Bis-imide derivatives of the heterometallic alkoxide Li4Ti 4O4(OiPr)12

Article abstract of DOI:10.1515/znb-2007-0325

The imide derivatives Li₄Ti₄O₂(NR) ₂(OⁱPr)₁₂ (R = CH₂C ₆H₅, C₆H₁₁, C₄H ₉) were obtained either by reaction of th

Full text of DOI:10.1515/znb-2007-0325

Note
487
Bis-Imide Derivatives of the
Heterometallic Alkoxide
i
Li4Ti4O4(O Pr)12
Helmut Fric and Ulrich Schubert
Institute of Materials Chemistry, Vienna University of
Technology, Getreidemarkt 9, A-1060 Wien, Austria
Scheme 1. The cluster core of Li4Ti2O2(OiPr)6 (1). The four
Reprint requests to Prof. Dr. U. Schubert.
Fax: +43-1-5880115399.
E-mail: Ulrich.Schubert@tuwien.ac.at
i
terminal OiPr ligands (one per Ti atom) and the Pr sub-
stituents of the bridging OiPr ligands were omitted for clarity.
The oxo ligands are drawn in bold letters.
Z. Naturforsch. 2007, 62b, 487 – 490;
received Sepetmber 4, 2006
In this article we describe the synthesis and struc-
tures of bis-imide derivatives of this cluster, where the
two µ2-oxo groups are replaced by µ2-NR groups.
Dedicated to Prof. Helgard G. Raubenheimer on the
occasion of his 65 th birthday
The imide derivatives Li4Ti4O2(NR)2(OiPr)12 (R =
CH2C6H5, C6H11, C4H9) were obtained either by reaction
of the amine adduct Ti2(OiPr)8(H2NR)2 with lithium di-
iso-propylamide or butyllithium, or when the primary amine
was first reacted with the base and then with Ti(OiPr)4. The
structures of the imide derivatives are the same as that of
Li4Ti4O4(OiPr)12 (= Li4Ti4(µ2-O)2(µ5-O)2(µ2-OiPr)4(µ3-
OiPr)4(OiPr)4) with the two µ2-oxo groups replaced by two
µ2-NR groups.
Results and Discussion
We obtained the bis-imide derivatives by two dif-
ferent synthesis protocols. In the first, benzylamine or
cyclohexylamine solutions in n-heptane were reacted
with one molar equivalent of lithium di-iso-propyl-
amide or butyllithium at −60 ◦C. One molar equivalent
of Ti(OiPr)4 was then added to this solution resulting
in a color change to dark yellow (with benzylamine) or
dark red (with cyclohexylamine). The solutions were
concentrated and stored at r. t. (cyclohexylamine reac-
Key words: Titanium Alkoxide Derivatives, Lithium
Alkoxide Derivatives, Imide Ligands
◦
tion) or at 4 C (benzylamine reaction). After a few
days mixtures of crystal were obtained which consisted
of colorless Li2Ti2(OiPr)10 [2] as the main product and
yellow Li4Ti4O2(OiPr)12(NR)2 (2a: R = CH2C6H5;
2b: R = C6H11) as a by-product. Li2Ti2(OiPr)10 was
identified by single crystal X-ray diffraction. The crys-
tals of 2a and 2b were separated manually.
Introduction
The heterometallic alkoxide Li4Ti4O4(OiPr)12 (1)
has been obtained previously by controlled hydrolysis
of Li2Ti2(OiPr)10 [1]. The interesting structure of this
compound can be described as a double (face-sharing)
cube of the composition Li4Ti2O2(OiPr)6 to which two
TiO(OiPr)3 units are condensed, or as six condensed
cubes with four missing corners (Scheme 1). The tita-
nium atoms within the double cube are six-coordinate,
while those outside are five-coordinate.
A formula taking the different bonding modes of
the oxo and alkoxo ligands into account is Li4Ti4(µ2-
O)2(µ5-O)2(µ2-OiPr)4(µ3-OiPr)4(OiPr)4. Each tita-
nium atom is bonded to a terminal OiPr ligand. The µ2-
OiPr, µ3-OiPr and µ5-oxo groups connect the lithium
and titanium atoms, while the µ2-oxo groups bridge
two titanium atoms.
In the second route, equimolar amounts of butyl-
amine and Ti(OiPr)4 were first reacted in n-heptane at
◦
−60 C. This resulted in the precipitation of the col-
orless amine adduct Ti2(OiPr)8(H2NC4H9)2, as pre-
viously described [3]. When a solution of one mo-
lar equivalent of lithium di-iso-propylamide or butyl-
lithium was slowly added, the color of the solution
again changed to yellow. The solution was concen-
trated and stored at 4 ◦C. After three days, dark yellow
crystals of Li4Ti4O2(OiPr)12(NBu)2 (2c) in a matrix of
Li2Ti2(OiPr)10 [2] were obtained.
The structures of the bis-imide derivatives 2a – c
were determined by single crystal X-ray diffraction.
The centrosymmetric clusters have the same overall
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488
Note
and 102.21(11)◦), compared to the Ti–O–Ti angles in
1 (107.0(1)◦), compensate to some extent the structural
influence of the longer Ti–N bonds.
The geometry of the clusters results in an un-
usual (distorted) trigonal pyramidal coordination of
the lithium atoms, with the µ5-O(1) in the apical po-
Table 1. Selected bond lengths (pm) and angles (deg) in 2a
(atoms with an asterisk denote inversion-related atoms).
Ti(2)–O(1)
Ti(2)–O(1)*
Ti(2)–N(1)
Ti(2)–O(2)
Ti(2)–O(3)
Ti(2)–O(5)
Ti(1)–O(1)
Ti(1)–N(1)
Ti(1)–O(4)
Ti(1)–O(7)
Ti(1)–O(6)
Li(1)–O(3)*
Li(1)–O(5)
Li(1)–O(6)
Li(1)–O(1)
Li(2)–O(5)
Li(2)–O(3)*
Li(2)–O(7)*
Li(2)–O(1)*
201.1(1)
214.5(1)
195.5(2)
180.3(1)
201.9(1)
203.9(1)
200.3(1)
190.2(2)
181.4(1)
194.3(1)
192.8(1)
191.1(3)
200.8(3)
192.4(3)
204.7(3)
190.8(3)
200.3(3)
191.4(3)
203.5(3)
O(1)–Ti(2)–O(1)*
O(3)–Ti(2)–O(5)
O(1)–Ti(2)–O(2)
N(1)–Ti(2)–O(2)
N(1)–Ti(2)–O(1)
N(1)–Ti(2)–O(1)*
N(1)–Ti(1)–O(1)
N(1)–Ti(1)–O(4)
O(1)–Ti(1)–O(4)
O(7)–Ti(1)–O(6)
N(1)–Ti(1)–O(6)
N(1)–Ti(1)–O(7)
Ti(1)–N(1)–Ti(2)
Ti(2)–O(1)–Ti(1)
O(3)*–Li(1)–O(1)
O(5)–Li(1)–O(1)
O(6)–Li(1)–O(1)
O(5)–Li(2)–O(1)*
O(3)*–Li(2)–O(1)*
O(7)*–Li(2)–O(1)*
76.55(5)
165.71(5)
178.54(5)
98.72(7)
79.82(6)
156.26(7) sition. The Li–µ5-O distances in 2a – c are in the
81.29(6)
100.34(7)
178.15(6)
132.58(6)
110.92(6)
112.61(6)
102.12(7)
96.74(5)
89.1(1)
87.0(1)
83.8(1)
88.7(1)
86.6(1)
range 201.3(4)– 204.7(3) pm, compared to 201.7(3)–
203.5(3) pm in 1. The Ti–OiPr distances in 2a – c and 1
do not differ significantly.
The Ti2O2 ring in the center of the clusters is formed
by the octahedrally coordinated Ti atoms (Ti(2) in
2a) and the µ5-oxo groups (O(1) in 2a). The pro-
nounced asymmetry of the Ti–O distances in this ring
of 197.6(2)– 201.1(1) vs. 214.2(2)– 220.3(2) pm in
2a – c (compared with 200.1(2) vs. 205.0(2) pm in 1)
is probably a consequence of the imide substituent,
which is trans to the longer Ti–O bond. The coordina-
tion octahedra of the central titanium atoms are com-
pleted by one terminal and two µ3-OiPr ligands. The
correspondingTi–O distances in 1 and 2a – c are nearly
the same.
83.8(1)
The outer titanium atoms are only 5-coordinate. The
axial positions of the (distorted) trigonal bipyramid
are occupied by the µ5-O atom and the terminal OiPr
group. The Ti–µ5-O distances of 2a – c (200.3(1)–
201.8(2) pm) are shorter than the corresponding dis-
tance in 1 (206.3(1) pm). Since the nitrogen atom is
located in the trigonal plane, the difference in bond
lengths is less pronounced than for the octahedral Ti
Fig. 1. Molecular structure of Ti4Li4O2(OiPr)12(NCH2- atoms. The bond angles at the Ti atoms in 1 and 2a – c
C6H5)2 (2a).
are very similar.
NMR spectroscopic investigations in solution were
only performed with 2a, because the solubility of 2b
and 2c was not high enough to obtain meaningful spec-
tra. However, the NMR data fully corresponded to
the solid state structure. Four sets of signals were ob-
served for the OiPr groups according to the molecu-
lar symmetry. The ratio of the signal intensities was
2 : 2 : 1 : 1 for four µ3-OiPr, four µ2-OiPr and 2 × 2
chemically different terminal OiPr groups. The CH
signal of the µ3-OiPr units appears at lowest field at
4.87 (13C 72.5) ppm, and the CH signal at highest field
(at 4.24 ppm; 13C 67.8 ppm) can be assigned to the
µ2-OiPr groups.
structure as the parent compound Li4Ti2O2(OiPr)6 (1)
(Scheme 1); only the µ2-oxo groups are replaced by
µ2-NR groups. The structure of 2a is shown in Fig. 1,
that of 2b and 2c are very similar. Selected bond
lengths and angles are given in Table 1.
Replacement of the µ2-oxo by µ2-NR groups re-
sults in only a slight distortion of the structure, be-
cause the Ti–N distances are somewhat longer than
the corresponding Ti–O distances in 1. Thus, the Ti–N
distances in 2a are 195.5(2) pm for Ti(2)–N(1) and
190.2(2) pm for Ti(1)–N(1), and the corresponding
distances in 2b and 2c are 194.9(2)/193.6(2) pm and
190.7(2)/193.6(2) pm, while the corresponding Ti–O
distances in 1 are 189.0(2) and 179.9(2) pm. The
longer distances correspond to the 6-coordinate Ti
atoms and the shorter ones to the 5-coordinate. The
Conclusions
The structures of the three Li4Ti4O2(NRꢀ)2(OiPr)12
smaller Ti–N–Ti angles in 2a – c (102.12(7), 101.33(9) derivatives (2) with different NR ligands reported in
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Note
489
this work are very similar to that of Li4Ti4O4(OiPr)12 ring, followed by the addition of 519 mg (1.83 mmol) of
Ti(OiPr)4. The pale brown solution was allowed to reach r. t.
(1) [1]. The two µ2-O groups of 1 were replaced by µ2-
within 1 h and was then concentrated to half its volume. Col-
orless crystals of Li2Ti2(OiPr)10◦ [2] and yellow crystals of
2a were obtained after 6 d at 4 C. The crystals of 2a were
separated manually. – 1H NMR (CD2Cl2, 21 ◦C) δ = 7.62 –
7.16 (m, C6H5), 5.83 (s, NCH2Ph), 4.87, 4.72, 4.32, 4.24
(m, OCHMe2), 1.27, 1.22, 1.17, 1.08 ppm (d, J = 6.1 Hz,
NR ligands. This modification of the cluster has only
little consequences on the structural and geometric pa-
rameters.
The imide-substituted clusters were reproducibly
obtained as by-products when the amine adduct
Ti2(OiPr)8(H2NC4H9)2 was reacted with a strong base
(LiNiPr2 or LiBu), or when benzylamine or cyclo-
hexylamine were first reacted with the base and then
with Ti(OiPr)4. The main product in each case was
Li2Ti2(OiPr)10 [2]. This leads to the conclusion that
the reaction sequence is probably rather complex, and
one can only speculate about potential intermediates in
the formation of 2.
1
OCH(CH3)2). – 13C{ H} NMR (CD2Cl2, 21 ◦C) δ = 127.4,
127.1, 124.9 (C6H5), 74.0, 73.9, 72.5, 67.8 (OCHMe2), 28.4,
27.6, 27.0, 26.1 (OCH(CH3)2) ppm. – 7Li-NMR (CD2Cl2,
21 ◦C) δ = 0.5 ppm.
Synthesis of Li4Ti4O2(O iPr)12(NC6H11)2 (2b)
An amount of 264 mg (2.66 mmol) of cyclohexyl-
amine (Aldrich 99 %, used as received)◦ was dissolved in
10 mL of n-heptane and cooled to −60 C. Then 1.48 mL
(2.61 mmol) of lithium di-iso-propylamide (1.8 M solution
in THF/heptane/ethylbenzene) was added slowly with stir-
ring, followed by the addition of 761 mg (2.67 mmol) of
Ti(OiPr)4. The dark red solution was allowed to reach r. t.
within 1 h and was then concentrated to half its volume. Col-
Li4Ti4O4(OiPr)12 was obtained by controlled hy-
drolysis of Li2Ti2(OiPr)10 [1]. The source of the oxo
groups in 2 is less obvious. Unintentional hydroly-
sis can be ruled out for several reasons. First, the
imide derivatives were reproducibly obtained in sev-
eral runs. Second, if water would be present, the strong
bases lithium di-iso-propylamide or butyllithum would
orless crystals of Li2Ti2(OiPr)10 [2] and yellow prismatic
◦
preferentially react with water and would thus re- crystals of 2a were obtained after 3 d at 4 C. The crystals
of 2b were separated manually.
move water from the system. It is very unlikely that
imide groups would be formed in the presence of
water. Third, 2 was obtained independent of whether
Ti(OiPr)4 was added before or after addition of the
base. Thus, the only reasonable source of the oxo
groups are the OR groups. Possible routes would be
the abstraction of an iPr group from an OiPr ligand (be-
ing activated by coordination to one or more Ti atoms)
with concomitant formation of tri-iso-propylamine, or
the elimination of di-iso-propylether. Non-hydrolytic
sol-gel processes (i. e. the formation of oxo groups
Synthesis of Li4Ti4O2(O iPr)12(NC4H9)2 (2c)
An amount of 131 mg (1.79 mmol) of 1-butylamine
(Aldrich 99.5 %, used as received) was added to a solution
of 485 mg (1.71 mmol) of Ti(OiPr)4 in 6 mL of n-heptane at
r. t. with stirring. Cooling of the reaction solution to −40 ◦C
led to the precipitation of a white solid. Then 0.95 mL
(1.67 mmol) of lithium di-iso-propylamide (1.8 M solution
in THF/heptane/ethylbenzene) was added slowly through a
rubber septum under stirring. The solution was allowed to
from metal alkoxides in the absence of water) are well reach r. t. within 1 h and was then concentrated to half its
volume. Colorless crystals of Li2Ti2(OiPr)10 [2] and yellow
known [4].
plate-like crystals of 2c were obtained after 3 d at 4 ◦C. The
crystals of 2c were separated manually.
Experimental Section
All operations were carried out in a moisture- and oxygen-
free argon atmosphere using the Schlenk technique. All sol-
vents were dried by standard methods. Ti(OiPr)4 (Aldrich,
97 %) was used as received.
X-Ray structure analyses
Data collection (Table 2): The crystals were mounted on a
Siemens SMART diffractometer (area detector) and measured
in a nitrogen cryo-stream. MoKα radiation (λ = 71.069 pm,
graphite monochromator) was used for all measurements.
The data collection at 173 K covered a hemisphere of the
Synthesis of Li4Ti4O2O iPr12(NCH2C6H5)2 (2a)
An amount of 196 mg (1.83 mmol) of benzylamine reciprocal space, by a combination of three or four sets of
(Aldrich 99 %, used as received) was dissolved in 5 mL exposures. Each set had a different φ angle for the crystal,
of n-heptane and cooled to −40 ◦C. Then 1.14 mL and each exposure took 20 s and covered 0.3◦ in ω. The
(2.01 mmol) of lithium di-iso-propylamide (1.8 M solution crystal-to-detector distance was 5 cm. The data were cor-
in THF/heptane/ethylbenzene) was slowly added with stir- rected for polarization and Lorentz effects, and an empirical
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490
Note
Table 2. Crystal-
lographic data of
2a – 2c.
2a
2b
2c
Empirical formula
Formula weight
Crystal system
Space group
a [pm]
Ti4Li4O2(OiPr)12(NCH2C6H5)2 Ti4Li4O2(OiPr)12(NC6H11
)
2
Ti4Li4O2(OiPr)12(NC4H9)2
1102.5
1170.7
1154.7
triclinic
triclinic
monoclinic
C2/c
2183.4(1)
1132.29(6)
2668.3(1)
90
112.612(1)
90
6089.5(6)
4
¯
¯
P1
P1
1143.24(8)
1222.82(8)
1355.48(9)
65.686(1)
89.888(1)
66.839(1)
1558.5(2)
1
1143.27(7)
1205.37(7)
1383.74(8)
66.457(1)
89.002(1)
63.157(1)
1528.5(2)
1
b [pm]
c [pm]
α [deg]
β [deg]
γ [deg]
V [pm3 ·106]
Z
Calcd. density [g cm−3] 1.247
1.254
1.203
Abs. coeff. µ [mm−1
θ Range [deg]
Crystal size [mm]
Refl. coll. / unique
Data / parameters
R(I ≥ 2s(I))
]
0.551
0.560
0.559
2.13 – 25.00
0.08×0.05×0.05
16111 / 5459
5459 / 334
0.033
0.090
1.051
2.02 – 25.00
0.12×0.07×0.05
13508 / 5377
5377 / 325
0.038
0.063
0.902
2.02 – 25.00
0.09×0.04×0.03
16065 / 5306
5306 / 302
0.049
0.125
0.977
wR2(I ≥ 2s(I))
GOF
−3
˚
∆ρ max / min [e A
]
0.408 / −0.328
0.704 / −0.363
0.509 / −0.777
absorption correction (SADABS) was employed. The cell di-
mensions were refined with all unique reflections.
Crystallographic data (excluding structure factors) have
been deposited with the Cambridge Crystallographic Data
The structures were solved by the Patterson method Centre (CCDC 619579 (2a), CCDC 619580 (2b) and CCDC
(SHELXS-97). Refinement was performed by the full- 619581 (2c)). Copies of the data can be obtained via
matrix least-squares method based on F2 (SHELXL-97) with www.ccdc.cam.ac.uk/data request/cif.
anisotropic thermal parameters for all non-hydrogen atoms.
Acknowledgements
Hydrogen atoms were inserted in calculated positions and
refined riding with the corresponding atom. In 2c one OiPr
This work was supported by the Fonds zur Fo¨rderung der
group was strongly disordered and was therefore refined us-
ing geometric restraints (DFIX, DANG).
wissenschaftlichen Forschung (FWF), Austria. The authors
thank Dr. Michael Puchberger for the NMR investigations.
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