Tuning of the structures of chiral phosphane-phosphites: Application to the highly enantioselective synthesis of α-acyloxy phosphonates by catalytic hydrogenation

Article abstract of DOI:10.1002/chem.200601032

A family of new chiral phosphane-phosphites 5 has been prepared and employed in the synthesis of rhodium complexes of formulation [Rh(cod)(5)]BF4 (7). The use of bulky phosphane or phosphite groups in the preparation of 7 avoids the formation of undesired

Full text of DOI:10.1002/chem.200601032

FULL PAPER
DOI: 10.1002/chem.200601032
Tuning of the Structures of Chiral Phosphane-Phosphites: Application to the
Highly Enantioselective Synthesis of a-Acyloxy Phosphonates by Catalytic
Hydrogenation
Miguel Rubio, Sergio Vargas, AndrØs Suµrez, Eleuterio lvarez, and Antonio Pizzano*[a]
Abstract: A family of new chiral phos-
phane-phosphites 5 has been prepared
and employed in the synthesis of rhodi-
um complexes of formulation [Rh-
tion plane. A detailed screening of li-
gands 1 and 5 in catalytic asymmetric
hydrogenations of enol phosphonates
12 demonstrated a critical influence of
the steric characteristics of the phos-
phane-phosphite in the course of the
reaction, and optimization of the two
phosphorus functionalities resulted in
the production of versatile and efficient
catalysts for this class of hydrogena-
tions: enantioselectivities of up to
98% ee were thus obtained with sub-
strates bearing an alkyl substituent in
the b-position, while for their challeng-
ing aryl counterparts values of up to
92% ee were achieved. The coordina-
tion mode of phosphonate 12a towards
a Rh phosphane-phosphite fragment
has also been investigated and a prefer-
ence of the olefin fragment to occupy
the position cis to the phosphite group
has been observed. From this observa-
tion an interpretation of the configura-
tions of the hydrogenated phospho-
nates has also been made.
A
phosphane or phosphite groups in the
preparation of 7 avoids the formation
of undesired disubstituted complexes,
one of which (9a) has been isolated
and characterized. Ligands 5 display
important differences from the bulkier
phosphane-phosphites 1: complexes
7—unlike their rigid [Rh(cod)(1)]BF4
G
Keywords: asymmetric catalysis
·
counterparts—show fluxional behav-
iour in solution, consistent with back-
bone oscillation around the coordina-
enantioselectivity · hydrogenation ·
P ligands · rhodium
Introduction
of a reaction,[3] or may even reduce the number of partici-
pant reaction intermediates, facilitating stereochemical con-
trol of the process.[4] In this regard, phosphane-phosphites
are appealing compounds, due to the differences in the
donor abilities of their phosphorus functions, arising from
the strong p-acceptor character of the phosphite group.[5]
The first applications of chiral phosphane-phosphites in
asymmetric catalysis, studied by Takaya and Nozaki, provid-
ed very high enantioselectivities in the hydroformylation of
olefins,[6] while more recently the scope of this class of li-
gands has been considerably expanded and they have pro-
vided efficient catalysts for several enantioselective transfor-
mations such as hydrogenation, hydroboration or allylic sub-
stitution, among others.[7] Moreover, the production of new
chiral catalysts containing phosphane and phosphite func-
tionalities by the use of mixtures of monodentate[8] or self-
assembled ligands[9] has also been studied.
À
The use of chiral bifunctional ligands (L L’) has become a
powerful strategy in catalyst design for enantioselective pro-
cesses. In recent years a wide variety of chelating ligands
[1]
combining P, S, N, C or O donor groups have been de-
scribed, and the optimization of their structures has pro-
duced impressive results in a broad range of enantioselective
catalytic transformations.[2]
À
Electronic dissimilarity in coordinating functions of L L’
À
is a highly useful feature. L L’ may allow better adjustment
À
than symmetric L L to the specific electronic requirements
[a] Dr. M. Rubio, S. Vargas, Dr. A. Suµrez, Dr. E. lvarez,
Dr. A. Pizzano
Instituto de Investigaciones Químicas
Consejo Superior de Investigaciones Científicas and
Universidad de Sevilla, Avda AmØrico Vespucio s/n
Isla de la Cartuja, 41092 Sevilla (Spain).
Fax : (+34)954-460-565
We have recently synthesized a family of modularly de-
signed phosphane-phosphites 1 and have employed them in
the highly enantioselective hydrogenation of dimethyl itaco-
nate and methyl (Z)-a-acetamidocinnamate (MAC).[5,10] Al-
ternatively, ligands of type 2 have provided enantioselectivi-
E-mail: pizzano@iiq.csic.es
Supporting information for this article is available on the WWW
under http://www.chemeurj.org/ or from the author.
Chem. Eur. J. 2007, 13, 1821 – 1833
ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
1821

ties around the 80% ee level in the asymmetric hydrogena-
tion of N-aryl imines.[11] The easily tuneable structures of
compounds 1 and 2 make them appropriate tools with which
to examine the hydrogenation of challenging substrates: the
reduction of enol ester phosphonates for the synthesis of
biologically[12] and synthetically[13] important chiral a-hy-
droxy phosphonates, for instance, is of great interest. Studies
covering the scope of this transformation have used impor-
tant rhodium catalysts bearing DuPHOS,[14a] BisP* or Mini-
phos ligands,[14b] and these investigations have provided ex-
cellent enantioselectivities in hydrogenations of b-alkyl-sub-
stituted phosphonates, although catalyst performance is sig-
nificantly reduced with b-aryl substrates. Notably, the latter
can provide convenient access[15] to important phosphorus
analogues of phenylalanine (A), tyrosine (B) or DOPA
Scheme 1. Synthesis of phosphane-phosphites 5.
prepared by a modification of the procedure described by
Schmalz (Scheme 2).[19] Finally, condensation of 3 with
phenol-phosphanes 4 readily provided the series of phos-
phane-phosphites 5.
Scheme 2. Preparation of phosphane 4e.
Synthesis and structures of catalyst precursors: With the
intent to apply ligands 5 in catalytic hydrogenations, we first
studied the synthesis of catalyst precursors of formulation
[Rh
ACHTREUNG
the case of ligands 1,[5] reactions between [Rh
stoichiometric amounts of chiral phosphane-phosphites 5b,
5e and 2a (Ar = Ph) provided the corresponding com-
AHCTREUNG
(C).[16] In this full account we report a detailed study of the
application of phosphane-phosphite (P-OP) ligands to the
enantioselective hydrogenation of enol-ester phosphonates
in studies including the synthesis of new ligands and catalyst
precursors, supplemented with X-ray and NMR structural
data for pertinent rhodium complexes. Part of this work has
been published in a preliminary form.[17]
plexes 7b, 7e and [Rh
N
N
when the reaction was attempted with ligand 5a a mixture
composed of the desired compound 7a and a second species
9a, in a ratio of 1:4, was observed. Characterization of the
latter complex only showed signals for coordinated 5a in the
1H NMR spectrum, while the 31P{1H} data consisted of two
complex multiplets in the regions characteristic of phos-
phanes and phosphites, respectively. These signals match a
simulated spectrum of a split (by coupling with the 103Rh nu-
cleus) AA’XX’ spin system (Figure 1).[20] Remarkable
among the calculated 31P–31P coupling constants is one of
high magnitude (400 Hz), diagnostic of a trans arrangement
of a phosphane and a phosphite group[21] and indicative of
the existence of two 5a molecules bonded to a Rh atom. Di-
nuclear-type structures for this compound were ruled out by
an X-ray analysis, which finally identified 9a as [Rh-
Results and Discussion
Ligand synthesis: After the observation of low reaction
rates in hydrogenations of a,b-unsaturated phosphonates
with catalysts based on ligands 1, we next examined structur-
ally related ligands bearing less sterically demanding phos-
phite groups. Accordingly, chlorophosphite 3 (Scheme 1)
was prepared from the corresponding bisphenol,[18] while to
provide the other component a set of phenol-phosphanes 4
was used. In addition to the previously reported 4a–c,[5,11]
additional examples were prepared in order to widen the tu-
neability of this ligand family. The 1-naphthyl derivative 4d
was thus synthesized by demethylation of the corresponding
o-anisyl phosphane,[5] while the tert-butyl phosphane 4e was
A
square-planar geometry with P-Rh-P angles between trans
disposed functionalities around 1658. The two ligands are co-
ordinated with phosphane and phosphite groups occupying
mutually trans positions, as might be expected from their
1822
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Chem. Eur. J. 2007, 13, 1821 – 1833

Enantioselective Hydrogenation Catalysts
FULL PAPER
a consequence of competition
between [Rh
A
[Rh(cod)(5)]BF4 for free 5, so
AHCTREUNG
in order to destabilize this sit-
uation we instead started from
the more labile [Rh
(thf)2]BF4, prepared by chloride
abstraction from [Rh(Cl)(cod)]2
A
AHCTREUNG
ACHTREUNG
by AgBF4 in THF.[23] In good
accord with our expectations,
addition of an equivalent of
ligand 5a to the THF solvate
yielded the monosubstituted
compound
[Rh
G
N
(complex 7a) in good yield.
This methodology was also ap-
plied to the synthesis of the o-
tolyl (7c) and 1-naphthyl (7d)
derivatives.
From
a practical point of
view it was pertinent to exam-
ine whether a phosphane-phos-
phite derived from the commer-
cially available BINOL would
behave similarly to ligands of
type 5, as the bisphenol used in
the preparation of the latter re-
quires several synthetic steps in
the laboratory. For this purpose
we chose the phosphane-phos-
phite 10, previously described
by Pringle,[24] and prepared the
corresponding complex [Rh-
Figure 1. Calculated (top) and experimentally measured (bottom) 31P{1H} NMR spectra for complex 9a. Cou-
pling constants used for the simulated spectrum: JPC,Rh = 121 Hz, JPO,Rh = 228 Hz, JPC,PC = JPO,PO = À70 Hz,
JPC,PO (cis) = 33 Hz, JPC,PO (trans) = 400 Hz.
(cod)(10)]BF4 (11) by the pro-
cedure described for 7a.
With the goal of gaining in-
matched electronic properties. Notably, the closeness of the
phosphane functionalities allows an offset p-stacked ar-
rangement between two phenyl rings,[22] with a distance of
3.77 Š between their centroids, so the arrangement of the
two 5a ligands gives rise to a rather congested structure that
should not be attainable with a tBu-substituted phosphite or
with phosphane-phosphites containing bulky phosphane
groups, explaining experimental observations.
While the dissimilar bonding abilities of phosphane and
phosphite functionalities are useful for stereocontrol in
asymmetric catalysis, they inherently favour the formation
of undesired disubstituted complexes. The simultaneous for-
mation of 1:1 and 1:2 rhodium/ligand compounds should be
formation relating to the structure of coordinated 5 in a cat-
alyst precursor, we performed an X-ray diffraction study of
compound 7a: an ORTEP view is depicted in Figure 3 along
with selected bond lengths and angles. Compound 7a dis-
plays a square-planar coordination geometry, with a P-Rh-P
bite angle of 868, somewhat smaller than that determined in
Rh(Cl)(CO)
(1a) (898; R = Ph).[5] On the other hand, the
A
dihedral angle between the aryl rings of the biphenyl is 548,
a value very similar to those found in BINOL moieties in
BINAPHOS derivatives (52–548)[25] and appreciably smaller
than that observed in coordinated 1a (638). The removal of
the tBu groups has thus produced a narrowing of the angle
between the aromatic halves of the biphenyl fragment,[26] an
Chem. Eur. J. 2007, 13, 1821 – 1833
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1823

A. Pizzano et al.
tionally causing the rigidity of
coordinated 1.[5] From these
considerations it might be ex-
pected that 7 should display
fluxional behaviour resulting
from backbone flipping, and to
investigate this possibility we
examined compounds [Rh-
A
ACHTREUNG
A
ACHTREUNG
(Figure 4). As a diagnostic mea-
sure of the mobility of the coor-
dinated P-OP system we exam-
ined the NOE signals between
the methyne protons of the iso-
propyl groups (Hb, Hc) and the
aromatic proton adjacent to the
phosphine group (Ha). As ex-
pected, the complex derived
from 1b only showed a NOE
with one of the isopropyl moi-
eties. Conversely, compound 7b
exhibited signals for the two
methynes, in good accord with
Figure 2. ORTEP view of the cation of 9a. H atoms have been omitted and bonds in the back ligand are
À
À
drawn dashed for clarity. Selected bond lengths [Š] and angles [8]: Rh1 P1 2.2198(16), Rh1 P2 2.3191(15),
P1-Rh1-P2 87.12(6), P1-Rh1-P51 93.94(6), P1-Rh1-P52 163.03(6), P2-Rh1-P52 98.65(6).
a
dynamic process involving
backbone oscillation around the
coordination plane. We further
tried to observe both conform-
ers separately, but only one set
of signals was observed down
to 180 K in the 31P{1H} experi-
ment. Thus, the removal of tBu
substituents in the phosphite
has a dual effect, both reducing
the hindrance exerted by this
group and increasing the flexi-
bility of the complex. This dy-
namic behaviour may be of im-
portance, since it causes a less
defined position of the phos-
phane substituents and, in addi-
tion, should permit better ac-
commodation of sterically con-
gested substrates such as phos-
phonates 12 (see below).[27]
Figure 3. ORTEP view of the cation of 7a. H atoms have been omitted for clarity. Selected bond lengths [Š]
À
À
À
À
À
and angles [8]. Rh1 P1 2.1913(11), Rh1 P2 2.2835(12), Rh1 C35 2.265(5), Rh1 C36 2.314(4), Rh1 C39
À
À
À
2.237(5), Rh1 C40 2.252(4), C35 C36 1.366(8), C39 C40 1.353(7), P1-Rh1-P(2) 85.69(4).
Hydrogenation of unsaturated
effect also observed in the calculated structures of a series
of iridium complexes bearing P-OP ligands.[11] An interest-
ing feature of this structure is the syn orientation of the
bridged phenylene with respect to the exo aryl part (consti-
tuted by carbons C7–C12) of the biphenyl fragment. This ar-
rangement, also observed in disubstituted 9a, is the opposite
of the anti orientation observed in complexes derived from
1, which has been attributed to an interaction between the
phenylene backbone and a tBu group of the phosphite, addi-
phosphonates: Catalyst screening for the hydrogenation of
phosphonates 12 was started with complexes [Rh-
A
(Scheme 3). Interestingly, the catalyst derived from ligand
1a produced a high enantioselectivity (entry 1, Table 1), but
the reaction was rather slow, and stronger conditions
(20 atm, 408C) were needed to complete the reaction at a
lower catalyst loading (entry 2). The reaction was further
slowed by any increase in the size of the b substituent of the
1824
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Enantioselective Hydrogenation Catalysts
FULL PAPER
À
(P
Table 1. Hydrogenation of 12a–12d in the presence of [Rh
G
OP)]BF4.[a]
Entry
Substrate
P-OP
Conversion
% ee (Conf.)
1[b]
2[b,c]
3
4
5
6
7
8
9
10
11
12[b]
13
14
15
16
17
18
19
20
12a
12a
12a
12a
12a
12a
12b
12b
12b
12b
12b
12b
12b
12b
12b
12b
12c
12c
12d
12d
1a
1a
1a
2a
5a
5b
1a
1b
2a
5a
5b
5b
5c
5d
5e
10
20
95 (S)
94 (S)
93 (S)
88 (S)
85 (R)
91 (R)
85 (S)
78 (S)
82 (S)
89 (R)
95 (R)
96 (R)
87 (R)
98 (R)
n.a.
100
100
100
100
100
25
18
93
100
100
100
70
100
10
100
100
100
100
100
86 (R)
91 (R)
98 (R)
91 (R)
96 (R)
5a
5b
5a
5b
[a] Conditions: 4 atm H2, 258C, CH2Cl2, S/C = 100, 24 h, unless other-
1
wise stated. Degree of conversion was determined by H NMR and enan-
tiomeric excess by HPLC, while absolute configuration was assigned by
comparison of optical rotation with literature values. n.a. = not analysed.
[b] S/C = 500. [c] 20 atm H2, 408C.
lyst precursor 8a produced a significant improvement in cat-
alyst activity, with a moderate enantioselectivity value
(entry 9). Likewise, precatalyst 7a exhibited good activity
and gave
a slightly increased optical purity of 13b
(entry 10). Most notably, though, use of the isopropyl com-
plex 7b gave a completed reaction with an excellent enan-
tioselectivity of 95% ee (entry 11). Interestingly, use of this
catalyst at a lower catalyst loading (S/C = 500) also pro-
duced a completed reaction without loss of enantiomeric
excess (entry 12).
Figure 4. Sections of the 2D NOESY experiments for compounds [Rh-
(cod)
G
U
E
To complete the study, the behaviour of ligands bearing
other phosphane substituents was also investigated. In the
hydrogenation of 12b the isopropyl catalyst was only slightly
outperformed by the 1-naphthyl derivative, which gave a
98% ee (entry 14), while 7c and 7e gave lower conversions
(entries 13, 15). Hydrogenation of substrates 12c and 12d
with precatalyst 7b also gave excellent enantioselectivities,
with 98 and 96% ee values, respectively (entries 18, 20). As
previously noted,[14b] the enantioselectivity increases with
the size of the b substituent of the phosphonate, as is dem-
onstrated in the results obtained with 7b: 91 (H), 95 (Et),
96 (nBu) and 98% ee (iPr).
Scheme 3. Hydrogenation of phosphonates 12.
Previous reports have demonstrated that compounds 12
with aryl substituents at the R’ position are particularly diffi-
cult to hydrogenate with high enantioselectivity, and in the
next step in our study we investigated the performance of 7
in the reduction of these aromatic derivatives. Studies were
initiated with a screening of the hydrogenation of 12h (a
convenient precursor for C), with the best conversion being
obtained with catalyst precursor 7a, which afforded a good
enantioselectivity of 82% ee (entry 7, Table 2), while use of
substrate, with uncompleted reactions being observed in the
hydrogenation of 12b in the presence of catalysts derived
from 1a or 1b (entries 7, 8).
Two strategies to improve catalyst activity were devised:
firstly, the use of ligands 2, with more flexible ethane back-
bones, and secondly, use of phosphane-phosphite systems
containing smaller phosphite groups. Accordingly, the cata-
Chem. Eur. J. 2007, 13, 1821 – 1833
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1825

A. Pizzano et al.
Table 2. Hydrogenation of b-aryl 12e–12h in the presence of [Rh(cod)-
A
G
U
[a]
À
A
of 12a. These reactions afforded samples not clean enough
for NMR analysis, with the exception of that starting with
Entry
Substrate
P-OP
Conversion
% ee (Conf)[b]
1
2
3
4
5
6
7
8
12e
12e
12 f
12 f
12g
12g
12h
12h
12h
12h
12h
12h
5a
5b
5a
5b
5a
5b
5a
5b
5c
5d
5e
10
100
100
100
80
100
43
100
60
2
82 (R)
92 (R)
87 (R)
83 (R)
82 (R)
91 (R)
82 (R)
86 (R)
n.a.
[Rh(nbd)(14)]BF4 (16, Scheme 4), which generated the
A
9
10
11
12
5
5
100
n.a.
n.a.
81 (R)
[a] See footnote in Table 1 for conditions and determinations. [b] The
configurations of 13 f and 13h were both tentatively assigned as R by
analogy with the signs of optical rotation and HPLC elution order of 13e
and 13g.
Scheme 4. Synthesis of 17.
precatalyst 7b increased the enantioselectivity to 86% ee
(entry 8), although it was less reactive. Moreover, bulkier
catalysts derived from 5c–e gave negligible conversions (en-
tries 9–11). Notably, the isopropyl catalyst 7b gave outstand-
ing enantioselectivities with phenyl and anisyl substrates—
92 and 91% ee, respectively—although in the latter case an
incomplete reaction (43% conversion) was observed (en-
tries 2, 6). Attempts to increase the levels of conversion
through the use of higher pressures were unsuccessful. Cata-
lyst precursor 7b was more enantioselective than the phenyl
derivative 7a both in the aliphatic and in the aromatic
series, the sole exception to this being represented by the p-
tolyl substrate 12 f, for which the best value (87% ee) was
obtained with the phenyl catalyst (entries 3, 4).
adduct [Rh(14)(12a)]BF4 (17). Compound 17 shows three
G
signals in its 31P{1H} NMR spectrum recorded at 240 K: a
doublet of doublets at d = 137.4 ppm (JP,Rh = 259 Hz, JP, P
= 68 Hz) due to the phosphite group, together with a dou-
blet of doublets of doublets at d = 6.1 ppm (JP, Rh = 149 Hz,
JP, P = 68, 12 Hz) for the phosphane function, while the coor-
dinated phosphonate appears as a doublet centred at
10.6 ppm due to the coupling with the 31P nucleus of the
1
phosphane. The JRh,P coupling constants are very similar to
those found in [Rh
N
N
bond occupies the position cis to the phosphite.[5] As report-
ed before for a diphosphine derivative,[14c] there is an ex-
change between free and coordinated 12a, and this process
allows ready identification of the proton positioned cis to
the phosphonate group of the coordinated olefin in the
phase-sensitive 2D NOESY. Interestingly, a NOE cross-
peak was observed between this proton and those of a tBu
substituent, these observations being indicative of a cis rela-
tionship between the olefin and the phosphite, which is in
good accord with the dominant importance of the latter
group in the stereochemical course of the reaction.
Finally, the catalyst precursor 11 behaved very similarly to
7a. The BINOL catalyst hydrogenated substrates 12a
(entry 16, Table 1) and 12g (entry 12, Table 2) with complete
conversion and with only slightly lower enantioselectivities
than 7a.
Coordination mode of 12 and mechanistic considerations:
Two elements for asymmetric induction can be considered
in the structures of phosphane-phosphites: the atropisomer-
ism of the phosphite group and the asymmetric distribution
of phosphane substituents (e.g., propeller-like structures in
ligands bearing PAr2 groups).[5] Although the second ele-
ment operates in rigid ligands 1, it should be minimized in
flexible 2a.[11] The relatively similar enantioselectivities pro-
vided by ligands 1a and 2a in the hydrogenation of 12a (93
and 82% ee, respectively) and 12b (85 and 82% ee, respec-
tively) point to the phosphite as the principal source of ste-
reoinduction.
An examination of the results collected in Tables 1 and 2
indicates that S products were in all cases obtained from cat-
alysts with ligands with S configurations (and conversely R
products from R ligands). The stereochemical sense of the
hydrogenation is also coincident with the hydrogenation of
MAC (Scheme 5).[14a] Interestingly, precatalyst 7a is much
more reactive towards hydrogenation of MAC than it is to-
wards 12, and can give completed reactions under similar
conditions at significantly lower catalyst loadings.
Because of the heterobifunctional nature of P-OP li-
gands, investigation of the coordination mode of olefins 12
towards the [Rh
(P-OP)]+ fragment may provide valuable
G
information about the course of the reaction. Several at-
tempts were made to generate a species of formulation [Rh-
A
G
Scheme 5. MAC hydrogenation.
1826
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Chem. Eur. J. 2007, 13, 1821 – 1833

Enantioselective Hydrogenation Catalysts
FULL PAPER
Investigations into Rh-catalysed asymmetric hydrogena-
tions of olefins tend to contemplate two alternatives for the
mechanism, known as the unsaturated and the dihydride
routes.[29] In the specific case of the reduction of substrates
12 with catalysts bearing electron-rich phosphanes, Gridnev
and Imamoto have proposed a mixed mechanism combining
both routes.[14b] The coincidence in stereochemistry of hy-
drogenations of MAC and 12 with our ligands allow the ap-
plication of models for enamide hydrogenation following
either mechanism to explain the configuration observed in
the hydrogenation of 12. With the aid of a quadrant dia-
gram[30] it can be visualized that an R phosphite should offer
greater encumbrance in the upper right quadrant (Figure 5).
chiral ligand on the course of the hydrogen addition.[32] Ap-
plication of this model to our system points to a preferred
addition of hydrogen to DR from the axial top position,
giving rise to dihydride ER.
In view, firstly, of the observation that intermediate com-
+[33]
À
À
plexes [Rh
A
(P P = diphosphine, S = sol-
vent) in the dihydride route are stabilized by strongly basic
ligands and, secondly, of the appreciably lower donor ability
of phosphane-phosphites in relation to diphosphanes, it is
plausible to expect a preference for the unsaturated route in
hydrogenations with P-OP ligands. On this assumption,
though without the intention to set out a mechanistic pro-
posal, it is, however, possible to make some additional com-
ments concerning the influence
of the phosphane-phosphite in
the process.
Because of the size of the
P(O)(OMe)2 group, phospho-
A
nates 12 are sterically more en-
cumbered than most of the ole-
fins so far subjected to study in
asymmetric
hydrogenations
(e.g., enamides, itaconates or
enol esters) possessing a planar
group bonded to the a-olefinic
carbon. The detrimental effect
of the P(O)(OMe)2 group on
G
the reaction rate was confirmed
by comparison of the hydroge-
nation of methyl a-benzoylox-
yacrylate with that of 12a
(Scheme 6). Under the condi-
tions of entry 1 in Table 1 the
enol ester was completely hy-
drogenated in less than 5 h,
while, as stated, 12a produced a
20% conversion after 24 h.
An important influence of
the size of the phosphite com-
ponent on the rate of the reac-
tion was observed during the
Figure 5. An interpretation of the stereochemical sense of the hydrogenation.
If a dihydride route were involved in these reactions, dihy-
drides with the olefin in the equatorial plane and the car-
bonyl oxygen in the axial position would be expected.[14b,31]
Now, if the preferential olefin coordination cis to the phos-
phite is kept, dihydrides F should be formed. Investigations
into the relative stabilities of these complexes suggest that
the chelated substrate produces the major steric impediment
and that preferred formation of FR (over FS) should there-
fore be expected. In an unsaturated mechanism, on the
other hand, the reaction should proceed through complexes
Scheme 6.
catalyst screening. On inspection of species D derived from
ligands 1 it would be expected that the P(O)(OMe)2 group
of composition [Rh
A
ACHTREUNG
calculations by Feldgus and Landis explained the different
reactivity of RhI adducts in terms of the influence of the dis-
similar interaction between the olefin fragment and the
should encounter steric encumbrance mainly with the upper
tBu group (for the R configuration in the phosphite) but
also to a significant extent with the lower tBu substituent.
Chem. Eur. J. 2007, 13, 1821 – 1833
ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
1827

A. Pizzano et al.
Me), 2.30 (s, 6H; 2”Me), 6.93 (d, JH,H = 8.0 Hz, 1H; H arom), 7.02 (d,
Logically, the phosphonate-phosphite interaction should be
significantly reduced with ligands 5. The phosphonate group
should also give rise to steric interaction with the phosphane
substituents in the dihydrides E, in good accord with the
lower levels of conversion obtained with catalysts containing
bulky phosphane groups. In this picture, the flexibility of the
Rh-(P-OP) fragment may play an important role in the reac-
tivity through diminution of its steric interaction with coor-
dinated 12.[34] This is shown by the faster reaction provided
JH,H
H arom); 13C{1H} NMR (CDCl3, 75 MHz): d = 17.8 (2”Ar-Me), 20.6
(Ar-Me), 20.7 (Ar-Me), 119.0 (d, JC,P = 2 Hz; CH arom), 119.2 (d, JC,P
= 8.0 Hz, 1H; H arom), 7.18 ppm (d, JH,H = 8.0 Hz, 2H; 2”
=
2 Hz; CH arom), 129.0 (Cq arom), 129.9 (CH arom), 130.5 (CH arom),
130.5 (Cq arom), 134.7 (Cq arom), 135.7 (Cq arom), 137.4 (Cq arom), 138.3
(Cq arom), 146.1 (d, JC,P = 4 Hz; OCq arom), 147.5 ppm (d, JC,P = 1 Hz;
OCq arom); 31P{1H} NMR (C6D6, 162 MHz): d
= 169.0 ppm; HRMS
(CI): m/z: calcd for C16H16O2PCl: 306.0576; found: 306.0574 [M]+.
(2-Hydroxyphenyl)-bis-(1-naphthyl)phosphane (4d): BBr3 (7.22 mL,
6.8 mmol) was added at À788C to a solution of (2-hydroxyphenyl)-bis-(1-
naphthyl)phosphine[35] (1.23 g, 3.1 mmol) in CH2Cl2 (40 mL). The result-
ing solution was stirred overnight at room temperature, the solvent was
evaporated, toluene (25 mL) was added to the obtained residue, and the
system was once more evaporated to dryness. The resulting solid was
treated with MeOH (20 mL) at 08C and stirred for two days, after which
solvent removal yielded the phosphonium bromide as a white solid,
which was suspended in Et2O (30 mL) and treated with NEt3. The mix-
ture was stirred for 2 h and filtered, and solvent removal yielded the
phosphine 4d as a white, foamy solid (0.54 g, 45%). 1H NMR (CDCl3,
300 MHz): d = 6.29 (brs, 1H; OH), 6.82 (m, 2H; 2”H arom), 6.97 (t,
JH,H = 6.0 Hz, 1H; H arom), 7.08 (t, JH,H = 6.0 Hz, 2H; 2”H arom),
7.31 (m, 3H; 3”H arom), 7.47 (m, 4H; 4”H arom), 7.86 (m, 4H; 4”
by 8a in relation to [Rh
N
N
namic effect should favour the higher activity of precatalysts
7 in relation to those derived from ligands 1.
Conclusion
A series of novel chiral phosphane-phosphites 5 has been
synthesized and used in the preparation of a series of com-
plexes [Rh(cod)(5)]BF4. These show important structural
E
=
8.0, 4.0 Hz, 2H; 2”H arom); 13C{1H}
differences from the analogues based on ligands 1 in terms
of steric encumbrance, dihedral angle of the biphenyl phos-
phite and dynamic properties. Extensive screening in hydro-
genations of unsaturated phosphonates 12 has shown this re-
action to be very sensitive to steric effects. Optimization of
the sizes of the two phosphorus functionalities in the chiral
ligands has resulted in enantioselectivities of up to 98% ee
with aliphatic substrates, while values of up to 92% ee have
been achieved for b-aryl olefins. The latter reagents signifi-
cantly outperform other catalysts examined for this reaction.
H arom), 8.34 ppm (dd, JH,H
NMR (CDCl3, 75 MHz): d = 115.9 (CH arom), 119.1 (Cq arom), 121.6
(CH arom), 126.0 (2”CH arom), 126.2 (CH arom), 126.4 (2”CH arom),
126.6 (CH arom), 126.8 (2”CH arom), 129.0 (2”CH arom), 130.3 (2”
CH arom), 131.2 (d, JC,P = 5 Hz; 2”Cq arom), 132.1 (CH arom), 133.0
(2”CH arom), 133.9 (d, JC,P = 5 Hz; 2”Cq arom), 135.4 (Cq arom), 135.5
(Cq arom), 135.8 (d, JC,P = 4 Hz; CH arom), 159.6 ppm (d, JC,P = 19 Hz;
Cq arom); 31P{1H} NMR (CDCl3, 121 MHz): d
=
À47.0 ppm; HRMS
(CI): m/z: calcd for C26H19OP: 378.1174; found: 378.1172 [M]+.
Di-tert-butyl-(2-tetrahydropyranoxyphenyl)phosphaneborane
(6e):
nBuLi (6.9 mL, 1.6m in hexanes, 11.0 mmol) was slowly added at À788C
to a solution of 2-phenoxytetrahydropyran[7c] (1.64 g, 9.2 mmol) in THF
(20 mL). The mixture was stirred for 0.5 h, allowed to warm to room
temperature and further stirred for 16 h, and the reaction mixture was
cooled to À788C and di(tert-butyl)chlorophosphine (2.1 mL, 11.0 mmol)
was added dropwise. The mixture was stirred for 1 h, BH3·SMe2 (1.0 mL,
10 mmol) was added, and the resulting mixture was stirred overnight,
after which water (20 mL) was added. The mixture was extracted with
CH2Cl2 (3”25 mL), and the organic fractions were collected, dried over
Na2SO4 and filtered. Evaporation of the resulting solution and purifica-
tion by column chromatography (n-hexanes/AcOEt 9:1), followed by re-
crystallization from Et2O/hexanes 1:1, yielded the corresponding phos-
A coordination study of the complex [Rh(14)(12a)]BF4, rep-
U
resentative of the RhI intermediate adduct of the hydroge-
nation unsaturated route, has shown that the olefin group
prefers the position cis to the phosphite. This arrangement is
in good accord with the configuration observed in the hy-
drogenated products.
Experimental Section
phane-borane as
300 MHz): d
CMe3), 1.34 (d, JH,P
CHH), 1.95 (m, 3H; CH2 and CHH), 3.64 (m, 1H; OCHH), 3.95 (m,
1H; OCHH), 5.33 (m, 1H; OCH(CH2)O), 7.00 (dd, JH,H = 8.5, 7.5 Hz,
1H; H arom), 7.19 (dd, JH,H = 8.4, JH,H = 2.1 Hz, 1H; H arom), 7.04
a
white solid (1.53 g, 49%). 1H NMR (CDCl3,
0.99 (brm, 3H; BH3), 1.30 (d, JH,P 12.9 Hz, 9H;
13.2 Hz, 9H; CMe3), 1.63 (m, 3H; CH2 and
=
=
=
General: All reactions and manipulations were performed under nitrogen
or argon, either in a Braun Labmaster 100 glovebox or by use of standard
Schlenk-type techniques. All solvents were distilled under nitrogen in the
presence of the following desiccants: sodium-benzophenone-ketyl for di-
ethyl ether (Et2O) and tetrahydrofuran (THF), sodium for n-hexane and
toluene, CaH2 for dichloromethane (CH2Cl2), and NaOMe for methanol
(MeOH). NMR spectra were obtained on Bruker DPX 300, DRX 400 or
DRX 500 spectrometers. 31P{1H} NMR shifts were referenced to external
85% H3PO4, while 13C{1H} and 1H shifts were referenced to the residual
signals of deuterated solvents. All data are reported in ppm downfield
from Me4Si. HPLC analyses were performed with a Waters 2690 instru-
ment, HRMS data were obtained with a Jeol JMS-SX 102 A mass spec-
AHCTREUNG
(dd, JH,H = 8.1, 7.5 Hz, 1H; H arom), 8.34 ppm (dd, JH,P = 14.1, JH,H
=
7.8 Hz, 1H; H arom); 13C{1H} NMR (CDCl3, 75 MHz): d = 21.1 (CH2),
25.0 (CH2), 29.5 (2”CMe3), 30.8 (CH2), 33.7 (d, JC,P = 24 Hz; CMe3),
34.0 (d, JC,P = 26 Hz; CMe3), 64.8 (OCH2), 98.9 (OCH
A
JC,P = 4 Hz; CH arom), 115.1 (d, JC,P = 39 Hz; Cq arom), 121.6 (d, JC,P
=
12 Hz; CH arom), 133.1 (CH arom), 140.4 (d, JC,P = 14 Hz; CH arom),
159.0 ppm (OCq arom); 11B{1H} NMR (CDCl3, 96 MHz): d = 2.5 ppm (d,
1JBP = 61 Hz); 31P{1H} NMR (CDCl3, 121 MHz): d = 55.6 ppm (brm);
HRMS (CI): m/z: calcd for C19H33BO2P: 335.2311; found: 335.2319
[MÀH]+.
trometer, and optical rotations were measured on
Model 341 polarimeter.
a Perkin–Elmer
Di-tert-butyl-(2-hydroxyphenyl)phosphane (4e): HBF4·OEt2 (1.8 mL,
54% wt in Et2O, 12.9 mmol) was added at 08C to a solution of 6e
(1.45 g, 4.3 mmol) in CH2Cl2 (30 mL). The mixture was stirred overnight
at room temperature and treated with deoxygenated water (20 mL), the
(R)-5,5’,6,6’-Tetramethyl-2,2’-bisphenoxyphosphorous chloride (3): (R)-
5,5’,6,6’-Tetramethyl-2,2’-bisphenol[18] (1.20 g, 4.95 mmol) was azeotropi-
cally dried with toluene (2”30 mL), dissolved in THF and added drop-
wise to a mixture of PCl3 (0.50 mL, 5.7 mmol) and pyridine (0.90 mL,
11.1 mmol) in THF. The suspension was stirred for 4 h and filtered, and
the solvent was evaporated under vacuum to yield 6 as a white, foamy
solid (1.29 g, 85%). 1H NMR (CDCl3, 400 MHz): d = 2.03 (s, 6H; 2”
resulting mixture was stirred for 12 h, and
a saturated solution of
NaHCO3 (40 mL) was added. The organic layer was separated, the aque-
ous one was extracted with CH2Cl2 (3”25 mL), the organic fractions
1828
www.chemeurj.org
ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2007, 13, 1821 – 1833

Enantioselective Hydrogenation Catalysts
FULL PAPER
were collected, dried over Na2SO4 and filtered, and the solvent was re-
moved under reduced pressure. The resulting residue was extracted with
n-hexanes (3”25 mL) and filtered, and solvent evaporation yielded 3e as
a white solid (0.80 g, 74%). Spectroscopic data obtained for this com-
pound are in accord with those reported in the literature.[36]
(R)-{2-[Di(1-naphthyl)phosphino]phenyl}-1,1’-(5,5’,6,6’-tetramethyl)bi-
phenyl-2,2’-diyl phosphite (5d): This compound was prepared as de-
scribed for 5a. White, foamy solid (0.18 g, 53%); [a]2D0 = À15.9 (c = 1.0,
THF); 1H NMR (CDCl3, 300 MHz): d = 1.89 (s, 3H; Me), 1.92 (s, 3H;
Me), 2.13 (s, 3H; Me), 2.23 (s, 3H; Me), 6.39 (d, JH,H = 8 Hz, 1H;
H arom), 6.51 (m, 1H; H arom), 6.62 (m, 2H; 2”H arom), 6.91 (t, JH,H
=
(R)-[2-(Diphenylphosphino)phenyl]-1,1’-(5,5’,6,6’-tetramethyl)biphenyl-
2,2’-diyl phosphite (5a): A solution of (2-hydroxyphenyl)diphenylphos-
phine (0.39 g, 1.6 mmol) in toluene (30 mL) was added dropwise to (R)-
7.2 Hz, 1H; H arom), 7.03 (m, 3H; 3”H arom), 7.29 (m, 4H; 4”
H arom), 7.46 (m, 4H; 4”H arom), 7.87 (m, 4H; 4”H arom), 8.53 ppm
(m, 2H; 2”H arom); 13C{1H} NMR (CDCl3, 125 MHz): d = 17.3 (s; Ar-
5,5’,6,6’-tetramethyl-2,2’-bisphenoxyphosphorous
chloride
(0.48 g,
Me), 17.4 (s; Ar-Me), 20.1 (s; Ar-Me), 20.2 (s; Ar-Me), 118.8 (d, JC,P
=
1.6 mmol) and NEt3 (0.33 mL, 2.4 mmol) dissolved in toluene (30 mL).
The resulting suspension was stirred for 24 h, the mixture was filtered,
volatiles were removed, and the obtained solid was dissolved in Et2O and
passed through a short pad of neutral alumina. The solution was evapo-
rated to yield a white solid (0.24 g, 28%). [a]2D0 = À17.5 (c = 1.0, THF);
1H NMR (CDCl3, 400 MHz): d = 1.96 (s, 3H; Me), 1.98 (s, 3H; Me),
2.23 (s, 3H; Me), 2.26 (s, 3H; Me), 6.72 (m, 2H; 2”H arom), 6.86 (d,
JH,H = 8.4 Hz, 1H; H arom), 6.95 (d, JH,H = 8.4 Hz, 1H; H arom), 7.02
(t, JH,H = 7.6 Hz, 1H; H arom), 7.11 (d, JH,H = 8.0 Hz, 1H; H arom),
8 Hz; CH arom), 120.3 (d, JC,P = 10 Hz; CH arom), 124.8 (s; CH arom),
125.8 (s; CH arom), 125.9 (s; CH arom), 126.3 (s, 2”CH arom), 126.4 (m;
2”CH arom), 126.5 (s; CH arom), 126.6 (s; CH arom), 126.7 (s;
CH arom), 126.8 (s; Cq arom), 126.9 (s; Cq arom), 127.0 (s; Cq arom),
128.3 (s; Cq arom), 128.5 (s; CH arom), 128.6 (s; CH arom), 129.3 (s;
CH arom), 129.6 (s; 2”CH arom), 129.7 (s; CH arom), 130.4 (s;
CH arom), 130.5 (s; Cq arom), 132.5 (s; Cq arom), 132.6 (s; Cq arom),
133.1 (s; CH arom), 133.3 (s; CH arom), 133.9 (d, JC,P
= 14 Hz;
Cq arom), 134.0 (s; Cq arom), 135.2 (s; CH arom), 135.3 (s; Cq arom),
135.8 (d, JC,P = 17 Hz; Cq arom), 136.3 (s; Cq arom), 137.4 (s; Cq arom),
146.1 (s; Cq arom), 146.3 (s; Cq arom), 154.4 ppm (m; Cq arom); 31P{1H}
7.19 (dd, JH,H
= 8.4, 4.4 Hz, 1H; H arom), 7.33 ppm (m, 11H; 11
H arom); 13C{1H} NMR (CDCl3, 75 MHz): d = 17.7 (Me), 17.8 (Me),
29.2 (2”Me), 119.1 (CH arom), 120.4 (d, JC,P = 10 Hz; CH arom), 124.9
(CH arom), 128.7 (CH arom), 128.8 (CH arom), 128.8 (CH arom), 128.9
(CH arom), 129.0 (CH arom), 129.2 (CH arom), 129.8 (CH arom), 130.0
(CH arom), 130.3 (Cq arom), 130.4 (CH arom), 130.9 (d, JC,P = 5 Hz;
Cq arom), 133.5 (2”Cq arom), 134.2 (2”CH arom), 134.4 (2”CH arom),
À
NMR (CDCl3, 162 MHz): d
=
À34.9 (d; P C), 134.5 ppm (d, JP, P
=
À
18 Hz; P O); HRMS (CI): m/z: calcd for C42H34O3P2: 648.1983; found:
648.1976 [M]+.
(R)-[2-(Di-tert-butylphosphino)phenyl]-1,1’-(5,5’,6,6’-tetramethyl)biphen-
yl-2,2’-diyl phosphite (5e): Application of the procedure described for 5a
yielded slightly impure compound 5e. Further purification attempts were
unsuccessful due to product decomposition, but these impurities do not
134.7 (CH arom), 136.3 (dd, JC,P
= 11, 3 Hz; Cq arom), 136.7 (2”
Cq arom), 137.8 (2”Cq arom), 146.5 (m; 2”Cq arom), 154.2 ppm (m;
Cq arom); 31P{1H} NMR (CDCl3, 162 MHz):
d
=
À17.1 (d, P C),
À
interfere in the preparation of [Rh
C
ACHTREUNG
À
134.5 ppm (d, JP, P
=
14 Hz; P O); HRMS (EI): m/z: calcd for
=
=
C34H30O3P2: 548.1670; found: 548.1673 [M]+.
10.8 Hz, 9H; CMe3), 1.23 (d, JH,P = 10.5 Hz, 9H; CMe3), 2.02 (s, 3H;
Me), 2.04 (s, 3H; Me), 2.29 (s, 3H; Me), 2.30 (s, 3H; Me), 7.13 (m, 7H;
7”H arom), 7.74 ppm (d, JH,H = 6.3 Hz, 1H; H arom); 13C{1H} NMR
(CDCl3, 75 MHz): d = 17.8 (2”Ar-Me), 20.5 (Ar-Me), 20.6 (Ar-Me),
(R)-[2-(Diisopropylphosphino)phenyl]-1,1’-(5,5’,6,6’-tetramethyl)biphen-
yl-2,2’-diyl phosphite (5b): This compound was prepared as described for
5a. White, foamy solid (0.20 g, 45%); [a]2D0 = À18.3 (c = 1.0, THF);
1H NMR (CDCl3, 500 MHz): d = 0.89 (m, 6H; CHMe2), 1.08 (m, 6H;
CHMe2), 2.02 (s, 3H; Me), 2.03 (s, 3H; Me), 2.16 (m, 2H; 2”CHMe2),
2.28 (s, 3H; Me), 2.30 (s, 3H; Me), 7.11 (m, 6H; 6”H arom), 7.30 (m,
1H; H arom), 7.43 ppm (m, 1H; H arom); 13C{1H} NMR (CDCl3,
125 MHz): d = 17.5 (2”Ar-Me), 19.7 (d, JC,P = 9 Hz; CHMe2), 20.2 (d,
JC,P = 17 Hz; CHMe2), 20.3 (2”Ar-Me), 23.1 (d, JC,P = 13 Hz; CHMe2),
23.4 (d, JC,P = 13 Hz; CHMe2), 118.8 (CH arom), 119.0 (CH arom), 120.0
(d, JC,P = 11 Hz; CH arom), 123.6 (CH arom), 128.6 (m; Cq arom), 129.1
(Cq arom), 129.4 (CH arom), 129.8 (CH arom), 130.1 (CH arom), 130.6
30.8 (d, JC,P = 8 Hz; CMe3), 31.0 (d, JC,P = 8 Hz; CMe3), 33.0 (d, JC,P
=
24 Hz, CMe3), 33.1 (d, JC,P 22 Hz, CMe3), 119.2 (d, JC,P 2 Hz;
=
=
CH arom), 119.4 (d, JC,P = 3 Hz; CH arom), 122.0 (dd, JC,P = 7, 3 Hz;
CH arom), 123.4 (CH arom), 129.4 (Cq arom), 129.7 (CH arom), 129.8
(Cq arom), 129.9 (CH arom), 130.5 (CH arom), 131.0 (d, JC,P = 4 Hz;
Cq arom), 133.3 (Cq arom), 134.2 (Cq arom), 136.2 (d, JC,P
CH arom), 136.8 (Cq arom), 137.7 (Cq arom), 147.2 (m, 2”OCq arom),
157.1 ppm (dd, JC,P
23, 5 Hz; OCq arom); 31P{1H} NMR (CDCl3,
= 3 Hz;
=
À
À
121 MHz): d = 9.7 (d, P C), 133.7 ppm (d, JP, P = 65 Hz; P O); HRMS
(CI): m/z: calcd for C30H39O3P2: 509.2374; found: 509.2372 [M+H]+.
(Cq arom), 133.3 (Cq arom), 134.1 (Cq arom), 135.2 (d, JC,P
= 10 Hz;
CH arom), 136.7 (Cq arom), 137.5 (Cq arom), 146.6 (2”Cq arom),
[Rh
A
G
(7a):
A
suspension of [Rh(cod)Cl]2 (0.040 g,
N
155.8 ppm (m; Cq arom); 31P{1H} NMR (CDCl3, 162 MHz): d = À1.8 (br,
0.082 mmol) and AgBF4 (0.032 g, 0.16 mmol) in THF (5 mL) was vigo-
rously stirred for 45 minutes protected from light. The resulting mixture
was filtered over a short pad of celite, ligand 5a (0.090 g, 0.16 mmol) in
THF (5 mL) was added dropwise, the reaction mixture was stirred for 1 h
and filtered, and the solvent was evaporated. The product was precipitat-
ed as an orange solid from CH2Cl2/Et2O 1:2 (0.090 g, 66%). 1H N MR
(CD2Cl2, 400 MHz): d = 1.90 (m, 1H; CHH), 1.97 (s, 3H; Me), 2.05 (s,
3H; Me), 2.20 (m, 3H; 3”CHH), 2.33 (s, 3H; Me), 2.37 (s, 3H; Me),
2.60 (m, 4H; 4”CHH), 4.10 (brs, 1H; =CH), 4.76 (brs, 1H; =CH), 5.73
(brs, 2H; 2”=CH), 7.02 (d, JH,H = 8 Hz, 1H; H arom), 7.08 (m, 2H; 2”
H arom), 7.31 (m, 6H; 6”H arom), 7.62 ppm (m, 9H; 9”H arom);
13C{1H} NMR (CDCl3, 75 MHz): d = 17.6 (Me), 17.8 (Me), 20.6 (2”Me),
27.2 (CH2), 28.4 (CH2), 32.4 (CH2), 32.9 (CH2), 100.7 (t, JC,P = 6 Hz,
JC,Rh = 6 Hz; =CH), 106.6 (t, JC,P = 7 Hz, JC,Rh = 7 Hz; =CH), 112.4 (dd,
JC,P = 10 Hz, JC,Rh = 6 Hz; =CH), 113.5 (dd, JC,P = 13 Hz, JC,Rh = 5 Hz;
À
À
P C), 135.3 ppm (d, JP, P = 25 Hz; P O); HRMS (CI): m/z: calcd for
C28H35O3P2: 481.2061; found: 481.2073 [M+H]+.
(R)-{2-[Di(o-tolyl)phosphino]phenyl}-1,1’-(5,5’,6,6’-tetramethyl)biphenyl-
A
2,2’-diyl phosphite (5c): The preparation of this phosphane-phosphite
was analogous to that described for 5a. White, foamy solid (0.19 g,
50%); [a]2D0 = À11.0 (c = 1.0, THF); 1H NMR (CDCl3, 300 MHz): d =
2.00 (s, 3H; Me), 2.03 (s, 3H; Me), 2.27 (s, 3H; Me), 2.31 (s, 3H; Me),
2.47 (s, 6H; 2”Me), 6.62 (d, JH,H = 8.1 Hz, 1H; H arom), 6.72 (m, 1H;
H arom), 6.81 (dd, JH,H = 12, 4 Hz, 2H; 2”H arom), 6.92 (d, JH,H
=
8 Hz, 1H; H arom), 6.99 (d, JH,H = 8 Hz, 1H; H arom), 7.11 (m, 4H; 4”
H arom), 7.32 ppm (m, 6H; 6”H arom); 13C{1H} NMR (CDCl3,
125 MHz): d = 17.8 (2”Ar-Me), 20.6 (2”Ar-Me), 21.4 (d, JC,P = 22 Hz,
Ar-Me), 21.6 (d, JC,P = 22 Hz, Ar-Me), 119.0 (CH arom), 121.0 (d, JC,P
=
9 Hz; CH arom), 125.2 (CH arom), 126.5 (CH arom), 128.5 (Cq arom),
128.8 (Cq arom), 129.1 (CH arom), 129.2 (CH arom), 129.8 (CH arom),
130.0 (CH arom), 130.3 (CH arom), 130.3 (CH arom), 130.4 (CH arom),
130.4 (CH arom), 130.5 (CH arom), 130.9 (m; Cq arom), 133.4 (Cq arom),
133.5 (CH arom), 133.7 (CH arom), 134.0 (Cq arom), 134.2 (Cq arom),
134.4 (Cq arom), 134.5 (CH arom), 136.8 (Cq arom), 137.8 (Cq arom),
143.0 (Cq arom), 143.3 (Cq arom), 146.7 (m; 2”Cq arom), 154.8 ppm (m;
=CH), 116.5 (d, JC,P
Cq arom), 118.4 (CH arom), 119.0 (CH arom), 122.2 (CH arom), 126.0 (d,
JC,P 8 Hz; CH arom), 126.7 (Cq arom), 127.7 (d, JC,P 10 Hz;
= 12 Hz; Cq arom), 117.2 (d, JC,P = 12 Hz;
=
=
Cq arom), 128.3 (Cq arom), 129.7 (CH arom), 129.9 (CH arom), 130.1
(CH arom), 130.2 (CH arom), 130.6 (CH arom), 131.1 (CH arom), 132.4
(CH arom), 133.1 (CH arom), 133.4 (2”CH arom), 133.5 (CH arom),
134.5 (CH arom), 134.7 (CH arom), 134.8 (CH arom), 135.7 (Cq arom),
136.2 (Cq arom), 138.2 (Cq arom), 138.6 (Cq arom), 145.8 (d, JC,P = 5 Hz;
Cq arom), 146.2 (d, JC,P = 13 Hz; Cq arom), 155.1 ppm (d, JC,P = 10 Hz;
Cq arom); 31P{1H} NMR (CDCl3, 162 MHz):
d
=
À32.7 (d, P C),
À
À
134.9 ppm (d, JP, P
=
30 Hz; P O); HRMS (CI): m/z: calcd for
C36H34O3P2: 576.1983; found: 576.1984 [M]+.
Chem. Eur. J. 2007, 13, 1821 – 1833
ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
1829

A. Pizzano et al.
Cq arom); 31P{1H} NMR (CD2Cl2, 162 MHz): d
=
16.4 (dd, JP, Rh
=
25.5 (CH2), 27.1 (CH2), 34.3 (CH2), 34.6 (CH2), 98.3 (m; =CH), 105.9 (m;
=CH), 111.8 (d, JC,P = 11 Hz; =CH), 114.4 (m; =CH), 118.3 (CH arom),
118.5 (Cq arom), 118.8 (CH arom), 120.3 (Cq arom), 120.9 (Cq arom),
123.1 (CH arom), 123.8 (Cq arom), 125.5 (m; Cq arom), 125.8 (Cq arom),
126.0 (2”CH arom), 126.2 (CH arom), 126.7 (CH arom), 127.5 (2”
CH arom), 127.7 (CH arom), 127.9 (CH arom), 128.0 (CH arom), 128.2
(Cq arom), 130.2 (CH arom), 130.6 (2”CH arom), 131.5 (CH arom),
À
À
136 Hz; P C), 132.3 ppm (dd, JP, Rh = 267 Hz, JP, P = 61 Hz; P O); ele-
mental analysis (%) calcd for C42H42BF4O3P2Rh: C 55.4, H 4.8; found: C
55.4, H 4.9.
[Rh
G
(5b)]BF4
ACHTREUNG
CH2Cl2 (10 mL) was added dropwise to a solution of [Rh
AHCTREUNG
(0.061 g, 0.15 mmol) in CH2Cl2 (5 mL). The resulting orange solution was
stirred for 3 h, concentrated, filtered and finally treated with Et2O
(30 mL), and the resulting solid was washed with Et2O and recrystallized
from CH2Cl2/Et2O 1:2, yielding 7b as yellow crystals (0.075 g, 65%).
132.8 (d, JC,P
= 10 Hz; Cq arom), 132.8 (Cq arom), 134.2 (CH arom),
134.2 (CH arom), 134.6 (CH arom), 134.7 (Cq arom), 135.5 (d, JC,P
=
7 Hz; Cq arom), 135.8 (CH arom), 136.0 (CH arom), 136.3 (CH arom),
138.4 (Cq arom), 138.9 (Cq arom), 144.4 (d, JC,P = 33 Hz; Cq arom), 146.2
1H NMR (CD2Cl2, 500 MHz): d
= 1.20 (dd, JH,H = 7.0 Hz, JH,P =
(d, JC,P
=
12 Hz; Cq arom), 154.0 ppm (d, JC,P
=
10 Hz; Cq arom);
14.0 Hz, 3H; CHMeMe), 1.35 (dd, JH,H = 7.0 Hz, JH,P = 15.5 Hz, 3H;
CHMeMe), 1.42 (dd, JH,H = 7 Hz, JH,P = 4.5 Hz, 3H; CHMeMe), 1.45
(dd, JH,H = 7.0 Hz, JH,P = 4.5 Hz, 3H; CHMeMe), 2.01 (s, 3H; Me), 2.08
(s, 3H; Me), 2.37 (s, 3H; Me), 2.38 (s, 3H; Me), 2.26 (m, 8H; 8”CHH),
2.71 (m, 1H; CHMe2), 2.88 (m, 1H; CHMe2), 3.88 (m, 1H; =CH), 5.55
31P{1H} NMR (CDCl3, 121 MHz): d = 17.7 (dd, JP,Rh = 139 Hz; P C),
À
À
139.0 ppm (dd, JP, Rh = 274 Hz, JP, P = 51 Hz; P O); elemental analysis
(%) calcd for C50H46BF4O3P2Rh·0.5CH2Cl2: C 61.3, H 4.8; found: C 60.9,
H 4.5.
(m, 1H; =CH), 5.89 (m, 1H; =CH), 6.49 (m, 1H; =CH), 6.83 (dd, JH,H
=
[Rh
(cod)
U
E
8.0, 4.5 Hz, 1H; H arom), 7.08 (d, JH,H = 8.5 Hz, 1H; H arom), 7.11 (d,
JH,H = 8.5 Hz, 1H; H arom), 7.32 (d, JH,H = 8.5 Hz, 1H; H arom), 7.33
(d, JH,H = 8.5 Hz, 1H; H arom), 7.36 (t, JH,H = 7.5 Hz, 1H; H arom),
7.52 (t, JH,H = 7.5 Hz, 1H; H arom), 7.56 ppm (t, JH,H = 7.5 Hz, 1H;
H arom); 13C{1H} NMR (CDCl3, 75 MHz): d = 17.7 (Ar-Me), 17.7 (d,
JC,P = 5 Hz; CHMeMe), 17.9 (Ar-Me), 18.2 (d, JC,P = 4 Hz; CHMeMe),
20.3 (d, JC,P = 5 Hz; CHMeMe), 20.5 (Ar-Me), 20.6 (d, JC,P = 4 Hz;
Orange solid (0.072 g, 60%); 1H NMR (CDCl3, 300 MHz): d = 1.33 (d,
JH,P = 14.7 Hz, 9H; CMe3), 1.68 (d, JH,P = 15.0 Hz, 9H; CMe3), 1.94 (s,
3H; Me), 2.01 (s, 3H; Me), 2.28 (m, 6H; 6”CHH), 2.31 (s, 6H; 2”Me),
2.68 (m, 2H; 2”CHH), 4.29 (m, 1H; =CH), 5.06 (m, 1H; =CH), 6.09 (m,
1H; =CH), 6.49 (dd, JH,H = 8.1 Hz, JH,P = 4.5 Hz, 1H; H arom), 6.67 (m,
1H; =CH), 7.10 (m, 5H; 5”H arom), 7.35 (t, JH,H
H arom), 7.83 ppm (t, JH,H
= 8.1 Hz, 1H;
=
6.6 Hz, 1H; H arom); 13C{1H} NMR
CHMeMe), 20.7 (Ar-Me), 26.6 (d, JC,P = 24 Hz, CHMe2), 27.4 (d, JC,P
22 Hz, CHMe2), 29.1 (CH2), 30.0 (CH2), 30.9 (CH2), 31.2 (CH2), 95.3 (t,
JC,P = JC,Rh = 8 Hz; =CH), 100.7 (t, JC,P = JC,Rh = 7 Hz; =CH), 108.9
=
(CDCl3, 125 MHz): d = 17.4 (Ar-Me), 17.6 (Ar-Me), 20.3 (2”Ar-Me),
26.3 (CH2), 28.1 (CH2), 30.0 (d, JC,P = 6 Hz; CMe3), 31.8 (CH2), 32.8
(CH2), 33.4 (d, JC,P = 6 Hz; CMe3), 39.4 (d, JC,P = 11 Hz, CMe3), 39.8 (d,
JC,P = 12 Hz, CMe3), 90.4 (dd, JC,P = 7, JC,Rh = 7 Hz; =CH), 94.6 (dd,
JC,P = 9, JC,Rh = 9 Hz; =CH), 107.5 (d, JC,P = 7 Hz; Cq arom), 112.6 (d,
(dd, JC,P
(CH arom), 118.9 (d, JC,P = 3 Hz; CH arom), 122.5 (CH arom), 125.8 (d,
JC,P 5 Hz; CH arom), 127.6 (Cq arom), 128.0 (Cq arom), 128.8
= 13 Hz, JC,Rh = 4 Hz; =CH), 113.3 (m; =CH), 118.6
=
JC,P
=
11 Hz; =CH), 115.5 (dd, JC,P
=
30, 10 Hz; Cq arom), 118.0
6 Hz; =CH), 121.7
(Cq arom), 130.5 (CH arom), 130.7 (CH arom), 132.3 (CH arom), 133.7
(CH arom), 135.6 (Cq arom), 136.3 (Cq arom), 138.0 (Cq arom), 138.8
(CH arom), 118.8 (CH arom), 119.0 (d, JC,P
=
(CH arom), 123.9 (CH arom), 127.3 (Cq arom), 128.7 (Cq arom), 130.1
(CH arom), 130.3 (CH arom), 133.5 (CH arom), 135.3 (CH arom), 136.1
(Cq arom), 137.4 (Cq arom), 138.7 (Cq arom), 145.5 (d, JC,P = 6 Hz;
(Cq arom), 145.7 (d, JC,P
Cq arom), 155.9 ppm (dd, JC,P
=
6 Hz; Cq arom), 146.6 (d, JC,P
= 13 Hz;
=
8, 3 Hz; Cq arom); 31P{1H} NMR
À
(CD2Cl2, 202 MHz): d = 21.6 (dd, JP, Rh = 137 Hz; P C), 132.2 ppm (dd,
OCq arom), 146.5 (d, JC,P = 13 Hz; OCq arom), 154.9 ppm (dd, JC,P = 8,
JP, Rh = 267 Hz, JP, P = 57 Hz; P O); elemental analysis (%) calcd for
6 Hz; OCq arom); 31P{1H} NMR (CDCl3, 121 MHz): d = 33.7 (dd, JP, Rh
À
À
À
C36H46BF4O3P2Rh: C 55.5, H 6.0; found: C 55.1, H 6.0.
= 133 Hz; P C), 127.5 ppm (dd, JP, Rh = 266, JP,P = 62 Hz; P O); ele-
mental analysis (%) calcd for C38H50O3BF4P2Rh: C 56.6, H 6.2; found: C
56.4, H 6.3.
[Rh
A
G
N
7a. Orange crystals (0.075 g, 60%); 1H NMR (CDCl3, 500 MHz): d =
1.67 (s, 3H; Me), 1.83 (m, 2H; 2”CHH), 1.89 (s, 3H; Me), 2.00 (s, 3H;
Me), 2.16 (m, 2H; 2”CHH), 2.24 (s, 3H; Me), 2.33 (s, 3H; Me), 2.53 (m,
2H; 2”CHH), 2.67 (s, 3H; Me), 2.79 (m, 2H; 2”CHH), 3.89 (m, 2H; 2”
=CH), 5.74 (m, 1H; =CH), 5.90 (m, 1H; =CH), 7.00 (m, 3H; 3”
H arom), 7.15 (s, 1H; H arom), 7.24 (m, 4H; 4”H arom), 7.56 (m, 7H;
[Rh
A
G
N
7b. Yellow solid (62%). 1H NMR (400 MHz; CDCl3): d = 1.59 (s, 9H;
CMe3), 1.65 (s, 9H; CMe3), 1.73 (s, 3H; Me), 1.82 (s, 3H; Me), 2.03 (m,
3H; 3”CHH), 2.14 (m, 1H; CHH COD), 2.22 (s, 3H; Me), 2.24 (s, 3H;
Me), 2.28 (m, 1H; CHH), 2.41 (m, 3H; 3”CHH), 2.59 (m, 1H; CHH),
3.07 (m, 1H; CHH), 4.00 (m, 1H; OCHH), 4.02 (brs, 1H; =CH), 4.38
(brs, 1H; =CH), 4.61 (m, 1H; OCHH), 5.17 (brs, 1H; =CH), 5.86 (brs,
7”H arom), 8.77 ppm (d, JH,H
=
17 Hz, 1H; H arom); 13C{1H} NMR
(CDCl3, 125 MHz): d = 17.2 (Ar-Me), 17.6 (Ar-Me), 20.2 (Ar-Me), 20.3
(Ar-Me), 22.7 (Ar-Me), 25.3 (Ar-Me), 26.9 (2”CH2), 34.0 (CH2), 34.4
(CH2), 97.9 (m; =CH), 105.6 (m; =CH), 111.9 (m; =CH), 113.1 (m; =
CH), 118.2 (CH arom), 118.3 (CH arom), 122.6 (CH arom), 125.1 (2”
Cq arom), 125.2 (CH arom), 125.5 (Cq arom), 125.9 (Cq arom), 126.9
(CH arom), 127.0 (CH arom), 127.3 (d, JC,P = 10 Hz; Cq arom), 127.5
(Cq arom), 128.0 (Cq arom), 130.4 (2”CH arom), 130.8 (CH arom), 132.7
(CH arom), 132.8 (CH arom), 132.9 (CH arom), 134.1 (CH arom), 135.5
(CH arom), 136.0 (CH arom), 138.0 (2”Cq arom), 138.7 (CH arom),
141.4 (Cq arom), 142.6 (Cq arom), 145.9 (Cq arom), 146.0 (Cq arom),
153.8 ppm (d, JC,P = 10 Hz; Cq arom); 31P{1H} NMR (CDCl3, 121 MHz):
1H; =CH), 7.14 (s, 1H; CH arom), 7.23 (s, 1H; CH arom), 7.34 (t, JH,H
=
8.4 Hz, 2H; 2”CH arom), 7.51 (m, 3H; 3”CH arom), 7.63 (m, 3H; 3”
CH arom), 8.02 ppm (t, JH,H = 9.2 Hz, 2H; 2”CH arom); 13C{1H} NMR
(75 MHz; CDCl3): d = 16.4 (CH3), 16.6 (CH3), 20.4 (CH3), 20.5 (CH3),
26.2 (dd, JC,P = 32, 12 Hz; CH2), 28.8 (CH2), 30.0 (2”CH2), 31.5 (CH2),
31.9 (CMe3), 32.8 (CMe3), 35.2 (2”CMe3), 64.8 (OCH2), 95.9 (brm; =
CH), 107.3 (brm; =CH), 107.6 (brm; =CH), 110.5 (brm; =CH), 128.8
(CH arom), 128.9 (Cq arom), 129.1 (Cq arom), 129.5 (CH arom), 129.6
(Cq arom), 129.7 (Cq arom), 129.8 (CH arom), 130.0 (2”CH arom), 130.2
(CH arom), 131.0 (CH arom), 131.1 (CH arom), 131.9 (d, JC,P = 3 Hz;
CH arom), 133.4 (CH arom), 134.4 (Cq arom), 134.6 (Cq arom), 135.4
(CH arom), 135.5 (CH arom), 135.8 (Cq arom), 136.6 (Cq arom), 137.3 (d,
À
d = 17.3 (dd, JP, Rh = 136 Hz; P C), 136.9 ppm (dd, JP, Rh = 277 Hz, JP, P
À
P O);
=
54 Hz;
elemental
analysis
(%)
calcd
for
C44H46BF4O3P2Rh·0.5CH2Cl2: C 58.3, H 5.2; found: C 58.6, H, 5.3.
JC,P
= 7 Hz; Cq arom), 137.5 (OCq arom), 144.2 (d, JC,P = 14 Hz;
OCq arom), 144.8 ppm (d, JC,P
=
10 Hz; OCq arom); 31P{1H} NMR
[Rh
A
G
G
1
À
(121 MHz; CDCl3): d = 5.1 (dd, JP, Rh = 142 Hz; P C), 130.9 ppm (dd,
scribed for 7a. Yellow solid (0.090 g, 70%); H NMR (CDCl3, 300 MHz):
d = 1.93 (s, 3H; Me), 2.04 (s, 3H; Me), 2.26 (s, 3H; Me), 2.37 (s, 3H;
Me), 2.10 (m, 8H; 8”CHH), 3.60 (m, 1H; =CH), 3.92 (m, 1H; =CH),
5.82 (m, 1H; =CH), 6.04 (m, 1H; =CH), 7.04 (m, 6H; 6”H arom), 7.32
(m, 3H; 3”H arom), 7.61 (m, 6H; 6”H arom), 7.84 (d, JH,H = 8 Hz, 1H;
H arom), 8.06 (m, 4H; 4”H arom), 8.41 (d, JH,H = 7 Hz, 1H; H arom),
À
JP, Rh = 245 Hz, JP, P = 61 Hz; P O); elemental analysis (%) calcd for
C46H58BF4O3P2Rh·0.5CH2Cl2: C 58.6, H 6.2; found: C 58.8, H 6.4.
[Rh
A
ACHTREUNG
(10 mL) was slowly added to
a
ACHTREUNG
0.15 mmol) in CH2Cl2 (5 mL). The resulting orange solution was stirred
for 1 h and treated with Et2O (30 mL) and the obtained solid was washed
with Et2O and recrystallized from CH2Cl2/Et2O 1:2 to give 9a as a
9.32 ppm (dd, JH,H
75 MHz): d = 17.6 (Ar-Me), 17.9 (Ar-Me), 20.6 (Ar-Me), 20.6 (Ar-Me),
=
21, 7 Hz, 1H; H arom); 13C{1H} NMR (CDCl3,
1830
www.chemeurj.org
ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2007, 13, 1821 – 1833

Enantioselective Hydrogenation Catalysts
FULL PAPER
yellow, crystalline solid (0.070 g, 80%). 1H NMR (CD2Cl2, 500 MHz): d
= 1.51 (s, 6H; 2”Me), 1.88 (s, 6H; 2”Me), 2.23 (s, 6H; 2”Me), 2.32 (s,
O); elemental analysis (%) calcd for C54H66BF4O3P2Rh: C 63.9, H 6.6;
found: C 63.4, H 6.3.
6H; 2”Me), 6.28 (d, JH,H = 8.0 Hz, 2H; 2”H arom), 6.73 (d, JH,H
8.0 Hz, 2H; 2”H arom), 6.97 (m, 12H; 12”H arom), 7.07 (t, JH,H
=
[Rh(nbd)(14)]BF4 (16): 2,5-Norbornadiene (1.06 mL, 9.90 mmol) was
G
=
slowly added to a solution of 15 (0.100 g, 0.10 mmol) in CH2Cl2 (10 mL).
The resulting solution was stirred for 48 h, the solvent was removed
under reduced pressure, and the resulting solid was washed with Et2O
(2”10 mL) and dissolved in CH2Cl2 (10 mL). Addition of Et2O (40 mL)
produced precipitation of 15 as an orange solid (0.082 g, 84%). 1H N MR
(CDCl3, 300 MHz): d = 1.33 (s, 18H; 2”CMe3), 1.34 (s, 18H; 2”CMe3),
1.60 (m, 2H; 2”CHH), 4.08 (m, 2H; 2”=CH), 4.75 (m, 2H; 2”CH),
8.0 Hz, 2H; 2”H arom), 7.19 (d, JH,H = 8.0 Hz, 2H; 2”H arom), 7.27 (t,
JH,H = 7.0 Hz, 2H; 2”H arom), 7.35 (t, JH,H = 7.0 Hz, 2H; 2”H arom),
7.44 (t, JH,H = 7.5 Hz, 4H; 4”H arom), 7.53 (t, JH,H = 7.5 Hz, 2H; 2”
H arom), 7.63 (m, 4H; 4”H arom), 7.68 ppm (t, JH,H = 7.5 Hz, 2H; 2”
H arom); 13C{1H} NMR (CDCl3, 125 MHz): d = 17.1 (2”Ar-Me), 17.3
(2”Ar-Me), 20.2 (2”Ar-Me), 20.6 (2”Ar-Me), 118.0 (2”CH arom),
118.6 (2”CH arom), 122.5 (2”CH arom), 124.1 (dd, JC,P = 11, 6 Hz; 2”
Cq arom), 124.5 (dd, JC,P = 13, 6 Hz; 2”Cq arom), 126.1 (2”CH arom),
127.3 (2”Cq arom), 127.8 (2”Cq arom), 128.2 (2”Cq arom), 128.8 (2”
CH arom), 128.9 (4”CH arom), 129.0 (2”CH arom), 129.5 (2”
CH arom), 129.7 (2”CH arom), 130.8 (2”CH arom), 131.5 (2”
CH arom), 132.4 (2”CH arom), 132.4 (2”CH arom), 132.5 (2”
CH arom), 133.2 (2”CH arom), 134.7 (2”Cq arom), 135.1 (2”Cq arom),
136.0 (2”CH arom), 136.1 (2”CH arom), 137.7 (2”Cq arom), 138.4 (2”
Cq arom), 145.8 (brs, 4”Cq arom), 153.0 ppm (m; 2”Cq arom); 31P{1H}
NMR (CD2Cl2, 202 MHz): d = 18.5 (m, JP,Rh = 121 Hz, JP, P = 400, 70,
5.28 (m, 2H; 2”=CH NBD), 7.05 (m, 2H; 2”H arom), 7.17 (d, JH,H
=
3 Hz, 2H; 2”H arom), 7.26 (m, 1H; H arom), 7.51 (m, 6H; 6”H arom),
7.62 ppm (m, 7H; 7”H arom); 13C{1H} NMR (CDCl3, 125 MHz): d =
31.0 (2”CMe3), 31.6 (2”CMe3), 35.2 (2”CMe3), 35.8 (2”CMe3), 55.0
(CH2), 71.9 (2”CH), 98.7 (m, 2”=CH); 120.6 (m, 2”=CH), 125.8 (2”
CH arom), 126.4 (Cq arom), 126.6 (2”Cq arom), 126.8 (2”Cq arom),
127.1 (Cq arom), 127.6 (2”CH arom), 130.2 (2”CH arom), 130.4 (2”
CH arom), 130.9 (2”Cq arom), 131.2 (2”CH arom), 132.6 (2”CH arom),
133.8 (2”CH arom), 133.9 (2”CH arom), 134.0 (CH arom), 140.4
(CH arom), 144.8 (Cq arom), 144.9 (Cq arom), 149.2 (Cq arom), 154.1 ppm
(m, OCq arom); 31P{1H} NMR (CDCl3, 121 MHz): d = 15.2 (dd, JP, Rh
=
À
À
33 Hz; P C), 149.4 ppm (m, JP, Rh = 228 Hz, JP, P = 400, 70, 33 Hz; P O);
elemental analysis (%) calcd for C68H60BF4O6P4Rh: C 63.5, H 4.7; found:
C 63.2, H, 4.6.
À
À
147 Hz; P C), 133.9 ppm (dd, JP, Rh = 279 Hz, JP, P = 67 Hz; P O); ele-
mental analysis (%) calcd for C53H62BF4O3P2Rh·0.5CH2Cl2: C 61.7, H
6.1; found: C 61.5, H 5.8.
[Rh(cod)(10)]BF4 (11): This compound was prepared from phosphane-
G
phosphite 10 by the procedure described for 7a. Yellow solid (0.065 g,
62%); 1H NMR (CDCl3, 300 MHz): d = 2.45 (m, 8H; 8”CHH), 4.14
(m, 1H; =CH), 4.82 (m, 1H; =CH), 5.66 (m, 1H; =CH), 5.82 (m, 1H; =
[Rh(14)(12a)]BF4 (17): Complex 16 (0.030 g, 0.03 mmol) was dissolved in
G
DME (5 mL) in a Fischer–Porter vessel, and this was charged with H2
(4 atm) at room temperature. The reaction mixture was stirred overnight
and depressurized, and 12a (0.030 g, 0.12 mmol) was then added under
Ar. The mixture was stirred for 4 h, solvent was removed under vacuum,
and the resulting residue was dissolved in CDCl3 for NMR characteriza-
tion. 1H NMR (CDCl3, 500 MHz): d = 1.31 (s, 18H; 2”CMe3), 1.36 (s,
18H; 2”CMe3), 3.51 (brs, 6H; 2”OMe), 4.51 (brs, 1H; =CH), 5.19 (brs,
1H; =CH), 6.81 (brm, 1H; CH arom), 7.07 (brm, 1H; CH arom), 7.26
(brs, 2H; 2”CH arom), 7.32 (brm, 1H; CH arom), 7.54 ppm (brm, 18H;
18 CH arom); 13C{1H} NMR (CDCl3, 75.5 MHz): d = 30.9 (CMe3), 31.5
(CMe3), 35.1 (CMe3), 35.8 (CMe3), 53.6 (2”OCH3), 54.1 (=CHH), 122.0
(CH arom), 125.5 (2”CH arom), 127.0 (2”Cq arom), 127.9 (2”
CH arom), 128.5 (CH arom), 129.0–130.6 (9”CH arom), 131.2 (2”
Cq arom), 132.5 (2”CH arom), 133.2 (CH arom), 133.9 (2”CH arom),
134.0 (2”CH arom), 134.4 (Cq arom), 134.8 (CH arom), 139.8 (2”
Cq arom), 145.7 (2”OCq arom), 148.8 (2”Cq arom), 154.0 (Cq arom),
CH), 7.05 (dd, JH,H
H arom), 7.59 (m, 12H; 12”H arom), 7.94 (d, JH,H
=
7.5, 5.0 Hz, 1H; H arom), 7.27 (m, 9H; 9”
8.0 Hz, 1H;
=
H arom), 8.03 (d, JH,H = 8.0 Hz, 1H; H arom), 8.07 (d, JH,H = 9.0 Hz,
1H; H arom), 8.33 ppm (d, JH,H = 9.0 Hz, 1H; H arom); 13C{1H} NMR
(CDCl3, 75 MHz): d = 27.4 (CH2), 28.6 (CH2), 32.1 (CH2), 32.6 (CH2),
100.6 (t, JC,P = JC,Rh = 7 Hz; =CH), 106.1 (t, JC,P = JC,Rh = 7 Hz; =CH),
113.6 (m, 2”=CH), 116.7 (d, JC,P = 10 Hz; Cq arom), 117.3 (d, JC,P
=
10 Hz; Cq arom), 120.6 (CH arom), 121.2 (CH arom), 122.2 (m;
CH arom), 122.6 (m; CH arom), 126.0 (Cq arom), 126.1 (m; CH arom),
126.3 (CH arom), 126.5 (CH arom), 126.7 (Cq arom), 127.1 (2”
CH arom), 127.3 (CH arom), 127.4 (CH arom), 128.1 (Cq arom), 128.8
(CH arom), 129.3 (CH arom), 129.8 (CH arom), 129.9 (CH arom), 130.3
(CH arom), 130.5 (CH arom), 131.4 (CH arom), 132.1 (Cq arom), 132.2
(Cq arom), 132.4 (CH arom), 132.5 (CH arom), 132.6 (Cq arom), 132.7
(Cq arom), 133.3 (CH arom), 133.5 (CH arom), 133.6 (CH arom), 134.6
(CH arom), 134.7 (CH arom), 134.9 (CH arom), 146.4 (d, JC,P = 5 Hz;
Cq arom), 147.1 (d, JC,P = 13 Hz; Cq arom), 155.1 ppm (d, JC,P = 10 Hz;
154.8 (OCq arom), 164.3 ppm (COO); no =C,P(OBz) resonance was ob-
C
served; 31P{1H} NMR (CDCl3, 162 MHz, 250 K): d = 6.0 (brdq, JP, Rh
=
À
147 Hz, JP, P = 68, 12 Hz; P OP), 10.6 (brd, JP, P = 12 Hz; P(O)
A
Cq arom); 31P{1H} NMR (CDCl3, 121 MHz):
d
=
15.7 (dd, JP, Rh =
À
137.4 ppm (dd, JP, Rh = 255 Hz, JP, P = 68 Hz; P OP).
À
À
135 Hz; P C), 137.8 ppm (dd, JP, Rh = 269 Hz, JP, P = 61 Hz; P O); ele-
mental analysis (%) calcd for C46H38BF4O3P2Rh·H2O: C 60.8, H 4.4;
found: C 60.8, H, 4.0.
(E)-1-Benzoyloxy-1-dimethylphosphonyl-2-(3,4-dimethoxyphenyl)ethene
(12g): P(OMe)3 (2.4 mL, 20 mmol) was slowly added at 08C to a solution
AHCTREUNG
of 2-(3,4-dimethoxyphenyl)acetyl chloride (4.3 g, 20 mmol) in THF
(15 mL). After the addition the mixture was heated under reflux for
0.5 h. Solvent was evaporated under reduced pressure and the resulting
residue was recrystallized in CH2Cl2/hexane 1:2 to give (E)-1-hydroxy-1-
dimethylphosphonyl-2-(3,4-dimethoxyphenyl)ethene (4.05 g, 70%).
[Rh(cod)(14)]BF4 (15): Compound 14 (0.080 g, 0.11 mmol) in CH2Cl2
E
(10 mL) was added dropwise to a solution of [(cod)2Rh]BF4 (0.046 g,
0.11 mmol) in CH2Cl2 (10 mL), and the orange solution was stirred for
45 min, concentrated to a fourth of the initial volume, filtered and finally
treated with Et2O (40 mL). The resulting solid was washed with Et2O
(2”10 mL) and dissolved in CH2Cl2 (5 mL), and addition of Et2O
DBU (1.5 mL, 10.4 mmol) was slowly added at 08C to a mixture of this
olefin (2.5 g, 8.67 mmol) and benzoic anhydride (2.35 g, 10.4 mmol) in
THF (50 mL). The reaction mixture was stirred for 20 min, allowed to
warm to room temperature, diluted with AcOEt (100 mL) and washed
with saturated aqueous solutions of NaHCO3 (3”50 mL) and NaCl (3”
50 mL), and the aqueous phases were reextracted with AcOEt (3”
40 mL). Organic layers were collected and dried over MgSO4 and fil-
tered, and evaporation under reduced pressure yielded a residue that was
purified by column chromatography (silica gel, AcOEt/hexane 6:1),
1
(40 mL) yielded 15 as a yellow solid (0.096 g, 84%); H NMR (400 MHz;
CDCl3): d = 1.31 (s, 18H; 2”CMe3), 1.34 (s, 18H; 2”CMe3), 2.24 (m,
8H; 4”CH2), 4.81 (brm, 2H; 2”=CH), 4.89 (brm, 2H; 2”=CH), 6.95
(m, 1H; CH arom), 7.17 (s, 2H; 2”CH arom), 7.23 (s, 1H; CH arom),
7.29 (t, JH,H
=
7.0 Hz, 1H; CH arom), 7.49 (m, 3H; 3”CH arom),
{1H NMR (125 MHz; CDCl3): d =
7.61 ppm (m, 10H; 10”CH arom); 13C
AHCTREUNG
29.6 (2”CH2), 31.0 (2”CH2), 31.3 (2”CMe3), 31.7 (2”CMe3), 35.2 (2”
CMe3), 35.7 (2”CMe3), 101.7 (brm, 2”=CH), 111.1 (brm, 2”=CH),
121.2 (2”Cq arom), 123.4 (2”Cq arom), 125.7 (2”CH arom), 126.9 (2”
Cq arom), 127.6 (2”CH arom), 129.9 (2”CH arom), 130.1 (2”CH arom),
130.7 (2”CH arom), 131.9 (2”CH arom), 132.8 (2”CH arom), 134.0 (2”
Cq arom), 134.1 (2”CH arom), 134.3 (2”CH arom), 140.2 (2”Cq arom),
149.3 ppm (2”Cq arom); 31P{1H} NMR (162 MHz; CDCl3): d = 13.0 (dd,
1
yielding 7g as a white solid (2.2 g, 65%). H NMR (CDCl3, 300 MHz): d
= 3.42 (s, 3H; Ar-OMe), 3.80 (s, 3H; Ar-OMe), 3.81 (d, JH,P = 11.0 Hz,
À
6H; 2”P OMe), 6.75 (d, JH,H = 8.0 Hz, 1H; H arom), 7.07 (m, 2H; 2”
H arom), 7.22 (d, JH,P = 11.7 Hz, 1H; =CH), 7.47 (d, JH,H = 8.0 Hz, 2H;
2”H arom), 7.62 (t, JH,H = 8.0 Hz, 1H; H arom), 8.14 ppm (d, JH,H
=
8.0 Hz, 2H; 2”H arom); 13C{1H} NMR (CDCl3, 75 MHz): d = 53.5 (d,
À
À
À
JP, Rh = 142 Hz; P C), 130.9 ppm (dd, JP, Rh = 267 Hz, JP, P = 52 Hz; P
JC,P
=
5 Hz, 2”P OMe), 55.5 (Ar-OMe), 56.1 (Ar-OMe), 111.2
Chem. Eur. J. 2007, 13, 1821 – 1833
ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
1831

A. Pizzano et al.
(CH arom), 111.7 (CH arom), 124.4 (CH arom), 125.1 (d, JC,P = 17 Hz;
Cq arom), 129.0 (Cq arom), 129.1 (2”CH arom), 130.5 (2”CH arom),
134.4 (CH arom), 134.8 (d, JC,P = 230 Hz; =CO), 135.0 (d, JC,P = 28 Hz;
=CH), 149.0 (Cq arom), 150.7 (Cq arom), 163.8 ppm (COO); 31P{1H}
NMR (CDCl3, 121 MHz): d = 12.5 ppm; elemental analysis (%) calcd
for C19H21O7P: C 58.2, H 5.4; found: C 58.1, H 5.5.
1-Benzoyloxy-1-dimethylphosphonyl-2-(3,4-dimethoxyphenyl)ethane
(13h): White solid; [a]D20 = À88.8 (c = 0.5, CHCl3); 1H NMR (CDCl3,
300 MHz): d
= 3.14 (dt, JH,P = 10.2 Hz, JH,H = 14.7, 10.2 Hz, 1H;
CHH), 3.26 (ddd, JH,P = 6.6 Hz, JH,H = 14.7, 4.0 Hz, 1H; CHH), 3.65 (s,
3H; Ar-OMe), 3.75 (d, JH,P 10.5 Hz, 3H; OMe), 3.76 (s, 3H; Ar-
OMe), 3.77 (d, JH,P = 10.5 Hz, 3H; OMe), 5.70 (ddd, JH,P = 8.2 Hz, JH,H
=
= 10.2, 4.0 Hz, 1H; CHOBz), 6.74 (m, 3H; 3”H arom), 7.40 (t, JH,H
7.0 Hz, 2H; 2”H arom), 7.53 (t, JH,H = 7.0 Hz, 1H; H arom), 7.97 ppm
(d, JH,H = 7 Hz, 2H; 2”H arom); 13C{1H} NMR (CDCl3, 75 MHz): d =
35.5 (CH2), 53.6 (d, JC,P = 6 Hz, OMe), 53.8 (d, JC,P = 7 Hz, OMe), 55.9
=
(E)-1-Benzoyloxy-1-dimethylphosphonyl-2-(p-tolyl)ethene (12h): This
compound was synthesized as described for 12g. White solid (2.4 g,
70%); 1H NMR (CDCl3, 400 MHz): d = 2.27 (s, 3H; Me), 3.81 (d, JH,P
= 11.2 Hz, 6H; 2”OMe), 7.07 (d, JH,H = 8.0 Hz, 2H; 2”H arom), 7.27
(d, JH,H = 11.6 Hz, 1H; =CH), 7.40 (d, JH,H = 8.0 Hz, 2H; 2”H arom),
(Ar-OMe), 56.0 (Ar-OMe), 68.9 (d, JC,P
= 165 Hz, CHOBz), 111.4
(CH arom), 112.5 (CH arom), 121.6 (CH arom), 128.8 (2”CH arom),
128.9 (Cq arom), 129.4 (Cq arom), 130.0 (2”CH arom), 133.7 (CH arom),
7.49 (t, JH,H
= 7.2 Hz, 2H; 2”H arom), 7.62 (t, JH,H = 7.2 Hz, 1H;
H arom), 8.13 ppm (d, JH,H = 7.2 Hz, 2H; 2”H arom); 13C{1H} NMR
(CDCl3, 125 MHz): d = 21.4 (Ar-Me), 53.3 (d, JC,P = 5 Hz; 2”OMe),
128.8 (2”CH arom), 129.2 (Cq arom), 129.3 (Cq arom), 129.6 (2”
CH arom), 129.7 (2”CH arom), 130.3 (2”CH arom), 134.0 (CH arom),
148.2 (Cq arom), 149.0 (Cq arom), 165.2 ppm (d, JC,P
= 5 Hz; COO);
31P{1H} NMR (CDCl3, 121 MHz): d = 21.8 ppm; HRMS (CI): m/z: calcd
for C19H23O7P: 394.1181; found: 394.1188 [M]+. Chiralpak AD, 308C,
hexane/propan-2-ol 90:10, flow rate 1.0 mLminÀ1: t1 = 17.8 min (R), t2
21.1 min (S).
=
134.9 (d, JC,P
= 28 Hz; =CH), 135.8 (d, JC,P = 229 Hz; =CO), 140.3
(Cq arom), 163.6 ppm (COO); 31P{1H} NMR (CDCl3, 162 MHz): d
=
Crystal data for 9a: C139H126B2Cl6F8O12P8Rh2, [2(C68H60O6P4Rh), CH2Cl2,
12.4 ppm; elemental analysis (%) calcd for C18H19O5P: C 62.4, H 5.5;
found: C 62.5, H 5.5.
CH2Cl2, CH2Cl2, 2(BF4)], Mw = 2828.30, yellow prism (0.27”0.26”
A
0.25 mm3) from CH2Cl2/hexane. Orthorhombic, space group P212121
(no. 19); a = 17.6291(14), b = 19.4308(16), c = 20.5509(16) Š; a = b =
Representative procedure for enantioselective hydrogenation: Hydroge-
nations were performed as demonstrated below for 12b. In a glove box, a
Fischer–Porter reactor (80 mL) was charged with 12b (0.073 g,
0.25 mmol) and catalyst precursor 8a (0.002 g, 0.002 mmol) in CH2Cl2
(5 mL). The vessel was removed from the glove box, subjected to
vacuum–hydrogen cycles and finally pressurized to 4 atm. The reaction
mixture was kept stirring for 24 h, the reactor was then depressurized,
and the obtained mixture was evaporated to dryness, treated with Et2O
and passed through a short pad of silica. The resulting residue was ana-
g = 908; V = 7039.7(10) Š3, Z = 2, 1calcd = 1.334 gcmÀ3, l
ACHTREUNG
0.71073 Š, F
ACHTREUNG
tions were collected with a Bruker–Nonius X8 Kappa Apex II CCD dif-
fractometer in the range 6.08 < 2q < 52.868 and 14341 independent re-
flections [R(int) = 0.0680] were used in the structural analysis. Reflec-
G
tions were corrected for Lorentz polarisation effects and absorption was
applied by (SADABS)[37]. The structure was solved by direct methods
(SIR2002)[38] and refined against all F2 data by full-matrix, least-squares
techniques (SHELXTL-6.12)[39] to final R1 = 0.0683 [I > 2s(I)], and to
wR2 = 0.2022 for all data, with a goodness-of-fit on F2 = 1.047 and 838
parameters. The absolute configuration of the structure has been un-
doubtedly established by anomalous dispersion effects in diffraction
measurements on the crystal [Flack parameter x = À0.03(3)].[40]
CCDC-612988 (9a) contains the supplementary crystallographic data for
this paper. These data can be obtained free of charge from The Cam-
bridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_
request/cif.
1
lysed by H NMR to determine conversion and by chiral HPLC for enan-
tiomeric excess as follows:
1-Benzoyloxy-1-dimethylphosphonylethane (13a): (Chiralcel OJ, 308C,
flow rate 1.0 mLminÀ1, hexane/propan-2-ol 98.5:1.5): t1 = 40.8 min (S), t2
= 47.8 min (R).
1-Benzoyloxy-1-dimethylphosphonylbutane (13b): (Chiralpak AD, 308C,
flow rate 1.0 mLminÀ1, hexane/propan-2-ol 95:5): t1 = 11.2 min (R), t2
13.4 min (S).
=
1-Benzoyloxy-1-dimethylphosphonyl-3-methylbutane (13c): (Chiralpa-
k AD, 308C, flow rate 1.0 mLminÀ1, hexane/propan-2-ol 95:5): t1
10.1 min (R), t2 = 12.5 min (S).
=
1-Benzoyloxy-1-dimethylphosphonylhexane (13d): (Chiralpak AD, 308C,
flow rate 1.0 mLminÀ1, hexane/propan-2-ol 95:5): t1 = 11.6 min (R), t2
13.0 min (S).
=
Acknowledgements
1-Benzoyloxy-1-dimethylphosphonyl-2-phenylethane (13e): (Chiralpa-
We gratefully acknowledge the Ministerio de Educación
y Ciencia
k AD, 308C, flow rate 1.0 mLminÀ1, hexane/propan-2-ol 95:5): t1
18.9 min (R), t2 = 21.0 min (S).
=
(PPQ2003-00975) and the Fundación Ramón Areces for financial sup-
port. M.R. and S.V. thank the Ministerio de Educación y Ciencia for FPI
and FPU fellowships, respectively.
1-Benzoyloxy-1-dimethylphosphonyl-2-(4-methoxyphenyl)ethane (13g):
(Chiralpak AD, 308C, flow rate 1.0 mLminÀ1, hexane/propan-2-ol 95:5):
t1 = 27.6 min (R), t2 = 37.0 min (S).
1-Benzoyloxy-1-dimethylphosphonyl-2-(p-tolyl)ethane (13 f): White solid;
[1] For some recent examples see: a) S. Bell, B. Wustenberg, S. Kaiser,
F. Menges, T. Netscher, A. Pfaltz, Science 2006, 311, 642–644; b) S.
Cabrera, R. G. Arrayas, I. Alonso, J. C. Carretero, J. Am. Chem.
Soc. 2005, 127, 17938–17947; c) X. H. Cui, J. W. Ogle, K. Burgess,
Chem. Commun. 2005, 672–674; d) L. H. Gade, V. CØsar, S. Belle-
min-Laponnaz, Angew. Chem. 2004, 116, 1036–1039; Angew. Chem.
Int. Ed. 2004, 43, 1014–1017; e) G. Hoge, H.-P. Wu, W. S. Kissel,
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Bappert, G. Helmchen, Adv. Synth. Catal. 2005, 347, 1495–1498;
h) Y. Yan, X. Zhang, J. Am. Chem. Soc. 2006, 128, 7198–7202.
[2] For illustrative studies of catalyst optimization guided by modular
design, see: a) O. Pàmies, M. DiØguez, C. Claver, J. Am. Chem. Soc.
2005, 127, 3646–3647; b) D. A. Evans, F. E. Michael, J. S. Tedrow,
K. R. Campos, J. Am. Chem. Soc. 2003, 125, 3534–3543; c) C. Hed-
berg, K. Källstrom, P. Brandt, L. K. Hansen, P. G. Andersson, J. Am.
Chem. Soc. 2006, 128, 2995–3001; d) A. H. Hoveyda, A. W. Hird,
1
[a]2D0 = À108.0 (c = 0.5, CHCl3); H NMR (CDCl3, 500 MHz): d = 2.23
(s, 3H; Ar-Me), 3.17 (dt, JH,P
= 10.5 Hz, JH,H = 14.5, 10.5 Hz, 1H;
CHH), 3.29 (ddd, JH,P = 7.0 Hz, JH,H = 14.5, 4.0 Hz, 1H; CHH), 3.75 (d,
JH,P = 11.0 Hz, 3H; OMe), 3.76 (d, JH,P = 11.0 Hz, 3H; OMe), 5.72
(ddd, JH,P = 8.5 Hz, JH,H = 10.5, 4.0 Hz, 1H; CHOBz), 7.00 (d, JH,H
=
8.0 Hz, 2H; 2”H arom), 7.11 (d, JH,H = 8.0 Hz, 2H; 2”H arom), 7.41 (t,
JH,H = 7.0 Hz, 2H; 2”H arom), 7.54 (t, JH,H = 7.0 Hz, 1H; H arom),
7.98 ppm (d, JH,H
=
7.0 Hz, 2H; 2”H arom); 13C{1H} NMR (CDCl3,
125 MHz): d = 21.0 (Ar-Me), 35.3 (CH2), 53.2 (d, JC,P = 6 Hz, OMe),
53.5 (d, JC,P = 7 Hz, OMe), 68.6 (d, JC,P = 160 Hz, CHOBz), 128.5 (2”
CH arom), 129.1 (2”CH arom), 129.2 (2”CH arom), 129.8 (2”
CH arom), 133.0 (Cq arom), 133.1 (Cq arom), 133.3 (CH arom), 136.4
(Cq arom), 165.1 ppm (d, JC,P
=
4 Hz; COO); 31P{1H} NMR (CDCl3,
162 MHz):
d = 21.9 ppm; HRMS (CI): m/z: calcd for C18H22O5P:
349.1205; found: 349.1199 [M+H]+. Chiralpak AD, 308C, hexane/
propan-2-ol 90:10, flow rate 1.0 mLminÀ1: t1 = 9.4 min (R), t2 = 11.9 min
(S).
1832
www.chemeurj.org
ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2007, 13, 1821 – 1833

Enantioselective Hydrogenation Catalysts
FULL PAPER
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1
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Received: July 18, 2006
Published online: November 29, 2006
Chem. Eur. J. 2007, 13, 1821 – 1833
ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
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