Stitching phospholanes together piece by piece: New modular di- and tridentate stereodirecting ligands

Article abstract of DOI:10.1002/chem.201101864

The modular one-pot synthesis of a large family of bi- and tridentate 2,5-dimethyl- and 2,5-diphenyl-substituted phospholanes employs air-stable chiral phospholanium chloride salts and primary amines or NH₄Cl as starting materials. These were t

Full text of DOI:10.1002/chem.201101864

FULL PAPER
DOI: 10.1002/chem.201101864
Stitching Phospholanes Together Piece by Piece: New Modular Di- and
Tridentate Stereodirecting Ligands
Julio Lloret Fillol, Achim Kruckenberg, Peter Scherl, Hubert Wadepohl, and
Lutz H. Gade*[a]
Abstract: The modular one-pot synthe-
sis of a large family of bi- and triden-
tate 2,5-dimethyl- and 2,5-diphenyl-
substituted phospholanes employs air-
stable chiral phospholanium chloride
salts and primary amines or NH4Cl as
starting materials. These were trans-
formed into the C2-symmetric dimeth-
yl- and diphenylphospholane ligands,
bound symmetrically, different coordi-
nation behaviour was found for the di-
phenyl-substituted complex 12, in
which the coordination of only two of
the three phospholane moieties to the
metal centre was observed. A DFT
study at the B3PW91 level established
minimum energy structures consistent
with experimental findings in solution
and in the solid state. The non-coordi-
nated phospholane unit present in 12
allowed further modification of the
the potential of the new ligands, the
enantioselective hydrogenation of
a
series of prochiral olefins as bench-
mark substrates, using isolated Rh
complexes as catalysts, was studied.
The substrates included methyl esters
of three dehydro-a-acetamido acids
and two itaconic acid derivatives. In
general good to excellent enantioselec-
tivities (of up to >99% ee) were ob-
served. Ligand backbone modification
which reacted with [Rh
(cod=1,5-cyclooctadiene) to yield the
rhodium complexes [Rh(L)(cod)]BF4
ACHTUNGTERN(NUNG cod)2]BF4
À
G
by coordination of bulky Au X sub-
(L=bisphospholane ligands). The cor-
responding trisphospholane complexes,
11 and 12, were obtained in high yields
(81 and 92%, respectively), and fully
characterised by NMR spectroscopy,
mass spectrometry and elemental anal-
ysis. Whilst in the C3-symmetric com-
plex 11, containing the tridentate 2,5-
dimethylphospholane, the ligand is
complex through the coordination of
stituents to the free phospholane unit
in complex 12 led to an outstanding en-
hancement of the catalyst performance
and there was a clear correlation be-
tween the properties of the complex
periphery and the enantioselectivity.
I
À
Au X (X=Cl, C6F5 and tris(trifluoro-
methyl)phenyl (FMes)) fragments to
the pendant phosphane. To investigate
Keywords: asymmetric catalysis
hydrogenation ligand design
phospholanes · rhodium
·
·
·
Introduction
the small number of publications related to bidentate ligand
families generally reflects the difficulty of their synthesis.[4]
This particularly applies to chiral trivalent phosphorus li-
gands because they are amongst the most useful ligands in
asymmetric catalysis.[5,6] A well-known piece of phosphorus
The field of asymmetric catalysis has grown rapidly during
recent decades and plays a key role in many areas of syn-
thetic chemistry, including the discovery of new drugs and
the production of fine chemicals.[1] Rational ligand design
and high-throughput screening methodologies have become
vital tools in catalysis research because a broad scope of
substrates requires the rapid development of customised li-
gands. Although only a limited number of “privileged”
chiral structures have become established,[2] the develop-
ment of synthetic pathways that facilitate access to new
classes of chiral ligands remains a key challenge.[3] Whilst
many libraries for monodentate ligands have been reported,
À
chemistry is the functionalisation of a P H bond by direct
reaction with a twofold excess of formaldehyde under acidic
conditions, which leads to the formation of an air- and mois-
ture-stable phosphonium salt.[7,8] Thus, these compounds are
more convenient starting points for the synthesis of a ligand
library than the highly air-sensitive secondary phosphanes.
Indeed, the treatment of a phosphonium salt with a base fol-
lowed by addition of a nucleophile, typically an amine (in-
cluding ammonia and primary or secondary amines) affords
tri-, bi- or monodentate ligands (Scheme 1).[9]
In this way, achiral mono-,[10] bi-[7,11] and tridentate[12] li-
gands were synthesised by combining two modules: the
phosphane unit and the amine group. It also allowed the in-
troduction of diphosphanes into dendrimers,[13] calixar-
enes,[14] proteins[15] and solid supports,[16] as well as other
forms of derivatisation.[17] Related systems exhibiting high
activity as catalysts for water reduction to form hydrogen
have been used as hydrogenase models.[18] Despite their ver-
[a] Dr. J. Lloret Fillol, A. Kruckenberg, P. Scherl, Prof. Dr. H. Wadepohl,
Prof. Dr. L. H. Gade
Anorganisch-Chemisches Institut, Universitꢀt Heidelberg
Im Neuenheimer Feld 270, 69120 Heidelberg (Germany)
Fax.: (+49)6221-545609
E-mail: lutz.gade@uni-hd.de
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201101864.
Chem. Eur. J. 2011, 17, 14047 – 14062
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14047

2,5-diphenyl ((S)-4 and (R)-4) bis(hydroxymethyl)phospho-
lanium chloride salts, by modification of the method report-
ed by Kemmitt et al.[7]
The starting materials, enantiopure secondary phosphanes
(2R,5R)-2,5-dimethylphospholane (1), (2S,5S)-2,5-diphenyl-
phospholane ((S)-2) and its enantiomer (R)-2, were pre-
pared as described in the literature.[26,27] Due to their strong
tendency to undergo oxidation, compounds such as these
are often difficult to handle. However, this approach did not
require the isolation of pure phospholanes 1 and (S)-2.
Instead, solutions of air-sensitive chiral secondary phos-
pholanes 1, (R)-2 and (S)-2 in THF were used in situ by
treatment with two equivalents of formaldehyde followed by
addition of one equivalent of concentrated hydrochloric
acid (Scheme 2). This leads to the formation of the air-
stable chiral phospholanium chloride salts 3, (R)-4 and (S)-
4, which were isolated as crystalline white powders. The
phospholanium salts were completely characterised by
NMR spectroscopy and elemental analysis. Furthermore, X-
ray diffraction analysis from a single crystal of compound 3
was obtained (see the Supporting Information).
Scheme 1. Modular synthesis of mono-, di- and triphosphane ligands via
air-stable phosphonium salts.
satility, only limited attempts to synthesise the correspond-
ing chiral amine-bridged di- and triphosphanes have been
made. Initially, mainly chiral amines and amino acids were
used,[7,19] and only recently have there been several reports
dealing with the introduction of chiral phosphorus building
blocks.[20]
We have therefore focused on the development of a mod-
ular synthesis of a large family of bi- and tridentate chiral
phospholane ligands and selected the 2,5-dimethyl- and 2,5-
diphenyl-substituted phospholanes as stereodirecting groups
because these two privileged chiral units had given rise to
remarkable reactivity and enantioselectivities with particular
impact on catalytic asymmetric hydrogenations.[21] Their effi-
ciency in inducing enantioselectivity was evaluated by em-
ploying the corresponding rhodium complexes in the indus-
trially important catalytic asymmetric hydrogenation of pro-
chiral olefins.[4g,22,23] We note that few examples of chiral C3-
symmetric trisphospholane ligands have been published to
date.[24,25]
Results and Discussion
Scheme 2. Synthesis of phospholane ligands by using amines and phos-
pholanium salts 3 and (S)-4 as key intermediates. Both R,R and S,S enan-
tiomers of 2 were obtained and converted into the corresponding phos-
pholanium salts. For clarity only one enantiomer is shown. Abbrevia-
tions: Th=thienyl, Fu=furanyl, Py=pyridyl, Ad=adamantyl.
Synthesis and characterisation of the new chiral phosphola-
nomethylamine ligands (5a–i and 6a–c): All chiral phospho-
lane ligands reported herein have been synthesised via
common key intermediates, the chiral 2,5-dimethyl (3) and
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Stitching Phospholanes Together Piece by Piece
FULL PAPER
Compounds 3 and 4 were transformed into the chiral C2-
symmetric dimethylphospholane (DMP; 5a–i) and diphenyl-
phospholane (DPP; 6a–c) ligands and the C3-symmetric li-
gands (DMP: 7 and DPP: 8) in one-pot reactions. The addi-
tion of one equivalent of triethylamine to a solution of com-
pound 3 in methanol led to quantitative formation of the hy-
droxymethylphospholane by elimination of one equivalent
formaldehyde. The assignment was based on the disappear-
ance of the 31P NMR resonance of the starting compound
(d=47.1 ppm) when the base was added with concomitant
formation of a new signal in the 31P NMR spectrum (d=
0.4 ppm). The same observations were made upon base
treatment of salt 4. Subsequent reaction of the in situ
formed intermediates with different amines at room temper-
ature led to the formation of the corresponding bisphospho-
lane ligands in high yields. It should be noted that racemisa-
tion is not observed either in the synthesis of the phosphola-
nium salts or in the synthesis of the ligands.
Scheme 3. Synthesis of C2-symmetric Rh complexes of bidentate DMP
and DPP substituted ligands.
While the C2-symmetric DMP-substituted ligands were
obtained as oily liquids, the C2-symmetric DPP-substituted
and both C3-symmetric ligands were crystalline solids. All li-
gands were characterised by NMR spectroscopy, mass spec-
trometry and elemental analysis. Single crystals of enantio-
pure C3-symmetric ligands 7 and (R)-8 suitable for X-ray
diffraction analysis were obtained. Their molecular struc-
tures are depicted in Figure 1.
Figure 1. Thermal ellipsoid plots (50% probability level; H atoms and
co-crystallised solvent omitted for clarity) of the X-ray structure of the
C3-symmetric 7 (left) and (R)-8 (right) ligands.
Synthesis and characterisation of C2-symmetric chiral rhodi-
um complexes of ligands 5a–i and 6a–c: The rhodium com-
plexes were synthesised by the addition of the ligand to a
À
Figure 2. Thermal ellipsoid plots (50% probability level; H atoms, BF4
anions and co-crystallised solvent omitted for clarity) of the X-ray struc-
ture of four representative Rh complexes with C2-symmetric DMP (top:
9b and 9h) and DPP ligands (bottom: 10c and 10a). Principal bond
lengths [ꢂ] and angles [8] are given in Table 1.
solution
of
[Rh
G
(cod=1,5-cyclooctadiene;
Scheme 3). All analytical data were in accordance with the
formation of cationic C2-symmetric rhodium complexes
[Rh(L)ACHTUNGTRENNUNG(cod)]BF4 (L=bisphospholane ligands 5a–i and 6a–
c). In addition to characterisation by NMR spectroscopy,
mass spectrometry and elemental analysis, single crystals of
seven C2-symmetric rhodium complexes were suitable for X-
ray diffraction analysis, four of which are presented in
Figure 2. Selected bond lengths and angles are given in
Table 1.
In all complexes we observed a distorted square-planar
coordination geometry, in which the cod ligand is twisted
out of the P(1)-Rh-P(2) plane by an angle of f because this
conformation reduces steric repulsion between the cod and
the phospholane substituents. Structural data suggest that
even minor modifications of the remote substituent have a
significant influence on the geometry of the catalytic centre
and provide a suitable method to induce subtle changes in
the complex geometry, that is, to fine-tune potential cata-
lysts. Large P(1)-Rh-P(2) bite angles (92.1–92.68) are ob-
served for complexes in which the amine substituent is con-
nected to the N atom through primary and secondary C
Chem. Eur. J. 2011, 17, 14047 – 14062
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14049

L. H. Gade et al.
Table 1. Geometrical data of crystal structures of five C2-symmetric
DMP and two DPP complexes.
[a]
a [8][b]
b [8][c]
f [8][d]
À
Compound
R’
d
(Rh P) [ꢂ]
9a
9b
9c
Me
iPr
Ad
2-PyCH2
2-ThCH2
PhCH2
2-ThCH2
2.277
2.281
2.284
2.298
2.299
2.292
2.294
92.13(4)
89.62(3)
88.28(2)
92.38(2)
92.57(3)
92.59(5)
92.64(5)
70.9
68.9
65.2
75.1
73.7
73.8
74.6
25.0
20.3
19.2
25.0
24.9
22.0
22.6
9 f
9h
10a
10c
Figure 3. Thermal ellipsoid plot (50% probability level; H atoms and
BF4 anion omitted for clarity) of the X-ray structure of Rh complex 9c.
b is a measure of the deviation of the N atom from the ring plane. It de-
scribes the angle between the C(1)-C(2)-N plane and the best least-
squares plane through P(1), P(2), C(1) and C(2). Principal bond lengths
[ꢂ] and angles [8] are given in Table 1.
À
À
[a] Mean value of dACHTUNGTRENNUNG(Rh P(1)) and dHCATUNGTRENN(UGN Rh P(2)). [b] Bite angle (P(1)-Rh-
P(2)). [c] See Figure 3. [d] Angle between the P(1)-Rh-P(2) plane and
À
the plane through Rh and the centres of the two C=C bonds of cod.
atoms. In contrast, slightly
smaller angles (88.3–89.68) are
found for complexes 9b and 9c,
which have sterically more de-
manding backbone substituents
(tertiary and quaternary
C
atoms). In all complexes the ge-
ometry of the six-membered
ring formed by the ligands and
the Rh atom can be described
approximately as a half chair,
in which the N atom is not part
of the ring plane. The degree to
Scheme 4. Coordination behaviour of C3-symmetric trisphospholane ligands 7 and (R)-8.
which the
N atom deviates
from this plane can be de-
scribed by the angle b shown in Figure 3.
Bulkier substituted complexes 9b and 9c exhibit signifi-
cantly smaller values for b than all other complexes. This de-
pendence suggests that the remote substituent at the amine
imposes steric pressure on the phospholane units, resulting
in a decrease of b: these steric interactions appear to induce
the varying bite angles referred to above.
Coordination chemistry of C3-symmetric ligands 7 and 8 in
RhI complexes: As described for the C2-symmetric bisphos-
pholane ligands, Rh complexes of the two C3-symmetric tri-
sphospholane ligands 7 and 8 were prepared by the addition
of the ligand to a solution of [RhACHTNUTRGNEUNG(cod)2]BF4. The resulting
Figure 4. Thermal ellipsoid plot (50% probability level; H atoms and
BF4 anion omitted for clarity) of the X-ray structure of the C3-symmet-
ric complex 11. Principal bond lengths [ꢂ] and angles [8] (one of three
À
compounds 11 and 12 (Scheme 4) were obtained in high
yields (81 and 92%, respectively), and fully characterised by
NMR spectroscopy, mass spectrometry and elemental analy-
sis. The 31P NMR spectrum of compound 11 exhibits a single
doublet resonance at d=8.1 ppm, indicating a distorted
trigonal bipyramidal complex, in which fluxional behaviour
(“Berry pseudo-rotation”) leads to pseudo-C3-symmetry
with the ligand binding to the rhodium atom in a tridentate
fashion. Moreover, X-ray diffraction analysis of a single
crystal shows that the trisphospholane rhodium unit is also
C3-symmetric in the solid state (Figure 4).
À
À
molecules in unit cell): P(1) Rh(1) 2.3542(14), P(2) Rh(1) 2.2971(14),
À
À
À
P(3) Rh(1) 2.4116(14), C
C
ACHTUNGTREN(NUNG 102) Rh(1) 2.270(5),
À
À
C
C
C
N
87.13(5), P(1)-Rh(1)-P(3) 87.43(5), P(2)-Rh(1)-P(3) 88.64(5).
can be explained by the coordination of only two of the
three phospholane moieties to the metal centre, leaving one
phosphorus atom non-coordinating. The 1H and 13C NMR
spectra are in accordance with this result.
Interestingly, different coordination behaviour was found
in the case of the diphenyl substituted and thus sterically
more demanding ligand 8. The presence of a doublet and a
singlet (at d=24.5 and À1.8 ppm, respectively) with a rela-
tive intensity of 2:1 in the 31P NMR spectrum of complex 12
Computational studies: To obtain further insight into the
nature of the difference in coordination behaviour of the
C3-symmetric ligands, a DFT study was carried out. All
compounds were calculated at the B3PW91 level with a 6-
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Stitching Phospholanes Together Piece by Piece
FULL PAPER
31g* basis set for all atoms except for rhodium, for which
the Stuttgart–Dresden pseudo-potential was used. Alterna-
tive coordination modes of the C3-symmetric ligands to the
rhodium centre and the effect of replacing cod with CO and
CH2CH2 were simulated for complexes 11 and 12. A sum-
mary of the electronic zero-point-corrected energies and
free energies of the transformation from a bi- to tridentate
coordination mode is given in Scheme 5.
Scheme 6. Computational study of the stability of complexes 11 and 12 in
di- and tridentate coordination modes when replacing the cod ligand with
methanol molecules. Values are differences in free energy between the
structures with the value for the structure lowest in energy set to zero
(all energies are given in kcalmolÀ1). [a] Only one methanol molecule
Scheme 5. DFT-calculated energies for rhodium complexes of ligands 7
and 8 in di- and tridentate coordination modes. The values given are dif-
ferences in energy (zero-point-corrected) and free energy (in brackets)
between the structures (all energies are given in kcalmolÀ1).
À
bound to Rh (Rh O distances: 2.225 and 3.249 ꢂ).
In all the cases studied, the calculated structures with the
lowest energies were consistent with experimental findings
in solution and in the solid state. The preference of the
methyl-substituted ligand for the tridentate coordination
mode in contrast to the phenyl-substituted ligand preferring
the bidentate mode reflects the influence of the large steric
bulk of ligand 8 on coordination chemistry.
Further computational studies indicated that this was still
true when the cod ligand was replaced with one or two
methanol molecules, as expected for intermediates in the
catalytic hydrogenation of olefins (Scheme 6). Therefore, de-
pending on the phospholane substituent (methyl or phenyl),
different intermediate species could be predominant during
catalysis.
significant range of steric demands to evaluate their poten-
tial steric effects in catalytic reactions.
Reaction of monometallic Rh complex 12 with [AuCl-
AHCTUNGRTEN(NGUN tht)] (tht=tetrahydrothiophene) in CH2Cl2 at room tem-
perature resulted in a large low-field shift of the singlet
(from d=À1.8 to 38.4 ppm) previously assigned to the non-
coordinating phospholane moiety in the 31P NMR spectrum.
This observation suggests the coordination of the gold atom
to this phosphorus atom (Scheme 7). The doublet arising
from the rhodium-bound phosphorus atoms experiences
only a negligible chemical shift (to higher field by 0.7 ppm).
À
Synthesis and characterisation of heterodinuclear Rh Au
complexes 13a–c: The non-coordinated phospholane unit
present in 12 allows further modification of the complex, for
instance, by coordination of an additional metal atom, in-
creasing steric bulk in the periphery of the molecule and the
complexity of the system. We explored that approach by the
I
À
use of Au X (X=Cl, C6F5 and tris(trifluoromethyl)phenyl
(FMes)) fragments due to their preferred linear coordina-
tion, which allowed the introduction of a spatially well ori-
ented, bulky group. Substituents X were selected to cover a
À
Scheme 7. Synthesis of heterodinuclear Rh Au complexes 13a–c.
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14051

L. H. Gade et al.
1
Further studies of H, 13C and 31P NMR spectra, as well as
Table 2. Hydrogenation of dehydroamino acid derivatives when using
DMP complexes as catalysts.[a]
the 2D correlation NMR spectra of complex 13a, showed
that the new signals corresponding to the phospholane units
were divided into two signal subsets, with relative intensities
of two to one, supporting the assumption of gold chloride
binding to the free phosphorus atom. The high-resolution
mass spectrum (HRMS-ESI) displayed the molecular ion at
m/z 1216.27944, which corresponded to [ClAu{N-
Entry
Cat.[a]
R’
MAC
MAA
MAB
A
E
ACHTUNGTRENNUNG(R’’=Me)
ee [%][b]
ee [%][c]
ee [%][b]
1
2
3
4
5
6
7
8
9
9a
9b
9c
9d
9e
9 f
9g
9h
9i
Me
iPr
Ad
PhCH2
Ph2CH
2-PyCH2
3-PyCH2
2-ThCH2
2-FuCH2
76 (R)
89 (R)[d]
79 (R)
86 (R)
84 (R)
84 (R)
79 (R)
87 (R)[d]
84 (R)[d]
98 (R)
99 (R)[d]
98 (R)
98 (R)
99 (R)
98 (R)
99 (R)
99 (R)
99 (R)[d]
72 (R)
80 (R)
70 (R)
80 (R)
81 (R)
75 (R)
83 (R)
81 (R)
75 (R)
ACHTUNGTRENNUNG(CH2DPP)3}RhACHTUNGTRENNUNG
(cod)]+, indicating that the gold substituent
was strongly bound to the phospholane. Finally, a single
crystal of 13a suitable for X-ray diffraction was obtained.
The result confirmed the assumed structure of this heterodi-
À
nuclear Rh Au complex in the solid state (Figure 5).
[a] Conditions: all reactions were performed in methanol under 5 bar H2
pressure (unless otherwise stated) at room temperature with 0.1 mol% of
9a–i and 0.001m catalyst; conversions were >99% after 1 h (determined
by 1H NMR spectroscopy). Absolute configurations were ascertained by
comparison of optical rotations with reported data[28] or by analogy.
[b] Determined by chiral HPLC. [c] Determined by chiral GC. [d] 1 bar
H2 pressure.
C2-symmetric DMP rhodium complexes 9a–i: All catalysts
showed high activity in the reduction of dehydroamino acid
derived olefins MAC, MAA and MAB (Table 2). For MAC,
catalyst loadings of 0.1 mol% of 9b, 9h and 9i led to full
conversion at a hydrogen pressure of 1 atm in less than
60 min at room temperature. The other C2-symmetric cata-
lysts exhibited a somewhat lower reactivity and higher hy-
drogen pressure (5.0 bar) was applied. With MAC as the
substrate, enantioselectivities observed for 9a–i were moder-
ate (76–89% ee) compared with known hydrogenation cata-
lysts;[29] however, subtle changes in the ligand backbone re-
sulted in substantial changes of enantioselectivity. For in-
stance, complexes 9a and 9h (methylamine and 2-thienyl-
methylamine derivates, respectively) give significantly differ-
ent ee values. Complexes 9a–i all catalysed the
hydrogenation of the sterically less demanding substrate
MAA to the corresponding amino acid derivative. Full con-
version was achieved in 60 min at 5.0 bar hydrogen pressure
with excellent selectivities of up to >99% ee. For this sub-
strate, the observed enantioselectivities were markedly less
ligand dependent.
À
Figure 5. Thermal ellipsoid plot (50% probability level; H atoms, BF4
anion and co-crystallised solvent omitted for clarity; only one of the two
sets of disordered atoms is shown) of the X-ray structure of heterodinu-
ACHTUTGNRENNU(G CH2DPP)3}RhACHTUNGTREN(NUGN cod)]BF4. Principal bond
lengths [ꢂ] and angles [8]: P(2) Rh 2.3153(15), P(3) Rh 2.3037(14),
P(1A) Au(1A) 2.2311(16), Au(1A) Cl(1A) 2.2906(16), C(52) Rh
2.223(4), C(53) Rh 2.235(4), C(56) Rh 2.217(4), C(57) Rh 2.233(4);
P(1A)-Au(1A)-Cl(1A) 175.51(6), P(3)-Rh-P(2) 86.67(4). Other set of dis-
ordered atoms: P(1B) Au(1B) 2.236(5), Au(1B) Cl(1B) 2.288(6); P(1B)-
Au(1B)-Cl(1B) 174.3(3).
clear complex 13a, [ClAu{N
À
À
À
À
À
À
À
À
À
À
À
The other two heterodinuclear Rh Au complexes
[(cod)Rh{N
(CH2DPP)3AuX}]BF4 with different substituents
F
at the gold atom (X=C6F5, Mes) (13b and 13c) were pre-
pared in the same manner. NMR spectroscopy, mass spec-
trometry and elemental analysis proved analogous configu-
rations and structures of these compounds.
The third dehydroamino acid derivative, MAB,[30] was
also smoothly hydrogenated by catalysts 9a–i. The reactions
were completed after 60 min at a hydrogen pressure of
5.0 bar. Notably, as for MAC, selectivities were moderate,
while the differences between the catalysts were significant,
with ee values ranging from 70 to 83%. As shown by these
first hydrogenation results, backbone substituents had a sig-
nificant influence on catalyst performance.
The substrate scope was extended to DMI and DMPI,
which were electron poorer and more weakly binding olefins
(Table 3). Hydrogenations of DMI were complete for most
catalysts after 60 min at a H2 pressure of one atmosphere
and room temperature. Only for complexes 9d, 9 f and 9g
Investigation of the rhodium complexes as enantioselective
hydrogenation catalysts: To investigate the potential of the
new ligands in catalysis, the enantioselective hydrogenation
of a series of prochiral olefins as benchmark substrates
when using isolated Rh complexes as catalysts were studied.
The substrates included methyl esters of three dehydro-a-
acetamido acids, namely, methyl (Z)-a-acetamidocinnamate
(MAC), methyl 2-acetamidoacrylate (MAA) and methyl 2-
acetamidobutenoate (MAB), as well as two itaconic acid de-
rivatives, dimethyl itaconate (DMI) and (E)-dimethyl-2-
phenyl itaconate (DMPI).
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Stitching Phospholanes Together Piece by Piece
FULL PAPER
Table 3. Hydrogenation of itaconic acid derivatives using DMP com-
plexes as catalysts.[a]
C2-symmetric DPP rhodium complexes 10a–c: As dis-
cussed above (Table 1), amine substituents in the ligand
backbone are thought to exert steric pressure on the phos-
pholane rings, thereby influencing the shape of the catalytic
site. To investigate the degree of this influence, we also
modified the stereodirecting unit itself, that is, the substitu-
tion pattern of the phospholane rings. We carried out the
same hydrogenation studies for our second series of cata-
lysts, complexes 10a–c, which featured DPP instead of DMP
ligands (Tables 4 and 5). In general high enantioselectivities
(>89%ee) were achieved.
Entry
Cat.
R’
DMI (R’’=H)
ee [%][b]
DMPI (R’’=Ph)
ee [%][c]
1
2
3
4
5
6
7
8
9
9a
9b
9c
9d
9e
9 f
9g
9h
9i
CH3
iPr
Ad
PhCH2
Ph2CH
2-PyCH2
3-PyCH2
2-ThCH2
2-FuCH2
95 (S)
95 (S)
85 (S)
70 (S)
35 (R)
88 [55] (S)
90 [93] (S)
93 [82] (S)
92 [78] (S)
91 (S)
87 (S)
96 (S)[d]
93 (S)
96 (S)[d]
96 (S)[d,e]
97 (S)
97 (S)
93 (S)
Table 4. Hydrogenation of dehydroamino acid derivatives using com-
plexes 10–13 as catalysts.[a]
[a] Conditions: all reactions were performed in methanol at room tem-
perature with 0.1 mol% of 9a–i and 0.001m catalyst; ee values were de-
termined by chiral HPLC. Absolute configurations were ascertained by
comparison of optical rotations with reported data[28] or by analogy.
[b] 1 bar H2 pressure, conversions >99% after 1 h (determined by
1H NMR spectroscopy). [c] 10 bar H2 pressure, reaction time 12 h, con-
versions were >95%, lower conversions given in square brackets.
[d] 5 bar H2 pressure. [e] No significantly different ee values were ob-
served in additional reactions with catalyst concentrations of 0.0001–
0.001m.
Entry Cat. R’
MAC
MAA
(R’’=H)
ee [%][c]
MAB
(R’’=Ph)
G
ACHTUNGTRENNUNG(R’’=Me)
ee [%][b]
ee [%][b]
1
2
3
4
5
6
7
8
10a
10b
10c
PhCH2
94 (R)
90 (R)
89 (R)
83 (R)
94 (S)
97 (S)
99 (S)
99 (R)
98 (R)
98 (R)
64 (R)
98 (S)
97 (R)
95 (R)
94 (R)
65 (R)
98 (S)
99 (S)
99.5 (S)
96 (S)
2-PyCH2
2-ThCH2
11[d] DMP-CH2
12
DPP-CH2
13a
13b
13c
ClAuDPP-CH2
C6F5AuDPP-CH2
>99.5 (S)
>99.5 (S)
>99.5 (S)
was a pressure of 5.0 bar required to achieve full conversion
within the same period of time. In general, the catalysts
showed good to very good enantioselectivities (87–97% ee);
the best results being found for complexes with medium-
sized ligand backbones, such as benzyl-substituted 9d and
9 f–i, which have heteroaromatic substituents at the amine.
A more challenging substrate for enantioselective hydro-
genation was trisubstituted DMPI. Indeed, we found that
higher hydrogen pressures and longer reaction times were
required when using a catalyst loading of 0.1 mol%. At
10 bar, alkyl-substituted catalysts 9a–c, as well as furanyl-
and thienyl-substituted complexes 9h and 9i, gave complete
conversions (>95%) after 12 h, whereas the other catalysts
gave conversions ranging from 55–93%. In this case, subtle
changes in the complex led to significant changes in catalytic
activity. Similarly, enantioselectivities were markedly depen-
dent on the ligand. Whilst the adamantyl-substituted com-
plex 9c gave only 35% ee, catalysts 9 f–i exhibited very
good enantioselectivities in the range of 91–93% ee. These
values rank among the highest observed for this substrate.[31]
The dependence of the ligand on selectivities is also reflect-
ed by the fact that (R)-dimethyl-2-benzylsuccinate was ob-
served as the major product for all catalysts, except adaman-
tyl-substituted 9c, which mainly yielded the S enantiomer.
Interestingly, these complexes showed higher enantiose-
lectivity than the closely related C2-symmetric propyl- and
penta-2,4-diyl-bridged dimethylphospholane rhodium com-
plexes with ligand backbones of three carbon atoms report-
ed by Burk and co-workers.[26b,32] In their studies the high
flexibility of the ligand backbone was assumed to be respon-
sible for low enantioselectivities, although our results seem
to contradict this simple interpretation.
FMesAuDPP-CH2 95 (S)
[a] Conditions: unless otherwise stated, all reactions were performed in
methanol under 5 bar H2 pressure at room temperature with 0.1 mol% of
catalyst, 0.001m catalyst; conversions were >99% after 1 h (determined
by 1H NMR spectroscopy). Absolute configurations were ascertained by
comparison of optical rotations with reported data[28] or by analogy.
[b] Determined by chiral HPLC. [c] ee value determined by chiral GC.
[d] Reactions performed with 0.5 mol% of catalyst (0.005m); conversions
were >98% after 72 h.
Table 5. Hydrogenation of itaconic acid derivatives using complexes 10–
13 as catalysts.[a]
Entry
Cat.
R’
DMI (R’’=H)
ee [%][b]
DMPI (R’’=Ph)
ee [%][c]
1
2
3
4
5
6
7
8
10a
10b
10c
11
PhCH2
2-PyCH2
2-ThCH2
DMP-CH2
95 (S)
96 (S)
93 (S)
55 (S)[e]
92 (R)
97 (R)
98 (R)
97 (R)
63 (S)
60 (S)
51 (S)
95 (S)[f]
57 (R)
n/a[d]
12
DPP-CH2
13a
13b
13c
ClAuDPP-CH2
C6F5AuDPP-CH2
FMesAuDPP-CH2
72 (R)
51 (R)
[a] Conditions: unless otherwise stated, all reactions were performed in
methanol at room temperature, (determined by 1H NMR spectroscopy).
Absolute configurations were ascertained by comparison of optical rota-
tions with reported data[28] or by analogy. [b] 0.1 mol% of catalyst; cata-
lyst concentration 0.001m, 5 bar H2 pressure; conversions were >99%
after 5 h, ee determined by chiral HPLC. [c] 0.5 mol% (0.005m) of cata-
lyst; catalyst concentration 0.005m, 40 bar H2 pressure; conversions were
>98% after 72 h; ee determined by chiral HPLC. [d] Very low conver-
sion. [e] 258C, 0.5 mol% (0.005m) of catalyst, t=72 h. [f] 40 bar H2 pres-
sure, 1.0 mol% (0.01m) of catalyst, t=72 h.
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14053

L. H. Gade et al.
C3-symmetric DMP (11), pseudo-C2-symmetric DPP (12)
and heterodinuclear DPP (13a–c) rhodium complexes: The
structurally different catalyst 11, containing the C3-symmet-
ric dimethylphospholane ligand 7, was also tested in the hy-
drogenation of the five olefinic substrates. Because the pre-
catalyst is a pentacoordinate 18-electron species (Figure 4),
decoordination of one phospholane unit may be required as
the first step of the catalytic reaction. Thus, longer induction
periods were expected and were also observed. Hydrogen
pressures of 5.0 bar, catalyst loadings of 0.5 mol% and reac-
tion times of 72 h were necessary to obtain complete conver-
sions in the case of MAC, MAA, MAB and DMI. For these
substrates, enantioselectivities were moderate (55–83% ee).
Remarkably, for DMPI very high enantioselectivity of
95% ee was achieved (Table 5, entry 4), despite the fact that
the catalyst loading and hydrogen pressure had to be in-
creased to 1.0 mol% and 40 bar, respectively.
In contrast to the low reactivity observed for complex 11,
complex 12 was far more active as a hydrogenation catalyst.
In the latter, the C3-symmetric DPP ligand 8 coordinates
with only two of its three phospholane units and, notably,
we found reactivity similar to C2-symmetric complexes 10a–
c. This difference in behaviour between complexes 11 and
12 supports the postulated need for decoordination of one
phospholane unit in 11 at one stage of the reaction.
Figure 6. Summary of enantioselectivities of the different catalysts for
MAC (top), MAB (middle) and MAA (bottom). A clear enantioselectiv-
ity dependence on the substituents of phospholane and amine is ob-
served.
As shown in Tables 4 and 5, selectivities similar to those
obtained with 10a were found for complex 12. This means
that introduction of a chiral centre in the backbone alone
does not result in better catalyst performance. As described
above, complex 12 could be easily modified by reaction with
different gold derivatives. Interestingly, ligand backbone
above, there appears to be a correlation between the proper-
ties of the complex periphery at a distance from the catalytic
centre and the enantioselectivity (Figures 6 and 7). In partic-
À
modification by coordination of bulky Au X substituents to
the free phospholane unit in complex 12 leads to an out-
standing enhancement of the catalyst performance in a con-
trolled manner. As shown in Tables 4 and 5, excellent enan-
tioselectivities were achieved for the hydrogenation of
MAC, MAA, MAB and DMI. It should be noted that in
control experiments, trinuclear Au complexes of ligands 7
and 8 did not show any activity as hydrogenation catalysts.
In the case of complex 13a (X=Cl), hydrogenation of
DMPI gave incomplete conversion because of catalyst de-
composition, most probably through reduction of gold at the
elevated hydrogen pressure applied. Interestingly, these re-
sults follow a marked trend on going from 12 and 13a (X=
Cl) to 13b (X=C6F5) in that enantioselectivities improved
with increasing steric demand of the gold substituents. How-
ever, introduction of the FMes group, 13c, as the largest
group did not lead to any further enhancement of enantiose-
lectivity and it appears that the AuC6F5 group constitutes
the steric optimum for this case. Finally, in this series of cat-
alytic hydrogenations, complex 13b generally delivered the
best enantioselectivities (99% ee for MAC, MAA and
MAB; 98% ee for DMI).
In general, predictions for the relationship between cata-
lyst structure and selectivity cannot be made. This applies
particularly to the case of catalysts for asymmetric hydroge-
nations that differ only in a remote substituent. As stated
Figure 7. Summary of enantioselectivities of the different catalysts for
DMPI (top) and DMI (bottom). A clear enantioselectivity dependence
on the substituents of phospholane and amine is observed.
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Stitching Phospholanes Together Piece by Piece
FULL PAPER
ular, a maximum of selectivity was found by increasing the
steric demand of the gold fragment in complexes 13.
Exposure of complex 12, with a pendant phospholane
unit, to hydrogen (5 bar) at 08C rapidly led to the formation
of a new compound. As for the complexes described above,
1
Stoichiometric reactivity of complexes 10a, 12, 13a and 13b
with dihydrogen: The different coordination modes ob-
served for RhI complexes of C3-symmetric ligands 7 and 8
can be attributed to the steric pressure exerted by the
phenyl groups. An interesting question was whether or not
the pendant phospholane unit of 12 played an active role in
the catalytic cycle. Hence, complexes 10a, 12, 13a and 13b
were examined under catalytic hydrogenation conditions (in
the absence of an olefinic substrate) by means of 1H and
31P NMR spectroscopy (Scheme 8). First, a solution of C2-
the 31P NMR resonances at d=63.4 (d, J
(Rh,P)=202.3 Hz,
2P) and À3.7 ppm (s, 1P) suggest the formation of the
methanol-solvated complex by hydrogenation of cod. Still,
only two of three phosphorus atoms coordinate to the
metal. However, the 31P NMR spectra show that this com-
pound rapidly reacts further, leading to the disappearance
of the initially formed intermediate to give a complex prod-
uct mixture.
Remarkably, upon the addition of 10 equivalents of
NaOMe to a solution of 12 in MeOD and subsequent pres-
surisation with 5 bar of hydrogen at room temperature, dif-
ferent reactivity was observed. Under these conditions, a
green precipitate formed immediately. The 31P NMR spec-
trum of the green solids in CD2Cl2 revealed a doublet at d=
32.3 ppm (1J
ACTHUNRTGNE(GNU P,Rh)=78.5 Hz). The presence of only one
doublet implicates the equivalence of the three phosphorus
atoms of the ligand, and therefore, suggests a C3-symmetric
compound in which all three phospholane units coordinate
to the Rh centre. The 1H and 13C NMR resonances are in ac-
1
cordance with this. In particular, the H
{31P} NMR spectrum
displays a high-field resonance at d=À9.35 ppm (d, 1J-
AHCTUNGTREG(NNNU H,Rh)=19.5 Hz), again supporting the proposed high mo-
Scheme 8. Reactivity of complexes 10a, 12, 13a, and 13b under hydrogen
pressure in absence of an olefinic substrate: The cod is hydrogenated;
the complexes are in the methanol solvated forms.
lecular symmetry. X-ray diffraction of a single crystal ob-
tained from a solution in MeOD confirmed the proposed
C3-symmetric structure of complex 14 (Scheme 9 and
symmetric, benzyl-substituted complex 10a in MeOD was
exposed to 5 bar of hydrogen in a high-pressure NMR tube.
Under these conditions, a methanol-solvated rhodium com-
plex rapidly formed by hydrogenation of the cod ligand. The
31P NMR spectrum revealed a low-field shift of the doublet
at d=24.8 (1J
203.2 Hz). The 1H NMR spectrum was also in accordance
with a complex of the form [RhL
(MeOH)2]+. No hydride
ACHTUNGTRENNUNG ACHUTNGTREN(NGUN P,Rh)=
(P,Rh)=145.9 Hz) to 61.1 ppm (1J
AHCTUNGTRENNUNG
signals were detected at 295 or 195 K. Likewise, solutions of
À
heterodinuclear Rh Au complexes 13a and 13b in methanol
were treated with 5 bar of hydrogen (to enhance solubility,
Scheme 9. Reactivity of 12·ACTHNUTRGNE(UNG MeOH)2 under hydrogen pressure.
CD2Cl2 was added in the case of 13a). In analogy to the pre-
vious observation, low-field shifts of the doublets at d=23.5
1
and 25.7 ppm (1J
(P,Rh)=145.9 Hz and J
N
Figure 8). Unfortunately, the hydrido ligands could not be
directly located and were added by using Orpenꢃs HYDEX
to d=60.9 and 61.7 ppm (1J
ACTHNUGRTNENUG(P,Rh)=202.5 Hz and JACHTUNGTERN(NUGN P,Rh)=
1
À
201.5 Hz), respectively, were found. Again, no hydride reso-
nances were present in the H NMR spectrum (recorded at
programme. NMR spectroscopic data, Rh P bond lengths
and P-Rh-P bond angles are in the range of the previously
1
295 and 220 K). These results were consistent with findings
previously reported, stating that solvate complexes were
usually formed in the case of rhodium diphosphane com-
plexes.[33] It is noteworthy that for complex 13a, precipita-
tion occurred upon pressurisation, and after leaving the
sample overnight, the characteristic resonances completely
disappeared. Apparently, decomposition takes place under
high hydrogen pressure, which may account for the low re-
activity observed for this particular complex in the reduction
of DMPI (Table 5, entry 6).
reported complex [RhH3ACHTNUGETRN(UNG triphos)], which comprises an achi-
ral tripodal ligand.[34] H/D exchange or an equilibrium be-
tween species of the form [RhH3L] and [RhH(H2)L] are
thought to give rise to intensities of the hydride signal that
are slightly lower than expected. The formation of the hy-
drides is thought to be in part due to solvent hydrides
(methanol/methanolate), as observed previously for various
platinum metals.[35]
Chem. Eur. J. 2011, 17, 14047 – 14062
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14055

L. H. Gade et al.
Experimental Section
General: All manipulations, except those indicated, were carried out
under the exclusion of air and moisture by using standard Schlenk and
glove box techniques. As an inert gas, Argon 5.0 purchased from Messer
Group GmbH was used after drying over Granusic phosphorpentoxide
granulate. Solvents were dried according to standard literature meth-
ods[36] and stored in glass ampules under an argon atmosphere. Diethyl
ether and n-pentane were distilled from sodium/potassium alloy; THF,
benzene and n-hexane were distilled from potassium; methanol was dis-
tilled from magnesium; dichloromethane and chloroform were distilled
from calcium hydride and toluene was distilled from sodium. Same pro-
cedures were used to dry the deuterated solvents. Degassed solvents
were obtained by three successive freeze–pump–thaw cycles. COD was
distilled and degassed; triethylamine was degassed. (2R,5R)- and (2S,5S)-
1-hydroxy-1-oxo-2,5-diphenylphospholane,[37] (2R,5R)-2,5-dimethyl-1-phe-
Figure 8. Molecular structure of the C3-symmetric complex 14,
[(H)3Rh(N(CH2DPP)3)]. Thermal ellipsoid plot (50% probability level;
H atoms and co-crystallised solvent omitted for clarity; the positions of
ACHTUNGTRENNUNG
HA, HB and HC were initially taken from atom-to-atom potential
À
energy calculations (HYDEX, Orpen, 1980) and refined with Rh H
nylphospholane,[38] [Rh
(cod)2]BF4,[39] [AuCl(tht)],[40] [AuC6F (tht)],[41]
ACHTUNGTERNUNGN ACHUTNTRGENUNGN 5ACHTUNGTRENNUNG
bond lengths restrained equal with an esd of 0.02). Principal bond lengths
[AuFMes(tht)],[42] MAC,[43] MAA,[44] MAB,[45] and DMPI[46] were pre-
AHCTUNGTRENNUNG
À
À
À
[ꢂ] and angles [8]: Rh P(1) 2.3130(12), Rh P(2) 2.3101(10), Rh P(3)
pared according to literature procedures. All other chemicals were used
as received from the supplier without further purification. For hydroge-
nation reactions, Hydrogen 5.0 supplied by Messer Group GmbH was
used. All other chemicals used as starting materials were obtained com-
mercially and used without further purification.
À
À
À
2.3002(10), Rh HA 1.52(2), Rh HB 1.53(2), Rh HC 1.52(2); P(1)-Rh-
P(2) 89.98(4), P(1)-Rh-P(3) 90.93(3), P(2)-Rh-P(3) 90.83(4), P(1)-Rh-HA
91.3(16), P(2)-Rh-HA 96.5(16), P(3)-Rh-HA 172.3(16), P(1)-Rh-HB
177.0(14), P(2)-Rh-HB 90.7(14), P(3)-Rh-HB 92.0(14), P(1)-Rh-HC
90.4(13), P(2)-Rh-HC 178.4(12), P(3)-Rh-HC 90.7(12), HA-Rh-HB
86(2), HA-Rh-HC 82(2), HB-Rh-HC 88.8(19).
NMR spectra were recorded on Bruker Avance II (400 MHz) and
Bruker Avance III (600 MHz) instruments. Chemical shifts are reported
in parts per million (ppm) and are referenced to the residual proton sol-
vent signals or carbon resonances.[47] H3PO4 (31P) and CCl3F (19F) were
used as external standards. The following abbreviations were used: s (sin-
glet), d (doublet), dd (doublet of doublets), t (triplet), m (multiplet), br
(broad signal), Th (thienyl), Fu (furanyl). For catalytic hydrogenations, a
Bꢄchi miniclave drive high-pressure stainless steel autoclave was used
and charged with the reaction vials inside a glove box. Enantioselectivi-
ties were measured, depending on the substrate, on a HPLC Agilent
Technologies 1200 Series instrument using a chiral Daicel Chiracel OD-
H column or on a Finnigan Focus GC device using a chiral Chiraldex B-
DM column. Optical rotation data were acquired by using a Perkin–
Elmer Model 341 polarimeter. Mass spectra were acquired on Bruker
ApexQe hybrid 9.4 T FT-ICR (HR-ESI) and JEOL JMS-700 magnetic
sector (HR-FAB) spectrometers at the mass spectrometry facility of the
Institute of Organic Chemistry of the University of Heidelberg. Elemen-
tal analyses were carried out in the Microanalysis Laboratory of the Hei-
delberg Chemistry Department.
Conclusion
We have developed an efficient modular synthesis of poly-
phospholanes based on the use of phospholanium salts as
key intermediates. Given the enormous number of amines
available, this strategy not only gives access to large ligand
libraries, but also opens up the possibility for fine-tuning of
the catalytic properties or easily introducing new properties
into the molecule. Generally, the synthesis of phospholane-
based ligands implies handling highly air- and moisture-sen-
sitive intermediates. Applying our new methodology bypass-
es this drawback by taking advantage of the air and mois-
ture stability of the corresponding phospholanium salts. This
should facilitate catalyst screening in future applications of
these systems.
Synthesis of 3: (2R,5R)-2,5-Dimethyl-1-phenylphospholane (2.0 g,
10.4 mmol) was added to a suspension of Li powder (200 mg, 28.8 mmol)
in THF (16 mL) at 08C. After being stirred for 2 h, excess Li was re-
moved by filtration, and the solid residue was washed with THF (2ꢅ
5 mL). Degassed H2O (2 mL) was added dropwise to the filtrate and the
mixture was stirred for 30 min. The solution was carefully distilled (trap-
to-trap, 0.5 mbar, 408C, N2 (l)). The distillation stopped before the re-
maining solid was completely dry. The concentration of phospholane 1 in
the solution in THF obtained was determined by 31P{1H} NMR spectros-
copy (945 mg (8.1 mmol) in THF (26 mL)). This solution was treated
with aqueous formaldehyde (1.32 mL, 16.3 mmol) followed by HCl (aq)
(37 wt%, 0.79 mL, 9.7 mmol HCl) after 10 min. After stirring reaction
mixture for 15 h at room temperature, 10 mL of THF were added. Addi-
tional stirring for 1 h at 108C afforded a white powder that was filtered
and washed with cold THF (2ꢅ2 mL) to afford 3 (1.1 g, 5.1 mmol, 49%).
In the context of developing new C3-chiral tridentate li-
gands, we have reported an interesting difference in the co-
ordination mode of the two different phospholane units.
Metallation of the dangling non-coordinated phosphane unit
in the rhodium(I) complex containing the 2,5-diphenyl-sub-
À
stituted phospholane gave access to the first chiral Rh Au
heterodinuclear complexes. The effect of the variation of
the gold substituent on catalyst activity and selectivity and
the controlled coexistence of two metal centres was investi-
gated and provided a novel “tuning screw” in the optimisa-
tion of a catalyst system. In principle, the different chemical
properties of such heterometallic moieties might be taken
advantage of in a bimetallic catalyst system operation with
complementary metal sites. Investigations into such applica-
tions are currently under way in our laboratory.
1H NMR (600.13 MHz, MeOD, 295 K): d=1.46 (dd, 3J
3J
(H,H)=7.2 Hz, 6H; CH3), 1.63–1.72 (m, 2H; CH2), 2.31–2.45 (m, 2H;
ACHTUNGTREN(NUNG H,P)=16.2 Hz,
AHCTUNGTRENNUNG
CH), 2.86–2.98 (m, 2H; CH2), 4.61–4.68 (m, 4H; P-CH2-OH), 4.90 ppm
(brs, 2H; OH); 13C NMR (150.92 MHz, MeOD, 295 K): d=12.8 (d, 2J-
(C,P)=2.3 Hz; CH3), 29.6 (d, 1J(C,P)=44.0 Hz; CH), 35.0 (d, 2J
AHCTUNGTREUNNGN ACHTUNGTRENNUNG ACHTUNGTRENNUNG
5.3 Hz; CH2), 51.7 ppm (d, 1J
ACHTUNGTRENNUNG
(MeOD, 242.92 MHz, 295 K): d=47.0 ppm (s); elemental analysis calcd
(%) for C8H18ClO2P: C 45.18, H 8.53; found: C 45.39, H 8.57.
Preparation of (R)-4: (2R,5R)-1-Hydroxy-1-oxo-2,5-diphenylphospholane
(2.33 g, 8.56 mmol) was suspended in toluene (15 mL) before phenylsi-
lane (1.435 g, 1.635 mL, 13.26 mmol) was added dropwise by syringe. The
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Stitching Phospholanes Together Piece by Piece
FULL PAPER
mixture was then heated at reflux (110
*
C) for 19 h. Evaporation of the
612.29435; found: 612.29452; elemental analysis calcd (%) for C41H43NP2:
C 80.50, H 7.09, N 2.29; found: C 80.82, H 7.17, N 2.34.
solvent yielded a gummy solid to which diethyl ether (15 mL) and water
(2.1 mL) was added. After stirring for 30 min, aqueous formaldehyde so-
lution (37 wt%, 1.274 mL, 17.11 mmol formaldehyde) and HCl (aq)
(37 wt%, 0.703 mL, 8.56 mmol HCl) were added and the mixture was
stirred overnight at room temperature, whereupon a white precipitate
was formed. The liquid was removed by cannula filtration and the resi-
due was washed with H2O (2ꢅ10 mL) and diethyl ether (2ꢅ15 mL). The
white solid was then recrystallised from methanol and dried in vacuo to
afford (R)-4 (1.61 g, 4.78 mmol, 56%). 1H NMR (MeOD, 600.13 MHz,
General procedure for the synthesis of C3-symmetric ligands 7 and 8:
Triethylamine (0.214 mL, 1.544 mmol) was added to a solution of phos-
pholanium salt 3 or 4 (1.514 mmol) in methanol (5 mL). After stirring for
30 min at room temperature, NH4Cl (27 mg, 0.505 mmol) and additional
triethylamine (0.214 mL, 1.544 mmol) were added. The mixture was
stirred overnight at room temperature and was then concentrated to
2 mL. Cannula filtration yielded a white solid, which was washed with
cold methanol (2ꢅ4 mL) and dried in vacuo.
Preparation of 8: Yield: 83% (326 mg, 0.421 mmol); 1H NMR (C6D6,
600.13 MHz, 295 K): d=1.48–1.58 (m, 6H; CH2, N-CH2-P), 1.83–1.97 (m,
6H; CH2), 2.25–2.33 (m, 3H; CH2), 3.26–3.36 (m, 6H; N-CH2-P, CH),
3.48–3.54 (m, 3H; CH), 6.94–7.26 ppm (m, 30H; CHAr); 13C NMR (C6D6,
2
295 K): d=2.55–2.64 (m, 2H; CH2), 2.69–2.83 (m, 2H; CH2), 4.18 (dd, J-
ACHTUNGTRENNUNG ACHTUNGTRENNUNG ACTUHNGTRENNNGU
(H,H)=14.3 Hz, 2J(H,P)=1.4 Hz, 2H; P-CH2-OH), 4.29 (d, 2J
2
14.3 Hz, JACHTUNGTRENNUNG
150.92 MHz, 295 K): d=32.8 (d, 2J
CH2), 46.3 (d, 1J(C,P)=13.6 Hz; CH), 48.3 (d, 1J
55.6 (dt, 1J(C,P)=11.5 Hz, 3J
(C,P)=7.0 Hz; CH2), 125.8–125.9 (m;
CHAr), 125.9–126.0 (m; CHAr), 127.8–127.9 (m; CHAr), 128.5 (s; CHAr),
128.7 (d,
(C,P)=11.1 Hz; CHAr), 128.7 (s; CHAr), 139.4 (s; CAr),
ACTHNUGTRNENUG
146.4 ppm (d, 2J(C,P)=16.7 Hz; CAr); 31P NMR (C6D6, 242.92 MHz,
(C,P)=3.9 Hz; CH2), 38.2–38.3 (m;
(C,P)=16.6 Hz; CH),
AHCTUNGTRENNUNG
G
ACHTUNGTRENNUNG
E
ACHTUNGTRENNUNG
E
ACHTUNGTRENNUNG
G
ACHTUNGTRENNUNG
E
ACHTUNGTRENNUNG
4.6 Hz; CPh(1)); 31P NMR (MeOD, 242.92 MHz, 295 K): d=42.2 ppm (s);
HRMS (FAB): m/z calcd for C18H22O2P [MÀCl]+: 301.1352; found:
301.1381; elemental analysis calcd (%) for C18H22ClO2P: C 64.19, H 6.58;
found: C 64.09, H 6.59.
JACHTUNGTRENNUNG
295 K): d=0.0 ppm (s); HRMS (FAB): m/z calcd for C51H55NP3 [M+H]+
: 774.3547; found: 774.3586; elemental analysis calcd (%) for C51H54NP3:
C 79.15, H 7.03, N 1.81; found: C 78.91, H 7.01, N 1.96.
General procedure for the preparation of ligands 5a–i: Triethylamine
(0.45 mL, 3.0 mmol) was added to a solution of phospholanium salt 3
(200 mg, 0.94 mmol) in methanol (4 mL) at room temperature, followed
by the corresponding primary amine R’NH2 (0.47 mmol). After stirring
for 18 h, the solvent was removed in vacuo and the product was extracted
from the oily residue with n-hexane (3ꢅ4 mL). All products 5a–i were
obtained as colourless oils by removing the solvent in vacuo.
General procedure for the synthesis of complexes 9a–i: A solution of
ligand 5a–i (0.4 mmol) in dichloromethane (2.5 mL) was slowly added to
a solution of an equimolar amount of [RhACTHNUTRGNEU(NG cod)2]BF4 in dichloromethane
(2.5 mL) at room temperature. After stirring for 30 min, the solvent was
removed from the orange solution in vacuo until about 0.5 mL remained.
This was followed by addition of Et2O (10 mL), leading to an orange
solid, which was isolated by filtration and washed with diethyl ether (3ꢅ
4 mL).
Compound 5d: Yield: 83.5%; 1H NMR (C6D6, 600.13 MHz, 295 K): d=
3
3
1.02–1.10 (m, 2H; CH2), 1.09 (dd, J
CH3), 1.20–1.29 (m, 2H; CH2), 1.35 (dd, 3J
7.3 Hz, 6H; CH3), 1.72–1.79 (m, 2H; CH2), 1.86–2.04 (m, 4H; CH2,
2CH), 2.04–2.12 (m, 2H; 2CH), 2.89 (d, 2J
(H,H)=12.8 Hz, 2H; N-CH2-
P), 2.94 (dd, 2J(H,H)=12.8 Hz, 2J
(H,P)=7.3 Hz, 2H; N-CH2-P), 3.78 (d,
2J
(H,H)=13.2 Hz, 1H; N-
N
ACHTUNGTRENNUNG
Compound 9d: Yield: 81.4%; 1H NMR (CD2Cl2, 600.13 MHz, 295 K):
G
ACHTUNGTRENNUNG
3
3
d=1.07 (dd, J
4H; CH2), 1.51 (dd, J
2.13 (m, 8H; 2CH2, 4CH), 2.19–2.25 (m, 4H; CH2cod), 2.46–2.52 (m, 4H;
CH2cod), 2.67 (dd, 2J(H,H)=13.6 Hz, 2J
(H,P)=3.9 Hz, 2H; N-CH2-P),
2.87 (d, 2J(H,H)=13.6 Hz, 2H; N-CH2-P), 3.58 (d, 2J
(H,H)=12.5 Hz,
1H; N-CH2Ph), 3.69 (d, J(H,H)=12.5 Hz, 1H; N-CH2Ph), 4.46–4.52 (m,
ACHUTNGTNERNUG(H,P)=13.1 Hz, JCAHTUGNTERN(NUGN H,H)=6.8 Hz, 6H; CH3), 1.22–1.31 (m,
3
3
ACHUTNGRENU(NG H,P)=17.4 Hz, JHCATUGNTREN(NUGN H,H)=6.8 Hz, 6H; CH3), 1.98–
AHCTUNGTRENNUNG
N
ACHTUNGTRENNUNG
A
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG ACHTUNGTRENNUNG
(H,H)=13.2 Hz, 1H; N-CH2Ph), 4.21 (d, 2J
G
ACHTUNGTRENNUNG
CH2Ph), 7.08–7.12 (m, 1H; CHAr(4)), 7.18–7.22 (m, 2H; CHAr(3,5)), 7.39–
7.44 (m, 2H; CHAr(2,6)); 13CNMR (C6D6, 150.92 MHz, 295 K): d=14.7 (s;
2
AHCTUNGTRENNUNG
2H; CHcod), 5.39–5.53 (m, 2H; CHcod), 7.24–7.27 (m, 2H; CHAr(2,6)), 7.28–
7.32 (m, 1H; CHAr(4)), 7.33–7.37 ppm (m, 2H; CHAr(3,5)); 13C NMR
(CD2Cl2, 150.92 MHz, 295 K): d=13.9 (s; CH3), 19.1–19.2 (m; CH3), 28.1
CH3), 21.4 (d, 2J
36.9 (d, 1J
2J(C,P)=4.5 Hz; CH2), 53.1 (dd, 3J
CH2-P), 61.2 (t, 3J
N
ACHTUNGTRENNUNG
U
ACHTUNGTRENNUNG
A
E
ACHTUNGTRENNUNG
(s; CH2cod), 33.8 (s; CH2cod), 34.3 (dd, 1J(C,P)=10.7 Hz, 2J
ACTHNUTRGENNUG ACHTUNGTRENNUNG(C,Rh)=
ACHTUNGTRENNUNG
1
2
11.9 Hz; CH), 35.5 (s; CH2), 37.0 (s; CH2), 40.6 (dd, J
ACHTUNGTREN(NGNU C,P)=12.2 Hz, J-
CHAr(3,5)), 129.9 (s; CHAr(2,6)), 139.9 (s; CAr); 31P NMR (C6D6,
242.92 MHz, 295 K): d=À12.8 ppm (s); elemental analysis calcd (%) for
C21H35NP2: C 69.40, H 9.71, N 3.85; found: C 69.41, H 9.69, N 4.00.
A
E
ACHTUNGTRENNUNG
3
CH2-P), 67.3 (t, JACTHNUTRGNEUNG
(C,P)=9.6 Hz; N-CH2Ph), 92.8–93.0 (m; CHcod), 102.7–
102.9 (m; CHcod), 128.7 (s; CHAr(4)), 129.1 (s; CHAr(3,5)), 130.5 (s;
CHAr(2,6)), 137.0 ppm (s; CAr); 31P NMR (CD2Cl2, 242.92 MHz, 295 K):
General procedure for the preparation of ligands 6a–c: Triethylamine
(0.157 mL, 1.133 mmol) was added to a solution of phospholanium salt
(S)-4 (375 mg, 1.113 mmol) in methanol (4 mL). After stirring for 30 min
at room temperature, R’NH2 (0.061 mL, 0.558 mmol) was added. The
mixture was stirred overnight at room temperature, whereupon a white
solid precipitated, which was filtered and washed with cold methanol (3ꢅ
2 mL) and dried in vacuo.
d=25.7 ppm (d, 1J
ACTHNUGRTENUNG(P,Rh)=140.2 Hz); HRMS (ESI): m/z calcd for
C29H47NP2Rh [MÀBF4]+: 574.22388; found: 574.22246; elemental analysis
calcd (%) for C29H47BF4NP2Rh: C 52.67, H 7.16, N 2.12; found: C 52.37,
H 7.02, N 2.22.
General procedure for the synthesis of complexes 10a–c: A solution of
6a–c (0.126 mmol) in dichloromethane (2 mL) was added dropwise to a
solution of [RhACTHNUTRGNEUNG(cod)2]BF4 (50 mg, 0.123 mmol) in dichloromethane
Compound 6a: Yield 93%; 1H NMR (C6D6, 600.13 MHz, 295 K): d=
1.50–1.59 (m, 2H; CH2), 1.74–1.83 (m, 2H; CH2), 1.88–1.98 (m, 4H; CH2,
(2 mL). After stirring for 30 min at room temperature, the mixture was
concentrated to 2 mL. Addition of diethyl ether (10 mL) produced a
yellow precipitate, which was washed with diethyl ether (2ꢅ10 mL) and
dried in vacuo.
N-CH2-P), 2.13–2.22 (m, 2H; CH2), 2.81 (d, 2J
ACHTUNGTRENNUNG
CH2-P), 2.88 (d, 2J
CH), 3.37–3.45 (m, 2H; CH), 3.91 (d, J
6.92–6.96 (m, 2H; CHPh(2)), 7.04–7.32 ppm (m, 23H; CHAr); 13C NMR
(C6D6, 150.92 MHz, 295 K): d=32.8 (d, 2J
(C,P)=4.0 Hz; CH2), 38.1 (s;
CH2), 46.2 (d, 1J(C,P)=15.3 Hz; CH), 49.7 (d, 1J
(C,P)=17.1 Hz; CH),
54.7 (dd, 1J(C,P)=14.8 Hz; 3J(C,P)=6.9 Hz; N-CH2-P), 59.2 (t, 3J
(C,P)=
9.0 Hz; N-CH2-Ph), 126.0 (d, J (C,P)=
(C,P)=1.7 Hz; CHAr), 126.0 (d, J
2.1 Hz; CHAr), 127.0 (s; CHPh), 128.0 (d, J(C,P)=3.4 Hz; CHAr), 128.2 (s;
CHPh), 128.5–128.6 (m; CHAr), 128.6 (d, J(C,P)=9.5 Hz; CHAr), 128.7 (s;
CHAr), 129.6 (s; CHPh(2)), 139.7–139.8 (m; CAr, CPh(1)), 145.9 ppm (d, 2J-
ACHTUNGTRENNUNG
2
AHCTUNGRTEG(NNNU H,H)=13.5 Hz, 1H; N-CH2-Ph),
1
Compound 10a: Yield: 80%; H NMR (CD2Cl2, 600.13 MHz, 295 K): d=
0.84–0.94 (m, 2H; CH2cod), 1.17–1.25 (m, 2H; CH2cod), 1.53–1.62 (m, 2H;
CH2cod), 1.75–1.82 (m, 2H; CH2cod), 2.03–2.18 (m, 4H; CH2), 2.20–2.29
AHCTUNGTRENNUNG
A
ACHTUNGTRENNUNG
(m, 2H; CH2), 2.40–2.49 (m, 2H; CH2), 2.82 (d, 2J
ACHTUNGTRENNUNG
A
R
ACHTUNGTRENNUNG
N-CH2-P), 2.93 (d, 2J
N
ACHTUNGTRENNUNG
A
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
12.0 Hz, 1H; N-CH2-Ph), 3.22–3.30 (m, 2H; CH), 3.38–3.44 (m, 3H; CH,
N-CH2-Ph), 4.02–4.08 (m, 2H; CHcod), 5.35–5.42 (m, 2H; CHcod), 6.80–
6.83 (m, 2H; CHAr, CHPh(2)), 7.15–7.20 (m, 3H; CHAr), 7.20–7.24 (m, 4H;
CHAr), 7.32–7.38 (m, 10H; CHAr), 7.43–7.47 (m, 2H; CHAr), 7.55–
7.59 ppm (m, 4H; CHAr); 13C NMR (CD2Cl2, 150.92 MHz, 295 K): d=
AHCTUNGTRENNUNG
ACHTUNGTRENNUNG
(C,P)=17.0 Hz; CAr); 31P NMR (C6D6, 242.92 MHz, 295 K): d=
À2.8 ppm (s); HRMS (ESI): m/z calcd for C41H44NP2 [M+H]+:
Chem. Eur. J. 2011, 17, 14047 – 14062
ꢁ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
14057

L. H. Gade et al.
27.1 (s; CH2cod), 31.6 (s; CH2), 32.6–32.7 (m; CH2cod, CH2), 46.6–46.8 (m;
CH), 50.8–51.0 (m; CH), 54.5–55.1 (m; N-CH2-P), 66.4 (t, 3J
(C,P)=
2.48 (m, 4H; CH2, N-CH2-P), 2.49–2.59 (m, 3H; CH2), 2.70–2.85 (m, 3H;
CH2, N-CH2-P), 3.25–3.35 (m, 4H; CH, N-CH2-P), 3.67–3.77 (m, 4H;
CH, N-CH2-P), 4.11–4.19 (m, 3H; CHcod, CH), 5.30–5.36 (m, 2H; CHcod),
AHCTUNGTRENNUNG
10.4 Hz; N-CH2-Ph), 92.1–92.3 (m; CHcod), 104.2–104.4 (m; CHcod),
128.0–128.1 (m; CHAr), 128.1–128.2 (m; CHAr), 128.6 (m; CHAr), 128.8 (s;
CHPh(4)), 128.9–129.0 (m; CHAr), 129.1 (s; CHAr), 129.2–129.3 (m; CHAr),
129.7–129.8 (m; CHAr), 130.7 (s; CHPh(2)), 136.1–136.2 (m; CAr), 136.7 (s;
CPh(1)), 139.9 ppm (s; CAr); 31P NMR (CD2Cl2, 242.92 MHz, 295 K): d=
7.08–7.48 ppm (m, 30H; CHAr); 13C NMR (CD2Cl2, 150.92 MHz, 295 K):
cod
d=27.3 (s; CH2cod), 32.1 (s; CH2), 32.5 (s; CH2), 32.6–32.7 (m; CH2
,
CH2), 37.1 (d, 2J
28.3 Hz; CH), 48.2 (d, J
CH2-P), 59.2 (dt, 1J(C,P)=19.3 Hz, 3J
(m; CHcod), 103.6–103.8 (m; CHcod), 127.9–128.0 (m; CHAr), 128.0 (d, J-
(C,P)=2.5 Hz; CHAr), 128.2 (d, J(C,P)=2.8 Hz; CHAr), 128.2–128.3 (m;
CHAr), 128.3–128.4 (m; CHAr), 128.9–129.0 (m; 2ꢅCHAr), 129.1 (d, J-
(C,P)=7.2 Hz; CHAr), 129.2–129.3 (m; CHAr), 129.6 (d, J
(C,P)=2.0 Hz;
CHAr), 129.7–129.8 (m; 2ꢅCHAr), 134.8 (d, 2J(C,P)=4.5 Hz; CAr), 135.6–
135.7 (m; CAr), 139.9 (m; CAr), 140.9 ppm (m; CAr); 31P NMR (CD2Cl2,
242.92 MHz, 295 K): d=23.8 (dd, 1J(P,Rh)=144.5 Hz, 4J
(P,P)=3.0 Hz,
2P), 38.4 ppm (t, 4J
(P,P)=3.3 Hz, 1P); HRMS (ESI): m/z calcd for
(C,P)=4.2 Hz; CH2), 46.2 (m; CH), 47.7 (d, 1J
ACHUTGTNRENNUG ACHTUNGTRENNUNG
1
AHCTUNGTRENNUNG
25.0 ppm (d, 1J
ACHTUNGTRENNUNG(P,Rh)=145.4 Hz); HRMS (ESI): m/z calcd for
A
ACHTUNGTRENNUNG
C49H55NP2Rh [MÀBF4À]: 822.28593; found: 822.28458; elemental analysis
calcd (%) for C49H55BF4NP2Rh: C 64.70, H 6.09, N 1.54; found: C 64.60,
H 6.06, N 1.88.
A
ACHTUNGTRENNUNG
A
ACHTUNGTRENNUNG
Synthesis of 11: A solution of 7 (100 mg, 0.249 mmol) in CH2Cl2 (6 mL)
was added dropwise to a solution of [RhACHTNUTRGNEUNG(cod)2]BF4 (101 mg, 0.249 mmol)
AHCTUNGTRENNUNG
in CH2Cl2 (2 mL). After stirring for 45 min at room temperature, the
mixture was concentrated to 1 mL. Addition of Et2O (10 mL) produced a
yellow precipitate, which was washed with Et2O (3ꢅ5 mL) and dried in
vacuo (141 mg, 0.202 mmol, 81%). 1H NMR (CD2Cl2, 600.13 MHz,
295 K): d=1.15–1.25 (m, 9H; CH3), 1.32–1.40 (m, 9H; CH3), 1.70 (m,
2H; CH2), 1.80 (m, 2H; CH2), 1.90–2.00 (m, 3H; CH2), 2.02–2.10 (m,
2H; CH2cod), 2.10–2.16 (m, 3H; CH2), 2.16–2.25 (m, 3H; CH), 2.30–2.37
(m, 2H; CH2cod), 2.60–2.70 (m, 4H; CH2 cod), 2.71–2.80 (m, 3H; CH),
A
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
C59H66AuClNP3Rh [MÀBF4À]: 1216.28117; found: 1216.27944; elemental
analysis calcd (%) for C59H66AuBClF4NP3Rh: C 54.33, H 5.10, N 1.07;
found: C 54.09, H 5.20, N 1.22.
Preparation of 14: NaOMe (2.5 mg, 0.0463 mmol) was added to a solu-
tion of 12 (5 mg, 0.00466 mmol) in MeOD (0.5 mL) in a high-pressure
NMR tube. After applying H2 (5 bar), a green solid precipitated. The so-
lution was decanted and the solid was dried in a flow of argon. Single
crystals suitable for X-ray diffraction were grown from a solution in
MeOD. The isolated bulk solid contained impurities that could not be re-
3.12 (d, 1J(H,H)=15.0 Hz, 3H; N-CH2-P), 3.29 (d, 1J
ACHTUNGTRENNUNG ACHTUTGNREN(NUGN H,H)=15.0 Hz,
3H; N-CH2-P), 3.90 (brs, 2H; CHcod), 4.30 ppm (brs, 2H; CHcod);
13C NMR (CD2Cl2, 150.92 MHz, 295 K): d=16.6 (s; CH3) 17.8 (s; CH3),
29.8 (s; CH2cod), 32.5 (s; CH), 33.0 (s; CH2), 34.1 (s; CH2), 34.3 (brs; 2ꢅ
CH2cod), 45.2 (m; CH), 50.6 (m; N-CH2-P), 79.1 (m; CHcod), 78.29 ppm
(m; CHcod);13P NMR (CD2Cl2, 199.92 MHz, 295 K): d=8.3 ppm (d, 1J-
moved. 1H
(H,Rh)=19.5 Hz, 3H; hydride), 1.27–1.31 (m, 3H; CH), 1.37–1.44 (m,
3H; CH2), 2.11–2.20 (m, 3H; CH2), 2.26 (d, 2J
(H,H)=15. Hz, 3H; N-
CH2-P), 2.27–2.36 (m, 3H; CH2), 2.36–2.45 (m, 3H; CH2), 2.47 (d, 2J-
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
A
612.25187; found: 612.25147; elemental analysis calcd (%) for
C29H54BF4NP3Rh: C 49.80, H 7.78, N 2.00; found: C 49.62, H 8.01, N
1.88.
AHCTUNGTREG(NNNU H,H)=15.4 Hz, 3H; N-CH2-P), 3.36–3.42 (m, 3H; CH), 6.70–7.23 ppm
(m, 30H; CHAr); 13C NMR (CD2Cl2, 150.92 MHz, 295 K): d=27.4 (m;
CH2), 31.3–31.5 (m; CH2), 42.2–42.4 (m; CH), 45.9–46.0 (m; CH2), 50.2–
50.4 (m; CH), 126.5–126.6 (m; CHAr), 127.4–127.5 (m; CHAr), 128.5–128.6
(m; CHAr), 129.0–129.1 (m; CHAr), 129.2–129.3 (m; CHAr), 130.0–130.4
Preparation of 12: A solution of (R)-8 (200 mg, 0.258 mmol) in dichloro-
methane (10 mL) was added dropwise to a solution of [RhACTHNUTRGNE(UNG cod)2]BF4
(105 mg, 0.259 mmol) in dichloromethane (10 mL). After stirring for 1 h
at room temperature, the mixture was concentrated to 2 mL. Addition of
diethyl ether (15 mL) produced a yellow precipitate, which was washed
with diethyl ether and dried in vacuo (254 mg, 0.237 mmol, 92%).
1H NMR (CD2Cl2, 600.13 MHz, 295 K): d=0.83–0.92 (m, 2H; CH2cod),
1.11–1.21 (m, 2H; CH2cod), 1.51–1.59 (m, 2H; CH2cod), 1.71–1.78 (m, 2H;
CH2cod), 1.78–1.87 (m, 1H; CH2), 2.00–2.11 (m, 5H; CH2), 2.37–2.63 (m,
(br; CHAr), 139.7–139.8 (m; CAr), 142.3–142.4 ppm (m; CAr); 31P NMR
1
(CD2Cl2, 242.92 MHz, 295 K): d=32.3 ppm (d, J
N
Catalytic hydrogenations
Catalytic asymmetric hydrogenation carried out under atmospheric pres-
sure: Stock solutions of complexes in dichloromethane with known con-
centrations were prepared in a glove box and stored in flasks equipped
with Young stoppers. Substrate (1.0 mmol) was placed in a Schlenk flask
with a magnetic stirrer bar and an appropriate amount of stock solution
containing catalyst (0.1 mol%) was added. The solvent was evaporated in
vacuo, the flask was evacuated and purged with hydrogen several times
before a hydrogen pressure of 1 atm was applied. Dry and degassed
methanol (1 mL) was added and the reaction mixture was stirred vigo-
rously at room temperature for the desired reaction time. After the reac-
tion, the solvent was removed in vacuo, the crude products were dis-
solved in n-hexane/ethyl acetate (1:1) or diethyl ether/dichloromethane
(1:1) and passed through a small column of silica to remove the catalyst.
After concentration, the hydrogenated compounds were yielded as solids
or oils. Conversions were determined by the relative intensities of start-
ing material and product signals in the 1H NMR spectra. The ee values
were measured by chiral HPLC or GC.
10H; CH2, N-CH2-P), 2.71 (d, 2J
ACTHNUTRGNEU(NG H,H)=14.1 Hz, 2H; N-CH2-P), 2.99–
3.05 (m, 1H; CH), 3.27–3.33 (m, 2H; CH), 3.52–3.62 (m, 2H; CH), 3.65–
3.74 (m, 1H; CH), 3.96–4.04 (m, 2H; CHcod), 5.26–5.31 (m, 2H; CHcod),
7.06–7.46 ppm (m, 30H; CHAr); 13C NMR (CD2Cl2, 150.92 MHz, 295 K):
d=27.1 (s; CH2cod), 31.6 (s; CH2), 32.5 (s; CH2cod), 32.9 (s; CH2), 33.5 (d,
2J(C,P)=4.1 Hz; CH2), 38.0 (s; CH2), 46.2 (d, 1J
ACHTUNGTRENNUNG ACHTUNGTERN(NUGN C,P)=13.5 Hz; CH),
46.4–46.6 (m; CH), 51.2–51.4 (m; 2ꢅCH), 55.8–56.2 (m; N-CH2-P), 63.4–
63.8 (m; N-CH2-P), 92.4–92.5 (m; CHcod), 103.8–104.0 (m; CHcod), 126.7
(m; CHAr), 126.9 (m; CHAr), 127.9–128.0 (m; CHAr), 128.0–128.1 (m;
CHAr), 128.3 (d,
JACHTUNGTRENNUNG
(C,P)=9.8 Hz; CHAr), 128.3–128.4 (m; 2ꢅCHAr),
129.0–129.1 (m; 2ꢅCHAr), 129.2–129.3 (m; CHAr), 129.3 (m; CHAr),
129.5–129.6 (m; CHAr), 136.0 (s; CAr), 139.5 (s; CAr), 139.8 (m; CAr),
ACHTUNGTRENNUNG
144.6 ppm (d, 2J(C,P)=16.9 Hz; CAr); 31P NMR (CD2Cl2, 242.92 MHz,
295 K): d=À1.8 (s, 1P), 24.5 ppm (d, 1J
ACHTUNGERTN(NUNG P,Rh)=145.6 Hz, 2P); HRMS
(ESI): m/z calcd for C59H66NP3Rh [MÀBF4À]: 984.34577; found:
984.34413; elemental analysis calcd (%) for C59H66BF4NP3Rh: C 66.12, H
6.21, N 1.31; found: C 66.17, H 6.15, N 1.59.
Catalytic asymmetric hydrogenation carried out under pressures higher
than atmospheric: Hydrogenations at pressures >1 bar were carried out
in a stainless-steel autoclave equipped with a holder for glass vials, which
allowed seven parallel reactions. In an argon-filled glove box, each vial
was charged with a solution of the substrate (1m) and the catalyst (0.1–
1.0 mol%) in methanol. The autoclave was then assembled and purged
with hydrogen several times to remove argon. Thereafter, the reaction
mixtures were stirred vigorously under hydrogen pressure for the desired
reaction time. Subsequent workup and analyses were performed accord-
ing to the procedure described above.
À
General procedure for the synthesis of heterodinuclear Rh Au com-
plexes 13a–c: A solution of [Au(tht)X] (0.072 mmol) in dichloromethane
G
(3 mL) was added slowly to a solution of 12 (75 mg, 0.070 mmol) in di-
chloromethane (5 mL) at room temperature. After stirring for 30 min,
the mixture was concentrated to 2 mL. Addition of dry diethyl ether
(15 mL) produced a yellow precipitate, which was washed with diethyl
ether and dried in vacuo.
Compound 13a: Yield: 69% (63 mg, 0.048 mmol); 1H NMR (CD2Cl2,
600.13 MHz, 295 K): d=1.05–1.14 (m, 2H; CH2cod), 1.32–1.39 (m, 2H;
CH2cod), 1.60–1.68 (m, 2H; CH2cod), 1.81–1.89 (m, 2H; CH2cod), 2.01–2.10
(m, 2H; CH2), 2.10–2.19 (m, 1H; CH2), 2.24–2.35 (m, 2H; CH2), 2.37–
Theoretical modelling: The DFT-B3PW91 computational tool was em-
ployed to model all of the systems with a 6-31 g(d) basis set for C, N and
H atoms[48] and SDD+f function effective core potential basis set[49] for
Rh. All of the calculations were carried out with the Gaussian 03
14058
www.chemeurj.org
ꢁ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2011, 17, 14047 – 14062

Stitching Phospholanes Together Piece by Piece
FULL PAPER
Table 6. Crystal structure determinations of (R)-7, (R)-8, 9a, 9b and 9c.
(R)-7
(R)-8·0.45MeOH
9a
9b
9c
C32H55BF4NP2Rh
9 f
formula
Mr
C21H42NP3
401.47
C51.25H55NO0.25P3
781.87
C23H43BF4NP2Rh
585.24
C25H47BF4NP2Rh
613.30
C28H46BF4N2P2Rh
662.33
705.43
crystal system
space group
a [ꢂ]
b [ꢂ]
c [ꢂ]
monoclinic
P21
9.7681(9)
14.4557(14)
9.8832(10)
triclinic
P1
orthorhombic
P212121
9.021(5)
10.652(5)
27.051(12)
tetragonal
P41
10.188(4)
orthorhombic
P212121
12.526(6)
13.153(5)
19.766(9)
orthorhombic
P212121
9.8825(12)
11.7149(14)
25.782(3)
11.5846(9)
13.5438(10)
14.9191(11)
82.800(1)
78.558(1)
73.992(1)
2199.1(3)
2
27.208(12)
a [8]
b [8]
118.756(2)
g [8]
V [ꢂ3]
Z
1223.4(2)
2
2599(2)
4
2823.7(17)
4
3256(2)
4
2984.9(6)
4
F000
440
0.248
833
0.171
1216
0.821
1280
0.759
1480
0.669
1376
1.474
1calcd [mgmÀ3
]
m
(MoKa) [mm]
1.090
1.181
1.495
1.443
1.439
0.725
max./min. transmission
q range [8]
index
0.7463/0.6575
2.4–28.3
À13ꢀhꢀ11
À19ꢀkꢀ19
0ꢀlꢀ13
25177
0.7464/0.6899
1.4–32.0
À17ꢀhꢀ16
À20ꢀkꢀ20
À21ꢀlꢀ21
53942
0.7464/0.6826
2.1–31.5
À13ꢀhꢀ13
À15ꢀkꢀ0
À39ꢀlꢀ0
65357
0.7464/0.6778
2.0–31.5
À10ꢀhꢀ10
0ꢀkꢀ14
À40ꢀlꢀ39
70862
0.4345/0.3844
1.9–32.2
À18ꢀhꢀ18
0ꢀkꢀ19
0ꢀlꢀ29
81890
0.7464/0.6765
2.2–32.3
À14ꢀhꢀ14
0ꢀkꢀ17
0ꢀlꢀ38
75832
ranges
reflns measured
reflns unique [Rint
]
6066 [0.0649]
4868
232
26663 [0.0279]
23483
1012
8586 [0.0721]
7337
306
9316 [0.0771]
7873
325
11011 [0.0393]
10292
386
10171 [0.0403]
9630
359
reflns obsd [Iꢁ2s(I)]
parameters
GooF on F2
1.140
1.061
1.094
1.081
1.123
1.075
R(F)/wR(F2) [F>4s(F)]
R(F)/wR(F2) (all data)
absolute structure parameter
0.0415/0.0843
0.0621/0.0914
À0.02(8)
0.286/À0.305
0.0400/0.0940
0.0525/0.1035
À0.05(3)
0.518/À0.246
0.0347/0.0641
0.0537/0.0734
À0.05(2)
1.077/À0.853
0.0349/0.0656
0.0557/0.0750
À0.06(2)
0.976/À0.642
0.0257/0.0601
0.0314/0.0639
À0.041(12)
À1.673/À0.338
0.0239/0.0542
0.0275/0.0564
À0.05(1)
0.933/À0.289
largest residual peaks [eꢂÀ3
]
9h
10a·2CH2Cl2
10c·xEt2O
11
13a·2CHCl3
14·3MeOH
formula
Mr
C27H45BF4NP2RhS C51H59BCl4F4NP2Rh C47H53BF4NP2RhS C29H54BF4NP3Rh C61H68AuBCl7F4NP3Rh C54H69NO3P3Rh
667.36
1079.45
915.62
699.36
1542.91
975.92
crystal system
space group
a [ꢂ]
b [ꢂ]
c [ꢂ]
orthorhombic
P212121
9.909(5)
11.530(6)
25.953(12)
orthorhombic
P212121
13.347(7)
19.083(11)
19.180(9)
orthorhombic
P212121
13.284(10)
19.003(16)
19.075(15)
trigonal
P32
16.9029(6)
triclinic
P1
orthorhombic
P212121
12.586(6)
15.026(8)
25.217(14)
11.394(5)
11.607(6)
11.791(5)
87.528(8)
82.82(1)
79.90(1)
1523(1)
1
27.851(2)
a [8]
b [8]
g [8]
V [ꢂ3]
Z
2965(2)
4
4885(4)
4
4815(7)
4
6891.1(6)
9
4769(4)
4
F000
1384
1.495
2224
1.468
1896
1.263
3294
1.517
770
1.682
2056
1.359
1calcd [mgmÀ3
]
m
(MoKa) [mm]
0.798
0.686
0.511
0.760
3.115
0.503
max./min. transmission
q range [8]
index
0.7464/0.6811
1.9–32.3
À14ꢀhꢀ14
0ꢀkꢀ17
0ꢀlꢀ38
74966
0.9822/0.8682
1.9–30.0
À18ꢀhꢀ18
0ꢀkꢀ26
0ꢀlꢀ27
115871
0.9847/0.9000
1.9–30.5
À18ꢀhꢀ18
0ꢀkꢀ27
0ꢀlꢀ27
91221
0.7464/0.6648
1.4–30.0
À23ꢀhꢀ11
0ꢀkꢀ23
À39ꢀlꢀ39
161719
0.8917/0.7488
1.8–32.2
À17ꢀhꢀ16
À17ꢀkꢀ17
À17ꢀlꢀ17
38118
0.9422/0.8627
2.1–30.5
À17ꢀhꢀ17
0ꢀkꢀ21
0ꢀlꢀ36
114448
ranges
reflns measured
reflns unique [Rint
]
10084 [0.0394]
9592
350
14271 [0.1054]
11639
589
14687 [0.0710]
12561
552
26839 [0.0736]
23632
1072
18614 [0.0423]
16257
843
14539 [0.0882]
12484
565
reflns obsd [Iꢁ2s(I)]
parameters
GooF on F2
1.072
1.027
1.046
1.079
1.073
1.035
R(F)/wR(F2) [F>4s(F)]
R(F)/wR(F2) (all data)
absolute structure parame-
ter
0.0242/0.0561
0.0276/0.0582
À0.04(1)
0.0571/0.1414
0.0798/0.1559
À0.03(3)
0.0403/0.0921
0.0526/0.0968
À0.05(2)
0.0555/0.1140
0.0656/0.1187
0.00(2)
0.0388/0.0744
0.0542/0.0808
À0.004(2)
0.0397/0.0824
0.0549/0.0897
À0.04(2)
largest residual peaks
1.152/À0.389
1.259/À1.179
0.759/À0.430
1.761/À1.945
1.343/À0.828
1.276/À0.47
[eꢂÀ3
]
program package.[50] Stationary points were verified by frequency analy-
sis.
X-ray crystal-structure determinations: Crystal data and details of the
structure determinations are listed in Table 6. Full shells of intensity data
were collected at 100 K with a Bruker AXS Smart 1000 CCD diffractom-
Chem. Eur. J. 2011, 17, 14047 – 14062
ꢁ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
14059

L. H. Gade et al.
eter (MoKa radiation, graphite monochromator, l=0.71073 ꢂ). Data
were corrected for air and detector absorption, Lorentz and polarisation
effects;[51] absorption by the crystal was treated numerically after face-in-
dexing[52] or with a semi-empirical multiscan method.[51,53] The structures
were solved by conventional direct methods[54,55] (compounds 7 and (R)-
8), by direct methods with dual-space recycling[56] (compounds 11 and
13a), by the heavy-atom method combined with structure expansion by
direct methods applied to difference structure factors[57] (compounds 9b,
9c, 9 f, 9h and 10a) or by the charge-flip procedure[58] (compounds 9a,
10c and 14). Refinement was carried out by full-matrix least-squares
methods based on F2 against all unique reflections.[54,59] All non-hydrogen
atoms were given anisotropic displacement parameters. Hydrogen atoms
were generally input at calculated positions and refined with a riding
model. When justified by the quality of the data, the positions of some
hydrogen atoms (in the heavy atom structures those on the carbon atoms
involved in coordination to Rh) were taken from difference Fourier syn-
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theses and refined with C H distances restrained to be equal. The hydri-
do ligands in complex 14 could not be located unambiguously in differ-
ence Fourier syntheses. In the tetrafluoroborate anions and chloroform
À
À
solvent molecules B F, F···F, C Cl and Cl···Cl distances were restrained
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CCDC-827258, 827259, 827260, 827261, 827262, 827263, 827264, 827265,
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Acknowledgements
We are grateful to Torsten Roth for experimental help in developing this
class of catalysts. We thank the Deutsche Forschungsgemeinschaft for fi-
nancial support of this work (SFB 623, TP B6) and the EU for the award
of a Marie Curie EIF postdoctoral fellowship (to J.L.F.). We also ac-
knowledge the award of a predoctoral fellowship to P.S. (Landesgraduier-
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Chem. Eur. J. 2011, 17, 14047 – 14062

Stitching Phospholanes Together Piece by Piece
FULL PAPER
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