Rhodium(I) bisaldimine complexes in transfer hydrogenation

Article abstract of DOI:10.1134/S1070363217110056

The reactions of hydrogen transfer from 2-propanol on acetophenone in the presence of the system [Rh(cod)Cl]₂–L] (L is bisaldimine ligands based on (R,R)-1,2-cyclohexanediimine and pyridine-, quinoline-, and thiophenecarboxaldehyde) were studie

Full text of DOI:10.1134/S1070363217110056

ISSN 1070-3632, Russian Journal of General Chemistry, 2017, Vol. 87, No. 11, pp. 2537–2545. © Pleiades Publishing, Ltd., 2017.
Original Russian Text © L.O. Nindakova, N.M. Badyrova, E.Kh. Sadykov, I.A. Ushakov, S.Ch. Vanzarakshaeva, 2017, published in Zhurnal Obshchei
Khimii, 2017, Vol. 87, No. 11, pp. 1794–1803.
Rhodium(I) Bisaldimine Complexes in Transfer Hydrogenation
a
a
b
L. O. Nindakova *, N. M. Badyrova , E. Kh. Sadykov ,
a
a
I. A. Ushakov , and S. Ch. Vanzarakshaeva
a
Irkutsk National Research Technical University, ul. Lermontova 83, Irkutsk, 664074 Russia
e-mail: nindakova@istu.edu
*
b
Favorskii Irkutsk Institute of Chemistry, Siberian Branch, Russian Academy of Sciences, Irkutsk, Russia
Received June 15, 2017
Abstract—The reactions of hydrogen transfer from 2-propanol on acetophenone in the presence of the system
Rh(cod)Cl] –L] (L is bisaldimine ligands based on (R,R)-1,2-cyclohexanediimine and pyridine-, quinoline-,
and thiophenecarboxaldehyde) were studied. Rhodium(I) complexes with optically active ligand showed a high
[
2
–
1
catalytic activity (up to 345 h ) and moderate enantioselectivity [up to 55% ee of (R)-1-phenyethanol]. The
structure of rhodium complex with N,N'-(1R,2R)-cyclohexane-1,2-diyl-bis[1-(pyridine-2-yl)methanimine] was
1
13
determined on the basis of the data of H and C NMR spectroscopy and quantum chemical calculations.
Keywords: rhodium, bisaldimine ligands, hydrogen transfer, acetophenone
DOI: 10.1134/S1070363217110056
Growing interest to the use of optically active
secondary alcohols in pharmaceutical chemistry
stimulated intensive development of the methods of
asymmetric reduction of prochiral aromatic ketones
including asymmetric hydrogenation of C=O bonds
with hydrogen transfer from its sources in the presence
of ruthenium(II), rhodium(I), and iridium(I) complexes
containing chiral bipyridines [1–3], alkylphenanthro-
lines [4], diimines [5–8], diamines [8–10], ureas, and
thioureas [11].
transition metal reduction to the elemental state, which
has occurred in some cases [9, 19].
Published data on the effectiveness of optically
active N,N- or N,N,N,N-rhodium complexes, in which
2
nitrogen atoms are in the sp -hybridization state, in
acetophenone transfer hydrogenation are highly
scattered. For example, enantioselectivity for [CpRhCl2]2
is reported to be from 12% ee with the ligand (R)-
pyridyl-3-i-propyloxazoline up to 51% ee with the
ligand (R)-2-pyridynal-l-phenylethylimine [20]. The ee
value of 48% of (S)-1-phenyethanol was obtained with
the ligand (R,R)-1,2-dibenzylidene 1,2-cyclohexanedi-
In recent decades attention of researchers was
focused on the synthesis and application of optically
active chiral ligands based on diamines and amino
alcohols, which, like the phosphine ligands, are not
easily oxidized in the transition metal coordination
sphere and at the same time retain high stereogenic
ability. Usually chiral N,N-ligands act as bidentate
donors [2, 12–16]. In particular, it is known that
ruthenium complexes containing (R,R)- and (S,S)-N-
imine on the dimeric complex [Rh(1,5-cod)µ-Cl] [7].
2
2
Iridium(I) and ruthenium(II) complexes with sp -
nitrogen bi- and tetradentate ligands [21, 22] also do
3
not permit high ee values to be reached with sp -
nitrogen ligands [17, 18].
It seems interesting to use ligands with chemilabile
donor functions that can take potentially vacant
coordination sites at metal centers in intermediates and
freed them when necessary for coordination of
substrates under conversion. Although functionalized
phosphines containing O- and N-donor fragments and
N,H,C-functionalized ligands [23–24] are the most
studied hemilabile ligands, also N,N,N,N- and S,N,N,S-
tetradentate ligands containing heteroatoms with
(toluenesulfonyl)-1,2-diphenyl-diaminoethane
as
ligands are highly efficient in the asymmetric reduction
of arylketones in both 2-propanol and in a mixture of
formic acid with triethylamine [17, 18]. The dis-
advantage of chiral diamines is a comparatively low
catalytic activity of their complexes with transition
metals in transfer hydrogenation reactions and in
2
537

2
538
NINDAKOVA et al.
Scheme 1.
O
_2
H O
2
*
+ 2 R
*
*
NH2
*
H
N
H N
N
2
R
R
_
1
2a 2c
R= 2-pyridyl (a), 2-quinolyl (b), 2-thienyl (c).
Scheme 2.
H C
O
H C
3
OH
3
H C
3
CH3
[Rh(cod)Cl]
2
+ L
H C
CH3
3
o
1
-PrOH, KOH, 78 C
OH
O
various coordinating properties may be of interest in
obtaining new systems applicable in homogeneous
catalysis [25–30].
Enantioselectivity of the catalytic reaction grows in
the series of the ligands: 2a < 2b < 2c (Table 1, exp.
nos. 7, 16, and 17). In the same order TOF for rhodium
catalysts decreases. When the reaction product rac-1-
phenylethanol (47.6 mmol/L, 1/2 of the initial ketone
concentration) is initially introduced in the reaction
mixture, the reaction rate and enantioselectivity are
slightly reduced (exp. nos. 5 and 14), whereas a
The aim of this work was to test rhodium(1+)
complexes with bis-aldimine ligands, generated in situ,
in hydrogen transfer of acetophenone and to determine
composition and structure of the rhodium complex with
N,N'-[(1R,2R)-cyclohexane-1,2-diyl]bis[1-(pyridine-2-
yl)]methanimine.
significant W reduction appears even at the concentra-
ini
tion equal to 1/4 of the initial acetophenone con-
centration. If the reaction product, acetone, was
introduced at the beginning of the reaction, the
enantiomer excess of (R)-1-phenylethanol increases
Bis-diimine ligands 2a–2c (Scheme 1) were
synthesized by the reaction of diamine 1 with alde-
hydes containing a dentate heteroatom in the α-posi-
tion (2-pyridinecarboxaldehyde, 2-quinolinecarboxal-
dehyde, and 2-thiophenecarboxaldehyde).
(
compare, for example, exp. nos. 4 and 15).
The bidentate coordination of N,N,N,N-ligands is
possible in rhodium cyclooctadiene complexes. To
determine the structure of forming complexes, we have
The active reaction catalyst is formed in situ when
the dimeric complex [Rh(1,5-cod)µ-Cl] interacts with
2
studied the reaction of [Rh(COD)Cl] with ligand 2a
a small excess of optically active N,N,N,N-ligands in a
solution of 2-propanol in the pre-sence of potassium
tert-butylate or KOH (Scheme 2). The reaction was
studied in the concentration ranges of acetophenone
2
1
13
by the methods of H and C NMR spectroscopy
Table 2). At –10°C in 10 min after the addition of
(
ligand 2a to a [Rh(cod)Cl] solution new signals
2
–
2
–4
appear, which indicate that the bisaldimine ligand is
coordinated to rhodium(I) (Table 2, exp. no. 2). The
position and distribution of intensities of these signals
(
1.9–19)×10 M, rhodium (3–22)×10 M, and 1-
–2
phenyethanol (6–10)×10 M.
2
It may be noted that the ketone transfer hydro-
genation in the presence of the catalyst with ligand 2a
occurs at a high rate. For example, in the case of
.5 mL (4.3 mmol) of acetophenone in the presence of
mol % of the catalyst 95–96% acetophenone
in the spectrum of C -symmetric ligand bound in a
complex indicate that they are magnetically non-
equivalent. So, one of protons of the azomethine fragment
undergoes the strongest downfield shift (Δδ = 1.13 ppm),
resonance signals of methine protons at the carbon
0
1
1
2
transformation to 1-phenylethanol is reached within
atoms C (3.30 ppm, Δδ = –0.21 ppm) and С (3.63 ppm,
Δδ = 0.15) of the cyclohexane ring, and chemical shifts
–1
1
h, TOF 345 h , no by-products are formed. In most
ini
1
1,11'
12, 12'
cases (R)-1-phenylethanol is presumably formed, and
only with ligand 2b excess of (S)-isomer is formed.
of protons at C
and C
atoms in the pyridine
fragments of the diimine ligand become nonequivalent.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 87 No. 11 2017

RHODIUM(I) BISALDIMINE COMPLEXES IN TRANSFER HYDROGENATION
2539
Parameters of proton signals of the cyclooctadiene
ligand in the complex Rh(cod)(2a)Cl, 3a, indicate that
the molecule remains bound with the rhodium(+1)
Table 1. Hydrogen transfer from 2-propanol on aceto-
phenone in the presence of the system [Rh(cod)Cl] –2
2
a
1
central atom (Table 3). The H NMR spectrum of the
rhodium complex contains three signal from four vinyl
protons of cyclooctadiene in the ratio of integral
intensities of 1 : 1 : 2 at δ ≈ 4.36, 4.73, and 4.79 ppm,
respectively, whereas the spectrum of the initial
biscyclooctadiene chloride complex [Rh(cod)Cl]2
contains only one resonance signal. A down-field shift
of signals from vinyl protons and approacing of
positions of resonances from СН and СН protons in
Exp.
no.
–1
ee, %
(R)
Ligand
TOF, h
b
1
2a
2a
2a
2a
2a
2a
2a
2a
2a
2a
2a
2a
2a
2a
310
35
60±4.2
17±1.0
39±2.0
108±5.5
155±7.6
68±3.4
200±12.2
31±1.8
31±1.5
35±1.7
28±1.3
32±1.6
30±1.5
37±1.7
26±1.1
35±1.6
28±1.4
32±1.5
17±0.8
32±1.6
32±1.6
49±2.5
38±1.8 (S)
2
3
5
6
4
А
В
86
65±3.2
the coordinated cyclooctadiene were observed when
the triphenylphosphine molecule was coordinated to
260
346
155
86
196±9.8
236±12.6
110±6.6
+
–
the rhodium complex [Rh(cod) ] CF SO [31].
2
3
3
Nonsymmetrical ligand coordination to rhodium in
13
1
c
the complex is confirmed by the C{ H} NMR spectra.
8
378±18.6 345±12.6
438±21.2 197±9.7
4
5
Thus, only carbon atoms C and C in the cyclohexane
d
9
86
fragment of ligand 1a are equivalent, whereas signals
3
6
e
of the pairs of atoms C (35.7 ppm), C (32.6 ppm),
10
172
172
172
86
58±2.7
24.0±1.3
11.0±0.4
113±6.6
65±3.8
19±1.1
1
2
and C (53.1 ppm), C (66.5 ppm), as well as
resonance signals of carbon atoms in azomethine
fragments (δN=CH 154.5 ppm; δN=CH 173.1 ppm) differ
significantly. Ten carbon atoms in two pyridine
fragments of the coordinated ligand and vinyl carbon
atoms in the cyclooctadiene molecule are also
f
1
1
1
2
g
d
h
i
13
548±23.1 248±12.3
1
1
4
5
172
172
172
71±3.2
24±1.1
74±3.4
129±6.4
44±2.6
1
1
11'
9
nonequivalent: 121.6 (C ) 126.1 (C ), 129.5 (C ),
9
'
10
10'
12
1
30.4 (C ), 137.6 (C ), 141.7 (C ), 149.6 (C ), 155.9
C ), 150.6 (C ), 162.1 (C ), 73.8 (2C, cod-CHvinyl),
16
133±7.0
2
b
1
2'
8
8'
(
8
1.0 (2C', cod-CHvinyl).
17
18
2c
172
11±0.6
70±3.7
37±1.8
–
20±1.1
122±6.8
16±1.0
–
43±2.3
35±2.5
53±2.5
To reveal catalytic activity of the catalyst under
2d 172
study it is necessary to add bases to the reaction mixture.
d,j
k
1
9
2a
43
20
Rh(cod)(2a)Cl + KO-iPr = Rh(cod)(2a)O-iPr(4) + KCl. (1)
20
2а
51
a
o
c
acetophenone = 95.2 mmol/L (172), cRh = 0.55 mmol/L, 78 C;
In the absence of the substrate the hydrogenation of
coordinated 1,5-cyclooctadiene occurs: signals of
protons of products of hydrogen transfer on a coor-
dinated diene, namely of free cyclooctene (2.29 and
b
с
t-BuOK or KOH, 2-propanol, toluene. cRh = 0.3 mmol/L. cRh
=
d
e
f
g
1
.1 mmol/L.
cRh = 2.2 mmol/L. 60°С. 50°С. 30°C.
7.3 mmol of 1-phenylethanol added. 23.6 mmol of acetone
added. Substrate was added after complete 1,5-cyclooctadiene
h
i
4
j
k
5
.42 ppm), cyclooctane (1.47 ppm), and acetone
hydrogenation. [Cp-RhCl
0°C [30].
2 2 2 2 2
] –HCO H/HCO Na, pH = 3.5, H O,
4
(
2.10 ppm) appear in the spectrum. When KOH and
acetophenone are introduced into the reaction mixture
the hydrogenation of this latter is accompanied by the
appearance of signals of 1-phenylethanol [2.5 (CH3),
and 3). Ligand 2a in the structure of rhodium
isopropoxide complex 4 is also coordinated asym-
3
.93 ppm (CH)] and acetone [1.99 ppm (CH )] along
1,2
3
metrically: protons of hydrogen atoms N–C H,
with cyclooctene and cyclooctane signals (Table 2,
Scheme 3).
10,10'
12,12'
C
H, C
H, and N=CH and vinyl protons in the
diene molecule are not equivalent. Resonances of
protons of the isopropoxide substituent at rhodium
appear as a multiplet at 3.52 ppm (СH) and a
broadened doublet at ~0.88 ppm (СH3).
Product 4 of the reaction of complex 3a with KOH
was isolated from the reaction mixture (parameters of
1
the H NMR spectrum in CDCl are shown in Tables 2
3
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 87 No. 11 2017

2
540
NINDAKOVA et al.
1
Table 2. Parameters of H NMR spectra of ligand 2a and complex Rh(cod)(2a)Cl in 1-propanole at –10°C
HA
HA
4
H 6
B
5
HB
H
HB
HB
HA
3
HA 1
2
N
N
H
9
8
8
' 9'
1
0
N
N 12' 10'
1
1 12
1
1'
2a
δ, ppm (Δδ)
Comp.
no.
4
,5
4
,5
C H
B
+
1,2
11,11'
10,10'
9,9'
12,12'
C H
A
3,6
NC H
C
H
C
H
C H
N=CH
8.28 s
C
H
C H
A B
H
2
3
a
1.50 m
1.80 m
3.51 br.s
7.35 d.d
J 4.5 Hz)
7.75 t
7.99 d
8.45 d
(
(J 7.8 Hz) (J 7.8 Hz)
(J 4.5 Hz)
а
1.68 s (2Н) 2.02 m (6Н) 3.30 m (1Н) 7.48 t (1Н,
7.98 t
(2Н,
J 7.7 Hz)
(0.22)
8.18 d
(2Н,
8.40 s (1Н)
8.57 d (1Н,
J 4.5 Hz) (0.12)
J 7.7 Hz) 9.41 s (1Н) 8.36 d (1Н,
(
–10°С)
(0.18)
(0.22)
(–0.20) J 6.0 Hz) (0.13)
.63 m (1H) 7.80 t (1Н,
(0.12)
3
(
0.12)
J 6.0 Hz) (0.45)
(0.19)
(1.13)
J 7.7 Hz) (–0.09)
+KОН
1.64 m
1.79 m
3.36–3.52 m
7.44 br.t
7.86 br.t
8.25 d
8.46 br.s
8.46 br.s
2
.10 s
(J 7.2 Hz)
(J 7.8 Hz) (J 8.2 Hz)
(acetone)
4
, CDCl
3
1.68 br.s
1.84 br.s 3.64 m (1H)
.78 m (1H)
7.62 br.s
7.72 t
(J 7.5 Hz) (J 4.5 Hz)
.79 t
J 7.5 Hz)
7.39 d
8.30 s
8.58 s
7.92 d (J 7.5 Hz)
8.19 d (J 7.5 Hz)
3
7
(
4
,
3
0.88 br.d(CH , J 6.3 Hz) 3.52 m ( СН)
Rh–O–iPr
1
Table 3. Parameters of H NMR spectra of 1,5-cod in complexes [Rh(cod)Cl]
2
and Rh(cod)(2a)Cl in 1-propanol
δ, ppm (Δδ)
CH
2.50 m (4Н)
Complex
CH
A
CH
B
CH
A B
CH
[
Rh(cod)Cl]
2
4.36 m (4Н)
4.36 m (1Н) (0.0), 4.73 m (1Н) (0.37),
.79 m (2Н) (0.43)
1.77 m (4Н)
Rh(cod)(2а)Cl (3а)
2.33 m (4Н) (–0.17)
2.02 m (4Н) (0.25)
4
а
а
а
4
(3а + KОН), 60°С
4.50 m (2H) (0.14) , 4.63 m (2H)
–0.10), 5.42 m (2Н, cyclooctene)
2.47 m (4Н) (0.14),
1.85 m (4Н) (–0.17)
(
2.29 (12Н, cyclooctene)
a
In relation to signals in complex 3a.
It can be assumed that binding of bisaldimine
To refine the complex geometry, we have carried
out calculations of rhodium complexes using the
B3LYP hybrid functional on the software package
Firefly version 8.1 [32]. Quantum chemical calcula-
tions with the use of the Lanl2dz basis set for rhodium
atom and 6-31(G)(d) for other atoms confirm the
formation of slightly distorted square-planar 18-elec-
tron rhodium(I) complex with 3aa-type bidentate
ligand 2a with rhodium central atom takes place
through one pyridine and one aldimine nitrogen 3a or,
in the case of symmetrical N,N-coordination of
nitrogen atoms, protons are not equivalent in pyridine
fragments (3b). Inequality of protons in two halves of
coordinated ligand 2a (Fig. 1) can take place in both
cases.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 87 No. 11 2017

RHODIUM(I) BISALDIMINE COMPLEXES IN TRANSFER HYDROGENATION
2541
Scheme 3.
N
Cl
Cl
N
N
N
Rh
Rh
N
N
N
N
3
a
3b
Scheme 4.
N1
Cl
Rh
7
8
C7
C C
C6
N2
1
C6
C
C8
N1
N2
C5
C1
N3
C2
Rh
N4
C5
Cl
C4
C2
C4
C3
C3
N3
N4
3aa
3
ab
coordination, in which a 1,5-cycloctadiene molecule
has the η -coordination and ligand 2a is bound with the
central atom through nitrogen atoms of one aldimine
and one pyridine fragments. The 16-electron Rh(I)
To refine the sequence of the C=O bond
hydrogenation in acetophenone and of double bonds in
1,5-cyclooctadiene, we monitored time changes of
concentrations of cyclooctadiene contained in the
complex [Rh(cod) (2a)Cl] and in a substrate. Kinetic
curves of their hydrogenation in the same experiment
are shown in Figs. 1 and 2. It can be seen that to the
moment of almost complete acetophenone hydrogena-
tion (τ 90 min, Fig. 1) 35% of initial 1,5-cyclo-
octadiene and 65% of cyclooctene (Fig. 2) remain in
the system, and full cyclooctadiene hydrogenation to
cyclooctane occurs within 17 h. Hence it follows that
the reaction of acetophenone transfer hydrogenation is
catalyzed by rhodium(I) cyclooctadiene and cyclo-
octene complexes, at least initially. In this experiment
ee value for the R-isomer was 32%.
4
complex 3ab is slightly more preferable in energy
0
(
ΔΔG = –0807 kcal/mol). The corresponding constant
of the equilibrium 3aa↔3ab is equal to four, which
corresponds to the 20% content of complex 3aa in the
equilibrium mixture. Some bond lengths and angles in
complexes 3aa and 3ab are shown in Table 4.
Optimized geometry of complex 3ab is a distorted
planar square. Steric repulsion between pyridine
fragment of ligand 2a and cyclooctadiene molecule
inhibits the interaction of the nitrogen atom in non-
coordinated azomethine fragment with rhodium atom.
It is probably 16-electron complex 3ab which reacts
with iPrOK to form compound 4. The chiral ligand
monodentate coordination is consistent with the data of
It should be noted that the introduction of the
substrate in the reaction solution after complete 1,5-
cyclooctadiene hydrogenation leads to an increase in
the enantioselectivity of the process from 35 to 53 ee
of (R)-1-phenylethanol (Table 1, exp. no. 19). Probably
1
13
the H and C NMR spectroscopy monitoring of its
interaction with dimeric chloride complex [Rh(cod)Cl]2
(
Scheme 4).
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 87 No. 11 2017

2
542
NINDAKOVA et al.
Table 4. Several bond lengths and angles between bonds in complexes 3aa and 3ab
d, Å
φ, deg
Bond
Angle
3
аa
3аb
3аa
3аb
1
Rh–Cl
2.643(80)
2.135(69)
2.162(28)
2.155(23)
2.196(01)
2.178(31)
2.157(73)
2.4476(6)
N RhCl
87.12(8)
99.52(3)
92.54(6)
141.12(9)
178.49(6)
87.38(1)
124.26(0)
128.83(3)
93.23(1)
84.19(3)
171.05(3)
149.60(0)
90.92(7)
101.48(7)
1
1
1
2
5
6
Rh–N
Rh–N
N RhC
2
1
2.181(63)
2.151(80)
2.184(63)
2.170(10)
2.197(18)
N RhC
1
2
5
6
1
Rh–C
Rh–C
Rh–C
Rh–C
N RhC
1
N RhC
1
ClRhC
ClRhC
ClRhC
89.90(7)
89.55(0)
166.62(0)
154.53(0)
88.74(5)
162.94(8)
159.58(1)
96.32(1)
92.71(3)
2
5
6
ClRhC
2
N RhCl
2
1
2
5
6
N RhC
2
N RhC
2
N RhC
2
N RhC
after the cyclic diene molecule departure from rhodium(I)
coordination sphere the tetradentate coordination of the
N,N,N,N-ligand takes place, and stereocontrol in
diastereomeric transition states increases. According to
NMR spectroscopy data, azomethine bonds in the
ligand are not reduced in the process of the
acetophenone transfer hydrogenation. The application
of diamine ligand 2d obtained by the diimine 2a
reduction with sodium tetrahydroborate leads to the in
situ formation of a rhodium(I) complex, which is also
active in transfer hydrogenation with a relatively high
TOF and ee 35% for (R)-1-phenylethanol (Table 1,
exp. no. 18).
The stage of rhodium hydride formation from the
rhodium isopropoxide complex Rh(cod)(2a)O-iPr
requires a free coordination site, which appears either
on the hydration of one double bond in the diene or on
the dissociation of the Rh–N bond that involves
changing the geometric structure of the complex and
also the concomitant from 2 to 1 in denticity of the
N,N,N,N-ligand in the complex. This decrease, in turn,
leads to a decrease in the degree of enantioface
differentiation of the prochiral ketone molecule in the
stage of chirality transfer. Thus, from the viewpoint of
enantioselectivity value of the acetophenone transfer
hydrogenation process, the presence of the
cycloctadiene ligand in the coordination sphere of the
rhodium(1+) complex is undesirable.
Thus, the rate of the catalytic reaction of the diene
transfer hydrogenation is significantly lower than that
of the ketone, therefore the catalysis occurs on the
rhodium(I) cyclooctadiene complexes with N,N'-
EXPERIMENTAL
Solvents and reagents [acetophenone, R,R-1,2-cyclo-
hexane diamine, 2-pyridinecarboxaldehyde, 2-quinoline-
carboxaldehyde (Aldrich)] used in this study were
thoroughly purified, dehydrated according to known
procedures [33], and stored in an argon atmosphere.
All syntheses were also carried out in argon.
(
1R,2R)-cyclohexane–1.2-diyl-bis[1-(pyridine-2-yl)-
methanimine] 2a. The presence of such a strong ligand
as 1,5-cyclooctadiene in the transition metal coor-
dination sphere prevents tetradentate coordination of
the N,N,N,N-ligand, which becomes possible only after
complete diene hydrogenation. In the absence of a
cyclooctadiene molecule from the metal coordination
sphere an increase in the product ee is observed.
Elemental analysis was carried out on a Euro
EA3000-Single instrument with argon as a carrier gas,
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 87 No. 11 2017

RHODIUM(I) BISALDIMINE COMPLEXES IN TRANSFER HYDROGENATION
2543
τ, min
τ, min
Fig. 2. Kinetic curves of 1,5-cyclooctadiene transfer
hydrogenation on the complex Rh(cod)(2a)Cl (cRh
ccyclooctadiene 2.22 mmol/L); (1) 1,5-cyclooctadiene,
(2) cyclooctene, and (3) cyclooctane.
Fig. 1. Transfer hydrogenation of acetophenone (cacetophenone
90.4 mmol/L, cRh = 2.22 mmol/L); (1) acetophenone and
2) 1-phenylethanol.
=
=
1
(
=
o
1
20 kPa, front oven temperature 980 C, and chroma-
30 min, then a solution of 9 mmol (0.96 g) of 2-
pyridine-carboxaldehyde in 20 mL of methanol was
added dropwise. The mixture was stirred for 4 h and
left overnight. The reaction was monitored by the TLC
method up to the complete aldehyde conversion. A
white precipitate was filtered off, washed with hexane,
o
1
13
tograph thermostat temperature 100 C. The H and C
NMR spectra were recorded on a Bruker DPX250
pulse
spectrometer
at
298
K
using
a
BBO5mmZ3074/58 broadband sensor, internal
reference HMDS. Concentrations of solutions for
1
13
23
recording Н NMR spectra were 5% and those for C
NMR spectra, 10%. The GLC analysis was fulfilled on
a Shimadzu QP2010 Plus gas chromatography mass
spectrometer in the electron impact mode at 70 eV
with subsequent scanning in the m/z range from 40 to
50 Da; an Equity 5 capillary column (30 m ×
.25 mm, 95% of dimethylpolysiloxane, 5% of di-
phenylpolysiloxane, carrier gas helium). Optical
rotation of samples was determined on an ADP410
automatic digital polarimeter at a wavelength of 589
nm (cell length 50 mm, concentration of solutions 2–
and dried. Yield 78% (0.91 g) [α]D 264 (c 1.0,
MeOH), mp 126–127°C, (mp 128–129°C [34]). IR
–
1
1
spectrum, (KBr), ν, cm : 1645 m (C=N). Н NMR
3
,6
spectrum (CDCl ), δ, ppm: 1.45–1.52 m (2H, C H H ),
3
A
B
3
,6
4,5
1.79–1.87 m (2H, C H H , 4H C H H ), 3.43–3.58
A
B
A
B
1
,2
11,11’
3
3
0
m (2H, NC H) 7.18 d.d. (2H, C
H, J = 7.5,
HH
1
0,10'
3
4.8 Hz), 7.60 d.d (2H, C
H, J = 7.5, 1.5 Hz), 7.85
9
,9'
3
br.d (2H, CH H, J = 7.5 Hz), 8.28 s (2H, CH=N),
H). Н NMR spectrum (CD OD), δ,
ppm: 1.50–1.62 m (2H, C H H ), 1.81–1.91 m (2H,
1
2,12'
1
8.51 d (2H, C
3
3
,6
A
B
3
,6
4,5
1,2
C H H ; 4H C H H H), 3.49–3.58 m (2H, NC H),
A
B
A
B
1
1,11'
3
3
0 g/100 mL of methanol). Excess of enantiomers in
7.37 d (2H, C
H, J = 5.5 Hz), 7.80 d.d (2H,
1
0,10'
3
12,12'
products was determined on a GC Agient 7890(A) gas
chromatograph equipped with a Dean switch, a flame
ionization detector, and a CYCLODEX-B chiral
capillary column (length 30 m, internal diameter
C
H, J = 7.8, 1.2 Hz), 7.90 d (2H, C
5.5 Hz). C NMR spectrum (CD OD), δ , ppm: 24.7
(C ), 32.9 (C ), 74.0 (C ), 121.6 (C ), 125.5
H, J =
1
3
3
C
4
,5
3,6
1,2
9,9'
1
1,11'
10,10'
12,12'
(C
), 137.3 (C
), 149.0 (C
), 154.7 (N=CH),
8
,8'
0
.25 mm).
161.4 (C ). Found, %: C 73.91; H 6.81; N 19.10.
C H N . Calculated, %: C 73.97; H 6.85; N 19.18.
2
6
24
4
Molecular geometry of rhodium(1+) complexes
was optimized using the B3LYP hybrid functional on
the Firefly version 8.1 software package [32]. The
Lanl2dz basis set was used for rhodium atom and
N,N'-(1R,2R)-Cyclohexane-1,2-diylbis-[1-(quino-
line-2-yl)methanimine] (2b) was obtained similarly.
23
23
Yield 62% (1.0 g) [α] +41.4 (c 1.0, MeOH); [α]
D
D
6
-31(G)(d) for other atoms.
23
+
92.0 (c 1.0, CH Cl ); [α] + 90.3 (c 1.0, CH Cl )
2
2
D
2
2
N,N'-(1R,2R)-Cyclohexane-1,2-diylbis[1-(pyridine-
-yl)methanimine] (2a). A solution of 4.4 mmol (0.5 g)
[35]; mp 207–208°C (C H OH) (mp 205–208 [36],
2 5
1
2
212–214°C [37]). Н NMR spectrum (CDCl ), δ, ppm:
3
3
,6
of (R,R)-1,2-cyclohexanediimine 1 {[α]D –8.17°C
c 8.7, C H )} in 30 mL of methanol was boiled for
1.50–1.58 m (2H, C H H ), 1.82–1.92 m (2H,
A B
3
,6
4,5
(
C H H , 4H, C H H H), 3.61–3.66 m (2H,
A (B) A B
6
6
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 87 No. 11 2017

2
544
NINDAKOVA et al.
1
,2
10,10'
3
1,2
N–C H), 7.46 d.d (2H, C
H, J = 7.3, 1.0 Hz), 7.63
3.39 m (2H, NC H), 4.30–4.42 (1H, cod-CHvinyl),
10,10'
3
d.d (2H, (C
H, J = 7.6, 1.5 Hz), 7.71 d (2H,
4.66–4.76 m (1H, cod-CH ), 4.75–4.85 m (2H, cod-
CH ), 7.50 t (1H, C H, J = 6.0 Hz), 7.80 t (1H,
vinyl
1
0,10'
3
9,9'
3
10
3
C
H, J = 8.2 Hz), 8.00 d (2H, C H, J = 8.6 Hz),
vinyl
10'
1
1,11'
3
11,11'
3
9,9'
3
8
.05 d (2H, C
H, J = 3.5 Hz), 8.06 d (2H, C
H,
C H, J = 6.0 Hz), 7.96 t (2H, C H, J = 7.5 Hz),
3
8
2'
3
11
J = 3.0 Hz), 8.50 s (2H, CH=N). Found, %: C 79.52;
H 6.05; N 14.21. C H N . Calculated, %: C 79.59; H
.12; N 14.29.
8.19 d (2H, C H, C H, J = 7.5 Hz), 8.34 d (1H, C H,
3
J = 7.5 Hz), 8.38–8.42 m (1H, CH=N), 8.56 d (1H,
C H, J = 4.5 Hz), 9.36–9.45 m (1H, C'H=N).
26
24
4
1
1'
3
13
6
C
NMR spectrum (i-PrOH), δ , ppm: 28.7 (cod-CH ),
C
2
N,N'-(1R,2R)-Cyclohexane-1,2-diylbis[1-(thiene-
-yl)methanimine] (2c). The compound was obtained
3
4,5
6
3
0.7 (cod-CH ), 32.6 (C ), 34.2 (C ), 35.7 (C ), 53.1
2
2
2
1
23
(C ); 66.5 (C ), 73.8 (cod-CH ), 81.0 (cod-CHvinyl),
121.6 (C ); 126.1 (C ); 129.5 (C ), 130.4 (C ), 137.6
(C ), 141.7 (C ), 149.6 (C ); 150.6 (C ), 154.5
(N=CH); 155.9 (C ), 162.1 (C ); 173.1 (N=C'H).
vinyl
similarly. Yield 74% (0.7 g), [α] 520 (c 1.0, MeOH),
D
1
1
11'
9
9'
1
mp 135–136°C (mp 137°C [37]). Н NMR spectrum
1
0
10'
12
8
3
,6
(
CDCl ), δ, ppm: 1.30–1.38 m (2H, C H H ), 1.60–
3 A B
1
2'
8'
3
,6
4,5
1
3
4
C
.69 m (2H, C H H ), 1.69–1.78 m (4H, C H H ),
A
B
A
B
1
,2
10,10'
3
.18–3.24 m (2H, N–C H), 6.84 t (2H, C
.3 Hz), 7.02 d (2H, C H, J = 4.5 Hz), 7.17 d (2H,
H, J = 4.5 Hz), 8.16 s (2H, CH=N). C NMR
spectrum (CD OD), δ , ppm: 24.3 (C ), 32.5 (C ),
3.3 (C ), 127.1 (C ), 128.1 (C ), 130.0 (C ),
42.5 (C ), 154.2 (CH=N). Found, %: C 63.46; H
.88; N 9.20; S 21.10. C H N S . Calculated %: C
H, J =
Transfer hydrogenation of acetophenone. The
cyclooctadiene dimeric complex [Rh(1,5-COD)µ-Cl]2
9
,9'
3
1
1,11'
3
13
(
0.025 mmol, 12.4 mg) and 25 mL of 2-propanol were
9
,10
8,11
3
C
placed in a vessel with a jacket of 100 mL blown
through with dry argon. To the bright yellow solution
of the complex 0.05 mmol of the ligand was added and
the reaction mixture was stirred for 15 min. As this
took place, the solution changed from pale yellow to
red-brown. Then 0.05 mol KOH or t-BuOK in 20 mL
of 2-propanol were added and the mixture was stirred
for 15 min. To the resulting bluish-green solution 0.2
mL of hexadecane as an internal reference and 0.5 mL
6
,7
3,3'
3,3'
2,2'
7
1
5
6
2
,2'
1
6
18
2 2
3.58; H 5.97; N 9.27; S 21.19.
N,N'-(1R,2R)-Bis(pyridine-2-yl-methyl)cyclo-
hexane-1,2-diamine (2d). The diamine was obtained
by reduction of 30 mL of compound 2a (0.8 g) alcohol
solution with sixfold NaBH excess at room tem-
4
(
4.3 mmol) of acetophenone were added. Then the
perature. After 20 h mixing and removal of the solvent
the formed white precipitate was washed several times
by diethyl ether, the joint extract was washed with
distilled water and dried over Na SO . After removal
temperature was quickly raised to 78°C, and the
reaction course was traced by the GLC-MS method by
sampling at 5–10 min intervals. The analysis was
performed on a GC-MS Shimadzu QP2010 Plus
chromatomass-spectrometry system and a GC Agient
2
4
of the solvent white precipitate was recrystallized from
1
ethanol. Yield 82%, mp 134.8–136.6°C. Н NMR spec-
4
,5
7
890A gas chromatograph. Configuration of the
trum (CDCl ), δ, ppm: 1.11–1.21 m (4H, C H H ),
3
A
B
3
,6
3
prevailing product was determined by com-parison
with the published data [38].
1
.64 d.d (2H, C H H , J = 9.2), 2.07 d (2H,
A B
3
,6
3
1,2
C H H , J = 12.5), 2.23-2.28 m (2H, NC H), 2.44
A
B
br.s (2H, NH), 3.77 d (2H, CH H ), 3.95 d (2H, C
A
B
1
1,11'
3
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RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 87 No. 11 2017

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RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 87 No. 11 2017