Towards New Oligomesogenic Phosphonic Acids as Stabilizers of Nanoparticles Colloids in Nematic Liquid Crystals

Article abstract of DOI:10.1055/s-0034-1379930

Several synthetic strategies for the construction of linear and branched oligomesogenic phosphonic acids are examined, which differ in the method of building the key bimesogen unit. An efficient synthetic approach to the most promising compounds employs regioselective Kumada cross-coupling between [11-(4′-pentylbiphenyl-4-yl)undecyl]magnesium bromide and 4-(11-bromoundecyl)-4′-iodobiphenyl as the key step. Preliminary studies on the ability of the new ligands to stabilize nanoparticles colloids in nematic liquid crystals are undertaken for the example of quantum dots.

Full text of DOI:10.1055/s-0034-1379930

SYNLETT
0
9
3
6
-
5
2
1
4
1
4
3
7
-
2
0
9
6
© Georg Thieme Verlag Stuttgart · New York
2015, 26, 1905–1910
letter
1905
M. F. Prodanov et al.
Letter
Synlett
Towards New Oligomesogenic Phosphonic Acids as Stabilizers of
Nanoparticles Colloids in Nematic Liquid Crystals
starting materials
Maksym F. Prodanov*
HO
Br
(HO)3
PO3H2
(CH2)11
O
Maksym Y. Diakov
Ganna S. Vlasenko
Valerii V. Vashchenko
I
Alk
O
8–12 steps
4–30% overall yields
State Scientific Institution ‘Institute for Single Crystals’,
NAS of Ukraine, 60 Lenin Ave., Kharkiv, Ukraine
prodanov@isc.kharkov.com
OH
P
OH
Alk
(CH2)11
(CH2)11O
O
O
3
(CH2)11
dendritic and linear oligomesogenic phosphonic acids
O
OH
OH
X
(CH2)11
P
Alk
X
(CH2)n
X
X
O
X = O or CH2
Received: 10.04.2015
Accepted after revision: 04.05.2015
Published online: 07.07.2015
also reported to induce mesomorphic properties in inor-
ganic NPs,24–28 although the colloidal stability of these com-
posite materials in LC host has not been studied.
DOI: 10.1055/s-0034-1379930; Art ID: st-2015-d0261-l
Clearly, an enhancement in the stabilizing ability of
promesogenic ligands could be achieved by increasing the
number of PMUs in the ligand molecule. However, it should
be performed along the long molecular axis to retain the
elongated flexible shape of the ligand favoring the efficient
interaction with the LC environment.5,10,14,15 Thus, a prom-
ising modification of the known ligands to the target struc-
tures can be schematically represented as a pass from
structures A and B to C and D (compounds 1 and 2; Figure
1). As a starting point for increasing the number of PMUs,
we opted for a doubling of the 4,4′-disubstituted biphenyl-
ene groups. The linkage of biphenyl units through the
alkoxy spacers (X = O; Figure 1) appeared to be synthetical-
ly more straightforward, therefore compounds 1a and 2a
were initially considered.
It is seen that target compound 1a comprises two asym-
metrically substituted 4,4′-dihydroxybiphenylyl moieties
(Scheme 1). To avoid any statistical reactions, related to
functionalization of commercially available 4,4′-dihydroxy-
biphenyl, we employed a direct method to assemble the bi-
phenylyl unit by Suzuki cross-coupling reaction of phenols
that already contain suitable protective groups (reaction
4→5; Scheme 1). Further, asymmetrically functionalized bi-
phenyl building blocks 7 and 8 were proposed, which can
be useful not only in the synthesis of bimesogens (e.g., 9,
10, and 1a) but also for subsequent multiplication of PMUs.
On the way to the target compound 1a, we encountered
low reactivity of some intermediates. In particular, the hy-
drogenation of 6 (6→8) did not proceed under the typical
reaction conditions, which was clearly due to its limited
solubility. We succeeded in obtaining 8 only after heating
the reaction mixture at elevated temperature (55–60 °C) for
five days with multiple additions of catalyst. Most of the
Abstract Several synthetic strategies for the construction of linear and
branched oligomesogenic phosphonic acids are examined, which differ
in the method of building the key bimesogen unit. An efficient synthet-
ic approach to the most promising compounds employs regioselective
Kumada cross-coupling between [11-(4′-pentylbiphenyl-4-yl)unde-
cyl]magnesium bromide and 4-(11-bromoundecyl)-4′-iodobiphenyl as
the key step. Preliminary studies on the ability of the new ligands to sta-
bilize nanoparticles colloids in nematic liquid crystals are undertaken for
the example of quantum dots.
Key words acylation, cross-coupling, phosphonic acids, total synthe-
sis, ligands
Colloids of inorganic nanoparticles (NPs) in liquid crys-
tals (LCs) are very promising materials for application in
displays, photonics, and metamaterials.1–6 However, the ap-
plication of these materials is hampered by a strong ten-
dency of NPs to aggregate in the LC even if the surface of the
NP is modified with ligands comprising promesogenic units
(PMUs).7–15 Recently, progress in the stabilization of colloids
of small Au nanospheres and quantum dots (QDs) in LC was
achieved by using mainly mixtures of promesogenic ligands
with aliphatic co-surfactants.5,7,8,10,12,14,16–19 In particular, we
have studied extensively the stabilizing ability of ligands
with different molecular shape in combination with vari-
able amounts of aliphatic co-surfactants of different length
in a nematic LC host10 and found that dendritic ligands (of
general structure B, Figure 1) are more efficient than linear
analogues (A). This approach was successfully extended for
the stabilization of spherical ferromagnetic NPs in nematic
LC20 and QDs in polymers.21 However, the proposed ligands,
apparently, have limited applicability for LC-colloids of
elongated NPs.11,22,23 Dendritic oligomesogenic ligands are
© Georg Thieme Verlag Stuttgart · New York — Synlett 2015, 26, 1905–1910

1906
M. F. Prodanov et al.
Letter
Synlett
Spacer
PMU
O
P
A
C
HO
HO
(CH2)11 PMU
=
1
anchoring
group
increasing the number of
promesogenic units and the
molecule length
O
O
O
(CH2)11 PMU
(CH2)11
(CH2)11
HO
P
O
O
(CH2)11
HO
O
PMU
PMU
=
2
D
B
X
X
(CH2)7–11
X
Alk
a: X = O
b: X = CH2
PMU =
Figure 1 Schematic representation of described (A, B) and proposed (C, D) promesogenic ligands; structures of proposed ligands 1 and 2
subsequent transformations (7→1a) also required unusual-
ly high temperatures (see the Supporting Information). Ul-
timately, the obtained target compound 1a appeared to
have a melting point (255 °C) that was higher than expect-
ed and the compound had an extremely low solubility in
most organic solvents. These properties seriously hamper
their use as ligands for NPs because it affects both the com-
pleteness of surface modification and the compatibility of
the organic shell of the NP with the surrounding LC. A low-
ered melting point and increased solubility could be ex-
pected for non-oxygen analogues of 1a; therefore, we fo-
cused further on the synthesis of compounds 1b and 2b
(Figure 1).
The alternative synthetic approach (Path B) employs
Kumada–Corriu cross-coupling of Grignard reagent 16 with
dihalo-derivative 19 as the key step. We did not find exam-
ples of Kumada–Corriu reactions that occur selectively at
the aromatic ring in the presence of a halogenated sp3-car-
bon. Nevertheless, selective coupling at the sp2-carbon can
be expected, because it is known that alkylhalides react
slower in oxidative addition to the palladium catalysts than
aryl halides.33 Therefore, the rate of the main reaction
(19→20) is expected to be considerably greater than that of
the side processes. To further enhance the selectivity, we
employed iodoarene as the most reactive halide (19;
Scheme 2).
The synthetic approaches toward target compounds 1b
and 2b are shown in Scheme 2. To construct the key inter-
mediate bromide 20a, two alternative synthetic pathways
were proposed. Path A is based on a combination of Frie-
del–Crafts acylation and reduction of the obtained ketones;
this route has only a few distant analogous reported exam-
ples: synthesis of symmetrical ω-bis(biphenylyl)alkanes29–
31 and an isolated example of the synthesis of an asymmet-
rically substituted analogue of 1332 comprising, however,
terminal phenyl groups instead of biphenylyl groups. The
drawback is that one of the acylation steps in path A
(12→13) is a statistical reaction due to presence of two
equivalent reaction centers in substrate 12.
Initially, the more documented path A (Scheme 2) was
examined. Acylation of biphenyl with nonanedioyl dichlo-
ride followed by reduction by using the Huang Minlon
method gave 1,9-di([1,1′-biphenyl]-4-yl)nonane (12) in 30%
overall yield. However, attempts to acylate this compound
with octanoyl chloride under typical reaction conditions
(AlCl3, CH2Cl2, r.t.) led to the formation of a complex mix-
ture of products (according to HPLC), from which the de-
sired monoacyl derivative 13 was isolated in poor yield
(4%). We attempted to optimize the acylation of 12 by vary-
ing the temperature and the catalyst for this reaction in
CH2Cl2 or 1,2-dichlorobenzene (DCB; Table 1).
(CH2)11OH
3
4
5
6
OH
OH
iv
Ac
v, vi
71%
i, ii, iii
56%
O
HO
Br
O
B
O
O
O
61%
Bn
O
vii
Bn
Bn
(CH2)11Br
85%
O
7
ix
66%
Bn
9
viii
O(CH2)11OH
O
(CH2)11 O
O
(CH2)11OH
98%
Bn
O
HO
8
36%
viii, x
(CH2)11
vii, xi, xii, xiii
O(CH2)11OH
10
O
O
O
(CH2)11
O
O
(CH2)11
O
O
O
P
47%
HO
C8H17
C8H17
1a
OH
Scheme 1 Synthesis of oligomesogenic phosphonic acids with O-linkages 1a. Reagents and conditions: (i) BnCl, K2CO3, MEK, reflux; (ii) Mg, THF, reflux;
(iii) B(OMe)3, THF then HCl (conc.); (iv) Pd(dppf)2, NaHCO3, SDS, toluene, H2O; (v) NaOH, H2O; (vi) 11-bromo-1-undecanol, K2CO3, MEK; (vii) PBr3, DMF;
(viii) H2, Pd/C, EtOAc, 65 °C; (ix) K2CO3, DMF, 120 °C; (x) C8H17Br, K2CO3, DMF, 130 °C; (xi) P(OEt)3, reflux; (xii) TMSBr, CH2Cl2, reflux; (xiii) MeOH, THF,
reflux.
© Georg Thieme Verlag Stuttgart · New York — Synlett 2015, 26, 1905–1910

1907
M. F. Prodanov et al.
Letter
Synlett
path A:
path B:
C5H11
I
11
14
17
86%
iv
iv, v
vi
30%
i, ii
(CH2)10
X
18a: X = Br
18b: X = Cl
(CH2)11 Br
(CH2)9
C5H11
12
I
O
15
59%
from 17
4%
v
iii
O
19a: X = Br
19b: X = Cl
C5H11
(CH2)11 MgBr
(CH2)11X
(CH2)9
I
C7H15
vii
16
13
iv, v
79%
20a: n = 11, Alk = C5H11, X = Br
20b: n = 11, Alk = C5H11, X = Cl
Alk
(CH2)n
(H2C)11
X
HO
O
O
O
key intermediate
OH
21
xi, ix, x
30%
HO
viii, ix, x
OEt
OEt
44%
O
P
(CH2)11
HO
2b: n = 11, Alk = C5H11
P
OH
Alk
(CH2)n
(CH2)11
(H2C)11
Alk
(CH2)n
O
O
O
O
OH
Alk
(CH2)n
(CH2)11
O
P
1b: n = 11, Alk = C5H11
linear bimesogenic phosphonic acid
OH
(CH2)11
O
(CH2)11
Alk
(CH2)n
dendritic oligomesogenic
phosphonic acid
Scheme 2 Synthesis of phosphonic acids with simple bond linkages 1b and 2b. Reagents and conditions: (i) nonanedioyl dichloride, AlCl3, CH2Cl2;
(ii) N2H4, KOH, DEG, 130 °C; (iii) octanoyl chloride, AlCl3, CH2Cl2; (iv) 11-bromoundecanoyl chloride, AlCl3, CH2Cl2; (v) (C2H5)3SiH, AlCl3, CH2Cl2; (vi) Mg,
THF, reflux; (vii) PdCl2(dppf), THF; (viii) P(OEt)3, 150 °C; (ix) TMSBr, CH2Cl2; (x) MeOH, THF; (xi) K2CO3, MEK.
Table 1 Content of 13 and Byproducts in the Reaction Mixture upon
Acylation of 12 with Octanoyl Chloride
starting material 12. Thus, we can conclude that the pres-
ence of a labile alkylaromatic moiety in the reaction prod-
uct 13 leads to the formation of a large amount of byprod-
ucts, and path A does not appear to be effective for obtain-
ing of the key intermediate 20.
Lewis acid
Temp (°С)
Solvent
Quantity after 90 min (%)a
13 Byproducts (total)
In path B (Scheme 2), for the synthesis of 4-(11-bro-
moundecyl)-4′-iodo-1,1′-biphenyl (19), starting 4-iodobi-
phenyl 17 was acylated with 11-bromoundecanoyl chloride
followed by one-pot reduction with triethylsilane.35 In this
reaction sequence, exchange of the 11-bromine atom with
chlorine unexpectedly occurred and the mixture of desired
11-bromo (19a) and 11-chloro (19b) undecyldiphenyl de-
rivatives (ca. 65:35 according to HPLC, GCMS analysis and
NMR spectroscopy, see the Supporting Information) was
formed. We found that prolonged stirring (ca. 24 h) of 11-
bromoundecanoyl chloride in the presence of AlCl3 in CH2-
Cl2 followed by quenching with methanol led to the forma-
tion of only the corresponding methyl 11-bromoundeca-
noate. However, in the presence of 4-iododiphenyl 17 at
0 °C, a mixture of 11-bromo and 11-chloro acylated prod-
ucts (18a and 18b) formed immediately, and their ratio re-
mained constant during the reaction. Although we failed to
avoid the formation of chlorinated product 19b, we used
this mixture without separation because both halides 19a
and 19b should yield the same products in the subsequent
transformations. The reason for halogen exchange is not
clear; moreover, in the case of acylation of 4-pentyldiphe-
nyl 14 (14→15), the chlorinated byproduct formed only in
trace amounts.
AlCl3
FeCl3
0
20
0
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
DCB
21
47
70
4
29 (4b)
11
20
70
0
15
7
25 (4b)
0
53
0
ZnCl2
CH2Cl2
DCB
90
100
0
0
DCB
trace
trace
a As estimated by internal standardized HPLC analyses.
b Yield of isolated product.
The results suggest that the use of both weaker Lewis
acids and lower temperature increases the selectivity of re-
action, however at the cost of low conversion (Table 1), and
we did not succeed in obtaining the desired monoacylated
product 13 with satisfactory yield. The large number of side
products can be caused by skeletal rearrangements of alky-
laromatic groups in substrate 12 and 13 in the presence of
strong Lewis acids, as is often observed in Friedel–Crafts al-
kylation.34 HPLC analysis revealed that treatment of 12 with
AlCl3 in DCB at 0–5 °C even for 30 minutes results in the for-
mation of several products at more than 50% conversion of
© Georg Thieme Verlag Stuttgart · New York — Synlett 2015, 26, 1905–1910

1908
M. F. Prodanov et al.
Letter
Synlett
The cross-coupling of dihalides 19a,b with Grignard re-
agents was initially studied by using a model reaction with
hexylmagnesium bromide. As we expected, the reaction oc-
curred selectively at the aromatic ring in high yield and it
was further successfully applied for cross-coupling of 19
with 16 to furnish the key intermediate 20a,b in 79%
yield.36 The target oligomesogenic phosphonic acids 1b and
2b were obtained by phosphorylation (in case of 1b) and by
alkylation of phosphonate 2137 (in case of 2b) followed by
mild hydrolysis of the intermediate diethyl phosphonates.
Overall yields of the desired compounds 1b, 2b based on 4-
pentylbiphenyl 14 were 30 and 20%, respectively (Scheme
2).
Compounds 1b and 2b did not possess any liquid crystal
properties, as was revealed by differential scanning calo-
rimetry and polarized optical microscopy. Notably, both
phosphonic acids 1b and 2b have substantially lower melt-
ing points (158 and 121 °C, respectively) than their oxygen-
bridged analogue 1a. Moreover, phosphonic acids 1b and
2b are considerably more soluble in toluene under heating
than 1a, which is almost insoluble. At ambient temperature,
dendritic phosphonic acid 2b is prone to gelatinize the
solution even in quite low concentration (5–6 mg/mL).
The stabilizing effect of new oligomesogenic ligands in
nematic LC colloids was examined by using spherical lumi-
nescent CdSe/ZnS nanoparticles (quantum dots, λmax = 530
nm, ηem ≈ 30%, d = 3.6 nm) in LC hosts: 4-pentyl-4′-cyanobi-
phenyl (5CB) and a commercially available nematic LC mix-
ture E7 (Merck). The surface modification of NPs with new
ligands was performed similarly to the method described
by Prodanov et al.10 and, as starting point, we used the same
molar ratios of promesogenic ligands and short-chain cos-
urfactant (hexylphosphonic acid, HPA): 1:2 in the case of
linear 1b and 1:4 for dendritic 2b (samples QD-1b-HPA and
QD-2b-HPA). Feed concentrations of modified QDs in 5CB
and E7 were approximately 0.25 wt%. All samples were sub-
jected to polythermal fluorescence microscopy (FM) at ex-
citation wavelength 405 nm. Under heating–cooling cycles,
all colloids reproducibly change from a homogeneously
emitting sample in their isotropic state (above 60 °C) to in-
homogeneous field with various amounts of aggregates (as
bright-green points) in the LC phase (see Figure 2).
It is clear that in QD-1b-HPA colloids (Figure 2, a, c, e),
the aggregates are larger, with almost non-luminescent
background. This result indicates a negligibly small concen-
tration of QDs in fine-dispersed state in the sample, similar
to what was observed for colloids of QDs coated with inap-
propriate ligand combinations or native surfactant.10 Con-
versely, the colloids containing QD-2b-HPA nanoparticles
reveal much more uniform emission between the small
bright-green spots (Figure 2, b, d), thereby suggesting a sig-
nificant amount of QDs was homogeneously distributed in
the samples. We also did not observe any significant differ-
ences between dispersions in 5CB and E7 for modified NPs.
Figure 2 FM images of 0.25 wt% dispersions of (a) QD-1b-HPA in 5CB;
(b) QD-2b-HPA in 5CB; (c) QD-1b-HPA in E7; (d) QD-2b-HPA in E7; (e,f)
The same areas as in (c,d) additionally illuminated with a halogen lamp.
The microphotographs were taken in nematic phase (at 25 °C) with the
same shooting parameters.
Thus, our preliminary studies show a higher stabilizing
ability in nematic LC nanocomposites for dendritic oligo-
mesogenic ligand 2b combined with hexylphosphonic acid.
To finally establish the potential of the new ligands, addi-
tional experiments are required; these include an adjust-
ment of the ratio and the length of the aliphatic co-surfac-
tants and a determination of the real composition of organ-
ic shells of modified NPs. This work is in progress and the
results will be published elsewhere.
In conclusion, we have developed an efficient synthetic
pathway to new oligomesogenic phosphonic acids of both
linear and branched molecular shape. The key bimesogenic
intermediate, 4-{11-[4′-(11-haloundecyl)biphenyl-4-yl]un-
decyl}-4′-pentylbiphenyl (20) was formed by cross-cou-
pling reaction. We demonstrated that Pd-catalyzed sp3–sp2
cross-coupling reactions of alkyl Grignard reagents with io-
doarenes occur selectively at the aromatic ring in the pres-
ence of an alkyl halide moiety in the substrate. An alterna-
tive route to the target compounds was found to be ineffec-
tive because of the instability of intermediate 1,ω-
bis(biphenylyl)alkanes in the presence of Lewis acids. Pre-
liminary results reveal a higher stabilizing effect of dendrit-
ic ligand compared with the linear analogues in nematic LC
colloids of quantum dots, albeit for unoptimized ligand
shell compositions. Studies on their influence on the colloi-
dal stability of other types of NPs both in nematic and
smectic LCs is in progress and will be published along with
details of the physical properties of the new materials sepa-
rately.
© Georg Thieme Verlag Stuttgart · New York — Synlett 2015, 26, 1905–1910

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M. F. Prodanov et al.
Letter
Synlett
Acknowledgment
(21) Matvienko, O. O.; Prodanov, M. F.; Gorobets, N. Yu.; Vashchenko,
V. V.; Vovk, O. M.; Babayevskaya, N. V.; Savin, Y. N. Colloid Polym.
Sci. 2014, 707.
(22) Prodanov, M.; Buluy, O.; Popova, E.; Kurochkin, O.; Gamzaeva,
S.; Reznikov, Y.; Vashchenko, V. Proceedings of the 25th Interna-
tional Liquid Crystal Conference, Trinity College Dublin, Ireland,
June 24–July 4 2014, Abstract N-O2.002.
Financial support from the National Academy of Science of Ukraine
(projects # 0112U004502, #0115U003044, and #0112U002186) is
gratefully acknowledged. We also thank Dr. N. Gorobets for valued
discussions and Dr. Olga V. Vashchenko for providing the DSC mea-
surements.
(23) Popova, E. V.; Gamzaeva, S. A.; Krivoshey, А. I.; Kryshtal, A. P.;
Fedoryako, A. P.; Prodanov, M. F.; Kolosov, M. A.; Vashchenko, V.
V. Liq. Cryst. 2015, 334.
Supporting Information
(24) Frein, S.; Boudon, J.; Vonlanthen, M.; Scharf, T.; Barbera, J.; Suss-
Fink, G.; Burgi, T.; Deschenaux, R. Helv. Chim. Acta 2008, 2321.
(25) Wojcik, M.; Lewandowski, W.; Matraszek, J.; Mieczkowski, J.;
Borysiuk, J.; Pociecha, D.; Gorecka, E. Angew. Chem. Int. Ed. 2009,
5167.
(26) Mischler, S.; Guerra, S.; Deschenaux, R. Chem. Commun. 2012,
2183.
(27) Buathong, S.; Ung, D.; Daou, T. J.; Ulhaq-Bouillet, C.; Pourroy, G.;
Guillon, D.; Ivanova, L.; Bernhardt, I.; Bégin-Colin, S.; Donnio, B.
J. Phys. Chem. C 2009, 12201.
(28) Demortière, A.; Buathong, S.; Pichon, B. P.; Panissod, P.; Guillon,
D.; Bégin-Colin, S.; Donnio, B. Small 2010, 1341.
(29) Barnes, P. J.; Douglass, A. G.; Heeks, S. K.; Luckhurst, G. R. Liq.
Cryst. 1993, 603.
(30) Schubert, H.; Sagitdinov, I.; Svetkin, J. V. Z. Chem. 1975, 222.
(31) Mallon, J. J.; Kantor, S. W. Mol. Cryst. Liq. Cryst. 1988, 157, 25.
(32) Lukáč, I.; Csaba, K.; Weiss, R. G. Photochem. Photobiol. Sci. 2009,
1389.
(33) Jana, R.; Pathak, T. P.; Sigman, M. S. Chem. Rev. 2011, 1417.
(34) In Organic Chemistry; McMurry, J., Ed.; Cengage Learning:
Boston, 2012, 8th ed., 575.
(35) To a suspension of AlCl3 (7.86 g, 59 mmol) in CH2Cl2 (250 mL), a
solution of iodobiphenyl 17 (15.0 g, 53 mmol) was added at
0 °C. To this mixture, a solution of 11-bromoundecanoyl chlo-
ride (16.7 g, 59 mmol) was added dropwise during 20 min at
0 °C. After stirring at 0°C for 2 h and at r.t. for 7 h, a solution of
triethylsilane (13.7 g, 0.12 mol) in CH2Cl2 (20 mL) was added
dropwise at r.t. during 45 min. The reaction mixture was stirred
overnight and then evaporated to dryness; the residue was dis-
solved in hexane (400 mL) and subjected to flash chromatogra-
phy through a short pad of silica (hexane). The solution was
evaporated to dryness and the residue was recrystallized from
i-PrOH (300 mL). The washed precipitate was transferred to a
modified Soxhlet extractor and washed with hot CCl4 (500 mL)
for 12 h. The solvent was evaporated and the residue was
recrystallized from i-PrOH. The colorless solid product was
dried in vacuo at 80–100 °C to give 19a and 19b as a mixture of
compounds. Yield: 16.3 g (59%). According to GCMS, HPLC and
NMR spectroscopy (Figure 2) the obtained mixture contained
about 35% of chloro derivative 19b. Mp 61–64 °C. IR (KBr):
2918, 2848, 1678, 1461, 1387, 1131, 1069, 1000, 857, 810, 792,
723, 686, 646, 472 cm–1. 1H NMR (200 MHz, CDCl3): δ = 1.29 (m,
14 H, 3-CH2, 4-CH2, 5-CH2, 6-CH2, 7-CH2, 8-CH2, 9-CH2), 1.56–
1.73 (m, 2 H, 10-CH2), 1.73–1.94 (m, 2 H, 2-CH2), 2.64 (t, J =
8.3 Hz, 2 H, 11-CH2), 3.41 (t, J = 6.9 Hz, 1.36 H, 1-CH2Br), 3.53 (t,
J = 6.7 Hz, 0.64 H, 1-CH2Cl), 7.25 (d, J = 7.8 Hz, 2 H, ArH), 7.32 (d,
J = 8.4 Hz, 2 H, ArH), 7.47 (d, J = 8.1 Hz, 2 H, ArH), 7.75 (d, J =
8.2 Hz, 2 H, ArH). MS (EI, 70 eV): m/z (%) = 468 (22) [M+, 19b],
512 (22) [M+, 19a], 293 (100), 207 (30), 165 (62).
Supporting information for this article is available online at
http://dx.doi.org/10.1055/s-0034-1379930.
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(36) To magnesium turnings (0.08 g, 3.3 mmol), activated with
iodine, anhydrous THF (100 mL) was added under Ar. To this
mixture, a few drops of 4-(11-bromoundecyl)-4′-pentylbiphe-
nyl solution in THF was added. The mixture was heated to 80 °C
© Georg Thieme Verlag Stuttgart · New York — Synlett 2015, 26, 1905–1910

1910
M. F. Prodanov et al.
Letter
Synlett
and a solution of 4-(11-bromoundecyl)-4′-pentylbiphenyl (15;
1.35 g, 2.9 mmol) was added dropwise during 1.5 h. The
obtained Grignard reagent was pumped through a Teflon capil-
lary tube into a dropping funnel under argon pressure. The Gri-
gnard reagent was then added dropwise at r.t. to a stirred
degassed suspension of PdCl2(dppf) catalyst (4 mol%) and 4-
(11-haloundecil)-4′-iodobiphenyl (19a,b; 1.14 g, 2.2 mmol) for
several minutes under Ar. The mixture was stirred for 1 h and
then poured into 17% solution of ammonium chloride in water.
The resulting mixture was extracted with toluene; the organic
extracts were collected, washed with water, dried over Na2SO4,
filtered, and evaporated to dryness. The crude product was
recrystallized from a mixture of MeCN–CH2Cl2 (50%, 30 mL).
Yield: 1.34 g (79%). According to HPLC analysis in combination
with NMR spectroscopy (see the Supporting Information) the
obtained mixture contained 33% 20b. Mp 72–74 °C. IR (KBr):
3033, 2918, 2847, 1909, 1499, 1468, 1401, 1135, 1003, 809, 793,
763, 718, 648, 591, 516, 483 cm–1 1H NMR (CDCl3, 200 MHz):
.
δ = 0.91 (br t, 3 H, CH3), 1.18–1.50 [m, 32 H, (CH2)16], 1.65 [m,
8 H, (CH2)4], 1.86 (m, 2 H, CH2), 2.64 [t, J = 7.7 Hz, 8 H, (CH2)4],
3.40 (t, J = 7.4 Hz, 1.41 H, CH2), 3.53 (t, J = 6.6 Hz, 0.59 H, CH2),
7.24 (d, J = 8.4 Hz, 8 H, ArH), 7.50 (d, J = 8.4 Hz, 8 H, ArH). MS
(MALDI TOF): m/z = 718.5 [M]+ (C51H71Cl), 757.5 [M + K]+
(C51H71ClK), 764.5 [M
+
2H]+ (C51H73Br), 808.5 [M+2Na]+
(C51H71BrNa2), 840.5 [M + 2K]+ (C51H71 BrK2).
(37) Prodanov, M. F.; Vashchenko, O. V.; Vashchenko, V. V. Tetrahe-
dron Lett. 2014, 275.
© Georg Thieme Verlag Stuttgart · New York — Synlett 2015, 26, 1905–1910