New enantiopure P,P-bidentate bis(diamidophosphite) ligands. Application in asymmetric rhodium-catalyzed hydrogenation

Article abstract of DOI:10.1021/om400119q

Two series of new enantiopure bidentate bis(diamidophosphite) ligands with diazaphospholidine and diazaphosphepine heterocyclic backbones were prepared. The ligands have a highly modular structure, which is well suited to the synthesis of a small library of compounds. Preparation was accomplished by the successive addition of enantiomerically pure substituted diamines (N,N′-dibenzylcyclohexane-1,2-diamine (1), N,N′-dimethylcyclohexane- 1,2-diamine (2), and N,N′-dimethyl-1,1′-binaphthyl-2,2′- diamine (3)) and enantiomerically pure diols (butanediol (a), cyclohexanediol (b), di-O-isopropylidenethreitol (c), and binaphthol (d)) to phosphorus trichloride. The corresponding bis(diamidophosphite) selenides were prepared, and the ¹J_PSe values were calculated in order to evaluate the σ-donor ability of the new ligands. The cationic Rh(I) complexes [Rh(COD)(P,P)]BF₄ were synthesized with 8 of the 12 new bis(diamidophosphite) ligands. The complexes were used as catalytic precursors for the asymmetric hydrogenation of benchmark substrates, namely methyl α-acetamidoacrylate (4), methyl (Z)-α-acetamidocinnamate (5), and dimethyl itaconate (6). The influence of the nature of both the terminal and bridging fragments of the bis(diamidophosphite) ligands on the asymmetric induction is discussed. Most proved to be effective catalysts for the process, attaining total conversion and excellent enantioselectivity (>99% ee) with the complex containing the (R;R_al,R_al;R)-3c ligand in the hydrogenation of the three substrates. The best performing catalytic precursor [Rh(COD)((R;R_al,R_al;R)-3c)]BF₄ was tested in the hydrogenation of selected cyclic enamides (7-9) and β-acetamidoacrylate (10).

Full text of DOI:10.1021/om400119q

Article
pubs.acs.org/Organometallics
New Enantiopure P,P-Bidentate Bis(diamidophosphite) Ligands.
Application in Asymmetric Rhodium-Catalyzed Hydrogenation
Maritza J. Bravo, Rosa M. Ceder, Guillermo Muller, and Merce Rocamora*
̀
́
́
Departament de Quımica Inorganica, Universitat de Barcelona, Martı i Franques 1-11, 08028-Barcelona, Spain
̀
̀
S
* Supporting Information
ABSTRACT: Two series of new enantiopure bidentate
bis(diamidophosphite) ligands with diazaphospholidine and
diazaphosphepine heterocyclic backbones were prepared. The
ligands have a highly modular structure, which is well suited to
the synthesis of a small library of compounds. Preparation was
accomplished by the successive addition of enantiomerically
pure substituted diamines (N,N′-dibenzylcyclohexane-1,2-
diamine (1), N,N′-dimethylcyclohexane-1,2-diamine (2), and
N,N′-dimethyl-1,1′-binaphthyl-2,2′-diamine (3)) and enantiomerically pure diols (butanediol (a), cyclohexanediol (b), di-O-
isopropylidenethreitol (c), and binaphthol (d)) to phosphorus trichloride. The corresponding bis(diamidophosphite) selenides
were prepared, and the 1JPSe values were calculated in order to evaluate the σ-donor ability of the new ligands. The cationic Rh(I)
complexes [Rh(COD)(P,P)]BF4 were synthesized with 8 of the 12 new bis(diamidophosphite) ligands. The complexes were
used as catalytic precursors for the asymmetric hydrogenation of benchmark substrates, namely methyl α-acetamidoacrylate (4),
methyl (Z)-α-acetamidocinnamate (5), and dimethyl itaconate (6). The influence of the nature of both the terminal and bridging
fragments of the bis(diamidophosphite) ligands on the asymmetric induction is discussed. Most proved to be effective catalysts
for the process, attaining total conversion and excellent enantioselectivity (>99% ee) with the complex containing the
(R;Ral,Ral;R)-3c ligand in the hydrogenation of the three substrates. The best performing catalytic precursor [Rh(COD)-
((R;Ral,Ral;R)-3c)]BF4 was tested in the hydrogenation of selected cyclic enamides (7−9) and β-acetamidoacrylate (10).
Such compounds are expected to have different activities and/
or enantioselectivities in comparison to phosphonites,
phosphoramidites, or phosphites when applied as ligands in
asymmetric catalysis. The substitution of oxygen atoms by
nitrogen should increase the electron density at the phosphorus
atom, and the presence of different substituents on the nitrogen
will create more steric bulk around the phosphorus.
INTRODUCTION
■
The design and synthesis of efficient chiral phosphorus ligands
has played an important role in the development of transition-
metal-catalyzed asymmetric reactions.1 Although phosphines
with either alkyl or aryl groups were the first effective
phosphorus donor ligands reported, nowadays a great variety
of P−O and P−N bond-containing ligands have been
demonstrated to have the capacity to accelerate and
enantioselectively catalyze a number of pivotal organic
processes. This class of ligands has the advantage of being
highly modular in nature and readily accessible via simple
condensation reactions. The vast majority of such ligands
contain a cyclic structure in which the phosphorus atom is a
component of a heterocyclic ring; a feature that contributes to
their stability and simplifies their preparation.2
Only a few chiral diamines have been used as scaffolds in the
synthesis of the diamidophosphite ligands (Figure 1). The in
Phosphonite (2P−O/1P−C), phosphite (3P−O), and
phosphoramidite (2P−O/1P−N) ligands containing a hetero-
cyclic ring derived from enantiopure chiral diols (i.e., BINOL,
TADDOL) and a P−C, P−O, or P−N exocyclic bond have
been found to have a wide scope in metal-catalyzed asymmetric
transformations. Among them, the ones that stand out the most
are conjugate addition reactions,3−5 Ir-catalyzed allylation,6−8
Pd-allylic alkylation,9,10 asymmetric hydrovinylation of vinyl-
arenes,11,12 and Rh-catalyzed asymmetric hydrogenation.13−18
Less research has been done on the synthesis and application of
chiral diamidophosphite ligands (2P−N/1P−O) containing
heterocyclic rings derived from enantiopure chiral diamines.
Figure 1. General structures of reported diamidophosphite ligands.
Received: February 11, 2013
© XXXX American Chemical Society
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situ formation of diamidophosphites (I and II in Figure 1)
derived from enantiopure 1,2-cyclohexyldiamine and racemic
chiral alcohols has long been reported as a method for
analyzing the enantiomeric composition of chiral alcohols by
1H and 31P NMR spectroscopy,19 but the coordination
chemistry of these kinds of ligands has only scarcely been
reported in the literature. Similar enantiopure ligands have been
applied to a limited range of asymmetric catalyzed trans-
formations, such as the hydrovinylation of styrene,20 Pd-allylic
substitution,21 and more recently vinyl-substituted trimethyle-
nemethane [3 + 2] cycloaddition.22
A family of P-chiral monodentate and bidentate diamido-
phosphite ligands, containing diazaphospholidine rings based
on 2-(anilinomethyl)pyrrolidine as the heterocyclic fragment
and several alcohols and diols such as BINOL, benzyltartar-
imide, and 1,4:3,6-dianhydromannitol have previously been
synthesized (III and IV in Figure 1). The corresponding
organometallic precursors have been prepared and tested in
asymmetric Pd-catalyzed allylic substitution and Rh-catalyzed
hydrogenation.23,24 It should be mentioned that, unlike
phosphoramidite ligands based on BINOL, monodentate
diamidophosphites are worse stereoselectors than bidentate
chelating agents in Rh-catalyzed hydrogenation.
A limited number of ligands with a P-containing heterocyclic
ring derived from an axially chiral 1,1′-binaphthyl-2,2′-diamine
have previously been described (V in Figure 1). Reetz reported
the corresponding monodentate diamidophosphite ligand with
a methoxy exocyclic fragment that was tested in the Rh-
catalyzed hydrogenation of the itaconic acid dimethyl ester.
Low conversion and enantioselectivity were achieved.25
Recently, we reported the synthesis of a new monodiamido-
phosphite ligand based on the same backbone and a chiral
bornyloxy group that was tested in hydrovinylation reactions
with encouraging results.20 A set of closely related chiral
phosphorus triamides based on the 1,1′-binaphthyl-2,2′-
diamine backbone and their application in the copper-catalyzed
conjugate addition of diethylzinc to cyclohex-2-enone and the
nickel-catalyzed hydrovinylation of styrene that yield good
activities and chemoselectivities and moderate enantioselectiv-
ities in both reactions have also previously been described.26
On the basis of the observation that chiral bidentate
diamidophosphites are effective ligands for the Rh-asymmetric
hydrogenation,23 we describe here the synthesis of a series of
modular chiral bis(diamidophosphite) compounds with the
general formula shown in Figure 2, which have been designed
to ensure systematic modifications of the ligands. Their
corresponding cationic rhodium(I) complexes were prepared
and fully characterized. They were tested in asymmetric
hydrogenation of the benchmark substrates: methyl α-
acetamidoacrylate, methyl (Z)-α-acetamidocinnamate, and
dimethyl itaconate. The best catalytic precursor was tested in
the hydrogenation of some challenging prochiral cyclic
enamides.
Figure 2. Building blocks for the synthesis of the new bis-
(diamidophosphite) ligands and numbering of the terminal and
bridging fragments.
influence of the steric bulk close to the phosphorus atom.
Bis(diamidophosphites) with an identical bridging fragment
and different heterocycles were prepared with the aim of
studying the influence of the terminal fragment. Furthermore,
both the terminal and bridging units with different absolute
configurations were combined in order to study the matching−
mismatching effects on the sense and extent of the asymmetric
induction of the catalyzed reactions.
RESULTS AND DISCUSSION
■
Synthesis of Bis(diamidophosphite) Ligands. The new
homochiral bidentate diamidophosphite (P,P) ligands were
prepared via two consecutive condensation reactions from
enantiomerically pure diamines and diols in the presence of a
base, following procedures reported in the literature with slight
modifications.20,22 The first step in the synthesis is the
formation of the heterocyclic terminal fragment [N2P] by the
reaction of the diamine with PCl3 (Scheme 1). This process is
accompanied by a favorable entropy change and is favored in
the presence of a base acting as an HCl acceptor.
Reaction conditions such as reaction time, molar ratio, the
length of the addition of the reagents, and the nature of the
HCl scavenger were appropriately chosen to ensure the
formation of the desired products with high yields. Different
reaction conditions were used for bis(diamidophosphites) with
terminal rings derived from cyclohexyldiamine and those
derived from binaphthyldiamine. The reaction of phosphorus
trichloride with the enantiomerically pure disubstituted cyclo-
hexyldiamine (R,R)-1 or (R,R)-2 in the presence of an excess of
Et3N led to the formation of the chlorodiazaphospholidine
derivatives ((R,R)-1Cl or (R,R)-2Cl) after 2 h of stirring. The
condensation reaction between PCl3 and the diamine N,N′-
dimethylbinaphthyldiamine ((R)-3 or (S)-3) required a longer
reaction time (20 h) and i-Pr2EtN as the hydrogen chloride
acceptor to ensure complete formation of the chlorodiazaphos-
phepine species (R)-3Cl or (S)-3Cl. The synthesis of chloride
Enantiomerically pure dimethyl-1,1′-binaphthyldiamine and
disubstituted cyclohexyldiamine were used to form the
heterocyclic rings (diazaphosphepine and diazaphospholidine,
respectively) as the terminal fragments, and different
enantiopure diols were used as the bridging fragments. For
the same terminal heterocyclic ring, the different bridging
fragments allowed us to study the effect of rigidity and length of
the bridge on the activity and enantioselectivity of the catalytic
process. Ligands with different substituents on the nitrogen and
identical bridging fragments were prepared to study the
B
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bone (R,R;Ra l ,Ra l ;R,R)-1a, (R,R;Sa l ,Sa l ;R,R)-1a,
(R,R;Ral,Ral;R,R)-1b, (R,R;Ral,Ral;R,R)-1c, and (R,R;Sal;R,R)-1d
were obtained. Slightly different conditions had to be applied
for the synthesis of bis(diamidophosphite) (R,R;Sal,Sal;R,R)-2a
and ligands with a diazaphosphepine backbone (R;Sal,Sal;R)-3a,
(S;Sal,Sal;S)-3a, (R;Ral,Ral;R)-3c, (S;Sal;S)-3d, (R;Sal;R)-3d, and
(S;Ral;S)-3d. The reaction of (R,R)-2Cl, (R)-3Cl, and (S)-3Cl
with the stoichiometric amount of the corresponding chiral
alcohol requires the addition of DMAP8 as a catalyst and excess
of Et3N as the HCl scavenger. In this case, the use of DMAP
proved to be advantageous, as it decreased the reaction time
and also reduced the amount of byproducts, as reported
previously.29,30 Moreover, slow addition of the diol in three
portions led to better yields. These conditions were particularly
important in the synthesis of diamidophosphite 3a, as 1,3-
butanediol (a) tends to cyclize into a dioxaphospholidine
derivative with the consequent cleavage of the diazaphospho-
lidine ring.19c Bis(diamidophosphite) ligands were obtained as
viscous oils for 1a−d and 2a and as yellow solids for 3a,c,d. The
new compounds were found to be easily hydrolyzed and
oxidized in open air but could be stored under inert conditions
at room temperature for at least a few months with little
degradation. The products from hydrolysis or oxidation
appeared in the δ ∼17−25 ppm range in the 31P NMR spectra.
As extensive manipulation led to ligand decomposition, they
were used without further purification both in the formation of
the corresponding rhodium cationic complexes and in
asymmetric hydrogenation reactions, when they were carried
Scheme 1. Synthesis of Chloride Derivatives
derivatives 1Cl, 2Cl, and 3Cl was monitored by phosphorus
NMR spectroscopy, and they were used immediately because of
their sensitivity to oxygen and moisture.20−28
The second step is the formation of the [POCnOP] bridge
between the two terminal rings by condensation of the
heterocyclic chloride derivative and the corresponding
enantiomerically pure chiral diol in the presence of a base
(Scheme 2).
To a solution of 2 equiv of the chlorophospholidine 1Cl and
excess Et3N was added 1 equiv of the corresponding chiral
alcohol ((Ral,Ral)-a, (Sal,Sal)-a, (Ral,Ral)-b, (Ral,Ral)-c, or (Sal)-d).
After 4 h of stirring at room temperature, bis-
(diamidophosphite) ligands with a diazaphospholidine back-
Scheme 2. Synthesis of New Bis(diamidophosphite) Ligands
C
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out in situ. The progress of the reactions and the purity of the
ligands were easily monitored by 31P NMR spectroscopy.
The new ligands were characterized by mass spectrometry
of the heterocyclic ring adopt different orientations with respect
to the phosphorus lone pair, as reported.23
Selenide Derivatives. Since both reactivity and selectivity
in catalytic processes are controlled by steric and electronic
factors, it is expected that phosphorus ligands with different
basicities and different steric requirements will give rise to
different results. A simple way to evaluate the electron-donating
ability of phosphorus toward metal acceptors is based on the
1
and 31P, H, and 13C NMR spectroscopy. 31P NMR data are
shown in Table 1. The 31P chemical shift values are in the same
a
Table 1. 31P NMR Data for P,P Ligands and Cationic
Rhodium(I) Complexes
1
magnitude of the J(77Se−31P) coupling of selenide derivatives.
1
δ((P,P)- JPSe((P,P)- δ([Rh(COD)(P,P)]
b
c
d
BF4) (1JPRh
)
It is known that the respective coupling constants increase as
the groups attached to the phosphorus become more electron
withdrawing, indicating an increased σ character of the
phosphorus lone pair and forming an apparently weaker
donor to metals.31
P,P
δ(P,P)
Se2)
Se2)
b
(R,R;Ral,Ral;R,R)-
138.2
86.6
888.9
136.8 (d, 216.2)
1a
b
(R,R;Sal,Sal;R,R)-1a
137.6
136.5
87.3
85.6
887.7
893.8
139.8 (d, 228.3)
(R,R;Ral,Ral;R,R)-
1b
134.8 (d, 216.2)
125.0 (d, 227.1)
The bis(diamidophosphite)diselenides (1a−d)-Se2, 2a-Se2,
and (3a,c,d)-Se2, were prepared by simply stirring the
phosphorus compounds with an excess of elemental selenium
in toluene at room temperature for 24 h (Scheme 3).
(R,R;Ral,Ral;R,R)-
1c
136.3
88.2
890.6
(R,R;Sal;R,R)-1d
(R,R;Sal,Sal;R,R)-2a
(R;Sal,Sal;R)-3a
(S;Sal,Sal;S)-3a
(R;Ral,Ral;R)-3c
(S;Sal;S)-3d
139.3
139.1
178.3
176.6
168.9
173.6
174.6
81.5
87.0
91.4
89.9
91.5
82.6
85.2
920.5
889.0
882.4
887.3
892.0
913.6
919.0
134.0 (d, 228.3)
130.7 (d, 228.3)
Scheme 3. Synthesis of Selenide Derivatives
129.4 (d, 227.1)
(R;Sal;R)-3d
132.0 (d, 222.2)
a
Conditions for 31P{1H} NMR: 298 K, 101.2 MHz, δ in ppm,
b
c
d
coupling constants in Hz. CDCl3. Toluene. CH2Cl2/toluene.
The diselenide compounds were characterized in situ by 31P
NMR spectroscopy. In each case a single new resonance that
exhibited coupling to 77Se, at fields higher than those for free
bis(diamidophosphites), was observed (Table 1). The 31P
NMR chemical shift of all the bis(diamidophosphite) selenides
occurs in a narrow range around δ 80−90 ppm. In contrast, free
bis(diamidophosphite) ligands with a diazaphospholidine
backbone (1a−d, 2a) showed δ values at around 140 ppm,
while for those with a diazaphosphepine backbone (3a,c,d) it
was approximately 170 ppm.
range as those reported for analogous monodentate diamido-
phosphites20,25 and mainly depend on the diamine scaffold.
With a cyclohexyldiamine terminal fragment (1a−d, 2a), the δ
values were in the δ ∼136−139 ppm range; while for ligands
containing binaphthyldiamine (3a,c,d), a deshielding effect
occurs around the phosphorus, bringing the δ values downfield
to the δ ∼168−178 ppm region. A small influence of the
bisalkoxy bridge was also observed. Slightly different chemical
shifts were found for the diastereoisomers of the same ligand,
(R,R;Ral,Ral;R,R)-1a and (R,R;Sal,Sal;R,R)-1a, (R;Sal,Sal;R)-3a
and (S;Sal,Sal;S)-3a, and (S;Sal;S)-3d and (R;Sal;R)-3d, showing
that the phosphorus atom experiences different environments
in each diastereoisomer.19b,d
1
The coupling constant values, JSeP, for the new selenide are
close to those reported for similar monodentate diamidophos-
phites20 showing a σ-donor character between phosphines and
phosphites (reported values31d for PPh3 phosphine and
1
1
1
In order to unequivocally assign H NMR spectra, it was
P(OPh)3 phosphite are JSeP = 745 Hz and JSeP = 1039 Hz,
respectively). From the magnitude of 1JSeP values it can be seen
that there are no significant differences between the selenides
containing different terminal rings and the same bridging
fragment. Within compounds with an identical heterocycle, the
necessary to undertake a two-dimensional HSQC experiment.
Those ligands derived from benzylcyclohexyldiamine, 1a−d,
exhibited four signals corresponding to the diastereotopic
benzylic protons, each of them coupled to the other geminal
proton and to the phosphorus atom. Consequently, they
appeared as four different signals with a triplet, doublet of
doublet, or overlapped multiplet structure depending on the
relative values of JHH and JPH, although usually JHH > JPH as
reported for other similar ligands.20,27 Protons bonded to the
cyclohexyl chiral carbon atoms always appeared as two
multiplets, in contrast to one multiplet in the parent free
amine. In bis(diamidophosphite) ligands with N,N′-dimethyl-
cyclohexyldiamine and N,N′-dimethylbinaphthyldiamine, the
N-methyl substituents appeared as two different doublets,
showing coupling with the phosphorus atom. All these data
suggest that the new bidentate diamidophosphite ligands show
C2 symmetry and that the local C2 symmetry of the free
diamine is lost. 13C NMR spectra of the new compounds
1
highest JSeP value was observed when the binaphthol group
was acting as the bridging fragment. Presumably the electron-
withdrawing character and the stereochemical requirements of
the binaphthol fragment reduce the σ-donor ability of the
1
ligands 1d and 3d. The JSeP values also had interesting
stereochemical dependencies; thus, different diastereoisomers
1
showed different values for JSeP, especially between selenides
with terminal fragments derived from binaphthyldiamine:
(R;Sal,Sal;R)-3a, (S;Sal,Sal;S)-3a and (S;Sal;S)-3d, (R;Sal;R)-3d.
Synthesis of Rhodium(I) Complexes. Rhodium com-
plexes, [Rh(COD)(P,P)]BF4, with 8 of the 12 novel bis-
(diamidophosphites) (P,P = (R,R;Ral,Ral;R,R)-1a,
(R,R;Sal,Sal;R,R)-1a, (R,R;Ral,Ral;R,R)-1b, (R,R;Ral,Ral;R,R)-1c,
(R,R;Sal,Sal;R,R)-2a, (R;Sal,Sal;R)-3a, (R;Ral,Ral;R)-3c, and
(R;Sal;R)-3d) were prepared. The complexes were synthesized
by reaction at room temperature of a dichloromethane solution
of the cationic complex [Rh(COD)2]BF4 and a stoichiometric
2
showed very different coupling constants JCP (∼40, ∼20 Hz)
for the two carbon atoms of the diamine substituents NCH3
and NCH2C6H5. These data show that the amino substituents
D
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amount of the corresponding diamidophosphite ligand. Free
COD was added in order to dissolve the [Rh(COD)2]BF4
complex in CH2Cl2 when it was not freshly prepared (Scheme
4).
bis(diamidophosphite) oxide, showing the high instability of
the rhodium complex. The same behavior has been reported for
cationic rhodium(I) complexes bearing related ligands.34 The
poor σ-donor ability of bis(diamidophosphite) 1d reflected in
its high coupling constants (1JPSe = 920 Hz and 1JRhP = 234 Hz)
would explain the low stability of the complex.
Scheme 4. Synthesis of Cationic Rhodium(I) Complexes
Rhodium-Catalyzed Asymmetric Hydrogenation. The
novel bis(diamidophosphite) ligands were initially tested in the
Rh-catalytic hydrogenation of benchmark substrates in order to
explore their scope and limitations (Scheme 5).
Scheme 5. Rh-Catalyzed Asymmetric Hydrogenation
Reaction
The new compounds are yellow solids that were found to be
stable under an inert atmosphere at room temperature and
soluble in common organic solvents. They were characterized
in the solid state by elemental analysis and/or mass
spectrometry. The mononuclear character of the complexes
was confirmed by HRMS/ESI spectrometry, which in all cases
showed molecular ions corresponding to the [Rh(COD)-
(P,P)]+ and [Rh(P,P)]+ cations. 1H and 31P NMR spectroscopy
allowed us to characterize these complexes in solution. The 31
P
NMR spectral data are summarized in Table 1. The spectra
1
show one doublet with a JPRh value of between 219 and 228
Hz, similar to those reported in the literature24,25,32,33 for
cationic rhodium complexes with a cis arrangement of two
phosphorus atoms. The phosphorus chemical shifts of
complexes with diamidophosphite ligands containing a
diazaphospholidine terminal fragment (1a−c, 2a) were at
values similar to that of the free ligand, but for complexes with
diazaphosphepine terminal fragment (3a,c,d) the signal lay
upfield.
The results for the asymmetric hydrogenation of methyl α-
acetamidoacrylate (4), methyl (Z)- α-acetamidocinnamate (5),
and dimethyl itaconate (6) catalyzed with the [Rh(COD)-
(P,P)]BF4 (P,P = 1a−c, 2a, 3a,c,d) complexes are given in
Tables 2 and 3. All the reactions were conducted under 10 bar
of H2 in CH2Cl2 at room temperature for 6 h, with a substrate:
a
Table 2. Asymmetric Hydrogenation of Substrates 4−6
Two-dimensional NMR heterocorrelation 1H−13C experi-
with [Rh(COD)(P,P)]BF4 (P,P = 1a−c, 2a)
1
ments were important to assign the different signals of the H
b
entry
P,P
substrate conversion (%)
ee (%)
spectra, in particular for the complexes [Rh(COD)-
((R,R;Sal,Sal;R,R)-1a)]BF4, [Rh(COD)((R,R;Ral,Ral;R,R)-
1c)]BF4, and [Rh(COD)((R;Sal,Sal;R)-3a)]BF4. Complexes
with ligands containing the dibenzylcyclohexyldiamine terminal
fragment, 1a−c, showed four signals for the benzylic protons,
usually overlapped. Complexes with the dimethylbinaphthyldi-
amine terminal fragment, 3a,c,d, showed all the proton signals
shifted to fields lower than those of the free ligand. For the
methyl substituents of the heterocycle, two different doublets
1
(R,R;Sal,Sal;R,R)-1a
(R,R;Ral,Ral;R,R)-1a
(R,R;Ral,Ral;R,R)-1b
(R,R;Ral,Ral;R,R)-1c
4
4
4
4
4
4
4
5
5
5
5
5
6
6
6
6
6
6
100
100
100
100
100
0
>99 (R)
70 (R)
70 (R)
26 (S)
23 (S)
2
3
4
c
5
(R,R;Ral,Ral;R,R)-1c
c
6
(R,R;Sal;R,R)-1d
7
(R,R;Sal,Sal;R,R)-2a
(R,R;Sal,Sal;R,R)-1a
(R,R;Ral,Ral;R,R)-1a
(R,R;Ral,Ral;R,R)-1b
(R,R;Ral,Ral;R,R)-1c
(R,R;Sal,Sal;R,R)-2a
(R,R;Sal,Sal;R,R)-1a
(R,R;Ral,Ral;R,R)-1a
(R,R;Ral,Ral;R,R)-1b
(R,R;Ral,Ral;R,R)-1c
100
100
100
100
100
100
70
74 (R)
95 (R)
75 (R)
76 (R)
Racemic
52 (R)
97 (S)
72 (S)
74 (S)
Racemic
-
8
1
9
(1JHP = 8 and JHP = 12 Hz) were observed. All the Rh(I)
10
11
12
13
14
15
16
17
18
complexes showed two groups of signals between 5.79 and 4.59
ppm and between 2.45 and 1.86 ppm for the methynic and
methylenic groups, respectively, of the 1,5-cyclooctadiene
ligand. All these data confirm that the complexes with the
new diamidophosphite ligands retain the C2 symmetry of the
free bidentate ligand in solution.
No stable cationic rhodium complex with the (R,R;Sal;R,R)-
1d ligand could be isolated under the described conditions. The
reaction was monitored by 31P NMR spectroscopy. A CDCl3
(10 mL) solution of (R,R;Sal;R,R)-1d with [Rh(COD)2]BF4 (1
equiv) showed a predominant doublet centered at δ 118.2 ppm
with a coupling constant 1JPRh of 234 Hz and a minor singlet at
20 ppm assigned to oxidized bis(diamidophosphite). Any
attempt to isolate the rhodium complex resulted in the rapid
disappearance of the doublet signal and the formation of
18
88
100
0
c
(R,R;Sal;R,R)-1d
(R,R;Sal,Sal;R,R)-2a
100
90 (S)
a
Standard reaction conditions: 25 mL of CH2Cl2, 1.00 mmol of
substrate, 0.01 mmol of [Rh(COD)(P,P)]BF4, 10 bar of H2, 6 h, room
temperature. Conversion and ee values were determined by GC. The
absolute configuration was determined by comparison with the known
sign of specific rotation. Catalyst formed in situ from 0.01 mmol of
b
c
[Rh(COD)2]BF4 and 0.011 mmol of (P,P).
E
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a
(6′). Moreover, the absolute configurations of the different
hydrogenation products depend on the configuration of the
chiral centers of the terminal fragment (entries 1, 8, and 13 vs
2, 9, and 14). Similar conversion and ee values and the same
configuration of the major enantiomer of the hydrogenated
products were obtained by changing the bridging fragment
derived from (R,R)-butanediol, in (R,R;Ral,Ral;R,R)-1a, for the
conformationally more rigid group derived from (R,R)-
cyclohexanediol, in (R,R;Ral,Ral;R,R)-1b (entries 2 vs 3, 9 vs
10, and 14 vs 15). These results indicate that with rhodium
complexes containing ligands 1a,b, which both have a short
spacer, the enantioselectivity is not affected by changing the
conformational rigidity of the bridge. Hydrogenation reactions
with a precursor containing the (R,R;Ral,Ral;R,R)-1c ligand
showed a very low enantiomeric excess (up to 26% for 4′ and
racemic for 5′ and 6′; entries 4, 11, and 16). The
conformational flexible and rather long spacer derived from
di-O-isopropylidenethreitol (c) diminishes the enantioselectiv-
ity of the process. A slightly lower enantioselectivity was
observed with the precursor containing the (R,R;Sal,Sal;R,R)-2a
ligand derived from the dimethylcyclohexyldiamine in compar-
ison to that with (R,R;Sal,Sal;R,R)-1a derived from the
dibenzylciclohexyldiamine (entries 1 vs 7, 8 vs 12, and 13 vs
18). Presumably the presence of the bulkier benzyl substituent
on the nitrogen atom induces greater steric crowding around
the phosphorus atom, resulting in increased enantiomeric
control.
Table 3. Asymmetric Hydrogenation of Substrates 4−6
with [Rh(COD)(P,P)]BF4 (P,P = 3a,c−e)
b
entry
P,P
substrate
conversion (%)
ee (%)
1
(R;Sal,Sal;R)-3a
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
6
6
6
6
6
6
100
100
100
100
100
100
100
100
100
100
100
100
100
90
28 (R)
98 (R)
>99 (R)
>99 (S)
>99 (S)
10 (R)
>99 (R)
>99 (R)
53 (R)
29 (R)
92 (S)
c
2
(S;Sal,Sal;S)-3a
(R;Ral,Ral;R)-3c
(R;Sal;R)-3d
3
4
c
5
(R;Sal;R)-3d
c
6
(S;Sal;S)-3d
c
7
(S;Ral;S)-3d
c
8
(S;Ral;S)-3d
d
9
(R;Sal)-3e
10
11
12
13
14
15
16
17
18
19
20
21
(R;Sal,Sal;R)-3a
c
(S;Sal,Sal;S)-3a
(R;Ral,Ral;R)-3c
(R;Sal;R)-3d
>99 (S)
96 (S)
c
(S;Sal;S)-3d
75 (S)
d
(R;Sal)-3e
100
100
100
100
92
79 (R)
9 (S)
(R;Sal,Sal;R)-3a
c
(S;Sal,Sal;S)-3a
98 (S)
(R;Ral,Ral;R)-3c
(R;Sal;R)-3d
>99 (R)
75 (R)
38 (S)
c
(S;Sal;S)-3d
53
d
(R;Sal)-3e
100
78 (S)
a
Standard reaction conditions: 25 mL of CH2Cl2, 1.00 mmol of
substrate, 0.01 mmol of [Rh(COD)(P,P)]BF4, 10 bar of H2, 6 h, room
temperature. Conversion and ee values were determined by GC. The
b
It is worth noting that the rhodium precursor based on the
ligand (R,R;Sal;R,R)-1d failed to hydrogenate the substrates 4
and 6. The reaction was carried out with the catalyst generated
in situ from [Rh(COD)2]BF4 and 1 equiv of (R,R,Sal,R,R)-1d.
This result is in agreement with the fact, explained in the
previous section, that all attempts to prepare the cationic
complex [Rh(COD)(R,R;Sal;R,R)-1d]BF4 were unsuccessful. In
contrast, Gavrilov et al.23 reported high activity and excellent
enantioselectivity in the hydrogenation of 5 and 6 with
bis(diamidophosphite) ligands with a terminal fragment
derived from anilinomethylpyrrolidine (diazaphospholidine
cycle) and the same binaphthol bridging fragment d.
absolute configuration was determined by comparison with the known
c
sign of specific rotation. Catalyst formed in situ from 0.01 mmol of
d
[Rh(COD)2]BF4 and 0.011 mmol of (P,P). Catalyst formed in situ
from 0.01 mmol of [Rh(COD)2]BF4 and 0.022 mmol of (R;Sal)-3e.
Table 3 gives the results obtained with rhodium complexes
containing the bidentate bis(diamidophosphite) ligands 3a,c,d
with the N,N′-dimethylbinaphthyldiamine terminal fragment.
Good activities were obtained for the hydrogenation of
substrates 4−6, but low conversions were achieved for dimethyl
itaconate when a precursor with the 3d ligand was used (entries
19 and 20). Large match−mismatch effects were noted with the
ligands 3a,d; while (S;Sal,Sal;S)-3a showed high enantioselec-
tivity (up to 98% ee, entries 2, 11, and 17), lower values were
obtained with the counterpart diastereoismer (R;Sal,Sal;R)-3a
(up to 29% ee, entries 1, 10, and 16). Similar results were
obtained with the ligand 3d; better ee values were obtained
with (R;Sal;R)-3d (entries 4, 13, and 19) than with (S;Sal;S)-3d
(entries 6, 14, and 20). On comparison of the results obtained
with (S;Ral;S)-3d and (R;Sal;R)-3d, the expected change in the
absolute configuration of the major enantiomer of the
hydrogenation product 4′ can be observed (entries 5 vs 7).
Excellent enantioselectvity was attained with the compound
[Rh(COD)((R,Ral,Ral,R)-3c)]BF4 in the hydrogenation of the
three benchmark substrates (up to >99% ee, entries 3, 12, and
18). Remarkably, this result is in sharp contrast with the low
levels of enantioselectivity when the ligand is (R,R;Ral,Ral;R,R)-
1c, which contains the same bridging fragment derived from di-
O-isopropylidene-threitol and the benzylcyclohexyldiamine
[Rh] ratio of 100:1 and the preformed catalyst unless stated.
Using the preformed catalyst ensured us that the catalytic
precursor was accurately defined and that the exact catalyst
loading was introduced in the reactor. Nevertheless, we tested
for the ligand (R,R;Ral,Ral;R,R)-1c (Table 2, entries 4 and 5)
and (R;Sal;R)-3d (Table 3, entries 4 and 5) hydrogenation
reactions with in situ conditions ([Rh(COD)2]BF4:P,P = 1:1.1)
and obtained similar results.
Table 2 shows the results obtained with Rh(I) complexes
containing ligands with disubstituted cyclohexyldiamine termi-
nal fragments. With the ligands 1a−c and 2a, complete
conversion of the dehydro amino acid methyl esters 4 and 5
was achieved in 6 h, showing a wide range of ee values. Lower
activity was accomplished for the hydrogenation of dimethyl
itaconate (6) with precursors containing the ligands 1a,b
((R,R;Sal,Sal;R,R)-1a, 70%; (R,R;Ral,Ral;R,R)-1a, 18%;
(R,R;Ral,Ral;R,R)-1b, 88%, entries 13−15). The highest ee
values were obtained with the (R,R;Sal,Sal;R,R)-1a ligand (99%
R for 4′, 95% R for 5′, 97% S for 6′; entries 1, 8 and 13). A
match−mismatch effect was seen for both (R,R;Sal,Sal;R,R)-1a
and its counterpart (R,R;Ral,Ral;R,R)-1a, with the former being
the matched combination for the selective preparation of (R)-
N-acetylalanine methyl ester (4′), (R)-N-acetylphenylalanine
methyl ester (5′), and (S)-2-methylsuccinic acid dimethyl ester
F
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Article
terminal fragment. A long and flexible bridging fragment
enhances enantioselectivity when the binaphthyl terminal
fragment is present. Reetz35 also observed good enantiose-
lectivity with BINOL-derived diphosphite and diphosphorami-
dite ligands containing long bridging fragments.
We also tested the hydrogenation reaction with a Rh(I)
precursor with the monodentate diamidophosphite (R,Sal)-3e
ligand described previously by our group.20 This ligand, which
contains a diazaphosphepine heterocyclic ring from (R)-
dimethylbinaphthyldiamine and the (S)-bornyloxy group as
the third substituent in the phosphorus atom (see footnote in
Table 3), led to good conversion and enantioselectivity in the
hydrovinylation reaction of styrene. Total conversion and
moderate enantioselectivity in the hydrogenation of the
substrates 4−6 were observed (53% R for 4′, 79% R for 5′,
78% S for 6′; entries 9, 15, and 21). On comparison of these
results with those described25 with a similar monodentate
diamidophosphite with the heterocyclic fragment (S)-dime-
thylbinaphthyldiamine and a methoxy group (ee 30% of 6′) it
can be concluded that the presence of the bulky chiral
bornyloxy group substantially improves the enantiomeric
excess, but the values are still far from those obtained with
monodentate phosphoramidite BINOL-based ligands.14
It is worth noting that no linear correlation was found
between the basicity of the new ligands (on the basis of their
1JPSe values) and the activity and selectivity of the hydro-
genation process.
Figure 3. Prochiral olefins hydrogenated with [Rh(COD)-
((R;Ral,Ral;R)-3c)]BF4 precursor.
a
Table 5. Asymmetric Hydrogenation of Substrates 7−11
with [Rh(COD)((R;Ral,Ral;R)-3c)]BF4
b
entry substrate substrate/[Rh] time (h) conversion (%)
ee (%)
c
d
1
2
3
4
5
7
100/1
50/1
50/1
50/1
50/1
6
6
100
77
55 (S)
51 (R)
e
8
ef
,
9
6
100
50
44 (R)
d
10
11
20
6
18 (S)
92 (S)
d
100
a
Standard reaction conditions: 25 mL of CH2Cl2, 0.5 mmol of
substrate, 0.01 mmol of [Rh(COD)(P,P)]BF4, 10 bar of H2, room
b
temperature. The absolute configuration was determined by
c
comparison with the known sign of specific rotation. 1 mmol of
d
substrate, 0.01 mmol of [Rh(COD)(P,P)]BF4. Conversion and ee
e
were determined by GC. Conversion and ee were determined by
After exploring the catalytic potential of the Rh(I) precursors
with the new ligands in the hydrogenation of 4−6, we were
interested in optimizing the reaction conditions when [Rh-
(COD)((R,Ral,Ral,R)-3c)]BF4 is used in the hydrogenation of
dehydro amino acid methyl ester 4 (Table 4).
f
HPLC. The absolute configuration was assigned assuming the same
enantioselection as in 8′.
the Rh-PennPhos, Rh-BIPHEP, and Rh-supraphos sys-
tems).36−38 As shown in Table 5, cyclic enamides 7−9 have
been hydrogenated with good yields and moderate enantiose-
lectivities (44−55% ee, entries 1−3). The aliphatic ((Z)-β-
methylacylamino)acrylate 10 was hydrogenated with low
efficiency in terms of both activity and enantioselectivity
(entry 4). The complete hydrogenation of substrate 11 that
contains a p-fluoro electron-withdrawing group confirms the
efficacy of (R;Ral,Ral;R)-3c in the hydrogenation of α-dehydro
amino acids. Only a slight decrease in the enantioselectivity in
comparison to the nonsubstituted substrate was observed
(entry 5 in Table 5 vs entry 12 in Table 3).
a
Table 4. Asymmetric Hydrogenation of Substrate 4 with
[Rh(COD)((R;Ral,Ral;R)-3c)]BF4
b
entry P (bar) 4/[Rh] time (h) conversion (%)
ee (%)
TOF
1
2
3
4
5
10
10
10
100/1
100/1
1000/1
100/1
100/1
6
100
100
98
>99 (R)
>99 (R)
>99 (R)
>99 (R)
>99 (R)
0.5
6
200
c
163
1.5
1.5
1
100
80
0.5
160
a
b
Reaction conditions: 25 mL of CH2Cl2, 0.01 mmol of [Rh]. In units
c
of (mol of substrate)(mol of cat.)−1 (h)−1. 5 × 10−3 mmol of [Rh].
CONCLUSIONS
■
The excellent enantioselectivity obtained (>99%) is not
affected by changing the pressure, reaction time, substrate:[Rh]
ratio, or catalyst concentration under the reaction conditions
described in Table 4. The highest TOF value (TOF = 200,
entry 2) is obtained at 10 bar of pressure, with a substrate:[Rh]
ratio of 100:1 and a 0.5 h reaction. The catalyst is also efficient
at 1.5 bar of pressure, reaching a TOF value of 160 (entry 3).
These values are close to those reported in the literature for Rh-
catalyzed asymmetric hydrogenation of similar substrates with
monodentate and bidentate phosphoramidite ligands.14,18
After the promising results obtained with [Rh(COD)-
((R;Ral,Ral;R)-3c)]BF4 precursor, we examined its efficiency in
the asymmetric hydrogenation of a structurally diverse array of
substrates shown in Figure 3. The results are summarized in
Table 5.
Two different series of new enantiopure bidentate bis-
(diamidophosphite) ligands have been prepared by a simple
two-step synthesis: one containing a heterocycle derived from
disubstituted cyclohexyldiamine (1 and 2) and the other
derived from dimethylbinaphthyldiamine (3). The correspond-
ing cationic complexes [Rh(COD)(P,P)]BF4 have been
prepared and fully characterized in order to be used as catalytic
precursors.
The new Rh(I) complexes have been tested in the
asymmetric hydrogenation of prochiral benchmark substrates
α-dehydro amino acid methyl esters and dimethyl itaconate.
Good conversion and ee values were obtained with most of
them. The precursors containing the ligand with a benzylcy-
clohexyl terminal fragment and the butanediol derived bridging
group ((R,R;Sal,Sal;R,R)-1a) yielded up to 99% ee. This result is
remarkable, as it is the only bidentate diamidophosphite ligand
without the atropoisomeric binaphthyl group that achieves
excellent enantioselectivity in asymmetric hydrogenation. It is
To the best of our knowledge, only a few catalytic systems
based on rhodium precursors have been efficient in the metal-
catalyzed asymmetric hydrogenation of cyclic enamides (e.g.,
G
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THF (10 mL) was added dropwise at 0 °C. After 4 h of stirring,
hexane (5 mL) was added and the white precipitate of triethylamine
hydrochloride was filtered off. The solvent was removed under
vacuum, and a yellowish oil was obtained and used without
purification.
noteworthy that excellent enantioselectivity (ee > 99%) was
obtained for the hydrogenation of all the tested substrates with
the complex containing the (R;Ral,Ral;R)-3c ligand. The activity
with this ligand is similar to those reported for bidentate
diamidophosphites and some monodentate phosphoramidites
with the binaphthyl fragment. Large match−mismatch effects
have been observed for the diastereoisomers of the ligands 1a
and 3a,d tested in the process studied. The results obtained
suggest that within bis(diaminophosphites) with a cyclohexyldi-
amine terminal fragment, those with a short and flexible bridge
induce better enantioselectivities, while for those with the
binaphthyldiamine terminal fragment, the best enantioselectiv-
ities are obtained when the bridging fragment is long and
flexible. We applied the best catalytic precursor, [Rh(COD)-
((R,Ral,Ral,R)-3c)]BF4, in the asymmetric hydrogenation of
cyclic enamides and β-amino esters, providing good conversion
and moderate enantioselectivities.
(R,R;Sal,Sal;R,R)-1a: yield 0.47 g (36%); HR-MS (ESI) m/z
C44H56N4O2P2 735.3943 [MH]+; [α]298(c 1.0, CH2Cl2) = −40.90°;
31P NMR (CDCl3, 101.25 MHz), δ (ppm) 137.6 (s); 1H NMR
(CDCl3, 400 MHz) δ (ppm) (J (Hz)) 7.46 −7.12 (om, 20H,
CH(Ar)), 4.40−4.17 (om, 6H, CH2(Bn)), 3.99 (m, 2H, OCH), 3.80
2
3
(dd, JHH= 15.2, JHP = 9.2, 2H, CH2(Bn)), 2.98 (m, 2H, CH(Cy)),
2.52 (m, 2H, CH(Cy)), 1.79−0.81 (om, 16H, CH2(Cy)), 1.11 (d, 3JHH
= 6.0, 6H, CH3); 13C NMR (CDCl3, 100 MHz) δ (ppm) (J (Hz))
3
3
141.4 (d, JCP = 9.0, 2C, C(Ar)), 140.8 (d, JCP = 3.0, 2C, C(Ar)),
129.3−126.5 (om, 20C, CH(Ar)), 72.1 (dd, 2JCP = 14.0, 3JCP = 3.0 2C,
OCH), 67.3 (d, JCP = 7.0, 2C, CH(Cy)), 66.2 (d, JCP = 8.0, 2C,
CH(Cy)), 50.2 (d, 2JCP = 33.0, 2C, CH2(Bn)), 48.3 (d, 2JCP = 14.0, 2C,
CH2(Bn)), 30.4 (s, 2C, CH2(Cy)), 30.2 (s, 2C, CH2(Cy)), 24.5 (s, 2C,
2
2
3
CH2(Cy)), 24.2 (s, 2C, CH2(Cy)), 16.4 (d, JCP = 2.0, 2C, CH3).
(R,R;Ral,Ral;R,R)-1a: yield 0.60 g (45%); HR-MS/ESI m/z
C44H56N4O2P2 735.3923 [MH]+; [α]298(c 1.0, CH2Cl2) = −36.12°;
31P NMR (CDCl3, 101.25 MHz) δ (ppm) 138.2 (s); 1H NMR
(CDCl3, 400 MHz) δ (ppm) (J (Hz)) 7.63−7.00 (om, 20H, CH(Ar)),
EXPERIMENTAL SECTION
■
General Remarks. All reactions were carried out under a purified
nitrogen atmosphere using standard Schlenk and vacuum-line
techniques. The solvents were purified by standard procedures and
distilled under nitrogen; Et3N and i-Pr2EtN were distilled from CaH2
and collected over 4 Å molecular sieves before use. The diols (R,R)-
and (S,S)-2,3-butanediol, (R,R)-1,2-cyclohexanediol, (−)-2,3-O-iso-
propylidene-D-threitol, and (R)- and (S)-1,1′-bi-2-naphthol, (R,R)-1,2-
cyclohexanediamine, (R,R)-N,N′-dimethyl-1,2-cyclohexanediamine,
(R)- and (S)-N,N′-dimethyl-1,1′-binaphthyl-2,2′-diamine, and PCl3
were used as supplied from Aldrich. (R,R)-N,N′-dibenzyl-1,2-cyclo-
hexanediamine was prepared as previously described.39 [Rh(COD)2]-
BF4 used in the synthesis of the precatalysts was purchased from Alfa
Aesar, and the starting substrates dimethyl itaconate and methyl 2-
acetamidoacrylate were obtained from Aldrich. (Z)-α-acetamidocinna-
mate was synthesized by a previously described method.40
4.40−4.11 (om, 6H, CH2(Bn)), 3.93 (m, 2H, OCH), 3.80 (dd, 2JHH
=
15.0, 3JHP = 10.2, 2H, CH2(Bn)), 2.98 (m, 2H, CH(Cy)), 2.48 (m, 2H,
3
CH(Cy)), 2.10−0.76 (om, 16H, CH2(Cy)), 1.14 (d, JHH = 6.4, 6H,
CH3); 13C NMR (CDCl3, 100 MHz), δ(ppm) (J (Hz)) 141.2 (d, 3JCP
= 8.0, 2C, C(Ar)), 140.5 (d, 3JCP = 3.0, 2C, C(Ar)), 129.7−126.6 (om,
2
3
20C, CH(Ar)), 72.1 (dd, JCP = 14.0, JCP = 2.0, 2C, OCH), 67.1 (d,
2JCP = 7.0, 2C, CH(Cy)), 66.0 (d, JCP = 8.0, 2C, CH(Cy)), 50.0 (d,
2
2JCP = 34.0, 2C, CH2(Bn)), 48.2 (d, JCP = 14.0, 2C, CH2(Bn)), 30.3
2
3
(d, JCP = 3.0, 2C, CH2(Cy)), 30.1 (s, 2C, CH2(Cy)), 24.4 (s, 2C,
CH2(Cy)), 24.2 (s, 2C, CH2(Cy)), 15.5 (d, JCP = 3.4, 2C, CH3).
3
(R,R;Ral,Ral;R,R)-1b: yield 0.28 g (22%); HR-MS/ESI m/z
C46H58N4O2P2 761.4079 [MH]+; [α]298(c 1.0, CH2Cl2) = −49.15°;
31P NMR (CDCl3, 101.25 MHz) δ (ppm) 136.5 (s); 1H NMR
(CDCl3, 400 MHz) δ (ppm) (J (Hz)) 7.64−7.12 (om, 20H, CH(Ar)),
4.50−4.06 (om, 6H, CH2(Bn)), 3.82 (m, 4H, 2OCH + 2CH2(Bn)),
3.00 (m, 2H, CH(Cy)), 2.47 (m, 2H, CH(Cy)), 2.05−0.81 (om, 24H,
CH2); 13C NMR (CDCl3, 100 MHz) δ (ppm) (J (Hz)) 141.6 (d, 3JCP
= 8.0, 2C, C(Ar)), 140.4 (s, 2C, C(Ar)), 129.0−125.2 (om, 20C,
1H, 13C (1H, 13C, standard SiMe4), and 31P (31P, standard H3PO4)
NMR spectra were recorded on Bruker DRX 250 (31P, 101 MHz),
Varian Unity 300 MHz (13C, 75 MHz; 31P, 121.4 MHz), Varian
Mercury 400 MHz (13C, 100 MHz; 31P, 161.9 MHz), and Varian
Mercury 500 MHz (13C, 125 MHz) spectrometers in CDCl3 unless
otherwise stated. Chemical shifts in ppm are reported downfield from
standards. The two-dimensional experiments were carried out on a
Varian Mercury 400 MHz or a Varian Mercury 500 MHz instrument.
Mass spectra were recorded with a LC/MSD-TOF (Agilent
Technologies) spectrometer (ESI). The GC analyses were performed
on a Hewlett-Packard 5890 Series II gas chromatograph (30 m
Chiraldex DM column for dimethyl itaconate 6, 25 m Chirasil-L-Val
for methyl α-acetamidoacrylate 4, (Z)-α-acetamidocinnamate 5, and
(Z)-α-acetamido(p-fluorophenyl)acrylate 11, 30 m Beta-DEX for
cyclic enamide 7, and (Z)-β-acetamidoacrylate 10) with an FID
detector. Enantiomeric excesses for hydrogenation products of cyclic
enamides 8 and 9 were determined by HPLC on a Chiracel OD H and
Chiracel OJ, respectively. Elemental analyses were carried out in an
Eager 1108 microanalyzer. Optical rotations were measured on a
Perkin-Elmer 241 MC spectropolarimeter at 25 °C.
General Procedure for the Synthesis of Bis-
(diamidophosphites) (R,R;Sal,Sal;R,R)-1a, (R,R;Ral,Ral;R,R)-1a,
(R,R;Ral,Ral;R,R)-1b, (R,R;Ral,Ral;R,R)-1c, and (R,R;Sal;R,R)-1d.
(R,R)-N,N′-Dibenzyl-1,2-cyclohexanediamine (1.06 g, 3.6 mmol) and
NEt3 (1.50 mL, 10.8 mmol) were dissolved in 10 mL of toluene. PCl3
(0.40 mL, 4.6 mmol) dissolved in 5 mL of toluene was added dropwise
at 0 °C. The mixture was warmed to room temperature and was stirred
for 2 h. The formation of the chlorodiazaphospholidine was monitored
by 31P NMR spectroscopy (δ 174.5 ppm), being complete after this
period. The solvent and the excess of PCl3 were thoroughly removed
under reduced pressure to afford a viscous oil. This oil was dissolved in
toluene (10 mL), and the corresponding diol (1.8 mmol) (R,R)-/
(S,S)-2,3-butanediol in toluene (10 mL) or (R,R)-1,2-cyclohexanediol,
(−)-2,3-O-isopropylidene-D-threitol, or (R)-/(S)-1,1′-bi-2-naphthol in
2
2
CH(Ar)), 73.5 (d, JCP = 12.0 2C, OCH), 66.5 (d, JCP = 7.0, 2C,
2
CH(Cy)), 66.3 (d, JCP = 8.0, 2C, CH(Cy)), 49.7 (d, 2JCP = 33.0, 2C,
CH2(Bn)), 48.3 (d, 2JCP = 14.0, 2C, CH2(Bn)), 30.4 (s, 2C, CH2(Cy)),
30.2 (s, 2C, CH2(Cy)), 29.8 (s, 2C, CH2(Cy)), 24.4 (s, 2C, CH2(Cy)),
24.2 (s, 2C, CH2(Cy)), 24.1 (s, 2C, CH2(Cy)).
(R,R;Ral,Ral;R,R)-1c: yield 0.54 g (41%); HR-MS/ESI m/z
C47H60N4O4P2 807.4163 [MH]+; [α]298(c 1.0, CH2Cl2) = −35.78°;
31P NMR (CDCl3, 101.25 MHz) δ (ppm) 136.3 (s); 1H NMR
(CDCl3, 400 MHz) δ (ppm) (J (Hz)) 7.68−7.05 (om, 20H, CH(Ar)),
4.39−4.15 (om, 6H, CH2(Bn)), 3.98−3.85 (om, 4H, 2CH2(Bn) +
2OCH2), 3.83 (m, 2H, OCH), 3.53 (m, 2H, OCH2), 3.01 (m, 2H,
CH(Cy)), 2.55 (m, 2H, CH(Cy)), 2.00−0.80 (om, 16H, CH2(Cy)),
1.40 (s, 6H, CH3); 13C NMR (CDCl3, 100 MHz), δ(ppm) (J (Hz))
3
3
140.9 (d, JCP = 7.0, 2C, C(Ar)), 140.5 (d, JCP = 3.0, 2C, C(Ar)),
129.1−126.4 (m, 20C, CH(Ar)), 109.4 (s, 1C, O2CMe2), 78.4 (d, 3JCP
= 4,0, 2C, OCH), 67.4 (d, 2JCP = 6.0, 2C, CH(Cy)), 66.4 (d, 2JCP = 8.0,
2C, CH(Cy)), 64.6 (d, 2JCP = 9.0, 2C, OCH2), 50.3 (d, 2JCP = 33.0, 2C,
CH2(Bn)), 48.1 (d, 2JCP = 14.0, 2C, CH2(Bn)), 30.3 (s, 2C, CH2(Cy)),
29.9 (s, 2C, CH2(Cy)), 27.2 (s, 2C, CH3), 24.5 (s, 2C, CH2(Cy)), 24.2
(s, 2C, CH2(Cy)).
(R,R;Sal;R,R)-1d: yield 1.11 g (84%); HR-MS/ESI m/z
C60H60N4O2P2Se2 1091.2580 [MH]+; [α]298(c 1.0, CH2Cl2) =
1
−9.59°; 31P NMR (toluene, 101.25 MHz) δ (ppm) 139.3 (s); H
NMR (C6D6, 400 MHz) δ (ppm) (J (Hz)) 7.81−6.85 (om, 32H,
2
3
CH(Ar)), 4.23−3.92 (om, 6H, CH2(Bn)), 3.09 (dd, JHH = 16.0, JHP
= 8.0, 2H, CH2(Bn)), 2.61 (m, 2H, CH(Cy)), 2.41 (m, 2H, CH(Cy)),
1.66−0.47 (ms, 16H, CH2(Cy)); 13C NMR (C6D6, 100 MHz) δ
(ppm) (J (Hz)) 151.6 (s, 2C, C(Ar)), 141.8 (m, 4C, C(Ar)), 140.4 (s,
H
dx.doi.org/10.1021/om400119q | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
2C, C(Ar)), 135.4 (s, 2C, C(Ar)), 130.4 (s, 2C, C(Ar)), 129.3−121.6
(om, 32C, CH(Ar)), 67.2 (bs, 2C, CH(Cy)), 66.9 (bs, 2C, CH(Cy)),
49.9 (d, JCP = 34.0, 2C, CH2(Bn)), 48.8 (d, JCP = 15.0, 2C,
CH2(Bn)), 30.7 (s, 2C, CH2(Cy)), 30.1 (s, 2C, CH2(Cy)), 24.5 (s, 2C,
CH2(Cy)), 24.3 (s, 2C, CH2(Cy)).
31P NMR (CDCl3, 121.44 MHz) δ (ppm) 176.6 (s); 1H NMR
(CDCl3, 400 MHz) δ (ppm) (J (Hz)) 7.97−7.00 (om, 24H, CH(Ar)),
2
2
3
4.26 (m, 2H, OCH), 2.96 (d, JHP = 12.0, 6H, CH3(NMe)), 2.90 (d,
3
3JHP = 12,0, 6H, CH3(NMe)), 1.25 (d, JHH = 4.0, 6H, CH3); 13C
NMR (CDCl3, 100 MHz) δ (ppm) (J (Hz)) 145.6 (s, 2C, C(Ar)),
2
Synthesis of Bis(diamidophosphite) Ligand (R,R;Sal,Sal;R,R)-
2a. (R,R)-N,N′-Dimethylcyclohexane-1,2-diamine (0.51 g, 3.6 mmol)
and NEt3 (1.50 mL, 10.8 mmol) were dissolved in 10 mL of toluene.
PCl3 (0.4 mL, 4.6 mmol) dissolved in 5 mL of toluene was added
dropwise at 0 °C. The mixture was warmed to room temperature and
was stirred for 2 h. The formation of the chlorodiazaphospholidine was
monitored by phosphorus NMR spectroscopy (δ 174.5 ppm), being
complete after this period. The solvent and the excess PCl3 were
thoroughly removed under reduced pressure to afford a viscous oil.
This oil was dissolved in toluene (10 mL), and DMAP (2.6 × 10−3 g,
0.021 mmol) was added. A solution of a stoichiometric amount of the
diol (S,S)-2,3-butanediol (0.16 g, 1.8 mmol) and 1.3 mL of NEt3 (9,0
mmol) in toluene (10 mL) was added dropwise in three portions at 0
°C. After the mixture was stirred overnight at room temperature,
hexane (5 mL) was added and the white precipitate of triethylamine
hydrochloride was filtered off. The solvent was removed under
vacuum, and a brownish oil was obtained and used without further
purification: yield 0.41 g (53.7%); HR-MS/ESI (m/z) C20H40N4O2P2
431.2697 [MH]+; [α]298(c 1.0, CH2Cl2) = −125.48°; 31P NMR
145.0 (s, 2C, C(Ar)), 142.2 (d, JCP = 6.0, 2C, C(Ar)), 133.1 (s, 2C,
C(Ar)), 132.7 (s, 2C, C(Ar)), 131.7 (s, 2C, C(Ar)), 131.3 (s, 2C,
C(Ar)), 130.7 (s, 2C, C(Ar)), 129.7−121.4 (om, 24C, CH(Ar)), 72,6
2
3
2
(dd, JCP = 19.0, JCP = 6.0, 2C, OCH), 37.7 (d, JCP = 45.0, 2C,
2
3
CH3(NMe)), 35.5 (d, JCP = 25.4, 2C, CH3(NMe)), 16.8 (d, JCP
3.5, 2C, CH3).
=
(R;Ral,Ral;R)-3c: yield 0.40 g (59%); HR-MS/ESI (m/z)
C51H48N4O4P2 843.3210 [MH]+; [α]298(c 1.0, CH2Cl2) = −325.13°;
31P NMR (CDCl3, 101.25 MHz) δ (ppm) 168.9 (s); 1H NMR
(CDCl3, 400 MHz) δ (ppm) (J (Hz)) 7.99−7.00 (om, 24H, CH(Ar)),
3.86 (m, 2H, OCH), 3.78 (m, 2H, OCH2), 3.68 (m, 2H, OCH2), 3.05
3
3
(d, JHP = 12.0, 6H, CH3(NMe)), 2.85 (d, JHP = 10.0, 6H,
CH3(NMe)), 1.42 (s, 6H, CH3); 13C NMR (CDCl3, 100 MHz) δ
(ppm) (J (Hz)) 144.9 (d, 2JCP = 5.0, 2C, C(Ar)), 142.7 (d, 2JCP = 7.0,
2C, C(Ar)), 133.0−121.1 (om, 36C, 12C(Ar) + 24CH(Ar)), 109.7 (s,
2
1C, O2CMe2), 77.9 (s, 2C, OCH), 64.3 (d, JCP = 7.0, 2C, OCH2),
38.0 (d, JCP = 44.2, 2C, CH3(NMe)), 35.1 (d, JCP = 26.2, 2C,
CH3(NMe)), 27.2 (s, 2C, CH3).
2
2
(S;Sal;S)-3d: yield 0.39 g (51.0%); HR-MS/ESI (m/z)
C64H48N4O2P2 967.3317 [MH]+; [α]298(c 1.0, CH2Cl2) = +202.93°;
31P NMR (CDCl3, 121.44 MHz) δ (ppm) 173.6 (s); 1H NMR
(CDCl3, 400 MHz) δ (ppm) (J (Hz)) 8.07−6.86 (om, 34H, CH(Ar)),
1
(CDCl3, 121.44 MHz) δ (ppm) 139.1 (s); H NMR (CDCl3, 400
MHz) δ (ppm) (J (Hz)) 4.06 (m, 2H, OCH), 2.69 (d, 3JHP = 16.0, 6H,
3
CH3(NMe)), 2.66 (m, 2H, CH(Cy)), 2.56 (d, JHP = 16.0, 6H,
CH3(NMe)), 2.30 (m, 2H, CH(Cy)), 2.10−1.00 (om, 16H,
4
3
5.98 (d, JHP = 2.0, 2H, CH(Ar)), 2.20 (d, JHP = 16.0, 6H,
3
CH2(Cy)), 1.11 (d, JHH = 4.0, 6H, CH3); 13C NMR (CDCl3, 100
CH3(NMe)), 1.98 (d, JHP = 8,0, 6H, CH3(NMe)); 13C NMR
(CDCl3, 100 MHz) δ (ppm) (J (Hz)) 151.3 (d, JCP = 8.0, 2C,
C(Ar)), 144.7 (d, JCP = 5.0, 2C, C(Ar)), 141.8 (d, JCP = 6.0, 2C,
C(Ar)), 134.2−120.1 (54C, 18C(Ar) + 36CH(Ar)), 36.5 (d, JCP
43.0, 2C, CH3(NMe)), 34.0 (d, JCP = 25.0, 2C, CH3(NMe)).
3
2
3
MHz, 298 K) δ (ppm) (J (Hz)) 71.8 (dd, JCP = 10.0, JCP = 3.0, 2C,
2
2
2
OCH), 69.4 (d, JCP = 7.0, 2C, CH(Cy)), 65.8 (d, JCP = 9.0, 2C,
CH(Cy)), 32.7 (d, 2JCP = 37.0, 2C, CH3(NMe)), 30.2 (d, 2JCP = 11.0,
2C, CH3(NMe)), 29.4 (s, 2C, CH2(Cy)), 29.1 (s, 2C, CH2(Cy)), 24.3
2
2
=
2
3
(s, 2C, CH2(Cy)), 24.2 (s, 2C, CH2(Cy)), 16.2 (d, JCP = 1.0, 2C,
(R,Sal,R)-3d: yield 0.34 g (44%); HR-MS/ESI (m/z) C64H48N4O2P2
CH3)
967.3322 [MH]+; [α]298(c 1.0, CH2Cl2) = −28.09°; 31P NMR
General Procedure for the Synthesis of Bis-
(diamidophosphites) (R;Sal,Sal;R)-3a, (S;Sal,Sal;S)-3a, (R;Ral,Ral;R)-
3c, (S;Sal;S)-3d, and (R;Sal;R)-3d. (R)- and (S)-N,N′-dimethyl-1,1′-
binaphthyldiamine (0.5 g, 1.6 mmol) and ethyldiisopropylamine (2.20
mL, 12.6 mmol) were dissolved in 10 mL of toluene at 0 °C. PCl3
(0.30 mL, 3.5 mmol) dissolved in 5 mL of toluene was added dropwise
at 0 °C. The mixture was warmed to room temperature and was stirred
for 20 h. The formation of the chlorodiazaphosphepine was monitored
by phosphorus NMR spectroscopy (δ 205.0 ppm), being complete
after this period. The solvent and excess PCl3 and ethyldiisopropyl-
amine were thoroughly removed under reduced pressure to afford a
viscous oil. This oil was dissolved in toluene (10 mL), and DMAP (2.6
× 10−3 g, 0.021 mmol) was added. The corresponding diol (0.8 mmol;
((S,S)-2,3-butanediol) in toluene (10 mL) or (−)-2,3-O-isopropyli-
dene-D-threitol or (R)-/(S)-1,1′-bi-2-naphthol) in THF (10 mL)) and
triethylamine (2.2 mL, 15.8 mmol) were added in three portions at 0
°C. After it was stirred overnight at room temperature, the mixture was
cooled at 4 °C. The white precipitate of amine hydrochloride was
filtered off. The solvent was removed under vacuum, and a yelow solid
was obtained and used without further purification.
1
(CDCl3, 101.25 MHz) δ (ppm) 174.6 (s); H NMR (CDCl3, 400
MHz) δ (ppm) (J (Hz)) 8.08−6.96 (om, 36H, CH(Ar)), 2.68 (d, 3JHP
= 13.6, 6H, CH3(NMe)), 2.21 (d,3JHP = 9.2, 6H, CH3(NMe)); 13C
NMR (CDCl3, 100 MHz) δ (ppm) (J (Hz)) 150.6 (d, 2JCP = 8.0, 2C,
2
2
C(Ar)), 144.8 (d, JCP = 5.0, 2C, C(Ar)), 141.7 (d, JCP = 6.0, 2C,
2
C(Ar)), 134.7−121.7 (54C, 18C(Ar) + 36CH(Ar)), 38.0 (d, JCP
50.0, 2C, CH3(NMe)), 34.7 (d, JCP = 24.0, 2C, CH3(NMe)).
=
2
(S,Ral,S)-3d: yield 0.39 g (51%); HR-MS/ESI (m/z) C64H48N4O2P2
967.3322 [MH]+; [α]298(c 1.0, CH2Cl2) = +23.30°.
General Procedure for the Synthesis of Selenide Deriva-
tives. 0.15 mmol of ligand dissolved in 2 mL of toluene in the
presence of 2.4 mmol of selenium powder was stirred under N2 for 24
h at room temperature. The reaction mixture was filtered through
Celite. The compounds were characterized by 31P NMR (101 MHz)
in toluene.
General Procedure for the Synthesis of Rhodium Com-
plexes. A solution of the corresponding bis(diamidophosphite) ligand
(0.1 mmol) in toluene (5 mL) was added dropwise to a vigorously
stirred CH2Cl2 solution (20 mL) of [Rh(COD)2]BF4 (0.041 g, 0.10
mmol), in the presence of free COD when not freshly prepared (0.032
g, 0.3 mmol). The mixture was stirred for an additional 15 min and
concentrated to dryness at reduced pressure. The solid was washed
with ether (3 × 8 mL) and dried under vacuum.
(R;Sal,Sal;R)-3a: yield 0.29 g (48%); HR-MS/ESI (m/z)
C48H44N4O2P2 771.3021 [MH]+; [α]298(c 1.0, CH2Cl2) = −263.35°;
31P NMR (CDCl3, 101.25 MHz) δ (ppm) 178.3 (s); 1H NMR
(CDCl3, 400 MHz) δ (ppm) (J (Hz)) 8.06−7.02 (om, 24H, CH(Ar)),
[Rh(COD)((R,R;Sal,Sal;R,R)-1a)]BF4: yellow solid; yield 0.062 g
3
(60%); mp 222−226 °C dec; 31P NMR (CDCl3, 121.44 MHz) δ
4.40 (m, 2H, OCH), 3.03 (d, JHP = 12.0, 6H, CH3(NMe)), 2.99 (d,
3
3JHP = 12.0, 6H, CH3(NMe)), 1.21 (d, JHH = 8,0, 6H, CH3); 13C
1
1
(ppm) (J (Hz)) 139.8 (d, JPRh = 228.3 Hz); H NMR (CD2Cl2, 500
MHz) δ (ppm) (J (Hz)) 7.84−6.96 (m, 20H, CH(Ar)), 5.70 (pt, 2JHH
NMR (CDCl3, 100 MHz) δ (ppm) (J (Hz)) 144.9 (d, 2JCP = 5.0, 2C,
2
= 3JHP = 12.5, 2H, CH2(Bn)), 5.42 (bs, 2H, CH(COD)), 5.29 (bs, 2H,
C(Ar)), 141.9 (d, JCP = 6.0, 2C, C(Ar)), 133.1 (s, 2C, C(Ar)), 132.8
2
(s, 2C, C(Ar)), 131.8 (s, 2C, C(Ar)), 131.2 (s, 2C, C(Ar)), 130.8 (s,
CH(COD)), 4.56 (bs, 4H, 2OCH + 2CH2(Bn)), 4.19 (dd, JHH
=
3
2
2C, C(Ar)), 129.0−121.3 (om, 26C, 2C(Ar) + 24CH(Ar)), 73.7 (dd,
17.5, JHP = 7.5, 2H, CH2(Bn)), 3.63 (d, JHH = 15.0, 2H, CH2(Bn)),
2.91 (m, 2H, CH(Cy)), 2.65 (m, 2H, CH(Cy)), 2.44 (m, 4H, CH2
(COD)), 2.28 (m, 4H, CH2(COD)), 2.15−0.75 (om, 16H,
3
2
2JCP = 23.5, JCP = 2.5, 2C, OCH), 37.8 (d, JCP = 45.0, 2C,
2
3
CH3(NMe)), 35.4 (d, JCP = 26.0, 2C, CH3(NMe)), 14.8 (d, JCP
5.0, 2C, CH3).
=
3
CH2(Cy)), 1.11 (d, JHH = 5.0, 6H, CH3); HR-MS (ESI) m/z
(S;Sal,Sal;S)-3a: yield 0.32 g (51%); HR-MS/ESI (m/z)
945.3874 [M]+. Anal. Calcd for C52H68BF4N4O2P2Rh: C, 60.47; H,
6.64; N, 5.42. Found: C, 59.55; H, 6.65; N, 5.82.
C48H44N4O2P2 771.3004 [MH]+; [α]298(c 1.0, CH2Cl2) = +327.15°;
I
dx.doi.org/10.1021/om400119q | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
[Rh(COD)((R,R;Ral,Ral;R,R)-1a)]BF4: yellow solid; yield 0.064 g
(62%); mp 222−228 °C dec; 31P NMR (CDCl3, 121.44 MHz) δ
2H, CH(Ar)), 5.18 (bs, 2H, CH(COD)), 5.08 (bs, 2H, CH(COD)),
3
3
3.31 (d, JPH = 8.0, 6H, CH3(NMe)), 2.50 (d, JPH = 12.0, 6H,
CH3(NMe)), 2.45−2.30 (m, 4H, CH2(COD)), 2.08 (m, 4H,
CH2(COD)); HR-MS (ESI) m/z C72H60BF4N4O2P2Rh 1177.3241
[M]+ . Anal. Calcd for C72H60BF4N4O2P2Rh: C, 68.37; H, 4.78; N,
4.43. Found: C, 67.69; H, 5.00; N, 4.57.
General Procedure for the Hydrogenation Reactions. Hydro-
genation reactions at 10 bar of hydrogen pressure were carried out in a
50 mL stainless steel autoclave, while experiments at 1.5 bar of
hydrogen pressure were carried out in a Fischer−Porter glass tube
reactor. In both cases the reactor was carefully dried and purged with
H2.
When the reaction was carried out with the preformed precursor, a
mixture of 0.01 mmol of [Rh(COD)(P,P)]BF4 and 1.0 mmol of
substrates 4−7 or 0.5 mmol of substrates 8−11 was dissolved in 25
mL of CH2Cl2 in a Schlenk tube under nitrogen. The yellow solution
was stirred at room temperature for 15 min and then was transferred
into the autoclave. For the in situ experiments a solution of the
bis(diamidophosphite) (0.011 mmol) with [Rh(COD)2]BF4 (0.01
mmol) in CH2Cl2 (5 mL) under nitrogen was used. After 15 min of
stirring at room temperature CH2Cl2 (20 mL) solutions of the
substrates 4−6 (1.0 mmol) were added and transferred into the
reactor. For both cases the reactor was pressurized with 10 or 1.5 bar
of H2 and stirred at 800 rpm. After 6 h (or the desired time) the
hydrogen pressure was carefully released. The reaction mixture was
filtered through a short pad of silica, eluted with CH2Cl2, and
subjected to conversion and ee determination by chiral GC analysis or
HPLC.
1
(ppm) (J (Hz)) 136.8 (d, JPRh = 216.2); 1H NMR (CDCl3, 300
MHz), δ (ppm) (J (Hz)) 7.76−6.73 (m, 20H, CH(Ar)), 5.84 (pt, 2JHH
= 3JHP = 15.0, 2H, CH2(Bn)), 5.74 (bs, 2H, CH(COD)), 5.08 (bs, 2H,
CH(COD)), 4.22 (bs, 4H, 2OCH + 2CH2(Bn)), 3.48 (m, 2H,
CH2(Bn)), 3.23 (m, 2H, CH2(Bn)), 2.91 (m, 4H, CH(Cy)), 2.49 (bs,
4H, CH2 (COD)), 2.38 (bs, 4H, CH2(COD)), 1.94− 0.87 (om, 16H,
3
CH2(Cy)), 1.14 (d, JHH = 3.0, 6H, CH3); HR-MS (ESI) m/z
945.3878 [M]+. Anal. Calcd for C52H68BF4N4O2P2Rh: C, 60.47; H,
6.64; N, 5.42. Found: C, 59.81; H, 6.59; N, 5.60.
[Rh(COD)((R,R;Ral,Ral;R,R)-1b)]BF4: yellow solid; yield 0.065 g
(61%). mp 202−216 °C dec; 31P NMR (CH2Cl2/toluene, 121.44
1
1
MHz) δ (ppm) (J (Hz)) 134.8 (d, JPRh = 216.2); H NMR (CDCl3,
400 MHz), δ (ppm) (J (Hz)) 7.82−6.82 (m, 20H, CH(Ar)), 5.91 (bs,
2H, CH2(Bn)), 5.79 (bs, 2H, CH(COD)), 5.04 (bs, 2H, CH(COD)),
2
4.22 (bs, 4H, 2OCH + 2CH2(Bn)), 3.49 (d, JHH = 20.0, 2H,
2
3
CH2(Bn)), 2.92 (dd, JHH = 20.0, JHP = 8.0, 2H, CH2(Bn)), 2.47−
2.32 (m, 8H, 4CH(Cy) + 4CH2(COD)), 2.08- 0.65 (om, 28H,
2 4 C H 2 ( C y )
+ 4 C H 2 ( C O D ) ) ; H R - M S ( E S I ) m / z
C54H70BF4N4O2P2Rh 971.4023 [M]+. Anal. Calcd for
C54H70BF4N4O2P2Rh: C, 61.25; H, 6.66; N, 5.29. Found: C, 60.32;
H, 6,66; N, 4.99.
[Rh(COD)((R,R;Ral,Ral;R,R)-1c)]BF4: yellow solid; yield 0.068 g
(62%). mp 220−223 °C dec; 31P NMR (CDCl3, 121.44 MHz) δ
1
(ppm) (J (Hz)) 125.0 (d, JPRh = 227.1); 1H NMR (CDCl3, 400
MHz) δ (ppm) (J (Hz)) 7.86−6.66 (m, 20H, CH(Ar)), 5.47 (pt, 2JHH
= 3JHP = 14.0, 2H, CH2(Bn)), 5.26 (bs, 2H, CH(COD)), 5.07 (bs, 2H,
CH(COD)), 4.42−4.34 (m, 4H, CH2(Bn)), 4.10−4.05 (m, 4H,
2CH2(Bn) + 2OCH2), 3.80 (bs, 2H, OCH), 3.05 (m, 2H, CH(Cy),
2.86 (m, 2H, CH(Cy)), 2.74 (m, 2H, CH2(COD)), 2.65 (m, 2H,
CH2(COD)), 2.40 - 0.56 (om, 22H, 16CH2(Cy) + 4CH2(COD) +
2OCH2), 1.15 (s, 6H, CH3); HR-MS (ESI) m/z 1017.4091 [M]+.
Anal. Calcd for C55H72BF4N4O4P2Rh: C, 59.79; H, 6.57; N, 5.07.
Found: C, 59.37; H, 6.21; N, 5.17.
ASSOCIATED CONTENT
* Supporting Information
■
S
Text giving experimental details for the determination
procedures of conversion and ee of the hydrogenation reaction
1
and figures giving H and 13C NMR spectra for the new
bis(diamidophosphite) ligands. This material is available free of
charge via the Internet at http://pubs.acs.org.
[Rh(COD)((R,R;Sal,Sal;R,R)-2a)]BF4: yellow solid; yield 0.046 g
(63%). mp 212−215 °C dec; 31P NMR (CH2Cl2/toluene, 121.44
1
1
MHz) δ (ppm) (J (Hz)) 134.0 (d, JPRh = 228.3); H NMR (CDCl3,
400 MHz) δ (ppm) (J (Hz)) 5.17 (bs, 2H, CH(COD)), 5.04 (bs, 2H,
AUTHOR INFORMATION
Corresponding Author
*M.R.: tel, (+34)-93 403 91 35; fax, (+34)-93 402 12 73; e-
mail, merce.rocamora@qi.ub.es.
■
3
CH(COD)), 4.18 (bs, 2H, OCH), 2.99 (d, JHP = 16.0, 6H,
3
CH3(NMe)), 2.59 (d, JHP = 16.0, 6H, CH3(NMe)), 2.17 (m, 2H,
CH(Cy)), 2.06 (m, 2H, CH(Cy)), 1.86 (bs, 8H, CH2(COD)), 1.10
3
(d, JHH = 4.0, 6H, CH3) 1.56−0.98 (om, 16H, CH2(Cy)); HR-MS
(ESI) m/z 533.1687 [M
C28H52BF4N4O2P2Rh: C, 46.17; H, 7.20; N, 7.69. Found: C, 45.94;
H, 7.05; N, 6.52.
−
(COD)]+. Anal. Calcd for
Notes
The authors declare no competing financial interest.
[Rh(COD)((R;Sal,Sal;R)-3a)]BF4: yellow solid; yield 0.047 g (44%).
ACKNOWLEDGMENTS
mp 204−210 °C dec; 31P NMR (CH2Cl2/toluene, 121.44 MHz) δ
■
1
(ppm) (J (Hz)) 130.7 (d, JPRh = 219.8); 1H NMR (CDCl3, 400
This work was supported by the Spanish Ministerio de Ciencia
́
y Tecnologia (CTQ2010-15292/BQU) and by the Generalitat
MHz) δ (ppm) (J (Hz)) 8.00−6.98 (m, 24H, CH(Ar)), 5.09 (bs, 2H,
CH(COD)), 4.87 (bs, 2H, OCH), 4.75 (bs, 2H, CH(COD)), 3.68 (m,
6H, CH3(NMe)), 3.05 (bs, 6H, CH3(NMe)), 2.33 (m, 2H, CH2
(COD)), 2.21 (m, 4H, CH2 (COD)), 2.08 (m, 2H, CH2 (COD)),
1.43 (bs, 6H, CH3); MALDI/TOF m/z 981.29 [M]+. Anal. Calcd for
C56H56BF4N4O2P2Rh: C, 62.93; H, 5.28; N, 5.24. Found: C, 62.24; H,
5.34; N, 4.92.
de Catalunya Departament d’Univeritats, Recerca i Societat de
la Informacio
IFARHU-SENACYT program. We thank Prof. A. Riera
(Departament de Quimica Organica, Universitat de Barcelona)
́
(2009SGR1164). M.J.B. is grateful to the
̀
for a generous gift of substrates 7−11.
[Rh(COD)((R;Ral,Ral;R)-3c)]BF4: yellow solid; yield 0.081 g (71%).
mp 216−220 °C dec; 31P NMR (CDCl3, 121.44 MHz) δ (ppm) (J
(Hz)) 130.6 (d, 1JPRh = 227.1); 1H NMR (CDCl3, 400 MHz) δ (ppm)
(J (Hz)) 8.05−6.81 (m, 24H, CH(Ar)), 5.56 (bs, 2H, CH(COD)),
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dx.doi.org/10.1021/om400119q | Organometallics XXXX, XXX, XXX−XXX

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dx.doi.org/10.1021/om400119q | Organometallics XXXX, XXX, XXX−XXX