Evidence for substrate binding by the lanthanide centers in [Li 3(thf)n(binolate)3Ln]: Solution and solid-state characterization of seven- and eight-coordinate [Li3(sol) n(binolate)3Ln(S)<s

Article abstract of DOI:10.1002/anie.200504275

(Chemical Equation Presented) A close bond: The heterobimetallic complexes [M₃(thf)_n(binolate)₃Ln] (M = Li, Na, K) are among the most effective asymmetric Lewis acid catalysts. Previous solution and solid-state studies pro

Full text of DOI:10.1002/anie.200504275

Angewandte
Chemie
Asymmetric Catalysts
structures are either six-coordinate (Figure 1) or seven-
coordinate when bound to a water molecule. Each main-
group-metal center is bound by one or two organic solvent
molecules. The lanthanide centers in sterically hindered
DOI: 10.1002/anie.200504275
Evidence for Substrate Binding by the Lanthanide
[
M3
A
H
R
U
G
A
H
R
U
G
Centers in [Li
A
C
H
T
R
E
U
N
G
(thf) (binolate) Ln]: Solution and
A
T
E
N
3
n
3
ity for water than for organic ligands, evidence for which was
found by crystallization of the hydrates above from THF and
Solid-State Characterization of Seven- and Eight-
Coordinate [Li
Adducts**
A
H
R
U
G
A
H
R
U
3
n
m
Et O. In this regard, the absence of structurally characterized
2
[
M3
A
H
R
U
G
A
H
R
U
G
plexes with Lewis basic organic ligands bound to the
lanthanide atom raises questions concerning the ability of
the lanthanide center to bind and activate substrates in
asymmetric catalysis.
Alfred J. Wooten, Patrick J. Carroll, and
Patrick J. Walsh*
One approach used by prior investigators to address these
concerns involved probing Ln–substrate binding interactions
in solution by using paramagnetic Pr, Eu, and Yb analogues.
Paramagnetic complexes provide greater chemical-shift dis-
persions than their diamagnetic counterparts, thereby allow-
ing the study of normally unobservable metal–substrate
Dedicated to Professor Larry Sneddon
on the occasion of his 60th birthday.
The heterobimetallic [M3
-naphthol; M = Li, Na, K; thf = tetrahydrofuran) catalysts
Figure 1) developed by Shibasaki and co-workers have
A
H
R
U
G
A
H
R
U
2
(
[
10]
1
interactions.
binding studies of [Na3
(binolate) Eu] with cyclohexenone showed small chemical-
Previously reported H NMR spectroscopic
A
H
R
U
G
A
H
E
N
ACHTREUNG
6
3
3
6
AHCTREUNG
3
shift differences for the a-vinyl proton of 0.1 and 0 ppm,
[
8]
respectively.
Similarly, addition of pivalaldehyde to
A
H
R
U
G
A
H
R
U
G
ACHTREUNG
3
6
3
[
11]
the formyl hydrogen atom of only 0.1 ppm. These small
lanthanide-induced shifts (LISs) could be attributed to
coordination of the carbonyl groups to the main-group
atoms. Alternatively, the small LIS may indicate weak,
reversible substrate binding to the lanthanide center. A
related NMR spectroscopic study with paramagnetic
Figure 1. [M
co-workers.
A
C
H
T
R
E
U
N
G
(thf) (binolate) Ln] catalysts developed by Shibasaki and
A
C
H
T
R
E
U
N
G
3
n
3
A
H
R
U
G
A
H
R
N
A
H
R
U
G
3
[
6]
does not even bind water.
proven to be among the most versatile and successful
To reconcile some of the differences in proposed mech-
anisms and experimental observations for this important class
of catalysts, we set out 1) to assess whether the lanthanide in
[
1–3]
asymmetric Lewis acid catalysts introduced to date.
Central to mechanistic proposals involving [M3(thf) -
AHCTREUNG
n
A
C
H
T
R
E
U
N
G
(binolate) Ln] heterobimetallic compounds is Lewis acid
[Li3
A
H
R
U
G
A
H
R
U
G
3
[
2–4]
activation of the substrate by the lanthanide.
Prior efforts
strates and substrate analogues in solution and in the solid
state, and 2) to examine the coordination numbers and
geometries of the resultant adducts.
to detect lanthanide–substrate interactions, however, have
not been successful. Herein, we disclose solid-state and
solution evidence that [Li3
A
H
R
U
G
A
H
R
U
G
Binding studies of [Li3
A
H
R
U
G
A
H
R
U
G
n
3
bind organic substrates and substrate analogues to form
seven- and eight-coordinate Ln centers.
complicated by the presence of two different Lewis acidic
metal centers, both of which can bind the substrate, thus
causing a LIS. To simplify the analysis of our binding studies,
we sought to inhibit substrate binding to the lithium centers
by addition of a tightly binding diamine. Thus, addition of
[
5,6]
Several [M3
A
C
H
T
R
E
U
N
G
(thf)
A
H
E
N
(binolate) Ln]
and [M3
A
H
R
U
G
n
3
[
1,5,7,8]
A
C
H
T
R
E
U
N
G
(binolate) Ln(OH )]
ACHTREUNG
complexes have been character-
3
2
[
9]
ized crystallographically. The lanthanide centers in these
N,N’-dimethylethylenediamine (dmeda) to [Li3(thf) -
A
C
H
T
R
E
U
N
G
6
[
1]
A
H
R
U
G
[*] Dr. A. J. Wooten, Dr. P. J. Carroll, Prof. P. J. Walsh
P. Roy and Diana T. VagelosLaboratories
Department of Chemistry, University of Pennsylvania
the formation of [Li3
A
H
R
U
A
H
E
G
1
Ln = La) as crystalline solids. The H NMR spectra of 3 and 4
suggest that they are single diastereomers. Importantly, the
diamine backbone of 3 experiences a LIS to lower frequencies
with the resonances being observed as two broad singlets at
d = À3.59 and À3.82 ppm. The diamine backbone is diaste-
reotopic due to the chiral environment of the binolate ligands
and indicates that the diamine is not dissociating from the
lithium on the NMR timescale.
231 South 34th Street, Philadelphia, PA 19104-6323 (USA)
Fax: (+1)215-573-6743
E-mail: pwalsh@sas.upenn.edu
[
**] We thank the National Institutes of Health and the National
Institute of General Medical Sciences (GM058101) for a postdoc-
toral fellowship to A.J.W. We are grateful to Professor John F.
Hartwig of Yale University for helpful discussions. sol=solvent;
S=substrate or solvent.
A comparison of the LISs of 1 and 3 could reveal whether
the cyclohexenone carbonyl group binds to the lithium or the
Supporting information for thisarticle isavailable on the WWW
under http://www.angewandte.org or from the author.
Angew. Chem. Int. Ed. 2006, 45, 2549 –2552
ꢀ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
2549

Communications
lanthanide centers. If cyclohexenone binds to the lithium
coordinating solvents owing to competition between [D ]THF
8
centers, the LISs of 1 and 3 will be significantly different
because the lithium centers in 3 are coordinatively saturated
and cannot bind the substrate. If binding takes place at the
lanthanide center, however, cyclohexenone will exhibit sim-
ilar LISs with both 1 and 3. The addition of 6 equivalents of
and cyclohexenone for binding at the europium center. We
attribute the larger LIS of the Eu–binolate-based complexes
over [Eu(hfc) ] to the greater steric hindrance about the
A
H
R
U
G
3
lanthanide center in the binolate derivatives, which results in
a greater selectivity for the less-crowded carbonyl oxygen
atom over the THF oxygen atom. For comparison, diamag-
netic 4 induced shifts of < 0.03 ppm in the resonances of the
vinyl group of cyclohexenone.
To obtain a larger LIS, we examined a substrate analogue
that would have an affinity for the lanthanide center greater
than that of cyclohexenone. Addition of 8 equivalents of N,N-
dimethylformamide (DMF) to 1 and 3 resulted in a LIS of
1.14 and 2.30 ppm, respectively, for the signals of the formyl
hydrogen atom. In contrast, addition of DMF to diamagnetic
cyclohexenone to 1 in [D ]THF resulted in significant LIS of
8
the vinyl a- and b-hydrogen atoms to higher frequencies,
giving chemical-shift differences consistent with reversible
substrate binding of 0.56 and 0.16 ppm, respectively (Table 1).
At the same concentration ratio for the dmeda adduct 3, the
resonances of the cyclohexenone vinyl a- and b-hydrogen
atoms shifted to similarly high frequencies, giving LISs of 0.66
and 0.18 ppm, with the diamine backbone remaining diaste-
reotopic.
4
resulted in a shift of 0.09 ppm. The binding studies with
cyclohexenone and DMF attest to the advantages of using
paramagnetic lanthanides to probe interactions that would be
otherwise difficult to evaluate.
Table 1: Measured induced shifts of cyclohexenone and DMF with
various shift reagents at given concentration ratios.
[
a]
Additional support for lanthanide–substrate binding in
solution was obtained by demonstrating that 4, which contains
coordinatively saturated lithium atoms, is an active catalyst.
Complex 2 often gives the highest enantioselectivities and
Shift reagent
and substrate
[SR]/
A
C
H
T
R
E
U
N
G
[Sub]
LIS
A
C
H
T
R
E
U
N
G
[m/m]
Dd Ha Dd Hb Dd H
Dd
Dd
CH3
A
H
R
N
[ppm]
A
T
E
N
[ppm]
A
H
R
U
G
A
H
R
U
G
A
H
R
U
G
[
3]
product yields. Therefore, the reaction of 1.2 equivalents of
1
+
0.032/0.193 0.56
0.037/0.186 0.66
0.032/0.193 0.46
0.032/0.193 0.05
0.193/0.193 0.30
0.032/0.194 0.03
0.16
0.18
0.28
0.00
0.06
0.02
–
–
–
–
–
–
–
–
–
–
–
–
[
13]
dimethyl phosphite with benzaldehyde in the presence of 4
10 mol%) at À788C in THF produced the a-hydroxy
phosphonate in 92% yield with 78% ee. In the asymmetric
cyclohexenone
(
3
+
cyclohexenone
[
14]
5
+
Henry reaction,
nitromethane (10 equiv) was added to
cyclohexenone
Eu(hfc) ] +
cyclohexenone
Eu(hfc) ] +
cyclohexenone
benzaldehyde in the presence of 4 (10 mol%) at À508C in
[
ACHTREUNG
3
THF to generate the nitroaldol product in 76% yield with
2
3
5% ee. Finally, addition of 1,3-cyclopentadiene (10 equiv) to
-(1-oxo-2-propenyl)-2-oxazolidinone in CH Cl at 08C in the
[
ACHTREUNG
3
2
2
presence of 4 (10 mol%) produced the Diels–Alder product
4
+
[
15]
cyclohexenone
in 54% yield with 32% ee.
1
3
4
+ DMF
+ DMF
+ DMF
0.032/0.258
0.032/0.258
0.032/0.258
–
–
–
–
–
–
1.14
2.30
0.09
1.26
1.06
0.04
0.61
0.77
0.02
Inspired by the observation of substrate binding to the
lanthanide center in THF, we explored the solid-state
structure of the substrate adducts. Pentane was diffused into
THF solutions of 1 and 2 at room temperature. Pale crystals
were obtained, and their structures determined. An ORTEP
[a] Internal reference: mesitylene at d=6.73 ppm (H) and d=2.22 ppm
(
CH ). Solvent: [D ]THF at d=3.58 and 1.73 ppm.
3 8
diagram of seven-coordinate [Li
A
H
R
U
G
A
H
R
U
G
ACHTREUNG
3
4
3
[
16]
is shown in Figure 2. Isostructural [Li3
3
[
17]
A
H
R
U
G
Further support for substrate binding was obtained with
Li3(thf) (binolate) Pr] (5), which induced LISs to lower
structures are consistent with competitive binding of [D ]THF
in the solution studies outlined above.
8
[
A
C
H
T
R
E
U
N
G
A
C
H
T
R
E
U
N
G
6
3
frequencies for the vinyl a- and b-hydrogen atoms of cyclo-
hexenone of 0.46 and 0.28 ppm, respectively. The contrasting
effect of Pr and Eucomplexes on the chemical shifts of bound
substrates to lower and higher frequencies, respectively, is
The gross structural features of 6 and 7 consist of a LnO7
core that can be described as a trigonally compressed capped
octahedron with THF as the capping group. In addition to the
chirality of the binolate ligands, the lanthanide ions are
stereogenic centers. As observed with the hydrates, use of
(R)-binol led to the D configuration at the lanthanide. Slight
differences in the bond lengths of 6 and 7 were observed
owing to the smaller ionic radius of Eu (1.09 Š) relative to La
(1.17 Š). The binolate LaÀO bond lengths in 7 ranged from
[
10,12]
well-known.
The LISs observed with cyclohexenone and
1
, 3, and 5 can only arise from binding of the carbonyl oxygen
atom to the lanthanide centers. To put these LISs in
perspective, the LISs of cyclohexenone was examined in the
presence of the well-known chiral shift reagent [Eu
hfc = 3-(heptafluoropropylhydroxymethylene)-d-camphor-
ato). At the above concentration ratio in [D ]THF, [Eu
A
T
E
N
(hfc) ]
3
(
2.403(5) to 2.485(3) Š, and the dative LaÀO
bond length
THF
A
H
R
U
G
was 2.567(5) Š. The EuÀO bond lengths for the binolate
8
3
caused only a small LIS for the vinyl a-hydrogen atom
0.05 ppm, Table 1). A 1:1 molar ratio of [Eu(hfc) ] to
ligands ranged from 2.302(3) to 2.400(4) Š, with a EuÀO
THF
(
A
H
R
U
G
bond length of 2.482(4) Š. Binding of THF to the lanthanide
3
cyclohexenone, however, resulted in a LIS of 0.30 ppm.
These shifts are smaller than would be observed in non-
pulled the La 0.767(4) Š out of the Li plane, whereas the
smaller Euwas displaced by 0.737(3) Š. Smaller displace-
3
2
550
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ꢀ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2006, 45, 2549 –2552

Angewandte
Chemie
coordination may explain why the chelating diamine dmeda
does not bind to the lanthanide centers in 3 and 4. The
binolate LaÀO bond lengths in 8 ranged from 2.439(2)–
2
.536(2) Š and were, on average, longer than the LaÀO bond
lengths in THF adduct 7 (2.403(5)–2.485(3) Š). The La atom
in eight-coordinate 8 was displaced by only 0.042 Š from the
Li plane. Although the eight-coordinate pyridine adduct has
3
not been used in asymmetric reactions to date, it is quite
relevant, because it clearly demonstrates that sterically
hindered [Li3
A
H
R
U
G
A
H
R
U
coordination number of eight. In solution, there is probably
rapid equilibria between six-, seven-, and eight-coordinate
complexes that result in signal averaging on the NMR
[
19]
timescale.
In summary, the solution and solid-state structures of the
seven- and eight-coordinate complexes described herein
provide the first definitive evidence that the lanthanide in
[
Li3
substrate analogues. Furthermore, several reactions catalyzed
by [Li3(thf) (binolate) Ln] complexes require an additive,
A
H
R
U
G
A
H
R
N
ACHTREUNG
n
3
such as water, to allow high enantioselectivity. It has been
proposed that in the aldol reaction, the seven-coordinate
Figure 2. Structure of [Li3
A
H
R
U
G
4
A
H
R
U
G
3
A
H
R
U
G
water adduct, [Li3
A
H
R
U
G
A
H
R
N
A
H
R
U
G
6
3
strate to give eight-coordinate [Li3
A
H
R
U
G
A
H
R
U
[
20,21]
A
H
R
U
G
The characterization of eight-coordi-
2
ments were observed for the seven-coordinate aqua adducts
Na3(thf) (binolate) Eu(OH )] (0.387 Š) and [Li (OEt ) -
(binolate) Eu
nate [Li (py)5
ACHTREUNG
(binolate) La(py) ] lends support to this pro-
3
3
2
[
A
C
H
T
R
E
U
N
G
A
C
H
T
R
E
U
N
G
A
T
E
N
A
H
R
U
G
posal for larger lanthanides and indicates that the lanthanide
centers can expand their coordination number beyond seven,
the proposed maximum for this important class of com-
6
3
2
3
2 3
[
5]
A
C
H
T
R
E
U
N
G
A
C
H
T
R
E
U
N
G
(OH )] (0.326 Š).
3
2
To probe the binding of softer ligands to the lanthanide
center, we crystallized [Li (py)5(binolate) La(py) ] (8) (py =
[
22]
A
H
R
U
G
pounds.
3
3
2
pyridine) by diffusion of pentane into a solution of 2 in
pyridine at room temperature. An ORTEP diagram of 8 is
[
18]
shown in Figure 3.
The complex consists of an eight-
Experimental Section
coordinate lanthanum center with two pseudo-trans pyridine
1
o
Determination of induced chemical shifts: The H NMR spectra in
this study were obtained on a Bruker DMX-300 Fourier transform
NMR spectrometer at 300 MHz. Mesitylene was used as an internal-
molecules (NÀLaÀN = 150.87(8) ; LaÀN bond lengths: La1À
N6 = 2.812(3) Š, La1ÀN7 = 2.773(3) Š). The observed trans
referencing standard for all experiments, and [D ]THF was used as
8
the solvent. Induced chemical shifts of cyclohexenone and DMF were
obtained by incremental addition of known masses of the solid
lanthanide complex to a substrate solution of known concentration.
The first shift reagent (SR) used with cyclohexenone and DMF was
[
0
Li3
.032m:0.193m and 0.032m:0.258m, respectively. [Li3
(binolate) Eu] was then used with cyclohexenone and DMF at a
A
H
R
U
G
A
H
R
N
A
H
R
U
G
AHCTREUNG
3
concentration ratio of 0.037m:0.186m and 0.032m:0.258m, respec-
tively. Finally, [Li (thf) (binolate) Pr] was used with cyclohexenone at
A
H
R
U
G
ACHTREUNG
3
3
3
a concentration ratio of 0.032m:0.193m. Each sample was allowed to
equilibrate for 15 min before acquisition of NMR data. All spectra
can be found in the Supporting Information.
4
: Under nitrogen, dmeda (0.143 mL, 0.118 g, 1.34 mmol) was
added to a solution of 2 (0.500 g, 0.407 mmol) in THF (40 mL). This
solution was stirred at room temperature for 4 h, after which all
volatile materials were removed in vacuo. The remaining white solid
was placed on a frit and washed with diethyl ether (3 ” 5 mL) to afford
the desired compound after drying under reduced pressure (0.470 g,
1
9
1% yield based on 2). H NMR (300 MHz, [D ]THF, 258C,
8
tetramethylsilane (TMS)): d = 0.61 (br s, 2H; NH), 1.60 (s, 6H;
NÀCH ), 1.69 (br d, 2H; NÀCH ), 1.96 (br d, 2H; NÀCH ), 6.83 (d,
3
2
2
1
3
1
2
H), 6.91 (m, 4H), 7.23 (d, 2H), 7.67 ppm (t, 4H); C{ H} NMR
(
75 MHz, [D ]THF): d = 36.1 (NÀCH ), 50.7 (NÀCH ), 119.4, 120.4,
8
3
2
1
25.0, 126.1, 127.2, 127.9, 128.2, 128.6, 136.6, 163.8 ppm; IR (KBr): n˜ =
Figure 3. Structure of [Li (py)5
A
H
R
U
G
3341, 3299, 3043, 2981,2952, 2890, 2855, 2802, 1612, 1588, 1553, 1499,
3
3
2
Angew. Chem. Int. Ed. 2006, 45, 2549 –2552
ꢀ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
2551

Communications
1
8
463, 1422, 1342, 1283, 1247, 1177, 1140, 1096, 1069, 994, 959, 935, 882,
[15] T. Morita, T. Arai, H. Sasai, M. Shibasaki, Tetrahedron:
Asymmetry 1998, 9, 1445.
À1
22, 746, 665, 632, 591, 574 cm ; elemental analysis: calcd (%) for
À1
C H Li O N La (1277.11 gmol ): C 67.71, H 5.68, N 6.58; found: C
[16] Crystal data for 7: C H O LaLi , M = 1373.18; monoclinic,
7
2
72
3
6
6
80 76 11
3
r
6
7.35, H 5.67, N 6.30.
: Under nitrogen, dmeda (0.141 mL, 0.117 g, 1.33 mmol) was
space group P21, a = 18.532(4), b = 11.479(3), c = 19.262(5) Š,
o
3
À3
3
b = 101.379(2) , V= 4017(2) Š , Z = 2, 1
= 1.135 gcm , m
calcd
À1
added to a solution of 1 (0.500 g, 0.403 mmol) in THF (40 mL). This
solution was stirred at room temperature for 4 h, after which all
volatile materials were removed in vacuo. The remaining solid was
placed on a frit and washed with diethyl ether (3 ” 5 mL) to afford the
(MoKa) = 5.84 cm , F000 = 1420, 2q range = 5.24–54.948, crystal
3
size = 0.25 ” 0.12 ” 0.05 mm , T= 143 K; 28983 reflections mea-
sured with 14622 used in refinement; R = 0.0585, wR = 0.1237
1
2
(11601 reflections with F > 4s(F)); R = 0.0767, wR = 0.1357,
1
2
desired compound after drying under reduced pressure (0.440 g, 85%
GoF = 1.035 (14622 unique, nonzero reflections and 857 varia-
bles).
1
yield based on 1). H NMR (300 MHz, [D ]THF, 258C, TMS): d =
8
À9.16 (br s, 2H; NH), À3.82 (br s, 2H; NÀCH ), À3.59 (br s, 2H;
[17] Crystal data for 6: C H O EuLi , M = 1386.24; monoclinic,
2
80 76 11
3
r
NÀCH ), 0.366 (s, 6H; NÀCH ), À1.69 (d, 2H), 3.04 (t, 2H), 5.56 (t,
space group P21, a = 18.2048(6), b = 11.4818(4), c =
2
3
3
2
H), 7.65 (d, 2H), 13.76 (br s, 2H), 40.56 ppm (br s, 2H);
18.9389(7) Š, b = 100.190(1)(, V=3896.2(2) Š , Z = 2, 1
=
calcd
1
3
1
À3
À1
C{ H} NMR (75 MHz, [D ]THF): d = 33.2 (NÀCH ), 43.8
1.182 gcm , m (MoKa) = 8.59 cm , F000 = 1432, 2q range =
5.28–55.128, crystal size = 0.38 ” 0.27 ” 0.08 mm , T= 143 K;
8
3
3
A
C
H
T
R
E
U
N
G
(NÀCH ), 85.99, 116.43, 116.86, 122.07, 122.58, 128.64, 130.49,
2
1
2
1
5
32.39, 134.54, 180.40 ppm; IR (KBr): n˜ = 3342, 3299, 3043, 2985,
952, 2875, 2856, 2803, 1612, 1589, 1554, 1501, 1463, 1423, 1342, 1283,
248, 1175, 1138, 1096, 1069, 995, 959, 935, 898, 821, 746, 665, 642, 591,
28807 reflections measured with 28807 used in refinement;
R = 0.0518, wR = 0.1584 (28033 reflections with F > 4s(F));
1
2
R
1
2
= 0.0536, wR = 0.1608, GoF = 1.151 (28807 unique, nonzero
À1
74 cm ; elemental analysis: calcd (%) for C H Li O N Eu·THF
reflections and 858 variables).
7
2
72
3
6
6
À1
(
5
1362.27 gmol ): C 67.01, H 5.92, N 6.17; found: C 67.26, H 6.35, N
.99.
[18] Crystal data for 8: C100H O N LaLi , M = 1645.45; monoclinic,
76
6
8
3
r
space group P21, a = 13.3600(8), b = 13.5347(8), c = 23.066(2) Š,
o
3
À3
8
: Complex 2 (30 mg) was added to a vial and dissolved in
b = 101.9270(10) , V= 4080.9(4) Š , Z = 2, 1
= 1.316 gcm , m
calcd
À1
pyridine (1.0 mL). This vial was then placed within a 20-mL screw-
capped vial that was half-filled with dry pentane. After several days,
(MoKa) = 5.84 cm , F000 = 1664, 2q range = 5.22–54.968, crystal
size = 0.42 ” 0.40 ” 0.22 mm , T= 143 K; 23262 reflections mea-
3
pale crystals suitable for an X-ray diffraction study were formed.
sured with 13727 used in refinement; R = 0.0308, wR = 0.0742
1
2
1
H NMR (500 MHz, [D ]THF, 258C, TMS): d = 6.79 (m, 4H), 6.89 (m,
(13052 reflections with F > 4s(F)); R = 0.0334, wR = 0.0768,
8
1
2
2
H), 6.98 (d, J
A
C
H
T
R
E
U
N
G
(H,H) = 8.7 Hz, 2H), 7.22 (m, 7H), 7.58 (d, J
A
H
R
U
G
GoF = 1.082 (13727 unique, nonzero reflections and 1064
variables). CCDC-284685, -284686, and -284687 (7, 8, 6,
respectively) contain the supplementary crystallographic 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.
8
.8 Hz, 2H), 7.60 (d, J
AHCTREUNG
(H,H) = 8.0 Hz, 2H), 7.65 (m, 3H), 8.52 ppm
1
3
1
(m, 7H); C{ H} NMR (125 MHz, [D ]THF): d = 119.1, 120.4, 124.4,
8
1
24.8, 126.8, 126.9, 128.1, 128.4, 128.5, 136.4, 136.7, 150.9, 163.5 ppm;
elemental analysis: calcd (%) for C H Li O N La (1566.35 gmol ):
C 72.85, H 4.57, N 6.26; found: C 72.98, H 4.78, N 6.12.
9
5
71
3
6
7
[
[
[
[
19] T. Kowall, F. Foglia, L. Helm, A. E. Merbach, J. Am. Chem. Soc.
Received: December 1, 2005
Published online: March 17, 2006
1995, 117, 3790.
20] N. Yoshikawa, Y. M. A. Yamada, J. Das, H. Sasai, M. Shibasaki,
J. Am. Chem. Soc. 1999, 121, 4168.
21] N. Yoshikawa, T. Suzuki, M. Shibasaki, J. Org. Chem. 2002, 67,
2556.
22] N. Yamagiwa, J. Tian, S. Matsunaga, M. Shibasaki, J. Am. Chem.
Soc. 2005, 127, 3413.
Keywords: asymmetric catalysis · lanthanides · Lewis acids ·
.
paramagnetic compounds· reaction mechani sm s
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Angew. Chem. Int. Ed. 2006, 45, 2549 –2552