Four- and Five-Coordinate Titanium(IV) Complexes Supported by the dpp-bian Ligand in ROP of L-Lactide

Article abstract of DOI:10.1002/ejic.201900715

A titanium(IV) alkoxido complex, (dpp-bian)Ti(OBn)₂ (2), as well as alkoxido chlorido complexes (dpp-bian)TiCl(OCH₂CH₂OMe) (3) and (dpp-bian)TiCl₂OBn (4), were synthesized from the titanium(IV) dichloride precursor [(dpp-bian)TiCl₂]₂ (1) by exchange with corresponding sodium salts (comps. 2 and 3) or by the alcoholysis with BnOH (comp. 4). The compounds 2–4 were fully characterized by elemental analysis, NMR or EPR, and IR spectroscopy. Molecular structures of the metal complexes in the solid state have been determined by single-crystal XRD analysis. Compounds 2–4 were tested as catalysts in the ROP of L-lactide in a toluene medium. Whereas complexes 2 and 3 produce cyclic PLAs with broad dispersities and unpredictable molecular weights, complex 4 acts as an efficient ROP catalyst which polymerizes the monomer in a highly controllable manner. It produces BnO-capped PLAs with narrow molecular weight distributions as well as linear dependence of M_ns on monomer conversion.

Full text of DOI:10.1002/ejic.201900715

A Journal of
Accepted Article
Title: Four- and five-coordinate titanium (IV) complexes supported by
the dpp-bian ligand in ROP of L-lactide
Authors: Alexander Morozov, Tatyana Martemyanova, Vladimir
Dodonov, Olga Kazarina, and Igor Fedushkin
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To be cited as: Eur. J. Inorg. Chem. 10.1002/ejic.201900715
Link to VoR: http://dx.doi.org/10.1002/ejic.201900715

European Journal of Inorganic Chemistry
10.1002/ejic.201900715
Four- and five-coordinate titanium (IV) complexes supported by
the dpp-bian ligand in ROP of L-lactide
[
a]
[a]
[a]
[a]
Alexander G. Morozov,* Tatyana V. Martemyanova, Vladimir A. Dodonov , Olga V. Kazarina,
[
a]
and Igor L. Fedushkin
Abstract: A titanium (IV) alkoxido complex, (dpp-bian)Ti(OBn)
2
(2),
toxicity of polyesters is avoided by using catalytic systems based
[
7]
[8a]
as
well
as
alkoxido
chlorido
complexes
(dpp-
on alkaline-earth metals , or group
4
metals
including
bian)TiCl(OCH
2
CH
2
OMe) (3) and (dpp-bian)TiCl
2
OBn (4), were
titanium and zirconium alkoxides, stabilized primarily by various
[
8b–i]
[9]
synthesized from the titanium (IV) dichloride precursor [(dpp-
bian)TiCl (1) by exchange with corresponding sodium salts
comps. 2 and 3) or by the alcoholysis with BnOH (comp. 4). The
multidentate Schiff base ligands
.
Recently , we
2
]
2
demonstrated that the chelate ene-bisamide form of the ligand
dpp-bian (=1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene)
(
0
compounds 2–4 were fully characterized by elemental analysis,
NMR or EPR, and IR spectroscopies. Molecular structures of the
metal complexes in the solid state have been determined by single-
crystal XRD analysis. Compounds 2–4 were tested as catalysts in
the ROP of L-lactide in a toluene medium. Whereas complexes 2
and 3 produce cyclic PLAs with broad dispersities and unpredictable
molecular weights, complex 4 acts as an efficient ROP catalyst
which polymerizes the monomer in a highly controllable manner. It
produces BnO-capped PLAs with narrow molecular weight
readily stabilizes the d configuration of the titanium atom with
2 2
the formation of the chlorido complex [(dpp-bian)TiCl ] , which
appears to be an easy-to-use precursor for further dpp-bian-
supported titanium derivatives. It should be noted that
magnesium and calcium complexes of dpp-bian have proved to
[
10]
be robust catalysts for the ROP of L- and rac-lactides , forming
[
11]
PLAs which are non-toxic toward human fibroblasts, while the
binuclear aluminum compound [(dpp-bian)Al] was found to be
an extremely active initiator of the controlled ROP of ε-
2
[
12]
distributions as well as linear dependence of M
conversion.
n
s on monomer
caprolactone at room temperature. In an effort to expand the
scope of non-toxic catalytic systems based on dpp-bian for the
polymerization of cyclic esters, we report on the synthesis and
catalytic activity of titanium alcoholates stabilized with dianionic
and radical anionic forms of dpp-bian, in the ROP of L-lactide (LA).
Introduction
Poly(α-hydroxy acids) are aliphatic polyesters of biomedical
interest, owing to their biocompatible and biodegradable
properties. In particular, poly(lactic acid), otherwise known as
polylactide (PLA), produced by catalytic ring-opening
Results and Discussion
Synthesis of (dpp-bian)Ti(OBn)
OMe)Cl (3) and (dpp-bian)Ti(OBn)Cl
2
(2), (dpp-bian)Ti(OCH
(4)
2 2
CH -
[1]
2
polymerization (ROP) of cyclic di-ester derivatives, or lactides ,
has been widely used in surgeryor, as component of
a
The compounds 2 and 3 were prepared by exchange reactions
between the titanium complex [(dpp-bian)TiCl (1), generated
copolymers, in various medical devices, such as dental implants,
stents, resorbable sutures, and erodible polymer vehicles for
2 2
]
in situ, and the sodium salts of benzyl alcohol and 2-
methoxyethanol, respectively (Scheme 1). A deep orange-red
color of the solutions of the complexes indicates the presence of
[
2]
controlled drug delivery . A wide range of metal complex-based
catalysts for controllable ROP of lactides has been studied
extensively over the last three decades. Coordination
[9]
four-coordinate titanium.
[
3]
[4]
[5]
compounds of tin , aluminum , or zinc together with rare-
[6]
earth elements , were found to be efficient catalysts for the
ROP of cyclic esters via a coordination-insertion mechanism.
However, harmful metallic remnants which cannot be entirely
removed from the resulting polymers constrain their further
utilization as implant materials in medicine. Catalyst-induced
dpp
N
dpp
N
Cl
Ti
Cl
Cl
0.5
Ti
N
N
Cl
dpp
dpp
1
dpp
dpp
N
O
O
N
[
a]
Dr. A.G. Morozov, T.V. Martemyanova, Dr. V.A. Dodonov,
Dr. O.V. Kazarina, Prof. Dr. I.L. Fedushkin
G.A. Razuvaev Institute of Organometallic Chemistry of the Russian
Academy of Sciences
i)
ii)
Ph
Ti
Ti
O
O
iii)
dpp = 2,6-iPr
iii)
-C
N
N
Cl
Ph
dpp
dpp
Tropinina str. 49, 603950 Nizhny Novgorod, Russian Federation
E-mail: morozov@iomc.ras.ru
2
3
2
6
H
3
Homepage:www.iomc.ras.ru
Scheme 1. Synthesis of 2 and 3. i) 2 eq. BnONa, toluene, 25 °C; ii) 1 eq.
MeOCH CH ONa, toluene, 25 °C; iii) hexane, 25 °C
Supporting information for this article is given via a link at the end of
the document
2
2
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European Journal of Inorganic Chemistry
10.1002/ejic.201900715
Complexes 2 and 3 were isolated by crystallization from hexane.
Another synthetic route to titanium alkoxides is the treatment of
appropriate chlorides with alcohols. For instance, adding 2 eq. of
BnOH to the solution of 1 causes an immediate color change
from green-brown to blue-violet (Scheme 2). We assume that
formation of 4 proceeds through hydrolysis of Ti–Cl bonds, with
The aliphatic protons of the alkoxido ligands in 2 appear as two
singlets, at δ 5.32 and 4.68 ppm, originating from the methylene
groups of two different benzylato ligands, whereas complex 3
reveals two triplets, at δ 4.41 and 3.24 ppm, arising from the two
non-equivalent methylene groups of the methoxyethylato moiety.
Furthermore, both complexes show the downfield set of
resonances characteristic of aromatic protons, of the
naphthalene backbone of dpp-bian and the phenyl substituents
of the benzylato ligands, respectively, at δ 7.5…6.5 ppm. In
contrast to 2 and 3, complex 4 proved to be paramagnetic.
Figure 2 shows the EPR spectrum of 4 at 330 K (upper spectra –
2
subsequent binding of the liberated HCl, to give dpp-bianH and
the titanium(III) alkoxy chloride. Quenching of the reaction
mixture with heptane allows one to isolate the blue crystalline
product 4, albeit in quite low yield (48 %).
experimental; lower spectra
–
simulated using EasySpin
dpp
N
dpp
NH
[13]
software
,
RMSD 3.26 %). Variable-temperature EPR
Cl
Cl
Cl
experiments (Fig. S4, SI) show the formation of another
paramagnetic species at low temperature (260 K and below)
which is in equilibrium with 4. The nature of this phenomenon will
be discussed elsewhere, as it is of no immediate interest to the
research reported here.
OBn
Ti
OBn
Ti
+
+
N
Cl
NH
dpp
dpp
4
Scheme 2. Synthesis of 4. i) 2 eq. BnOH, toluene, 25 °C; ii) heptane, 25 °C.
Compounds 2–4 have been characterized by elemental analysis, IR
spectroscopy, and single-crystal X-ray analysis. The solution
structures of 2 and 3 were investigated by NMR spectroscopy, while
paramagnetic complex 4 was examined using X-band EPR
spectroscopy. Compounds 2–4 efficiently initiate the ring-opening
polymerization of L-lactide, with complex 4 carrying out the process
in a highly controllable manner to give a linear poly-L-lactide.
Solution Spectroscopy Studies of Complexes 2–4
Compounds 2 and 3 are diamagnetic and thus amenable to
1
straightforward NMR spectroscopic characterization. H-NMR
spectra of their toluene solutions (Fig. 1) reveal similar sets of
signals from the ligand isopropyl groups, which represent four
methyl doublets at δ 1.30, 1.15, 1.10, 1.01 ppm for 2 and δ 1.51,
1.31, 1.12, 0.91 ppm for 3, respectively, as well as two methine
septets at δ 3.62 and 3.15 ppm for 2 and at δ 3.92 and 2.86 ppm
2–
for 3. This spectral pattern is typical for {dpp-bian }-containing
metal complexes that have one mirror plane of symmetry.
Figure 2. X-band EPR spectrum of 4 in toluene at 330 K.
On the whole, in a toluene solution, compound 4 reveals a
complicated EPR signal, due to the coupling of the unpaired
47
electron to the titanium nucleus ( Ti: I = 5/2, natural abundance
4
9
7
.44 %; Ti: I = 7/2, natural abundance 5.41 %), two chlorine
3
5
37
nuclei ( Cl: I = 3/2, natural abundance 75.78 %; Cl: I = 3/2,
14
natural abundance 24.22 %), and two nitrogen nuclei ( N: I = 1,
natural abundance 99.63 %). The spectral parameters of the
4
7, 49
given signal, in particular,
g
i
= 1.997,
i
a(
Ti)
= 0.556,
35, 37
14
a
i
(2 ×
Cl) = 0.129 and a( N) = 0.071 mT, are essentially
i
independent of temperature and can be referred to the system
where the spin density is localized either on the ligand (form A),
[
14]
or the metal center (form B, Scheme 3). Kaim reported on a
series of titanium isopropoxido complexes with π-acceptor
substrates,
including
α-diimines,
where
paramagnetic
1
Figure 1. H NMR spectra of 2 (top) and 3 (bottom) in toluene-d
8
(298 K).
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European Journal of Inorganic Chemistry
10.1002/ejic.201900715
III
IV
[15]
compounds were described as Ti or Ti /radical species,
depending on the reduction potential of the ligand.
Complex 2 (Fig. 3) crystallizes in the triclinic space group P1,
with two molecules in the unit cell. The Ti atom has a distorted
tetrahedral environment formed by N(1), N(2), O(1) and O(2)
ꢂ
atoms (geometry index ꢀ is equal to 0.54). The lengths of the
Ti–N(av.) and Ti–O(av.) bonds are 1.942(5) and 1.795(3) Å,
respectively, which is very close to those in similar titanium
ꢁ
dpp
N
dpp
N
Cl
Cl
TiIV
OBn
TiIII
OBn
alcoholates (tBuNC(CH
Ti–N(av.) 1.393(10)
2
Ph)=C(CH
and
2
Ph)NC
Ti–O(av.)
6
H
3
Me
2
)Ti(OC
6
H
3
iPr
Å),
2
)
2
N
Cl
N
Cl
(
1.818(13)
dpp
dpp
{PhNC(CH SiMe )=C(CH SiMe )=NPh}Ti(OC H Ph ) (Ti–N(av.)
2
3
2
3
6
3
2 2
A
B
[
18]
1
2
1
.902(15) and Ti–O(av.) 1.834(8) Å)
,
6 3 2
Ti(OC H Ph -
[
19]
2
,6) {N(xy)CMeCMeN(xy)}
(Ti–N(av.) 1.926(5) and Ti–O(av.)
Scheme 3. Probable structures of compound 4 in toluene solution.
[
9]
.838(5) Å) and (dpp-bian)Ti(OtBu)
2
(Ti–N(av.) 1.949(2) and
Ti–O(av.) 1.798(2) Å). The deviation of the angles C(13)–N(1)–
N(2) and C(25)–N(2)–N(1) (160.35(12)° and 161.51(12)°,
respectively) from 180°, along with the non-orthogonal
The ligand dpp-bian, which is a π-acceptor of reasonable
[
16]
strength, has a first reduction potential of –1.0 V , and is
expected to be present as a radical anion. The relatively low
disposition
of
the
N-aryl
substituents
toward
the
47, 49
bisamidoacenaphthylene fragment (the dihedral angles between
the described planes are 77.46(25)° and 102.81(21)°,
respectively), reflect the mutual repulsion of the iPr-groups of the
dpp-bian and benzylato ligands.
value of the
Ti hyperfine coupling (HFC) constant,
accompanied by a g-factor very close to 2, lead us to suggest
that the structure of the metal complex 4 in toluene solution is A.
14
[17]
An unusually low N HFC constant
indicates that the
unpaired electron is localized to a lesser extent on the dpp-bian
ligand than on the titanium atom.
Molecular Structures of 2–4
Crystals of the complexes 2 and 3 suitable for x-ray diffraction
analysis were obtained at room temperature from hexane
solutions while 4 was recrystallized from toluene. Selected bond
lengths and angles for complexes 2–4 are listed in Table 1.
Table 1. Selected bond lengths and angles for complexes 2–4.
2
3
4
Ti–O(1)
1.806(3)
1.784(3)
1.951(6)
1.938(3)
–
1.755(4)
1.741(2)
–
Ti–O(2)
–
Ti–N(1)
1.926(3)
2.178(2)
2.068(2)
2.288(1)
2.240(1)
2.940(3)
2.905(3)
1.439(4)
1.308(4)
1.325(3)
153.03(10)
–
[
a]
Ti–N(2)/N(1')
Ti–Cl(1)
1.926(3)
2.286(2)
Ti–Cl(2)
–
–
Figure 3. Molecular structure of compound 2. Thermal ellipsoids are at 50%
Ti–C(1)
2.373(3)
2.381(4)
1.411(4)
1.382(3)
1.382(3)
115.50(7)
112.47(7)
–
2.401(4)
probability. Hydrogen atoms are omitted for clarity.
[
a]
Ti–C(2)/C(1')
2.401(4)
[
a]
C(1)–C(2)/C(1')
N(1)–C(1)
1.472(5)
1.378(5)
[
a]
[a]
Complex 3 (Fig. 4), which crystallizes in the orthorhombic space
N(2)/N(1') –C(2)/C(1')
N(1)–Ti–O(1)
1.378(5)
group Pnma with four molecules in the unit cell, has almost
113.11(10)
ꢂ
regular tetrahedral coordination geometry at Ti (ꢀ = 0.95). A
N(1)–Ti–O(2)
–
ꢁ
N(1)–Ti–Cl(1)
112.26(9)
86.22(7)
98.87(7)
90.76(11)
–
molecule of 3 has a mirror plane σ which is orthogonal to the
acenaphthylene backbone and bisects the angle N(1)–Ti–N(1’),
containing the atoms Ti, Cl(1), O(1), C(20), C(6) and C(7). The
bond length Ti–N (1.926(3) Å) is close to those in 2 and other
ene-bisamide-supported titanium complexes. Conversely, the
Ti–O(1) bond (1.755(4) Å) in the alkoxido chlorido complex 3
appears slightly shorter than in the homo-alkoxido complexes
mentioned above. The interatomic distance Ti···O(2), at
4.127(7) Å, is significantly longer than the sum of the related van
der Waals radii, indicating a lack of auxiliary coordination of the
alcoholato ligand to the metal center carrying the methoxy group.
The Ti atoms in 2 and 3 are, respectively, 1.2729(3) Å and
N(1)–Ti–Cl(2)
–
–
[
a]
N(2)/N(1') –Ti–O(1)
N(2)–Ti–O(2)
116.38(6)
106.93(7)
–
113.11(10)
–
[
a]
N(2)/N(1') –Ti–Cl(1)
N(2)–Ti–Cl(2)
112.26(9)
148.90(7)
101.34(7)
94.00(9)
106.84(9)
106.58(4)
–
–
–
O(1)–Ti–Cl(1)
–
112.42(12)
O(1)–Ti–Cl(2)
–
–
Cl(1)–Ti–Cl(2)
–
–
O(1)–Ti–O(2)
112.17(7)
170.96(14)
154.56(16)
–
[
a]
Ti–O(1)–C(37)/C(20)
Ti–O(2)–C(44)
172.27(40)
–
160.18(22)
–
[
a] Alternative atom numbering is given for compound 3.
1.1914(9) Å away from the bisamidoacenaphthylene plane that
is caused by π-type interaction between the C=C fragment and
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European Journal of Inorganic Chemistry
10.1002/ejic.201900715
[
20]
[23]
the metal center . The observed values are slightly higher than
(2.0940(11) Å) , where bian acts as a monoanionic ligand.
those in the starting complex 1 (1.0576(3) Å) as well as in the
Moreover, the bond lengths Ti–Nav. in 4 are intermediate
t
[9]
similar alkoxide (dpp-bian)Ti(O Bu)
2
(1.1665(3) Å).
between those in the compounds 2 and 3 described above and
0
the Ar-bian -supported metal complex (tmp-BIAN)TiCl
2
4
(Ti–Nav.
[
24]
.269(2) Å) , which also confirms the radical anion state of
dpp-bian in 4.
ROP of L-lactide catalyzed by complexes 2–4
The compounds 2–4 were tested as ROP catalysts for L-lactide
(
LA) polymerization in toluene (Scheme 4).
O
O
O
toluene, 70 °C
O
O
cat. = 24
n
O
O
O
LA
PLA
Scheme 4. ROP of LA catalyzed by complexes 2–4.
Figure 4. Molecular structure of compound 3. Thermal ellipsoids are at 50%
probability. Hydrogen atoms are omitted for clarity.
As shown in Table 2, complex 2 reveals moderate catalytic
activity, converting up to 300 eq. of LA within 24 hours, whereas
compound 3 takes twice as long to convert only 25 eq. In both
cases, the polydispersity index of the resulting PLAs varies from
moderate (1.40, entry 3) to sufficiently high values (2.85,
entry 4); along with unpredictable polymer molecular weights,
By contrast, the titanium atom in 4 (Fig. 5), which has a square
pyramidal environment (ꢀ = 0.07), is nearly in the ligand plane
ꢃ
(0.2737(5) Å away), which points to a considerable decrease of
π-d interaction. The C(1)–C(2) bond in 4 is almost 0.03 Å longer
than that in 2 and 3 (1.439(4) Å vs. 1.411(4) and 1.421(5) Å,
respectively). Meanwhile, the C–N(av.) bonds are shorter by
this amounts to uncontrollable ROP. The lower experimental M
n
(
when compared with the calculated values) may originate from
0
.06 Å when moving from 2 and 3 to 4 (1.382(3) and 1.378(5) Å
vs. 1.317(4) Å, respectively). In this way, dpp-bian in compounds
and 3 constitutes a dianionic reduced form, whereas in 4 the
1
chain transfer reactions. According to the
H NMR data
(Fig. S7, SI) the PLA obtained using complex 3 has a cyclic
2
structure most likely due to intramolecular termination by way of
a “backbiting” reaction. Compound 2 gives preferably linear
BnO-capped polymer mixed with low molecular byproduct that
ligand has a radical-anionic character as inferred from the
diagnostic C–N and C–C bond lengths, which are intermediate
between those in neutral dpp-bian (1.282(4) Å and 1.534(6) Å,
1
[
21]
2–
was proved by the H NMR spectroscopy (Fig. S6, SI) whereas
respectively)
compounds
and (dpp-bian) in 2 and 3 and other similar
[
12, 15, 22]
the results of ESI mass spectrometry confirm the cyclic structure
of a low-molecular fraction (Fig. S9, SI).
.
[
a]
Table 2. ROP of L-lactide catalyzed by compounds 2–4.
[
b]
[c]
[d]
[f]
[g]
Entry
Cat.
LA
equiv.)
Time
(h)
Conv
(%)
M
n, theor
M
n, exp
Đ
[
e]
(
[
[
[
h]
h]
h]
1
2
3
4
5
6
7
8
9
2
2
2
3
4
4
4
4
4
50
24
24
24
48
24
20
24
20
95
95
95
25
90
67
82
35
72
6840
8100
1.69
2.36
1.40
2.85
1.26
1.30
1.23
1.23
1.15
100
300
100
50
13680
41040
3600
4950
17750
3450
[
h]
6480
8400
100
100
200
300
9650
11320
14270
12130
33730
11810
10080
31100
[
h]
165
[
a] Polymerization conditions: [LA]
equiv versus catalyst. [c] Reaction time. [d] Monomer conversion.
e] Calculated using Mn, theor = [LA] /[catalyst] × MLA × conversion. [f] Measured
0
= 0.5 M, toluene, 70 °C. [b] Amount in
Figure 5. Molecular structure of compound 4. Thermal ellipsoids are at 30%
[
0
0
probability. Hydrogen atoms are omitted for clarity.
by GPC in THF (30 ˚C) using PS standards and corrected by applying the
appropriate correcting factor (0.58). [g] Measured by GPC in THF (30 ˚C).
[
h] Time was not optimized.
The Ti–N bond lengths in 4 (av. 2.123(2) Å) correspond to those
in the tris(semiquinonate) complex [Ti(dmp-BIANisq) ]
3
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European Journal of Inorganic Chemistry
10.1002/ejic.201900715
By contrast, 4 readily polymerizes L-lactide in a controlled
manner, reflected by narrow dispersities and a near-perfect
match of the theoretical and experimental chain lengths of the
desired polymers. Additional kinetic studies carried out for a
and used in situ for the further syntheses. (3S)-cis-3,6-Dimethyl-1,4-
dioxane-2,5-dione (L-lactide, Purac, Netherlands) was purified by single
-
2
vacuum sublimation (95°С, 5×10 mbar) and stored under an inert
atmosphere. C, H, N combustion analysis was conducted with a Flash
1
13
1
112 Series (Thermo Finnigan) elemental analyzer. H and C NMR
1
:100 mixture of 4/LA showed a first-order dependence on LA
spectra were recorded on Bruker Avance II 200 MHz and 400 MHz
spectrometers using the deuterated solvent as an internal standard.
Molecular weights of PLA samples were determined by gel permeation
−
1
concentration (Fig. 6, kobs = 0.0573 h ) as well as a linear
correlation between monomer conversion and the M values of
n
the PLA produced (Fig. S10, SI). MALDI-TOF mass
spectrometric data gathered for the polymer produced from a
chromatography (GPC) on
a chromatograph “Knauer Smartline”
4
equipped with Phenogel Phenomenex Columns 5u (300×7.8 mm) 10 ,
5
1
0 and Security Guard Phenogel Column with RI and UV detectors (254
nm). The mobile phase was tetrahydrofuran, and the flow rate was
ml/min. Phenomenex Medium and High Molecular Weight Polystyrene
5
0:1 LA/4 mixture is in good agreement with linear PLA capped
with benzyloxy end groups (Figs. S11 and S 12, SI). Overall, the
collected experimental data may suggest the mechanism of
ROP of L-lactide in the system LA/4 to be of the coordination-
2
Standard Kits with peak MW from 2700 to 2 570 000 Da were used for
calibration, and the Mark–Houwink correction factor for PLA (0.58) was
applied to account for the difference in hydrodynamic volumes between
[
25]
insertion type (Scheme S1, SI).
[
26]
polystyrene and polylactide.
Mass spectra of PLA samples were
recorded on a Thermo Fisher Scientific LTQ Orbitrap XL equipped with
ESI ion source and a Bruker Microflex LT mass spectrometer for MALDI
TOF MS measurements which were performed in linear mode using (4-
hydroxybenzilydene)malonitrile as a matrix and THF as a solvent.
Sodium alcoholates. Sodium benzylate as well as sodium 2-
methoxyethylate were synthesized by the reaction of 60 % sodium
hydride (0.40 g, 10 mmol) with benzyl alcohol (1.11 g, 10.28 mmol) or 2-
methoxyethanol (0.78 g, 10.26 mmol) correspondingly. The resulting
mixture in n-hexane was stirred overnight at room temperature. The
white precipitates were filtered off, washed with hexane and dried in
vacuum at elevated temperature (100 °C) for two hours. The yield of
1
BnONa: 1.10 g (85 %); H NMR (400 MHz, toluene-d
8
, 298 K), δ, ppm:
7
.15 (d, J = 4.5 Hz, 4H); 7.08 (m, 1H); 4.37 (s, 2H). The yield of
1
2 2 8
MeOCH CH ONa: 0.78 g (80 %); H NMR (400 MHz, toluene-d , 298 K),
0
Figure 6. Plot of ln([M] /[M]) as a function of time in the ROP of L-lactide using
complex 4 as catalyst (M = LA, conditions: LA/4 in a 100:1 ratio, [M] = 0.5 M,
0
δ, ppm: 4.43 (br. s, 2H); 3.63 (br. s, 2H); 3.39 (s, 3H).
toluene, 70 °C).
(
dpp-bian)Ti(OBn)
2
(2). To a toluene solution of 1, prepared from 0.5 g
(
1.0 mmol) of dpp-bian in 25 ml toluene, a suspension of 2.08 equiv.
sodium benzylate (0.27 g, 2.08 mmol) in toluene (5 ml) was added at
room temperature. After stirring of the mixture during 1 hour, the solvent
was vaporized and n-hexane (25 ml) was added. The mixture was stirred
within 15 min and the volatiles were evaporated in vacuo for complete
disposal of toluene residues. The crude product was dissolved again in
n-hexane (25 ml) and the precipitated was filtered off. The solution was
concentrated to a volume of 10 ml. Complex 2 was isolated as plate dark
Conclusions
We have obtained and characterized three new titanium(IV)
alkoxides supported by non-innocent bis(arylimino)acenaphthe-
ne. In compounds 2 and 3, the bisamide chelate ligand acts as a
2
σ π-donor, whereas the monomeric five-coordinated complex 4
red crystals. Total yield: 0.65 g (85 %). Anal. calc. for C50
8.72; H, 7.14; N, 3.67 %. Found: C, 78.33; H, 7.30; N, 3.54%. H NMR
200 MHz, toluene-d , 298 K), δ, ppm: 7.29…7.12 (m, 11H); 6.97…6.87
m, 4H), 6.80…6.57 (m, 7H); 5.32 (s, 2H), 4.68 (s, 2H), 3.62 (sept, J =
54 2 2
H N O Ti: C,
is stabilized by radical anionic dpp-bian. While all of the species
demonstrate catalytic activity in the ROP of L-lactide, compound
1
7
(
(
8
4
carries out a living polymerization. It readily polymerizes L-
–1
lactide, at a relatively low rate (0.0573 h ) but in a highly
controlled manner, producing BnO-capped polymer chains with
predictable molecular weights and narrow dispersities. The
weaker binding of the ligand to the metal center, due to
decreasing π-d interaction, leads to enhanced catalytic activity
of compound 4 in ROP of L-lactide through a coordination-
insertion mechanism, in comparison with 2 and 3.
6
.8 Hz, 2 H), 3.15 (sept, J = 6.8 Hz, 2 H), 1.30 (d, J = 6.8 Hz, 6H), 1.15 (d,
13
J = 6.8 Hz, 6H), 1.11 (d, J = 6.8 Hz, 6H), 1.01 (d, J = 6.8 Hz, 6H).
NMR (50 MHz, toluene-d , 298 K), δ, ppm: 23.49, 23.99, 24.65, 25.77,
28.39, 28.47, 75.85, 78.00, 115.43, 122.22, 123.50, 124.19, 125.38,
1
1
C
8
26.14, 126.44, 126.61, 126.76, 127.12, 127.87, 127.98, 128.21, 128.35,
29.15, 134.18, 135.90, 141.72, 141.95, 142.57, 143.81, 146.18. IR
-
1
(
Nujol) ν/cm : 1330 (m, C–N), 1125 (s, C–O).
(
2 2
dpp-bian)TiCl(OCH CH OMe) (3). Sodium 2-methoxyethylate (0.10 g,
1
.02 mmol) as a suspension in toluene (5 ml) was added to a solution
Experimental Section
of 1, prepared from 0.5 g (1.0 mmol) of dpp-bian in 25 ml toluene. The
mixture was stirred within 1 hour and the solvent was changed to n-
hexane twice in an analogous manner to the synthesis of 2. The solids
were filtered off and the n-hexane solution was concentrated to a volume
of 5 ml. Complex 3 was isolated as needle-like red crystals. Total yield:
General Remarks. All manipulations were carried out under nitrogen
using Schlenk techniques or in a nitrogen-filled MBraun Unilab glovebox.
Toluene, n-hexane, and n-heptane were distilled from sodium/benzophe-
none and stored over 4 Å molecular sieves under nitrogen.
0.51 g (77 %). Anal. calc. for C39
4.25 %. Found: C, 70.41; H, 7.34; N, 4.12%. H NMR (400 MHz,
2 2
H47ClN O Ti: C, 71.07; H, 7.19; N,
[9]
1
[
2 2
(dpp-bian)TiCl ] (1) was prepared according to a published procedure
This article is protected by copyright. All rights reserved.

European Journal of Inorganic Chemistry
10.1002/ejic.201900715
Toluene-d
2
8
8
, 298 K) δ 7.27 (dd, J = 7.7, 1.9 Hz, 2H), 7.21 (t, J = 7.6 Hz,
H), 7.17 (d, J = 8.2 Hz, 2H), 7.11 (dd, J = 7.7, 1.9 Hz, 2H), 6.89 (dd, J =
.3, 7.0 Hz, 2H), 6.74 (d, J = 7.0 Hz, 2H), 4.40 (t, J = 5.0 Hz, 2H), 3.91
analysis of metal complexes and chemical analysis of polymers
by ESI mass spectrometry and in particular to Prof. Dr. Andreas
Grohmann for fruitful discussion. We appreciate Dr. Viacheslav
A. Kuropatov (IOMC RAS) for the registration of EPR spectra
and Dr. Ivan D. Grishin (Nizhniy Novgorod State University) for
the recording of MALDI TOF mass spectra of PLA.
(
2
hept, J = 6.8 Hz, 2H), 3.23 (t, J = 4.9 Hz, 2H), 2.84 (hept, J = 6.8 Hz, 2H),
.76 (s, 3H), 1.50 (d, J = 6.8 Hz, 6H), 1.30 (d, J = 6.8 Hz, 6H), 1.11 (d,
J = 6.8 Hz, 6H), 0.90 (d, J = 6.8 Hz, 6H). We could not obtain the
13
appropriate C NMR data for alkoxy chloride complex 3 due to its
-
1
insufficient solubility. IR (Nujol) ν/cm : 1324 (m, C–N), 1140 (s, C–O),
110 (s, C–O).
1
Keywords: titanium • bis(arylimino)acenaphthenes • non-
innocent ligands • ring-opening polymerization • L-lactide
(
2
dpp-bian)TiOBnCl (4). A solution of 0.98 equiv. benzyl alcohol (0.105
g, 0.98 mmol) in toluene (2 ml) was added dropwise to a toluene solution
of 1, prepared from 0.5 g (1.0 mmol) of dpp-bian in 25 ml toluene, under
constant stirring at room temperature. The color of the reaction mixture
changed from green to blue-violet. The solvent was evaporated in vacuo
and n-heptane (30 ml) was added. Within few minutes complex 4
precipitated as a dark-blue crystalline solid which was filtered off, washed
with n-heptane and dried in vacuo. Total yield: 0.34 g (47 %). Anal. calc.
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35, 37
(
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= 1.997, a
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Acknowledgments
We thank the Russian Science Foundation (grant 17-73-20356)
for financial support of this work. We are grateful to the Institute
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This article is protected by copyright. All rights reserved.

European Journal of Inorganic Chemistry
10.1002/ejic.201900715
FULL PAPER
Entry for the Table of Contents
FULL PAPER
Titanium catalysts for ROP
Dr. Alexander G. Morozov*, Tatyana V.
Martemyanova, Dr. Vladimir A.
Dodonov, Dr. Olga V. Kazarina, and
Prof. Dr. Igor L. Fedushkin
Page No. – Page No.
Titanium (IV) alkoxido and alkoxido chlorido complexes supported by
bis(arylimino)acenaphthene ligand dpp-bian in different reduced forms were
obtained and fully characterized. Benzoxido dichlorido titanium derivative (dpp-
Four- and five-coordinate titanium
(IV) complexes supported by the dpp-
bian ligand in ROP of L-lactide
bian)TiOBnCl
2
proved to be an efficient catalyst for the living ROP of L-lactide
providing a PLA in a highly controlled manner.
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