Lithium complexes supported by tripodal diaminebis(aryloxido) ligands: Synthesis and structure

Article abstract of DOI:10.1039/c1dt11498k

The diaminebis(aryloxido) ligand precursors H₂L¹ and H₂L² [H₂L¹ = Me₂NCH ₂CH₂N(CH₂-4-CMe₂CH ₂CMe₃-C₆H

Full text of DOI:10.1039/c1dt11498k

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PAPER
Lithium complexes supported by tripodal diaminebis(aryloxido) ligands:
Synthesis and structure†
Zofia Janas,* Tomasz Nerkowski, Ewa Kober, Lucjan B. Jerzykiewicz and Tadeusz Lis
Received 8th August 2011, Accepted 23rd September 2011
DOI: 10.1039/c1dt11498k
The diaminebis(aryloxido) ligand precursors H2L1 and H2L2 [H2L1 = Me2NCH2CH2N(CH2-4-CMe2-
CH2CMe3-C6H3OH)2; H2L2 = Me2NCH2CH2N(CH2-4-Me-C6H3OH)2] were synthesized by a straight-
forward single-step Mannich condensation. Their reactions with 2 molar equivalents of MeLi in thf
4
afforded [Li4(m-L-k O,N,N,O)2(thf)2] (1a, L1; 1b, L2) and unexpectedly small amounts (~9%) of [Li6(m-
4
3
L-k O,N,N,O)2(m -Cl)2(thf)4]·thf (2a·thf; L1; 2b·thf, L2). Stoichiometric reactions of LiCl, MeLi and
ligand precursors H2L led to the formation of 2a and 2b in high yield (~80%). All compounds were
characterized by chemical and physical techniques including X-ray crystallography for H2L1, H2L2, 1b,
2a and 2b.
Introduction
Polydentate diaminebis(aryloxido) (ONNO) ligands have been
used extensively in transition-metal coordination chemistry in
catalyst development,1 metalloenzyme mimicry,2 and cytotoxicity
against particular cells.3 Such broad application range arises from
the great modification possibilities either on the phenyl group or
amine leading to convenient variation of steric factors and donor
ability of this class of ligands.
One method to realize synthesis of transition-metal com-
plexes supported by diaminebis(aryloxido) ligands is through a
metathesis route that often involves lithium derivatives. To fully
Fig. 1 Tetradentate diaminebis(aryloxido) ligand precursors.
exploit this method, it is necessary to identify the structure
of starting materials. However, only few lithium compounds
of general formula [Li2(ONNO)] with diaminebis(aryloxido)
ligands, being of our research interest, have been fully
characterized.4,5 Kerton and co-workers showed that isomeric
tripodal [Me2NCH2CH2N(CH2-2,4-tBu2C6H2O)2]2- and linear
(so-called salan) [MeNCH2CH2NMe(CH2-2,4-tBu2C6H2O)2]2- lig-
ands in the presence of 1,4-dioxane generated lithium complexes
that exhibited a polymeric and a 1,4-dioxane bridged dimeric
structure in the solid-state, respectively.5 The same tripodal
[Me2NCH2CH2N(CH2-2,4-tBu2C6H2O)2]2- ligand in the absence
of neutral strong bases as coligands creates the tetra-lithium
complex revealing boat-like structure.4 This shows that the final
structure of these lithium species are strongly dependent upon the
choice of solvent (Lewis basicity) used to their synthesis.
Results and discussion
The synthesis of the diaminebis(aryloxido) ligand precursors
H2L1 and H2L2 was based on a straightforward single-step
Mannich condensation between N,N-dimethylethylenediamine,
paraformaldehyde and 4-(1,1,3,3-tetramethylbutyl)phenol or p-
cresol, respectively in a 1 : 2 : 2 molar ratio according to a known
procedure.6 The H2L1 and H2L2 products precipitated as white
solids with high yield, and were characterized with NMR spectra
and mass spectrometry. The 1H NMR spectra of H2L1 and
H2L2 suggest the presence of intramolecular hydrogen bonds
OH ◊ ◊ ◊ N either in the solid state or in solution (Experimental
section). To confirm this structural feature the crystal structures
of H2L1 and H2L2 were obtained. However, due to the insufficient
quality of the H2L1 crystal only qualitative information could
be extracted and illustrated as the DIAMOND drawing in Fig.
2a.‡ These data demonstrate that compound H2L1 contains two
intramolecular hydrogen-bond interactions OH ◊ ◊ ◊ N in the solid
During the course of our investigation into the vanadium
coordination chemistry involving diaminebis(aryloxido) ligands,
new ligand precursors shown in Fig. 1, and their lithium salts were
prepared and structurally characterized.
Faculty of Chemistry, University of Wrocław, 14, F. Joliot-Curie, 50-383,
Wrocław, Poland. E-mail: zj@wchuwr.pl
† CCDC reference numbers 832240–832242. For crystallographic data in
CIF or other electronic format see DOI: 10.1039/c1dt11498k
‡ Crystal data for H2L1: C34H56N2O2, M = 524.43, orthorhombic, space
˚
group Pca21, a = 12.106(5), b = 7.740(5), c = 69.239(16) A, Z = 8, V =
3
˚
6487(16) A .
442 | Dalton Trans., 2012, 41, 442–447
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Scheme 1
(Aldrich Chemical Co.). This has been previously noticed by
synthetic chemists and it is well documented that the quantity
of LiCl in commercial chemical agents is important in many
organolithium reactions.8 This knowledge allowed to optimize
the yield of compound 2a to 84% using in its synthesis MeLi,
H2L1 and LiCl at 2 : 1 : 1 molar ratio in thf. Crystals of 2a suitable
for an X-ray determination were grown from a saturated thf
solution at room temperature. However, because they displayed
poor diffraction, the X-ray data for 2a allowed to extract only a
model of the structure.§ Fortunately, a similar synthetic procedure
as for 1a and 2a carried out using H2L2 (see Experimental section)
Fig. 2 (a) DIAMOND drawing of the molecular structure of H2L1;
(b) Molecular structure of H2L2 with thermal ellipsoids drawn at the
50% probability level. Only hydrogen atoms involved in the hydrogen
bonds are shown Selected parameters (bonds, A; angles, ◦): N1–C2
˚
1.4807(17), N1–C3 1.4813(17), N1–C1 1.4862(17), N2–C6 1.4687(18),
N2–C5 1.4700(18), N2–C4 1.4762(17) O11–H11A ◊ ◊ ◊ N2 2.7720(17),
O21–H21A ◊ ◊ ◊ N1 2.6858(18); O11–H11A ◊ ◊ ◊ N2 153.4, O21–H21A ◊ ◊ ◊ N1
146.7.
4
successfully led to the formation of [Li4(m-L2-k O,N,N,O)2(thf)2]
4
3
(1b) and [Li6(m-L2-k O,N,N,O)2(m -Cl)2(thf)4]·thf (2b·thf) as crys-
tals for which satisfactory X-ray structural data were achieved. The
molecular structures of 1b and 2b·thf and selected bond lengths
and angles are shown in Fig. 3 and 4, respectively.
state. Similar structural trends have been found in the tripodal
[Me2NCH2CH2N(CH2-2,4-R2C6H2OH)2] (R = Me,7a tBu,7b) Man-
nich bases having alkyl substituents at ortho and para positions
of the phenolate rings. Ultimately, good quality of the H2L2
crystal allowed to obtain well solved X-ray data and to confirm
compatibility between the model of H2L1 and the structure of
H2L2. The molecular structures of H2L2 and selected bond lengths
and angles are shown in Fig. 2b.
Compound 1b contains a ‘cubanoid’ Li4O4 core comprising
four lithium atoms and four Oaryloxide atoms of the L2 ligands.
In the structure of 1b two of the lithium atoms have five-
coordinate environments, and are bound to the nitrogens and
the m3-oxygens of the L2 ligands. The angles involving the bonds
coordinated to these lithium atoms are all distorted from the
idealized trigonal-bipyramidal angles. Each of the other two
lithium atoms is bonded by three aryloxide m3-oxygen atoms, with
the remainder of the coordination sphere occupied by one oxygen
atom of the thf molecule, resulting in a distorted tetrahedral
geometry with angles m3-O–Li–m3-O of 92.08–98.89◦ and m3-O–
Li–Othf of 105.79–136.05◦. The Li1–(m3-O) bond distances of
Reaction of the ligand precursor H2L1 with 2 molar equiv-
alents of MeLi in thf affords after work-up two colorless
4
compounds [Li4(m-L1-k O,N,N,O)2(thf)2] (1a) (87.2%) and [Li6(m-
4
3
L1-k O,N,N,O)2(m -Cl)2(thf)4]·thf (2a·thf) (8.5%) as shown in
Scheme 1.
Compound 1a is very well soluble in all organic solvents in
contrast to 2a which has moderate solubility in cold thf. Analyt-
ically and spectroscopically pure forms of these compounds were
obtained with easy interpretable NMR spectra. Unfortunately,
attempts to obtain single crystals of 1a were unsuccessful. We have
proved analytically that the chloride ions found in 2a originated
from residual LiCl (0.18%) present in the commercial MeLi
˚
˚
2.001 A (av.) are longer than the Li2–(m3-O) ones of 1.972 A
(av.) as expected from the change in coordination number, and
are very similar to those observed in the salen-based tetra-lithium
§ Crystal data for 2a: C88H148Cl2Li6N4O9, M = 1518.72, triclinic, space
¯
˚
group P1, a = 12.829(12), b = 13.991(12), c = 15.454(12) A, a = 73.26, b =
◦
3
˚
73.76, g = 66.78 , Z = 1, V = 2385.8(2) A .
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for tetrahedral lithium compounds e.g. [Li(dmp)(thf)]4 (dmp =
˚
2,6-Me2C6H3O) (av. 2.078 A) and [Li4(ONep)4(thf)3] (ONep =
Me3CCH2O) (av. 1.982 A).10 Compound 1b has a similar structural
˚
motif like those found for tetra-lithium Schiff base complexes
also containing tetrahedral and trigonal-bipyramidal geometry
around metal centers.9 However, the structure of 1b markedly
differs from structures of lithium salts generated with the tripo-
dal [Me2NCH2CH2N(CH2-2,4-tBu2C6H2OH)2] ligand precursor,
the ortho and para sterically demanding analogue of H2L1
and H2L2. As was mentioned in Introduction, polymeric and
tetranuclear lithium structures created by [Me2NCH2CH2N(CH2-
2,4-tBu2C6H2OH)2] depending on reaction conditions have four-
coordinate lithium atoms, but they reside in different geometries,
tetrahedral and trigonal pyramidal.4,5
Compound 2b consists of two non-planar, six-membered
Li3O2Cl rings, with one ring rotated 180◦ relative to the other,
which are linked by four m3-oxygens of the L2 ligands and two
chlorides as displayed in Fig. 4. In this structure two lithium
atoms adopt a distorted trigonal-bipyramidal geometry formed
by two oxygens and the tripodal nitrogen of the L2 ligand
occupying equatorial positions and one chloride atom and the
second nitrogen of the L2 ligand situated in axial sites. The
remaining four lithium atoms reside in a distorted tetrahedral
environment coordinated by the Cl atom and three oxygen atoms:
two from the L2 ligand and one ether oxygen atom of the thf
Fig. 3 Molecular structure of 1b with thermal ellipsoids drawn at the
50% probability level. Hydrogen atoms are omitted for clarity. Selected
parameters (bonds, A; angles, ◦): Li1–N1 2.257(2), Li1–N2 2.325(2),
˚
Li1–O11 1.967(2), Li1–O21 2.034(2), Li2–O11 2.059(2), Li2–O21 1.931(2),
Li2–O31 1.994(2); N2–Li1–O11 141.52(10), N2–Li1–O21 123.10(10),
O11–Li–O21 93.71(9), O11–Li2–O31 136.05(10), O11–Li2–O21 94.04(9),
O21–Li2–O31 105.79(9).
˚
molecule. The Li1–(m3-O) and Li2–(m3-O) bond lengths of 1.947 A
(av.) are significantly shorter than the bond distances between
˚
Li3 to m3-O of 2.007 A (av.) due to the geometry around these
˚
lithium atoms in 2b. The Li–Othf distances of 2.002 A (av.) are
within statistical agreement with those in 1b and with Li–Othf
bond lengths of the literature compounds.10 The Li–N distances
˚
of 2.158(3) and 2.213(3) A exhibited by trigonal-bipyramidal
Li(3) are considerably shorter than those noted for 1b probably
because of the reduction in electron donation by the coordinated
chloride atom, and are markedly longer comparing to those
found in the lithium-diaminebis(aryloxide) compounds [2.024(6)–
2.129(5) A], containing tetrahedral lithium centers.4,5 The bridging
˚
m3-chloride atoms show Li–Cl bond lengths of 2.299(3), 2.320(3)
˚
and 2.761(3) A where the highest value, longer than in a pure LiCl
˚
crystal (2.57 A), can be a result of either the trans interaction
of chloride with nitrogen atom situated in axial positions, or
higher coordination number of Li3 atom than those of Li1 and
Li2. Incorporation of a chloride in place of an oxygen in lithium
aryloxide polynuclear structures is very rare, and so far, only four
examples have been known.11 In all those compounds the lithium
atoms are bound in a distorted tetrahedral geometry and together
with oxygen and chloride atoms are arranged in a distorted cubane.
The 1H NMR spectra of 2a and 2b are similar and fully consis-
tent with the solid-state structure established by crystallography
for 2b. They reveal the presence of only one set resonances of
protons due to the L1 and L2 ligands, respectively, and consist
of an AB system for the Ar–CH2–N methylene units (d 4.68
and 2.88 ppm in 2a, 4.62 and 2.84 ppm in 2b). Additionally
one of the two resonances assigned to the methylenic protons
of the NCH2CH2NMe2 unit is substantially shifted to higher
field compared to the ligand precursors (d 2.31 and 1.29 ppm
in 2a, 2.48 and 1.32 ppm in 2b, vs. 2.33 and 2.05 ppm in
H2L1, 2.51 and 2.48 ppm in H2L2) suggesting that the sidearm
NMe2 group is bound to the lithium atoms. By contrast, the
Fig. 4 Molecular structure of 2b·thf with thermal ellipsoids drawn at the
50% probability level. Hydrogen atoms bonded to carbon, the thf solvent
species and second position of disordered thf molecule are omitted for
˚
clarity. Selected bond lengths (A): Li1–O11 1.938(3), Li1–O41 2.013(5),
Li1–Cl1 2.320(3), Li2–O11 1.945(3), Li2–O31 1.991(3), Li2–Cl1 2.299(3),
Li3–O11 1.997(3), Li3–O21 2.016 (3), Li3–N1 2.158(3), Li3–N2 2.213(3),
Li3–Cl1 2.761(3).
9
˚
complexes. The Li1–N bond lengths of 2.257(2) and 2.325(2) A
in 1b are significantly longer than those found in the lithium
complexes with the [Me2NCH2CH2N(CH2-2,4-tBu2-C6H2O)2] lig-
and having tetrahedral lithium centers.4,5 The Li–Othf distance
˚
[1.994(2) A] is within the normal range reported in the literature
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1H NMR spectra of compounds 1a and 1b exhibit two sets of
resonances at room temperature signifying the presence of two
different species in solution in a ratio ~1 : 1 (Scheme 2). One set
of resonances with two close triplets assigned to the methylenic
protons of the NCH2CH2NMe2 unit (2.63 and 2.42 ppm in 1a¢,
2.53 and 2.48 ppm in 1b¢) like in the ligand precursors suggests the
dangling character of the sidearm NMe2 group. The second set
of resonances shows similar shifts of the corresponding protons
(2.31 and 1.56 ppm in 1a, 2.28 and 1.64 ppm in 1b) to those in
2a and 2b, confirming a coordination of the sidearm NMe2 to
lithium, in accordance with the ground-state structure established
by crystallography for 1b. These observations prove that structures
of 1a and 1b do not stay intact in solution and participate in a
advantage of the use of L2 ligand is moderate solubility of its
lithium complexes in organic solvents which results in their easy
isolation and crystal growth. The molecular structures of 1b, 2a
and 2b revealed that the lack of a substituent at ortho position
to the phenolic oxygen atom in the ligands L1 and L2 resulted in
distinctly different coordination geometry around lithium atoms
than their analogues reported in literature, containing both ortho
and para substituents. The presence of chloride atoms in 2a and
2b results in that their structures in the solid state are consistent
with solution NMR data, in contrast to the structures of 1a and
1b, which undergo equilibration with new species 1a¢ and 1b¢,
respectively.
The knowledge of the structures of the new diaminebis-
(aryloxido)lithium complexes will allow us to explore the synthetic
methodology for synthesis of low-valent vanadium complexes
which are currently under way in our laboratory.
3
facile equilibrium with [Li4(m-L1-k O,N,O)2(thf)2] (1a¢) and [Li4(m-
3
L2-k O,N,O)2(thf)2] (1b¢) species, respectively. The sidearm NMe2
unit in 1a¢ and 1b¢ is not coordinated to the lithium centers and
tetrahedral geometry around all metal centers is observed. In
addition, variable-temperature NMR studies (in CDCl3, from 223
to 323 K) on these systems exhibited significant differences in the
equilibrium shown in Scheme 2. At lower temperatures (below 273
K) mainly species 1a and 1b exist in solution and their conversion
to 1a¢ and 1b¢, respectively, increases with the temperature, leading
to almost complete absence of 1a and 1b at 323 K.
Experimental
General considerations
All operations were carried out under a dry dinitrogen atmosphere,
using standard Schlenk techniques. All the solvents were distilled
under dinitrogen from the appropriate drying agents prior to
use. The compounds 4-(1,1,3,3-tetramethylbutyl)phenol, p-cresol,
N,N-dimethylethylenediamine, paraformaldehyde and LiMe were
obtained from the Aldrich Chemical Co. and used without
further purification unless stated otherwise. Infrared spectra were
recorded on a Bruker 113v FTIR spectrophotometer in Nujol
mulls. NMR spectra were performed on a Bruker ARX 500 spec-
trometer. The electrospray mass spectra (ES-MS) were recorded on
a Bruker MicrOTOF-Q mass spectrograph. Microanalyses were
conducted with a ASA-1 (GDR, Carl-Zeiss-Jena) instrument (in-
house).
Synthesis of H2L1. A mixture of 4-(1,1,3,3-tetramethylbutyl)-
phenol (10 g, 48.5 mmol), paraformaldehyde (1.45 g, 48.5 mmol)
and N,N-dimethylethylenediamine (2.7 cm3, 24.3 mmol) in EtOH
(100 cm3) was stirred for 3 days at room temperature. A white
precipitate formed which was filtered off, washed with ice-cold
ethanol (3 ¥ 20 cm3), and dried in vacuo for 4 h to yield a fine
white powder (9.15 g, 72.0%). Anal. Calc. for C34H56N2O2: C,
77.80; H, 10.76; N, 5.34. Found: C, 77.60; H, 10.73; N, 5.33%.
1H NMR (500 MHz, CDCl3, 298 K): d 9.61 (br s, 2H, ArOH);
7.15–7.11 (m, 6H, C6H3); 3.54 (s, 4H, ArCH2N); 2.33 [t, 2H,
NCH2CH2N(CH3)2]; 2.05 [t, 2H, NCH2CH2N(CH3)2]; 1.99 [s,
6H, N(CH3)2]; 1.72 [s, 4H, C(CH3)2CH2C(CH3)3]; 1.39 [s, 12H,
C(CH3)2CH2C(CH3)3]; 0.81 (s, 18H, C(CH3)2CH2C(CH3)3]. 13C
NMR (500 MHz, CDCl3, 298 K): d 155.2, 139.7, 127.9, 127.4,
121.7, 116.7 (C6H3); 57.2 [NCH2CH2N(CH3)2], 56.0 (ArCH2N);
55.3 [C(CH3)2CH2C(CH3)3]; 55.7 [NCH2CH2N(CH3)2]; 48.8
[N(CH3)2]; 44.3 [C(CH3)2CH2C(CH3)3]; 37.6 [C(CH3)2-
CH2C(CH3)3]; 32.2 [C(CH3)2CH2C(CH3)3]; 31.7 [C(CH3)2-
CH2C(CH3)3]. ES-MS: m/z: 525.4 [H2L1 + H]+.
Scheme 2
It seems most likely that one of the reasons responsible for
instability of the structure of 1a and 1b in solution might be the
distinctly long Li–N distance of the sidearm NMe2 detected in 1b,
˚
longer by more than 0.1 A than in 2b and even more than found in
the lithium-diaminebis(aryloxide) compounds containing tetra-
hedral lithium centers.4,5 This confirms the stabilizing influence
of chloride in 2a and 2b on the trigonal-bipyramidal geometry
around lithium atoms ligated by tetradentate tripodal (ONNO)
ligands.
Conclusion
The diaminebis(aryloxido)lithium complexes 1a–2b of new
tetradentate tripodal (ONNO) ligands, comprising of different
substituents at position para to the phenolic oxygen atom,
C(CH3)2CH2C(CH3)3 in L1 and CH3 in L2 have been prepared
in good yields. Their structures, including also ligand precursors
H2L1 and H2L2, have been characterized both in solution (by
NMR spectroscopy) and in the solid state (except for 1a) by
X-ray determination, allowing to conclude that these substituents
do not cause a remarkable change in the lithium coordination
geometry and in structures of the ligand precursors. However the
Single crystals of H2L1 suitable for X-ray studies were grown
from a saturated solution in n-hexane at room temperature after
few days.
Synthesis of H2L2. The synthesis of the ligand precursor H2L2
was carried out using a similar preparation as for compound H2L1
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starting from p-cresol (18.88 g, 17.5 mmol), paraformaldehyde
(5.25 g, 17.5 mmol) and N,N-dimethylethylenediamine (9.56 cm3,
8.8 mmol) in MeOH (100 cm3). Compound H2L2 was isolated
as a white powder (21.77 g, 75.9%). Anal. Calc. for C20H28N2O2:
C, 73.12; H, 8.60; N, 8.53. Found: C, 73.01; H, 8.58; N, 8.51%.
1H NMR (500 MHz, CDCl3, 298 K): d 9.48 (br s, 2H, ArOH);
6.88–6.66 (m, 6 H, C6H3); 3.50 (s, 4H, ArCH2N); 2.51 [t, 4H,
NCH2CH2N(CH3)2]; 2.48 [t, 4H, NCH2CH2N(CH3)2]; 2.21 (s, 6H,
ArCH3); 2.14 [s, 6H, N(CH3)2]. 13C NMR (500 MHz, CDCl3,
298 K): d 154.5, 130.6, 129.9, 128.0, 122.1, 116.6 (C6H3); 56.2,
55.7, [NCH2CH2N(CH3)2]; 49.1 (ArCH2N) 44.8 [N(CH3)2]; 20.4
(ArCH3). ES-MS: m/z: 329.2 [H2L2 + H]+.
(C6H3); 67.9 (thf); 62.6 [NCH2CH2N(CH3)2]; 58.9 (NCH2Ar);
56.4 [C(CH3)2CH2C(CH3)3]; 50.2 [NCH2CH2N(CH3)2]; 44.9
[N(CH3)2]; 37.5 [C(CH3)2CH2C(CH3)3]; 32.6 [C(CH3)2-
CH2C(CH3)3]; 32.0 [C(CH3)2CH2C(CH3)3]; 31.9 [C(CH3)2CH2C-
(CH3)3].
Single crystals of 2a suitable for X-ray studies were grown from
a saturated solution in thf at room temperature after a few days.
Synthesis of [Li4(l-L2-j4O,N,N,O)2(thf)2] (1b). A solution of
MeLi (5.4 cm3, 8.72 mmol, 1.6 M in Et2O) was added dropwise
to a suspension of H2Li (1.43 g, 4.36 mmol) in thf (30 cm3)
at room temperature and the mixture was stirred for 16 h. A
small amount of white solid of 2b was then filtered off and the
filtrate was evaporated to dryness, leading to 1b as a colorless
solid (1.14 g; 63.3%). Anal. Calc. for C48H68Li4N4O6: C, 69.85;
Single crystals of H2L2 suitable for X-ray studies were grown
from a saturated solution in n-hexane at room temperature after
few days.
1
H, 8.31; N, 6.79. Found: C, 69.74; H, 8.29; N, 6.78%. H NMR
Synthesis of [Li4(l-L1-j4O,N,N,O)2(thf)2] (1a) and [Li6(l-L1-
j4O,N,N,O)2(l3-Cl)2(thf)4]·thf (2a·thf). To a solution of H2L1
(2.0 g, 3.90 mmol) in thf (50 cm3), precooled to 273 K was slowly
added MeLi (4.90 cm3, 7.80 mmol, 1.6 M in Et2O). The reaction
mixture was stirred at 273 K for 1 h and then at room temperature
for further 4 h. The volatile components were removed under
reduced pressure. The residue was redissolved in thf (20 cm3) and
allowed to stand overnight in a refrigerator. After a few days
colorless crystals of 2a were formed, which were filtered off and
dried in vacuo (0.24 g, 8.5%). Subsequent evaporation of thf from
the filtrate gave a white solid of 1a (2.07 g, 87.2%). Anal. Calc. for
C76H124Li4N4O6 (1a): C, 74.94; H, 10.27; N, 4.60. Found: C, 74.79;
H, 10.25; N, 4. 59%.
Anal. Calc. for C88H148Cl2Li6N4O9 (2a): C, 69.60; H, 9.83; Cl,
4.61; N, 3.69. Found: C, 69.48; H, 9.81; Cl, 4. 60; N, 3.68%.
1H NMR (500 MHz, CDCl3, 298 K) for 2a: d 6.88–6.41 (m, 12
H, C6H3); 4.68 (d, 4H, NCH2Ar); 3.58 (m, 20H, thf); 2.88 (d, 4H,
NCH2Ar); 2.31 (t, 4H, NCH2CH2NMe2); 1.72 (m, 20H, thf); 1.62
[s, 8H, C(CH3)2CH2C(CH3)3]; 1.46 [s, 24H, CH2C(CH3)2C(CH3)3];
1.29 [t, 4H, NCH2CH2N(CH3)2]; 1.21, 1.18 [s, 12H, N(CH3)2];
0.68 [s, 36H, C(CH3)2CH2C(CH3)3]. 13C NMR (500 MHz,
CDCl3, 298 K): d 163.7, 135.8, 128.4, 127.6, 119.2, 116.0
(C6H3); 67.9 (thf); 62.6 [NCH2CH2N(CH3)2]; 58.9 (NCH2Ar);
56.4 [C(CH3)2CH2C(CH3)3]; 50.2 [NCH2CH2N(CH3)2]; 44.9
[N(CH3)2]; 37.5 [C(CH3)2CH2C(CH3)3]; 32.6 [C(CH3)2-
CH2C(CH3)3]; 32.0 [C(CH3)2CH2C(CH3)3]; 31.9 [C(CH3)2-
CH2C(CH3)3].
(500 MHz, CDCl3, 298 K): d 6.88–6.39 (m, 24 H, C6H3); 4.17
(d, 2H, ArCH2N); 3.75 (d, 2H, ArCH2N); 3.61 (br t, 16H, thf);
3.42 (d, 2H, ArCH2N); 3.15 (d, 2H, ArCH2N); 2.53 [t, 4H,
NCH2CH2N(CH3)2]; 2.48 [t, 4H, NCH2CH2N(CH3)2]; 2.28 [t,
4H, NCH2CH2N(CH3)2]; 2.14, [s, 12H, ArCH3]; 2.10 [(s, 12H,
N(CH3)2]; 2.09 [s, 12H, ArCH3]; 1.74 (br pnt, 16H, thf); 1.64 (t, 4H,
NCH2CH2NMe2); 1.40 (s, 12H, N(CH3)2). 13C NMR (500 MHz,
CDCl3, 298 K): d 162.9, 130.4, 128.1, 127.4, 121.9, 118.6 (C6H3);
66.9 (thf); 61.0 [NCH2CH2N(CH3)2]; 57.7, 56.6 (NCH2Ar); 49.9
[NCH2CH2N(CH3)2]; 44.0, 43.6 [N(CH3)2]; 24.4 (thf); 19.3, 19.2
(ArCH3).
Crystals suitable for X-ray diffraction were obtained by dis-
solving 1b in warm n-hexane and allowing to stand at room
temperature for few days.
Synthesis of [Li6(l-L2-j4O,N,N,O)2(l-Cl)2(thf)4]·thf (2b·thf).
The synthesis of compound 2b was carried out using a similar
preparation as for 2a starting from H2L2 (1.40 g, 4.27 mmol),
MeLi (5.30 cm3, 8.54 mmol) and LiCl (0.18 g, 4.27 mmol) in thf
(30 cm3) (1.64 g, 68.3%). Anal. Calc. for C60H92Cl2Li6N4O9: C,
64.02; H, 8.24; Cl, 6.22; N, 4.98. Found: C, 63.87; H, 8.23; Cl,
1
6.21; N, 4.97%. H NMR (500 MHz, CDCl3, 298 K): d 6.71–
6.38 (m, 12 H, C6H3); 4.62 (d, 4H, NCH2Ar); 3.52 (m, 20H, thf);
2.84 (d, 4H, NCH2Ar); 2.31 [t, 4H, NCH2CH2N(CH3)2]; 2.11 [s,
12H, ArCH3]; 1.67 (m, 20H, thf); 1.47 (s, 12H, N(CH3)2); 1.32
(t, 4H, NCH2CH2NMe2). 13C NMR (500 MHz, CDCl3, 298 K):
d 164.0, 131.5, 129.1, 128.3, 122.9, 119.6 (C6H3); 68.0 (thf); 62.1
[NCH2CH2N(CH3)2]; 58.8 (NCH2Ar); 50.5 [NCH2CH2N(CH3)2];
45.0 [N(CH3)2]; 25.5 (thf); 20.2 (ArCH3).
Synthesis of [Li6(l-L1-j4O,N,N,O)2(l-Cl)2(thf)4]·thf (2a·thf)
by reaction of H2L, MeLi and LiCl. A suspension of H2L1 (1.0
g, 1.90 mmol) and LiCl (0.081 g, 1.91 mmol) in thf (50 cm3)
was precooled to 273 K and slowly added MeLi (2.4 cm3,
3.84 mmol, 1.6 M in Et2O). After 20 h of stirring at room
temperature, the reaction mixture was filtered to afford a white,
analytically pure solid of 2a (1.21 g, 84%). Anal. Calc. for
C88H148Cl2Li6N4O9: C, 69.60; H, 9.83; Cl, 4.61; N, 3.69. Found:
C, 69.49; H, 9.80; Cl, 4. 60; N, 3.68%. 1H NMR (500 MHz,
CDCl3, 298 K): d 6.88–6.41 (m, 12 H, C6H3); 4.68 (d, 4H,
NCH2Ar); 3.58 (m, 20H, thf); 2.88 (d, 4H, NCH2Ar); 2.31
(t, 4H, NCH2CH2NMe2); 1.72 (m, 20H, thf); 1.62 [s, 8H,
C(CH3)2CH2C(CH3)3]; 1.46 [s, 24H, CH2C(CH3)2C(CH3)3];
1.29 [t, 4H, NCH2CH2N(CH3)2]; 1.21, 1.18 [s, 12H, N(CH3)2];
0.68 [s, 36H, C(CH3)2CH2C(CH3)3]. 13C NMR (500 MHz,
CDCl3, 298 K): d 163.7, 135.8, 128.4, 127.6, 119.2, 116.0
Single crystals of 2b·thf suitable for X-ray studies were grown
from saturated solution in thf at room temperature.
X-Ray crystallography
Diffraction data for complexes H2L2 and 1a were collected on
a KM4 diffractometer with a CCD sapphire camera and for
2b·thf with graphite-monochromated Mo-Ka radiation (l =
12
˚
0.71073 A). All structures were solved by direct methods and
refined by full-matrix least-squares techniques on F2.13 All non-
hydrogen atoms were refined with anisotropic thermal parameters.
All H atoms were placed in geometrically calculated positions
and refined by using a riding model with Uiso set at 1.2Ueq(C)
for aromatic and formic H atoms, and 1.5Ueq(C) for methyl H
atoms. In the structures of 1a and 2b. some atoms of the THF
446 | Dalton Trans., 2012, 41, 442–447
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Table 1 Crystal data and structure refinement details for compounds H2L2, 1b and 2b·thf
Compound
H2L2
1b
2b·thf
Formula
Mr
C20H28N2O2
328.44
C48H68Li4N4O6
824.82
C56H84Cl2Li6N4O8·C4H8O
1125.92
Crystal system
Space group
Monoclinic
P21/c
Orthorhombic
Pbcn
11.397(3)
17.772(4)
22.892(5)
90.00
4636.7(19)
4
1.182
0.16 ¥ 0.15 ¥ 0.06
0.08
2.9–28.0
33997
5567
Monoclinic
C2/c
23.417(8)
12.217(4)
23.689(8)
109.91(5)
6372(4)
˚
a/A
14.820(3)
6.049(3)
21.294(5)
107.48(3)
1820.8(11)
4
1.198
0.42 ¥ 0.18 ¥ 0.05
0.08
3–27.5
12298
4128
0.035
˚
b/A
˚
c/A
b/◦
3
˚
V/A
Z
4
Dc/Mg m-3
1.174
0.19 ¥ 0.18 ¥ 0.17
0.16
2.9–30.0
29932
8667
0.048
410
Crystal size/mm
m/mm-1
q/◦
Reflections collected
Unique reflections
Rint
0.033
303
Parameters
229
Final R1, wR2 [I > s(I)]
Final R1, wR2 (all data)
Goodness-of-fit (S)
0.040, 0.090
0.070, 0.095
0.983
0.039, 0.103
0.054, 0.108
1.064
0.053, 0.113
0.087, 0.144
1.018
molecules were partially disordered and they were refinement
in two positions. Moreover, in 2b some molecules of THF
were refined with SAME instruction (C–C bond distances were
restrained to be the same as in corresponding solvent molecules).
Table 1 lists the key crystallographic parameters for H2L2, 1b and
2b·thf.
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Acknowledgements
The authors thank the State Committee for Scientific Research
(Poland) for financial support of this work (grant No N N204
028238).
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