Synthesis of a functionalized chromane derivative via a TiCl 4-mediated cyclization reaction

Article abstract of DOI:10.1007/s00706-012-0890-6

The reaction of 1-methoxy-1,3-bis(silyloxy)-1,3-butadiene with N-salicylideneaniline results in the formation of a functionalized chromane derivative. Diffuse reflectance UV-Vis, ATR-IR, and Raman spectroscopic investigations showed that the reaction proceeds via formation of a titanium complex consisting of TiCl₄ and two molecules of the N-salicylideneaniline. In situ ATR-IR spectroscopy reveals that this 2:1 complex is responsible for the subsequent mode of interaction with the 1,3-bis(silyloxy)-1,3-butadiene and formation of the product.

Full text of DOI:10.1007/s00706-012-0890-6

Monatsh Chem (2013) 144:421–428
DOI 10.1007/s00706-012-0890-6
ORIGINAL PAPER
Synthesis of a functionalized chromane derivative
via a TiCl4-mediated cyclization reaction
•
Leif R. Knopke Sebastian Reimann Anke Spannenberg Peter Langer
•
•
•
¨
•
Angelika Bru¨ckner Ursula Bentrup
Received: 30 July 2012 / Accepted: 25 November 2012 / Published online: 17 January 2013
Ó Springer-Verlag Wien 2013
Abstract The reaction of 1-methoxy-1,3-bis(silyloxy)-
1,3-butadiene with N-salicylideneaniline results in the
formation of a functionalized chromane derivative. Diffuse
reflectance UV–Vis, ATR-IR, and Raman spectroscopic
investigations showed that the reaction proceeds via for-
mation of a titanium complex consisting of TiCl4 and two
molecules of the N-salicylideneaniline. In situ ATR-IR
spectroscopy reveals that this 2:1 complex is responsible
for the subsequent mode of interaction with the 1,3-
bis(silyloxy)-1,3-butadiene and formation of the product.
with ketene acetals 2a, 2b (Scheme 1) [1]. On the basis of
our studies different intermediates of the reaction could be
identified. The use of TiCl4 as Lewis acid leads to the for-
mation of a bis-chelate complex of 2 and TiCl4 which plays
a role during the formation of salicylates 3. In contrast,
in the presence of trimethylsilyl-trifluoromethanesulfonate
(TMSOTf) pyran-4-ones 4 (mostly cyclohexenones) were
formed because only one site of 2 is attacked by the
TMSOTf.
Herein, we report, for the first time, the reaction of
1-methoxy-1,3-bis(silyloxy)-1,3-butadiene 1 with N-sali-
cylideneaniline (5) which provides a convenient access to a
functionalized chromane derivative. The mechanism of the
reaction was studied by in situ spectroscopic experiments.
Keywords Cycloadditions Á Reaction mechanism Á
In situ spectroscopy Á IR spectroscopy Á
UV–Vis spectroscopy
Introduction
Results and discussion
Recently, we reported mechanistic studies of the Lewis acid
Reaction of 1,3-bis(silyloxy)-1,3-butadiene
with N-salicylideneaniline and TiCl4
mediated cyclization of 1,3-bis(silyloxy)-1,3-butadiene 1
The TiCl4-mediated reaction of 1-methoxy-1,3-bis(silyl-
oxy)-1,3-butadiene 1 with N-salicylideneaniline (5) afforded
the functionalized chromane methyl 2-[2-hydroxy-4-(phe-
nylamino)chroman-2-yl]acetate (7) in 82 % yield as a
mixture of two diastereomers (Scheme 2). The formation of
the product can be explained by Lewis acid mediated attack
of the terminal carbon atom of the diene onto the imine and
cyclization by attack of the phenol oxygen atom onto the
carbonyl group of the b-ketoester moiety. The theoretically
possible formation of naphthalene derivative 6 by cycliza-
tion via an aromatic carbon atom was not observed. The
structure of 7 was independently confirmed by X-ray crystal
structure analysis (Fig. 1, Supplementary Material).
Electronic supplementary material The online version of this
article (doi:10.1007/s00706-012-0890-6) contains supplementary
material, which is available to authorized users.
¨
L. R. Knopke Á S. Reimann Á A. Spannenberg Á P. Langer Á
A. Bru¨ckner Á U. Bentrup (&)
¨
Leibniz-Insitut fu¨r Katalyse e.V. an der Universitat Rostock
(LIKAT), Albert-Einstein-Str. 29a, 18059 Rostock, Germany
e-mail: ursula.bentrup@catalysis.de
P. Langer
e-mail: peter.langer@uni-rostock.de
S. Reimann Á P. Langer
¨
Institut fu¨r Chemie, Universitat Rostock, Albert-Einstein-Str. 3a,
18059 Rostock, Germany
123

¨
L. R. Knopke et al.
422
In a second experiment, 5 and TiCl4 were mixed in a
ratio of 1:1 in CH2Cl2 in a concentration of 0.5 mol/dm3.
Similar to the previous experiment, a dark red precipitate is
formed which was also isolated and analyzed. The ATR-
IR, diffuse reflectance UV–Vis, Raman spectra, and the
obtained XRD patterns of both precipitates were very
similar. Obviously, two molecules of 5 always interact with
one TiCl4 molecule.
The diffuse reflectance UV–Vis spectrum of the solid
formed from the 2:1 mixture of 5 and TiCl4 (Fig. 2a) shows
a broad band containing two maxima at 286 and 484 nm
with a shoulder at 533 nm. The diffuse reflectance UV–Vis
spectrum of neat (solid) 5 (Fig. 2b) has a different shape as
compared to the spectra recorded in diluted solutions. This
is caused by bulk effects like intermolecular hydrogen
bonding. The spectrum of 5 shows three maxima at 257,
300/315, and 395 nm. The band at 257 nm can be assigned
to r ? p* transitions and the band at 300 and 315 nm to
p ? p* transitions of the phenyl ring of salicylideneani-
line. The band at 395 nm can be assigned to a p ? p*
transition as well. A proper assignment seems to be diffi-
cult in this case because the band of the p ? p* transition
of the benzyl ring occurs in the liquid phase at 339 nm,
whereas the long-wave band of the quinoid tautomer
occurs at 427 nm [7, 8].
Scheme 1
Interaction between N-salicylideneaniline and TiCl4:
ex situ analysis
To study the mechanism of the reaction of 1 with 5 com-
prehensive spectroscopic studies comprising ATR-IR,
diffuse reflectance UV–Vis, and Raman spectroscopic
investigations were performed. It is known that N-salicy-
lideneaniline can form bidentate complexes with transition
metals [2–6]. The coordination takes place via both the
nitrogen and the oxygen atom.
According to our previous studies, the shift to longer
wavelengths indicates the formation of a bis-chelate com-
plex like structure 8 (Scheme 3). This type of compound
was previously described by Birdar and Kulkarni [9], but
its color was yellow. This is contrary to the dark red color
of the precipitate observed in the present study. Hence, a
different structure than 8 has to be assumed. However, an
examination of the preparation methods of 8 and related
compounds [2, 3, 5, 6, 9] revealed that to obtain the desired
To elucidate the interaction between 5 and TiCl4
a
mixture of both compounds was prepared in a ratio of 2:1
in CH2Cl2. The concentration of 0.5 mol/dm3 was similar
to the concentration of the reactants during the reaction.
After mixing both components, a dark red precipitate is
immediately formed which was isolated and structurally
studied.
Scheme 2
123

Synthesis of a functionalized chromane derivative via a TiCl4-mediated cyclization reaction
423
Fig. 1 Molecular structure of
7. Displacement ellipsoids are
drawn at the 30 % probability
level
with 8 and instead seems to have the empirical formula
C26H22Cl4N2O2Ti. The differences between calculated and
experimental mass percentages indicate that the new
compound is not pure. However, the N/Cl ratio is 1:2
which points to the formation of C26H22Cl4N2O2Ti.
The Raman and ATR-IR spectra of the dark red pre-
cipitate and the ATR-IR spectrum of 5 in different spectral
ranges are shown in Fig. 3. As a result of the strong fluo-
rescence of pure 5, no Raman spectrum could be obtained.
The spectrum of neat solid 5 (Fig. 3A, spectrum a)
shows characteristic bands at 1613, 1587, 1568, and
1273 cm-1 which correspond to m(C=N), m(Ph–N), m(Ph–C),
and m(C–O) vibrations, respectively [2, 10, 11]. In the
spectrum of the dark red precipitate (Fig. 3A, spectrum b) a
band at 1638 cm-1 is observed (at 1641 cm-1 in the
Raman spectrum c), which can be assigned to the shifted
m(C=N) vibration mode caused by the protonation of the
C=N double bond in 5. Such an effect has already been
observed by studying the interaction of imines with Lewis
acidic heterogeneous catalysts [12]. Obviously, the inter-
action between the Lewis acid TiCl4 and 5 takes place in a
similar way.
Fig. 2 Ex situ diffuse reflectance UV–Vis spectra of the precipitate
derived from the 2:1 mixture of 5 and TiCl4 (a) and of the neat solid 5
(b). The UV–Vis transmission spectrum of TiCl4 dissolved in CH2Cl2
(c = 0.5 mol/dm3) is shown for comparison (c)
The spectrum of the precipitate shows more strong
bands located at 1600 and 1588 cm-1 in the ATR-IR
spectrum and at 1602 and 1589 cm-1 in the Raman spec-
trum (Fig. 3a, spectra b and c). They can be assigned to
m(Ph–N) and m(Ph–C) modes. These bands are shifted due
to protonation as well, because the charge stabilization
takes place via the complete azomethine moiety [13]. A
further new band occurs at 1544 cm-1 in the ATR-IR and
1549 cm-1 in the Raman spectrum, respectively. This band
Scheme 3
Table 1 Calculated and obtained element percentages for different
assumed compositions of the complex formed between 5 and TiCl4
chelate compound a final treatment of the reaction mixture
with bases like NEt3 or heating is necessary to remove HCl.
In Table 1 the calculated elemental percentages for
different assumed compositions of the complex formed by
reaction of 5 with TiCl4 are compared with the experi-
mental values. The obtained values clearly show that the
composition of the dark red precipitate is not comparable
Composition
Ti
Cl
N
Ratio Ti/Cl/N
C26H20Cl2N2O2Ti [9]
8.82 13.08 5.16 1.0:2.0:2.0
8.21 24.29 4.80 1.0:4.0:2.0
C
26H22Cl4N2O2Ti (calc.)
Complex [5 ? TiCl4] (exp.) 9.50 23.80 4.66 1.0:3.4:1.7
123

¨
L. R. Knopke et al.
424
was also observed when imines adsorb on the surface of
solid Al2O3 and can be assigned to a m(C=C) vibration
induced by formation of a protonated azomethine moiety
[12, 14].
corresponding Raman spectrum. This suggests that the
observed band at 1302 cm-1 in the Raman spectrum is
IR-inactive. In the low-frequency range (Fig. 3B) a new
strong band occurs at 602 cm-1 in the ATR-IR and Raman
spectra of the dark red precipitate derived from the mixture
of 5 and TiCl4. This band might be due to a m(Ti–O)
vibration which was also observed in trichlorotitanium(IV)
alkoxides [16].
The bands at 330/321 cm-1 in the Raman spectrum
(Fig. 3B, spectrum c) are related to m(Ti–Cl) vibrations
[5, 16]. Alternatively, this band could be also be assigned
to the m1 vibration of TiCl62- and the band at 272 cm-1 to
the respective m2 vibration [17]. But the formation of
TiCl62- in significant amounts should be expected only if 5
and TiCl4 are mixed in 1:1 ratio. Characteristic bands of
TiCl4 or TiCl3 [17–20] do not appear in the spectra, and
The ATR-IR spectrum of neat solid 5 (Fig. 3A, spec-
trum a) shows another strong band at 1273 cm-1 which is
observed in the spectrum of the precipitate (Fig. 3A,
spectrum b), too. This band can be assigned to d(OH) [15]
or to the m(C–O) vibration [2]. However, this band was not
observed in the Raman spectrum (Fig. 3A, spectrum c).
Instead, a very strong band is detected at 1302 cm-1 which
is not present in the corresponding ATR-IR spectrum.
However, reference spectra of 5 dissolved in CCl4 revealed
a strong band at 1286 cm-1 and a very weak band at
1322 cm-1 in the ATR-IR spectrum but a weak band at
1286 cm-1 and a strong band at 1322 cm-1 in the
Fig. 3 ATR-IR spectra of the
neat solid 5 (a), the dark red
precipitate derived from the 2:1
mixture (molar ratio) of 5 and
TiCl4 (b), and Raman spectrum
of the dark red precipitate
derived from the 2:1 mixture of
5 and TiCl4 (c) in the spectral
range ranges 1650–1250 cm-1
(A) and 625–400/250 cm-1 (B)
123

Synthesis of a functionalized chromane derivative via a TiCl4-mediated cyclization reaction
425
there was no evidence for the presence of TiCl3 from XRD
analysis. The absence of Ti(III) species has been proved
also by EPR spectroscopy.
the nitrogen atom and is bonded via the electron lone pair
of the nitrogen atom. A comparison of the IR spectroscopic
data described for 9 with the data obtained for the dark red
precipitate derived from the mixture 5 and TiCl4 (Table 2)
reveals that both substances are structurally very similar.
As a result of the very poor solubility of 10 in various
solvents, a further characterization by NMR spectroscopy
or X-ray crystal structure analysis was not possible. On the
basis of the comparison with 9, we believe that the reaction
of TiCl4 with imine 5 results in the formation of complex
10 (Scheme 4).
In summary, the vibrational spectra indicate that the
C=N double bond of 5 is involved in the interaction with
TiCl4. The formation of Ti–O bonds obviously proceeds
with participation of the OH group of 5. Otherwise the
elementary analysis reveals the formation of a complex of
TiCl4 with two imine molecules.
Strauch et al. [6] reported the synthesis and structural
properties of salicylaldiminato complexes of titanium.
They described the structure of the red 1:2 complex 9
(Scheme 4) which was formed by reaction of TiCl4 with
two molar equivalents of N-(2,6-diisopropylphenyl)sali-
cylimine in CH2Cl2.
Reaction monitoring using in situ ATR-IR spectroscopy
To get an insight into the overall reaction of TiCl4 with 1,3-
bis(silyloxy)-1,3-butadiene 1 and N-salicylideneaniline,
in situ ATR-IR spectroscopic investigations were per-
formed. These were carried out under the same reaction
conditions which were used in our previous study [1] (cf.
Scheme 1). The application of in situ UV–Vis transmission
spectroscopy failed because the formation of the red pre-
cipitate 9 at the beginning of the reaction perturbed the
measurements.
The molecular structure of this compound indicates that
two imines are bonded via their oxygen atoms to the tita-
nium atom, while the four chlorine atoms remain
coordinated, leading to an octahedral coordination sphere
of titanium. The proton of the hydroxyl group migrated to
The in situ ATR-IR spectra obtained during the reaction
of 5 with 1 are displayed in Fig. 4. The spectra of 5 in
CH2Cl2 at 0 °C (spectrum a), of the mixture of 5 and TiCl4
at -60 °C (spectrum b), and of 1 ? TiCl4 (1:1 molar ratio)
in CH2Cl2 at 25 °C (spectrum n) were included for
comparison.
The spectrum of 5 dissolved in CH2Cl2 (Fig. 4a) is
comparable with that measured in the solid state (Fig. 3a).
Merely the band of the m(C=N) vibration is shifted from
1613 to 1617 cm-1 because the intermolecular interactions
occurring in solution are weaker than in the solid state [10].
The addition of TiCl4 to 5 effects characteristic shifts
(Fig. 4, spectrum b) which were discussed above. This
interaction occurs in CH2Cl2 independently from temper-
ature. For this reason only the spectrum of the 1:1 mixture
of 5 with TiCl4 at -60 °C is shown in Fig. 4.
Scheme 4
Table 2 Selected IR frequencies/cm-1 of the solid complexes 9 and
10
By addition of 1 at -50 °C the resulting spectrum of the
reaction mixture (Fig. 4, spectrum c) can be perceived as
a summation of spectrum b (5 ? TiCl4) with spectrum
n (1 ? TiCl4). With increasing temperature the band at
1004 cm-1 decreases, and a new band at 985 cm-1
appears. Additionally, a band at 1526 cm-1 arises at
-15 °C the assignment of which is difficult. However,
from the bands in the range 1060–950 cm-1 some conclu-
sions can be made concerning the changes of the m(C–O)
vibrations. The band at 1004 cm-1, observed in spectrum b
(Fig. 4), results from m(C–O) vibrations where the oxygen
is coordinated to Ti (cf. 10 in Scheme 4). The bands at
1062 and 954 cm-1 in spectrum n (Fig. 3) can be assigned
to mas(C–O) and ms(C–O) of the complex which is formed
9a
10b
Assignment
1635 (vs)
1549 (s)
1469 (vs)
1283 (vs)
1144 (m)
916 (m)
798 (s)
1638 (s)
1544 (s)
1472 (vs)
1275 (vs)
1146 (vs)
912 (m)
801 (s)
m(C=N)
m(Ph–NH?)
m(C–O)
m(Ti–O)
753 (m)
613 (s)
756 (vs)
602 (vs)
a
Ref. [6]
b
This work
123

¨
L. R. Knopke et al.
426
Fig. 4 In situ ATR-IR spectra
of the TiCl4-mediated reaction
between 5 and 1 in CH2Cl2: 5 at
0 °C (a), 5 ? TiCl4 (1:1 molar
ratio) at -60 °C (b),
5 ? TiCl4 ? 1 (1:1:2 molar
ratio) at -50, -40, -35, -30,
-25, -20, -15, -10, -5, -3,
and -2 °C (c–m). The spectrum
of 1 ? TiCl4 (1:1 molar ratio) is
given for comparison (n)
between 1 and TiCl4 [1]. A possible structure of the
complex 11 is given in Scheme 5.
During heating of the complete reaction mixture (Fig. 4,
spectra c–m) bands at 1052, 1004, and 985 cm-1 can be
observed where only the intensity of the first band does not
change. At the end of the reaction at -2 °C, only the bands
at 1052 and 985 cm-1 remain which can be related to the
mas(C–O) and ms(C–O) modes of a titanium complex similar
to 10 and 11. Obviously, TiCl4 interacts with both reactants
without preferring one of them.
Scheme 5
These results clearly demonstrate, as already observed
in the reaction of ketene acetal 2b with diene 1 [1], that the
work-up procedure is part of the reaction and influences the
formation and nature of the final product.
It should be mentioned at this point that the dark red
precipitate 10, which is formed at the beginning of the
reaction, is slowly dissolved after addition of 1 and
warming of the reaction mixture. This suggests that
reactant 1 interacts with complex 10 and undergoes par-
tial elimination of TMSCl to form a new intermediate
Mechanistic considerations
The formation of the chromane derivative 7 can be
explained by the nature of intermediate 10 (cf. Scheme 4)
which obviously directs the addition of 1. A possible
transition state for the reaction of the titanium complex
with diene 1 is schematically shown in Scheme 6.
complex in which
1
additionally coordinates via
the released oxygen atoms to titanium. As a result, two
m(C–O) vibrations at 1052 and 985 cm-1 are observed.
Their band positions differ from those observed for
complexes 10 and 11.
The formed 2:1 complex controls the formal addition of 1
in a special way preferring a concerted interaction of two
molecules of 1 with the protonated nitrogens of 5. The
favored elimination of TMSCl by HCl addition causes a
rearrangement of the complex 12 leading consequently to the
splitting of the complex into two molecules of 7 and TiCl4.
According to the synthetic protocol [1] the reaction is
quenched with aqueous HCl. Thus, the reaction was stop-
ped after 4 h at 0 °C, and aqueous HCl was added. The
respective ATR-IR spectra of the reaction mixture before
and after quenching are shown in Fig. 5.
The most interesting features are the new bands at 1745
and 1719 cm-1 which indicate the formation of different
carbonyl groups in this reaction step (Fig. 5b). After the
purification with flash chromatography, only one intensive
carbonyl band at 1707 cm-1 is observed, whereas the
carbonyl bands at 1745 and 1719 cm-1 vanish (Fig. 5c).
Conclusion
The presented ex situ and in situ spectroscopic investigations
of the TiCl4-mediated reaction of N-salicylideneaniline (5)
123

Synthesis of a functionalized chromane derivative via a TiCl4-mediated cyclization reaction
427
Fig. 5 In situ ATR-IR spectra
obtained at the end of the
reaction: before (a) and after
quenching with HClaq (b) and
ATR-IR spectrum of the
isolated solid product 7 after
work-up with flash
chromatography (c)
As indicated by in situ ATR-IR measurements, the
formed 2:1 complex manages the formal addition of 1 pre-
ferring a concerted interaction of two molecules of 1 with
the protonated nitrogens of 5. This is a slow process indi-
cated by the continuous decrease of a distinct m(C–O–Ti)
band at 1004 cm-1 and the simultaneous rising of a new one
at 985 cm-1 over 4 h. Obviously, the proceeding dissolution
of the solid 2:1 complex in the presence of 1 is the rate-
determining step. The obtained yield of the chromane
derivative 7, isolated after flash chromatography, was high
(82 %). The ATR-IR measurements showed that the work-
up procedure is part of the reaction and significantly influ-
ences the formation and nature of the final product as
already observed in the reaction of ketene acetals with 1.
Scheme 6
and 1,3-bis(silyloxy)-1,3-butadiene 1 have demonstrated, as
already shown in a former study using fluorinated ketene
acetals and 1 as substrates [1], that the nature of the inter-
mediately formed titanium complex markedly influences the
subsequent reaction with 1. The possible formation of bis-
chelate complexes like TiCl2(OOR)2 and TiCl2(ONR)2 on
the one hand, or TiCl4(OR)2 on the other hand, offers dif-
ferent interaction possibilities for the second reactant.
Although 5 is known to form bis-chelate complexes with
TiCl4, the investigations show that, under the applied con-
ditions, a solid dark red complex TiCl4(OR)2 is formed in
which two molecules of 5 are bonded via their oxygen atoms
only to the titanium atom. This type of intermediate titanium
complex is responsible for the subsequent mode of interac-
tion with 1 leading finally to chromane 7 instead of the
naphthalene derivative 6 (Scheme 2).
Experimental
Titanium(IV) chloride was obtained from Aldrich (99.995 %)
and was used without further purification as was the
used CH2Cl2 which was obtained by ACROS Organics
(99.8 % extra dry over molecular sieves, stabilized).
1,3-Bis(silyloxy)-1,3-butadiene 1 was prepared according
to the literature method [21]. N-Salicylideneaniline (5) was
used as received from Aldrich (97 %).
The reaction was carried out in manner analogous to the
procedure described elsewhere [1]. Cooling of the home-
made reaction cell was done by a Julabo cryostat. The
reaction cell was flushed with argon before reaction and
during addition of the reactants. Compound 5 (788 mg,
4 mmol) was dissolved in CH2Cl2 at room temperature.
The solution (0.44 cm3, 4 mmol) was cooled and TiCl4
123

¨
L. R. Knopke et al.
428
was added when a temperature of 0 °C was reached. The
cooling was continued, and 2,080 mg 1,3-bis(silyloxy)-1,3-
butadiene 1 (8 mmol) was added at -60 °C. Afterwards,
the mixture was warmed to 0 °C over 4 h. Finally, the
reaction was quenched by addition of 60 cm3 10 % HCl
solution and worked up by flash chromatography. Details
concerning the preparation procedure and characterization
of the chromane derivate 7 are available in the Supple-
mentary Material.
contains the supplementary crystallographic data for this
paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via http://www.
ccdc.cam.ac.uk/data_request/cif.
Acknowledgments The authors would like to thank Dr. M. Schnei-
der, W. Winkler, and A. Lehmann for the XRD, ATR-IR, and
elemental analysis of the solid complex 10. SR gratefully thanks the
University of Rostock (scholarship of the interdisciplinary faculty of
the University of Rostock/Dept. LLM) and the state of Mecklenburg-
Vorpommern, and LRK thanks the Leibniz Society for financial
support.
ATR-IR spectra were measured with a Bruker Alpha
FT-IR spectrometer which was equipped with a Platinum
ATR single reflection diamond ATR module. All spectra
were recorded with 32 scans at 4 cm-1 resolution. For the
in situ ATR-IR studies a fiber optic diamond ATR probe
(infrared fiber sensors, Aachen, Germany) was connected
to a Nicolet Avatar 370 (Thermo Electron) FT-IR spec-
trometer. The probe was immersed in the reaction mixture.
All spectra were recorded with 128 scans at 4 cm-1
resolution.
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˚
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˚
3
˚
˚
c = 13.9584(6) A, b = 91.285(3)°, V = 1550.04(10) A ,
T = 150 K, Z = 4, qcalcd = 1.343 g cm-3
,
l = 0.095
mm-1, 29640 reflections measured, 4,180 independent
reflections (Rint = 0.0425), final R values (I[2r(I)):
R1 = 0.0449, wR2 = 0.1040, final R values (all data):
R1 = 0.0840, wR2 = 0.1126, 252 parameters. CCDC 865825
123