Water-soluble organometallic catalysts from carbohydrates. 2. A strategy for the preparation of catalysts with pendant quaternary ammonium groups using D-salicin

Article abstract of DOI:10.1021/jo001686g

A series of water-soluble chelating bis-phosphinite ligands have been prepared from D-salicin (2-(hydroxymethyl)phenyl β-D-glucopyranoside). The 4- and 6-hydroxyl groups of salicin were protected as a cyclic ketal. Mitsunobu reaction with phthalimide at the benzylic position was used to install the aminomethyl side-chain in the C₁-aromatic substituent. Formation of the bis-2,3-O-diarylphosphinite was accomplished by reaction of the resulting diol with chlorodiarylphosphine. Quaternization with Meerwein's salt (Me₃O⁺ BF₄^-) followed by reaction with Rh⁺(COD)₂ BF₄^- gave precatalysts with limited aqueous solubility. Deprotection of the ketal group with acidic resin in methanol gave water-soluble cationic Rh complexes that are competent to carry out highly efficient hydrogenation of acetamidoacrylic acid derivatives in organic, aqueous, or biphasic media. However, enantioselectivities of these reactions in neat aqueous or biphasic media are generally lower than those observed in organic medium.

Full text of DOI:10.1021/jo001686g

J . Org. Chem. 2001, 66, 3277-3283
3277
Wa ter -Solu ble Or ga n om eta llic Ca ta lysts fr om Ca r boh yd r a tes. 2. A
Str a tegy for th e P r ep a r a tion of Ca ta lysts w ith P en d a n t
Qu a ter n a r y Am m on iu m Gr ou p s Usin g D-Sa licin
Yuan-Yong Yan and T. V. RajanBabu*
Department of Chemistry, The Ohio State University, 100 W. 18th Avenue, Columbus, Ohio 43210
rajanbabu.1@osu.edu
Received November 30, 2000
A series of water-soluble chelating bis-phosphinite ligands have been prepared from D-salicin (2-
(hydroxymethyl)phenyl â-D-glucopyranoside). The 4- and 6-hydroxyl groups of salicin were protected
as a cyclic ketal. Mitsunobu reaction with phthalimide at the benzylic position was used to install
the aminomethyl side-chain in the C1-aromatic substituent. Formation of the bis-2,3-O-diarylphos-
phinite was accomplished by reaction of the resulting diol with chlorodiarylphosphine. Quater-
nization with Meerwein’s salt (Me3O+ BF4-) followed by reaction with Rh+(COD)2 BF4 gave
-
precatalysts with limited aqueous solubility. Deprotection of the ketal group with acidic resin in
methanol gave water-soluble cationic Rh complexes that are competent to carry out highly efficient
hydrogenation of acetamidoacrylic acid derivatives in organic, aqueous, or biphasic media. However,
enantioselectivities of these reactions in neat aqueous or biphasic media are generally lower than
those observed in organic medium.
In tr od u ction
diarylphosphinite-Rh complexes derived from phenyl
â-D-glucopyranoside for asymmetric hydrogenation of
dehydroamino acids in water.4 In an attempt to circum-
vent the limited solubility of monosaccharide-derived
ligands we5 and others6 have resorted to disaccharides
such as trehalose (1-glucopyranosyl glucopyranoside) as
ligand precursors, with the expectation that increased
number of hydroxyl groups would improve solubility in
water. Indeed very high enantioselectivities were achieved
for such a catalyst in the Rh-catalyzed asymmetric
hydrogenations in aqueous medium. Our investigations
of the partition coefficient for these Rh-complexes be-
tween organic solvents and water (by ion-coupled plasma
method) also revealed that despite the increased number
of hydroxyl groups, the disaccharide-derived Rh(1) com-
plexes (e.g., 1) still possessed considerable solubility in
organic solvents.5 Alternatively, use of tetraalkylammo-
Of the various strategies for solubilizing an organo-
metallic catalyst in water, use of a carbohydrate scaf-
folding for the attachment of the metal has the distinct
advantage that the backbone incorporates easily tunable
chiral elements.1 Consequently, under optimum condi-
tions, reactions catalyzed by such complexes can be
expected to be stereoselective. Use of the highly hydro-
philic, polyhydroxylic backbone also helps circumvent
some of the problems associated with the sulfonation
protocol often used to prepare water-soluble ligands.2 A
number of different procedures have been used to attach
catalytically active metal ions to carbohydrates.3-7 In
their pioneering work, Selke and co-workers used vicinal
(1) For general reviews on the subject of aqueous organic chemistry,
see: (a) Sinou, D. Bull. Soc. Chim. Fr. 1986, 480. (b) Kunz, E. G.
Chemtech 1987, 570. (c) Herrmann, W. A.; Kohlpaintner, W. Angew.
Chem., Int. Ed. Engl. 1993, 32, 1524. (d) Aqueous Organometallic
Chemistry and Catalysis; Horva´th, I. T., J oo´, F., Eds.; Kluwer:
Dodrecht, 1995. (e) For thematic issues dedicated to applications of
water-soluble organometallic compounds, see: J . Mol. Catal. A.: Chem.
1997, 116 (1,2), 1-309. Catal. Today, 1998, 42(4), 371-478. For
outstanding examples of the use of water-soluble organometallic
catalysts in fine chemical synthesis, see: (f) Casalnuovo, A. L.;
Calabrese, J . C. J . Am. Chem. Soc. 1990, 112, 4324 and references
therein. (g) Wan, K. T.; Davis, M. E. Nature 1994, 370, 449 and
references therein.
(2) For a discussion of these problems and a solution, see: (a) Ding,
H.; Hanson, B. E.; Bakos, J . Angew. Chem., Int. Ed. Engl. 1995, 34,
1645 and references therein. (b) Hanson, B. E. Coord. Chem. Rev. 1999,
185-186, 795.
(3) For other examples of the use of carbohydrates for the prepara-
tion of water-soluble phosphines, see: (a) Mitchell, T. N.; Heesche-
Wagner, K. J . Organomet. Chem. 1992, 436, 43. (b) Sawamura, M.;
Kitayama, K.; Ito, Y. Tetrahedron: Asymmetry 1993, 4, 1829. (c) Beller,
M.; Krauter, J . G. E.; Zapf, A. Angew. Chem., Int. Ed. Engl. 1997, 36,
772. See also: (d) Ferrara, M. L.; Orabona, I.; Ruffo, F.; Funicello, M.;
Panunzi, A. Organometallics 1998, 17, 3832.
nium moiety for the preparation of chiral water-soluble
phosphine ligands have been explored by Nagel8a and
Hanson,8b and some of the resulting quaternized deriva-
tives of Rh+-complexes of BDDP, Chiraphos, and DIOP
have been described as having “unlimited water solubil-
ity”. We wondered whether such a strategy could be
(4) (a) Kumar, A.; Oehme, G.; Roque, J . P.; Schwarze, M.; Selke, R.
Angew. Chem., Int. Ed. Engl. 1994, 33, 2197 and references therein.
(b) Selke, R. J . Organomet. Chem. 1989, 370, 241; also p 249.
(5) Shin, S.; RajanBabu, T. V. Org. Lett. 1999, 1, 1229.
(6) Yonehara, K.; Hashizume, T.; Ohe, K.; Uemura, S. J . Org. Chem.
1999, 64, 5593, 9381.
(7) Some more recent examples: (a) Holz, J .; Heller, D.; Stu¨rmer,
R.; Bo¨rner, A. Tetrahedron Lett. 1999, 40, 7059. (b) Selke, R.; Holz, J .;
Riepe, A.; Bo¨rner, A. Chem. Eur. J . 1998, 4, 769. (c) Li, W.; Zhang, Z.;
Xiao, D.; Zhang, X. J . Org. Chem. 2000, 65, 3489.
(8) (a) Nagel, U.; Kinzel, E. Chem. Ber. 1986, 119, 1731. (b) To´th,
I.; Hanson, B. E. Tetrahedron Asymmetry 1990, 1, 895.
10.1021/jo001686g CCC: $20.00 © 2001 American Chemical Society
Published on Web 04/18/2001

3278 J . Org. Chem., Vol. 66, No. 10, 2001
Yan and RajanBabu
Sch em e 1. D-Glu cose-Der ived P h osp h in ites for th e
Syn th esis of Am in o Acid s9b,c
Instead of the expected Rh complex 11, a mixture of
products was obtained as indicated by the 31P NMR (eq
2). Instead of the doublet of doublet (J Rh-P and J P-P
)
usually observed for each of the phosphorus atoms in a
typical bis-phosphinite chelate, a multitude of peaks,
including one large doublet (J Rh-P ) 172 Hz), were
observed. As subsequent experiments (vide infra) would
show, the presence of the dimethylamino group, which
can act as a chelating group is most probably responsible
for this complication. Quaternization of the amine with
Meerwien’s salt produces 8, which was converted into the
Rh complex 9 without any problems. However, the robust
benzylidene protecting group, which survives the form-
aldehyde/formic acid reaction for the dimethylamine
synthesis, could not be removed without destroying the
complex, and alternate protecting group strategy4,5 was
developed for the synthesis of the unprotected precatalyst
10.
employed in connection with the remarkably successful
sugar phosphinite ligands which have been found to have
wide applications in asymmetric catalysis.9 For example,
we have shown that cationic Rh-complexes of D-glucose-
derived ligands can be used to prepare both R and S
amino acid derivatives in (ee 97-99%) depending on the
juxtaposition (2,3 or 3,4) of the diarylphosphinoxy groups
(Scheme 1).9b,9c Highest recorded enantioselectivity for
asymmetric hydrocyanation reaction of olefins was
achieved using Ni(0)-complexes of structurally related
sugar phosphinites.9d,9e In this paper we report the details
of the synthesis of bis-phosphinite ligands with pendant
quaternary ammonium groups starting with a readily
available monosaccharide, D-salicin (2-hydroxymethyl-
phenyl â-D-glucopyranoside, 2). Preliminary results on
the applications of these ligands in Rh-catalyzed hydro-
genation of acetamidoacrylic acid derivatives are also
reported.
The replacement of the 4,6-O-benzylidene protecting
group with a more labile isopropylidene group was
carried out by substituting 2,2-dimethoxypropane for
dimethoxytoluene in the initial protection scheme. The
isopropylidene derivative 3b was converted into the
benzylamine 5b as described before. Reductive amination
with formaldehyde and NaB(CN)H3 gave the tertiary
amine 6b. Formation of the bis-diarylphosphinites and
the corresponding Rh(1)-complexes (13a , 13b, and 13c)
proceeded without any complications (Scheme 3). The
isopropylidene group is easily removed by treatment with
acidic resin (AG 50 WX-8) in methanol5 to liberate the
unprotected complexes 10a , 10b, and 10c which were
subsequently used for catalytic studies.
Resu lts a n d Discu ssion
Hyd r ogen a t ion St u d ies. Since the Rh-catalyzed
hydrogenation of dehydroamino acid derivatives has
received more attention than any other asymmetric
reactions conducted in an aqueous medium, we chose this
system for our initial study.4-8,9a-c,10 Hydrogenation reac-
tions of a variety of methyl R-acetamidoacrylic acid
derivatives were conducted as described in our earlier
publications,9c and the results are shown in Tables 1-4.
The substrates chosen for this study have generally been
found to give lower selectivities compared to the more
commonly studied methyl R-acetamidocinnamate.9a-c In
addition, use of the bis-diarylphosphinite ligands with
these substrates permits an examination of the effect of
P-Ar substituents on the hydrogeantion selectivity. Recall
that we had established a strong electronic effect of the
ligands on the enantioselectivity of these reactions.9b,11
Typically 0.1 mmol of the substrate was dissolved in the
solvent in a Fischer-Porter tube, and to this was added
0.01 equiv of the preformed cationic Rh-catalyst. The tube
was sealed while inside the drybox and it was degassed
thoroughly. The reaction vessel was charged with ∼40
F u n ction a liza tion of D-Sa licin . A general route to
convert salicin to the 4,6-dialkylidene-protected deriva-
tive with a dimethylaminomethyl side-chain is shown in
Scheme 2. Treatment of salicin with 1,1-dimethoxytolu-
ene under acidic conditions produced the acetal 3a which
was readily converted into the phthalimido-derivative 4a
by a selective Mitsunobu reaction at the more reactive
benzylic position. The amino group was liberated by
treatment of 4a with hydrazine hydrate. Installation of
the dimethylamino group is accomplished by reaction of
5a with formic acid and formaldehyde. The diol 6a thus
produced was readily converted into the bis-diarylphos-
phinites through the dipotassium salt. The first huddle
in projected synthesis of the Rh complex appeared when
the diphosphinite 7a was treated with Rh+(COD)2 SbF6
.
-
(9) Applications of sugar phosphinites in asymmetric catalysis. Rh-
catalyzed hydrogenations: (a) Selke, R. React. Kinetic. Catal. Lett.
1979, 10, 135. (b) RajanBabu, T. V.; Ayers, T. A.; Casalnuovo, A. L. J .
Am. Chem. Soc. 1994, 116, 410. (c) RajanBabu, T. V.; Ayers, T. A.;
Halliday, G. A.; You, K. K.; Calabrese, J . C. J . Org. Chem. 1997, 62,
6012. Ni-catalyzed hydrocyanation: (d) Casalnuovo, A. L.; RajanBabu,
T. V.; Ayers, T. A.; Warren, T. H. J . Am. Chem. Soc. 1994, 116, 9869.
(e) RajanBabu, T. V.; Casalnuovo, A. L. J . Am. Chem. Soc. 1996, 118,
6325. Hydroformylation: (f) RajanBabu, T. V.; Ayers, T. A. Tetrahedron
Lett. 1994, 35, 4295. Hydrovinylation: (g) Park, H.; RajanBabu, T. V.
Unpublished results. Pd-catalyzed allylation: (h) Clyne, D.; Mermet-
Bouvier, Y. C.; Nomura, N.; RajanBabu, T. V. J . Org. Chem. 1999, 64,
7601.
(10) For a comprehensive review, see: Chaloner, P. A.; Esteruelas,
M. A.; J oo´, F.; Oro, L. A. In Homogeneous Hydrogenation; Noels, A.
F., Grazini, M., Hubert, A. J ., Ed.; Kluwer Academic: Dordrecht, 1994;
p 183.
(11) RajanBabu, T. V.; Radetich, B.; You, K.; Ayers, T. A.; Casaln-
uovo, A. L.; Calabrese, J . C. J . Org. Chem. 1999, 64, 3429.

Catalysts with Pendant Quaternary Ammonium Groups
J . Org. Chem., Vol. 66, No. 10, 2001 3279
Sch em e 2. F u n ction a liza tion of Sa licin
Sch em e 3. Syn th esis of Wa ter -Solu ble Rh -P h osp h in ite Com p lexes fr om Sa licin
Ta ble 2. Hyd r ogen a tion of Aceta m id oa cr yla tes Usin g
Ta ble 1. Asym m etr ic Hyd r ogen a tion of
Ca ta lysts 13a , 13b, a n d 13ca
Aceta m id oa cr yla tes Usin g Ca ta lysts 9a a n d 9ba
enantioselectivity/sub:cat ratio
enantioselectivitye
substrate R
in eq 1
entry
solvent
THF
MeOH
EtOH
H2O
13a
13b
13c
substrate
catalyst 9a catalyst 9b
entry solvent (R in eq 1) conversion
(9c)
(9d )
1
2
3
4
5
6
7
8
9
H
H
H
H
H
87/150
54/150
-
93/100
37/100
89/100
2/100b
2/100
97/150
7/100
96/100
95/100
0/150
-
1
2
3
4
5
6
7
THF
THF
THF
THF
THF
THF
H2O
2-F-C6H4
3-F-C6H4
3-Br-C6H4
2-thienyl
3-thienyl
H
100
100
100
-
66 (89)
63 (89)
74 (89)
26 (85)
28 (87)
86 (-)
14 (-)
94 (97)
96 (97)
95 (97)
80 (96)
92 (97)
90 (97)
-
-
53/150
-
b
c
H2O/EtOAcc 6/100
-
Ph
Ph
THF
-
-
-
-
-
-
H2O/EtOAcc
-
100
3-Br-C6H4 THF
3-F-C6H4 THF
-
H
100d
2/100
a
Conditions: 2 mL solvent/0.1 mL substrate, 40 psi H2, rt, 3 h.
a
b
b
Conditions: 2 mL solvent/0.1 mL substrate, 40 psi H2, rt. At
35% conversion (12 h) % ee is 57.8. c 1:1 ratio.
For catalyst 9a and 9b, 91% and 28% conversions, respectively.
c 86% and 68%, respectively. Reaction time 19 h. e Determined
by GC; in brackets are ee’s for 9c and 9d , the Rh complexes
without the [CH2NMe3]+ side-chain in the aglycone.
d
Finally the tube was charged with 40 psi of hydrogen,
and the mixture was stirred vigorously at room temper-
ature for the times indicated. At the end of the reaction,
the tube was vented, and the product was extracted into
psi of hydrogen and was subsequently evacuated. This
operation of filling and evacuation was done three times.

3280 J . Org. Chem., Vol. 66, No. 10, 2001
Yan and RajanBabu
Ta ble 3. Effect of Wa ter Con ten t in Asym m etr ic
Hyd r ogen a tion of Meth yl r-Aceta m id oa cr yla te (R ) H in
eq 1) Usin g Ca ta lysts 13ba
acetate/water mixtures leads to significant deterioration
of enantioselectivity (Table 2, column 5), even though
quantitative conversions are still observed. The surpris-
ing observation that methanol is a better solvent than
the biphasic combinations of water and ethyl acetate has
been made before,2,5,6 and this observation does not
portend well for the use of this technique for immobiliza-
tion of the catalyst. Use of the bis(3,5-bis(trifluorometh-
yl)phenyl)phosphinite-Rh complex 13c, even in THF
gave nearly racemic products (entries 1 and 9). In
previous studies of the electronic effects of phosphinite
ligands we had noticed this remarkable trend with the
CF3-substituent.9c,11
entry
solvent
sub./cat. time (h) conv ee %
1
2
3
4
5
6
7
8
9
THF
EtOH
100
150
100
100
100
100
150
100
150
150
3
1
2
3
7
3
3
21
12
1
100
100
100
100
100
100
100
100
35
93
89
87
37
90
74
57
2
H2O/THF (3:1)
MeOH
MeOH/ H2O (1:1)
MeOH/ H2O (1:3)
MeOH/ H2O (1:20)
H2O
H2O
H2O/EtOH (1:1)
58
85
10
100
a
Conditions: 2 mL solvent/0.1 mL substrate, 40 psi H2, rt, 3 h.
The enantioselectivities of these reactions were found
to depend on the solvent and reaction time. We were
intrigued by this variation of selectivities observed with
13b. Results of a study of solvent effect using this ligand
are shown in Table 3. Reactions done in THF gave the
highest ee, with ethanol a close second. Aqueous THF is
an acceptable solvent, where as neat methanol or water
are not. Selectivity in methanol appears to be a function
of the amount of water present; as the mole fraction of
water increases the ee drops from 90% to 57% (entries
5-8). When reactions have to be run longer to effect
higher conversions in water, nearly racemic products
(entry 8) are obtained. At low conversions (short reaction
times) higher ee of the product (up to 58%) is observed
(entry 9). One possibility is that the primary product
undergoes racemization in water (vide infra, Table 4). As
for the longer reaction times in water, even with the
quaternary ammonium group, it is likely that these
complexes with the hydrophobic 4,6-benzylidene or iso-
propylidene protecting groups are not completely soluble
in water,12 and hence the need for longer reaction times.
The solubility of the catalyst can be improved by
removing the isopropylidene protecting group from 13b.
When the protecting group is completely removed, mak-
ing the catalyst totally soluble in water, the hydrogena-
tion can be completed in less than 60 min and conse-
quently higher ee’s can be realized (entry 1, Table 4,
compare to entry 8 in Table 3). However, if the product
is left in contact with water for longer periods of time
under the reaction conditions, enantioselectivity drops
off precipitously (entries 3 and 4), another indication that
some racemization is possible in water. The completely
deprotected derivative 10b has sufficient solubility in
THF to effect complete reduction of acetamidoacrylic acid
(ee 86%) in ∼60 min at 1 mol % catalyst loading (entry
4, Table 4). Note that the corresponding protected deriva-
tive under similar conditions gives an ee of 93% (entry
1, Table 3). One possible explanation for the deterioration
of enantioselectivity in water is the intervention of
protonolysis of the putative Rh-C bond before the final
reductive elimination.13 Since significant R-deuterium
incorporation has been observed in reactions run in D2O-
containing media,13,5 it has been suggested that Rh-H/
Rh-D exchange could also take place in the penultimate
intermediate in the catalytic cycle. The exact mechanism
Ta ble 4. Asym m etr ic Hyd r ogen a tion of Meth yl
r-Aceta m id oa cr yla te (R ) H in eq 1) Usin g Ca ta lysts 10ba
entry
solvent
sub./cat. time (h) conversion ee %
1
2
3
4
H2O
150
100
100
150
1
3
3
1
100
99
95
61
8
5
H2O (run 1)
H2O (run 2)
THF
100
86
a
Conditions: 2 mL solvent/0.1 mL substrate, 40 psi H2, rt.
ether or chloroform and analyzed by gas chromatography.
The ee’s reported are based on chiral GC analysis where
baseline separation of the two isomers was observed. The
reproducibility of the measurements of ee’s based on the
integration of the areas under the appropriate peaks is
(0.3%. Accordingly, only two significant figures are
reported for the ee’s.
The enantioselectivity for the hydrogenation of several
dehydroamino acids using the 4,6-benzylidene-protected
precatalysts 9a and 9b are shown in Table 1. Shown in
brackets in the last column are the values for the
corresponding Rh-complexes (9c and 9d )9b without the
Me3N+CH2 side-chain of the aglycone. In all cases a
quantitative reaction ensues giving the R-amino acid
ester. As expected from our previous studies,9c in each
case, the catalyst carrying the 3,5-dimethyl substituents
on the P-aryl groups shows an increased selectivity. The
pendant quaternary ammonium group appears to have
some effect on the enantioselectivity of the Rh-catalyzed
hydrogenation reaction, the effect being dependent on the
nature of the P-aromatic substituent. In general the ee’s
are lower for the ammonium derivatives. The difference
is more pronounced in the case of simple diphenylphos-
phinite ligands (9a vs 9c) as compared to the 3,5-
dimethylphenylphosphinite derivatives (9b vs 9d ). The
catalyst 9a has sufficient solubility in water to be able
to effect the hydrogenation of R-acetamidocinnamate in
quantitative yield (entry 7). However, the reactivity (19
h to complete the reaction) and enantioselectivity re-
mains unacceptably poor.
(12) Even though we have not carried out any quantitative studies
on the solubilities of these and related compounds in water, an
indication of the solubility can be gleaned from the attempts to run
31P NMR spectra of 10a (the completely deprotected complex). Com-
pared to 13a (in CDCl3) a saturated solution of 10a in water takes a
minimum of 5 times longer to provide a satisfactory 31P NMR of with
similar signal-to-noise ratio. Even the deprotected derivatives therefore
appear to have limited solubility in water.
Rhodium complexes 13a , 13b, and 13c (Scheme 3) with
the 4,6-di-O-isopropylidene protecting groups behave
similarly. Hydrogenations of methyl R-acetamidoacrylate
and various R-acetamidocinnamates in THF (Table 2,
entries 1, 6, 8, and 9) using 13b give ee’s comparable to
9b. Use of these complexes in methanol, water, or ethyl
(13) Laghmari, M.; Sinou, D. J . Mol. Catal. 1991, 66, L15.

Catalysts with Pendant Quaternary Ammonium Groups
J . Org. Chem., Vol. 66, No. 10, 2001 3281
(28 µL) was added to neutralize the acid, and the solvent was
removed on a rotary evaporator. The crude product was
purified by silica gel column chromatography, eluting with
EtOAc:hexane (5:1) to get 1.326 g (71%) of 3a as a white
of this reaction and its stereochemical consequences
remain unknown. A further complication in the resolu-
tion of this issue is that the extent of D-incorporation is
dependent on the ligand and solvent.14
1
powder. Mp: 203-204 °C. H NMR (CDCl3): δ 2.36 (b s, 3H),
Sta bility of Dia r ylp h osp h in ite Com p lex 10a in
Wa ter . A saturated solution of 10a in D2O was pre-
pared,12 and the deterioration of the complex was followed
by the disappearance of the characteristic doublet of
doublets for each phosphorus signals (P1: 124.40, dd,
J Rh-P1 ) 174; J P1-P2 ) 33; P2: 131.94, dd, J Rh-P2 ) 173;
J P1-P2 ) 33. There was very little change in the spectrum
in 24 h, clearly showing that under the hydrogenation
reaction conditions, the Rh-complexes were surprisingly
stable. Some discernible degradation (<10%) could be
observed after 96 h. At the end of 216 h, more than 50%
of the complex had undergone decomposition, with ap-
pearance of new signals in the 31P NMR spectrum at δ
36.72 and 36.35.
3.56-3.67 (m, 2H), 3.78-3.90 (m, 3H), 4.38-4.45 (m, 2H),
4.86-4.94 (m, 2H), 5.56 (s, 1H), 7.04-7.32 (m, 4H), 7.34-7.40
(m, 3H), 7.48-7.52 (m, 2H).
4,6-O-(1-Meth yleth ylid en e)-D-sa licin (3b). A dry 150 mL
round-bottomed flask was charged with 2.86 g (10.0 mmol) of
D-salicin in 80 mL of distilled acetonitrile. To the heteroge-
neous mixture was added 68 mg of p-toluenesulfonic acid
followed by 1.47 mL (12 mmol) of 2,2-dimethyoxypropane.
After 2 h, a homogeneous solution was formed. Neat triethyl-
amine (56 µL) was added to neutralize the acid, and the solvent
was removed on a rotary evaporator. The crude product was
purified by silica gel column chromatography eluting with
EtOAc:hexane (3:1) to get 2.335 g (72%) of 3b as a white
powder. 1H NMR (DMSO-d6): δ 1.34 (s, 3H), 1.45 (s, 3H), 3.42
(m, 4H), 3.70 (t, J ) 10.1 Hz, 1H), 3.83 (dd, J ) 5.0, 10.4 Hz,
1H), 4.47 (dd, J ) 6.1, 14.4 Hz, 1H), 4.65 (dd, J ) 5.5, 14.3
Hz, 1H), 4.97 (m, 2H), 5.25 (d, J ) 4.3 Hz, 1H), 5.55 (d J ) 4.3
Hz, 1H), 7.04 (m, 2H), 7.20 (ddd, J ) 1.6, 7.7, 15.4 Hz, 1H),
7.38 (dd, J ) 1.0, 7.4 Hz, 1H). 13C NMR(DMSO-d6): δ 19.13,
29.09, 48.65, 58.16, 61.48, 66.81, 73.09, 74.38, 98.85, 101.55,
114.72, 121.97, 127.27, 127.66, 131.64, 154.32.
Con clu sion s
We have discovered new synthetic routes to water-
soluble, chiral vicinal bis-diarylphosphinite complexes
starting with a readily available carbohydrate precursor,
D-salicin. The Rh-complexes of these ligands are compe-
tent to carry out highly efficient asymmetric hydrogena-
tion of acetamidoacrylic acid derivatives in organic,
aqueous or biphasic media. However, enantioselectivities
of these reactions in a neat aqueous or biphasic media
are generally lower than those observed in organic
medium, raising serious doubts about the viability of this
technique for catalyst recovery. Reactions where such
recovery of the catalyst is not an issue could still benefit
from this new strategy for solubilizing organometallic
reagents. Potential examples of this include reactions of
substrates that are mostly soluble in water. Explorations
along these lines will be reported in the future.
2-(P h th a lim id om eth yl)p h en yl 4,6-O-(P h en ylm eth yli-
d en e)glu cop yr a n osid e (4a ). In a drybox, to a solution of 4.97
g of 3a , 1.95 g of phthalimide, and 3.48 g of triphenylphosphine
in 80 mL of anhydrous THF was slowly added a solution of
2.31 g of diethyl azodicarboxylate (abbreviated as DEAD) in
20 mL of the same solvent. The orange color of DEAD
disappeared after each drop, and a thick white precipitate
formed. The mixture was stirred at room temperature for 24
h and then brought out of drybox. The solvent was removed
on a rotary evaporator. The residue was dissolved 350 mL of
hot ethyl acetate, filtered, washed three times with ethyl
acetate, and dried under high vacuum overnight. After column
chromatography eluting with CHCl3/CH3OH (40:1), the prod-
1
uct was obtained 4a as a white solid (5.40 g, 83%). H NMR
(CDCl3): δ 3.69 (m, 2 H), 3.83 (m, 2 H), 3.97 (m, 1 H), 4.42
(dd, J ) 4.4, 10.4 Hz, 1 H), 4.49 (m, 3 H), 5.58 (s, 1 H), 7.08
(m, 2 H), 7.27 (m, 1 H), 7.37 (m, 3 H), 7.52 (m, 2 H), 7.60 (m,
1 H), 7.72 (m, 2 H), 7.81 (m, 2 H). Anal Calcd for C28H25NO8:
C 66.79; H 5.00; N 2.78. Found, C 63.24; H 4.98; N 2.61.
Exp er im en ta l Section
Gen er a l. All anaerobic reactions were carried out in an
2-(P h t h a lim id om et h yl)p h en yl 4,6-O-(1-Met h ylet h yli-
d en e)glu cop yr a n osid e (4b). In a drybox, to a solution of 2.51
g (7.69 mmol) of 3b, 1.13 g of phthalimide, and 2.02 g of
triphenylphosphine in 50 mL of anhydrous THF was added
dropwise a solution of 1.34 g of DEAD in 5 mL of the same
solvent. The orange color of DEAD disappeared after each
drop. The mixture was stirred at room-temperature overnight
and then brought out of drybox. The solvent was removed on
a rotary evaporator. The residue was purified by column
chromatography on silica gel, eluting with EtOAc/Hexanes (6:
4), to get 3.24 g (93%) of 4b as a white solid. 1H NMR
(CDCl3): δ 1.46 (s, 3H), 1.52 (s, 3H), 3.46 (m, 1H), 3.76 (m,
4H), 3.96 (dd, J ) 5.3, 10.7 Hz, 1H), 4.87 (m, 3H), 7.03 (m,
2H), 7.24 (m, 1H), 7.55 (dd, J ) 1.6, 7.5 Hz, 1H), 7.65 (m, 2H),
7.78 (m, 2H). 13C NMR (CDCl3): δ 19.22, 29.20, 37.17, 62.21,
67.79, 73.05, 73.24, 74.65, 77.44, 100.04, 102.36, 115.03,
123.12, 123.58, 124.88, 130.02, 132.06, 132.40, 134.32, 155.41,
168.71.
2-(Am in om eth yl)p h en yl 4,6-O-(P h en ylm eth ylid en e)-
glu cop yr a n osid e (5a ). A 15 mL glass autoclave was charged
with 0.503 g of 4a , 99 µL of hydrazine monohydrate (98%),
and 6 mL of anhydrous ethanol. The mixture was stirred in
120 °C oil bath for 5 h. The crude product was dissolved in 50
mL of warm ethanol and then filtered. The filtrate was
evaporated, and the residue was purified by column chroma-
tography eluting with CHCl3/CH3OH/Et3N (100:10:1), to get
0.298 g (68%) of 5a as a white powder. 1H NMR (CDCl3): δ
2.75 (s, 4H), 3.68-3.75 (m, 3H), 3.82-3.93 (m, 3H), 4.13-4.17
(m, 1H), 4.44-4.47 (m, 1H), 4.85-4.88 (m, 1H), 5.59 (s, 1H),
inert atmosphere of nitrogen in
a Vacuum Atmospheres
drybox, or using Schlenk techniques. Methylene chloride was
distilled from calcium hydride under nitrogen and stored over
4 Å molecular sieves. Tetrahydrofuran (THF) and diethyl ether
were distilled under nitrogen from sodium/benzophenone ketyl.
All chemicals were purchased from Aldrich Chemical Co.
unless otherwise noted. Analytical TLC was done on E. Merck
precoated (0.25 mm) silica gel 60 F254 plates. Column chro-
matography was conducted by using silica gel 40 (Scientific
Adsorbents Incorporated, Microns Flash). 1H NMR spectra
were recorded in CDCl3 unless otherwise mentioned. Gas
chromatographic (GC) analyses were performed on a chro-
matograph equipped with an HP-ultra-1 cross-linked methyl
silicone capillary column (25 m length H 0.2 mm i.d.) and an
FID detector with helium as carrier gas. The ee’s of the
products were determined by chiral GC (Chirasil-L-Val on
WCOT fused silica 25m × 0.25 mm).
4,6-O-P h en ylm eth ylid en e-D-sa licin (3a ). A dry 100 mL
round-bottomed flask was charged with 1.43 g (5.0 mmol) of
D-salicin in 25 mL of distilled acetonitrile. To the heteroge-
neous mixture was added 30 mg of p-toluenesulfonic acid
followed by 0.90 mL (6.0 mmol) of 1,1-dimethyoxytoluene. After
2 h, a homogeneous solution was formed. Neat triethylamine
(14) Other studies of the solvent effects on Rh-catalyzed asymmetric
hydrogenation: Lecomte, L.; Sinou, L.; Bakos, J .; To´th, I.; Heil, B. J .
Organomet. Chem. 1989, 370, 277. See also: Bakos, J .; Karaivanov,
R.; Laghmari, M.; Sinou, D. Organometallics 1994, 13, 2951. Sinou,
D.; Amrani, Y. J . Mol. Catal. 1986, 36, 319.

3282 J . Org. Chem., Vol. 66, No. 10, 2001
Yan and RajanBabu
7.02-7.06 (m, 1H), 7.14-7.21 (m, 2H), 7.26-7.30 (m, 1H),
7.36-7.38 (m, 3H), 7.50-7.52 (m, 2H).
purified by flash chromatography, eluting with ether/hexane
(1:1) and Et3N (3%), to get 0.381 g (89%) of 7a as a white
powder. 31P NMR (CDCl3): δ 113.69 (d, J P-P ) 3 Hz), 116.59
(d, J P-P ) 3 Hz).
2-(Am in om et h yl)p h en yl 4,6-O-(1-Met h ylet h ylid en e)-
glu cop yr a n osid e (5b). A 15 mL glass autoclave was charged
with 0.455 g (1.0 mmol) of 4b, 99 µL of hydrazine monohydrate
(98%), and 6 mL of anhydrous ethanol. The mixture was
stirred in a 115 °C oil bath for 5 h. The crude product was
dissolved in 50 mL of warm ethanol and then filtered. The
filtrate was evaporated, and the residue was purified by
column chromatography eluting with CHCl3/CH3OH (10:1), to
2-(Dim eth yla m in om eth yl)p h en yl 2,3-Di-O-(bis(3,5-d i-
m et h ylp h en yl)p h osp h in o)-4,6-O-(p h en ylm et h ylid en e)-
glu cop yr a n osid e (7b). Compound 7b was prepared by a
route similar to the previous experiment for the synthesis of
7a using bis(3,5-dimethylphenyl)chlorophosphine instead of
chlorodiphenylphosphine. Yield: 76%. 31P NMR (CDCl3): δ
114.99 (d, J p-p ) 3 Hz), 120.34 (d, J P-P ) 3 Hz).
1
get 0.280 g (86%) of 5b as a white powder. H NMR (CDCl3):
-
δ 1.43 (s, 3H), 1.48 (s, 3H), 3.31 (m, 1H), 3.59-3.97 (m, 6H),
4.21 (d, J ) 12.4 Hz, 1H), 4.67 (d, J ) 7.4 Hz, 1H), 6.56 (s,
2H), 6.87-7.03 (m, 2H), 7.13-7.23 (m, 2H), 7.48 (b s, 1H), 7.90
(b s, 1H).
Th e Ca tion ic Rh od iu m Com p lex, (COD)Rh +[8] SbF 6
(Ar ) 3,5-d im eth ylp h en yl) (9b). In a drybox, to a suspension
of 17.7 mg (0.12 mmol) of trimethyloxonium tetrafluoroborate
in 1 mL of anhydrous CH2Cl2 was added 105.8 mg (0.12 mmol)
of 7b in 1 mL of the same solvent and stirred overnight at
room temperature. To the reaction mixture was added a
2-(Dim eth yla m in om eth yl)p h en yl 4,6-O-(P h en ylm eth -
ylid en e)glu cop yr a n osid e (6a ). To a 25 mL of round-bottom
flask was added 0.220 g of 5a in 2 mL of THF. The flask was
cooled in an ice bath and 87 µL of formic acid was slowly added
followed by 150 µL of formaldehyde. The flask was equipped
with a magnetic stirrer and a condenser and placed in a 78
°C oil bath for 24 h. The mixture was cooled and made basic
with 25% aqueous sodium hydroxide, and the product was
extracted three times with 15 mL portions of ether. The ether
layers were combined, washed with brine (3 mL), and then
dried over anhydrous magnesium sulfate. The solvent was
removed under rotary evaporator. The crude product was
purified by silica gel column chromatography eluting with
CHCl3/CH3OH (20:1), to obtain 0.175 g (76%) of 6a as a white
solid. MP. 158-160 °C; 1H NMR (CDCl3): δ 2.21 (s, 6 H), 2.87
(d, J ) 11.8 Hz, 1 H), 3.63 (m, 2 H), 3.75 (t, J ) 8.2 Hz, 1 H),
3.84 (t, J ) 8.6 Hz, 1 H), 3.88 (t, J ) 9.9 Hz, 1 H), 4.11 (d, J
) 11.9 Hz, 1 H), 4.44 (dd, J ) 4.4, 10. 4 Hz, 1 H), 4.80 (d, J )
7.5 Hz, 1 H), 5.58 (s, 1 H), 7.03 (t, J ) 7.4 Hz, 1 H), 7.11 (d, J
) 7.2 Hz, 1 H), 7.18 (d, J ) 8.1 Hz, 1 H), 7.31 (t, J ) 7.7 Hz,
1 H), 7.36 (m, 3 H), 7.51 (t, J ) 3.7 Hz, 2 H). 13C NMR
(CDCl3): δ 44.60, 60.22, 67.08, 68.71, 72.97, 75.07, 80.23,
101.85, 106.20, 117.33, 123.21, 126.28, 127.06, 128.18, 129.10,
129.95, 131.76, 137.04, 157.82. Anal Calcd for C22H27NO6: H
6.78; C 65.82; N 3.49. Found: H 6.83; C 66.09; N 3.45.
2-(Dim eth yla m in om eth yl)p h en yl 4,6-O-(1-Meth yleth -
ylid en e)glu cop yr a n osid e (6b). To a stirred solution of 5b
(1.43 g, 4.39 mmol) and 1.7 mL (22.6 mmol) of 37% aqueous
formaldehyde in 10 mL of acetonitrile was added 0.442 g (7.0
mmol) of sodium cyanoborohydride. A vigorous exothermic
reaction ensued, and a yellow white residue separated. The
reaction mixture was stirred for 20 min, and then glacial acetic
acid was added dropwise until the solution tested neutral on
a wet pH paper. Stirring was continued for an additional 2 h,
glacial acetic acid being added occasionally to maintain the
pH near neutrality. The solvent was evaporated under reduced
pressure, and 20 mL of 2 N KOH was added to the residue.
The resulting mixture was extracted with three 10 mL portions
of ether. The combined ether extract was washed with 20 mL
of 0.5 N KOH and then dried over K2CO3. The solvent was
removed on a rotary evaporator. The crude product was
purified by silica gel column chromatography, eluting with
CHCl3/CH3OH (20:1), to get 0.884 g (57%) of 6b as a white
powder. 1H NMR (CDCl3): δ 1.45 (s, 3H), 1.53 (s, 3H), 2.25 (s,
6H), 2.91 (d, J ) 11.9 Hz, 1H), 3.43 (m, 1H), 3.68 (m, 3H),
3.87 (t, J ) 10.5 Hz, 1H), 4.02 (dd, J ) 5.4, 10.8 Hz, 1H), 4.13
(d, J ) 11.9 Hz, 1H), 4.75 (m, 1H), 7.01 (ddd, J ) 1.1, 7.4,
14.7 Hz, 1H), 7.13 (m, 2H), 7.29 (ddd, J ) 1.7, 7.7, 15.4 Hz,
1H). 13C NMR (CDCl3): δ 19.27, 29.24, 44.86, 60.37, 62.39,
68.20, 73.07, 73.75, 75.25, 99.99, 106.30, 117.50, 123.38,
126.95, 130.28, 132.02, 158.03. Anal. Calcd for C18H27NO6: H
7.70; C 61.17; N 3.96. Found: H 7.20; C 57.56; N 3.87.
2-(Dim eth yla m in om eth yl)p h en yl 2,3-Bis-O-(d ip h en yl-
p h osp h in o)-4,6-O-(p h e n ylm e t h ylid e n e )glu cop yr a n o-
sid e (7a ). In a drybox, to a stirring solution of 0.223 g of 6a
in 2 mL of anhydrous THF was added slowly 45 mg of
potassium hydride. After 1 h, a solution of 0.245 g of chlo-
rodiphenylphosphine in 1 mL of the same solvent was added,
and stirring was continued at room-temperature overnight.
The solvent was removed under high vacuum. The residue was
solution of 66.6 mg (0.12 mmol) of Rh+(COD)2 SbF6 in 1 mL
-
of CH2Cl2 and continued stirring for 3 h at room temperature.
The solvent was removed under vacuum. The residue was
collected, washed three times with Et2O, and dried under high
vacuum overnight. A fine powder of the Rh-complex was
obtained (100%). 31P NMR (CDCl3): δ 130.58 (dd, J p-p ) 30
Hz, J P-Rh ) 173 Hz), 132.44 (dd, J P-P ) 30 Hz, J P-Rh ) 177
Hz).
Th e Ca tion ic Rh od iu m Com p lex, (COD)Rh +[8] SbF 6
-
(Ar ) p h en yl) (9a ). This complex was prepared in a quan-
titative yield by a route similar to the previous experiment
for the synthesis of 9b. 31P NMR (CDCl3): δ 130.44 (dd, J P-P
) 29 Hz, J P-Rh ) 176 Hz), 132.62 (dd, J P-P ) 29 Hz, J P-Rh
173 Hz).
)
2-(Dim eth yla m in om eth yl)p h en yl 2,3-Di-O-(bis(3,5-d i-
m et h ylp h en yl)p h osp h in o)-4,6-O-(1-m et h ylet h ylid en e)-
glu cop yr a n osid e (12b). In a drybox, to a stirring solution of
0.67 g (1.90 mmol) of 6b in 4 mL of anhydrous THF was slowly
added 0.183 g (2.4 equiv) of potassium hydride. After 1 h, a
solution of 1.577 g (3.0 equiv) of bis(3,5-dimethylphenyl)-
chlorophosphine in 3 mL of the same solvent was added, and
the stirring was continued at room-temperature overnight. The
solvent was removed under high vacuum. The residue was
purified by flash chromatography, eluting with ether/hexane
(3:2) containing Et3N (1%), to obtain 1.22 g (77%) of 12b as a
1
white powder. H NMR (CDCl3): δ 0.82 (s, 3H), 1.10 (s, 3H),
1.94 (s, 6H), 2.06 (s, 6H), 2.12 (s, 6H), 2.17 (s, 6H), 2.26 (s,
6H), 2.80 (d, J ) 14.0 Hz, 1H), 3.24 (d; J ) 14.0 Hz, 1H), 3.38
(m, 1H), 3.65 (m, 2H), 3.85 (dd, J ) 5.3, 10.8, Hz, 1H), 4.38
(m, 1H), 4.50 (m, 1H), 5.26 (d, J ) 7.1 Hz, 1H), 6.55 (s, 1H),
6.63 (s, 1H), 6.80 (s, 1H), 6.84 (s, 1H), 6.92 (m, 6H), 7.05 (ddd,
J ) 1.8, 7.7, 15.5 Hz, 1H), 7.17 (m, 2H), 7.21 (m, 1H). 31P NMR
(CDCl3): δ 115.40 (d, J P-P ) 3 Hz), 120.23 (d, J P-P ) 3 Hz).
Anal. Calcd for C50H61NO6P2: H 7.37; C 72.01; N 1.68. Found:
H 7.52; C 72.20; N 1.66.
2-(Dim eth yla m in om eth yl)p h en yl 2,3-Di-O-(d ip h en yl-
p h osp h in o)-4,6-O-(1-m e t h yle t h ylid e n e )glu cop yr a n o-
sid e (12a ). The title compound was prepared by a route
similar to the previous experiment for the synthesis of 12b
using chlorodiphenylphosphine instead of bis(3,5-dimethylphe-
nyl)chlorophosphine (yield, 87%). 1H NMR (CDCl3): δ 0.83 (s,
3H), 1.12 (s, 3H), 2.19 (s, 6 H), 2.97 (d, J ) 13.9 Hz, 1H), 3.32
(d, J ) 13.9 Hz, 1H), 3.40 (m, 1H), 3.69 (m, 2H), 3.86 (dd, J )
5.3, 10.7 Hz, 1H), 4.45 (m, 2H), 5.25 (d, J ) 7.0 Hz, 1H), 6.63
(d, J ) 8.0 Hz, 1H), 6.93 (t, J ) 7.3 Hz, 1H), 7.05 (m, 10 H),
7.27 (m, 10 H), 7.56 (m, 2H). 31P NMR (CDCl3): δ 113.42 (s),
116.24 (s).
2-(Dim eth yla m in om eth yl)p h en yl 2,3-Di-O-(bis(3,5-d i-
t r iflu r om et h ylp h en yl)p h osp h in o)-4,6-O-(1-m et h ylet h -
ylid en e)glu cop yr a n osid e (12c). The title compound was
prepared by a route similar to the previous experiment for the
synthesis of 12b using bis(3,5-di(trifluromethyl)phenyl)chlo-
rophosphine instead of bis(3,5-dimethylphenyl)chlorophos-
1
phine (yield, 78%). H NMR (CDCl3): δ 0.98 (s, 6H), 2.15 (s,
6H), 2.90 (d, J ) 13.3 Hz, 1H), 3.22 (d, J ) 13.2 Hz, 1H), 3.42
(m, 1H), 3.67 (t, J ) 0.5 Hz, 1H), 3.77 (t, J ) 9.2 Hz, 1H), 3.87
(dd, J ) 5.4, 10.9 Hz, 1H), 4.55 (m, 2H), 5.25 (d, J ) 7.1 Hz,
1H), 6.46 (dd, J ) 0.8, 8.2 Hz, 1H), 6.91 (ddd, J ) 1.1, 7.4,

Catalysts with Pendant Quaternary Ammonium Groups
J . Org. Chem., Vol. 66, No. 10, 2001 3283
14.8 Hz, 1H), 7.01 (ddd, J ) 1.8, 7.8, 15.5 Hz, 1H), 7.13 (dd, J
) 1.8, 7.4 Hz, 1H), 7.53 (d, J ) 1.2 Hz, 2H), 7.57 (bs, 1H), 7.67
(d, J ) 1.4 Hz, 2H), 7.69 (d, J ) 1.5 Hz, 2H), 7.72 (bs, 1H),
7.74 (bs, 1H), 7.86 (d, J ) 0.5 Hz, 1H), 7.93 (bs, 1H), 7.96 (d,
J ) 0.5 Hz, 1H). 31PNMR (CDCl3): δ 107.14(s), 109.47(s).
Th e Ca tion ic Rh od iu m Com p lex 13b. In a drybox, to a
suspension of 35.5 mg (0.24 mmol) of trimethyloxonium
tetrafluoroborate in 2 mL of anhydrous CH2Cl2 was added 200
mg (0.24 mmol) of 12b in 3 mL of the same solvent, and the
mixture was stirred overnight at room temperature. To the
reaction mixture was added a solution of 97.4 mg (0.24 mmol)
of 13b except using 12c instead of 12b (yield: 97%). 31P NMR
(CD3OD): δ 134.87 (dd, J P-P ) 70 Hz, J Rh-P ) 198 Hz), 137.16
(dd, J P-P ) 70 Hz, J Rh-P ) 201 Hz).
Th e Ca tion ic Rh od iu m Com p lex 10b. In a drybox, to a
solution of 140 mg (0.113 mmol) of 13b in 4 mL of methanol
was added 40 mg of resin (AG 50 WX-8). The resin had been
previously swollen in methanol overnight at room temperature,
filtered, and washed three times with methanol before use in
this experiment. The reaction mixture was stirred at room-
temperature overnight. The resin was filtered through Celite.
The solvent was removed under high vacuum, and the residue
was washed three times with Et2O and dried under high
vacuum to get 0.112 g (83%) of 10b as a white powder. 31P
NMR(CD3OD): δ 123.09 (dd, J P1-P2 ) 31.5, J Rh-P1 ) 173.9 Hz),
130.46 (dd, J P1-P2 ) 32 Hz, J Rh-P2 ) 172 Hz).
Th e Ca tion ic Rh od iu m Com p lex 10a . This complex was
prepared by a route similar to the previous experiment for the
synthesis of 10b (yield: 70%). 31P NMR (CD3OD): δ 125.25
(dd, J P-P ) 32 Hz, J Rh-P ) 176 Hz), 130.82 (dd, J P-P ) 32 Hz,
J Rh-P ) 173 Hz), 31P NMR (D2O): δ 124.40 (dd, J P-P ) 34 Hz,
J Rh-P ) 174 Hz), 131.94 (dd, J ) 33 Hz, J Rh-P ) 173 Hz).
+
of Rh+(COD)2BF4 in 2 mL of CH2Cl2, and the stirring was
continued for 3 h. The solvent was removed under vacuum.
The residue was collected, washed three times with Et2O, and
dried under high vacuum overnight to get 0.28 g (95%) of a
fine powder of the Rh-complex 13b. 31P NMR (CDCl3): δ 131.14
(dd, J P-P ) 29 Hz, J Rh-P ) 144 Hz), 132.87 (dd, J P-P ) 29,
J Rh-P ) 149 Hz). Anal. Calcd for RhC59H76NO6P2B2F8: H 6.21;
C 57.44; N 1.14. Found H 5.95; C 54.13; N 1.13.
Th e Ca tion ic Rh od iu m Com p lex 13a . The title com-
pound was prepared by a route similar to the previous
experiment for the synthesis of 13b except starting with 12a
instead of 12b (yield: 99%). 31P NMR (CDCl3): δ 131.36 (dd,
Ack n ow led gm en t. This work was supported bythe
EPA (Technology for Sustainable Environment, R826120-
01-0) and NSF (CHE-9706766 and CHE-0079948).
J P-P ) 29 Hz, J Rh-P ) 163 Hz), 133.09 (dd, J ) 29 Hz, J Rh-P
159 Hz).
)
Th e Ca tion ic Rh od iu m Com p lex 13c. was prepared by
a route similar to the previous experiment for the synthesis
J O001686G