Chiral ionic phosphites and diamidophosphites: A novel group of efficient ligands for asymmetric catalysis

Article abstract of DOI:10.1002/adsc.200600372

Seven members of a new class of chiral P-monodentate cationic phosphites and diamidophosphites have been synthesized for the first time and tested as ligands in asymmetric transition metal catalysis. Up to 96% ee was achieved in the rhodium-catalyzed asym

Full text of DOI:10.1002/adsc.200600372

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DOI: 10.1002/adsc.200600372
Chiral Ionic Phosphites and Diamidophosphites: A Novel Group
of Efficient Ligands for Asymmetric Catalysis
Konstantin N. Gavrilov,a,* Sergey E. Lyubimov,b Oleg G. Bondarev,c
Marina G. Maksimova,a Sergey V. Zheglov,a Pavel V. Petrovskii,b
Vadim A. Davankov,b and Manfred T. Reetzc,*
a
Department of Chemistry, Ryazan State University, Svoboda Str. 46, 390000 Ryazan, Russia
Fax : (+7)-495-135-6471; e-mail: chem@rspu.ryazan.ru
Institute of Organoelement Compounds, Russian Academy of Sciences, Vavilov Str. 28, 119991 Moscow, Russia
Max-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz 1, 45470 Mülheim/Ruhr, Germany
b
c
Fax : (+49)-208-306-2985; e-mail: reetz@mpi-muelheim.mpg.de
Received: July 24, 2006
Dedicated to Professor Masakatsu Shibasaki on the occasion of his 60th birthday.
Abstract: Seven members of a new class of chiral alyzed allylic allylation. Applications of the immobi-
P-monodentate cationic phosphites and diamido- lized cationic rhodium complex to asymmetric cata-
phosphites have been synthesized for the first time lytic synthesis have also been demonstrated.
and tested as ligands in asymmetric transition metal
catalysis. Up to 96% ee was achieved in the rhodi-
um-catalyzed asymmetric hydrogenation of function- Keywords: allylation; asymmetric catalysis; hydroge-
alized olefins and up to 99% ee in the palladium-cat- nation; P ligands; palladium; rhodium
Introduction
compounds,[6] the novel phosphites and diamidophos-
phites L1–L3 were synthesized by a direct phosphory-
In 2000 it was reported that monodentate BINOL-de- lation of an appropriate ionic liquid in CH2Cl2
rived phosphites,[1] phosphonites,[2] and phosphorami- (Scheme 1).
dites[3] are excellent ligands in Rh-catalyzed olefin hy-
The ligands were isolated in pure form and charac-
drogenation. Since then this chemistry has been gen- terized by NMR spectroscopy and mass spectrometry
eralized to include other reaction types and other as well as elemental analysis. Interestingly, despite
monodentate P ligands,[4] and the first detailed mecha- their ionic nature compounds L1–L3 are readily solu-
nistic study has appeared.[5] None of these chiral li- ble in commonly used solvents such as CH2Cl2, CHCl3
gands has been prepared and used catalytically in or THF and also ionic liquids. They are stable enough
ionic form. However, recently a study regarding the to tolerate washing of their dichloromethane solutions
use of ionic forms of achiral phosphites in catalysis with water.
appeared.[6] Moreover, a chiral ionic phosphoramidite
was described, but it was not used directly in catalysis.[7] ligands in reactions with [Rh
The new compounds act as typical P-monodentate
(COD)2]BF4 and
AHCTREUNG
Herein we report the synthesis of chiral cationic [Pd
phosphites and diamidophosphites along with their
ACHTREUNG
application in the Rh-catalyzed asymmetric hydroge- and IR spectroscopy and mass spectrometry. A high
nation of prochiral olefins and Pd-catalyzed allylation 1JP,Rh value for complex 1 (309.6 Hz, in DMSO-d6) in-
as well as their successful immobilization by ionic in- dicates pronounced electron-accepting character of
teraction on an anionic support.
cationic phosphite L1. The electronic properties of L1
were also revealed by the 31P NMR and IR spectro-
scopic data of its rhodium(I) carbonyl complex 2. The
1JP,Rh and n(CO) data for complex 2 (289.0 Hz;
2012 cmÀ1, in CHCl3) indicate that L1 is a highly p-ac-
Results and Discussion
Unlike the traditional synthetic approach to ionic cepting aryl phosphite.[9]
phosphites through quaternization of P,N-bidentate
Adv. Synth. Catal. 2007, 349, 609 – 616
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Scheme 1. Synthesis of cationic ligands L1–L3.
Scheme 2. Complexation of the ligands L1–L3 with Rh(I) and Pd(II).
lents of an appropriate ionic ligand (Rh/substrate=
1:1000, in CH2Cl2) led to very different enantioselec-
tivities, depending upon the nature of the chiral auxil-
iary (Table 1). It is noteworthy that the use of
BINOL-based phosphite L1 provided ꢀ 93% ee and
100% conversion for all substrates (9, 11, 13). This is
in line with the results obtained when using analogous
Table 1. Rh-catalyzed hydrogenation of olefins (CH2Cl2,
1.3 bar H2, 228C, 20 h).
Entry
Substrate
Ligand
Conversion [%]
ee [%]
1
9
9
9
11
11
13
13
L1
L1
L3
L1
L3
L1
L3
100[a]
100
42
100
100
100
59
94 (S)[a]
79 (S)
58 (S)
93 (R)
33 (R)
96 (R)
46 (R)
2[b]
3
Scheme 3. Rh-catalyzed enantioselective olefin-hydrogena-
tion.
4
5
6
7
The efficacy of the new ionic ligands L1 and L3
was evaluated in the Rh-catalyzed asymmetric hydro-
genation of olefins 9, 11 and 13 (Scheme 3).
[a]
The reaction was also performed for a shorter time
(12 h), likewise leading to complete conversion (meaning
TOF=83 hÀ1).
In these reactions the catalysts formed in situ by
[b]
standard mixing of [Rh
A
Reaction conditions: solvent [BDMIM]BF4; 25 bar H2.
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Chiral Ionic Phosphites and Diamidophosphites
eropoly acid.[11a] Complex 1 was immobilized by
direct ion exchange of acidic sites on silica. The rhodi-
um content (1.31 wt%) of the catalyst estimated by
energy-dispersive X-ray analysis (EDX) was in good
agreement with those obtained from ICP-AES analy-
sis (1.23 wt%). The immobilized catalyst was then
tested in the hydrogenation of dimethyl itaconate 9
(Scheme 3) in five consecutive runs. The results are
shown in Table 2.
Table 2. Rh-catalyzed hydrogenation of dimethyl itaconate 9
using immobilized complex 1.[a]
Run
Conversion [%]
ee [%]
Rh leaching [ppm][b]
1
2
3
4
5
100
100
100
87
89 (S)
89 (S)
88 (S)
78 (S)
57 (S)
0.83
0.76
0.78
0.67
0.43
78
[a]
In the first run immobilized catalyst 1 shows good
Reaction conditions: solvent CH2Cl2 (5 mL); 228C; H2
1.5 bar; 20 h; substrate/Rh mol ratio 100/1; 0.1 g catalyst. enantioselectivity, although a little lower than that in
[b]
Percentage of total amount of Rh determinated by ICP
of the filtrate.
homogeneous catalysis. Importantly, only 0.83 ppm of
Rh was found in the filtrate, demonstrating that very
little leaching occurs. This result is also of significance
when addressing the question of undesired amounts
BINOL-derived monodentate phosphites which are of transition metals in a reaction product, an issue
not ionic.[1,4] The experiment described in entry 1 of that is often ignored in academic work. Apart from
Table 1 was repeated using the isolated cationic com- this positive result, a decrease in activity after run 3
plex 1 as the catalyst, which resulted in the same cata- was observed, which defines the limitation of this
lytic profile (100% conversion; 94% ee). It is interest- method. However, we were also interested to use a
ing to see that considerable reduction in enantioselec- substrate/Rh mol ratio 1000/1 in order to compare
tivity of the product was observed (Table 1, entry 2) catalytic results which are normally obtained in ho-
when using the ionic liquid [BDMIM]BF4 as solvent, mogeneous reaction. As before, 0.1 g of catalyst was
a phenomenon that was not studied in detail. In this used, but the concentration of substrate 9 was in-
medium the catalyst is completely soluble. It should creased proportionally. Use of immobilized complex 1
be noted that the H2 pressure was not varied, al- and the substrate/Rh mol ratio 1000/1 gave 10 with
though it is known that this parameter in addition to 90% ee in 77% conversion. In this case only
the viscosity of the solvent can effect enantioselectivi- 0.51 ppm of Rh was detected in the filtrate containing
ty.[10] Cationic diamidophosphite L3 provided only the product, which is a significant observation. Con-
moderate enantioselectivity, up to 58% ee.
sistently and in accord with a truly asymmetric heter-
We then turned to immobilization by ionic interac- ogeneous reaction, no catalytic activity was observed
tions between the doubly cationic Rh-containing pre- when using solutions recovered after any of the cata-
catalysts and an appropriate solid support.[11,12] The lytic cycles reported in the present study. Thus, al-
goal of immobilization of homogeneous catalysts on though the solution may contain minute amounts of
supports is to combine the superior activity and selec- Rh, in unknown form, it is not enough to catalyze the
tivity displayed by them with the ease of separation reaction.
and the possibility of recycling the respective hetero-
In further work the novel ligands L1–L3 and their
geneous catalysts. We selected phosphotungstic acid neutral and cationic palladium complexes 3–5 and 6–8
(H3PW12O40) on silica as support material, because were shown to provide excellent enantioselectivities
this is well known for efficient ionic anchoring.[11] The in the asymmetric Pd-catalyzed allylic sulfonylation,
ratio of H3PW12O40 to silica was fixed at 10 wt% het- amination and alkylation processes (Scheme 4,
Scheme 4. Pd-catalyzed enantioselective allylic substitution.
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Table 3. Pd-catalyzed allylic sulfonylation of 15 with p-TolSO2Na (208C, 48 h) and allylic alkylation of 15 with dimethyl mal-
onate (BSA, KOAc, 208C, 48 h).
Entry
Catalyst
L/Pd
Solvent
Conversion [%]
ee [%]
Allylic sulfonylation
1
2
3
4
5
6
7
8
9
[Pd
3
6
[Pd
4
7
[Pd
5
8
N
2/1
1/1
2/1
2/1
1/1
2/1
2/1
1/1
2/1
THF
THF
THF
THF
THF
THF
THF
THF
THF
31[a]
31[a]
73[a]
83[a]
43[a]
20[a]
18[a]
72[a]
0[a]
83 (R)
81 (R)
99 (R)
60 (S)
44 (S)
16 (S)
55 (S)
97 (S)
-
Allylic alkylation
10
11
12
13
14
15
16
17
18
19
20
[Pd
[Pd
4
7
7
[Pd
[Pd
5
5
8
U
2/1
2/1
1/1
2/1
2/1
2/1
2/1
1/1
1/1
2/1
2/1
THF
68
89
60
66
70
46
82
20
0
71 (S)
93 (S)
90 (S)
45 (S)
86 (S)
51 (S)
74 (S)
5 (S)
CH2Cl2
CH2Cl2
THF
CH2Cl2
THF
CH2Cl2
THF
CH2Cl2
THF
-
42
78
83 (S)
84 (S)
8
CH2Cl2
[a]
Isolated yield of product 16.
Table 4. Pd-catalyzed allylic amination of 15 with pyrrolidine and di-n-propylamine.[a]
Entry
Catalyst
L/Pd
Solvent
With pyrrolidine
Conversion [%]
ee [%]
1
2
3
4
5
6
[Pd
4
7
[Pd
5
C
2/1
1/1
2/1
2/1
1/1
2/1
THF
THF
THF
THF
THF
THF
95
83
90
62
45
100
90 (R)
75 (R)
70 (R)
85 (R)
93 (R)
77 (R)
8
With di-n-propylamine
7
8
9
10
11
12
[Pd
4
7
[Pd
5
G
2/1
THF
THF
THF
THF
THF
THF
100
94
70
100
98
98
90 (+)
82 (+)
15 (+)
97 (+)
94 (+)
61 (+)
1/1
2/1
2/1
1/1
2/1
8
[a]
Reactions conditions: 208C, 48 h.
Table 3 and Table 4). Again, the degree of asymmetric markable result which is currently difficult to explain.
induction was found to depend upon the ligand used. Interestingly, catalytic systems with a molar ratio of
Using cationic palladium complex 6 with BINOL- L3/Pd=2 were the least efficient (Table 3, entries 7
based ionic phosphite L1, sulfonylated product 16 was and 9).
obtained in 99% ee, which is the highest enantioselec-
Diamidophosphites L2 and L3 were found to be
tivity described so far using any ligand.[8a,13] (S)-2-Ani- good stereoselectors in the Pd-catalyzed allylic alkyla-
linomethylpyrrolidine-derived diamidophosphite L2 tion of 15 (up to 93 and 84% ee, respectively). Both
gave moderate to poor enantioselectivity (up to results were obtained in CH2Cl2 at a molar ratio of
60%), while its homologue L3 possessing an N-heptyl- L/Pd=2 (Table 3, entries 11 and 20). It should be
imidazolium fragment afforded 97% ee. This is a re- noted that under the conditions of catalytic allylic al-
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kylation comparable to those described for com- Experimental Section
pounds L2 and L3, NCN-derivatives of (1R,2R)-trans-
diaminocyclohexane-based
imidazolium-phosphites General Remarks
provided only 42% ee.[7] Surprisingly phosphite L1
and its palladium complexes 3 and 6 showed low
asymmetric induction (up to 38% ee) in the allylic al-
kylation of 15 with dimethyl malonate and in the al-
lylic amination of 15 with pyrrolidine and di-n-propyl-
amine. These poor results could not be improved de-
spite variation of solvent (CH2Cl2 and THF), molar
ratio L1/Pd (1 and 2) and nature of base (BSA and
Cs2CO3).
In the Pd-catalyzed allylic amination of 1,3-diphe-
nylallyl acetate 15 with pyrrolidine (Scheme 4) in
THF, both ligands L2 and L3 gave 18 with similar
enantioselectivity (90 and 93% ee, respectively;
Table 4, entries 1 and 5).
In allylic amination with di-n-propylamine the li-
gands L2 and L3 provided 90 and 97% ee and quanti-
tative conversion of 15 (THF, L/Pd=2, Table 4, en-
tries 7 and 10). The excellent enantioselectivity
(97%) achieved in this reaction exceeds the best pre-
viously reported result (90% ee) shown by the ana-
logues of L2 and L3 lacking an ionic liquid frag-
ment.[14] Table 3 and Table 4 show that activity (and
enantioselectivity) depend upon the nature of the
ligand, a conclusion noted earlier in other systems.[6]
IR spectra were recorded on a Specord M80 or Nicolet 750
instruments. 31P, 13C and 1H NMR spectra were recorded
with a Bruker AMX 400 instrument (162.0 MHz for 31P,
1
100.6 MHz for 13C and 400.13 MHz for H). Complete as-
signment of all the resonances in 13C NMR spectra was
achieved by the use of DEPT techniques. Chemical shifts
(ppm) are given relative to Me4Si (1H and 13C) and 85%
H3PO4 (31P NMR). Mass spectra were recorded with a
Varian MAT 311 spectrometer (EI) and a Finnigan LCQ
Advantage spectrometer (electrospray ionization technique,
ESI). The rhodium content of the catalyst was determined
by energy-dispersive X-ray analysis (EDX) performed on a
Hitachi S-3500N scanning electron microscope equipped
with an OXFORD EDX system and by inductively coupled
plasma atomic emission (ICP-AES, UNICAM PU 700). Ele-
mental analyses were performed at the Laboratory of Mi-
croanalysis (Institute of Organoelement Compounds,
Moscow). The ionic liquid [BDMIM]BF4 was obtained from
Fluka; it contains ꢁ0.1% water and ꢁ50 mg halogen as
chloride per kg.
Optical yields of product 16 were determined using
HPLC [(R,R)-WHELK-01 column) according to the litera-
ture.[16] Conversion of substrate 15[17] and optical purity of
products 17[17] and 18[18] were determined using HPLC
(Daicel Chiralcel OD-H column) as described previously.
Optical yields of product 19 were determined using HPLC
(Chiralcel OD-H column) according to the literature.[19] All
reactions were carried out under a dry argon atmosphere in
freshly dried and distilled solvents.
Conclusions
Phosphorylating reagents: (Sax)-2-chlorodinaphtho[2,1-
d:1’,2’-f]
G
In summary, we have prepared and characterized the
first representatives of a new class of P-monodentate
phosphite ligands bearing ionic liquid fragments. In
general, they are excellent ligands in Rh-catalyzed
olefin hydrogenation (up to 96% ee) and in Pd-cata-
lyzed allylic substitution (up to 99% ee) in organic
solvents. It is noteworthy that in these processes the
novel cationic ligands are complementary: BINOL-
based phosphite L1 is an excellent stereoselector for
Rh-catalyzed olefin hydrogenation, while (S)-2-anili-
nomethylpyrrolidine-derived diamidophosphites L2
and L3 are more efficient in Pd-catalyzed allylation.
Our results show that the rhodium complex with the
new ligand L1 can be easily immobilized by ionic in-
teraction with a negatively charged support. On the
practical side, this new class of modular P-containing
compounds enlarges the structural diversity of chiral
phosphites and amidophosphites. This means that
they can also be used combinatorially as components
in mixtures of monodentate P ligands.[15] The ligands
are also attractive candidates for other asymmetric
transition metal-catalyzed reactions and for the devel-
opment of reusable catalytic systems, whereby ionic
supports other than the ones used in the present
study need to be considered.[12]
phenyl-1,3-diaza-2-phosphabicyclo[3.3.0]octane were pre-
pared as published.[8a,20] The 1-(2-hydroxyethyl)-3-methylimi-
dazolium tetrafluoroborate and starting substrate 15 were
synthesized as published.[21,22] Dimethyl malonate, BSA
[N,O-bis(trimethylsilyl)acetamide] and sodium p-toluenesul-
finate were commercially available. [Pd
[acacRh(CO)2][23] and [Rh
SiO2 support[11a,f] were synthesized using literature proce-
dures. Rhodium(I) complex 2 was synthesized for the
31P NMR and IR experiments in chloroform, analogously to
the known procedures.[9] The syntheses of palladium(II)
complexes followed techniques similar to that reported.[8a]
Catalytic experiments: allylic sulfonylation of substrate 15
with sodium p-toluenesulfinate, allylic alkylation with di-
methyl malonate, allylic amination with pyrrolidine, and al-
lylic amination with dipropylamine were performed accord-
ing to the appropriate procedures.[8,14]
Preparation of 1-(2-Hydroxyethyl)-3-heptylimi-
dazolium Tetrafluoroborate
A mixture of 1-(2-hydroxyethyl)-3-hepthylimidazolium chlo-
ride (obtained similar to the literature[6] without characteri-
zation) (8.0 g, 0.032 mol), KBF4 (12.6 g, 0.1 mol) and dry
acetonitrile (50 mL) was heated to reflux with stirring for
48 h. Upon cooling, the white precipitate was filtered off
and washed with acetonitrile (3”20 mL). The organic fil-
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trate was concentrated in vacuum to give a liquid product;
yield: 8.0 g (84%). H NMR (400 MHz, CDCl3): d=8.71 (s,
mental analysis: calcd. (%) for C60H56B3F12N4O6P2Rh: C
53.21, H 4.17, N 4.14; found: C 53.27, H 4.20, N 4.11.
1
1H), 7.44 (s, 1H), 7.26 (s, 1H), 5.28 (s, 1H), 4.28 (t, J=
4.6 Hz, 2H), 4.13 (m, 2H), 3.87 (t, 2H), 1.84 (m, 2H), 1.29
(m, 4H), 1.24 (m, 4H), 0.84 (t, 6.8 Hz, 3H); MS (ESI): m/z
(I,%)=211 (100, [MÀBF4]+); elemental analysis (%) calcd.
for C12H23N2OBF4: C 48.34, H 7.78, N 9.4; found: C 48.41,
H 7.81, N 9.37.
Neutral Palladium Complexes
[Pd(allyl)(L1)Cl] (3): White solid; yield: 97%; mp 1208C.
A
31P NMR (CDCl3): d=141.4: MS (ESI): m/z (I,%)=624
(100, [MÀBF4]+), 441 (18, [LÀBF4]+); IR (nujol): n
A
À
Cl)=274 cmÀ1
;
elemental analysis: calcd. (%) for
C29H27BClF4N2O3PPd: C 48.98, H 3.83, N 3.94; found: C
49.02, H 3.87, N 3.90.
General Procedure for Preparation of Ligands
A solution of the appropriate phosphorylating reagent
(2.8 mmol) in CH2Cl2 (15 mL) was added dropwise to a vig-
orously stirred solution of an ionic liquid (2.8 mmol) and
NEt3 (3 mmol) in CH2Cl2 (15 mL). The mixture was stirred
for additional 3 h. The obtained solution was washed with
water (200 mL), dried over Na2SO4, filtered, and concentrat-
ed. The residue was purified by flash chromatography (silica
gel, CH2Cl2) to give the desired product; yields: 40–67%.
[Pd(allyl)(L2)Cl] (4): White solid; yield: 93%; mp 1128C.
R
31P NMR (CDCl3): d=122.2; MS (ESI): m/z (I,%)=514
(24, [MÀBF4]+), 331 (100, [LÀBF4]+); IR (nujol): n
C
À
Cl)=268 cmÀ1
;
C20H29BClF4N4OPPd: C 39.96, H 4.86, N 9.32; found: C
40.01, H 4.89, N 9.30.
[Pd(allyl)(L3)Cl] (5): White solid; yield: 96%; mp 988C.
G
31P NMR (CDCl3): d=122.6 (53%), 122.4 (47%); MS
(ESI): m/z (I,%)=598 (100, [MÀBF4]+), 415 (39,
A
N
[LÀBF4]+); IR (nujol): n
C
pine)oxyethyl}-3-methylimidazolium tetrafluoroborate (L1):
À
White solid; yield: 0.66 g (40%; mp 608C. 31P NMR
(CDCl3): d=140.9; 13C NMR (CDCl3): d=147.7 (d, JC,P
=
2
6.6 Hz), 146.6 (d, 2JC,P =3.3 Hz), 133.5, 133.0, 132.4, 132.1,
131.3, 130.8, 130.5, 130.4, 128.8, 128.3, 128.0, 126.9, 126.7,
126.5, 125.2, 124.3, 123.5, 122.8, 121.3, 121.0, 117.8, 62.1 (d,
Cationic Palladium Complexes
3
2JC,P =8.4 Hz, OCH2), 49.9 (d, JC,P =5.8 Hz, NCH2), 35.7 (s,
[Pd
C
G
NCH3); MS (ESI): m/z (I,%)=441 (100, [MÀBF4]+), 426 (7,
[MÀBF4ÀCH3]+); elemental analysis: calcd. (%) for
C26H22BF4N2O3P: C 59.12, H 4.20, N 5.30; found: C 59.18, H
4.24, N 5.24.
=
120.2 Hz, AB system); MS (ESI): m/z (I,%)=1203 (6,
[MÀBF4]+), 441 (100, [LÀBF4]+); elemental analysis: calcd.
(%) for C55H49B3F12N4O6P2Pd: C 51.18, H 3.83, N 4.34;
found: C 51.23, H 3.87, N 4.31.
A
N
octane)oxyethyl}-3-methylimidazolium
tetrafluoroborate
[Pd
U
A
(L2): White solid; yield: 0.52 g (54%); mp 658C. 31P NMR
(CDCl3): d=122.4; 13C NMR (CDCl3): d=145.2 (d, JC,P
16.0 Hz, CPh), 129.3 (s, CHim), 129.1 (s, CHPh), 123.2 (s,
=
2
3
CHim), 122.8 (s, CHim), 119.1 (s, CHPh), 114.6 (d, JC,P
=
=
[Pd
2
2
12.4 Hz, CHPh), 63.3 (d, JC,P =8.8 Hz, C-5), 59.9 (d, JC,P
848C. 31P NMR (CDCl3): d=115.9 (broad s); elemental
analysis: calcd. (%) for C49H77B3F12N8O2P2Pd: C 47.50, H
6.26, N 9.04; found: C 47.56, H 6.29, N 9.01.
2
5.1 Hz, OCH2), 54.8 (d, JC,P =6.6 Hz, C-4), 50.6 (s, NCH2),
2
48.6 (d, JC,P =37.9 Hz, C-8), 36.0 (s, NCH3), 32.3 (s, C-6),
3
26.2 (d, JC,P =3.6 Hz, C-7); MS (ESI): m/z (I,%)=331 (100,
[MÀBF4]+), 266 (8, [MÀBF4ÀC4H3N]+); elemental analysis:
calcd. (%) for C17H24BF4N4OP: C 48.83, H 5.78, N 13.40;
found: C 48.89, H 5.83, N 13.37.
Immobilization of Complex 1
H3PW12O40/SiO2 support (400 mg) was suspended in 5 mL of
CH2Cl2 and stirred at room temperature for 15 min. The
complex 1 (30 mg) was dissolved in 3 mL of CH2Cl2 and
added to the support suspension. After 3 h of stirring, the
solid was collected by filtration and washed thoroughly with
30 mL portions of CH2Cl2 until the washings were colorless
(approximately 5 times). Finally, the catalyst was dried
under vacuum for 3 h. The resulting catalyst loading was
13.1 mgRh/g.
A
R
octane)oxyethyl}-3-heptylimidazolium
Tetrafluoroborate
(L3): White solid; yield: 0.8 g (67%); mp 588C. 31P NMR
(CDCl3): d=122.1; 13C NMR (CDCl3): d=144.8 (d, JC,P
=
2
15.3 Hz, CPh), 129.8 (s, CHim), 128.8 (s, CHPh), 122.7 (s,
3
CHim), 121.5 (s, CHim),118.7 (s, CHPh), 114.3 (d, JC,P
=
2
11.7 Hz, CHPh), 62.9 (d, JC,P =8.8 Hz, C-5), 59.5 (s, OCH2),
2
54.4 (d, JC,P =7.3 Hz, C-4), 50.3 (s, NCH2), 49.5 (s, NCH2
2
heptyl), 48.0 (d, JC,P =37.9 Hz, C-8), 31.7 (s, C-6), 26.0 (s, C-
7); 31.1, 29.5, 28.1, 25.6 and 22.1 (s, CH2 heptyl), 13.6 (s, CH3);
MS (ESI): m/z (I,%)=415 (100, [MÀBF4]+), 330 (7,
[MÀBF4ÀC6H13]+); elemental analysis: calcd. (%) for
C23H36BF4N4OP: C 54.99, H 7.22, N, 11.15; found: C 55.04,
H 7.27, N 11.12.
Procedure for Hydrogenation in [BDMIM]BF4
A dry autoclave under argon atmosphere was charged with
a
mixture of the rhodium complex 1 (1.25 mg; 2”
10À3 mmol) and 316 mg (2 mmol) of substrate 9 in 2 mL of
[BDMIM]BF4. Hydrogen was blown through, and hydrogen
at 25 bar was introduced. Hydrogenation was subsequently
carried out for 20 h. Following extraction with hexane (3”
5 mL), conversion was determined by gas chromatography
(GC). To determine the ee value, about 1.5 mL of the reac-
Cationic Rhodium Complex
[Rh
U
G
614
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Hydrogenation of dimethyl itaconate with 1 was carried out
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The immobilized catalyst 100 mg was added to a solution of
1.26 mmol of dimethyl itaconate in 5 mL of CH2Cl2. The
heterogeneous catalyst was recycled with standard methods
(the catalyst was filtered off, washed with 3 mL of CH2Cl2
and reused in the next cycle at the same substrate/catalyst
ratio).
Acknowledgements
This work was supported by the INTAS Open Call 2005–
2006 Grant (INTAS Ref. No. 05–1000008–8064) and RFBR
Grant No. 06–03–90898-Mol-a. O.G.B. thanks the Alexander
von Humboldt Foundation for a research fellowship. M.T.R.
also thanks the Fonds der Chemischen Industrie for generous
support.
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