Asymmetric hydrogen-transfer hydrogenation on rhodium(I) complexes with new optically active salen ligands derived from (4S,5S)-4,5-Bis(aminomethyl)-2,2- dimethyl-1,3-dioxolane

Article abstract of DOI:10.1134/S1070428012010083

New optically active C2-symmetric salen-type ligands were synthesized on the basis of (4S,5S)-4,5-bis(aminomethyl)-2,2-dimethyl-1,3-dioxolane. These ligands were used to obtain cationic (trifluoromethanesulfonate) and neutral (chloride) rhodium(I) complexes with [(4S,5S)-2,2-dimethyl-5-{[(E)-pyridin-2- ylmethylidene]aminomethyl}-1,3-dioxolan-4-yl]-N-[(E)-pyridin-2-ylmethylidene] methanamine and [2,2-dimethyl-5-{[(E)-quinolin-2-ylmethylidene]aminomethyl}-1,3- dioxolan-4-yl]-N-[(E)-quinolin-2-ylmethylidene] methanamine. The latter complex ensured preparation of (S)-2-phenylethanol with an optical yield of 34.8% by transfer hydrogenation of acetophenone. Pleiades Publishing, Ltd., 2012.

Full text of DOI:10.1134/S1070428012010083

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2012, Vol. 48, No. 1, pp. 59–63. © Pleiades Publishing, Ltd., 2012.
Original Russian Text © L.O. Nindakova, B.A. Shainyan, N.M. Badyrova, F.M. Lebed’, 2012, published in Zhurnal Organicheskoi Khimii, 2012, Vol. 48,
No. 1, pp. 65–69.
Asymmetric Hydrogen-Transfer Hydrogenation on Rhodium(I)
Complexes with New Optically Active Salen Ligands Derived
from (4S,5S)-4,5-Bis(aminomethyl)-2,2-dimethyl-1,3-dioxolane
a
b
a
a
L. O. Nindakova , B. A. Shainyan , N. M. Badyrova , and F. M. Lebed’
a
Irkutsk State Technical University, ul. Lermontova 83, Irkutsk, 664074 Russia
e-mail: nindakova@istu.edu
b
Favorskii Irkutsk Institute of Chemistry, Siberian Division, Russian Academy of Sciences,
ul. Favorskogo 1, Irkutsk, 664033 Russia
e-mail: bagrat@irioch.irk.ru
Received April 9, 2011
Abstract—New optically active C
2
-symmetric salen-type ligands were synthesized on the basis of
(
4S,5S)-4,5-bis(aminomethyl)-2,2-dimethyl-1,3-dioxolane. These ligands were used to obtain cationic (tri-
fluoromethanesulfonate) and neutral (chloride) rhodium(I) complexes with [(4S,5S)-2,2-dimethyl-5-{[(E)-pyri-
din-2-ylmethylidene]aminomethyl}-1,3-dioxolan-4-yl]-N-[(E)-pyridin-2-ylmethylidene]methanamine and
[
2,2-dimethyl-5-{[(E)-quinolin-2-ylmethylidene]aminomethyl}-1,3-dioxolan-4-yl]-N-[(E)-quinolin-2-yl-
methylidene]methanamine. The latter complex ensured preparation of (S)-2-phenylethanol with an optical yield
of 34.8% by transfer hydrogenation of acetophenone.
DOI: 10.1134/S1070428012010083
Transition metal complexes with Schiff bases (so-
called salen complexes) in which the donor centers are
oxygen and nitrogen atoms are extensively studied due
to the possibility for controlling their steric and elec-
tronic properties via appropriate selection of primary
mono- and diamine precursors and substituted alde-
hydes [1–6]. Chiral salen metal complexes effectively
catalyze various processes. Catalytic asymmetric epox-
idation and cyclopropanation reactions in the presence
of Mn(III), Co(III), and Cr(III) salen complexes [2–6],
including complexes intercalated into zeolite pores and
macromolecules [7], were studied in most detail.
amines or cyclohexane-1,2-diamine. The known ex-
ception is chiral salen ligands derived from binaph-
thyldiamine; the corresponding complexes were used
in the synthesis of cyclic carbonates [13]. Unlike
3
amine ligands with sp -hybridized nitrogen atoms,
2
nitrogen-containing salen ligands with sp -nitrogen
atoms are softer bases which do not reduce the metal
ion in the complex. Therefore, asymmetric transforma-
tions catalyzed by such complexes are expected to
occur without reduction of the transition metal ion
which often accompanies reactions in the presence of
complexes with diamine ligands.
Chiral C -symmetric salen ligands (and the corre-
sponding metal complexes) obtained from optically
active 1,2-diarylethane-1,2-diamines or cyclohexane-
2
Taking the above stated into account, in continua-
tion of our studies on enantioselective reduction in the
presence of cobalt [14] and rhodium complexes
1
,2-diamine were used most frequently [3, 8–10].
[
15–17] in the present work we synthesized novel
N,N,N,N-salen ligands on the basis of (4S,5S)-4,5-bis-
aminomethyl)-2,2-dimethyl-1,3-dioxolane. As initial
These complexes showed a high catalytic activity and
moderate enantioselectivity (up to ee 73%) in boro-
hydride reduction of aromatic ketones [11]. The use of
rhodium salen complexes in the reduction of prochiral
compounds was reported [1, 12].
(
primary diamine we used (2S,3S)-3,4-isopropylidene-
dioxybutane-1,4-diamine (I) which was prepared ac-
cording to Scheme 1 [16]. Optically active salen
ligands II and III were synthesized in moderate yield
by condensation of diamine I with pyridine-2-carbal-
dehyde and quinoline-2-carbaldehyde, respectively
There are almost no published data on the synthesis
of salen-type ligands and their metal complexes on the
basis of other diamines than 1,2-diarylethane-1,2-di-
5
9

6
0
NINDAKOVA et al.
Scheme 1.
O
O
O
O
O
HO
HO
Me
Me
O
O
O
O
Me
Me
OEt
OEt
Me
Me
NH2
NH
NH3
OEt
OEt
MeO
MeO
*
*
*
*
*
+
*
–2MeOH
LiAlH4
–2EtOH
2
O
O
Me
Me
NH2
*
*
NH2
O
I
Scheme 2.
CHR
CHR
Me
Me
O
NH2
NH2
Me
Me
O
*
N
N
*
*
+
2RCHO
–2H O
*
2
O
O
I
II, III
II, R = pyridin-2-yl; III, R = quinolin-2-yl.
(
Scheme 2). The structure of compounds II and III
nitrogen atoms to the metal ion. Table 1 shows chemical
shifts of protons in compound II and complexes VI
and VII. Complex VII demonstrates a strong upfield
shift of the N=CH signal (Δδ = –1.07 ppm), an ap-
preciable downfield shift of signals from 3-H and
4-H in the pyridine ring (Δδ = 0.34 and 0.29 ppm),
and a weak upfield shift of the 5-H signal (Δδ =
–0.07 ppm). Obviously, no such shifts of signals from
protons in the heteroring would be observed in the
absence of coordination of the pyridine nitrogen atom
to the central metal ion. Moreover, in this case the
CH=N proton signal would be shifted downfield rather
than upfield.
was confirmed by elemental analyses and spectral data.
Rhodium(I) complexes with ligand II were obtained
from neutral dinuclear complex [(1,5-COD)RhCl]2
(
IV) and cationic trifluloromethanesulfonate complex
+
–
3
[(1,5-COD)Rh] CF SO (V); the latter was prepared
3
by treatment of IV with silver trifluoromethanesul-
fonate according to the procedure described in [17]
(
Scheme 3).
The structure of complexes VI and VII was analo-
gous to the structure of manganese salen complexes
18] and was confirmed by IR and NMR spectroscopy.
The IR spectrum of free ligand II contained an absorp-
[
–
1
tion band at 1650 cm , which almost did not change
its position on going to cationic complex VII
(
the C=N bond is retained as a result of opposite
effects of coordination of the azomethine and pyridine
Apart from compound II, we also synthesized
ligand III containing bulkier quinoline fragments. We
expected increased steric hindrances in the coordina-
tion sphere of Rh(I) in the corresponding complex at
the stage of chirality transfer to the substrate, which
–
1
1648 cm ). This means that the double character of
Scheme 3.
AgOTf
TfO–
Rh
Me
O
Me
O
Me
O
Me
O
Cl
Rh
Rh
Cl
V
IV
II
N
N
N
N
–
1,5-COD
–1,5-COD
Rh
Rh
Cl
N
N
N
N
TfO–
VII
VI
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 48 No. 1 2012

ASYMMETRIC HYDROGEN-TRANSFER HYDROGENATION ON RHODIUM(I)
61
1
Table 1. Chemical shifts of protons (δ, ppm) in the H NMR spectra of ligand II and rhodium complexes VI and VII
Compound no. Solvent
CH
3
CH
2
CH
=CH
3-H
4-H
5-H
6-H
II
CDCl
CDCl
3
1.41
1.43
1.31
1.39
3.96
4.36
3.74, 3.95
4.35
8.44
5.56
8.40
7.34
8.02
7.84 – 8.61
8.04
7.73
7.30
8.64
VI
VI
VII
3
3.46
Acetone
Acetone
3.90, 3.99
3.89, 3.72
7.83
8.12
7.41
7.34
8.62
8.63
4.32
8.38
should enhance enantioselectivity of the reduction
process. According to the NMR and IR spectra,
diimine III was isolated as individual substance. It was
used in the transfer hydrogenation of acetophenone
with propan-2-ol in the presence of neutral complex IV
(enantioselectivity) in the transfer hydrogenation of
acetophenone and higher catalytic activity as compared
to VI and VII (31.5 and 7.0–8.0 mol of acetophenone
per mole of Rh per hour).
(
Scheme 4).
EXPERIMENTAL
Scheme 4.
O
Acetophenone and solvents (propan-2-ol, toluene)
were thoroughly purified and dehydrated and were
stored under argon. All reactions were carried out in
an argon atmosphere.
OH
Me
+
Me
OH
Me
The IR spectra were recorded in KBr on an IKS 29
1
13
spectrometer. The H and C NMR spectra were
measured on a Bruker DPX 400 spectrometer at 400
*
O
[
Rh(C H )Cl] (IV), III
Me
8
12
2
1
13
+
( H) and 100 MHz ( C) using hexamethyldisiloxane
as internal reference (the chemical shifts are given
relative to tetramethylsilane). GLC analysis was per-
formed on an LKhM 80 chromatograph equipped with
a thermal conductivity detector (2000×3-mm column
packed with 5% of SE-30 on Chromaton N-AW-
DMCS; carrier gas helium) and on a Shimadzu
QP2010 Plus GC–MS system (electron impact, 70 eV,
a.m.u. range from 40 to 350; Equity 5 capillary column,
Me
Me
Figure shows the plot of concentration of aceto-
phenone versus reaction time. Three parts of the
kinetic curve can be distinguished. The first part is
likely to correspond to hydrogenation of cycloocta-
diene molecule and concurrent reaction involving com-
plexes containing no cyclooctadiene. The next part
reflects the highest activity of the system, and the third
part corresponds to slow hydrogenation.
3
5
0 m×0.25 mm, 95% of dimethylpolysiloxane and
% of diphenylpolysiloxane; carrier gas helium; oven
The results obtained in the presence of different
catalysts are collected in Table 2. Salen complexes
ensure higher conversion as compared to diamine
rhodium(I) complexes [14]. Furthermore, no deposi-
tion of rhodium metal is observed in the reactions
catalyzed by salen complexes. Complex IV with salen
ligand III (which is more sterically hindered than
ligand II) showed both higher asymmetric induction
temperature programming from 110 to 250°C, injector
temperature 250°C, interface and ion source tempera-
ture 200°C). The mass spectra corresponding to the
apices of chromatographic peaks were compared with
reference spectra in the NIST05 library. The optical
rotations were measured on an ADP410 automatic
digital polarimeter at λ 589 nm (cell path length
50 mm, concentration 2–30 g/100 ml, solvent metha-
Table 2. Transfer hydrogenation of acetophenone on Rh(I) complexes (solvent propan-2-ol, base KOH, 78°C)
Conversion,
%
r
max
,
Maximal activity, mol of PhC(O)Me
per mole of Rh per hour
Complex
cRh, mM cPhC(O)Me/cRh Time, min
–1 –1
ee, %
mmol l h
VI
1.7
1.6
1.1
1.1
80
86
86
86
540
525
535
270
79.8
23.0
68.0
84.0
13.4
07.9
07.7
34.7
08.0
05.0
07.0
31.5
00.9 (S)
06.7 (S)
02.5 (S)
34.8 (S)
VII
VII
IV + III
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 48 No. 1 2012

6
2
NINDAKOVA et al.
anol was added dropwise over a period of 40–50 min.
1
00
The resulting brown solution was heated for 2 h under
reflux with stirring, cooled, and left overnight. The
light brown precipitate was filtered off, washed with
diethyl ether, and dried under reduced pressure. Yield
8
6
4
2
0
0
0
0
0
1
8%, mp 114–115°C, [α] = –8.17° (c = 8.7, C H ).
D 6 6
–1
1
IR spectrum, ν, cm : 1646, 1597, 1561. H NMR
spectrum (CDCl ), δ, ppm: 1.45 s (3H, CH ), 4.05 m
3
3
(
2H, CH ), 4.45 m (1H, OCH), 7.58 t (1H, 6-H, J =
2
7
.3 Hz), 7.75 t (1H, 7-H, J = 7.6 Hz), 7.83 d (1H, 5-H,
J = 7.9 Hz), 8.12 d (1H, 8-H, J = 8.4 Hz), 8.17 m (1H,
-H, 4-H), 8.62 s (1H, N=CH). Found, %: C 74.11;
H 6.05; N 12.67. C H N O . Calculated, %: C 73.95;
0
1
2
3
4
3
Time, h
2
7
26
4
2
Plot of acetophenone concentration in propan-2-ol versus
time in the transfer hydrogenation using the system
H 5.98; N 12.78.
(
[2,2-Dimethyl-5-{[(E)-pyridin-2-ylmethylidene]-
2
[Rh(COD)Cl] –III; cRh = 1.1 mM, [III]:[Rh] = 3, 75°C.
aminomethyl}-1,3-dioxolan-4-yl]-N-[(E)-pyridin-2-
ylmethylidene]methanamine)rhodium(I) chloride
(VII). A test tube was charged in a stream of argon
nol). The optical yields were calculated with respect to
the specific rotation of (S)-(–)-1-phenylethanol ([α] =
with 0.1 mmol (49.3 mg) of [Rh(COD)Cl] , 10 ml of
2
–
45.0°, c = 5, MeOH) [19].
4S,5S)-(2,2-Dimethyl-1,3-dioxolane-4,5-diyl)bis-
N-[(1Z)-pyridin-2-ylmethylidene]methanamine}
II). (4S,5S)-4,5-Bis(aminomethyl)-2,2-dimethyl-1,3-
dioxolane (I) ([α] = –8.17°, c = 8.7, PhH), 0.016 mol
THF was added, and the mixture was stirred until com-
plete dissolution. A solution of 0.2 mmol (67.6 mg) of
compound II in a small amount of THF was then
added, and the blue–violet solution was stirred for 24 h
and evaporated to a volume of 3 ml. The blue–violet
precipitate was washed with several small portions of
diethyl ether and dried under reduced pressure. Yield
(
{
(
D
(
0.8 g), was dissolved under stirring in 30 ml of metha-
nol, the solution was heated to the boiling point, and
a solution of 0.032 mol (1.126 g) of pyridine-2-carb-
aldehyde in 20 ml of methanol was added dropwise
over a period of 30–40 min. The mixture was stirred
for 2 h and left overnight, and the light brown precip-
itate (large crystals) was filtered off, washed with hex-
–
1
0
.09 g (95%). IR spectrum, ν, cm : 1648, 1590, 1567.
1
The H NMR spectrum is given in Table 1.
([2,2-Dimethyl-5-{[(E)-pyridin-2-ylmethylidene]-
aminomethyl}-1,3-dioxolan-4-yl]-N-[(E)-pyridin-
2-ylmethylidene]methanamine)rhodium(I) tri-
fluoromethanesulfonate (VII). A test tube was
charged in a stream of argon with 0.1 mmol (49.3 mg)
2
5
5
46
ane, and dried. Yield 86%, mp 92–95°C, [α] = –6.7°
–
1
(
1
c = 0.80, CHCl ). IR spectrum, ν, cm : 1650, 1580,
3
1
565. H NMR spectrum (CDCl ), δ, ppm: 1.41 s (3H,
of [Rh(COD)Cl] , 10 ml of THF was added, and the
3
2
CH ), 3.92 d.d (1H, CH , J = 12.5, 3.7 Hz), 3.99 d.d
mixture was stirred until complete dissolution. A solu-
tion of 0.2 mmol (51.4 mg) of silver trifluoromethane-
sulfonate in 20 ml of THF was added, and the mixture
was stirred for 30 min. The precipitate was filtered off
through a layer of silica gel and washed on a filter with
several small portions of THF. A solution of 0.2 mmol
(67.6 mg) of compound II in a small volume of THF
was added, and the resulting dark red solution was
stirred for 24 h and evaporated to a volume of 3 ml.
The dark red precipitate was washed with several
portions of diethyl ether and dried under reduced pres-
3
2
(
1H, CH , J = 12.5, 2.4 Hz), 7.30 m (1H, 5-H),
2
7
.73 d.d (1H, 4-H, J = 7.6, 1.0 Hz), 8.02 d (1H, 3-H,
J = 7.8 Hz), 8.44 s (1H, N=CH), 8.64 d (1H, 6-H, J =
13
4
.2 Hz). C NMR spectrum (CDCl ), δ , ppm: 27.22
3 C
(
1
1
CH ), 63.10 (CH ), 78.56 (OCH), 109.43 (OCO),
3 2
3
5
4
6
21.30 (C ), 124.80 (C ), 136.47 (C ), 149.38 (C ),
2
54.33 (C ), 164.09 (N=CH). Found, %: C 67.11;
H 6.65; N 16.67. C H N O . Calculated, %: C 67.44;
1
9
22
4
2
H 6.55; N 16.56.
(
[2,2-Dimethyl-5-{[(E)-quinolin-2-ylmethyli-
–
1
sure. Yield 112 mg (95%). IR spectrum, ν, cm : 1648,
dene]aminomethyl}-1,3-dioxolan-4-yl]-N-[(E)-quin-
olin-2-ylmethylidene]methanamine) (III). Com-
pound I, 0.016 mol (2.57 g), was dissolved under
stirring in 40 ml of methanol, the solution was heated
to the boiling point, and a solution of 0.040 mol
1
1
638, 1597. The H NMR spectrum is given in Table 1.
Transfer hydrogenation of acetophenone with
propan-2-ol. A vessel was charged in a stream of
argon with 0.025 mmol (12.4 mg) of dinuclear
(
6.28 g) of quinoline-2-carbaldehyde in 30 ml of meth-
rhodium complex [Rh(COD)Cl] and 45 ml of propan-
2
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 48 No. 1 2012

ASYMMETRIC HYDROGEN-TRANSFER HYDROGENATION ON RHODIUM(I)
63
2
-ol. Compound III, 0.05 mmol (22.1 mg), was added
9. Kim, G-J. and Shin, J.-H., Catal. Lett., 1999, vol. 63,
p. 83.
to the bright yellow solution which immediately turned
brown, 0.2 ml of hexadecane (internal standard) and
0
10. Sun, W., Xia, C-G., and Zhao, P-Q., J. Mol. Catal. A,
2
002, vol. 184, p. 51.
.15 mmol (8.4 mg) of KOH (co-catalyst) were added,
the mixture was stirred for 15 min, 4.3 mmol (0.5 ml)
of acetophenone was added, and the mixture was
stirred for 5 min and maintained at 75°C. Samples for
GLC analysis were taken every 30 min.
11. Gozzi, P.G., Chem. Soc. Rev., 2004, vol. 33, p. 410.
12. Cortez, N.A., Flores-López, C.Z., Rodriguez-Apo-
daca, R., Flores-López, L.Z., Parra-Hake, M., and
Somanathan, R., Arkivoc, 2005, vol. 6, p. 162.
1
3. Shen, Y.-M., Duan, W.-L., and Shi, M., J. Org. Chem.,
REFERENCES
2003, vol. 68, p. 1559.
1
4. Nindakova, L.O., Lebed’, F.M., Zamazei, A.Yu.,
and Shainyan, B.A., Russ. J. Org. Chem., 2007, vol. 43,
p. 1322.
1
. Deligonul, N., Tumer, M., and Serin S., Transition Met.
Chem., 2006, vol. 31, p. 920.
2
3
. Katsuki, T., Adv. Synth. Catal., 2002, vol. 344, p. 131.
. Zhang, W., Loebach, J.L., Wilson, S.R., and Jacob-
1
5. Nindakova, L.O., Shainyan, B.A., and Belonogova, L.N.,
Russ. J. Org. Chem., 2003, vol. 39, p. 1484.
sen, E.N., J. Am. Chem. Soc., 1990, vol. 112, p. 2801.
. Jacobsen, E.N., Zhang, W., Muci, A.R., Ecker, J.R., and
Deng, L., J. Am. Chem. Soc., 1991, vol. 113, p. 7063.
1
6. Shainyan, B.A., Ustinov, M.V., Bel’skii, V.K., and
Nindakova, L.O., Russ. J. Org. Chem., 2002, vol. 38,
p. 104.
4
5
6
. Larrow, J.F. and Jacobsen, E.N., Top. Organomet. Chem.,
17. Nindakova, L.O., Shainyan, B.A., Albanov, A.I., and
Ustinov, M.V., Russ. J. Org. Chem., 2000, vol. 35,
p. 1660.
2
004, vol. 6, p. 123.
. Youssef, N.S., El-Zahany, E.A., Barsoum, B.N., and El-
Seidy, A.M.A., Transition Met. Chem., 2009, vol. 34,
p. 905.
. Leung, A.C.W. and McLachlan, M.J., J. Inorg. Organo-
met. Polym. Mater., 2007, vol. 17, p. 57.
1
8. Lu, X.-H., Xia, Q.-H., Zhan, H.-J., Yuan, H.-X.,
Ye, C.-P., Su, K.-X., and Xu, G., J. Mol. Catal. A, 2006,
vol. 250, p. 62.
7
8
1
9. Gladiali, S., Chelucci, G., Soccolini, F., Delogu, G., and
Chessa, G., J. Organomet. Chem., 1989, vol. 370,
p. 285.
. Irie, R., Noda, K., Ito, Y., Matsumoto, N., and Katsu-
ki, T., Tetrahedron Lett., 1990, vol. 31, p. 7345.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 48 No. 1 2012