Evidence on palladacycle-retaining pathway for Suzuki coupling. Inapplicability of Hg-drop test for palladacycle catalysed reactions

Article abstract of DOI:10.1016/j.jorganchem.2013.03.050

Investigation of the model atroposelective Suzuki reaction catalysed by chiral CN-palladacycles have shown that two types of catalytic cycle may operate simultaneously, with strong dependence of their contributions upon the palladacycle structure and conditions used. Dominant contribution of palladacycle retaining pathway was provided by the non-metallocene planar chiral iminate CN-palladacycle (R_pl)-4a using as catalyst, in reaction performed in toluene under aerobic conditions with KF as a base, affording (S_a)-2-methoxy-1,1′-binaphthalene with enantioselectivity up to 53% ee. The catalyst was recovered almost quantitatively as an iodide-bridged dimer, whose structure was confirmed by an X-ray diffraction study of its phosphine derivative. It was also shown that the common Hg drop test was unsuitable for mechanistic testing of palladacycle-catalysed reactions because of the transmetallation product formation, whose structure was confirmed by an X-ray diffraction study.

Full text of DOI:10.1016/j.jorganchem.2013.03.050

Journal of Organometallic Chemistry 737 (2013) 59e63
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Communication
Evidence on palladacycle-retaining pathway for Suzuki coupling. Inapplicability of
Hg-drop test for palladacycle catalysed reactions
Ol’ga N. Gorunova a, Michail V. Livantsov b, Yuri K. Grishin b, Michail M. Ilyin Jr. a,
Konstantin A. Kochetkova, Andrei V. Churakovc, Lyudmila G. Kuz’mina c, Victor N. Khrustalev a,
,
Valery V. Dunina b
*
a A.N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, Vavilova St. 28, 119991 Moscow, Russian Federation
b Department of Chemistry, M.V. Lomonosov Moscow State University, Lenin Hills 1, 119991 Moscow, Russian Federation
c N.S. Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences, Leninsky Prospect 31, 119991 Moscow, Russian Federation
a r t i c l e i n f o
a b s t r a c t
Article history:
Investigation of the model atroposelective Suzuki reaction catalysed by chiral CN-palladacycles have
shown that two types of catalytic cycle may operate simultaneously, with strong dependence of their
contributions upon the palladacycle structure and conditions used. Dominant contribution of pallada-
cycle retaining pathway was provided by the non-metallocene planar chiral iminate CN-palladacycle
(Rpl)-4a using as catalyst, in reaction performed in toluene under aerobic conditions with KF as a base,
affording (Sa)-2-methoxy-1,10-binaphthalene with enantioselectivity up to 53% ee. The catalyst was
recovered almost quantitatively as an iodide-bridged dimer, whose structure was confirmed by an X-ray
diffraction study of its phosphine derivative. It was also shown that the common Hg drop test was
unsuitable for mechanistic testing of palladacycle-catalysed reactions because of the transmetallation
product formation, whose structure was confirmed by an X-ray diffraction study.
Received 20 February 2013
Received in revised form
26 March 2013
Accepted 28 March 2013
Keywords:
Suzuki cross-coupling
Asymmetric catalysis
Non-metallocene CN-palladacycle
Parallel catalytic cycles
Hg drop test
Ó 2013 Elsevier B.V. All rights reserved.
1. Introduction
cyclopalladated catalyst are in contradiction with a classical Pd0/
PdII scenario. The most valuable experimental evidence in support
Herrmann’s discovery of the unique catalytic activity of palla-
dacycles for cross-coupling reactions [1] launched a new era in
homogeneous catalysis. Impressive advances in its achiral versions
[2] have stimulated the development of enantioselective catalysis
by chiral cyclopalladated compounds (CPCs) [3]. Excellent results
have been obtained for transformations based on palladacycles
acting as mild Lewis acids, especially in Overman rearrangement
[3,4] and hydrophosphination reactions [5]. In contrast, attempts to
catalyse asymmetric cross-coupling reactions have so far been
unsuccessful [6]. Such failures are usually explained by palladacycle
destruction in the frames of the traditional Pd0/PdII redox cycle.
However, recent computational [7] and experimental [8]
research has provided a great deal of evidence in favour of alter-
native mechanistic schemes that may retain an intact state of pal-
ladacycle(s) in the catalysis. The negative Hg drop test, absence of
an induction period in the catalysis without visible Pd black for-
mation, and the high yield of recovered (after the reaction)
of the PdII/PdIV catalytic cycle for the Heck cross-coupling has been
provided by Vicente’s recent research [9]. Although the possibility
of two reaction pathways operating in parallel is often recognized
[8c,10], any attempts to estimate the relative contributions of two
catalytic cycles were not attempted until now.
This preliminary communication describes our efforts to esti-
mate some factors determining the contribution of palladacycle-
retaining pathway of Suzuki reaction (via PdIV or anionic [(EXC)
Pd0]ꢀ intermediates [10b]), required for the development of its
asymmetric version. The important advantage of Suzuki cross-
coupling is that it can normally occur under milder conditions
[11] than those required for the Heck reaction (140e180 ꢁC [12]),
with some reactions even proceeding at room temperature (rt) [13].
The use of low-temperature regime is important not only for
improving the enantioselectivity but also as a route for decreasing
the possible contribution of a parallel Pd0/PdII pathway. Therefore,
the enantioselective catalysis of Suzuki cross-coupling by chiral
CPCs seemed to be more promising. To the best of our knowledge,
only two prior studies have involved the catalysis of the Suzuki
reaction by chiral NCN- [14] or PCN-pincer complexes [15] with
moderate enantioselectivity (20e49% ee).
* Corresponding author. Tel.: þ7 (495) 939 5376; fax: þ7 (495) 932 8846.
E-mail address: dunina@org.chem.msu.ru (V.V. Dunina).
0022-328X/$ e see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jorganchem.2013.03.050

60
O.N. Gorunova et al. / Journal of Organometallic Chemistry 737 (2013) 59e63
Table 1
2. Results and discussion
Catalyst and reaction condition screening.a
Previously, we have shown that the use of the known CN-pal-
ladacycle rac-1 as the (pre)catalyst provides extremely mild con-
ditions for Suzuki cross-coupling: the model non-chiral reaction of
p-tolyl bromide with phenylboronic acid can be conducted not only
at rt but even at ꢀ18 ꢁC [16]. Taking into account these results and
numerous other evidence of high catalytic activity of CN-pallada-
cycles in non-chiral Suzuki reactions [17], CPCs of this kind were
used to find conditions for palladacycle-retaining pathway for the
Suzuki reaction.
catalyst
10 mol% of Pd
B(OH)2
OMe
base, solvent,
rt, 24 h, in air
I
+
MeO
6
7
(Sa)-8
Entry
Catalyst
Base
Solvent
Yieldb (%)
ee (%)c (config)d
We have selected planar chiral CN-palladacycles with ferrocenyl
(1 [18], 2 [19]) or [2.2]paracyclophanyl backbone (3 [20], 4a [21]) as
1
2
3
rac-1
(Spl)-1
(SCRpl)-2
rac-2
rac-2
K2CO3
KF
K2CO3
Cs2CO3
KF
MeOH
Toluene
MeOH
MeOH
MeOH
MeOH
Toluene
MeOH
40
29
41
45
51
60
79
89
87
70
52
93
68
77
94
38
28
e
1.7(Sa)
0
potential (pre)catalysts; the C*-chiral CN-dimer
5 [22] was
employed for comparison purposes (Fig. 1).
4
e
5e
e
The catalytic activity and enantioselectivity of selected CPCs
was estimated for the model atroposelective reaction of 1-
naphthylboronic acid 6 with 1-iodo-2-methoxy-1-naphthalene 7
to afford 2-methoxy-1,10-binaphthalene 8 (Table 1).
The efficiency of CN-dimer 1 in binaphthyl 8 formation (entries 1,
2) was decreased compared to that previously found for biphenyl
formation under conditions more typical for Pd(II)/Pd(0)-catalysis
[16]. After base and solvent screening, the better results were ob-
6f
rac-2
KF
e
7
8
9
(SCRpl)-2
(SCRpl)-2
(SCRpl)-2
(SCRpl)-2
rac-3
(Rpl)-4a
(Rpl)-4a
(Rpl)-4a
(Rpl)-4a
(Rpl)-4a
(RC)-5
K3PO4
CsF
KF
KF
KF
KF
K3PO4
KF
KF
KF
0
0
0
MeOH
10
11
12
13
14
15e,g
16h
17
Toluene
Toluene
MeOH
7.9(Ra)
e
15.0(Sa)
23.5(Sa)
29.3(Sa)
37.3(Sa)
53.0(Sa)
10.2(Sa)
DCE
Toluene
Toluene
Toluene
Toluene
tained using its a-Me-substituted analogue 2 (entries 3e10). This
catalyst can operate at rt and at decreased loading (1.0 and 0.1 mol%
of Pd, entries 5, 6), providing a high yield of binaphthyl product 8,
with optimal conditions affording 87e89% (entries 8, 9). General
drawbacks of aminate CN-catalysts 1e3 include Pd black precipi-
tation and the complete absence of asymmetric induction in re-
actions conducted in methanol (entries 3, 8, and 9).
Enantioselectivity of the aminate CN-catalysts appears to be
relatively low, even in toluene varying in the range of <2% ee for
(Spl)-1 to w8% ee for (SCRpl)-2, and w10% ee for (RC)-5 (entries 2, 10,
and 17, respectively). The best optical yields were obtained in ex-
periments using imine catalyst (Rpl)-4a, with enantioselectivity
increasing from 15% ee in MeOH up to w29% ee in toluene at rt, and
then to 53% ee on reducing the temperature to 5 ꢁC (entries 12, 14,
and 16, respectively).
KF
a
Conditions: 0.212 mmol of aryl boronic acid 6, 0.106 mmol of aryl iodide 7,
5.0 eq. of base (0.5302 mmol), 5 mol% of dimeric catalyst (0.0053 mmol), and 2 mL of
solvent were reacted in air at the rt for 24 h, unless otherwise noted.
b
Isolated yields.
c
Determined by HPLC on a Chiralcel OJ Column.
d
The absolute configuration of product (þ)D-8 was determined to be (Sa) by
comparison with the reported HPLC-data.
e
Catalyst loading was decreased to 1.0 mol% of Pd.
Catalyst loading was decreased to 0.1 mol% of Pd and reaction time increased to
f
96 h.
g
Reaction time was increased to 7 days.
Reaction was conducted at 5 ꢁC for 35 days.
h
Imine catalyst (Rpl)-4a has several advantages: it can operate at
rt and at reduced temperatures, providing good yields of
binaphthyl 8 even at only 1 mol% Pd loading (94%, entry 15), and
without visible evidence of Pd black formation. This catalyst can be
almost quantitatively recovered after the reaction (92e96% for
entries 13, 14, and 16) as an iodide-bridged dimer (Rpl)-4b, whose
structure was confirmed by spectral and X-ray diffraction studies of
its phosphine derivative (Rpl)-4c (Fig. 2).
2
Cl
Pd
H
NMe2
2
NMe2
Pd
Me
H
Fe
NMe2
Pd
Fe
(SCRpl)-2
Cl
(Spl)-1
Cl
Me
2
Cl
(RC)-5
2
Me
N
Pd
NMe2
Me
Pd
Cl
2
ꢀ
Fig. 2. Molecular structure of (Rpl)-4c; selected bond lengths (A): Pd(1)eC(4) 2.024(3);
(Spl)-3
(Rpl)-4a
Pd(1)eI(1) 2.7085(4); Pd(1)eN(1) 2.110(3); Pd(1)eP(1) 2.2715(10). Selected bond an-
gles (ꢁ): C(4)ePd(1)eN(1) 80.44(13); C(4)ePd(1)eP(1) 97.51(10); I(1)ePd(1)eN(1)
96.30(8); P(1)ePd(1)eI(1) 90.26(3).
Fig. 1. CPCs selected for catalytic testing.

O.N. Gorunova et al. / Journal of Organometallic Chemistry 737 (2013) 59e63
61
Our experimental findings are in agreement with the presence
of two different catalytic cycles operating simultaneously, with
their contributions strongly dependent on both catalyst structure
and reaction conditions. One pathway, based on the common
Pd0/PdII redox cycle, is dominant in all CN-palladacycle catalysed
reactions carried out in methanol. As well as the progressive Pd
black precipitation, the absence of enantioselectivity may be
considered as additional stereochemical evidence of heterogeneous
Pd0 catalysis. Aminate palladacycle destruction due to the PdII to
Pd0 reduction, even in toluene, was indicated by the formation of
the near-racemic product 8 in the reaction catalysed by the planar
chiral complex (Spl)-1 (<2% ee, entry 2), which is in accordance with
the catalyst transformation into a non-chiral compound after PdeC
bond cleavage.
There is a great deal of experimental evidence in favour of the
dominant contribution of a palladacycle-retaining pathway for the
imine dimer (Rpl)-4a catalysed Suzuki coupling in toluene. Firstly,
the rather high enantioselectivity (up to 53% ee) indicates that the
palladacyclic structure of the catalyst is preserved during the re-
action. Secondly, the two-fold higher enantiomeric enrichment of
product (Sa)-8 isolated from the reaction in toluene compared to
that of product (Sa)-8 isolated from the reaction in methanol (29
and 15% ee, entries 14 and 12, respectively) may be caused by a
decreased contribution of the destructive PdII/Pd0 redox cycle in the
aprotic solvent. Thirdly, all reactions conducted in toluene occurred
in air without any visible evidence of Pd black formation. And
finally, the cyclopalladated catalyst was almost quantitatively
recovered after the reaction.
To support our mechanistic assumptions, we measured the ki-
netics of dimer (Rpl)-4a-catalysed reactions in toluene and meth-
anol at rt (entries 14 and 12) using a 1H NMR control (Fig. 3).
The reaction in toluene did not reveal any induction period
(Fig. 3a), which is required for palladacycle reduction during the
pre-activation stage [23], and it is indicative of the dominant
contribution of the palladacycle-retaining pathway under these
conditions. The decreased conversion is caused by the conditions of
ꢀ
Fig. 4. Molecular structure of rac-9; selected bond lengths (A): Hg(1)eC(4) 2.075(4);
Hg(1)eCl(1) 2.3435(10); Hg(1)eN(1) 2.586(3). Selected bond angles (ꢁ): C(4)eHg(1)e
N(1) 76.65(13); C(4)eHg(1)eCl(1) 179.10(11); Cl(1)eHg(1)eN(1) 104.07(8).
In support of this conjecture we can mention more than two-
fold decreasing of the final product (Sa)-8 enantiopurity (16.8% ee
at 83% conversion) compared to that of the binaphthyl (Sa)-8 iso-
lated at the initial stage (36.0% ee at 4% conversion) due to its
subsequent “dilution” with racemic binaphthyl rac-8 formed via
Pd0/PdII pathway. In contrast, only minor changes in the product
(Sa)-8 enantiopurity were observed in course of the reaction per-
formed in toluene (31.9 and 29.4% ee at 15 and 50% conversion,
respectively).
Furthermore, these two reactions were subjected to the Hg drop
test. Unexpectedly, the suppression of catalysis by Hg0 (which is
usually considered as evidence for heterogeneous catalysis [23b] or
catalysis via a Pd0 intermediates [23a,c]) was observed in the re-
actions conducted both in methanol and toluene (<1% conversion).
As this was not consistent with our other acquired data, control
experiments were carried out. In reactions of dimer rac-4a with ca.
300 eq. of Hg0 in both solvents, CPC conversion into a new complex
was observed. This was identified as the redox-transmetallation
NMR-monitoring excluding efficient stirring. By contrast,
a
sigmoidal-shaped kinetic curve was obtained for the reaction
conducted in methanol (Fig. 3b). However, during the induction
period of ca. 2e3 h the reaction rate was low but not zero, followed
by a drastic increase in conversion to w100% after 6 h. This anomaly
allows us to assume that initially the coupling reaction is mainly
catalysed by the palladacycle, providing some asymmetric induc-
tion, followed by more rapid non-chiral catalysis by the formed Pd0
particles.
product [{k
2(N,C)-L}HgCl] (rac-9) by spectral and X-ray diffraction
studies (Fig. 4).
Consequently, the efficient inhibition of catalysis by Hg0 may be
caused not only by the amalgamation of heterogeneous or soluble
Fig. 3. Conversion vs. time: (Rpl)-4a catalysed reactions in d8-toluene (a) and in d4-methanol (b).

62
O.N. Gorunova et al. / Journal of Organometallic Chemistry 737 (2013) 59e63
4.2. General procedure for the CPC-catalysed Suzuki coupling
reaction
Me
N
Me
N
Hg(0) 300 eq.
Me
Me
Hg
A mixture of 1-naphthylboronic acid 6 (0.211 mmol), 1-iodo-2-
Pd
Toluene
Cl
methoxynaphtalene 7 (0.106 mmol), selected base (0.53 mmol)
and dimeric cyclopalladated catalyst (0.0053 mmol) in the selected
solvent (2 mL) was stirred at indicated temperature in air and
evaporated. The residue was dissolved in dichloromethane (5 mL),
washed with water (3 ꢂ 5 mL), the combined organic solutions
were dried over magnesium sulphate, and solvent was removed
under reduced pressure. The crude material was purified using dry
column chromatography on silica (h ¼ 3.5 cm, d ¼ 2 cm; petroleum
ether/dichloromethane 8:1, 5:1, 3:1 and 1:1) to give target 2-
methoxy-1,10-binaphtalene 8 as a colourless amorphous powder.
If TLC data indicates palladacycle retaining after catalysis, an
additional dry column chromatography (h ¼ 4 cm, d ¼ 2 cm; pe-
troleum ether, toluene, toluene/acetone 15:1) was used to recover
or MeOH
Cl
2
rac-4a
rac-9
Scheme 1. Redox-transmetallation of the catalyst rac-4a.
Pd0 species [23a,c,24], but also by the decomposition of the ho-
mogeneous PdII containing catalyst, due to its interaction with Hg0
(Scheme 1).
In order to avoid erroneous mechanistic conclusions from the
Hg poisoning test, it would be necessary to perform control ex-
periments to exclude the possibility of cyclopalladated catalyst
reaction with metallic Hg. Unfortunately, examples of such control
studies for cross-coupling catalyst behaviour towards Hg0 are very
rare [25]; in their absence the deductions about the Pd0/PdII cata-
lytic cycle cannot be considered as absolutely correct.
the catalyst as the iodide-bridged dimer (RplRpl)-4b: mp (decomp.)
22
160e161 ꢁC; Rf 0.56 (toluene); [
a
]
ꢀ80 (c 0.25, CH2Cl2). For
D
confirmation of the iodide-bridged dimer (RplRpl)-4b structure it
was transformed into its mononuclear PPh3 derivative [(CXN)
PdI(PPh3)] (Rpl)-4c by standard method [21]. Single crystals of
phosphine adduct (Rpl)-4c were obtained by slow diffusion of light
petroleum ether into its solution in CH2Cl2. Its 1H and 31P NMR
spectra are identical with those of the complex rac-4c prepared by
independent route (see ESI).
3. Conclusion
In summary, this preliminary study has shown that the non-
pincer type CN-palladacycle (Rpl)-4a may work as a true catalyst
in the Suzuki reaction under aprotic conditions, providing enan-
tioselectivity up to 53% ee at low temperatures. We have also shown
that the use of the Hg poisoning test for mechanistic studies of
palladacycle-catalysed reactions requires preliminary control ex-
periments because the suppression of the catalysis may be caused
by a CPC/Hg0 interaction, which was unambiguously confirmed by
X-ray studies of the transmetallation product.
4.3. Kinetic studies of Suzuki coupling reaction
A mixture of 1-naphtaleneboronic acid 6 (0.0181 g, 0.1055 mmol),
1-iodo-2-methoxynaphtalene 7 (0.015 g, 0.0527 mmol) and KF
(0.0153 g, 0.2634 mmol) in d8-toluene or d4-methanol (0.5 mL) was
loaded into the NMR-tube, and 1H NMR spectrum was measured
before catalyst bringing in. Then dimer (Rpl)-4a (0.00251 g,
0.00265 mmol) was added into the same tube, and after 1 min
spectra measurements were started. The conversion was calculated
using integral values of 2-MeO group signals of product 8 and
starting iodide 7.
4. Experimental
4.1. General information
The 1H and 31P NMR spectra were recorded on the Agilent 400-
MR spectrometer operating at the frequencies 400.0 and 161.9 MHz
for 1H and 31P nuclei, respectively. The measurements were carried
out at ambient temperature in CDCl3 solutions. The chemical shifts
4.4. Independent synthesis of the transmetallation product rac-9
are reported in
d
-scale in parts per million relative to TMS as an
A mixture of dimer rac-4a (0.0102 g, 0.0106 mmol) and metallic
mercury excess (0.708 g, 0.00252 mmol, 330 eq.) in toluene (5 mL)
was intensively stirred at r.t. for 48 h, that is accompanied by colour
changing from yellow to light-yellow. After removing the metallic
mercury by filtration, the light-yellow solution was evaporated in a
vacuum to dryness. The crude product was purified using short dry
column chromatography on silica (h ¼ 4 cm, d ¼ 2.5 cm; petroleum
ether, toluene, toluene/acetone 10:1) to afford transmetallation
product rac-9 (0.0073 g, 60%) as an yellow amorphous powder.
Monocrystals of the complex rac-9 were obtained by slow evapo-
ration of its solution in a solvent mixture toluene/petroleum
ether/chloroform. Data for rac-9: mp (decomp.) 239e241 ꢁC;
Rf ¼ 0.27 (toluene); 1H NMR (CDCl3): aromatic protons of the [2.2]
internal standard for 1H NMR and relative to H3PO4 as an external
reference for the 31P NMR spectra. The signal assignments were
performed using COSY and NOESY techniques. Unless otherwise
stated, the reactions were carried out without precautions against
light or atmospheric oxygen or moisture. Reaction progress and
purity of compounds formed were monitored by TLC on Silufol UV-
254 with visualization under the UV light or in iodine vapour.
“Short dry column” [26] or flash-chromatography on Fluka 60 silica
gel was used for preparative isolation and purification of com-
pounds obtained. Enantiomeric analysis of the (Sa)-2-methoxy-1,10-
binaphthyl (8) samples was performed by HPLC (Bischoff) on
Chiralcel OJ (250 ꢂ 4.6 mm) with heptane/iPrOH 9/1 as eluent; the
absolute configuration of (þ)D-8 was assigned by comparison with
literature data [27].
paracyclophane moiety:
d
6.43 (dd, 1H, 3JHH 7.8, 4JHH 1.9, H13), 6.56
(dd, 1H, 3JHH 7.8, 4JHH 1.9, H12), 6.57 (d, 1H, 3JHH 7.7, H7), 6.59 (dd, 1H,
3JHH 7.8, 4JHH 1.9, H16), 6.63 (dd, 1H, 3JHH 7.8, 4JHH 1.9, H15), 6.83 (dd,
Toluene was dried over CaCl2, refluxed over Na and then
distilled. Anhydrous MeOH was prepared by distillation from
MeONa. Chloroform and dichloromethane were passed through a
short Al2O3 column and distilled under argon. Hexane and light
petroleum ether were distilled from Na. Acetonitrile was distilled
under argon from P2O5. DME, 1-Naphthylboronic acid (6), 2-
methoxynaphthalene, N-iodosuccinimide, (RC)-1-(10-N,N-dime-
thylaminoethyl)naphthalene, CDCl3 (from Aldrich), KF (from Acrus)
and mercury (from Merck, >99.998% purity) were used as received.
3
4
1H, JHH 7.7, JHgH 78.0, H8); methylene protons of the [2.2]para-
2
3
3
cyclophane moiety:
d 2.89 (ddd, 1H, JHH 13.3, JHH 6.6, JHH 10.3,
H
10s), 3.06 (ddd, 1H, 2JHH 14.0, 3JHH 6.6, 3JHH 10.4, H9a), 3.17 (ddd, 1H,
2JHH 13.5, 3JHH 4.0, 3JHH 10.9, H2s), 3.24 (ddd, 1H, 2JHH 13.5, 3JHH 4.0,
3JHH 10.8, H1a), 3.27 (ddd, 1H, 2JHH 13.5, 3JHH 3.7, 3JHH 10.9, H1s), 3.29
(ddd, 1H, 2JHH 13.3, 3JHH 2.1, 3JHH 10.4, H10a), 3.39 (ddd, 1H, 2JHH 13.5,
3JHH 3.7, 3JHH 10.8, H2a), 3.59 (ddd, 1H, JHH 14.0, JHH 2.1, JHH 10.3,
2
3
3
H
9s); side chain protons:
d 2.30 (s, 6H, 2Me), 7.01e7.05 (m, 1H, A

O.N. Gorunova et al. / Journal of Organometallic Chemistry 737 (2013) 59e63
63
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AB2 system, JAB 7.5, meta-H, C6H3), 8.63 (s, 1H, JHgH 10.4, CH]N).
4
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Acknowledgements
The authors thank the Russian Foundation for Basic Researches
(grant number 13-03-01169) for partial financial support. This work
has been also supported in part by M.V. Lomonosov Moscow State
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