Synthesis of New Chiral Palladium Complexes with

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2018, Vol. 54, No. 9, pp. 1285–1289. © Pleiades Publishing, Ltd., 2018. Original Russian Text © Ya.A. Gur’eva, O.A. Zalevskaya, I.A. Alekseev, P.A. Slepukhin, A.V. Kutchin, 2018, published in Zhurnal Organicheskoi Khimii, 2018, Vol. 54, No. 9, pp. 1274–1278.

Synthesis of New Chiral Palladium Complexes with Multidentate Camphor Schiff Bases Ya. A. Gur’evaa,* O. A. Zalevskayaa, I. A. Alekseeva, P. A. Slepukhinb, c, and A. V. Kutchina a

Institute of Chemistry, Komi Scientific Center, Ural Branch, Russian Academy of Sciences, ul. Pervomaiskaya 48, Syktyvkar, 167000 Russia *e-mail: [email protected] b

Postovskii Institute of Organic Synthesis, Ural Branch, Russian Academy of Sciences, ul. S. Kovalevskoi/Akademicheskaya 22/20, Yekaterinburg, 620990 Russia c

Yeltsin Ural Federal University, ul. Mira 19, Yekaterinburg, 620002 Russia Received March 28, 2018

Abstract—New enantiomerically pure Schiff bases have been synthesized starting from (–)-3-bromocamphor and ethylenediamine, and their palladium chelates have been obtained.

DOI: 10.1134/S1070428018090026 Palladium complexes with enantiomerically pure ligands showed good results in catalyzing asymmetric syntheses of biologically active compounds [1–4]. Platinum and palladium complexes with diamine ligands exhibit antitumor activity, and they have found application in practical oncology [5, 6]. Therefore, development of methods of synthesis of new chiral palladium complexes and study of their properties seem quite promising. We studied terpene derivatives of ethylenediamine that are used as chiral auxiliaries [7], components of catalytic systems [8], and ligands for transition metal complexes, including palladium complexes [9–11]. Herein we describe the synthesis of new chiral ligands, camphor Schiff bases, and palladium complexes derived therefrom. A classical method of synthesis of Schiff bases is the condensation of carbonyl compounds with amines in the presence of a catalytic amount of an acid. However, camphor failed to react with ethylenediamine under these conditions. Therefore, we resorted to a nontrivial procedure for the synthesis of camphor imines via debromination of optically pure 3-bromocamphor (1) with ethylenediamine [12]. The reaction was carried out by heating a mixture of 1 mol of compound 1 and 25 mol of ethylenediamine at 120°C for 10 h. Two products of this reaction, monoimine 2 and diimine 3 were separated by column chromatography on silica gel and were isolated in 51

and 15% yield, respectively (Scheme 1). The reaction of 2 with salicylaldehyde in methanol at room temperature afforded unsymmetrical diimine 4 in 94% yield (after crystallization). The structure of compounds 2–4 was studied by NMR spectroscopy. Schiff base 2, symmetricall diimine 3, and unsymmetrical diimine 4 were formed as single isomers, and their NMR spectra contained only one set of signals. The NOESY spectra of 2 and 3 showed correlations between methylene protons of the ethylene bridge (11-H) and protons in position 3 of the bornane skeleton. In the NOESY spectrum of 4 we observed cross peaks between the azomethine proton (13-H) and 12-H protons of the ethylenediamine fragment, as well as between 13-H and ortho-proton of the benzene ring (19-H). These findings indicated E configuration of the azomethine bond. Mono- and diimines 2–4 were used as multidentate chelating ligands to obtain palladium complexes. Compounds 2 and 3 reacted with lithium tetrachloropalladate in methanol to give palladium chelates 5 and 6 in 72 and 86% yields, respectively (Scheme 1). Unsymmetrical diimine 4 is a salen type tridentate ligand; its reaction with LiPdCl4 afforded complex 7 in 92% yield. The structure of complexes 5–7 was studied by NMR spectroscopy. Their 1H and 13C NMR spectra were consistent with the proposed structures. In going

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Scheme 1. 10

Me

Me

O

Me

8

H2N(CH2)2NH2, ∆

Me

6

9

Me

Me 5

Br

7 4

Me

Me

1

N

12

11

NH2

2 3

Me

2

CHO , MeOH OH

Me

3

NOE

N

Me

Li2PdCl4, MeOH

N

Me Cl

Me

N

HO 4

2

N 7

Me Cl

Me

O Pd

Me

Me

Li2PdCl4, MeOH

Me

N

Me

NOE

1

N

Me

+

Cl Pd

Me

N

NH2

5

3

Cl Me

Me Cl

Me

Li2PdCl4, MeOH

Me

Pd

Me

N

Me

N 6

The 1H and 13C NMR spectra of complex 6 contained double sets of signals, but the reason is not the presence of two isomers but unsymmetrical structure of the molecule containing two terpene fragments. Analogous pattern was observed for the pinane palladium complex synthesized by us previously, which is a structural analog of 6. The 1H NMR spectrum of ligand 4 displayed a broadened signal at δ 13.2 ppm due to proton of the hydroxy group in the aromatic ring. No such signal was observed in the spectrum of complex 7 even when the solvent was replaced by

from ligand 2 to its palladium complex 5, the signals of the C1, C2, C3, and C7 atoms located in the vicinity of the palladium chelate ring shifted significantly downfield; in particular, the shift of the C1 signal from δC 52.6 to 62.2 ppm is induced by steric effect of the chlorine; such shift was observed for all ligands and the corresponding complexes. The effect of chlorine is also responsible for the downfield shift of the C10H3 proton signal of all complexes by 1–2 ppm, as well as for differentiation of signals of four protons of the ethylenediamine bridge upon chelation.

C4

C

C9

N1

2

C C5

C8

C7

3

C18

N2

C1

10

C

Pd1 C6

C15 C16 C

C

O1

C19 12

Cl1

C14 17

11

C13

C

Fig. 1. Structure of the molecule of [2-({[2-({(2E,1S,4S)-1,7,7-trimethylbicyclo[2.2.1]hept-2-ylidene}amino)ethyl]imino}methyl)phenolato-N1,N2,O]palladium(II) chloride (7) according to the X-ray diffraction data. Non-hydrogen atoms are shown as thermal vibration ellipsoids with a probability of 50%. Solvate chloroform molecule is not shown. RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 54 No. 9 2018

SYNTHESIS OF NEW CHIRAL PALLADIUM COMPLEXES

DMSO-d 6 . The IR spectrum of 7 lacked phenolic OH stretching band typical of the initial diimine (3370 cm –1 ). Thus the NMR and IR data suggest participation of the phenolic hydroxy group of ligand 4 in the coordination to palladium. The structure of complex 7 was confirmed by X-ray analysis. It crystallized as 1 : 1 solvate with chloroform in the chiral space group belonging to the orthorhombic crystal system (Fig. 1). The central palladium atom has the expected distorted square-planar configuration. The organic ligand forms two chelate rings, six- and five-membered. The six-membered ring is planar within 0.07 Å, and the five-membered ring adopts an envelope conformation. The geometric parameters of molecule 7 generally correspond to the expected values (Table 1). The oxygen atom is involved in a short intermolecular contact with proton of the solvate chloroform molecule [symmetry operation: 1 + x, y, z). The absolute configuration of complex 7 was determined on the basis of the ligand configuration and was confirmed by the anomalous scattering effect. Thus, the obtained optically pure camphor Schiff bases behave as N,N-bidentate and N,N,O-tridentate ligands in the coordination to palladium, thus forming chiral palladium chelate complexes. EXPERIMENTAL The IR spectra were recorded on a Shimadzu IR Prestige 21 spectrometer with Fourier transform from samples prepared as thin films or KBr discs. The 1H and 13 C NMR spectra were measured on a Bruker Avance II 300 spectrometer at 300 and 75 MHz, respectively, using the residual proton and carbon signals of the deuterated solvent as reference (CHCl3, δ 7.27 ppm, δC 77.00 ppm; DMSO-d5, δ 2.50 ppm). Signals in the NMR spectra were assigned using DEPT pulse sequence and two-dimensional 1H–1H (COSY, NOESY) and 1 H– 13 C correlation spectra (HSQC, HMBC). The melting points were determined with a Sanyo Gallenkamp melting point apparatus. The optical rotations were measured at λ 589 nm on an Optical Activity PolAAr 3001 automated digital polarimeter. The elemental analyses were obtained with a EA 1110 automated CHNS-O analyzer. The progress of reactions and the purity of the isolated compounds were monitored by TLC on Sorbfil plates. Silica gel (70/230 mesh, Alfa Aesar) was used for column chromatography.

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Table 1. Selected bond lengths and bond angles in the molecule of complex 7 according to the X-ray diffraction data Bond

d, Å

Pd1–N1 1

Pd –O

1

1

2

Pd –N 1

1

Pd –Cl 1

7

1

8

1

1

2

10

2

9

7

2

1

2

N –C N –C O –C N –C N –C C –C C –C

1.966(5) 1.978(5) 2.025(5) 2.3133(19) 1.288(9) 1.454(9) 1.317(9) 1.264(8) 1.460(7) 1.415(10) 1.423(10)

Angle

ω, deg

N1Pd1O1 1

1

1

1

087.79(17)

2

1

1

095.99(16)

1

1

1

1

N Pd N

2

094.2(2)

1

O Pd Cl N Pd Cl O Pd N

2 1

N Pd Cl 7

1

8

7

1

1

8

1

1

CNC

C N Pd C N Pd 10

C N Pd

166.38(18) 125.5(4) 113.6(4)

2

2

176.1(2) 120.2(5)

1

C N Pd 9

082.3(2)

1

135.0(4) 104.2(4)

Ethylenediamine (freshly distilled), (1S,3R,4R)3-bromocamphor {[α]D = –134.3° (c = 4.4, EtOH)}, and palladium chloride of chemically pure grade were used without additional purification. All solvents were dried and purified according to standard procedures. Single crystals of complex 7 for X-ray analysis were obtained by slow evaporation of its solution in chloroform–hexane. The X-ray diffraction data were obtained at 295(2) K on an Xcalibur 3 automated fourcircle diffractometer with a CCD detector according to standard procedure (monochromatized Mo Kα radiation, ω-scanning with a step of 1°). A correction for absorption was applied empirically. The structure was solved and refined using SHELXTL software package [13]. The structure was solved by the direct statistical method (SHELXS) and refined against F2 by the fullmatrix least-squares method in anisotropic approximation for all non-hydrogen atoms (SHELXL). Hydrogen atoms attached to carbons were placed in geometrically calculated positions which were refined in isotropic approximation. Crystallographic data: C 20 H 26 Cl 4 N 2 Pd, M 558.63, orthorhombic crystal system, space group P212121; unit cell parameters: a = 7.5170(5), b = 10.0973(7), c = 30.3081(18) Å; V = 2300.4(3) Å3; Z = 4; μ(Mo Kα) = 1.285 mm–1. Total of 34 819 reflection intensities were measured in the range 2.79 < θ < 33.66°, including 8497 independent reflections (Rint = 0.0636). Final divergence factors: R1 = 0.0919, wR2 = 0.2166 (all independent reflections); R1 = 0.0746, wR2 = 0.2079 [reflections with I > 2σ(I)]; goodness of fit S = 1.021; Δρē (max/min) = 1.461/–3.495 ē Å–3; Flack parameter 0.03(6).

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C o m p o u n d s 2 a n d 3 . A mixtu re of 1.0 g (4.3 mmol) of (–)-3-bromocamphor (1) and 6.4 g (107 mmol) of ethylenediamine was heated for 10 h at 120°C on a glycerol bath. The mixture was cooled, treated with brine, and extracted with diethyl ether (3 × 50 mL). The combined extracts were washed with brine (50 mL), dried over anhydrous magnesium dichloride, and evaporated under reduced pressure. The residue was separated by silica gel column chromatography using chloroform–methanol as eluent to isolate 0.40 g (51%) of monoimine 2 (E isomer) and 0.36 g (15%) of diimine 3 (E,E isomer). N-[(2E,1S,4S)-1,7,7-Trimethylbicyclo[2.2.1]hept2-ylidene]ethane-1,2-diamine (2). Yellow oily material, [α] D = –13.8 (c = 0.4, CHCl 3 ). IR spectrum: ν 1662 cm–1 (C=N). 1H NMR spectrum (CDCl3), δ, ppm: 0.78 s (3H, C9H3), 0.95 s (3H, C8H3), 0.99 s (3H, C10H3), 1.22 m (1H, 5-H), 1.55 br.m (2H, NH2), 1.37 m (1H, 6-H), 1.86 m (1H, 6-H), 1.87 d (1H, 3-H, J = 16 Hz), 1.88 m (1H, 5-H), 1.96 d.d (1H, 4-H, J = 4.5, 4.6 Hz), 2.38 m (1H, 3-H, J = 16 Hz), 2.96 d.d.d (2H, 12-H, J = 2.1, 6.3, 7.7 Hz), 3.28 m (2H, 11-H). 13 C NMR spectrum (CDCl3), δC, ppm: 11.4 (C10), 19.0 (C8), 19.6 (C9), 27.5 (C5), 32.3 (C6), 35.9 (C3), 42.8 (C12), 43.9 (C4), 47.0 (C7), 53.6 (C1), 54.9 (C11), 183.4 (C2). Found, %: C 74.27; H 11.40; N 14.39. C12H22N2. Calculated, %: C 74.23; H 11.34; N 14.43. N,N′-Bis[(2E,1S,4S)-1,7,7-trimethylbicyclo[2.2.1]hept-2-ylidene]ethane-1,2-diamine (3). Yellow oily material, [α]D = –8.5 (c = 0.4, CHCl3). IR spectrum: ν 1684 cm–1 (C=N). 1H NMR spectrum (CDCl3), δ, ppm: 0.77 s (3H, C9H3), 0.94 s (3H, C8H3), 0.97 s (3H, C10H3), 1.22 m (1H, 5-H), 1.36 m (1H, 6-H), 1.66 m (1H, 6-H), 1.86 m (1H, 5-H), 1.94 d (1H, 3-H, J = 17 Hz), 1.95 d.d (1H, 4-H, J = 4.5, 4.6 Hz), 2.45 m (1H, 3-H, J = 17 Hz), 3.51 m (2H, 11-H). 13C NMR spectrum (CDCl3), δC, ppm: 11.4 (C10), 18.9 (C9), 19.7 (C8), 27.5 (C5), 32.2 (C6), 35.9 (C3), 43.4 (C4), 46.9 (C 7 ), 53.2 (C 11 ), 53.5 (C 1 ), 182.8 (C 2 ). Found, %: C 80.55; H 10.89; N 8.52. C22H36N2. Calculated, %: C 80.49; H 10.97; N 8.54. 2-({2-[(2E,1S,4S)-1,7,7-Trimethylbicyclo[2.2.1]hept-2-ylideneamino]ethyl}iminomethyl)phenol (4). A solution of 0.2 g (1.2 mmol) of Schiff base 2 and 0.1 g (1.2 mmol) of salicylaldehyde in 5 mL of anhydrous methanol was stirred for 5 h at 23°C. The solvent was removed under reduced pressure, the residue was recrystallized from diethyl ether–hexane, and the precipitate was filtered off and washed with hexane. Yield 0.33 g (94%), yellow plates, [α]D =

–19.7 (c = 0.3, CHCl3). IR spectrum, ν, cm–1: 3254 (OH), 1679 (C=N). 1H NMR spectrum (CDCl3), δ, ppm: 0.62 s (3H, C9H3), 0.87 s (3H, C8H3), 0.95 s (3H, C10H3), 1.01 m (1H, 5-H), 1.18 m (1H, 6-H), 1.58 m (1H, 6-H), 1.72 m (1H, 5-H), 1.85 m (1H, 4-H), 1.88 m (1H, 3-H), 2.35 m (1H, 3-H), 3.62 m (2H, 11-H), 3.95 m (2H, 12-H), 6.86 d.d (1H, 18-H, J = 7.7, 8.4 Hz), 6.94 d (1H, 16-H, J = 7.0 Hz), 7.30 d.d (1H, 17-H, J = 7.0, 8.4 Hz), 7.23 d (1H, 19-H, J = 7.7 Hz), 8.32 s (1H, 13-H), 13.2 br.s (1H, OH). 13C NMR spectrum (CDCl 3 ), δ C , ppm: 11.4 (C 10 ), 18.8 (C 8 ), 19.3 (C9), 27.1 (C5), 32.4 (C6), 36.1 (C3), 43.7 (C4), 46.9 (C7), 52.1 (C11), 53.9 (C1), 59.8 (C12), 116.8 (C18), 118.4 (C14), 118.7 (C16), 131.2 (C19), 132.2 (C17), 161.3 (C15), 166.0 (C13), 184.6 (C2). Found, %: C 76.59; H 8.66; N 9.35. C19H26N2O. Calculated, %: C 76.51; H 8.72; N 9.39. cis-[{N-(2E,1S,4S)-1,7,7-Trimethylbicyclo[2.2.1]hept-2-ylidene}ethane-1,2-diamine-N1,N2]palladium (II) dichloride (5). A suspension of 0.04 g (0.2 mmol) of palladium(II) chloride and 0.01 g (0.4 mmol) of lithium chloride in 5 mL of methanol was refluxed for 1 h on a water bath. The resulting dark red solution of lithium tetrachloropalladate was added to a solution of 0.04 g (0.2 mmol) of Schiff base 2 in 2 mL of methanol. The mixture was stirred for 5 h at room temperature, the solvent was removed under reduced pressure, and the residue was recrystallized from chloroform. Yield 45 mg (65%), yellow powder, mp 132°C (decomp.), [α]D = +42.5 (c = 0.1, CHCl3). IR spectrum: ν 1637 cm–1 (C=N). 1H NMR spectrum (CDCl3), δ, ppm: 0.75 s (3H, C9H3), 0.90 s (3H, C8H3), 1.17 m (1H, 5-H), 1.54 m (1H, 6-H), 1.73 m (1H, 6-H), 1.75 m (1H, 5-H), 1.82 m (1H, 4-H), 1.84 s (3H, C10H3), 2.09 d (1H, 3-H, J = 16 Hz), 2.94 d (1H, 3-H, J = 16 Hz), 2.13 m (1H, 12-H), 2.41 m (1H, 12-H), 3.61 m (1H, 11-H), 3.95 m (1H, 11-H), 4.97 br.m (1H, NH 2 ), 5.26 br.m (1H, NH 2 ). 13 C NMR spectrum (CDCl3), δC, ppm: 13.4 (C10), 19.2 (C8), 19.9 (C9), 26.6 (C5), 30.8 (C6), 40.2 (C3), 42.5 (C12), 44.9 (C4), 51.6 (C7), 55.9 (C11), 62.3 (C1), 194.7 (C2). Found, %: C 38.94; H 7.51; N 5.89. C12H22Cl2N2Pd. Calculated, %: C 38.88; H 7.56; N 5.94. Complexes 6 and 7 were synthesized in a similar way. cis-[Bis{N,N′-(2E,1S,4S)-1,7,7-trimethylbicyclo[2.2.1]heptan-2-ylidene}ethane-1,2-diamine-N1,N2]palladium(II) dichloride (6). Yield 0.11 g (75%), yellow powder, mp 141°C (decomp.), [α]D = +37.8 (c = 0.1, CHCl3). IR spectrum: ν 1649 cm–1 (C=N). 1 H NMR spectrum (CDCl 3 ), δ, ppm: first terpene

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SYNTHESIS OF NEW CHIRAL PALLADIUM COMPLEXES

fragment: 0.79 s (3H, C9H3), 1.06 s (3H, C8H3), 1.22 m (1H, 5-H), 1.62 m (1H, 6-H), 1.86 m (1H, 6-H), 1.94 m (1H, 5-H), 2.04 m (1H, 4-H), 2.09 m (1H, 3-H), 2.52 m (1H, 3-H), 2.69 s (3H, C10H3), 4.06 m (1H, 11-H), 4.42 m (1H, 11-H); second terpene fragment: 0.91 s (3H, C 9 H 3 ), 1.08 s (3H, C 8 H 3 ), 1.39 m (1H, 5-H), 1.68 m (1H, 6-H), 1.84 m (1H, 6-H), 1.94 m (1H, 5-H), 2.04 m (1H, 4-H), 2.70 m (1H, 3-H), 2.78 s (3H, C10H3), 2.92 m (1H, 3-H), 5.62 m (2H, 11-H). 13C NMR spectrum (CDCl3), δC, ppm: first terpene fragment: 15.5 (C10), 19.1 (C8), 19.9 (C9), 26.8 (C5), 32.1 (C6), 41.6 (C3), 43.6 (C4), 49.6 (C7), 56.8 (C11), 57.9 (C1), 199.8 (C2); second terpene fragment: 15.6 (C10), 19.1 (C8), 20.1 (C9), 26.8 (C5), 32.8 (C6), 41.6 (C3), 43.7 (C4), 50.1 (C7), 56.9 (C11'), 58.1 (C1), 200.4 (C2). Found, %: C 52.36; H 7.08; N 5.51. C22H36Cl2N2Pd. Calculated, %: C 52.34; H 7.14; N 5.55. [2-({[2-({(2E,1S,4S)-1,7,7-Trimethylbicyclo[2.2.1]hept-2-ylidene}amino)ethyl]imino}methyl)phenolato-N1,N2,O]palladium(II) chloride (7). Yield 0.3 g (64%), yellow powder, mp 141°C (decomp.), [α ] D = +53 .2 (c = 0.1 , C HCl 3 ) . I R sp e ct ru m: ν 1666 cm–1 (C=N). 1H NMR spectrum (DMSO-d6), δ, ppm: 0.76 s (3H, C 9 H 3 ), 0.91 s (3H, C 8 H 3 ), 1.23 m (1H, 5-H), 1.60 m (1H, 6-H), 1.80 s (3H, C 10 H 3 ), 1.81 m (1H, 5-H), 1.87 m (1H, 6-H), 1.89 m (1H, 4-H), 2.21 m (1H, 3-H), 3.11 m (1H, 3-H), 3.44–4.07 m (4H, 11-H, 12-H), 6.58 d.d (1H, 18-H, J = 7.0, 7.5 Hz), 6.77 d (1H, 16-H, J = 8.5 Hz), 7.28 d.d (1H, 17-H, J = 7.0, 8.5 Hz), 7.39 d (1H, 19-H, J = 7.5 Hz), 8.07 s (1H, 13-H). 13C NMR spectrum (DMSO-d6), δC, ppm: 13.4 (C10), 19.3 (C8), 19.9 (C9), 26.6 (C5), 30.7 (C6), 41.4 (C3), 42.6 (C4), 50.6 (C7), 56.1 (C1), 60.9 (C11), 61.0 (C12), 115.1 (C18), 120.3 (C16), 120.5 (C14), 134.9 (C19), 135.2 (C 17 ), 160.1 (C 13 ), 163.2 (C 15 ), 196.8 (C 2 ). Found, %: C 52.09; H 5.68; N 6.34. C19H25ClN2OPd. Calculated, %: C 52.01; H 5.70; N 6.39. This study was performed using the facilities of the Chemistry Joint Center (Institute of Chemistry, Komi

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Scientific Center, Ural Branch, Russian Academy of Sciences) and Spectroscopy and Analysis of Organic Compounds Joint Center (Postovskii Institute of Organic Synthesis, Ural Branch, Russian Academy of Sciences). REFERENCES 1. Gupta, K.C. and Sutar, A.K., Coord. Chem. Rev., 2008, vol. 252, p. 1420. 2. Garoufis, A., Hadjikakou, S.K., and Hadjiliadis, N., Coord. Chem. Rev., 2009, vol. 253, p. 1384. 3. Zawartka, W., Gniewek, A., and Trzeciak, A.M., Inorg. Chim. Acta, 2017, vol. 455, p. 595. 4. Satheesh, C.E., Kumar, P.R., Sharma, P., Lingaraju, K., Palakshamurthy, B.S., and Rajanaika, H., Inorg. Chim. Acta, 2016, vol. 442, p. 1. 5. Johnstone, T.C., Suntharalingam, K., and Lippard, S.J., Chem. Rev., 2016, vol. 116, p. 3436. 6. Wang, Q., Huang, Z., Ma, J., Lu, X., Wang, X., and Wang, P.G., Dalton Trans., 2016, vol. 45, p. 10 366. 7. Mino, T., Suzuki, A., Yamashita, M., Narita, S., Shirae, Y., Sakamoto, M., and Fujita, T., J. Organomet. Chem., 2006, vol. 691, p. 4297. 8. Salehi, P., Dabiri, M., Kozehgary, G., and Baghbanzadeh, M., Tetrahedron: Asymmetry, 2009, vol. 20, p. 2609. 9. Zalevskaya, O.A., Vorobieva, E.G., Dvornikova, I.A., Alekseev, I.N., Mironova, E.V., Krivolapov, D.B., Litvinov, I.A., and Kuchin, A.V., Russ. J. Coord. Chem., 2011, vol. 37, p. 211. 10. Gur’eva, Ya.A., Alekseev, I.N., Zalevskaya, O.A., Slepukhin, P.A., and Kutchin, A.V., Russ. J. Org. Chem., 2016, vol. 52, p. 781. 11. Kwon, K.S., Nayab, S., Lee, H.I., and Jeong, J.H., Polyhedron, 2017, vol. 126, p. 127. 12. Markovic, S., Markovic, V., Joksovic, M.D., Todorovic, N., Joksovic, L., Divjakovic, V., and Trifunovic, S., J. Braz. Chem. Soc., 2013, vol. 24, p. 1099. 13. Sheldrick, G.M., Acta Crystallogr., Sect. A, 2008, vol. 64, p. 112.

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