New ionic phosphite ligands: Synthesis and application in asymmetric Rh-catalyzed hydrogenation

Article abstract of DOI:10.1007/s11172-009-0051-1

A series of chiral ionic phosphite-type ligands bearing pyridinium and imidazolium fragments were prepared. Testing of these ligands in Rh-catalyzed asymmetric hydrogenation of dimethyl itaconate and methyl 2-acetamidoacrylate resulted in 95% ee of the products with 100% conversion of the reactants.

Full text of DOI:10.1007/s11172-009-0051-1

528
Russian Chemical Bulletin, International Edition, Vol. 58, No. 3, pp. 528—531, March, 2009
New ionic phosphite ligands: synthesis and application in
asymmetric Rhꢀcatalyzed hydrogenation
S. E. Lyubimov, P. V. Petrovskii, and V. A. Davankov
A. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences.
2
8 ul. Vavilova, 119991 Moscow, Russian Federation.
Fax: +7 (499) 135 6471. Eꢀmail: lssp452@mail.ru
A series of chiral ionic phosphiteꢀtype ligands bearing pyridinium and imidazolium fragꢀ
ments were prepared. Testing of these ligands in Rhꢀcatalyzed asymmetric hydrogenation of
dimethyl itaconate and methyl 2ꢀacetamidoacrylate resulted in 95% ee of the products with
1
00% conversion of the reactants.
Key words: ionic phosphites, rhodium complexes, asymmetric hydrogenation.
Catalytic asymmetric hydrogenation of prochiral oleꢀ
Scheme 1
fins is a convenient approach to the synthesis of valuable
optically active compounds due to low cost of molecular
hydrogen, rather high reaction rates, and low catalyst conꢀ
sumption.1 Most of the currently known effective chiral
ligands, including those used in industry, are bidentate
,2
2
phosphines. Relatively recently, it was shown that the
use of synthetically more accessible monodentate phosꢀ
phite and amidophosphite ligands also provides high
enantiomeric excess values (>99% ee) at 100% converꢀ
sion of the reactants in asymmetric hydrogenation.3
A promising group of monodentate ligands is the group of
ionic chiral phosphites and diamidophosphites that we
developed. These compounds synthesized on the basis of
imidazolium ionic liquids and quaternized amino alcohols
provide high asymmetric induction both in asymmetric
—6
hydrogenation and in allylic substitution reactions (up to
9% ee).7 An interesting task is the search for other
—9
9
effective catalytic systems based on the cationic phosphiteꢀ
type ligands and their testing in asymmetric catalytic
reactions.
Here we describe the synthesis of new ionic phosphite
ligands comprising oneꢀstep phosphorylation of pyriꢀ
dinium and imidazolium ionic liquids and their use in
Rhꢀcatalyzed asymmetric hydrogenation.
R = H (2, 5), Me (3, 6)
i. 150 °C, 2 h. ii. KBF , Me CO/EtOH, 72 h. iii. KBF , Me CO,
4
2
4
2
7
2 h.
Novel chiral ionic phosphites 9—11 were prepared by
oneꢀstep phosphorylation of hydroxylꢀcontaining pyriꢀ
Results and Discussion
dinium (5, 6) and imidazolium (7) ionic liquids in CH Cl
2
2
(
Scheme 2). All ligands 9—11 are readily soluble in polar
organic solvents such as CH Cl , CHCl , acetonitrile and
are stable on longꢀterm storage in a dry atmosphere.
Hydroxylꢀcontaining ionic liquids 5—7 were prepared
by quaternization of readily accessible compounds such
as pyridine, 2,5ꢀdimethylpyridine, and 1,2ꢀdimethylꢀ
imidazole with 2ꢀchloroethanol (1) followed by replaceꢀ
ment of the counterꢀion by tetrafluoroborate in the interꢀ
mediates 2—4 (Scheme 1).
2
2
3
We studied the reactions of phosphites 9—11 with
[
Rh(COD) ]BF (COD is cyclooctaꢀ1,5ꢀdiene). Ligands
2 4
9
and 11 are coordinated in the monodentate mode to
give complexes [Rh(COD)L ]BF (Scheme 3), which was
2
4
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 516—519, March, 2009.
066ꢀ5285/09/5803ꢀ0528 © 2009 Springer Science+Business Media, Inc.
1

New ionic phosphite ligands
Russ.Chem.Bull., Int.Ed., Vol. 58, No. 3, March, 2009
529
Scheme 2
R = H (9), Me (10)
confirmed by 31P NMR data and by elemental analysis.
Conversely, phosphite 10 shows nonselective coordiꢀ
nation as indicated by two doublets (δ1 = 125.9, d,
The efficiency of novel ionic catalytic systems conꢀ
taining phosphites 9—11 and complexes 12 and 14 was
tested in Rhꢀcatalyzed asymmetric hydrogenation of
methyl esters of prochiral unsaturated acids: dimethyl
itaconate (15) and methyl 2ꢀacetamidoacrylate (16)
(Scheme 4); the results are summarized in Table 1.
In the case of ligands 9 and 11, quantitative converꢀ
sion for both substrates (15 and 16) at low hydrogen presꢀ
sure (5 atm) and, in addition, high enantiometric excesses
J
3
= 260.0 Hz, 61% and δ = 140.9, d, J
= 207.4 Hz,
P,Rh
2
P,Rh
9%) in the 31P NMR spectrum of the isolated complex.
Probably, this is caused by steric reasons.
Scheme 3
(
92—95% ee) were achieved. Note that the process
enantioselectivity does not change on using the catalysts
formed in situ from ligands 9 and 11 or the isolated comꢀ
plexes 12 and 14 (see Table 1, runs 1, 2, and 4—9). The
Table 1. Asymmetric hydrogenation of dimethyl itaconate 12
and methyl 2ꢀacetamidoacrylate 14 (5 atm H , CH Cl )
2
2
2
L = 9, 10, 11
Run
Catalyst
Subꢀ t/h
strate
Conꢀ ее (%)b,c
version
а
Scheme 4
1
2
3
4
5
6
7
8
9
[Rh(COD)L ]BF /9
15
15
15
15
15
16
16
16
16
16
15
20
16
16
16
16
16
16
100
100
95
100
100
100
100
100
100
94 (R)
95 (R)
70 (R)
94 (R)
94 (R)
93 (S)
94 (S)
92 (S)
94 (S)
2
4
12
[Rh(COD)L ]BF /10
2
4
[Rh(COD)L ]BF /11
2
4
14
[Rh(COD)L ]BF /9
2
4
12
[Rh(COD)L ]BF /11
2
4
14
а
1
Determined by H NMR.
b
The enantiomeric excess of 17 was determined by HPLC,
i
–1
Chiralcel ODꢀH column, C H /Pr OH = 98/2, 0.8 mL min
,
6
14
2
19 nm, t 9.21 min, t 16.14 min. The absolute configuration of
R S
product 17 was determined with account of the optical rotation sign.
с
The enantiomeric excess of 18 was determined by HPLC,
i
–1
Chiralcel OJꢀH column, C H /Pr OH = 95/5, 1.0 mL min
,
6
14
2
19 nm, tR 14.01 min, t 16.01 min. The absolute configuration
S
of product 18 was determined with account of the optical rotaꢀ
Conditions: H (5 atm), CH Cl , cat*.
tion sign.
2
2
2

530
Russ.Chem.Bull., Int.Ed., Vol. 58, No. 3, March, 2009
Lyubimov et al.
use of phosphite 10 containing a 2,5ꢀdimethylpyridinium
fragment results in lower enantioselectivity (70% ee) and
incomplete conversion (see Table 1, run 3) caused, most
likely, by its nonselective coordination.
In summary, we synthesized a novel series of ionic
chiral phosphites based on pyridinium and imidazolium
ionic liquids. The use of these compounds as ligands in
asymmetric Rhꢀcatalyzed hydrogenation results in high
enantioselectivity in hydrogenation of both dimethyl
itaconate (up to 95% ee) and methyl 2ꢀacetamidoacrylate
1ꢀ(2ꢀHydroxyethyl)ꢀ2,5ꢀdimethylpyridinium tetrafluoroborate
6). Yield 65%, yellowish oil. Found (%): C, 45.45; H, 6.12;
(
N, 5.90. C H BF NO. Calculated (%): C, 45.23; H, 5.90;
9
14
4
1
N, 5.86. H NMR (DMSOꢀd ), δ: 2.49 (s, 3 H, CH ); 2.75 (s,
6
3
3
H, CH ); 3.85 (t, 2 H, CH , J = 5.0 Hz); 4.72 (t, 2 H, CH N,
3
2
2
J = 5.0 Hz); 5.32 (s, 1 H, OH); 7.86 (t, 1 H, J = 6.6 Hz); 8.36
d, 1 H, J = 7.8 Hz); 8.74 (d, 1 H, J = 5.8 Hz). ESI MS, m/z
Irel (%)): 152 [M – BF4]+ (100).
1ꢀ(2ꢀHydroxyethyl)ꢀ2,3ꢀdimethylimidazolium tetrafluoroꢀ
borate (7). Yield 72%, yellowish oil. Found (%): C, 37.03;
(
(
H, 5.93; N, 12.38. C H BF N O. Calculated (%): C, 36.88;
7
13
4
2
1
H, 5.75; N, 12.29. H NMR (DMSOꢀd ), δ: 2.58 (s, 3 H, CH );
(
up to 94% ee) with 100% reactant conversion. It is noteꢀ
6
3
3
.70 (t, 2 H, CH , J = 4.9 Hz); 3.76 (s, 3 H, CH ); 4.18 (t, 2 H,
worthy that relatively high enantiometric excess in the
Rhꢀcatalyzed hydrogenation makes these ligands attractive
for testing in other asymmetric processes such as allylic
substitution. Moreover, the presence of electrically charged
moiety in their molecules makes them suitable for immoꢀ
bilization on solid substrates and in ionic liquids.7
2
3
CH , J = 4.9 Hz); 5.1 (s, 1 H, OH); 7.59 (s, 2 H, 2 CH). ESI
2
MS, m/z (Irel (%)): 141 [M – BF4]+ (100).
Synthesis of ligands 9—11 (general procedure). Triethylamine
0.2 mL, 1.4 mmol) and the specified ionic synthon (5—7)
(
(
1.4 mmol) were added to a solution of (S )ꢀ2ꢀchlorodinaphthoꢀ
ax
,9
[2,1ꢀd:1´,2´ꢀf][1,3,2]dioxaphosphepine (8) (0.5 g, 1.4 mmol) in
CH Cl (25 mL), the mixture was stirred for 2 h at 20 °C, and
2
2
then the reaction solution was washed with water (45 mL). The
Experimental
organic phase was separated, dried over Na SO , and filtered,
2
4
and the solvent was evaporated in vacuo (40 Torr). The products
were purified by flash chromatography on a column with silica
gel (CH Cl , 300 mL).
3
1
P, H, and 13C NMR spectra were recorded on a Bruker
1
Avance 400 instrument (161.98, 400.13 and 100.61 МHz) relative
to 85% H PO in D O and Me Si, respectively. The C NMR
2
2
13
3
4
2
4
(R )ꢀ1ꢀ[2ꢀ(Dinaphtho[2,1ꢀd:1´,2´ꢀf][1,3,2]dioxaphosphepinꢀ
ax
signals were assigned using Jꢀmodulated spin echo procedure.
ESI mass spectra were run on a Finnigan LCQ Advantage
instrument. Hydrogenation was carried out on a Parr 4843 reactor
equipped with a 25ꢀmL autoclave. The enantiomeric excesses of
products 17 and 18 were determined by HPLC on a Varian 5000
chromatograph. Elemental analysis was carried out at the
Laboratory of microanalysis of the Institute of Organoelement
Compounds. Optical rotation was measured on a Perkin—
Elmerꢀ141 polarimeter.
4
ꢀyloxy)ethyl]pyridinium tetrafluoroborate (9). Yield 58%, white
18
powder, m.p. 80—83 °C, [α]D = –128 (c 0.8, CH Cl ). Found (%):
C, 61.96; H, 4.29; N, 2.50. C H BF NO P. Calculated (%):
2
2
2
7
21
4
3
31
C, 61.74; H, 4.03; N, 2.67. P NMR (CDCl ), δ: 141.25.
3
13
C NMR (CDCl ), δ: 61.7 (s, CH ); 62.3 (d, CH , J = 6.8 Hz);
3
2
2
1
21.0, 121.1, 122.2, 123.4 (all d, J = 5 Hz); 124.4, 124.4, 125.1
(
2 CH, pyridinium); 126.3, 126.4, 126.5, 126.6, 128.2, 128.3,
130.4, 130.5, 130.8, 131.3, 132.0, 132.3, 144.3 (2 CH, pyridinium);
1
46.3 (CH, pyridinium); 146.4, 147.5 (d, aryl, J = 5 Hz). ESI
MS, m/z (Irel (%)): 438 [M – BF4]+ (100).
All reactions were carried out under dry argon in anhydrous
solvents. The phosphorylating reagent (S )ꢀ2ꢀchlorodinaphthoꢀ
a
(R )ꢀ1ꢀ[2ꢀ(Dinaphtho[2,1ꢀd:1´,2´ꢀf][1,3,2]dioxaphosphepinꢀ
ax
[
2,1ꢀd:1″,2″ꢀf][1,3,2]dioxaphosphepine 8 (see Ref. 10) and the
4
ꢀyloxy)ethyl]ꢀ2,5ꢀdimethylpyridinium tetrafluoroborate (10).
starting complex [Rh(COD) ]BF (see Ref. 11) were prepared
18
2
4
Yield 50%, white powder, m.p. 75—78 °C, [α]D = –145
c 1.0, CH Cl ). Found (%): C, 63.12; H, 4.68; N, 2.71.
by published procedures. Dimethyl itaconate (15) and methyl
(
2
2
2
ꢀacetamidoacrylate (16) were purchased from Aldrich.
C H BF NO P. Calculated (%): C, 62.95; H, 4.55; N, 2.53.
2
9
25
4
3
31
13
Synthesis of ionic substrates 5—7 (general procedure).
A mixture of 2ꢀchloroethanol 1 (2.5 g, 31 mmol) and heterocyclic
amine (24.8 mmol) was refluxed for 2 h with vigorous stirring at
P NMR (CDCl ), δ: 140.31. C NMR, CDCl : 16.2 (CH );
3
3
3
1
1
9.4 (CH ); 58.0 (CH ); 62.2 (d, CH , J = 6.9 Hz); 120.9,
21.0, 122.1, 123.2 (all d, J = 4.7 Hz); 124.2, 124.2, 125.1 (CH,
3 2 2
1
50 °C under argon. Products 2—4 were washed with boiling
pyridinium); 126.2, 126.3, 126.4, 126.4, 128.2, 128.3, 130.3, 130.5,
30.7, 131.2, 132.0, 132.3, 138,2 (C, pyridinium); 143.2 (CH,
benzene (4×20 mL), dried in vacuo (1 Torr), and used in the next
step without further purification. Compounds 2—4 (20 mmol)
were dissolved in an acetone—ethanol mixture (80 : 20 mL for
substrates 2, 3) or in acetone (80 mL for substrate 4), an excess
1
pyridinium); 145.4 (CH, pyridinium); 146.3, 147.5 (d, aryl,
J = 4.8 Hz); 154.5 (C, pyridinium). ESI MS, m/z (I (%)): 466
rel
[
M – BF4]+ (100).
of КBF was added (70 mmol), and the mixture was stirred for
4
(R )ꢀ1ꢀ[2ꢀ(Dinaphtho[2,1ꢀd:1´,2´ꢀf][1,3,2]dioxaphosphepinꢀ
ax
7
2 h. The solutions thus obtained were filtered through a short
4
ꢀyloxy)ethyl]ꢀ2,3ꢀdimethylimidazolium tetrafluoroborate (11).
column with silica gel, the solvent was evaporated under reduced
pressure (40 Torr), and the products were dried for 3 h in vacuo
19
Yield 65%, white powder, m.p. 70—72 °C, [α]D = –132 (c 0.9,
CH Cl ). Found (%): C, 60.01; H, 4.59; N, 5.31. C H BF N O P.
Calculated (%): C, 59.80; H, 4.46; N, 5.17. P NMR (CDCl ),
δ: 142.02. 13C NMR (CDCl ), δ: 9.0 (CH ); 34.6 (CH );
2
2
27 24
4
2 3
31
(
1 Torr).
3
1
ꢀ(2ꢀHydroxyethyl)pyridinium tetrafluoroborate (5). Yield
3
3
3
7
0%, yellowish oil. Found (%): C, 39.70; H, 4.98; N, 6.44.
4
8,5 (CH ); 62.4 (d, CH , J = 8.4 Hz); 121.0, 121.2, 122.3,
2 2
C H BF NO. Calculated (%): C, 39.85; H, 4.78; N, 6.64.
7
10
4
123.5 (all d, J = 5.5 Hz); 125.1, 125.1, 126.3 (CH, imidazoꢀ
lium); 126.3, 126.3, 126.4, 126.6, 128.3, 128.4, 130.2, 130.6,
130.8, 131.4, 132.1, 132,4, 144.7 (C, imidazolium); 146.6,
1
H NMR (DMSOꢀd ), δ: 3.85 (t, 2 H, CH , J = 4.9 Hz); 4.70
6
2
(
t, 2 H, CH N, J = 4.9 Hz); 5.46 (s, 1 H, OH); 8.17 (t, 2 H,
2
J = 6.8 Hz); 8.62 (t, 1 H, J = 7.8 Hz); 9.07 (d, 2 H, J = 6.2 Hz).
1
47.6 (d, aryl, J = 4.8 Hz). ESI MS, m/z (I (%)): 455
rel
+
ESI MS, m/z (Irel (%)): 124 [M – BF4] (100).
+
[M – BF4] (100).

New ionic phosphite ligands
Russ.Chem.Bull., Int.Ed., Vol. 58, No. 3, March, 2009
531
Synthesis of rhodium complexes 12 and 14 (general proꢀ
cedure). A solution of corresponding ligands 9—11 (0.2 mmol)
in CH Cl (2 mL) was added dropwise over a period of 20 min
References
2
2
1
2
. C. Najera, J. Sansano, Chem. Rev., 2007, 107, 4584.
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to a solution of [Rh(COD) ]BF (0.04 g, 0.1 mmol) in CH Cl
2
4
2
2
(
2 mL), the mixture was stirred for 20 min, the solvent was
evaporated in vacuo (40 Torr), and the product was washed with
ether (2×5 mL) and dried in vacuo (1 Torr).
3
4
Bis{(R )ꢀ1ꢀ[2ꢀ(dinaphtho[2,1ꢀd:1´,2´ꢀf][1,3,2]dioxaphosꢀ
ax
phepinꢀ4ꢀyloxy)ethyl]pyridinium}(ηꢀ(cyclooctaꢀ1,5ꢀdiene)rhodiumꢀ
(
+1) tris(tetrafluoroborate) (12). Yield 94%, orange powder,
m.p. 112—121 °C (dec.). Found (%): C, 55.40; H, 4.21;
5
6
. M. T. Reetz, G. Mehler, Angew. Chem., Int. Ed., 2000, 39,
N, 2.02. C H B F N O P Rh. Calculated (%): C, 55.23;
6
2
54
3
12
2
6 2
3
889.
3
1
H, 4.04; N, 2.08. P NMR (CDCl ), δ: 123.8 (d, J = 260.0 Hz).
3
. S. E. Lyubimov, A. A. Tyutyunov, V. N. Kalinin, E. E. Saidꢀ
Galiev, A. R. Khokhlov, P. V. Petrovskii, V. A. Davankov,
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Petrovskii, K. N. Gavrilov, J. Mol. Catal. A: Chem., 2006,
Bis{(R )ꢀ1ꢀ[2ꢀ(dinaphtho[2,1ꢀd:1´,2´ꢀf][1,3,2]dioxaphosꢀ
ax
phepinꢀ4ꢀyloxy)ethyl]ꢀ2,3ꢀdimethylimidazolium}(ηꢀ(cyclooctaꢀ
1
,5ꢀdiene)rhodium(+1) tris(tetrafluoroborate) (14). Yield 96%,
7
8
orange powder, m.p. 102—112 °C (dec.). Found (%): C, 54.04;
H, 4.51; N, 3.92. C62H60B F N O P Rh. Calculated (%):
3
12
4
6 2
2
59, 183.
31
C, 53.87; H, 4.37; N, 4.05. P NMR (CH Cl ), δ: 126.7 (d,
2
2
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J = 259.2 Hz).
Asymmetric hydrogenation of dimethyl itaconate and
methyl 2ꢀacetamidoacrylate (general procedure). The complex
[
Rh(COD) ]BF (2.5 mg, 0.006 mmol) and corresponding ligand
2 4
9
9
—11 (0.012 mmol) or preꢀsynthesized rhodium complex (12
or 14) (0.006 mmol) were dissolved in CH Cl (4 mL). Then
2
2
dimethyl itaconate 15 or 2ꢀacetamidoacrylate 16 (0.6 mmol)
was added. The closed autoclave was purged with argon, then
purged two times with hydrogen and stirred under a hydrogen
pressure of 5 atm. The reaction mixture was diluted with hexane
1
1
(
4 mL) and filtered through a short pad of silica gel. The solvents
1
1
2. X.ꢀP. Hu, Z. Zheng, Org. Lett., 2004, 6, 3585.
3. R. Hoen, M. van den Berg, H. Bernsmann, A. J. Minnaard,
J. G. de Vries, B. L. Feringa, Org. Lett., 2004, 6, 1433.
were evaporated in vacuo (40 Torr). The spectroscopic data for
asymmetric hydrogenation products 17 and 18 fully correspond
1
2,13
to previously published data.
This work was supported by the INTAS (grant
No. 05ꢀ1000008ꢀ8064).
Received March 11, 2008;
in revised form September 22 , 2008