Titanium(IV) Complexes Based on Tridentate N,N,O Ligands - Synthesis, Structure, and Thermal Decomposition

Article abstract of DOI:10.1002/ejic.201500881

New tridentate N,N,O-type ligands MeN(CH₂CH₂NHTs)(CH₂CR₂OH) [Ts = tosyl; R = H, 6, (N,N,O^H)H₂; R = Ph, 7 (N,N,O^Ph)H₂] were prepared. The corresponding diisopropoxide c

Full text of DOI:10.1002/ejic.201500881

FULL PAPER
DOI:10.1002/ejic.201500881
Titanium(IV) Complexes Based on Tridentate N,N,O
Ligands – Synthesis, Structure, and Thermal
Decomposition
Valeriy S. Cherepakhin,[a] Kirill V. Zaitsev,*[a] Yuri F. Oprunenko,[a]
Andrei V. Churakov,[b] Elmira Kh. Lermontova,[b]
Galina S. Zaitseva,[a] and Sergey S. Karlov[a]
Keywords: Titanium / N,N,O ligands / Thermochemistry / Sulfonamides / Amino alcohols
New tridentate N,N,O-type ligands MeN(CH2CH2NHTs)-
(CH2CR2OH) [Ts = tosyl ; R = H, 6, (N,N,OH)H2; R = Ph, 7
(N,N,OPh)H2] were prepared. The corresponding diisoprop-
oxide complexes (N,N,OH)Ti(OiPr)2 (8) and [N,N,OPh]Ti-
(OiPr)2 (9) were obtained through the reactions of 6 and 7
with Ti(OiPr)4. These complexes are thermally unstable and
transform into the bisligated complexes [N,N,OH]2Ti (10) and
{[N,N,OPh]Ti(OiPr)}2O (11). The molecular structures of 10
and 11 were investigated by X-ray diffraction analysis. The
synthesis of 11 from 9 as a thermal decomposition process
was studied.
Introduction
Titanium complexes based on tridentate alkoxide O,N,O-
type ligands have a range of applications as catalysts in
organic synthesis,[1] initiators for alkene[2,3] or lactone[4,5]
polymerization, and precursors for nanomaterials.[6] The
most characteristic ligand structures, including aminodi-
alcohols,[1a,3b,3c,7] aminophenols,[8] 2,6-bis(alkylhydroxy)-
pyridines,[9] aminodiphenols,[10] and pyridinediphen-
ols,[3d,11] are presented in Scheme 1.
Scheme 2. Nitrogen-containing polydentate ligands used for Ti
complexes.
On the contrary, tridentate N,N,O ligands have only been
investigated superficially, and no isolated complexes of
these ligands have been reported.[14] This is because the cor-
responding complexes are usually obtained in situ and used
in catalysis without purification.[12e,12h,15] Therefore, it
would be a promising scientific ambition to investigate the
properties and structures of metal complexes containing
N,N,O ligands. Like the related derivatives described above
(Schemes 1 and 2), such complexes could be used widely as
catalysts.
Scheme 1. Polydentate aminoalcohol ligands used for the synthesis
of Ti complexes.
For the synthesis of simple alkoxides (OEt, OPr) of vari-
ous metals (Ba, rare-earth elements, Ti, Zr, Hf, Bi, Nb, Ta,
Mo, W, U, Al, Re, Cu, and Pb),[16] the corresponding oxo-
alkoxides (M–O–M or M=O fragments) may be formed as
products of oxidation or thermolytic decomposition [with
the formation of volatile alcohols,[17] ethers (Bradley reac-
tion),[18] aldehydes, saturated[19] or unsaturated hydro-
carbons,[20] and chloroalkanes][21] and not of occasional
hydrolysis.[22] Very often, such processes may proceed even
at room temperature. The appearance of an oxo group in
these cases is not occasional because the yields of the iso-
lated products are high and the experiments are reproduc-
Titanium complexes based on bidentate N,O[12] and tri-
dentate N,N,N ligands[13] have also been prepared and char-
acterized fully (Scheme 2).
[a] Chemistry Department, Moscow State University,
B-234 Leninskie Gory, 1, 3, 119991 Moscow, Russia
E-mail: zaitsev@org.chem.msu.ru
http://www.chem.msu.ru/eng/welcome.html
[b] N.S. Kurnakov Institute of General and Inorganic Chemistry,
Russian Academy of Science,
Leninskiipr., 31, 119991 Moscow, Russia
Supporting information and ORCID(s) from the author(s) for
this article are available on the WWW under http://dx.doi.org/
10.1002/ejic.201500881.
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ible. Therefore, the destruction of homoleptic alkoxides
through the formation of an oxo group is well-known.
These oxoalkoxides are actively used as precursors of oxide
materials in sol–gel technology[23] and modern nano-
technology.[24]
For titanium alkoxides (homoleptic alkoxides[18b,25] or
complexes of polydentate ligands),[8,26] controlled hydrolysis
is usually regarded as a route to Ti oxoalkoxides, although
some authors still consider oxoalkoxides as products of un-
controlled (random) hydrolysis[27] or simply do not discuss
the appearance of the oxo groups. There are several cases
of oxidative[25d] or thermal decomposition of simple Ti alk-
oxides [such as Ti(OEt)4 in an autoclave],[18b] and there are
no such examples so far for Ti alkoxides with polydentate
ligands. Furthermore, no correlation between the nature of
the alkoxide group and the nature of the decomposition
products has been investigated.
Scheme 4. The synthesis of 2 and 5.
In this article, we present the synthesis of N,N,O-type
ligands (6 and 7) and several titanium complexes (8–11)
based on them. The goals of the work were to study the
structures of the complexes obtained and to define how the
ligand structure influences the thermal decomposition of
the Ti diisopropoxide complexes (8 and 9).
tiplet or triplet, δ = 2.40–3.00 ppm), and p-C6H4 (usually
two doublets, δ = 7.20–7.30 and 7.60–7.80 ppm) groups
have signals at characteristic fields. A similar situation is
observed in the 13C NMR spectra for the NMe (δ = 40.0–
42.0 ppm) and p-C6H4Me groups (δ = 21.4, 127.1, 129.6,
136.7, 143.2 ppm). In the IR spectra of 6 and 7, the typical
bands[33] of the NH/OH groups appear at ν = 3220, 3480,
and 3312 cm–1. The bands of the symmetric stretching vi-
brations of the sulfonamide groups (νs SO2N) are observed
at ν = 1169 and 1161 cm–1, and the asymmetric stretching
vibrations (νas SO2N) are at ν = 1335, and 1316 cm–1.
Results and Discussion
Synthesis of the Ligands
In the course of the work, two new ligands (6 and 7) were
obtained through the nucleophilic ring-opening reaction of
N-tosylaziridine (2) and monoethanolamine derivatives (5
and 5a, Scheme 3).
Synthesis of the Titanium Complexes
Two new Ti diisopropoxide complexes (8 and 9) were
prepared from equimolar amounts of Ti(OiPr)4 and the li-
gands (6 and 7) in anhydrous toluene (or CH2Cl2) under
argon (Scheme 5).
Scheme 3. The synthesis of ligands 6 and 7.
This reaction is very convenient because pure ligands can
be obtained quantitatively without chromatographic purifi-
cation. It should be underlined that these ligands differ
greatly in terms of steric volume. 2-(Methylamino)ethanol
(5a) is a commercially available compound, whereas the
sterically hindered diphenyl-substituted ethanolamine 5[28]
Scheme 5. The synthesis of 8 and 9.
The acidity of the NHTs (Ts = tosyl) group is sufficient
was prepared from ethyl glycinate hydrochloride in two for the reaction of the free ligands 6 or 7 and Ti(OiPr)4 to
steps from 3[29] and 4 (Scheme 4).[30] N-Tosylaziridine (2) proceed at room temperature to evolve 2-propanol.[34] The
was prepared from 1[31] according to reported procedures reaction mixtures were stirred for 10 h, the solvent was re-
with slight modifications.[31a,31b,31d,31e,31g,32]
moved, and the complexes were obtained as colorless li-
All of the compounds were isolated in the pure state and quids, which are soluble in toluene and chloroform and in-
1
characterized by H and 13C NMR spectroscopy (see Ex- soluble in hexane. The compositions of 8 and 9 were estab-
1
perimental Section). The compositions of 6 and 7 were de- lished on the basis of H and 13C NMR spectroscopy (ad-
termined by elemental analysis. Compounds 6 and 7 were mixtures with 10 and 11 were observed, respectively) and
isolated as colorless powders, which are soluble in EtOH, MALDI mass spectrometry. A more detailed investigation
CHCl3, and PhMe but insoluble in hexane. In the 1H NMR of complexes 8 and 9 is complicated by their high lability
spectra, the NMe (singlet, δ = 1.90–2.10 ppm), NCH2 (mul- and sensitivity.
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Only one set of signals was observed in the NMR spectra moved several times in vacuo with heating to remove 2-
of 8 and 9. The broadened signals of the OiPr, Ph, and CH2 propanol.
1
groups in the H NMR spectrum of 9 (the signals of the
Complexes 10 and 11 were isolated as colorless powders,
OiPr and Ph groups are broad even in the 13C NMR spec- which are soluble in tetrahydrofuran (THF) and CHCl3,
trum) indicate that dynamic processes occur in solution, slightly soluble in toluene, and insoluble in hexane. They
1
which are related to the examples established previous- were characterized by H NMR, 13C NMR, and IR spec-
ly.[3b,13g] Furthermore, the variation of the temperature in troscopy, and their compositions were confirmed by ele-
various NMR experiments affects the signals of the OiPr mental analysis and MALDI mass spectrometry.
1
and Ph groups in H NMR spectrum of 9 (see Supporting
Information). Clearly, this is caused by the rapid exchange
Structural Investigation of 10 and 11
between the equatorial and axial Ti–OiPr groups and the
exchange between the diastereotopic Ph groups. A similar
situation was observed for 8. From the previously reported
data,[35] it may be proposed that no (S)OǞTi coordination
occurs in 8 and 9 for five-coordinate Ti complexes.
We tried to recrystallize 8 and 9 from toluene, but instead
of isolating them in pure form, we obtained the new Ti
complexes 10 and 11, respectively, which precipitated from
toluene (Scheme 6).
The solid-state structures of 10 (Figure 1) and 11 (Fig-
ure 2) were investigated by X-ray analysis (Table 1).
Figure 1. Molecular structure of 10. Hydrogen atoms are omitted
for clarity. Displacement ellipsoids are shown at 50% probability
level. Selected bond lengths [Å] and angles [°]: Ti(1)–O(2)
1.8313(11), Ti(1)–O(1) 1.8439(11), Ti(1)–N(2) 2.0740(13), Ti(1)–
N(4) 2.1194(13), Ti(1)–N(1) 2.3285(13), Ti(1)–N(3) 2.3460(13);
O(2)–Ti(1)–O(1) 97.92(5), O(2)–Ti(1)–N(2) 93.41(5), O(1)–Ti(1)–
N(2) 144.27(5), O(2)–Ti(1)–N(4) 143.47(5), O(1)–Ti(1)–N(4)
94.99(5), N(2)–Ti(1)–N(4) 95.72(5), O(2)–Ti(1)–N(1) 94.43(5),
O(1)–Ti(1)–N(1) 74.35(5), N(2)–Ti(1)–N(1) 71.07(5), N(4)–Ti(1)–
N(1) 121.99(5), O(2)–Ti(1)–N(3) 75.16(5), O(1)–Ti(1)–N(3)
88.81(5), N(2)–Ti(1)–N(3) 126.89(5), N(4)–Ti(1)–N(3) 71.09(5),
N(1)–Ti(1)–N(3) 158.96(5).
Scheme 6. The structures of 10 and 11.
We developed procedures for the preparative synthesis of
10 and 11. Complex 10 was prepared in good yield through
the reaction of Ti(OiPr)4 and 2 equiv. of 6. Complex 11 was
prepared in satisfactory yield by the reaction of equimolar
amounts of Ti(OiPr)4 and 7 (Scheme 7). In both cases, we
used prolonged reflux in toluene, and the toluene was re-
Complex 10 is mononuclear in the solid state owing to
the formation of two intramolecular TiǟN coordination
bonds. The coordination sphere of the Ti atom may be de-
scribed as a distorted octahedron. The two N,N,O ligands
are of meridional disposition [the angle between the N(2)–
Ti–O(1) and N(4)–Ti–O(2) planes is 88.59(8)°], which is
atypical for ligands with an sp3-hybridized coordinative N
atom and usually observed for sterically voluminous ligands
or compounds with sp2-hybridized N atoms. By comparing
10 and the closely related [MeN(CH2CH2O)2]2Ti,[7a] it is
established that the substitution of an O atom by a NTs
group decreases the Ti–O (1.838 vs. 1.861 Å) and Ti–N
(2.337 vs. 2.422 Å) bond lengths; this decrease may be ex-
plained by the change of geometry (fac to mer) or the in-
creased Lewis acidity of the Ti atom in sulfonamide deriva-
tives in comparison with those in dialkanolamine com-
pounds. The Ti–O [average 1.838(1) Å] and TiǟN bond
lengths are close those in the related Ti mer complex
Scheme 7. The synthesis of 10 and 11.
erythro-[MeN(CH2CH2O)(CHPhCHPhO)]2Ti
(average
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1.875 and 2.325 Å),[7c] and the Ti–NSO R (bond lengths
2
2.0740 vs. 2.099 Å) are close to that in the related diethyl-
enetriamine complex [N(CH2CH2OMe)(CH2CH2NMs)]-
Ti(OiPr)2.[13g] It should be noted that such a relative ligand
arrangement makes the complex chiral. As both enantio-
¯
mers are present in the crystal, the complex is racemic (P1
group, Z = 2). The Ti–N coordination bonds [Ti–N(1), Ti–
N(3), average 2.337(1) Å] are longer than the covalent
bonds [Ti–N(2), Ti–N(4), average 2.097(1) Å], as expected.
The substituents at the covalently bonded N(2) and N(4)
atoms are almost planar (the average sum of angles at N is
358.60°), unlike those at the N(1) and N(2)atoms, which are
tetrahedral, as is typical for effective N–S conjugation.
There is one set of signals in the NMR spectra of 10,
including a multiplet for the diastereotopic protons of the
CH2 groups. According to these data, it may be stated that
10 exists in solution as a single geometric isomer with
strong NǞTi coordination and that the overall complex
possesses high symmetry (as in the solid state) with two
equivalent ligand fragments.
Complex 11 is dinuclear and contains two Ti atoms
bridged by a μ-O atom (Ti–O–Ti fragment). The coordina-
tion sphere of Ti is a distorted octahedron; each Ti atom is
bound to a tridentate N,N,O ligand, an OiPr group, a μ-O
atom, and an O atom of the SO2N group of another ligand.
The N,N,O ligand adopts a mer disposition [the O(11)–Ti–
N(12) angle is 149.00/149.67°]. The μ-O atom occupies the
trans position to the N(Me) atom, and the O(iPr) atom is
trans to the O(SO) atom. Both Ti atoms are chiral and have
the same configuration, but the other enantiomer is also
Figure 2. Molecular structure of 11. Hydrogen atoms and the tolu-
ene molecule are omitted for clarity. Displacement ellipsoids are
shown at 50% probability level. Selected bond lengths [Å] and
angles [°]: Ti(1)–O(12) 1.772(2), Ti(1)–O(1) 1.810(2), Ti(1)–O(11)
1.844(2), Ti(1)–N(12) 2.105(3), Ti(1)–N(11) 2.272(3), Ti(1)–O(23)
2.390(2), O(1)–Ti(2) 1.800(2), O(14)–Ti(2) 2.306(2), Ti(2)–O(22)
1.799(2), Ti(2)–O(21) 1.837(2), Ti(2)–N(22) 2.135(3), Ti(2)–N(21)
2.273(3);
100.69(11), O(1)–Ti(1)–O(11) 101.08(10), O(12)–Ti(1)–N(12)
95.95(11), O(1)–Ti(1)–N(12) 99.95(10), O(11)–Ti(1)–N(12)
O(12)–Ti(1)–O(1)
104.10(10),
O(12)–Ti(1)–O(11)
149.00(10), O(12)–Ti(1)–N(11) 98.00(10), O(1)–Ti(1)–N(11)
157.84(10), O(11)–Ti(1)–N(11) 76.09(9), N(12)–Ti(1)–N(11)
75.83(10), O(12)–Ti(1)–O(23) 175.31(10), O(1)–Ti(1)–O(23)
79.06(9), O(11)–Ti(1)–O(23) 81.94(9), N(12)–Ti(1)–O(23) 79.99(9),
N(11)–Ti(1)–O(23) 78.78(9), Ti(2)–O(1)–Ti(1) 141.06(12).
¯
present (crystallographic cell; P1 group, Z = 2), and the
crystal is racemic. In general, the complex belongs to the
C2 point group.
Table 1. The crystallographic data for 10 and 11.
10
11
Empirical formula
Mw
C24H36N4O6S2Ti
588.59
C54H66N4O9S2Ti2·C7H8
1167.16
Temperature [K]
Size [mm]
Crystal system
Space group
173(2)
120(2)
0.25ϫ0.16ϫ0.06
triclinic
0.08ϫ0.05ϫ0.03
triclinic
¯
P1
¯
P1
a [Å]
b [Å]
c [Å]
α [°]
10.1029(11)
10.1300(11)
14.8493(16)
98.735(2)
109.8370(10)
105.9760(10)
1322.8(2)
13.7570(11)
14.0948(11)
16.2924(12)
79.1500(10)
81.5540(10)
73.7640(10)
2964.0(4)
β [°]
γ [°]
V [Å3]
Z
2
2
ρcald [gcm–3]
1.478
0.529
620
1.308
0.398
1232
Absorption coefficient [mm–1]
F(000)
θ range [°]
Collected/unique reflections
Rint
2.17–27.54
12694/5973
0.0190
1.28–28.00
30870/14288
0.0864
Data/restraints/parameters
Goodness of fit on F2
Final R indices [IϾ2σ(I)]
R indices (all data)
Largest diff. peak/hole [e/Å3]
5973/0/338
1.019
R1 = 0.0307, wR2 = 0.0846
R1 = 0.0354, wR2 = 0.0876
0.422/–0.317
14288/0/713
0.963
R1 = 0.0630, wR2 = 0.1101
R1 = 0.1341, wR2 = 0.1341
0.389/–0.491
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It should be noted that there are only two crystal struc-
The coordination of the sulfonyl group (intra-[34a,37,38b,39,40]
tures of Ti amides containing a Ti–O–Ti fragment.[36] The or intermolecular)[35] has been observed for related N,N-
Ti-(μ-O) bond length in 11 is close to those of known ones type ligands (Scheme 8). Some examples of uncoordinated
(1.81–1.82 Å). The Ti–O–Ti angle (141.06°) is very large in sulfonamide groups are also shown. At the same time, for
comparison with those of related structures. The Ti–O(iPr) additional dimerization, the coordination of the sulfonyl
bond length is close to those of related six-coordinate com- group occurs only if a chlorine acceptor is present
pounds (1.758–1.790 Å) based on sulfonamides.[13g,37] The (Scheme 8, complex A).
Ti–O bond length is shorter for the OiPr group [average
There is one set of signals in the NMR spectra of 11;
1.786(2) Å] than for the CPh2O group [average 1.841(2) Å] therefore, the two ligand frameworks are equivalent, but all
or μ-O atom [average value is 1.805(2) Å]. This can be ex- protons of the CH2 and Ph groups in each ligand frame-
plained by the different steric volumes of the substituents work are diastereotopic. Therefore, a single isomer with C2
near the oxygen atoms.
symmetry is present in solution. At the same time, it is diffi-
The longest Ti–O bond length is that of the TiǟOS(O) cult to determine the presence of TiǟOS(O) coordination
coordination bond [average value 2.348(2) Å], which be- in solution. However, from the literature data for related
longs to the longest part of this bond-length range (2.125– compounds[35] (Scheme 8, complex A),[41] it may be pro-
2.390 Å)[38] for related six-coordinate derivatives containing posed that the dissociation of the TiǟOS(O) coordination
one bond of such type. The coordination of the SO2 group bond occurs at room temperature, and some broadening of
results only in a slight change to the bonding parameters the NMR signals indicates a dynamic behavior of the five-
of the sulfonamide group (elongation of the coordination coordinate Ti species formed (Berry pseudorotation).[3b,42]
S=O bond, average values 1.443 vs. 1.457 Å; and shortening Furthermore, the IR spectrum of 11 contains only one set
of the N–S bond in comparison with those of uncoordi- of SO2N vibrations (like that of 10) and, therefore, only one
nated analogs, compare 10 and 11, 1.582 vs. 1.594 Å), as is type of S=O group is present, that is, the S=O group is not
typical for related structures.
coordinated to the Ti atom. A comparison of the IR spectra
The TiǟN bond length is close to those in related six- of 10 and 11 [ν = 1270–1284 (SO2N νas), 1142–1148 cm–1
coordinate dialkanolamine mer derivatives (2.231–2.339 Å) (νs)] with those of the free ligands 6 and 7 shows that the
and sulfonamide derivatives (2.24–2.28 Å).[13g] The cova- bands are shifted to lower frequencies (owing to complex
lently bonded N atoms [N(12) and N(22)] are almost planar formation), and the νas bands are shifted more significantly
(average sum of angles is 359.90°) owing to the strong N– (the difference is more than 50 cm–1) than the νs bands (the
S(O2) interaction.[39] The Ti–N(SO2) bond length (average difference is less than 21 cm–1), as is usually observed for
2.120 Å) is somewhat longer than those in related sulfon- an uncoordinated SO2N group.[43]
amide structures (Scheme 8; 2.045–2.120 Å) and demon-
It should be mentioned one more time that the mer dis-
strates the poor donation ability of the sulfonamide group position of the ligand in the coordination sphere of the Ti
and the probable intense electron donation from the O atom, as observed in the crystal structures of 10 and 11,
atoms (2pπ–3dπ bonding). The Ti–O(CPh2) bond is signifi- has been observed previously only for sterically voluminous
cantly shorter than those in related six-coordinate mer-di- substituents (for six-coordinate Ti atoms, fac disposition is
alkanolamine derivatives (1.864–1.910 Å), and the C–O–Ti usually observed).[1a,7c] Therefore, effective conjugation
angle (average 129.74°) is sufficient for extra bonding.
along the N–Ti–O fragment may be proposed, and the co-
ordination of the N atom is similar to that described by
Schrock et al.[42]
Thermal Decomposition Investigation of 8 and 9
To study the thermal behavior of 8 and 9, several ad-
ditional experiments were performed. First, it was estab-
lished that 10 and 11 may be obtained (in vacuo without
solvent at 120 °C) directly from 8 and 9, respectively.
Furthermore, the NMR analysis of the solution of 8 un-
der prolonged heating ([D8]toluene, 100 °C) revealed the
slow disappearance of the signal at δ = 79.5 ppm (TiOiPr
group) and the appearance of a new signal at stronger field
(δ = 76.2 ppm), which may be identified as the signal of
Ti(OiPr)4.
The thermal stability of 9 was investigated by thermogra-
vimetry [TG, differential thermogravimetry (DTG)] and
differential scanning calorimetry (DSC; Table S1 and Fig-
ure S1, Supporting Information). The degradation of 9 is
complex. Decomposition begins at 80–90 °C and gradually
Scheme 8. Ti complexes containing sulfonamide ligands with vari-
ous coordination modes.
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proceeds to 250 °C, at which sharp mass loss occurs and
On the basis of the experimental results and material bal-
comes to an end at ca. 350 °C. In the TG curve, the weight ance, we propose the decomposition schemes for 8 and 9
changes continuously without any plateau; therefore, it is shown in Schemes 9 and 10. Regarding the structural differ-
impossible to accurately determine the range limits of the ence between the products 10 and 11 obtained at similar
mass losses. We also cannot determine the precise mass conditions, we deduced that it is the structure of the ligand
losses percentages or assign the mass losses to any chemical that plays the crucial role in the decomposition process. For
processes. The most valuable information that we obtained the Ti diisopropoxide complex (8) with an unsubstituted
from this experiment was the relatively low degradation ligand (6), heating provokes ligand exchange to produce
temperature of 9 (80–90 °C). Therefore, the decomposition homoligand compounds, Ti(OiPr)4, and 10. We suppose
of 9 may occur even in boiling toluene (b.p. 111 °C) during that ligand exchange is possible owing to the formation of
the recrystallization of 9.
dimeric complex 8a.
The volatile decomposition products of 9 were investi-
We believe that ligand exchange is not possible for 9: it
gated by mass-spectral analysis. Complex 9 was placed in is difficult to form a dimeric structure because of the bulki-
an aluminum crucible and heated at 100 °C in a flow of ness of the sterically hindered diphenyl-substituted ligand.
argon, which was directed into a mass spectrometer. The EI That is why the decomposition proceeds by the other route,
mass spectrum of the gas contains peaks of propene (m/z = namely, the destruction of one OiPr group (with propene
42, 41, 39, 27) and 2-propanol (m/z = 45, 43, 37). Thus, evolution), which ultimately transforms to a bridging oxy-
the data strongly support the destruction of the OiPr group gen atom (Scheme 10). A similar decomposition route has
during the degradation and prove the formation of propene, been found only in a few cases, for example, in the reaction
2-propanol, and Ti–O–Ti fragments (Figure S2). According of Ti(OiPr)4 with silica.[44a] Therefore, in this case, a rare
to the results, the signals of various possible gaseous prod- example of C–H activation (γ-proton shift) by Ti alkoxide
ucts may overlap (with those of propane, m/z = 44, 39, 29, complexes is observed.[44b,44c] In any case, the decomposi-
28), but it is evident that no acetone (m/z = 58, 43) or di- tion of Ti complexes is very rare and is usually observed
isopropyl ether (m/z = 87, 59, 45, 43, 41) is present. It for organometallic Ti compounds (with Ti–C bonds).[45]
should be noted that occasional hydrolysis is impossible un-
It should be pointed out that Ti diisopropoxide O,N,O
der these conditions, the appearance of 2-propanol may be complexes of dialkanolamines (five-coordinate Ti atom) are
observed only after oxo bridge formation, and the de- stable.[1a,3b] The related N,N,N complexes of diethylenetri-
hydration of 2-propanol is also improbable. Furthermore, amines are isolated only if additional coordination (six-co-
upon heating a solution of 9 ([D8]toluene, 100 °C), it is pos- ordinate Ti atom) by THF or a pendant group from a li-
sible to locate the signals of propene (δ = 5.97, 5.13, gand is implemented.[13g,34b,46] Only one crystal structure of
1.67 ppm) in the NMR spectrum of the reaction mixture.
a Ti complex with the [N,N,O]Ti(OiPr)2 coordination type
Scheme 9. Supposed decomposition mechanism of 8.
Scheme 10. Supposed decomposition mechanism of 9.
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has been reported previously (Scheme 11, B).[12a] However,
unlike those in 8 and 9, the coordinating atoms in B are
separated into two independent ligating molecules to realize
a stable coordination configuration. Therefore, the instabil-
ity and two decomposition routes of 8 and 9 with N,N,O
ligands presented here are explained by the ligand struc-
tures and their steric volumes.
reflux and distilled from sodium. Dichloromethane was distilled
from CaH2. Ethanol was refluxed and distilled from CaH2. C6D6
was distilled from sodium under argon. CDCl3 was distilled from
CaH2 under argon.
Monoethanolamine 5a, ethyl glycinate hydrochloride, bromobenz-
ene, Mg, LiAlH4, 2-(methylamino)ethanol, and tosyl chloride are
commercial reagents (Aldrich) and were used as received. Ti-
(OiPr)4 was distilled before use and stored under an argon atmo-
sphere.
N-{2-[(p-Tolylsulfonyl)oxy]ethyl}-p-tolylsulfonamide (1): Mono-
ethanolamine (12.00 g, 0.197 mol) was dissolved in anhydrous pyr-
idine (15 mL), and the solution was cooled to 0 °C with an ice bath.
Finely powdered tosyl chloride (80.00 g, 0.419 mol) was suspended
in pyridine (50 mL), and the suspension was cooled to –50 °C. The
ethanolamine solution was added, and the temperature was main-
tained below 10 °C for 30 min. The mixture was kept at room tem-
perature for 6 h and then at 4 °C overnight. The mixture was
poured, with stirring, onto crushed ice (500 g) and acidified with
glacial acetic acid (20 mL), whereupon the oily material solidified.
The solid was crushed to a slurry in water, collected, and washed
with water. The product was dried in a vacuum desiccator with
P2O5. Recrystallization of the crude product (69 g) from hot CHCl3
(50 mL) and the addition of cold CCl4 (200 mL) gave 1 as a white
powder (55.00 g, 76%), m.p. 87–88 °C (ref.[47] 86–87 °C). 1H NMR
(400 MHz, CDCl3): δ = 2.41 (s, 3 H, Me), 2.44 (s, 3 H, Me), 3.18–
3.22 (m, 2 H, CH2), 4.03 (t, J = 5.3 Hz, 2 H, CH2), 5.00 (br s, 1
H, NH), 7.27 (d, J = 8.3 Hz, 2 H, p-C6H4), 7.33 (d, J = 8.3 Hz, 2
H, p-C6H4), 7.68 (d, J = 8.3 Hz, 2 H, p-C6H4), 7.73 (d, J = 8.3 Hz,
2 H, p-C6H4) ppm. 13C NMR (100 MHz, CDCl3): δ = 21.4, 21.6
(2ϫMe), 42.0, 68.7 (2ϫCH2), 127.0, 127.9, 129.8, 130.0, 132.2,
136.6, 143.7, 145.2 (2ϫC6H4) ppm.
Scheme 11. The structure of complex B.
Conclusions
In this work, new N,N,O ligands (6 and 7) were obtained
and used for the synthesis of titanium complexes. The mon-
oligated titanium diisopropoxide complexes 8 and 9 are
thermally unstable and transform into new complexes (10
and 11) through moderate heating. We have determined
that the route for the transformation is directed by the li-
gand structure. For the unsubstituted ligand (6), the corre-
sponding bisligated complex (10) is obtained. For the steri-
cally demanding ligand, the dinuclear Ti oxo complex (11)
is formed. The decomposition temperature of 9 was esti-
mated, and the volatile degradation products were deter-
mined; the degradation of 9 represents a rare example of
OiPr ligand destruction to form propene. It is also a rare
example of the decomposition of a Ti complex with a
polydentate ligand. The N,N,O-type ligands occupy the mer
position in the coordination spheres of the Ti atoms.
N-p-Tosylaziridine (2): A solution of 20% aqueous KOH (50 mL)
was added rapidly to a solution of 1 (13.00 g, 0.035 mol) in benzene
(200 mL). The two-phase mixture was stirred vigorously, and a
white solid appeared. After 1 h, the organic phase was washed with
water and dried with Na2SO4, and all volatile materials were evapo-
rated at a temperature below 50 °C. The crude material was recrys-
tallized from ethyl acetate to afford 2 as colorless crystals (6.20 g,
90%), m.p. 65–66 °C (ref.[32b] 63–64 °C). 1H NMR (400 MHz,
CDCl3): δ = 2.35 (br s, 4 H, CH2CH2), 2.43 (s, 3 H, CH3), 7.33 (d,
J = 8.3 Hz, 2 H, p-C6H4), 7.81 (d, J = 8.3 Hz, 2 H, p-C6H4) ppm.
13C NMR (100 MHz, CDCl3): δ = 21.5 (CH2), 27.3 (CH3), 127.9,
129.6, 134.8, 144.6 (p-C6H4) ppm.
Experimental Section
General Methods and Remarks: All operations with Ti derivatives
were conducted in a dry argon atmosphere by using standard
Schlenk techniques. The 1H (400.130 MHz) and 13C
(100.613 MHz) NMR spectra were recorded with Bruker 400 or
Agilent 400 spectrometers at 295 K (unless otherwise stated).
Chemical shifts are given in ppm relative to internal Me4Si. The
elemental analyses were performed with a Heraeus Vario Ele-
mentar instrument. The melting points were measured with a
WRS-2A melting point apparatus. The IR spectra were recorded
with a Thermo Nicolet 200 apparatus. The MALDI mass spectra
were recorded with a Bruker Autoflex II [full width at half-maxi-
mum (FWHM) resolution 18000] equipped with a nitrogen laser
with a wavelength of 337 nm and a time-of-flight (TOF) mass ana-
lyzer operating in reflectron mode. The accelerating voltage was
20 kV. The samples were applied to a substrate made of polished
steel. The spectra were recorded in the positive-ion mode. The re-
sulting spectra were the sum of 300 spectra obtained at different
points of the sample.
Ethyl [(Ethoxycarbonyl)amino]acetate (3): An aqueous solution of
Na2CO3 (1 m, 230 mL) and ethyl chloroformate (26.04 g,
0.240 mol) was added to a stirring solution of ethyl glycinate hydro-
chloride (27.92 g, 0.200 mol) in water (200 mL). The mixture was
stirred vigorously for 3 h. The organic phase was extracted with
diethyl ether, dried with MgSO4, and evaporated (vacuum, 90 °C)
to afford the crude product (28.23 g). After vacuum distillation, 3
was obtained as a colorless oily liquid (25.37 g, 72%); b.p. 145 °C,
20 Torr, (ref.[48] 128–130 °C, 15 Torr). 1H NMR (400 MHz,
CDCl3): δ = 1.17–1.30 (m, 6 H, 2ϫMe), 3.80–4.00 (m, 2 H, CH2),
4.05–4.25 (m, 4 H, 2ϫCH2), 5.25 (br s, 1 H, NH) ppm. 13C NMR
(100 MHz, CDCl3): δ = 14.0, 14.4 (2ϫMe), 42.6, 61.1, 61.3
(3ϫCH2), 156.5, 170.1 (2ϫCO) ppm.
Ethyl (2-Hydroxy-2,2-diphenylethyl)carbamate (4): A solution of
bromobenzene (103.90 g, 0.662 mol) in THF (150 mL) was added
dropwise to a stirring mixture of Mg turnings (18.47 g, 0.770 mol)
and THF (250 mL). After the vigorous reaction started, addition
was continued, and the mixture was allowed to boil. After all of
the bromobenzene was added, the mixture was heated under reflux
Solvents were dried by the usual procedures. Tetrahydrofuran and
diethyl ether were stored under solid KOH and then distilled from
sodium/benzophenone. Toluene and n-hexane were heated under
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for 1 h to finish the reaction. Compound 3 (29.00 g, 1.166 mol) was
added dropwise to a cold (10 °C) stirring solution of PhMgBr, and
the mixture was kept below 20 °C. The mixture was then left over-
night at room temperature. The mixture was treated with a satu-
rated aqueous solution of NH4Cl. The organic phase was sepa-
rated, and the aqueous phase was extracted with diethyl ether. The
combined organic phases were dried (MgSO4), and the solvents
were evaporated. After recrystallization from ethyl acetate/ethanol,
4 was obtained as a colorless powder (35.72 g, 70%), m.p. 125 °C,
CDCl3): δ = 21.5 (C6H4Me), 40.7 (NMe), 43.5, 58.0, 67.6
(3ϫCH2), 75.5 (CPh2), 127.1, 129.6, 136.6, 143.2 (p-C6H4), 125.7,
126.8, 128.2, 146.3 (2ϫPh) ppm. IR (Nujol): ν = 3480 (m) and
3312 (m, NH and OH), 2952 (w), 1320 (s, νas SO2N), 1161 (s, νs
SO2N), 1108 (m), 1030 (m), 972 (m) cm–1. C24H28N2O3S
(424.5557): calcd. C 67.90, H 6.65, N 6.60, S 7.55; found C 68.12,
H 6.88, N 6.50, S 7.41.
General Procedure for the Synthesis of Titanium Diisopropoxide
Complex (8 and 9): The ligand (6 or 7; 4.00 mmol), toluene or
dichloromethane (40 mL), and Ti(OiPr)4 (1.14 g, 4.00 mmol) were
successively placed in a Schlenk flask filled with argon. The solu-
tion was stirred at room temperature under an argon atmosphere
overnight. Then, the solution was heated slightly (no greater than
50 °C) to remove the solvent, a small amount of toluene was added,
and the solution was filtered. Then, all volatile materials were re-
moved to afford a colorless liquid residue.
1
(ref.[28] 124–125 °C). H NMR (400 MHz, CDCl3): δ = 1.18 (t, J =
7.1 Hz, 3 H, CH3), 3.99 (d, J = 6.1 Hz, 2 H, CH2NH), 4.05 (q, J
= 7.1 Hz, 2 H, CH2O), 5.04 (br s, 1 H, NH), 7.20–7.45 (m, 10 H,
2ϫPh) ppm. 13C NMR (100 MHz, CDCl3): δ = 14.4 (CH3), 50.5
(CH2NH), 61.2 (CH2O), 78.2 (CPh2), 126.1, 127.1, 128.3, 144.5
(2ϫPh), 157.6 (CO) ppm.
2-Methylamino-1,1-diphenylethanol (5): Compound
4 (32.00 g,
Compound 8: Colorless oil, yield 1.75 g (95%). 1H NMR
(400 MHz, CDCl3): δ = 1.15–1.31 (m, 12 H, 2ϫCHMe2), 2.34 (s,
3 H, p-C6H4Me), 2.55 (br s, 3 H, NMe), 2.74 (br s, 2 H, CH2), 2.95
(br s, 2 H, CH2), 3.30 (br s, 2 H, CH2), 4.33–4.41 (m, 2 H, CH2),
4.79 (br s, 2 H, 2ϫCHMe2), 7.18 (d, J = 7.7 Hz, 2 H, p-C6H4), 7.76
(d, J = 7.7 Hz, 2 H, p-C6H4) ppm. 13C NMR (100 MHz, CDCl3): δ
= 21.3 (p-C6H4Me), 25.8 (CHMe2), 44.5 (NMe), 47.0, 53.8, 60.6,
69.8 (4ϫCH2), 79.5 (CHMe2), 126.9, 128.9, 139.5, 141.4 (p-C6H4)
ppm. MS (MALDI-TOF): m/z = 436.8 [M]+ (C18H32N2O5STi).
Compound 9: Colorless oil, yield 2.35 g (95%). 1H NMR
(400 MHz, CDCl3): δ = 1.02–1.61 (m, 12 H, 2ϫCHMe2), 2.08–
2.24 (m, 1 H, CH2), 2.32 (s, 3 H, NMe), 2.41 (s, 3 H, p-C6H4Me),
2.77–3.03 (m, 2 H, CH2), 3.19–3.34 (m, 1 H, CH2), 3.65–3.84 (m,
2 H, CH2), 4.78–5.00 (m, 2 H, 2ϫCHMe2), 7.06–7.58 (m, 12 H,
aromatic protons), 7.75 (d, J = 7.8 Hz, 2 H, p-C6H4) ppm. 13C
NMR (100 MHz, CDCl3): δ = 21.3 (p-C6H4Me), 25.9 (CHMe2),
45.5 (NMe), 46.6, 55.6, 70.3 (3ϫCH2), 79.7 (CHMe2), 87.9 (CPh2),
126.9, 128.9, 139.6, 141.4 (p-C6H4), 124.6, 126.4, 128.1, 148.5,
149.1 (broad signals, 2ϫPh) ppm. MS (MALDI-TOF): m/z =
588.8 [M]+ (C30H40N2O5STi).
0.112 mol) was added portionwise to suspension of the LiAlH4
(12.77 g, 0.336 mol) in anhydrous diethyl ether (350 mL) under ar-
gon. The mixture was stirred for 5 d. Then, the reaction was
quenched by the successive addition of water (13 mL), 15% aque-
ous NaOH (13 mL), and water (39 mL) with stirring. The organic
phase was separated, and the aluminum hydroxide was washed with
a small amount of diethyl ether. The combined organic phases were
extracted with aqueous HCl (2 m), and the aqueous solution of
5·HCl was treated with excess solid Na2CO3 (Caution: carbon diox-
ide evolution!). Compound 5 was extracted with diethyl ether, the
organic phase was dried (MgSO4), and all volatile materials were
evaporated. After recrystallization from hexane (with small amount
of ethanol), 5 was obtained as colorless crystals (14.00 g, 55%),
m.p. 60–62 °C (ref.[28] 58–62 °C). 1H NMR (400 MHz, CDCl3): δ
= 2.44 (s, 3 H, CH3), 2.90 (br s, 2 H, NH, OH), 3.30 (s, 2 H, CH2),
7.23 (t, J = 7.3 Hz, 2 H, aromatic protons), 7.32 (t, J = 7.5 Hz, 4
H, aromatic protons), 7.48 (d, J = 7.3 Hz, 4 H, aromatic protons)
ppm. 13C NMR (100 MHz, CDCl3): δ = 36.5 (CH3), 61.0 (CH2),
76.1 (CPh2), 126.0, 126.8, 128.2, 145.6 (2 ϫPh) ppm.
General Procedure for the Synthesis of 6 and 7: N-Tosylaziridine (2;
1.97 g, 0.010 mol) and the corresponding 2-(methylamino)ethanol
derivative (0.010 mol) were dissolved in anhydrous ethanol
(50 mL). The solution was stirred for 24 h at room temperature.
The reaction was monitored by TLC (Silufol, hexane/ethyl acetate
1:1). After the reaction was over, the mixture was filtered, and all
volatile materials were evaporated (vacuum, 90 °C). The product
was analytically pure and used without further purification.
Compound 10: Ligand 6 (2.18 g, 8.00 mmol), toluene (20 mL), and
Ti(OiPr)4 (1.14 g, 4.00 mmol) were placed successively in a Schlenk
flask filled with argon. The solution was heated to reflux under an
argon atmosphere for 10 h. Then, the solution was heated under
vacuum to remove the solvent, and the residue was dissolved in
toluene (20 mL). The reflux and evaporation procedure was re-
peated until the residue became solid (three times). The product in
a small amount of toluene was heated under reflux, the solution
was cooled, and the product was collected by filtration, washed
with toluene, and dried in vacuo. Compound 10 was obtained as a
colorless crystalline powder, yield 1.65 g (70%). 1H NMR
(400 MHz, CDCl3): δ = 2.36 (s, 6 H, p-C6H4Me), 2.53–2.62 (m, 2
H, CH2), 2.66 (s, 6 H, NMe), 2.78–2.88 (m, 2 H, CH2), 3.32–3.63
(m, 6 H, CH2), 3.98–4.00 (m, 2 H, CH2), 4.37–4.49 (m, 2 H, CH2),
4.99–5.09 (m, 2 H, CH2), 7.22 (d, J = 7.8 Hz, 4 H, p-C6H4), 7.94
(d, J = 7.8 Hz, 4 H, p-C6H4) ppm. 13C NMR (100 MHz, CDCl3):
δ = 21.4 (p-C6H4Me), 45.0 (NMe), 48.8, 58.6, 64.7, 76.8 (4ϫCH2),
128.2, 128.9, 138.6, 141.6 (p-C6H4) ppm. IR (Nujol): ν = 2980 (w),
1284 (s, νas SO2), 1148 (s, νs SO2), 1076 (m), 982 (m) cm–1. MS
(MALDI-TOF): m/z = 588.6 [M]+. C24H36N4O6S2Ti (588.5628):
calcd. C 48.98, H 6.17, N 9.52, S 10.90; found C 48.62, H 6.40, N
9.11, S 10.57.
2-{[2-(p-Tosylamino)ethyl]methylamino}ethanol (6): Colorless solid,
yield 2.55 g (97%); m.p. 45–46 °C. 1H NMR (400 MHz, CDCl3): δ
= 2.09 (s, 3 H, NMe), 2.39 (s, 3 H, C6H4Me), 2.40–2.48 (m, 4 H,
2NCH2), 2.97 (t, J = 5.2 Hz, 2 H, NCH2), 3.55 (t, J = 5.2 Hz, 2
H, OCH2), 5.50 (br s, 2 H, NH, OH), 7.27 (d, J = 8.0 Hz, 2 H, p-
C6H4), 7.75 (d, J = 8.0 Hz, 2 H, p-C6H4) ppm. 13C NMR
(100 MHz, CDCl3): δ = 21.4 (C6H4Me), 41.2 (NMe), 40.4, 55.9,
58.9, 58.9 (4ϫCH2), 127.1, 129.6, 136.7, 143.2 (p-C6H4) ppm. IR
(Nujol): ν = 3220 (m, NH, OH), 2960 (w), 1335 (s, νas SO2N),
1169 (s, νs SO2N), 1100 (m), 1060 (m), 996 (m) cm–1. C12H20N2O3S
(272.3638): calcd. C 52.92, H 7.40, N 10.29, S 11.77; found C 53.38,
H 7.59, N 10.42, S 11.62.
2-{[2-(p-Tosylamino)ethyl]methylamino}-1,1-diphenylethanol
(7):
Colorless solid, yield 4.16 g (98%); m.p. 88–89 °C. 1H NMR
(400 MHz, CDCl3): δ = 1.93 (s, 3 H, NMe), 2.39 (s, 3 H, C6H4Me),
2.45 (t, J = 6.0 Hz, 2 H, NCH2CH2), 2.85 (t, J = 6.0 Hz, 2 H, Compound 11: Ligand 7 (1.70 g, 4.00 mmol), toluene (20 mL), and
NCH2CH2), 3.22 (s, 2 H, CH2CPh2), 4.85 (br s, 1 H, NH), 7.16–
Ti(OiPr)4 (1.14 g, 4.00 mmol) were placed successively in a Schlenk
7.30 (m, 8 H, aromatic protons), 7.39–7.47 (m, 4 H, aromatic pro-
flask filled with argon. The solution was heated to reflux under an
tons), 7.67 (d, J = 8.1 Hz, 2 H, p-C4H4) ppm. 13C NMR (100 MHz, argon atmosphere for 10 h. Then, the solvent was removed, and
Eur. J. Inorg. Chem. 2015, 5903–5912
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CDCl3): δ = 1.15 (d, J = 4.7 Hz, 6 H, CHMe2), 1.23 (d, J = 4.7 Hz,
6 H, CHMe2), 2.16 (s, 6 H, 2ϫNMe), 2.28 (s, 6 H, 2ϫp-C6H4Me),
2.31 (s, 3 H, TolH), 2.35–2.51 (m, 2 H, CH2), 3.19–3.35 (m, 2 H,
CH2), 3.66–3.89 (m, 6 H, CH2), 4.18 (d, J = 11.4 Hz, 2 H, CH2),
4.87–5.00 (m, 2 H, CHMe2), 6.85–7.78 (m, 33 H, aromatic protons)
ppm. 13C NMR (100 MHz, CDCl3): δ = 21.3 (p-C6H4Me), 25.1,
25.5 (CHMe2), 45.2 (NMe), 48.6, 60.6, 74.0 (3ϫCH2), 78.8
(CHMe2), 90.1 (CPh2), 126.7, 128.6, 140.0, 140.3 (p-C6H4), 124.9,
125.4, 125.7, 126.0, 127.57, 127.8, 148.9, 150.4 (2ϫPh), 21.4, 125.3,
128.2, 129.0 (TolH) ppm. IR (Nujol): ν = 2950 (w), 1270 (s, νas
SO2N), 1142 (s, νsSO2N), 1103 (m), 1028 (m), 997 (m), 722 (w,
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Crystallography Details: The experimental intensities for 10 and 11
were measured with a Bruker SMART APEX II diffractometer
(graphite-monochromated Mo-Kα radiation, λ = 0.71073 Å). The
structures were solved by direct methods and refined by full-matrix
least-squares techniques on F2 (SHELXTL) with anisotropic ther-
mal parameters for all non-hydrogen atoms. In 11, the isopropyl
atom C16 is disordered over two positions with an occupancy ratio
of 0.64/0.36. All hydrogen atoms were placed in calculated posi-
tions and refined by using a riding model. Details of the X-ray
diffraction experiments are given in Table 1.
[10]
CCDC-1052398 (for 10) and -1052399 (for 11) contain the supple-
mentary crystallographic data for this paper. These data can be
obtained free of charge from The Cambridge Crystallographic
Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
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Acknowledgments
This work was financially supported by the Russian Fund of Basic
Research (RFBR) (grant number 12-03-00206-a), the Russian
President Grant for Young Russian Scientists (MD-3634.2012.3)
and in part by the M. V. Lomonosov Moscow State University
(Program of Development). The authors are grateful to S. V. Savi-
lov (MSU) for the thermal analysis.
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Received: August 4, 2015
Published Online: November 25, 2015
Eur. J. Inorg. Chem. 2015, 5903–5912
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