Ureaphosphanes as hybrid, anionic or supramolecular bidentate ligands for asymmetric hydrogenation reactions

Article abstract of DOI:10.1002/ejic.201000213

We report the coordination behavior of ureaphosphane ligand 1-[2-(diphenylphosphanyl)ethyl]-3-phenylurea (L1) towards different rhodium precursor complexes. Depending on the nature of the anion and the ligand/metal ratio, L1 acts either as a hybrid P,O-coordinating chelate, as an anionic P,N-coordinating chelate or as a supramolecular (hydrogenbonded) bidentate ligand. The different types of complexes were investigated in the asymmetric hydrogenation of three olefinic substrates using ureaphosphanes L2 and L3, which are chiral analogues of L1. For methyl 2-acetamidoacrylate (S1) and dimethyl itaconate (S2) the neutral complex [Rh(L2-κ²P,N)(cod)], containing an anionic P,N-coordmatmg ureaphosphane ligand, provided the best enantioselectivity (69.2 and 24.3%, respectively). For N-(3,4-dihydro-2- naphthalenyl)acetamide (S3) the best enantioselectivity was obtained with the cationic complex [R.h(L3-κ²P,O)(nbd)]BF₄, containing a hybrid P,O-coordinating ureaphosphane ligand (86.1%).

Full text of DOI:10.1002/ejic.201000213

FULL PAPER
DOI: 10.1002/ejic.201000213
Ureaphosphanes as Hybrid, Anionic or Supramolecular Bidentate Ligands for
Asymmetric Hydrogenation Reactions
Jurjen Meeuwissen,[a] Remko Detz,[b] Albertus J. Sandee,[a,c] Bas de Bruin,[a]
Maxime A. Siegler,[d] Anthony L. Spek,[d] and Joost N. H. Reek*[a]
Keywords: Asymmetric hydrogenation / Rhodium / Phosphorus ligands / Coordination chemistry / Hydrogen bonds
We report the coordination behavior of ureaphosphane li-
gand 1-[2-(diphenylphosphanyl)ethyl]-3-phenylurea (L1)
towards different rhodium precursor complexes. Depending
on the nature of the anion and the ligand/metal ratio, L1 acts
either as a hybrid P,O-coordinating chelate, as an anionic
P,N-coordinating chelate or as a supramolecular (hydrogen-
bonded) bidentate ligand. The different types of complexes
were investigated in the asymmetric hydrogenation of three
olefinic substrates using ureaphosphanes L2 and L3, which
are chiral analogues of L1. For methyl 2-acetamidoacrylate
(S1) and dimethyl itaconate (S2) the neutral complex [Rh(L2-
κ2P,N)(cod)], containing an anionic P,N-coordinating urea-
phosphane ligand, provided the best enantioselectivity (69.2
and 24.3%, respectively). For N-(3,4-dihydro-2-naphth-
alenyl)acetamide (S3) the best enantioselectivity was ob-
tained with the cationic complex [Rh(L3-κ2P,O)(nbd)]BF4,
containing a hybrid P,O-coordinating ureaphosphane ligand
(86.1%).
process
in
presence
of
a
transition
metal.
Introduction
Ureaphosphanes are part of this type of ligands and were
used as supramolecular bidentate ligands in the rhodium-
catalyzed asymmetric hydrogenation of several (industrially
relevant) substrates.[7] In addition, we showed that urea-
phosphanes also can be employed as hybrid P,O-coordinat-
ing bidentate ligands in the asymmetric hydrogenation of
cyclic enamides.[9] In this contribution, we report on the
different coordination behavior of ureaphosphanes, de-
pending on the conditions applied. The new ureaphos-
phane-rhodium(I) complexes have been characterized in de-
tail using NMR spectroscopy, mass spectrometry, IR spec-
troscopy, X-ray crystallography and computational meth-
ods. In addition, these new complexes were investigated in
the asymmetric hydrogenation reaction to evaluate the ef-
fect of the coordination behavior on the enantioselectivity
in catalysis.
The use of supramolecular approaches in ligand design
for transition metal catalysis is an upcoming research field,
which has already brought forth several success stories
within a relatively short period of time.[1] The design of the
ligand structure and the binding motif are crucial aspects
herein. Examples of binding motifs that have been success-
fully employed for supramolecular architectures are hydro-
gen bonding,[2] metal–ligand[3] and ionic[4] interactions. In
some cases, the binding motif can also show affinity for the
metal center or the counterion of the complex, potentially
giving rise to unexpected new (supramolecular) coordina-
tion geometries. Although these complexes are in first in-
stance unwanted, they can provide important insight in the
mechanistic aspects of the binding motif in catalysis and
may lead to new useful catalysts.
We[5,6] and the group of Love[8] have recently introduced
urea-functionalized ligands, which form a supramolecular
hydrogen-bonded bidentate ligand via a self-assembly
Results and Discussion
[a] Homogeneous and Supramolecular Catalysis, Van ’t Hoff
Institute for Molecular Sciences,
We investigated the coordination behavior of ureaphos-
phanes towards different rhodium(I) precursors using 1-[2-
(diphenylphosphanyl)ethyl]-3-phenylurea (L1) as a model
compound. The structure of L1 consists of a diphenyl phos-
phane backbone, which is connected via a flexible spacer to
a phenyl urea moiety. In a dilution study of L1 in CDCl3,
monitored by 1H NMR spectroscopy, the urea-protons
showed a strong shift to low field as a function of concen-
tration, which is indicative of (intermolecular) hydrogen
bonding via self-association of the urea moieties.[10,11] Inter-
estingly, this property can be utilized for the formation of
Nieuwe Achtergracht 166, 1018 WV Amsterdam, The
Netherlands
Fax: +31-20 5255604
E-mail: j.n.h.reek@uva.nl
[b] InCatT B.V.,
Roetersstraat 35, 1018 WB Amsterdam, The Netherlands
[c] BASF Nederland B.V.,
Strijkviertel 67, 3454 PK De Meern, The Netherlands
[d] Crystal and Structural Chemistry, Bijvoet Centre for
Biomolecular Research, Faculty of Science, Utrecht University,
Padualaan 8, 3584 CH Utrecht, The Netherlands
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201000213.
2992
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2010, 2992–2997

Asymmetric Hydrogenation Reactions
a supramolecular bidentate ligand connected via (intra- revealed that L1 coordinated to the rhodium in a hybrid
molecular) hydrogen bonding. Addition of two equivalents (P,O-coordinating) bidentate fashion, forming a seven-
of L1 to the cationic rhodium precursor [Rh(nbd)2]BF4 membered chelate ring.[12,13] The IR spectroscopic data pro-
(nbd = 2,5-norbornadiene) in CDCl3, led to the appearance vided support that L1 formed a hybrid chelate, showing a
of a doublet in the 31P{1H} NMR spectrum, resonating at typical shift of the coordinating urea carbonyl to lower
δ = 18.4 ppm (1JP-Rh = 152 Hz), which corresponds to a wavenumber (L1: 1672 cm–1, C2: 1572 cm–1). The DFT-op-
bisligated complex (C1) in a cis geometry (Scheme 1). In timized structure of C2 showed the hybrid coordination
1
the H NMR spectrum, the urea protons in this complex mode of L1 that is consistent with experimental observa-
showed a large downfield shift with respect to the free li- tions (Figure 1).
gand, which is indicative of hydrogen bonding. The DFT-
optimized structure of C1 supports the structure of a supra- precursors [{RhCl(cod)}2] (cod
The coordination behavior of L1 to the neutral rhodium
1,5-cyclooctadiene),
=
molecular bidentate ligand that is connected via a bifur- [Rh(acac)(CO)2] (acac = acetylacetonate) and [Rh(acac)-
cated hydrogen bond (1.925 and 2.057 Å) between the urea (cod)] was subsequently investigated (Scheme 2). Upon ad-
moieties (Figure 1).
dition of one equivalent of L1 to half an equivalent of
[{RhCl(cod)}2] (Rh/L1 = 1:1) in CDCl3 the 31P{1H} NMR
spectrum showed a doublet, resonating at δ = 21.1 ppm
(1JP-Rh = 148 Hz), which indicated that a new complex (C3)
has been formed.[14] The 1H NMR spectrum and mass spec-
trometry revealed that the cod remained coordinated, which
means that C3 is of the form [RhCl(L1)(cod)]. Remarkably,
the aliphatic urea proton (CH2NH) of L1 showed a rela-
tively large downfield shift (ca. 0.9 ppm) with respect to the
free ligand, while the shift of the phenylic urea proton
(NHPh) was almost unchanged. Therefore, the aliphatic
urea proton is likely hydrogen-bonded to the chloride,
forming a seven-membered chelate ring.[15] This was sup-
ported by a dilution study of C3 that showed that the shift
of the aliphatic proton is practically independent of the
concentration in a range of 10–40 m, which is indicative of
an intramolecular hydrogen bond.[10] The DFT-optimized
structure of C3 supports the presence of a hydrogen bond
(2.236 Å) between the aliphatic urea proton and the chlo-
ride (Figure 2).
Scheme 1. Reactivity of L1 with [Rh(nbd)2]BF4.
Figure 1. DFT [BP86,SV(P)]-optimized structures of C1 [Rh(L1)2-
(nbd)]BF4 and C2 [Rh(L1-κ2P,O)(nbd)]BF4. CH hydrogen atoms
–
and the BF4 counterion have been omitted for clarity.
However, after addition of only one equivalent of L1 to
[Rh(nbd)2]BF4 a different complex (C2) was formed and
the ureaphosphane acts as a hybrid P,O-coordinating bi-
dentate ligand (Scheme 1).[9] The 31P{1H} NMR spectrum
showed a doublet, resonating at δ = 31.4 ppm (1JP-Rh
=
170 Hz). Mass spectrometry and 1H NMR spectroscopy
indicated that the structure of C2 is of the form [Rh(L1-
κ2P,O)(nbd)]BF4, containing only one ligand and one nbd
coordinated to the metal center. In the 13C{1H} NMR spec-
trum of C2 the urea carbonyl signal was shifted downfield
Scheme 2. Reactivity of L1 with [{RhCl(cod)}2], [Rh(acac)(CO)2]
with δ ≈ 5.5 ppm with respect to the free ligand. This shift and [Rh(acac)(cod)].
Eur. J. Inorg. Chem. 2010, 2992–2997
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
2993

J. N. H. Reek et al.
FULL PAPER
an intramolecular hydrogen bond, is 6.4 kcalmol–1 more
stable than the optimized structure of C4, that does not
contain an intramolecular hydrogen bond.[11]
Figure 2. DFT [BP86,SV(P)]-optimized structures of C3
[RhCl(L1)(cod)] and C5 [Rh(L1-κ2P,N)(cod)]. CH hydrogen atoms
have been omitted for clarity.
When two equivalents of L1 were added to [Rh(acac)-
(CO)2] in CDCl3 the 31P{1H} NMR spectrum showed two
doublets of doublets, resonating at δ = 19.7 ppm (1JP-Rh
=
136 Hz) and δ = 52.2 ppm (1JP-Rh = 129 Hz), each with a
large phosphorus-phosphorus coupling constant (2JP,P
=
Figure 4. Displacement ellipsoid plot (50% probability level) of C4
[Rh(L1-κ2P,N)(L1-κP)(CO)]·2(CD2Cl2). CH hydrogen atoms and
solvent molecules have been omitted for clarity.
310 Hz), indicating that a new complex (C4) has been
formed that contains two inequivalent phosphorus ligands
in a mutual trans geometry (Figure 3).[16] Remarkably, the
1H NMR spectrum showed only one of the aliphatic urea
protons and the presence of Hacac, which is presumably
explained by the transfer of the acidic aliphatic urea proton
from one of the ligands to the acac– ligand via an acid–
base reaction. This behavior was previously observed for
METAMORPhos ligands that contain a very acidic sulfon-
Addition of one equivalent of L1 to [Rh(acac)(cod)] in
CDCl3 resulted in a similar reaction of the ligand as in C4,
giving a new complex (C5).[13] The 31P{1H} NMR spectrum
showed a doublet, resonating at δ = 20.7 ppm (1JP-Rh
=
148 Hz). In the 1H NMR spectrum, the evolution of Hacac
1
was visible. Because in the H NMR spectrum also the ali-
amide proton and react in
a similar manner with
phatic urea proton of the ligand has disappeared, the urea-
phosphane probably coordinated as an anionic P,N-coordi-
nating chelate as in C4. Mass spectrometry supports that
the structure of C5 is of the form [Rh(L1-κ2P,N)(cod)]. The
DFT-optimized structure of C5 supports such a structure,
showing L1 as an anionic P,N-coordinating ligand (Fig-
ure 2).
[Rh(acac)(CO)2].[2a,17]
The rich coordination chemistry of ureaphosphane L1
was demonstrated by the preparation of complexes C1–C5.
These complexes likely lead to very different behavior in
catalysis. Therefore, we prepared chiral analogues of C1–
C5, which were investigated in the asymmetric hydrogena-
tion reaction. For this purpose, the chiral ureaphosphanes
L2 and L3 were employed, which are structurally similar
to L1 (Figure 5). Ureaphosphane L2 contains a stereogenic
phosphepine backbone, an ethyl spacer and a phenylurea
motif. The structure of L3 is similar to L2, only L3 contains
two additional stereogenic carbon atoms in the spacer.
Figure 3. 31P{1H} NMR spectrum of C4 [Rh(L1-κ2P,N)(L1-
κP)(CO)].
Single crystals of C4, suitable for X-ray analysis, were
obtained by slow diffusion of a layer of hexanes on top of
a solution of C4 in CD2Cl2. The solid-state structure
showed to be consistent with the solution structure, having
the two inequivalent ligands in a trans geometry from which
the anionic ligand in a five-membered P,N-coordinating
chelate ring (Figure 4). This means that indeed a proton of
the least acidic aliphatic urea proton was transferred to the
acac– ligand. Furthermore, the crystal structure shows that
one CO ligand remained coordinated, revealing that C4 is
of the form [Rh(L1-κ2P,N)(L1-κP)(CO)]. In the crystal
structure, two C4 molecules are linked by intermolecular
N–H···O hydrogen bonds. Although in the crystal structure
there is no intramolecular hydrogen bonding between the
two coordinated ligands, the DFT-optimized structure does
show a intramolecular hydrogen bond between the two li-
Figure 5. Structures of the chiral ureaphosphanes L2 and L3.
Three different olefinic substrates were hydrogenated:
gands (1.932 Å).[11] In the 1H NMR spectrum the single methyl 2-acetamidoacrylate (S1), dimethyl itaconate (S2)
aliphatic urea proton (CH2NH) shows a strong downfield and N-(3,4-dihydro-2-naphthalenyl)acetamide (S3). S1 and
shift, which supports that the two ligands indeed interact S2 are frequently used benchmark substrates in the asym-
via hydrogen bonding in solution. In addition, DFT calcu- metric hydrogenation reaction, however, S3 is a relatively
lations show that the optimized structure of C4, containing difficult substrate to hydrogenate and only few systems are
2994
www.eurjic.org
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2010, 2992–2997

Asymmetric Hydrogenation Reactions
reported that provide high enantioselectivity for this sub-
Interestingly, the asymmetric hydrogenation of S3, using
strate.[18] The reaction mixtures were prepared in situ by the neutral complexes [RhCl(L2)(cod)] and [Rh(L2-
addition of solvent (CH2Cl2) to a mixture of the appropri- κ2P,N)(cod)], led to relatively high conversions (entry 13
ate amounts of metal precursor, ligand and substrate. Next, and 14). Furthermore, in the hydrogenation of S3 using
the reaction mixtures were put under an atmosphere of di- [Rh(L2-κ2P,O)(nbd)]BF4 no decomposition of the catalyst
hydrogen. The results of the asymmetric hydrogenation of was observed in the reaction mixture after the reaction (en-
S1, S2 and S3 are presented in Table 1.
try 12). These results suggest that S3 coordinates more
strongly to the metal center, which explains the higher con-
versions obtained using [RhCl(L2)(cod)] and [Rh(L2-
κ2P,N)(cod)] and the absence of decomposition using
[Rh(L2-κ2P,O)(nbd)]BF4. Although the neutral complexes
[RhCl(L2)(cod)] and [Rh(L2-κ2P,N)(cod)] provided rela-
tively good conversion in the hydrogenation of S3, the ob-
tained enantioselectivities were poor (entry 13 and 14)
However, both cationic complexes [Rh(L2)2(nbd)]BF4
(55.3%, entry 11) and [Rh(L2-κ2P,O)(nbd)]BF4 (56.5%, en-
try 12) led to moderate enantioselectivities. Because rela-
tively good conversions were obtained for substrate S3, this
substrate was additionally investigated using the chiral urea-
phosphane L3. With the complexes [RhCl(L3)(cod)] and
[Rh(L3-κ2P,N)(cod)] again high conversion was obtained,
but the enantioselectivity was disappointing (entry 17 and
19). Interestingly, hydrogenation of S3 using [Rh(L3)2(nbd)]
BF4 led to an ee of 85.2%, although the conversion was
only 26.2% (entry 15). Possibly, the additional bulky phenyl
substituents in the spacer of L3 decrease the activity of this
complex because of steric reasons. However, using [Rh(L3-
κ2P,O)(nbd)]BF4 an ee value of 86.1% obtained at full con-
version (entry 16). The use of [Rh(L3-κ2P,N)(L3-κP)(CO)]
could not improve these results (entry 18), which seems
logical because the substrate is less likely to influence the
creation of a vacant site on the metal center.
Table 1. Asymmetric hydrogenation of S1, S2 and S3.[a]
Entry Complex
sub
Conv. (%)
ee (%)
1
[Rh(L2)2(nbd)]BF4
S1
S1
S1
S1
S1
S2
S2
S2
S2
S2
S3
S3
S3
S3
S3
S3
S3
S3
S3
100
100
0
57.4 (S)
4.2 (R)
–
2[b]
3
[Rh(L2-κ2P,O)(nbd)]BF4
[RhCl(L2)(cod)]
4
5
6
[Rh(L2-κ2P,N)(L2-κP)(CO)]
[Rh(L2-κ2P,N)(cod)]
[Rh(L2)2(nbd)]BF4
0
–
20.5
74.8
100
6.5
2.4
6.8
100
100
77.6
100
26.2
100
71.1
0
69.2 (S)
23.2 (S)
3.8 (R)
4.1 (R)
9.2 (S)
24.3 (R)
55.3 (+)
56.5 (+)
15.1 (+)
13.9 (+)
85.2 (+)
86.1 (+)
26.3 (+)
–
7[b]
8
[Rh(L2-κ2P,O)(nbd)]BF4
[RhCl(L2)(cod)]
9
10
[Rh(L2-κ2P,N)(L2-κP)(CO)]
[Rh(L2-κ2P,N)(cod)]
[Rh(L2)2(nbd)]BF4
11[c]
12[c]
13[c]
14[c]
15[c]
16[d]
17[d]
18[d]
19[d]
[Rh(L2-κ2P,O)(nbd)]BF4
[RhCl(L2)(cod)]
[Rh(L2-κ2P,N)(cod)]
[Rh(L3)2(nbd)]BF4
[Rh(L3-κ2P,O)(nbd)]BF4
[RhCl(L3)(cod)]
[Rh(L3-κ2P,N)(L3-κP)(CO)]
[Rh(L3-κ2P,N)(cod)]
100
11.2 (+)
[a] Reaction conditions: [Rh] = 1 m, [S] = 100 m, reaction time:
12 h, temperature: room temp., pressure: 20 bar H2, solvent:
CH2Cl2. [b] Formation of rhodium black. [c] [S] = 50 m, pressure:
40 bar H2, reaction time: 72 h. [d] [S] = 50 m.
Conclusions
It appeared that for S1 and S2 the cationic rhodium
complexes gave significantly higher conversions than the
neutral rhodium complexes. For instance, S1 was hydroge-
nated by the two cationic complexes (entry 1 and 2) to full
conversion, while the neutral complexes gave relatively low
conversions (entry 3, 4 and 5). Likely, the neutral com-
plexes, [RhCl(L2)(cod)] and [Rh(L2-κ2P,N)(cod)] that con-
tain the strongly σ-donating ureaphosphane are too elec-
tron-rich, which hampers substrate coordination to the
metal center.[19] On the other hand, the neutral complex
[Rh(L2-κ2P,N)(L2-κP)(CO)] is coordinatively saturated,
which leaves no vacant site for coordination of the sub-
strate.[20] Nevertheless, the highest ee for the hydrogenation
of both S1 (69.2%, entry 5) and S2 (24.3%, entry 10) was
obtained using the neutral complex [Rh(L2-κ2P,N)(cod)].
With the cationic complex [Rh(L2)2(nbd)]BF4 slightly lower
ee values for S1 (57.4%, entry 1) and S2 (23.2%, entry 6)
were obtained. The cationic complex [Rh(L2-κ2P,O)(nbd)]-
BF4 seemed relatively unstable in the hydrogenation of S1
and S2 because after completion of the reaction rhodium
black was observed in the reaction mixture. The instability
of this complex possibly explains the low ee values obtained
(entry 2 and 7).
In summary, new ureaphosphane-rhodium(I) complexes
have been synthesized, which show the rich coordination
chemistry of these ligands. Depending on the nature of the
anion and the ligand/metal ratio, the ureaphosphane acts
either as a hybrid P,O-coordinating chelate, as an anionic
P,N-coordinating chelate or as a supramolecular (hydrogen-
bonded) bidentate ligand. These differences in coordination
chemistry are translated into the results in catalysis, involv-
ing asymmetric ureaphosphanes. The activity and the
enantioselectivity showed to be strongly dependent on the
complex used. In addition, for a different substrate also a
different complex was required to obtain the best activity
and enantioselectivity. These results demonstrate that em-
ploying the different coordination modes of ureaphos-
phanes in catalysis is a valuable strategy to enlarge the sub-
strate scope of these ligands.
Experimental Section
General Procedures: Unless stated otherwise, reactions were carried
out under an inert atmosphere of nitrogen or argon using standard
Schlenk techniques. CH2Cl2 was distilled from CaH2; hexanes were
Eur. J. Inorg. Chem. 2010, 2992–2997
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
2995

J. N. H. Reek et al.
1JP-Rh = 129, JP,P = 310 Hz) ppm. 13C{1H} NMR (CDCl3,
FULL PAPER
2
distilled from sodium under a nitrogen atmosphere. All reagents
were purchased from commercial suppliers and were used without
further purification. L1, L2 and L3 were synthesized according to a
published procedure.[9] S3 was synthesized according to a published
procedure.[21] NMR spectra were measured on a Varian Mercury
(1H: 300 MHz, 31P{1H}: 121.5 MHz and 13C{1H}: 75.5 MHz) or
a Varian Inova spectrometer (1H: 500 MHz, 31P{1H}: 202.3 MHz,
13C{1H}: 125.7 MHz) at room temperature. Chemical shifts are re-
ported in ppm and are given relative to TMS (1H and 13C{1H}) or
H3PO4 (31P{1H}) as external standards. High resolution mass spec-
tra (HRMS) were recorded at the department of mass spectrometry
at the University of Amsterdam using FAB+ ionization on a JEOL
JMS SX/SX102A four sector mass spectrometer with 3-nitrobenzyl
alcohol as the matrix. IR spectra were recorded on a Thermo, Nic-
olet Nexus 670 FT-IR apparatus.
125.7 MHz): δ = 29.303 (d, JC,P = 22 Hz, CH2), 31.006 (d, JC,P
33 Hz, CH2), 35.849 (d, JC,P = 8.7 Hz, CH2), 47.283 (d, JC,P
=
=
5.9 Hz, CH2), 118.298, 118.592, 121.067, 121.269, 128.499, 128.549,
128.852, 128.926, 129.041, 129.059, 130.478, 130.832, 132.793,
132.889, 133.073, 133.170, 133.413, 133.757, 134.368, 134.699,
140.417, 140.477, 155.785 (NHCONH) 162.215 (NCONH), 192
(br., Rh-CO) ppm. HRMS (FAB+): m/z calculated for
C43H42O3N4P2Rh ([MH]+): 827.1787; observed: 827.1784. Solution
IR (20 m, CDCl ), ν = 1981 cm–1 (Rh–CO band).
˜
3
[Rh(L1-κ2P,N)(cod)] (C5): Yellow powder. 1H NMR (CDCl3,
500 MHz): δ = 2.77 (m, 2 H, CH2CH2N), 3.96 (m, 2 H, CH2N),
7.0–7.7 (m, 16 H, 15 ArH + 1 NHPh) ppm. 31P{1H} NMR (CDCl3,
1
202.3 MHz): δ = 20.7 (d, JP-Rh = 148 Hz) ppm. HRMS (FAB+):
m/z calculated for C29H33N2OPRh ([MH]+): 559.1386; observed:
559.1373. The presence of side product in the catalyst mixture pre-
vented to report unambiguously the 13C{1H} NMR signals.
General Procedure Complex Synthesis: To a Schlenk flask, filled
with the appropriate amounts of ureaphosphane and metal precur-
sor, was added CH2Cl2. After five minutes of vigorous stirring, sol-
vents were evaporated in vacuo.
General Procedure Hydrogenation Experiments: The hydrogenation
experiments were carried out in an Accelerator SLT workstation of
Chemspeed Technologies (Http://www.chemspeed.com) under inert
conditions. The reaction mixtures were prepared in situ by addition
of CH2Cl2 to a Schlenk flask filled with the appropriate amounts of
metal precursor, ligand and substrate. The reaction mixtures were
subsequently injected manually into a reaction vial of the Accelera-
tor SLT workstation. Next, the automated program of the Acceler-
ator SLT workstation was started, putting the reaction mixtures
under an atmosphere of dihydrogen and mixing the reaction mix-
tures by vortex shaking. Product samples of methyl-2-acetamido-
acrylate (S1), dimethyl itaconate (S2) and N-(3,4-dihydro-2-naph-
thalenyl)acetamide (S3) were prepared directly after completion of
the program and analyzed by using an Interscience Trace GC Ultra
(FID detector) for S1 and S3 or an Interscience Focus GC for S2.
Both GC’s were equipped with a CP-Chiralsil-DexCB column. For
S3 the signs were reported to emphasize changes in the absolute
chirality of the product as measured by GC, however, they do not
reflect a measured optical rotation.
[Rh(L1)2(nbd)]BF4 (C1): Yellow powder. 1H NMR (CDCl3,
500 MHz): δ = 1.522 (s, 2 H, Rh-nbd), 2.407 (br. s, 4 H,
CH2CH2NH), 3.497 (br. s, 4 H, CH2NH), 3.875 (s, 2 H, Rh-nbd),
4.445 (s, 4 H, Rh-nbd), 5.975 (br., 2 H, CH2NH), 6.959 (t, J =
6.9 Hz, 2 H, ArH), 7.1–7.2 (m, 6 H, 5 ArH + 1 NHPh), 7.3–7.5
(m, 24 H, ArH) ppm. 31P{1H} NMR (CDCl3, 202.3 MHz): δ = 18.4
1
(d, JP-Rh = 152 Hz) ppm. 13C{1H} NMR (CDCl3, 125.7 MHz): δ
= 27.418 (CH2), 37.005 (CH2), 53.027 (Rh-nbd) 68.89 (Rh-nbd,
CH2), 81.898 (Rh-nbd, CH), 119.138 (CH), 122.325 (CH), 128.876
(CH), 129.48 (CH), 131.384 (CH), 132.539 (CH), 139.631 (Cquat),
155.835 (NHCONH) ppm. HRMS (FAB+): m/z calculated for
C49H50O2N4P2Rh ([MH]+): 891.2464; observed: 891.2468.
[Rh(L1-κ2O,P)(nbd)]BF4 (C2): Yellow powder. 1H NMR (CDCl3,
500 MHz): δ = 1.44 (s, 2 H, Rh-nbd), 2.58 (t, J = 10 Hz, 2 H,
CH2CH2NH), 3.26 (s, 2 H, Rh-nbd), 3.84 (m, 2 H, CH2NH), 3.92
(s, 2 H, Rh-nbd), 5.35 (s, 2 H, Rh-nbd), 6.68 (t, J = 5.5 Hz, 1 H,
CH2NH), 7.1–7.6 (m, 15 H, ArH), 7.71 (s, 1 H, NHPh) ppm.
31P{1H} NMR (CDCl3, 202.3 MHz): δ = 31.4 (d, JP-Rh = 170 Hz)
1
X-ray Crystallography of C4: C43H41N4O3P2Rh·2(CD2Cl2), a =
11.8876(3), b = 12.0474(3), c = 16.8658(5) Å, α = 75.752(2), β =
ppm. 13C{1H} NMR (CDCl3, 125.7 MHz): δ = 29.567 (JC,P
=
24 Hz), 39.066 (JC,P = 3.2 Hz), 51.9981 (Rh-nbd), 64.116 (Rh-nbd),
90.512 (Rh-nbd), 120.729, 124.234, 128.648, 128.813, 129.010,
129.286, 129.369, 131.435, 132.657, 132.754, 137.365, 161.506
(NHCONH) ppm. HRMS (FAB+): m/z calculated for
C28H29N2OPRh ([MH]+): 543.1073; observed: 543.1074. Solution
¯
89.596(2), γ = 75.529(2)°, triclinic, P1, Z = 2, Mw = 1000.51, Dx
= 1.469 g/cm3. Mo-Kα, λ = 0.71073 Å, T = 150 K. X-ray data were
collected on a Nonius KappaCCD [10391 unique reflections,
θ(max) = 27.5°]. The images were processed with EVALCCD. The
structure was solved with DIRDIF99 and refined with SHELXL-
97. One of the two CD2Cl2 solvent molecules was refined with a
disorder model (0.621:0.379). R = 0.0282 [8944 reflections with
IϾ2σ(I)], wR2 = 0.0699 (10393 reflections), S = 1.058, 569 refined
parameters, residual density range –0.63:0.44 e/Å3. The structure
was validated with PLATON/CheckCIF.
IR (20 m, CDCl ), ν = 1572 cm–1 (COurea band).
˜
3
[RhCl(L1)(cod)] (C3): Yellow powder. 1H NMR (CDCl3,
500 MHz): δ = 1.88 (s, 2 H, Rh-cod), 2.03 (s, 2 H, Rh-cod), 2.33
(d, J = 6 Hz, 4 H, Rh-cod), 2.76 (m, 2 H, CH2CH2NH), 3.09 (s, 2
H, Rh-cod), 3.98 (q, J = 6.5 Hz, 2 H, CH2NH), 5.48 (s, 2 H, Rh-
cod), 6.35 (s, 1 H, NHCH2), 6.79 (s, 1 H, NHPh), 7.02 (t, J = 7 Hz,
1 H, ArH), 7.2–7.7 (m, 14 H, ArH) ppm. 31P{1H} NMR (CDCl3,
CCDC-743287 (for C4) contains the supplementary crystallo-
graphic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
202.3 MHz): δ = 21.1 (d, JP-Rh = 148 Hz) ppm. 13C{1H} NMR
1
(CDCl3, 125.7 MHz): δ = 28.897, 29.103, 33.053, 37.573, 71.465,
105.471, 119.526, 122.796, 128.478, 128.551, 129.093, 130.411,
132.322, 132.653, 133.484, 133.567, 139.322, 155.631 (NHCONH)
ppm. HRMS (FAB+): m/z calculated for C29H34ClN2OPRh
([MH]+): 595.1152; observed: 595.1164.
[Rh(L1-κ2P,N)(L1)(CO)] (C4): Yellow-orange powder. 1H NMR
(CDCl3, 500 MHz): δ = 2.35 (t, J = 7 Hz, 2 H, CH2), 2.65 (br. s, 2
Dilution Studies: 1H NMR dilution experiments were carried out
by preparing a 0.5 mL sample at a known concentration: 10, 20,
30 and 40 m in CDCl3 for L1 and for C3. The position of the
solvent signal was used as a reference for the urea NH signal.
DFT Calculations: The geometry optimizations were carried out
H, CH2), 3.43 (br. s, 2 H, CH2), 3.8 (br. s, 2 H, CH2), 6.44 (s, 1 H, with the Turbomole program[22] coupled to the PQS Baker opti-
ArH), 6.7 (br. s, 1 H, NHCH2), 6.75–7.75 (m, 30 H, 29 ArH + 1
mizer.[23] Geometries were fully optimized at the BP86[24] level
using the SV(P) basis set[25] on all atoms (small-core pseudopoten-
NHPh), 8.0 (s, 1 H, NHPh) ppm. 31P{1H} NMR (CDCl3,
202.3 MHz): δ = 19.7 (dd, JP-Rh = 136, JP,P = 310 Hz), 52.2 (dd, tial[26] on rhodium).
1
2
2996
www.eurjic.org
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2010, 2992–2997

Asymmetric Hydrogenation Reactions
[9]
J. Meeuwissen, R. J. Detz, A. J. Sandee, B. de Bruin, J. N. H.
Reek, Dalton Trans. 2010, 39, 1929–1931.
For an account on intra- and intermolecular interactions, see:
A. Mulder, J. Huskens, D. N. Reinhoudt, Org. Biomol. Chem.
2004, 2, 3409–3424.
Supporting Information (see also the footnote on the first page of
this article): Optimized geometries of the species of the DFT calcu-
lations are supplied as pdb files.
[10]
[11]
[12]
See Supporting Information.
Acknowledgments
a) L. Song, P. Stang, Inorg. Chim. Acta 1991, 188, 107–111; b)
M. Kuriyama, K. Nagai, K.-i. Yamada, Y. Miwa, T. Taga, K.
Tomioka, J. Am. Chem. Soc. 2002, 124, 8932–8939.
For reviews on hemilabile ligands, see: a) P. Braunstein, F.
Naud, Angew. Chem. Int. Ed. 2001, 40, 680–699; b) P.
Braunstein, J. Organomet. Chem. 2004, 689, 3953–3967; c) A.
Bader, E. Lindner, Coord. Chem. Rev. 1991, 108, 27–110.
Addition of more equivalents of L1 led to a mixture of species.
For a related system, see: C. Meyer, M. Scherer, H. Schönberg,
H. Rüegger, S. Loss, V. Gramlich, H. Grützmacher, Dalton
Trans. 2006, 137–148.
This research is financially supported by BASF B.V., The Univer-
sity of Amsterdam and The Netherlands and the Dutch Ministry
of Economic Affairs by way of SenterNovem. J. W. H. Peeters is
acknowledged for the mass spectrometric experiments. The Neder-
landse Organisatie voor Wetenschappelijk Onderzoek, Chemische
Wetenschappen (NWO-CW) is kindly acknowledged for financial
support to A. L. S.
[13]
[14]
[15]
[1] For reviews see: a) M. J. Wilkinson, P. W. N. M. van Leeuwen,
J. N. H. Reek, Org. Biomol. Chem. 2005, 3, 2371–2383; b) B.
Breit, Angew. Chem. Int. Ed. 2005, 44, 6816–6825; c) A. J.
Sandee, J. N. H. Reek, Dalton Trans. 2006, 3385–3391.
[2] a) F. W. Patureau, M. Kuil, A. J. Sandee, J. N. H. Reek, Angew.
Chem. Int. Ed. 2008, 47, 3180–3183; b) B. Breit, W. Seiche, J.
Am. Chem. Soc. 2003, 125, 6608–6609; c) B. Breit, W. Seiche,
Angew. Chem. Int. Ed. 2005, 44, 1640–1643; d) M. Weis, C.
Waloch, W. Seiche, B. Breit, J. Am. Chem. Soc. 2006, 128,
4188–4189; e) F. Chevallier, B. Breit, Angew. Chem. Int. Ed.
2006, 45, 1599–1602; f) C. Waloch, J. Wieland, M. Keller, B.
Breit, Angew. Chem. Int. Ed. 2007, 46, 3037–3039; g) M.
de Greef, B. Breit, Angew. Chem. Int. Ed. 2009, 48, 551–554; h)
Y. Liu, C. A. Sandoval, Y. Yamaguchi, X. Zhang, Z. Wang, K.
Kato, K. Ding, J. Am. Chem. Soc. 2006, 128, 14212–14213.
[3] a) V. F. Slagt, M. Röder, P. C. J. Kamer, P. W. N. M.
van Leeuwen, J. N. H. Reek, J. Am. Chem. Soc. 2004, 126,
4056–4057; b) X.-B. Jiang, L. Lefort, A. H. M. de Vries,
P. W. N. M. van Leeuwen, J. G. de Vries, J. N. H. Reek, Angew.
Chem. Int. Ed. 2006, 45, 1223–1227; c) M. Kuil, P. E. Goud-
riaan, P. W. N. M. van Leeuwen, J. N. H. Reek, Chem. Com-
mun. 2006, 4679–4681; d) M. Kuil, P. E. Goudriaan, A. W.
Kleij, D. M. Tooke, A. L. Spek, P. W. N. M. van Leeuwen,
J. N. H. Reek, Dalton Trans. 2007, 2311–2320; e) J. M. Takacs,
D. S. Reddy, S. A. Moteki, D. Wu, H. Palencia, J. Am. Chem.
Soc. 2004, 126, 4494–4495; f) J. M. Takacs, K. Chaiseeda, S. A.
Moteki, D. S. Reddy, D. Wu, K. Chandra, Pure Appl. Chem.
2006, 78, 501–509; g) S. A. Moteki, J. M. Takacs, Angew.
Chem. Int. Ed. 2008, 47, 894–897.
[4] a) H. Gulyás, J. Benet-Buchholz, E. C. Escudero-Adan, Z.
Freixa, P. W. N. M. van Leeuwen, Chem. Eur. J. 2007, 13, 3424–
3430; b) L. Pignataro, B. Lynikaite, J. Cvengrosˇ, M. Marchini,
U. Piarulli, C. Gennari, Eur. J. Org. Chem. 2009, 2539–2547;
c) Y. Li, Y. Feng, Y.-M. He, F. Chen, J. Pan, Q.-H. Fan, Tetra-
hedron Lett. 2008, 49, 2878–2881.
[5] L. K. Knight, Z. Freixa, P. W. N. M. van Leeuwen, J. N. H.
Reek, Organometallics 2006, 25, 954–960.
[6] A. J. Sandee, A. M. van der Burg, J. N. H. Reek, Chem. Com-
mun. 2007, 864–866.
[7] J. Meeuwissen, M. Kuil, A. M. van der Burg, A. J. Sandee,
J. N. H. Reek, Chem. Eur. J. 2009, 15, 10272–10279.
[8] P. A. Duckmanton, A. J. Blake, J. B. Love, Inorg. Chem. 2005,
44, 7708–7710.
[16]
Using only one equivalent of L1 also led to the evolution of
Hacac. The 31P{1H} NMR spectrum showed a doublet, reso-
nating at δ = 39.8 ppm (1JP-Rh = 171 Hz), that likely belongs
to [Rh(L1-κ2P,N)(CO)x]. However, we were unable to fully
characterize this species.
For a related system, see: J. A. Fuentes, M. L. Clarke, A. M. Z.
Slawin, New J. Chem. 2008, 32, 689–693.
[17]
[18] F. W. Patureau, S. de Boer, M. Kuil, J. Meeuwissen, P.-A. R.
Breuil, M. A. Siegler, A. L. Spek, A. J. Sandee, B. de Bruin,
J. N. H. Reek, J. Am. Chem. Soc. 2009, 131, 6683–6685 (ee
81%) and reference 3b (ee 94%).
[19] Likely, the neutral complexes [RhCl(L2)(cod)] and [Rh(L2-
κ2P,N)(cod)] lose the cod ligand and remain inactive in the
reaction mixture as RhIII dihydride species, due the low affinity
of these complexes towards substrates S1 and S2.
[20] For an example involving Rh(acac)(CO)2 as a precursor for an
active hydrogenation catalyst, see: C. J. Scheuermann née Tay-
lor, C. Jaekel, Adv. Synth. Catal. 2008, 350, 2708–2714.
[21] J. L. Renaud, P. Dupau, A.-E. Hay, M. Guingouain, P. H.
Dixneuf, C. Bruneau, Adv. Synth. Catal. 2003, 345, 230–238.
[22] a) R. Ahlrichs, M. Bär, H.-P. Baron, R. Bauernschmitt, S.
Böcker, M. Ehrig, K. Eichkorn, S. Elliott, F. Furche, F. Haase,
M. Häser, C. Hättig, H. Horn, C. Huber, U. Huniar, M. Kat-
tannek, A. Köhn, C. Kölmel, M. Kollwitz, K. May, C. Ochsen-
feld, H. Öhm, A. Schäfer, U. Schneider, O. Treutler, K. Tseret-
eli, B. Unterreiner, M. von Arnim, F. Weigend, P. Weis, H.
Weiss, Turbomole, version 5, January 2002. Theoretical Chem-
istry Group, University of Karlsruhe; b) O. Treutler, R.
Ahlrichs, J. Chem. Phys. 1995, 102, 346–354.
[23] a) PQS version 2.4, 2001, Parallel Quantum Solutions, Fayette-
ville, Arkansas, USA (the Baker optimizer is available sepa-
rately from PQS upon request); b) J. Baker, J. Comput. Chem.
1986, 7, 385–395.
[24] a) A. D. Becke, Phys. Rev. A 1988, 38, 3098–3100; b) J. P. Per-
dew, Phys. Rev. B 1986, 33, 8822–8824.
[25] A. Schäfer, H. Horn, R. Ahlrichs, J. Chem. Phys. 1992, 97,
2571–2577.
[26] a) Turbomole basisset library, Turbomole Version 5; b) D. And-
rae, U. Haeussermann, M. Dolg, H. Stoll, H. Preuss, Theor.
Chim. Acta 1990, 77, 123–141.
Received: February 22, 2010
Published Online: May 14, 2010
Eur. J. Inorg. Chem. 2010, 2992–2997
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
2997