 40 min and was then slowly
warmed up to 20 °C. YCl3 (0.20 g, 1.03 mmol) was added, and the
reaction mixture was stirred overnight. The solvent was evaporated
in vacuo, and the solid residue was extracted with toluene (2ϫ
20 mL). The toluene extracts were filtered, and the solvent was
evaporated in vacuo. After recrystallization of the residue from a
mixture of hexane/dme, pale-yellow crystals of 4 were obtained in
20 °C): δ = 1.46 (s, 18 H, CMe3), 7.36–8.71 (m, 6 H, aryl), 10.34 a yield of 0.45 g (45%). C40H52ClN4O2Y (745.3): calcd. C 64.47, H
(br. s, 2 H, NH) ppm. 13C{1H} NMR (50 MHz, C5D5N, 20 °C): δ 7.03, Y 11.93; found C 64.21, H 6.85, Y 11.86. 1H NMR
= 27.6 [s, C(CH3)], 40.0 [s, C(CH3)], 123.5, 123.6, 124.6, 124.7, (200 MHz, C6D6, 20 °C): δ = 0.88 [s, 18 H, C(CH3)3], 2.46 (s, 12
126.7, 136.2 (s, C aryl), 179.263 (C=O) ppm. IR (Nujol, KBr): ν =
H, CH3), 2.67 (br. s, 4 H, OCH2, dme), 2.99 (br. s, 6 H, OCH3,
˜
3374 (s, NH), 3065 (w, aryl), 1655 (s, C=O), 1580 (m), 1498 (s), dme), 6.79–7.49 (m, 12 H, C-H aryl) ppm. 13C{1H} NMR
1278 (m), 1252 (w), 1231 (m), 1192 (m), 1169 (m), 1034 (m), 940 (50 MHz, C6D6, 20 °C): δ = 20.1 (CH3), 30.3 [C(CH3)3], 42.9
(m), 833 (m), 808 (m) cm–1. MS (EI): m/z = 326.2 [M+].
[C(CH3)3], 61.2 (s, OCH3, dme), 69.9 (s, OCH2, dme), 120.5, 121.7,
122.1, 124.8, 128.0, 130.7, 135.7, 145.6, 148.7 (s, aryl), 179.9 (d,
1,8-C10H6{N=C(Cl)tBu}2 (2): PCl5 (3.30 g, 15.80 mmol) was added
in portions to a solution of 1 (2.60 g, 7.90 mmol) in chlorobenzene
(30 mL) in vacuo to give a cloudy, green solution, which was stirred
at 65 °C for 3 d. The solution was filtered, the volatiles were re-
moved in vacuo at room temperature, and the solid residual was
extracted with hexane (2ϫ 20 mL). The hexane extracts were fil-
tered, slowly concentrated in vacuo at room temperature to half of
the initial volume, and left overnight at 0 °C. The mother liquor
was separated by decantation and the pale-yellow crystalline solid
was washed with cold hexane (15 mL) and dried in vacuo at room
temperature for 40 min to yield 1.20 g (42%) of 2. C20H24Cl2N2
(363.4): calcd. C 66.12, H 6.66, Cl 19.52, N 7.71; found C 66.01,
1JY-C = 2.4 Hz, NCN) ppm. IR (Nujol, KBr): ν = 3054 (w), 1673
˜
(m), 1569 (m), 1503 (w), 1261 (w), 1218 (m), 1172 (m), 1091 (s),
1046 (s), 934 (w), 860 (s), 764 (s) cm–1.
[1,8-C10H6{NC(tBu)N-2,6-Me2–C6H3}2]Nd(dme)(µ-Cl)2Li(dme) (5):
A solution of nBuLi in hexane (6.13 mL, 0.79 N, 4.84 mmol) was
added to a solution of 3 (1.29 g, 2.42 mmol) in thf (30 mL) at 0 °C;
the reaction mixture was stirred for 40 min and was then slowly
warmed up to 20 °C. NdCl3 (0.61 g, 2.42 mmol) was added to the
solution, and the reaction mixture was stirred overnight. Volatiles
were removed in vacuo, and the remaining solid was extracted with
toluene (2ϫ 20 mL). The extracts were filtered, and toluene was
removed in vacuo. The solid residue was treated with dme and
recrystallized from diethyl ether. Pale-yellow crystals of 5 were ob-
1
H 6.35, Cl 19.05, N 7.43. H NMR (200 MHz, CDCl3, 20 °C): δ =
1.46 (s, 18 H, CMe3), 6.62–7.69 (m, 6 H, aryl) ppm. 13C{1H} NMR
(200 MHz, CDCl3, 20 °C): δ = 27.1 [C(CH3)], 27.6 [C(CH3)], 39.9 tained in a yield of 0.98 g (47%). C52H82Cl2LiN4NdO8 (1113.4):
[C(CH3)], 124.1, 124.4, 125.6, 127.4, 132.9, 136.1 (s, C aryl), 179.2 calcd. C 56.10, H 7.42, Nd 5.03; found C 56.03, H 7.01, Nd 4.95.
(N=C) ppm. IR (Nujol, KBr): ν = 3050 (w), 1673 (s, N=C), 1611 IR (Nujol, KBr): ν = 1590 (s), 1258 (m), 1122 (w), 1122 (w), 1047
˜
˜
(w), 1569 (s), 1477 (m), 1327 (m), 1263 (m), 1210 (s), 1033.9 (m),
(s), 931 (s), 861 (m), 890 (m), 806 (m), 759 (s) cm–1.
934 (s), 835 (s), 808 (s), 791 (m), 760 (s) cm–1.
[1,8-C10H6{NC(tBu)N-2,6-Me2–C6H3}2]Sm(thf)(µ-Cl)2Li(thf)2 (6):
1,8-C10H6[NHC(tBu)=N(2,6-Me2–C6H3)][N=C(tBu)NH(2,6-Me2– A solution of nBuLi in hexane (1.56 mL, 1.08 N, 1.68 mmol) was
C6H3)] (3): 2,6-Dimethylaniline (1.53 g, 12.70 mmol) was added in
portions to a solution of 2 (2.00 g, 5.52 mmol) in chlorobenzene
(30 mL) in vacuo to give a yellow solution. The reaction mixture
added to a solution of 3 (0.45 g, 0.84 mmol) in thf (30 mL) at 0 °C;
the reaction mixture was stirred for 40 min and was then slowly
warmed up to 20 °C. SmCl3 (0.22 g, 0.84 mmol) was added, and the
3296
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Eur. J. Inorg. Chem. 2010, 3290–3298

Lanthanide Complexes Coordinated by a Dianionic Bis(amidinate) Ligand
reaction mixture was stirred overnight. The solvent was removed in
Acknowledgments
vacuo, and the solid residue was extracted with toluene (2ϫ
20 mL). The toluene extracts were filtered, and the solvent was re-
moved in vacuo. Recrystallization of the residue from a hexane/thf
This work was supported by the Russian Foundation for Basic Re-
search (Grant No 08-03-00391-a), the Program of the Presidium of
the Russian Academy of Science (RAS), and the RAS Chemistry
and Material Science Division.
mixture afforded pale-yellow crystals of
6 (0.50 g, 61%).
C48H66Cl2LiN4O3Sm (975.4): calcd. C 59.11, H 6.82, Sm 15.42;
found C 58.83, H 6.91, Sm 14.98. 1H NMR (200 MHz, C5D5N,
20 °C): δ = 1.54 [s, 9 H, C(CH3)3], 1.55 (br. s, 12 H, thf β-CH2),
1.66 [s, 9 H, C(CH3)3], 2.16 (s, 12 H, CH3), 3.60 (br. s, 12 H, thf
α-CH2), 6.49–8.56 (m, 12 H, C-H aryl) ppm. 13C{1H} NMR
(50 MHz, C5D5N, 20 °C): δ = 19.0 (CH3), 26.0 (thf, β-CH2) 29.5
[C(CH3)3], 29.8 [C(CH3)3], 40.2 [C(CH3)3], 41.0 [C(CH3)3], 67.9
(thf, α-CH2), 113.4, 116.9, 118.2, 120.6, 121.6, 122.5, 124.6, 125.9,
127.9, 128.8, 129.5, 134.4, 137.3, 138.8, 146.7, 148.0 (s, aryl), 154.5
(s, NCN), 164.9 (s, NCN) ppm. 7Li NMR (78 MHz, C5D5N,
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20 °C): δ = 5.4 ppm. IR (Nujol, KBr): ν = 3041 (w), 1638 (s), 1565
˜
(m), 1566 (m), 1257 (m), 1223 (m), 1180 (m), 1113 (w), 1095 (s),
1053 (s), 1050 (m), 1030 (m), 929 (w), 775 (s), 764 (m) cm–1.
Reaction of [1,8-C10H6{NC(tBu)N-2,6-Me2–C6H3}2]Sm(thf)(µ-Cl)2-
Li(thf)2 with LiCH2SiMe3. Synthesis of 7: To a solution of 6 (0.38 g,
0.39 mmol) in toluene (20 mL) was slowly added a solution of Me3-
SiCH2Li (0.04 g, 0.47 mmol) in toluene (10 mL) at 0 °C, and the
reaction mixture was stirred for 1 h. The yellow solution was fil-
tered, the solvent was removed in vacuo, and the solid residue was
recrystallized from a mixture of hexane/dme to give yellow crystals
of 7 (0.12 g, 24%). C72H100LiN7O6Sm (1316.1): calcd. C 65.67, H
7.65, Sm 11.42; found C 65.19, H 7.32, Sm 11.38. 1H NMR
(400 MHz, C6D6, 20 °C): δ = 0.15 [br. s, 18 H, C(CH3)3], 0.42 [br.
s, 9 H, C(CH3)3], 1.24 (br. s, 6 H, CH3), 1.54 (br. s, 12 H, CH3),
3.11 (br. s, 18 H, OCH3, dme), 3.32 (br. s, 12 H, OCH2, dme), 6.17–
7.71 (m, 21 H, C-H aryl) ppm. 13C{1H} NMR (50 MHz, C6D6,
20 °C): δ = –0.2 [C(CH3)3], 1.0 [C(CH3)3], 28.9 (CH3), 29.7 (CH3),
39.1 [C(CH3)3], 40.4 [C(CH3)3], 58.3 (s, OCH3, dme), 71.9 (s,
OCH2, dme), 113.6, 114.7, 115.9, 116.7, 119.2, 120.4, 121.4, 122.1,
122.9, 123.7, 124.1, 124.3, 126.1, 127.0, 127.2, 128.5, 129.7, 133.4,
135.4, 137.4 (s, CH aryl), 157.1, 158.7, 162.2 (NCN) ppm. 7Li
NMR (156 MHz, C D , 20 °C): δ = 6.0 ppm. IR (Nujol, KBr): ν
˜
6
6
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3297

M. V. Yakovenko, A. V. Cherkasov, G. K. Fukin, D. Cui, A. A. Trifonov
FULL PAPER
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Eur. J. Inorg. Chem. 2010, 3290–3298