Palladium complexes with 1-methyl-3-phenylindazole ligands

Article abstract of DOI:10.1007/s11172-017-1763-2

1-Methyl-3-phenylindazole reacts with lithium tetrachloropalladate and palladium acetate to give new coordination and (C,N)-cyclometallated dimeric and monomeric palladium complexes.

Full text of DOI:10.1007/s11172-017-1763-2

Russian Chemical Bulletin, International Edition, Vol. 66, No. 3, pp. 502—505, March, 2017
502
Palladium complexes with 1ꢀmethylꢀ3ꢀphenylindazole ligands
L. A. Bulygina, N. S. Khrushcheva, N. S. Ikonnikov, and V. I. Sokolov
A. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences,
28 ul. Vavilova, 119991 Moscow, Russian Federation.
Fax: +7 (499) 135 5085. Eꢀmail: stemos@ineos.ac.ru
1ꢀMethylꢀ3ꢀphenylindazole reacts with lithium tetrachloropalladate and palladium acetate
to give new coordination and (C,N)ꢀcyclometallated dimeric and monomeric palladium
complexes.
Key words: 1ꢀmethylꢀ3ꢀphenylindazole, cyclopalladated complex, coordinated palladium
complex.
Cyclopalladation of phenylꢀsubstituted azaheterocycles
and K2CO3, nearly complete conversion was achieved at
room temperature within 5 h. Thin layer chromatography
monitoring of the reaction mixture revealed only traces of
the starting iodide 2; complete conversion of 2 was
achieved by heating the reaction mixture at 65 °C for 15 min.
In the next step, we studied the reaction of the syntheꢀ
sized ligand 3 with palladating agents. It is known that the
reaction of 1ꢀphenylindazole with sodium tetrachloropalꢀ
ladate is accompanied with the replacement of the benzꢀ
ene ring hydrogen atom with Pd to give cyclopalladate
complex.6 Palladation of 3ꢀphenylꢀsubstituted derivative
3 with lithium tetrachloropalladate under standard condiꢀ
tions (sodium acetate, methanol, room temperature, stirꢀ
ring) selectively produces coordination complex 4. Strucꢀ
and studies of the properties of the resulting complexes is
well documented. (C,N)ꢀCyclopalladated heterocyclic
complexes exhibiting photoluminescent properties1 and
liquid crystalline behavior2 have also been reported. Howꢀ
ever, the general interest to these compounds is mainly
due to their efficiency as catalysts and precatalysts for
various types of chemical transformations and, first of all,
for the C—C bond forming reactions.3 Thus, cyclopallaꢀ
dated complexes of 1ꢀNꢀphenylꢀ4 and 3ꢀCꢀphenylꢀsubstiꢀ
tuted5 pyrazoles have been synthesized and characterized.
For other representatives of azoles, i.e., 1Hꢀindazoles,
reaction with palladium salt was studied for only 1ꢀNꢀphenꢀ
ylꢀsubstituted derivative.6 The aim of the present work is
the synthesis of new palladium complexes of 1ꢀNꢀmethylꢀ
indazole bearing C(3)ꢀphenyl substituent.
Ligand 3 was synthesized as shown in Scheme 1. The
starting 3ꢀiodoꢀ1Hꢀindazole 1 was synthesized in two steps
from oꢀtoluidine following the known procedures.7,8 It is
known that the nitrogenꢀunsubstituted azole derivatives
exist in tautomeric equilibrium due to the proton transfer
between nitrogen atoms. The tautomeric equilibrium exꢀ
plains the failure to synthesize any palladium complexes
of pyrazole derivatives.5a Therefore, we started from meꢀ
thylation of compound 1 with iodomethane in the presꢀ
ence of KOH. Compound 2 was separated from a mixture
with the minor 2ꢀmethylꢀsubstituted
1
ture of complex 4 was examined by IR and H NMR
spectroscopy and confirmed by microanalysis data. Inteꢀ
gral intensities of 1H NMR signals of the aromatic protons
indicate the presence of the monosubstituted benzene ring
in the structure of 4. This was confirmed by IR spectroꢀ
scopy showing absorptions at 702 and 750 cm–1 4a,5a
Conꢀ
.
sequently, it can be concluded that compound 4 has strucꢀ
ture of a coordination complex. IR spectrum of complex 4
exhibits only one absorption in the range of the Pd—Cl
stretching vibrations at 353 cm–1 thus indicating trans
1
stereochemistry of complex 4.5,6 Moreover, in H NMR
spectrum of compound 4 the NMe protons are shifted
downfield by 0.37 ppm compared with the starting ligand.
For the closely related complexes of NMeꢀsubstituted pyrꢀ
azoles, Alonso at al.5b found that similar downfield shift is
characteristic of the trans complexes, whereas the cis comꢀ
plexes exhibit upfield shift.
isomer by silica gel column chromaꢀ
tography. Reaction of compound 2
with phenylboronic acid catalyzed by
palladium complex 9 gives 1ꢀmethylꢀ
3ꢀphenylindazole (3). Catalytic perꢀ
formance of complex 9 in the Suzuki
reaction in the model reactions was
studied by us earlier.9 In the reaction of iodide 2 with
phenylboronic acid in the presence of cyclopalladate 9
Cyclopalladated complexes of ligand 3 were accessed
under more drastic conditions as it was described earlier
for the pyrazole derivatives.5b Complex 5 was synthesized
by heating compound 3 with palladium acetate in acetic
acid. Structure of complex 5 was established by IR spectroꢀ
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 0502—0505, March, 2017.
1066ꢀ5285/17/6603ꢀ0502 © 2017 Springer Science+Business Media, Inc.

Palladation of 1ꢀmethylꢀ3ꢀphenylindazole
Russ.Chem.Bull., Int.Ed., Vol. 66, No. 3, March, 2017
503
Scheme 1
L = Pyꢀd5 (7), Ph3P (8)
Reagents and conditions: i. MeI, KOH, acetone; ii. PhB(OH)2, K2CO3, 9, MeOH, H2O; iii. Li2PdCl4, AcONa•3 H2O, MeOH;
iv. Pd(OAc)2, AcOH; v. LiCl, acetone, H2O; vi. CDCl3, pyridineꢀd5 (for 7); vii. PPh3, CH2Cl2 (for 8).
scopy, 1H and 13C NMR spectroscopy, mass spectrometry
and confirmed by elemental analysis.
1
In H NMR spectrum of complex 5, integral intensiꢀ
ties of the aromatic proton signals correspond to the diꢀ
substituted benzene ring. This fact is also confirmed by the
presence in its IR spectrum of the absorption typical for
orthoꢀdisubstituted benzene ring at 740 cm–1 4a,6
These
.
data allow us to conclude that the palladium atom reꢀ
placed the proton of the benzene ring and compound 5 is
the (C,N)ꢀcyclopalladated complex. This conclusion is
also supported by the appearance in the 13C NMR specꢀ
trum of 5 of the fourth signal of low intensity in the resoꢀ
nance range typical of the quaternary aromatic carbon
atoms as well as the microanalysis data. IR spectrum of
complex 5 exhibits two absorptions at 1567 and 1411 cm–1
corresponding to symmetrical and asymmetrical vibrations
of the carboxyl groups. The difference between positions
of these vibrations of 156 cm–1 indicates that the carboxyl
groups form (O,O´)ꢀbridges.4b,10 Thus, complex 5 is
(C,N)ꢀcyclopalladated dimeric complex with the acetate
bridges.
Cyclopalladated dimeric complex 5 may exists as either
syn (A) or anti isomer (B). These isomers can be distinꢀ
1
guished by H NMR spectroscopy by the presence of
Complex 5 reacts with lithium chloride in aqueous
acetone to give cylopalladated dimer with the chloride
bridges 6. Complex 6 was found almost insoluble in all
common organic solvents. IR spectrum of complex 6 exꢀ
hibits the absorption at 745 cm–1 characteristic of the
orthoꢀsubstituted benzene ring,4a,6 and two absorptions of
one (in the case of anti isomer) or two (in the case of
syn isomer) signals of the methyl group of the acetate
moiety.4b,5b 1H NMR spectrum of cyclopalladate 5 conꢀ
tains the only one signal at δ 2.3 thus suggesting its anti
stereochemistry.

504
Russ.Chem.Bull., Int.Ed., Vol. 66, No. 3, March, 2017
Bulygina et al.
compound 3. 1H NMR (CDCl3), δ:14 4.16 (s, 3 H); 7.21— 7.27
(m, 1 H); 7.38—7.48 (m, 3 H); 7.53 (t, 2 H, J = 7.6); 7.99 (d, 2 H,
J = 7.4 Hz); 8.05 (d, 1 H, J = 8.2 Hz). 13C NMR (CDCl3), δ:
35.58; 109.23; 120.94; 121.37; 121.62; 126.30; 127.41; 127.84;
128.84; 133.71; 141.45; 143.74.
the Pd—Cl stretching vibrations at 337 and 226 cm–1 typꢀ
ical of the cyclopalladated dimers with the chloride bridgꢀ
es.6 Microanalysis data agree well with the structure of
complex 6. Cyclopalladated structure of complex 6 was
additionally confirmed by its conversion into monomeric
complex 7 by addition of a drop of pyridineꢀd6 to a susꢀ
pension of complex 6 in CDCl3. Integral intensities of the
1H NMR signals of the aromatic protons of complex 7
unambiguously indicate the presence of disubstituted
benzene ring.
Another monomeric palladacycle 8 was synthesized by
reacting compound 6 with triphenylphosphine in CH2Cl2.
Structure of complex 8 was established by 1H and 13C NMR
spectroscopy, mass spectrometry, IR spectroscopy and
confirmed by elemental analysis. IR spectrum of comꢀ
plex 8 contains the absorption at 1096 cm–1 attributed to
the coordinated Ph3P fragment.10 31P NMR spectrum of 8
exhibits signal at δ 46.7.5a
Dichloroꢀbis[(1ꢀmethylꢀ3ꢀphenylindazole)ꢀN,N´}palladium
(4). A suspension of palladium chloride (0.1724 g, 0.9 mmol)
and lithium chloride (0.0811 g, 1.9 mmol) in MeOH (15 mL)
was refluxed for 1 h, cooled to room temperature, and treated
dropwise with a solution of compound 3 (0.1872 g, 0.9 mmol)
and AcONa•3H2O (0.1224 g, 0.9 mmol) in MeOH (5 mL). The
reaction mixture was stirred at room temperature for 5 h and
concentrated. Water was added to the residue and the mixture
was extracted with CHCl3. The organic layer was dried with
Na2SO4, filtered through a Celit pad (elution with CHCl3), and
concentrated. The residue was successively washed with diethyl
ether and acetone and dried to give 0.1372 g (40%) of comꢀ
pound 4. Found (%): C, 56.44; H, 4.05; Cl, 11.77; N, 9.34.
C28H24Cl2N4Pd. Calculated (%): C, 56.63; H, 4.07; Cl, 11,94;
N, 9.43. MS (EI), m/z (Irel (%)): 208 [0.5(M – 2 Cl – Pd)]+
(100). IR, ν/cm–1: 750 (C6H5), 702 (C6H5), 490 (Pd—N), 353
(Pd—Cl). 1H NMR (CDCl3), δ: 4.53 (s, 3 H); 7.22 (m, 1 H);
7.39 (m, 1 H); 7.48 (m, 1 H); 7.66—7.77 (m, 4 H); 8.40 (d, 2 H,
J = 8.4 Hz).
Experimental
NMR spectra were recorded on a BrukerꢀAvance 400 inꢀ
strument (working frequencies of 400.13 (1H), 100.61 (13C), and
161.98 (31P) MHz) in CDCl3. Chemical shifts are given in the δ
scale and were measured relative to the residual solvent signal
(1H), the solvent 13C resonance (13C), a signal of 85% H3PO4
Diꢀμꢀacetatoꢀbis[2ꢀ(1ꢀmethylindazolꢀ3ꢀyl)phenylꢀC,N]diꢀ
palladium (5). A suspension of compound 3 (0.1872 g, 0.9 mmol)
and palladium acetate (0.2021 g, 0.9 mmol) in acetic acid (30 mL)
was heated at 90 °C for 3 h, cooled, and concentrated. The
residue was dissolved in CH2Cl2, washed twice with a 10% aqueous
NaHCO3, dried with Na2SO4, filtered through a Celit pad
(elution with CH2Cl2), and concentrated. The residue was
washed with diethyl ether and acetone and dried to give 0.3063 g
(91%) of compound 5. Found (%): C, 48.15; H, 3.34; N, 6.91.
C16H14N2O2Pd•0.5CH2Cl2. Calculated (%): C, 47.73; H, 3.64;
N, 6.75. MS (EI), m/z (Irel (%)): 372 [M/2]+ (21), 313
[0.5(M – 2 AcO)]+ (32), 208 [0.5(M – 2 AcO – 2 Pd) + 1]+
(78), 207 [0.5(M – 2 AcO – 2 Pd)]+ (100). IR, ν/cm–1: 1567
(C=Oasym), 1411 (C=Osym), 740 (1R,2R´—C6H4). 1H NMR
(CDCl3), δ: 2.26 (s, 3 H); 3.42 (s, 3 H); 6.54 (d, 1 H, J = 7.4 Hz);
6.70 (t, 1 H, J = 7.3 Hz); 6.80 (t, 1 H, J = 7.5 Hz); 6.90 (d, 1 H,
J = 8.5 Hz); 7.00 (d, 1 H, J = 7.6 Hz); 7.07—7.17 (m, 1 H); 7.36
(dd, 2 H, J = 15.1 Hz, J = 8.0 Hz). 13C NMR (CDCl3), δ: 24.83;
34.01; 109.72; 118.00; 120.43; 121.32; 121.45; 124.06; 124.76;
127.39; 130.76; 137.94; 140.27; 145.41; 149.45; 181.54.
Diꢀμꢀchloroꢀbis[2ꢀ(1ꢀmethylindazolꢀ3ꢀyl)phenylꢀC,N]diꢀ
palladium (6). To a suspension of compound 5 (0.3009 g,
0.81 mmol) in acetone (15 mL), a solution of lithium chloride
(0.1028 g, 2.42 mmol) in water (3 mL) was added. The mixture
was stirred for 8 h, the precipitate was collected by filtration, washꢀ
ed successively with water, acetone, and dichloromethane, and dried
in vacuo to give 0.1395 g (50%) of compound 6. Found (%):
C, 47.43; H, 3.43; N, 7.80. C14H11ClN2Pd•0.1CH2Cl2. Calcuꢀ
lated (%): C, 47.36; H, 3.16; N, 7.83. MS (EI), m/z (Irel (%)): 208
[0.5(M – 2 Cl – 2 Pd) + 1]+ (100), 207 [0.5(M – 2 Cl – 2 Pd)]+
(60). IR, ν/cm–1: 745 (1R,2R´—C6H4), 434 (Pd—N), 337
(Pd—Cl), 226 (Pd—Cl).
(
31P, an internal standard) and recounted with respect to Me4Si.
IR spectra were recorded with a Bruker Tensor 37 FTIR spectroꢀ
meter in the KBr pellets or in Nujol. Electron impact (EI) mass
spectrometry was performed with a Finnigan Polaris Q instruꢀ
ment at 70 eV electron energy. Electrospray ionization (ESI)
mass spectrometry was carried out on a Finnigan LCQ Advantage
instrument. 1HꢀIndazole,7 3ꢀiodoꢀ1Hꢀindazole 1,8 phenylꢀ
boronic acid,11 and complex 912 were synthesized by the known
procedures.
3ꢀIodoꢀ1ꢀmethylꢀ1Hꢀindazole (2). To a solution of compound 1
(18.4 g, 0.075 mol) in acetone (200 mL), KOH (6.3 g, 0.113 mol)
was added at 0 °C and the mixture was stirred for 15 min. Then
MeI (4.7 mL, 0.075 mol) was added dropwise at 0 °C and stirring
was continued for 2 h. The solvent was removed in vacuo, the
residue was dissolved in ethyl acetate, washed with water and
brine, dried with Na2SO4, and concentrated. Purification of the
residue by silica gel column chromatography (elution with
hexane—AcOEt, 100 : 0→70 : 30) afforded 12.8 g (66%) of comꢀ
pound 2. 1H NMR (CDCl3), δ:13 4.12 (s, 3 H); 7.23 (t, 1 H,
J = 7.5 Hz); 7.38 (d, 1 H, J = 8.5 Hz); 7.48 (dd, 2 H, J = 16.1 Hz,
J = 7.6 Hz). 13C NMR (CDCl3), δ: 36.05; 90.60; 109.09; 121.30;
121.56; 127.43; 128.29; 140.57.
1ꢀMethylꢀ3ꢀphenylꢀ1Hꢀindazole (3). Cyclopalladate 9 (0.053 g
(1 mol.%)) was added to a suspension of phenylboronic acid
(1.28 g, 0.01 mol), compound 2 (1.81 g, 0.007 mol), and K2CO3
(1.93 g, 0.014 mol) in a mixture of MeOH (45 mL) and water
(15 mL) and the resulting mixture was stirred at 21 °C for 5 h.
Then the mixture was heated at 65 °C for 15 min, cooled, diluted
with water, and extracted with CH2Cl2. The organic layers were
washed with water, brine, dried with Na2SO4, and concentrated.
Purification of the residue by silica gel chromatography (elution
with hexane—AcOEt, 100 : 0→90 :10), afforded 1.30 g (89%) of
Chloro[2ꢀ(1ꢀmethylindazolꢀ3ꢀyl)phenylꢀC,N](pyridineꢀd5)ꢀ
palladium (7). The synthesis was carried out in a standard NMR
tube. To a suspension of compound 6 (5 mg, 0.01 mmol) in
CDCl3 (0.6 mL), three drops of a solution containing CDCl3
(0.1 mL) and one drop of pyridineꢀd5 were added. The NMR

Palladation of 1ꢀmethylꢀ3ꢀphenylindazole
Russ.Chem.Bull., Int.Ed., Vol. 66, No. 3, March, 2017
505
tube was shaken until complete dissolution of compound 6.
1H NMR (CDCl3), δ: 4.53 (s, 3 H); 5.98 (d, 1 H, J = 7.8 Hz);
6.82 (t, 1 H, J = 7.5 Hz); 7.15 (t, 1 H, J = 7.3 Hz); 7.31 (m, 1 H);
7.43 (d, 1 H, J = 8.5 Hz); 7.53 (m, 1 H); 7.79 (d, 1 H, J = 7.4);
8.14 (d, 1 H, J = 8.4 Hz).
L. Douce, A. Skoulios, R. Ziessel,g. Angew. Chem., Int. Ed.,
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Chloro[2ꢀ(1ꢀmethylindazolꢀ3ꢀyl)phenylꢀC,N](triphenylphosꢀ
phine)palladium (8). To a suspension of compound 6 (0.0603 g,
0.17 mmol) in CH2Cl2 (7 mL), PPh3 (0.0453 g, 0.17 mmol) was
added. The mixture was stirred for 2 h and concentrated. Purifiꢀ
cation of the residue by silica gel column chromatography (eluꢀ
tion with CH2Cl2) afforded 0.0764 g (74%) of compound 8.
Found (%): C, 59.99; H, 4.25; N, 4.27. C32H26ClN2PdP•
•0.5CH2Cl2. Calculated (%): C, 59.70; H, 4.16; N, 4.28. MS
(ESI), m/z: 575 [M – Cl]+ (100). IR, ν/cm–1: 1096 (PPh3), 745
(1R,2R´—C6H4). 1H NMR (CDCl3), δ: 4.57 (s, 3 H); 6.50—6.40
(m, 1 H); 6.58 (t, 1 H, J = 7.0 Hz); 7.02 (t, 1 H, J = 7.3 Hz); 7.32
(t, 1 H, J = 7.5 Hz); 7.51—7.37 (m, 10 H); 7.61—7.52 (m, 1 H);
7.98—7.78 (m, 7 H); 8.24 (d, 1 H, J = 8.3 Hz). 13C NMR
(CDCl3), δ: 36.87; 110.09; 118.20; 121.37; 122.23; 123.75;
124.41; 126.35; 128.07; 128.54; 130.85; 131.44; 135.58; 138.71;
140.84; 142.61; 150.44; 151.79. 31P NMR (CDCl3), δ: 46.70.
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This work was financially supported by the Russian
Foundation for Basic Research (Project No. 14ꢀ03ꢀ00467).
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Received March 20, 2016;
in revised form June 16, 2016