Synthesis and structure of titanium alkoxides based on tetraphenyl substituted 2,6-dimethanolpyridine moiety

Article abstract of DOI:10.1016/j.ica.2006.10.027

Novel titanocanes and spirobititanocanes based on 2,6-bis[hydroxy(diphenyl)methyl]pyridine (1a) and 2,6-di(hydroxymethyl)pyridine (1b) - [2,6-C₅H₃N(CPh₂O)₂]Ti(O-i-Pr)₂ (2a), [2,6-C₅H_3<

Full text of DOI:10.1016/j.ica.2006.10.027

Inorganica Chimica Acta 360 (2007) 2507–2512
www.elsevier.com/locate/ica
Note
Synthesis and structure of titanium alkoxides based on
tetraphenyl substituted 2,6-dimethanolpyridine moiety
a
a
a,
a
Kirill V. Zaitsev , Maxim V. Bermeshev , Sergey S. Karlov *, Yuri F. Oprunenko ,
b
c
a
Andrei V. Churakov , Judith A.K. Howard , Galina S. Zaitseva
a
Chemistry Department, Moscow State University, Leninskie Gory, 119899 Moscow, Russia
Institute of General and Inorganic Chemistry, RAS, Leninskii Pr. 31, Moscow 119991, Russia
b
c
Department of Chemistry, University of Durham, South Road, DH1 3LE Durham, UK
Received 9 August 2006; received in revised form 24 October 2006; accepted 29 October 2006
Available online 7 November 2006
Abstract
Novel titanocanes and spirobititanocanes based on 2,6-bis[hydroxy(diphenyl)methyl]pyridine (1a) and 2,6-di(hydroxymethyl)pyridine
(1b) – [2,6-C5H3N(CPh2O)2]Ti(O-i-Pr)2 (2a), [2,6-C5H3N(CPh2O)2]2Ti (3a), [2,6-C5H3N(CH2O)2]2Ti (3b), [2,6-C5H3N(CPh2O)2]TiCl2 (4)
– as well as the closely related N-phenyl derivative PhN(CH2CH2O)2Ti(Cl)Cp (5) have been synthesized. Complexes 2–5 were charac-
terized by 1H and 13C NMR spectroscopy and elemental analysis data. The molecular structure of 3a was determined by X-ray structure
analysis.
ꢀ 2006 Elsevier B.V. All rights reserved.
Keywords: 2,6-Pyridinedimethanol ligand; Transannular interaction; Alkoxides; Crystal structure
1. Introduction
property’’ is compounds containing an additional intramo-
lecular donor group. This group may form the transannular
bond with titanium center. The presence of such a bond in
molecules allows to govern the structural and electronic
parameters of the titanium derivative such as coordination
number of Ti atom as well as the type of its coordination
polyhedron and Lewis acidity and hence to vary the cata-
lytic properties of titanium compound. Among these com-
pounds the derivatives of trialkanolamines as ligands
(titanatranes) have been investigated in considerable extent.
The different structural features and catalytic applications
were found for these substances (see key references and ref-
erences cited therein) [14–18]. The derivatives of dialkanol-
amines (titanocanes) and monoalkanolamines are less
studied [19–30]. However, these classes of compounds could
be more promising objects for investigations due to their
greater chemical and structural flexibility. Titanocanes
derivatives containing pyridine moiety (for example 2,6-
di(hydroxymethyl)pyridine) are particularly interesting
due to the special electronic and steric properties of the pyr-
idine group. Although these derivatives were previously
During the last five decades, alkoxytitanium derivatives
have found widespread application as catalysts in various
organic processes [1–8]. Usually, in fine organic reactions,
tetraalkoxytitanium derivatives are used jointly with co-cat-
alysts, such as (R)-BINOL or (L)-(+)-tartrate which form
during the reaction the catalytic active species due to the
substitution of alkoxy groups at titanium center [9–13].
However, the structure of these species is postulated and
studied in detail very seldom. At the same time the investi-
gations of such species are important because they give new
information about the structural titanium chemistry as well
as about an organic reaction mechanism. It should be noted
that there are several ligand types which form enough stable
complexes with Ti(O-i-Pr)4 to study their structure and
reactivity. A very promising class of titanium alkoxides
which is suitable for relationship ‘‘structure – catalytic
*
Corresponding author.
E-mail address: sergej@org.chem.msu.ru (S.S. Karlov).
0020-1693/$ - see front matter ꢀ 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2006.10.027

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K.V. Zaitsev et al. / Inorganica Chimica Acta 360 (2007) 2507–2512
prepared [31], their structural investigations are not known
to date.
in 0.40 g (95%) of a white solid. Suitable crystals were
obtained by slow evaporation of solution of 3a in toluene.
Anal. Calc. for C62H46N2O4Ti: C, 79.99; H, 4.98; N, 3.01.
Found: C, 79.40; H, 5.22; N, 2.93%. 1H NMR
In continuation of our studies on titanatrane and titano-
cane chemistry [32,33], we present here the synthesis and
characterization of new cyclic titanium alkoxides with trans-
annular interaction. Their structure in solution is discussed
based on NMR spectroscopy data. The structure of com-
pound 3a was determined by single-crystal X-ray analysis.
3
(400.1 MHz, CDCl3) d (ppm): 7.68 (t, JHH = 7.8 Hz, 2H,
3
H1), 7.32 (d, JHH = 7.8 Hz, 4H, H2, H20), 7.22 (m,
16H), 7.10 (m, 8H), 7.01 (m, 16H). 13C NMR
(100.61 MHz, CDCl3) d (ppm): 172.17 (C3, C30), 147.43
(C-i), 140.04 (C1), 128.13 (C-m), 127.66 (C-o), 126.62 (C-
p), 121.14 (C2, C20), 98.48 (C4, C40).
2. Experimental
All manipulations were carried out under argon atmo-
sphere using standard Schlenk techniques. Solvents were
dried by standard methods and distilled before use.
Ti(O-i-Pr)4 (Aldrich) was distilled before use. 2,6-
Di(hydroxymethyl)pyridine (1b) (Aldrich) was used as sup-
plied. 2,6-Bis[hydroxy(diphenyl)methyl]pyridine (1a) [34],
TiCl2(NMe2)2 [35] and CpTiCl3 [36] were synthesized
according to the literature procedures. CDCl3 was obtained
from Deutero GmbH and dried over P4O10. 1H (400 MHz)
and 13C NMR (100 MHz) spectra were recorded on a Bru-
ker Avance 400 spectrometer (in CDCl3 at 295 K unless
otherwise stated). Chemical shifts in the 1H and 13C
NMR spectra are given in ppm relative to internal Me4Si.
Elemental analyses were carried out by the Microanalytical
Laboratory of the Chemistry Department of the Moscow
State University.
2.2.2. Method B
To a solution of 1a (0.8 g, 1.80 mmol) in toluene
(25 mL) at ꢀ78 ꢁC was added dropwise a solution of BuLi
in hexane (1.90 mmol), and the resulting mixture was stir-
red at the same temperature for 1 h. Then the temperature
was raised to 0 ꢁC and maintained for 2 h. TiCl4 (0.19 mL,
1.80 mmol) was added dropwise at ꢀ78 ꢁC to the obtained
suspension, and the mixture was stirred overnight. The
solution was filtered and the solvent was evaporated under
reduced pressure to leave a white powder. The powder was
recrystallized from toluene yielding 0.46 g (54%) of com-
pound 3a.
2.3. Synthesis of [2,6-Py(CH2O)2]2Ti (3b)
Ti(O-i-Pr)4 (1.22 g, 4.3 mmol) was added dropwise to a
solution of 1b (0.60 g, 4.3 mmol) in DMSO (20 mL). After
45 h of stirring, the formed solid was filtered and washed
with dichloromethane resulting in 0.62 g (90%) of an
orange solid. Anal. Calc. for C14H14N2O4Ti: C, 52.20; H,
4.38; N, 8.70. Found: C, 52.05; H, 4.48; N, 8.59%. 1H
2.1. Reaction of Ti(O-i-Pr)4 with 2,6-
bis[hydroxy(diphenyl)methyl]pyridine (1a); the formation
of [2,6-Py(CPh2O)2]Ti(O-i-Pr)2 (2a)
To a solution of 1a (1.0 g, 2.08 mmol) in chloroform
(25 mL) at 20 ꢁC was added dropwise Ti(O-i-Pr)4
(0.62 mL, 2.08 mmol), and the resulting mixture was stirred
and refluxed for 5 h. The solvent was then evaporated under
reduced pressure to leave a white powder. The powder was
recrystallized from a mixture of methylene chloride (3 mL)
and hexane (0.5 mL). Compound 2a was isolated in 85%
NMR (400.1 MHz, DMSO-d6)
d
(ppm): 8.05 (t,
3
3JHH = 7.6 Hz, 2H, H1), 7.50 (d, JHH = 7.6 Hz, 4H, H2,
H20), 5.53 (s, 8H, CH2). 13C NMR (100.61 MHz, DMSO-
d6) d (ppm): 167.91 (C3, C30), 141.04 (C1), 116.90 (C2,
C20), 77.38 (C4, C40).
1
yield (contains a small amount of 3a; H and 13C NMR
spectroscopy data). 1H NMR (400.1 MHz, CDCl3) d
2.4. Synthesis of [2,6-Py(CPh2O)2]TiCl2 (4)
3
3
(ppm): 7.78 (t, JHH = 7.8 Hz, 1H, H1), 7.34 (d, JHH
=
7.8 Hz, 2H, H2, H20), 7.39 (m, 8H), 7.26 (m, 12H), 4.47
A solution of 1a (1.07 g, 2.42 mmol) in chloroform
(20 mL) was added to a suspension of TiCl2(NMe2)2
(0.5 g, 2.42 mmol) in chloroform (40 mL) at 20 ꢁC. The
mixture was stirred for 60 h. After that, the mixture was fil-
tered through Celite and the solvent was evaporated in vac-
uum. The crude product was recrystallized from methylene
chloride obtaining 0.27 g (20%) of a fine white solid. Anal.
Calc. for C31H23Cl2NO2Ti: C, 66.45; H, 4.14; N, 2.50.
Found: C, 65.24; H, 3.76; N, 2.03%. 1H NMR
3
3
(sept, JHH = 6.1 Hz, 2H, OCH), 0.99 (d, JHH = 6.1 Hz,
12H). 13C NMR (100.61 MHz, CDCl3): d (ppm): 171.29
(C3, C30), 146.70 (C-i), 140.23 (C1), 127.90 (C-m), 127.50
(C-o), 127.22 (C-p), 121.46 (C2, C20), 95.92 (C4, C40),
76.19 (C5, C50), 25.82 (C6, C60). The satisfactory results
of elemental analyses were not obtained due to the presence
of traces of 3a.
3
(400.1 MHz, CDCl3): d 7.99 (t, JHH = 7.8 Hz, 2H, H1),
2.2. Synthesis of [2,6-Py(CPh2O)2]2Ti (3a)
3
7.53 (d, JHH = 7.8 Hz, 4H, H2, H20), 7.40 (m, 8H), 7.27
(m, 12H). 13C NMR (100.61 MHz, CDCl3) d (ppm):
170.85 (C3, C30), 143.57 (C-i), 142.20 (C1), 128.21 (C-m),
128.00 (C-o), 127.72 (C-p), 122.08 (C2, C20), 98.71 (C4,
C40).
2.2.1. Method A
Ti(O-i-Pr)4 (0.14 mL, 0.45 mmol) was added dropwise to
a solution of 1a (400 mg, 0.90 mmol) in toluene (10 mL).
After 15 h refluxing, the solvent was evaporated resulting

K.V. Zaitsev et al. / Inorganica Chimica Acta 360 (2007) 2507–2512
2509
2.5. Attempt at synthesis of [2,6-Py(CPh2O)2]TiCl2 (4)
from TiCl4 Æ 2THF and 1a in the presence of Et3N
(10:3) 0.56 g (57%) of 5 as a yellow solid was obtained.
Anal. Calc. for C15H18NO2TiCl: C, 54.99; H, 5.54; N,
4.28. Found: C, 52.60; H, 5.30; N, 4.20%. 1H NMR
(400.1 MHz, CDCl3) d (ppm): 7.32–7.30, 6.82–6.78, 6.73–
6.71 (3m, 5H, C6H5-group), 6.22 (s, 5H, C5H5), 4.87–4.81
(m, 2H, OCH2), 4.34–4.30 (m, 2H, OCH2), 3.93–3.89 (m,
2H, NCH2) 3.28–3.31 (m, 2H, NCH2). 13C NMR
(100.61 MHz, CDCl3) d (ppm): 147.51, 129.72, 117.44,
111.39 (C6H5-group), 116.45 (C5H5), 78.98 (OCH2), 58.15
(NCH2).
To a solution of TiCl4 Æ 2THF (0.75 g, 2.30 mmol) in
methylene chloride (30 mL) at ꢀ30 ꢁC was added dropwise
a solution of 1a (1.00 g, 2.30 mmol) and Et3N (0.64 mL,
4.60 mmol) in methylene chloride (30 mL), and the result-
ing mixture was stirred at the same temperature for 1 h.
Then the mixture was heated to room temperature and stir-
red overnight. The solvent was evaporated under reduced
pressure, the crude product was extracted into benzene
(2 · 40 mL) and the solution was filtered. After removing
of the solvent and recrystallization from a mixture of meth-
ylene chloride and heptane, 0.40 g (32%) of compound 4
was obtained, which contains approximately 30% of 3a.
2.7. X-ray crystallography
Crystal data, data collection, structure solution and
refinement parameters for 3a are listed in Table 1. The
structure was solved by direct methods [37] and refined
by full matrix least-squares on F2 [38] with anisotropic
thermal parameters for all non-hydrogen atoms (except
solvent toluene molecules). Solvent toluene was found to
be disordered over two positions with occupancies ratio
0.69/0.31. All hydrogen atoms of the main organometallic
molecule were found from diff. Fourier synthesis and
refined with isotropic thermal parameters, hydrogen atoms
2.6. Synthesis of [PhN(CH2CH2O)2]Ti(Cl)Cp (5)
PhN(CH2CH2OH)2 (0.54 g, 3.0 mmol) and Et3N
(0.91 g, 9.0 mmol) were added dropwise to a stirred solu-
tion of CpTiCl3 (0.66 g, 3.0 mmol) in dichloromethane
(50 mL) at ꢀ78 ꢁC. The reaction mixture was stirred for
1 h at this temperature and then overnight at room temper-
ature. All volatiles were removed in vacuo and the residue
was extracted with benzene (2 · 40 mL). The solids were fil-
tered off, the solvent was removed in vacuo and then after
recrystallization from dichloromethane: n-hexane mixture
Ph
Ph
O
O-i-Pr
Ph
Ph
Ph
Ph
Ti(O-i-Pr)4
Ti(O-i-Pr)4
Ti
N
N
+ 3a (traces)
O-i-Pr
OH
OH
O
Table 1
1a
2a
Ph
Crystal data, data collection and refinement parameters for 3a
Ph
Compound
3a
C
1023.04
Ph
Ph
Ph
Ph
Empirical formula
Formula weight
Crystal system
Space group
69H54N2O4Ti
O
O
O
O
triclinic
Ph
Ph
Ph
Ph
ꢀ
P1
Ti
N
N
N
Unit cell dimensions
˚
OH
OH
1. 2 n-BuLi
2. TiCl4
1a
a (A)
11.602(4)
14.627(5)
15.874(5)
˚
Ph
Ph
Ph
Ph
b (A)
3a
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
85.735(7)
82.715(8)
79.346(15)
2622.5(15)
2
1.296
0.218
1072
Bruker SMART 6K
120
0.71073
2.60–28.00
ꢀ15 6 h 6 15, ꢀ18 6 k 6 19,
ꢀ20 6 l 6 20
17812
11837 [0.0225]
11837/0/858
1.049
O
O
O
Ti(O-i-Pr)4
3
˚
V (A )
Z
Ti
N
N
N
OH
OH
Dcalc (g cmꢀ3
Absorption coefficient (mmꢀ1
F(000)
Diffractometer
Temperature (K)
)
O
1b
)
3b
Ph
Ph
N
O
˚
Radiation k (A)
h Range (ꢁ)
Cl
Cl
Ph
Ph
Ph
Ph
(Me2N)2TiCl2
Ti
N
Index ranges
OH
OH
O
1a
4
Reflections collected
Ph
Ph
Independent reflections [Rint
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2r(I)]
R indices (all data)
]
.
TiCl4 2 THF / Et3N
3a + 4
R1 = 0.0490; wR2 = 0.1179
R1 = 0.0652; wR2 = 0.1248
0.444/ꢀ0.413
CpTiCl3 / Et3N
PhN(CH2CH2OH)2
PhN(CH2CH2O)2Ti(Cl)Cp 5
Largest difference in peak/hole
ꢀ3
˚
(e A
)
Scheme 1.

2510
K.V. Zaitsev et al. / Inorganica Chimica Acta 360 (2007) 2507–2512
of solvent toluene molecules were placed in calculated posi-
tions and refined using a riding model.
two signals of pyridine group protons as well as two signals
of isopropoxy group protons (CH and CH3). Seven signals
of aromatic carbons (four from Ph-groups and three from
Py group) as well as two signals of isopropoxy group car-
bons were found in the 13C NMR spectrum of 2. Thus, this
compound is monomeric in CDCl3 solution at room tem-
perature. It should be noted that all previously prepared
diisopropoxytitanocanes are also monomeric in solution
[19,33]. The dimerization takes place in the case of non-
bulky alkoxy groups (such as methyl) [33]. Also, the equiv-
alence of CPh2 groups in 4 and CH2CH2O arms in 5 allows
us to conclude that these compounds are expectedly mono-
meric in solution at room temperature. According to the
NMR spectroscopic data, spirobititanocanes 3a and 3b
possess a monomeric structure in solution and exist as
one geometric isomer.
3. Results and discussion
3.1. Synthesis of complexes
Our synthetic results are shown in Scheme 1.
According to the literature, compounds of general for-
mula L2Ti and LTiX2 (where L = dialkanolamine moiety
and X = Hal or alkoxy group) are perspective for catalytic
investigations [7,14,39,40]. Thus, these derivatives are com-
pounds in question in this report. As we have recently
shown, the transalkoxylation reaction is the most suitable
route for the preparation of titanocanes and spirobititano-
canes [33].
We have found that dialkanolamine 1a reacted readily
with an equimolar amount or 0.5 equiv. of Ti(O-i-Pr)4 at
reflux temperature in chloroform or toluene solution to give
2a or 3a in high yields (Scheme 1). Analogously, unsubsti-
tuted analogue of 3a – compound 3b – was prepared from
1b and Ti(O-i-Pr)4. The inseparable mixture of 4 and 3a
was found in the reaction of 1a with TiCl4 Æ 2THF in the
presence of triethylamine. On the contrary, pure dichloride
5 was obtained in moderate yield from the similar reaction
between PhN(CH2CH2OH)2 and CpTiCl3.
3.3. Crystal structure
The structure of 3a was studied by X-ray diffraction
(Fig. 1). Table 2 lists selected geometrical parameters
for this compound. The monomeric nature of this species
with a hexacoordinate titanium center in solid state was
confirmed. The coordination polyhedron of the titanium
atom represents a distorted octahedron with a rare trans
disposition (trans, mer geometry) of the two nitrogen
atoms at the Ti atom [33,41,42]. The Ti–N distances in
˚
3.2. NMR spectra
3a are very short (2.160(2), 2.161(2) A). These values are
smaller than those previously found in the studied
bis(dialkanolamine) derivatives which vary over the range
2.310(2)–2.471(3) A [33] and in closely related derivatives
1
The H NMR spectrum of the prepared Py-containing
˚
titanocane 2a comprises of multiplets of Ph groups and
Fig. 1. Molecular structure of 3a. Hydrogen atoms and toluene molecule are omitted for clarity.

K.V. Zaitsev et al. / Inorganica Chimica Acta 360 (2007) 2507–2512
2511
Table 2
Appendix A. Supplementary material
˚
Selected bond lengths (A) and angles (ꢁ) for 3a
˚
Bond lengths (A)
CCDC 612584 contains the supplementary crystallo-
graphic data for this paper. These data can be obtained free
of charge via http://www.ccdc.cam.ac.uk/conts/retriev-
ing.html, or from the Cambridge Crystallographic Data
Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax:
(+44) 1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk.
Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/j.ica.2006.
10.027.
Ti–O(21)
Ti–O(12)
Ti–O(22)
Ti–O(11)
Ti–N(2)
Ti–N(1)
1.884(1)
1.887(1)
1.891(1)
1.898(1)
2.160(2)
2.161(2)
Bond angles (ꢁ)
O(21)–Ti–O(12)
O(21)–Ti–O(22)
O(12)–Ti–O(22)
O(21)–Ti–O(11)
O(12)–Ti–O(11)
O(22)–Ti–O(11)
O(21)–Ti–N(2)
O(12)–Ti–N(2)
O(22)–Ti–N(2)
O(11)–Ti–N(2)
O(21)–Ti–N(1)
O(12)–Ti–N(1)
O(22)–Ti–N(1)
O(11)–Ti–N(1)
N(2)–Ti–N(1)
94.82(6)
146.48(5)
96.73(6)
93.99(6)
146.61(5)
93.42(6)
73.62(6)
105.58(6)
72.99(5)
107.81(6)
108.25(6)
73.06(6)
105.21(5)
73.58(6)
177.69(6)
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of pyridine ligands containing one alkoxy arm: Me2Ti(Cp*)-
˚
(OCMePy2), 2.307(3) A [43], Cl2Ti(Cp)[OC(i-Pr)2Py],
˚
2.254(1) A [44]. However, these values are close to those
previously found in triaza derivatives: {2,6-Py[CH2N-
˚
(2,6-Me2C6H3)]2}Ti(Br)CH2CMe2Ph, 2.126(6) A [45];
{2,6-Py[CH2N(2,6-i-Pr2C6H3)]2}Ti[–C(SiMe3)@CHC(SiMe3)
˚
@CH–], 2.172(8) A [46]. Obviously, the special steric
requirements in bis-chelates but not the electronic proper-
ties of the substituents around Ti atom cause the shorten-
ing of Ti–NPy in 3a. All atoms of eight-membered ring
TiOCCNCCO lie in the same plane. This strictly differs
from the tendency previously established for bis(dialknol-
amine)titanium derivatives where five-membered rings of
the ocane skeletons adopt an ‘‘envelope’’-like conforma-
tion [33]. As we previously found, the shorter Ti–N bonds
in the spirobititanocane molecules correspond to longer
Ti–O bonds [33]. This tendency is also supported by the
structural data for 3a where Ti–O bond distances are
appreciably longer than those in the only X-ray studied
monomeric tetraalkoxy titanium derivative with a tetraco-
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