New optically active cn-palladacycles based on 2α-hydroxypinan-3-one and camphor derivatives

Article abstract of DOI:10.1007/s10600-014-1044-3

The ligand (-)-2α-hydroxypinan-3-one diphenylmethylimine was synthesized and studied. New dinuclear CN-palladacycles and their mononuclear triphenylphosphine derivatives were obtained. It was shown that ortho-palladation of terpene diphenylmethylimines pr

Full text of DOI:10.1007/s10600-014-1044-3

Chemistry of Natural Compounds, Vol. 50, No. 4, September, 2014 [Russian original No. 4, July–August, 2014]
NEW OPTICALLY ACTIVE CN-PALLADACYCLES BASED ON
2
ꢀ-HYDROXYPINAN-3-ONE AND CAMPHOR DERIVATIVES
1
*
2
1
Ya. A. Gurꢁeva, O. A. Zalevskaya, I. N. Alekseev,
1
3
1
L. L. Frolova, P. A. Slepukhin, and A. V. Kuchin
The ligand (–)-2ꢀ-hydroxypinan-3-one diphenylmethylimine was synthesized and studied. New dinuclear
CN-palladacycles and their mononuclear triphenylphosphine derivatives were obtained. It was shown that
ortho-palladation of terpene diphenylmethylimines produced pure stereoisomers.
Keywords: chiral imines, monoterpenoids, palladium, palladacycles, stereoisomers, diastereoselectivity, X-ray crystal
structure analysis.
Natural monoterpenoids that are isolated from renewable plant sources are convenient chiral starting materials for
synthesizing important classes of compounds, in particular, for preparing chiral cyclopalladated complexes, which are being
applied more and more widely in asymmetric synthesis [1, 2]. They were used successfully as catalysts for cross-coupling
reactions [3, 4], alkene hydroarylation [5], and allyl alkylation [6].
We selected the bicyclic monoterpenoids ꢀ-pinene and camphor as the starting materials for synthesizing homochiral
ligands. This was due to their commercial availability and facile chemical modification. It was especially noteworthy that
ligands could possibly be obtained as pure enantiomers.
Oxidation of (+)-ꢀ-pinene produced (–)-2ꢀ-hydroxypinan-3-one (1) [7], condensation of which with
diphenylmethylamine synthesized the (1S,2S,5S)-diphenylmethylimine (2) in 54% yield (Scheme 1). We reported previously
the synthesis of the (1R,2R,5R)-enantiomer of 2ꢀ-hydroxypinan-3-one diphenylmethylimine [8].
Cl
OH
2
Pd
1
0
15
OH
OH
13
N
O
N
11 Ph
Ph
a
1
9
b
1
7
3
H
Ph
7
6
H
5
H
1
2
3
NOE
a. H NCH(Ph)-Ph, PhH, BF 4Et O; b. Li PdCl
2
3
2
2
4
Scheme 1
Cyclopalladation of 2ꢀ-hydroxypinan-3-one and camphor benzylimines was studied before [8–10]. The
ꢀ-hydroxypinan-3-one derivatives, in contrast with bornane ligands, were rather easily cyclopalladated upon reaction with
2
Li PdCl . The new dinuclear palladacycle 3 was synthesized in 58% yield under these conditions (Scheme 1).
2
4
The structure of 3 was confirmed by NMR spectroscopy. The ortho-disubstituted aromatic ring was identified by
characteristic NMR resonances in the region of aromatic protons that included four non-equivalent proton resonances with a
characteristic splitting. The multiplicity and integrated intensity of proton resonances for the second mono-substituted benzene
ring persisted in the PMR spectra.
1
) Institute of Chemistry, Komi Scientific Center, Ural Branch, Russian Academy of Sciences, Russian Federation,
1
67982, Syktyvkar, Ul. Pervomaiskaya, 48, fax: (8212) 21 84 77, e-mail: gurjeva-ja@chemi.komisc.ru; 2) Syktyvkar State
University, 167023, Syktyvkar, Ul. Petrozavodskaya, 120; 3) I. Ya. Postovskii Institute of Organic Synthesis, Ural Branch,
RussianAcademy of Sciences, 620137, Ekaterinburg, Ul. S. Kovalevskoi, 22. Translated from Khimiya Prirodnykh Soedinenii,
No. 4, July–August, 2014, pp. 562–565. Original article submitted March 14, 2014.
648
0009-3130/14/5004-0648 ©2014 Springer Science+Business Media New York

C33
C34
C3
C4
C5
C31
C28
C35
C29
C2
C1
C32
C26
C6
Cl 1
C30
C9
C10
Pd 1
C8
C7
C27
Ph
Ph
N1
P1
P
H
C11
C19
C20
C12
Cl 2
Cl
H
C13
Pd
C18
C17
N
C21
C22
C14
C25
C24
H
H
C16
C15
H
C23
Fig. 1.
Fig. 2. Molecular structure of 8 from an XSA with 50% probability
thermal ellipsoids.
An additional chiral center appeared in the 11-position during ortho-palladation of the homochiral
1
3
diphenylmethylimines. The PMR and C NMR spectra of 3 showed one set of resonances. This indicated that a pure
diastereomer had formed. Thus, the ortho-palladation occurred with 100% diastereoselectivity. The relative configuration of
the new chiral center was determined using two-dimensional correlation spectra. The NOESY spectrum of 3 showed that
benzyl proton H-11 was coupled with endo-proton H-4 of the terpene fragment. This corresponded to the 11R-configuration.
Opening of the chloride bridges upon reaction with additional ligands is a known reaction for dinuclear complexes. It
forms mononuclear mixed-ligand complexes [11]. Such a synthetic capability was interesting considering the potential of
using the resulting Pd complexes in various asymmetric transformations. We studied the reaction of the obtained pinane and
bornane palladacycles with the monodentate ligand triphenylphosphine (PPh ). Complex 3 was found to be unstable in the
3
presence of PPh and formed dichloro-bis-(PPh )Pd (4) (Scheme 2).
3
3
2
Cl
OH
2
Cl
2
Cl
Pd Cl
Pd
Pd
N
N
N
Ph
H
Ph
H
Ph
3
5
7
2
PPh
3
2 PPh
Cl
2 PPh
3
3
PPh
Pd Cl
Ph
3
PPh
3
PPh
3
Cl
Pd 13
11
1
0
15
Cl Pd Cl
1
N
N
9
17
PPh
3
2 5
2
3
H
Ph
4
6
8
Scheme 2
Dinuclear complexes 5 and 7, which were prepared from bornane benzylimines, were studied in an analogous reaction
for comparison. The syntheses of these complexes were described in our previous works [8, 10]. Bornane palladacycle 5
turned out to be more stable. Mononuclear palladacycle 6 formed in 92% yield upon its reaction with PPh (Scheme 2).
3
Resonances for all protons of the ortho-palladated fragment persisted and resonances for protons of coordinated PPh appeared
3
in the PMR spectrum of 6.
649

TABLE 1. Selected Bond Lengths and Angles in 8
°
Bond
A
Angle
Deg.
Pd(1)-N(1)
Pd(1)-P(1)
Pd(1)-Cl(1)
Pd(1)-Cl(2)
N(1)-C(26)
N(1)-C(19)
2.122 (5)
2.2399 (17)
2.2905 (17)
2.2975 (15)
1.271 (6)
N(1)-Pd(1)-Cl(1)
P(1)-Pd(1)-Cl(1)
N(1)-Pd(1)-Cl(2)
P(1)-Pd(1)-Cl(2)
Cl(1)-Pd(1)-Cl(2)
C(26)-N(1)-C(19)
C(26)-N(1)-Pd(1)
C(19)-N(1)-Pd(1)
89.16 (12)
93.28 (6)
92.09 (12)
85.54 (5)
176.79 (7)
119.3 (5)
131.9 (4)
108.7 (3)
1.487 (6)
We used NOESY spectroscopy in order to determine the P,N -geometry of obtained complex 6. A NOE-coupling of
the ortho-proton H-14 of the di-substituted aromatic ring and the ortho-protons of the PPh ligand was observed. This
3
confirmed that trans-(P,N )-isomer 6 had formed. Moreover, the large size of the PPh substituent prevented the cis-(P,N)-
3
isomer from forming. We also observed this during an attempt to model the structure. Figure 1 shows characteristic NOE-
interactions in 6.
Dinuclear complex 7 with a monodentate coordinated bornane benzylimine also reacted with PPh to open the chloride
3
bridges. As a result, mixed-ligand complex 8 formed (Scheme 2). Its structure was confirmed by an X-ray crystal structure
analysis (XSA). Thus, the empirical formula was C H Cl NPPd. The compound crystallized in a chiral orthorhombic space
3
5
38
2
group. The absolute structure parameter was not determined. The absolute configuration of the compound was established
using knowledge of the configuration of the starting chiral ligand. Figure 2 shows a general view of the complex and the
atomic numbering.
The observed bond lengths and angles were close to the standard values. The coordination included a central ion in
a distorted square with trans-Cl atoms (Table 1). The central atom did not affect substantially the C–N bond, in particular, the
imine bond length. The C(19)N(1)C(26) imine plane was situated at an angle of 66° to the plane of the inner coordination
sphere. Shortened contacts were not found in the crystal packing.
The information obtained by us on the structure and relative stability of various dinuclear and mononuclear Pd
complexes with bornane and pinane imines could be useful for plans to use these compounds as catalysts because the ability
to alter a stable metal coordination environment is an important aspect in catalytic processes.
EXPERIMENTAL
IR spectra were measured in thin layers or KBr pellets on an IR Prestige 21 instrument (Shimadzu). PMR and 13C
1
NMR spectra were recorded in CDCl on a Bruker Avance-II-300 instrument at operating frequency 300 MHz ( H), 75 MHz
3
1
3
31
(
C), and 121 MHz ( P). The CHCl (ꢂ 7.27 and ꢂ 77.00 ppm) and (CH ) SO (ꢂ 2.62 and ꢂ 40.76 ppm) resonances
were used as internal standards. Resonances were assigned using C NMR spectra recorded in JMOD mode and 2D H– H
COSY, NOESY) and H– C (HSQC, HMBC) correlation spectra. Optical rotation was measured on a Kruss P3002RS
3 H C 3 2 H C
1
3
1
1
1
13
(
automated polarimeter (Germany). Elemental analysis was performed on an EA 1110 elemental analyzer (CHNSO).
The course of reactions was monitored using TLC on Sorbfil plates and C H –Et O and C H –Me CO. Compounds
6
14
2
6
6
2
were detected by treating plates with I vapor. Column chromatography used silica gel (70–230 ꢃm, Alfa-Aesar).
2
Diphenylmethylamine (Alfa-Aesar), PdCl , and Pd(OAc) were used as received.
2
2
2
0
(
1S,2S,5S)-2-Hydroxypinan-3-one (1), [ꢀ] –38° (c 1.0, CHCl ), mp 39–40°C, was prepared by oxidation of
-pinene ([ꢀ] +42°) by KMnO as described before [7]. The bornane imines were synthesized from (1S,4S)-camphor,
D 3
2
0
ꢀ
[
D 4
2
0
ꢀ] –41° (c 1.0, CHCl3).
D
The XSA experiment was performed on an Xcalibur S automated diffractometer using the standard procedure
[
Mo Kꢀ-radiation, graphite monochromator, 295(2) K, ꢄ-scanning in 1° steps]. A chip (0.28 ꢅ 0.13 ꢅ 0.02 mm) from a plate-
like yellow crystal was used for the XSA. Absorption corrections were applied analytically. A set of 18,032 reflections was
collected in the scan range 2.61 < ꢆ < 26.37. Of these, 3,715 were independent (Rint = 0.0524) including 2,093 with I > 2ꢇ(I).
°
The completeness was 99.6%. The crystal was orthorhombic, space group P2 2 2 , a = 9.9239(7) A , b = 16.3584(8),
1
1 1
°
3
3
–1
c = 19.9632(10), V = 3240.8(3) A , Z = 4 for C H Cl NPPd, d = 1.396 g/cm , ꢃ = 0.811 mm , F(000) = 1400.
3
5
38
2
650

The structure was solved and refined using the SHELXTL program package [12]. Non-hydrogen atoms were refined
anisotropically. H atoms were included in the refinement as a rider model with isotropic dependent thermal parameters. The
final refinement parameters were R = 0.0317, wR = 0.0602 for reflections with I > 2ꢇ(I); R = 0.0719, wR = 0.0636 (for all
1
2
1
2
°
–3
reflections); S = 1.001; ꢈꢉ = 0.925/–0.430 eA .
e
The imines and Pd complexes were synthesized according to known methods [8, 10].
1S,2S,5S)-3-(Diphenylmethylimino)2,6,6-trimethylbicyclo[3.1.1]heptan-2-ol (2). Oily yellow liquid, 54% yield,
(
2
1
[
ꢀ] +32.3° (c 0.2, CHCl ). The spectral data corresponded to the opposite enantiomer of the reported one [8].
D
3
Di- ꢃ- c h l o ro -bis - { 2 - [ ( 1S , 2 S, 5 S , 11R ) - 2 - h y d ro x y - 2 , 6 , 6 - t r i m e t h y l b i c y c l o [ 3 . 1 . 1 ] h e p t - 3 -
ylideneaminophenylmethyl]phenyl-C,N}dipalladium(II) (3). Yellow powder, soluble in CHCl , Me CO, C H , DMSO.
3
2
6 6
2
0
R 0.3 (Sorbfil, C H –Me CO, 10:1, I detector), yield 133 mg (58%), mp 159–160°C (dec.), [ꢀ] –117.9° (c 0.4, CHCl3).
f
6
6
2
2
D
–1
1
C H N O Pd Cl . IR spectrum (ꢊ, cm ): 3204 (ÎÍ), 1632 (C=N). Í NMR spectrum (DMSO-d , ꢂ, ppm, J/Hz): 0.60 (3H,
4
6
52
2
2
2
2
6
s, CH -8), 1.23 (3H, s, CH -9), 1.32 (1Í, d, J
= 11.0, Í -7), 1.54 (1Í, d, J
= 19.0, Í -4), 1.83 (3H, s, CH -10), 1.90 (1Í, m,
3
3
7n,7e
n
4n,4e
n
3
Í-5), 1.97 (1Í, dd, J1,5 = 5.3, J1,7e = 5.6, Í-1), 2.40 (1Í, m, Í -7), 3.00 (1Í, dd, J
J14,15 = 7.0, Í-14), 6.36 (1Í, s, Í-11), 6.76 (1Í, dd, J16,15 = 7.0, J16,17 = 7.0, Í-16), 6.84 (1Í, dd, J15,14 = 7.0, J
e
4e,5
e
7.31 (2Í, d, Íarom), 7.3–7.4 (3Í, m, Íarom), 7.35 (1Í, d, J17,16 = 7.0, Í-17), 8.31 (1Í, d, JÎÍ,1 = 3.6, ÎÍ). C NMR spectrum
(
DMSO-d , ꢂ, ppm): 22.94 (Ñ-8), 27.20 (Ñ-9), 28.70 (Ñ-7), 28.70 (Ñ-10), 35.12 (Ñ-4), 38.28 (Ñ-5), 51.41 (Ñ-1), 75.18 (Ñ-11), 87.54
6
(Ñ-2), 124.09 (Ñ-14), 124.80 (Ñ-15), 125.16 (Ñ-16), 127.81 (î-Ph), 128.19 (p-Ph), 129.39 (m-Ph), 135.50 (Ñ-17), 139.97 (Ñ-12),
143.26 (Ar), 156.27 (Ñ-13), 187.07 (Ñ-3).
Chloro{2-[(1S,4S,11S)-1,7,7-trimethylbicyclo[2.2.1]hept-2-ylideneaminophenylmethyl]phenyl-
C,N}(triphenylphosphine-P)palladium(II) (6). Yellow powder, soluble in CHCl , Me CO, C H , DMSO. R 0.6 (Sorbfil,
3
2
6
6
f
2
0
C H –Me CO, 10:1, I detector), yield 13 mg (92%), mp 119–120°C (dec.), [ꢀ] +33.3° (c 0.1, CHCl ), C H NPdPCl.
6
6
2
2
D
3
41 41
–
1
1
IR spectrum (ꢊ, cm ): 1629 (C=N). Í NMR spectrum (300 MHz, CDCl , ꢂ, ppm, J/Hz): 0.71 (3H, s, CH -9), 0.97 (3H, s,
3
3
CH -8), 1.31 (1Í, m, Í-5 ), 1.83 (3H, s, CH -10), 1.84 (1Í, m, Í -6), 1.91 (1Í, m, Í-5 ), 1.96 (1Í, m, Í-4), 2.14 (1H, d,
3
n
3
n
e
4
J
= 18, H-3 ), 2.50 (1Í, m, Í -6), 2.97 (1H, m, J
= 18, H-3 ), 5.88 (1H, d, J = 3, H-11), 6.17 (1H, dd, J14,15 = 7,
3
n,3e
n
e
3e,3n
e
11,P
4
J14,P = 6.3, H-14), 6.40 (1H, dd, J15,14 = 7, J15,16 = 7.1, H-15), 6.85 (1H, dd, J
J17,16 = 7.1, J
= 7.1, J16,17 = 7.1, H-16), 7.15 (1H, dd,
16,15
5
13
= 1.3, H-17), 7.22–7.77 (20H, m, Ar). C NMR spectrum (CDCl , ꢂ, ppm, J/Hz): 12.59 (C-10), 19.02
17,P
3
(
1
C-8), 20.14 (C-9), 27.01 (C-5), 31.10 (C-6), 39.16 (C-3), 42.87 (C-4), 49.67 (C-7), 55.56 (C-1), 78.30 (C-11), 122.21 (C-17),
4
23.25 (C-16), 124.98 (d, J
= 5, C-15), 127.59, 127.71, 127.85, 128.51, 130.10, 131.40 (d, J = 50, C -P), 135.15 (6Ñ, d,
1
5,P
Ar
3
31
J = 12, P-Phortho), 137.00 (d, J
= 10, C-14), 141.51 (Ñ ), 149.31 (C-12), 151.87 (C-13), 189.85 (C-2). P NMR spectrum
14,P
Ar
(
CDCl , ppm): 56.9.
3
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