Potent new heterogeneous asymmetric catalysts

Article abstract of DOI:10.1002/hlca.200390145

A set of new, air-stable. Rh¹-based heterogeneous asymmetric hydrogenation catalysts have been synthesised, characterised, and tested. Individual members of this new family all exhibit good enantioselectivity.

Full text of DOI:10.1002/hlca.200390145

Helvetica Chimica Acta ± Vol. 86 (2003)
1753
Potent New Heterogeneous Asymmetric Catalysts
a
a
a
a
by Jacques Rouzaud ), Matthew D. Jones ), Robert Raja ), Brian F. G. Johnson* ), John Meurig
b
c
a
Thomas* ) ), and Melinda J. Duer )
a) Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, UK
(
phone: ‡441223-336339; fax: ‡441223-336017; e-mail: bfgj1@cam.ac.uk)
b) Department of Materials Science and Metallurgy, New Museums Site, Pembroke Street,
Cambridge CB2 3QZ, UK(phone: ‡441223-334467; fax: ‡441223-334567; e-mail: jmt@ri.ac.uk)
c
)
The Royal Institution of Great Britain, Davy Faraday Research Laboratory, 21 Albemarle Street,
London W1S 4BS, UK
Dedicated to Professor Jack D. Dunitz on the occasion of his 80th birthday
I
A set of new, air-stable, Rh -based heterogeneous asymmetric hydrogenation catalysts have been
synthesised, characterised, and tested. Individual members of this new family all exhibit good enantioselectivity.
Introduction. ± Even though enzymes are currently more extensively used [1]
industrially than asymmetric transition-metal complexes for enantiselective catalytic
conversions involving pharmaceuticals and agrochemicals, the latter are of growing
importance [2 ± 6]. Such complexes have, however, overwhelmingly been utilized
homogeneously, and their heterogeneous asymmetric counterparts have hitherto
performed disappointingly [7], so far as their enantiselectivity is concerned, largely
because they contained a range of different kinds of active centres, each with its own
catalytic selectivity. Earlier, we have shown [8 ± 11] that, provided the active organo-
metallic moiety is heterogenised in a single-site fashion, superior catalytic performance
may be achieved. Such asymmetric heterogeneous catalysts are intrinsically more
convenient than their homogeneous precursors since they provide an expedient,
inexpensive route to introducing chiral centres without recourse to costly separations
or use of expensive solvents (such as supercritical CO or ionic liquids) [12].
2
Results and Discussion. ± The ligands employed in this study are (S,S,S)-[2-(4,5-
dihydro-4',5'-diphenyloxazol-2'-yl)ferrocenyl]phosphine ((S,S,S)-dipof; 1a), l-trypto-
phan benzyl ester (1b), (À)-(S)-2-(aminomethyl)-1-ethylpyrrolidine (1c), and ( ‡ )-
(1R,2R)-1,2-diphenylethane-1,2-diamine (1d) (Fig. 1).
Reaction of 1 mol-equiv. of each of these ligands with the rhodium cation
‡
[
Rh(cod)(THF) ] (cod ˆ cycloocta-1,5-diene), previously obtained from the reaction
2
between [RhCl(cod)] and AgCF SO , produced the homogeneous catalyst designated
2
3
3
2
a ± 2d, respectively (see also the Table) [Rh(cod)L-L]CF SO in near quantitative
3 3
yield. The final compounds are air-stable and easily handled. In all cases, the new
1
13
31
compounds were characterised by H-, C-, and P- (where appropriate) NMR, by

1
754
Helvetica Chimica Acta ± Vol. 86 (2003)
NH2
Ph
O
O
N
Ph
Ph
Fe
PPh2
O
N
H
1
a
1b
Ph
Ph
N
NH2
H N
2
NH2
Et
1
c
1d
Fig. 1. The chiral ligands employed in this study. The atoms in bold are those that ligand to the Rh(I) centre.
mass spectrometry and single-crystal X-ray diffraction. A segment of the crystal
structure of 2b is shown in Fig. 2.
It is noteworthy that the metal is coordinated to the O-atom of the CˆO group and
to one of the N moieties, which is a relatively rare occurrence in organometallic
chemistry. It is also noteworthy that the tryptophan ring is tilted towards the Rh centre,
affording a high degree of steric hindrance conducive for asymmetric catalysis. The
crystal structure of catalyst 2c was also determined, and the key feature is presented in
Fig. 3. The structure of 2d is shown in Fig. 4.
Fig. 2. Afragment of the crystal structure for the homogeneous catalyst 2b (the triflate anion is omitted for
clarity). The ellipsoids are at the 50% probability level. Rh(1)ÀN(1): 2.119(5) ä, Rh(1)ÀO(1): 2.144(5) ä,
C(9)ÀO(1): 1.233(8) ä, N(1)ÀRh(1)ÀO(1): 78.30(9)8, C(10)ÀN(1)ÀRh(1): 110.3(4)8, Rh(1)ÀO(1)ÀC(9):
1
13.4(4)8.

Helvetica Chimica Acta ± Vol. 86 (2003)
1755
Fig. 3. Afragment of the crystal structure for the homogeneous catalyst 2c (the triflate anion is omitted for
clarity). The ellipsoids are at the 50% probability level. Rh(1)ÀN(1): 2.178(3) ä, Rh(1)ÀN(2): 2.112(3) ä,
C(8)ÀRh(1): 2.126(3) ä, C(11)ÀRh(1): 2.124(4) ä, C(12)ÀRh(1): 2.129(3) ä, C(15)ÀRh(1): 2.146(3) ä,
N(1)ÀRh(1)ÀN(2): 91.26(15)8.
Fig. 4. Afragment of the crystal structure for the homogeneous catalyst 2d (the triflate anion is omitted for
clarity). The ellipsoids are at the 50% probability level. Rh(1)ÀN(1): 2.105(5) ä, Rh(1)ÀN(2): 2.128(5) ä,
C(18)ÀRh(1): 2.146(7) ä, C(15)ÀRh(1): 2.121(7) ä, C(21)ÀRh(1): 2.116(7) ä, C(22)ÀRh(1): 2.126(7) ä,
N(1)ÀRh(1)ÀN(2): 80.16(19)8.
A number of organometallic homogeneous catalysts may be heterogenised in a
single-site fashion onto the inner walls of high-area, mesoporous silica supports (using
an appropriate alkyl bromide tether). But, recently, an even more straightforward
method of anchoring an asymmetric organometallic catalyst has emerged, entailing
tethering via a noncovalent interaction [4]. This involves the use of the polar counter-
À
ion, CF SO , which, through quite strong H-bonding, is −anchored× to the pendant
3
3
silanol groups of the mesoporous silica [13]. One of the principal purposes of this paper
is to demonstrate the advantages of the simple triflate anion method (devised recently
by Rege et al. [4]) in heterogenising viable precursor homogeneous asymmetric
catalysts. For this purpose, we have taken two entirely new ligands, 1a and 1b, and two

1
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Helvetica Chimica Acta ± Vol. 86 (2003)
others, 1c and 1d, that we have already used for the preparation of heterogeneous
catalysts by our earlier [10] anchoring method.
Our heterogeneous chiral catalysts were easily prepared by simple sorption of the
homogeneous catalysts from a CH Cl slurry onto the surface of the mesoporous silica.
2
2
The presence of the chiral catalyst inside the mesopore was established by elemental
31
analysis and, for catalyst 3a (where 3a is the heterogeneous analogue of 2a), by P-CP/
MAS (cross-polarization magic angle spinning) NMR. (The spectrum shows a broad
signal centred at d 22.9 ppm, which is comparable to that observed with the
homogeneous precursor (d 23.9 ppm (CD Cl )).
2
2
To investigate the asymmetric catalytic performance of the heterogenised catalysts,
their efficiency in the hydrogenation of the CˆC bond was studied, the conversion of
(
(
E)-a-phenylcinnamic acid to 2,3-diphenylpropanoic acid being our test reaction
Table).
Table 1. The Activities, Selectivity (for 2,3-diphenylpropionic acid) and Enantiomeric Excess (ee) for the Various
Homogeneous and Heterogeneous Catalysts for the Hydrogenation of (E)-a-Phenylcinnamic acid
Form of the
Rh catalyst
Ligand
Conversion Selectivity ee
I
[%]
[%]
[%]
Homogeneous
2a
(S,S,S)-dipof (1a)
l-Tryptophan benzyl ester (1b)
65
88
70
59
84
84
64
62
67
47
84
91
73
67
83
66
94
88
91
69
97
90
2
2
2
b
c
d
(À)-(S)-2-(Aminomethyl)-1-ethylpyrrolidine (1c) 86
(‡)-(1R,2R)-1,2-Diphenylethane-1,2-diamine (1d) 64
Heterogeneous 3a
(S,S,S)-dipof (1a)
79
85
79
81
a
3
3
3
3
3
a* (S,S,S)-dipof ) (1a)
a
b
c
(S,S,S)-dipof recycled
l-Tryptophan benzyl ester (1b)
(À)-(S)-2-(Aminomethyl)-1-ethylpyrrolidine (1c) 90
d
(‡)-(1R,2R)-1,2-Diphenylethane-1,2-diamine (1d) 70
a) Catalyst 3a* is catalyst 3a after being stored for 6 months. Reaction conditions: substrate, ca. 0.5 g; solvent
MeOH), ca. 30 ml; homogeneous catalyst, ca. 10 mg; heterogeneous catalyst, ca. 50 mg; pressure, 20 bar;
(
temperature, 313 K; time 24 h.
The results show a marked increase in the enantiomeric excess once the catalyst is
anchored onto the mesoporous material. The change in stereoselectivity confirms the
importance of confinement in chiral catalysis and the role mesoporous silica plays in
these systems [8 ± 12][14]. We have demonstrated that prolonged storage of the
catalyst 3a, under normal conditions, does not alter the catalytic performance. The
recycling test of 3a shows little change in enantioselectivity and conversion, thus
confirming that, despite a relatively low-energy bonding of the homogeneous catalyst
onto the mesoporous silica surface, the system is not readily susceptible to leaching. In
summary, we have illustrated the ease of synthesis of several stable new asymmetric
homogeneous catalysts, as well as the ease of producing potent heterogeneous
analogues.
We gratefully acknowledge the EPSRC (UK) for a rolling grant to J. M. T. and B. F. G. J., a studentship to
M. D. J. and for financial support for the single-crystal diffractometer, Bayer AG, D-Leverkusen, for their
support to R. R., the Marie Curie fellowship scheme for J. R., ICI and the Newton trust for M. D. J. We thank Dr.
J. E. Davies for determining the crystal structures.

Helvetica Chimica Acta ± Vol. 86 (2003)
1757
Experimental Part
1
. Synthesis and Characterisation of Homogeneous Catalysts. All compounds were purchased from Aldrich,
unless otherwise stated. The solvents were all predried by standard methods. The reactions were carried out
under a N atmosphere by standard Schlenk line techniques. The NMR measurements were performed on a
Bruker DPX (500 MHz) employing cryo-probe technology or a Bruker 400-MHz spectrometer.
Rh(Cycloocta-1,5-diene){(S,S,S)-dipof}]CF SO (2a). [RhCl(cod)] (46 mg, 0.09 mmol) was dissolved in
THF (5 ml), to which AgCF SO (37 mg, 0.19 mmol) was added, and this soln. was stirred for 1 h at r.t. The soln.
2
[
3
3
2
3
3
was then filtered (to remove AgCl), and to the filtrate (S,S,S)-dipof (1a; 110 mg, 0.19 mmol) was added, and the
soln. left to stir for 1 h. Then, the soln. was slightly concentrated in vacuo, and hexane (25 ml) was added to
precipitate the required product. The soln. was filtered and the product washed with hexane (2 Â 20 ml) and
1
Et
2
2
O (2 Â 20 ml), and dried in vacuo: 2a (100 mg, 55%). Orange powder. H-NMR (CDCl
3
, 400 MHz): 1.79 ±
.72 (m, 8 H); 3.40 (m, 1 H); 3.65 (m, 1 H); 3.74 (m, 1 H); 4.77 (s, 5 H); 4.80 (m, 1 H); 5.05 (m, 1 H); 5.15
m, 1 H); 5.18 (m, 1 H); 5.28 (m, 1 H); 5.45 (m, 1 H); 6.64 ±7.73 (m, 20 H). P-NMR (CDCl
3
1
(
(
3
): 23.9
1
d, J(P,Rh) ˆ 149.8). ESI-MS (pos.): 803 (100).
[
Rh(Cycloocta-1,5-diene)(l-tryptophan Benzyl Ester)]CF
3
SO
(62 mg, 0.24 mmol) was added and the soln. was stirred for 1 h at
r.t. The soln. was then filtered (to remove AgCl) and to the filtrate l-tryptophan benzyl ester (1b; 72 mg,
.24 mmol) was added, and the soln. was left to stir for 1 h. Then, the soln. was slightly concentrated in vacuo,
and hexane (25 ml) was added to precipitate the required product. The soln. was filtered, and the product was
3 2
(2b). [RhCl(cod)] (60 mg, 0.12 mmol) was
3 3
dissolved in THF (5 ml) to which AgCF SO
0
washed with hexane (2 Â 20 ml) and dried in vacuo. The residue was recrystallized in CH
2 2
Cl to give 2b (121 mg,
, 400 MHz): 1.50 ± 1.69 (m, 4 H, cod); 2.09 ± 2.30 (m, 4 H, cod); 3.25
1
7
7%). Yellow crystals. H-NMR (CD
2
Cl
2
3
3
(
d, J ˆ 6.0, CH
2
CH); 3.58 (m, 4 H, cod); 4.15 (t, J ˆ 6.0, CH
2
CH); 5.26 (s, CH
2
O); 7.16 ± 7.72 (m, 10 H, Ph,
CH); 69.9 (CH O);
1
3
C
8
H
6
N); 9.28 (s, NH). C-NMR (CD
2
Cl
2
): 29.5, 30.8 (CH
2
, cod); 30.1 (CH CH); 56.3 (CH
2
2
2
8
1
4
2.9 (d, J(Rh,C) ˆ 63, CH, cod); 103.2, 112.5, 119.0, 119.6, 120.4, 121.2, 122.2, 124.5, 129.0, 129.3, 129.4, 134.3,
38.0 (Ph and C RhS: C 49.55, H
N); 179.3 (CˆO). ESI-MS (pos.): 505 (85%). Anal. calc. for C27
.62, N 4.28; found C 48.42, H 4.57, N 4.05.
Rh{(À)-(S)-2-(Aminomethyl)-1-ethylpyrrolidine}(cycloocta-1,5-diene)]CF
100 mg, 0.20 mmol) was dissolved in THF (10 ml), to which AgCF SO (104 mg, 0.40 mmol) was added, and
this soln. was stirred for 1 h at r.t. The soln. was then filtered (to remove AgCl) and to the filtrate ( À )-(S)-2-
aminomethyl)-1-ethylpyrrolidine (1c; 52 mg, 0.40 mmol) was added, and the soln. was left to stir for 1 h. Then,
the soln. was slightly concentrated in vacuo, and hexane (25 ml) was added to precipitate the required product.
8
H
6
30 3 2 5
H F N O
[
3
SO
3
(2c). [RhCl(cod)]
2
(
3
3
(
The soln. was filtered, and the product was washed with hexane (2 Â 20 ml) and Et
2
O (2 Â 20 ml), and dried in
vacuo: 2c (172 mg, 88%). Yellow powder.
1H-NMR (CDCl
): 1.54 (t, J ˆ 7, Me(1)); 1.74 (br. s, 2 CH
(cod)); 1.80 ± 2.09 (m, CH
(3)); 2.90 (m, CH(6)); 3.10 (m, CH
(7)); 3.57 (d, J(Rh,H) ˆ 37,
): 12.2 (C(1)); 21.7 (C(4)); 24.4 (C(5)); 29.6
3
2
2 2
(4), CH (5)); 2.30 (br.
1
s, 2 CH
2
(cod)); 2.45 ± 2.70 (m, CH
2
(2), CH
2
2
1
13
2
CH (cod)); 3.75 (d, J(Rh,H) ˆ 74, 2 CH (cod)). C-NMR (CDCl
3
(
(
(
d, J(Rh,C) ˆ 12, CH
2
(cod)); 30.5 (d, J(Rh,C) ˆ 36, CH
2
(cod)); 45.5 (C(7)); 50.9 (C(2)); 56.5 (C(3)); 67.1
‡
C(6)); 79.6 (d, J(Rh,C) ˆ 65, CH (cod)); 83.6 (d, J(Rh,C) ˆ 240, CH (cod)). ESI-MS (pos.): 339 (M ), 231
‡
[M À cod] ). Anal. calc. for C16
28 3 2 3
H F N RhSO : C 39.34, H 5.74, N 5.74; found: C 39.84, H 5.54, N 5.69. Crystals
2 2 2
suitable for X-ray diffraction were obtained by recrystallisation in CH Cl /Et O.
[
Rh(Cycloocta-1,5-diene){(‡)-(1R,2R)-1,2-diphenylethan-1,2-diamine}]CF
3
SO
3
(2d). [RhCl(cod)]
2
(
100 mg, 0.20 mmol) was dissolved in THF (10 ml), to which AgCF
3
SO
3
(104 mg, 0.40 mmol) was added, and
this soln. was stirred for 1 h at r.t. The soln. was then filtered (to remove AgCl) and to the filtrate (‡)-(1R,2R)-
1,2-diphenylethane-1,2-diamine (1d; 83 mg, 0.40 mmol) was added, and the soln. was left to stir for 1 h. Then, the

1
758
Helvetica Chimica Acta ± Vol. 86 (2003)
soln. was slightly concentrated in vacuo, and hexane (25 ml) was added to precipitate the required product. The
soln. was filtered, and the product was washed with hexane (2 Â 20 ml) and Et
2
O (2 Â 20 ml) and dried in vacuo:
); 2.46 (br. m, 2 CH ); 4.01
); 66.3
3
RhSO :
1
2
d (195 mg, 86%). Yellow powder. H-NMR (CD
3
OD): 1.95 (br. m, 2 CH
2
2
1
3
(
(
s, 2 NCH); 4.24 (m, 2 CH); 4.35 (m, 2 CH); 7.1 ±7.3 (m, 10 arom. H). C-NMR (CD
3
OD); 31.5 (CH
2
‡
NCH); 81.4 (CH); 128.4, 129.2, 129.6, 140.5 (Ph). ESI-MS (pos.): 423 (M ). Anal. calc. for C23
H
28
F
3
N
2
C 48.25, H 4.90, N 4.90; found C 47.95, H 4.83, N 4.60. Crystals suitable for X-ray diffraction were obtained from
a MeOH/Et O soln.
. Synthesis and Characterisation of Heterogeneous Catalysts. The triflate salt (50 mg) was dissolved in
Cl (20 ml), to which dry calcined MCM-41 (500 mg) was added to form a slurry. This was left stirring at r.t.
for 3 h; during this time the solid took on the colour of the Rh complex, and the soln. became pale. The soln. was
filtered and the MCM-41 was washed with copious amounts of CH Cl until the washings were colourless. The
catalyst was then dried in vacuo and isolated as a pale yellow solid. Elemental analysis: 3c: C 3.77, H 0.83, N 0.42;
2
2
CH
2
2
2
2
1
9
3
d: C 3.76, H 0.72, N 0.39. F-MAS Measurements of catalyst 3d, of the homogeneous catalyst and the
3
1
heterogeneous catalyst were identical. P-CP/MAS (spinning 6 kHz, contact time 5 ms, recycle delay 5 s) of
catalyst 3a is given, the isotropic chemical shift (22.9 ppm) is consistent with that of its homogeneous counter-
part in solution.
3
. Description of the Hydrogenation Experiment and Analytical Methods. The catalytic reactions
(
(
enantioselective hydrogenations) were carried out in a high-pressure stainless-steel catalytic reactor
100 ml) lined with Poly Ether Ether Ketone (PEEK). The homogeneous catalyst (10 mg; or 50 mg of the
mesoporous silica anchored heterogeneous catalyst), which was previously evacuated and stored under inert
conditions (N or Ar), was transferred under an inert atmosphere to the catalyst-delivery unit, which was
2
subsequently sealed and introduced to the high-pressure reactor (using dry He).
The substrate ((E)-a-phenylcinnamic acid; 0.5 g), solvent (MeOH; 30 g) and a suitable internal standard
(
cyclododecane) were then introduced into the reactor, and the reactor was sealed. The reactor as well as the
inlet and outlet ports were inertized with dry N (thrice) prior to the introduction of H (5 bar). A leak test was
carried out, and the reactor was then pressurized to 20 bar with H . The reactor was then heated to the desired
2
2
2
temp. (313 K), and the contents were stirred using a mechanical stirrer at 400 rpm. (Where kinetic and rate
effects were studied, a mini-robot liquid-sampling valve was employed to remove small aliquots of the sample
without perturbing the pressure in the reactor.)
At the end of the reaction, the heating was turned off, and the contents of the reactor were cooled
(quenched). The reactor was then depressurised. A mass-balance calculation was made at this stage to check for
handling and weight losses. The products were analysed (using a suitable internal standard) by GC (Varian,
model 3400 CX) employing a HP-1 capillary column (25 m  0.32 mm) and flame ionisation detector with a
variable-ramp-temperature program from 433 to 493 K. The identities of the products were first confirmed using
authenticated standards, and their individual response factors were determined using a suitable internal
standard (calibration method). The conversions and selectivities were determined as defined by the following
equations, and the yields were normalised with respect to the response factors obtained as above:
Conversion [%] ˆ [(moles of initial substrate ± moles of residual substrate)/(moles of initial substrate)] Â
1
00
Selectivity [%] ˆ [(moles of individual product)/(moles of total products)]  100
1
13
3
The products were further identified by NMR spectroscopy ( H and C in CD OD), which showed loss of
the CˆC and gain of a CÀC moiety. The enantioselectivities (ee×s) were first determined by GC (Hewlett-
Packard, HP 5890) using a chiral column (g-cyclodextrin dialkyl (Chiraldex), 20 m  0.25 mm), and the
identities of the chiral products were further confirmed by LCMS (Shimadzu LCMS-QP8000) equipped with a
chiral detector (OR-990, JASCO), again, using a chiral column (CHIRALCEL OJ-R, DAICEL). ee Values
were calculated from the peak areas of the enantiomers using the following formula:
ee ˆ ([R] À [S])  100/([R] ‡ [S])
Finally, as a further confirmation, the products were isolated from the reaction mixture and esterified to the
methyl ester by the following procedure: 300 ml of the sample was taken in a glass vial, 2 ml of 14% BF
MeOH was added to the glass vial, which was sealed with a Teflon-lined stopper and heated for 1 h at 353 K. The
sample was cooled to r.t. and 2 ml of Milli-Q reagent water was added with mild shaking. HPLC-Grade CH Cl
2 ml) was added before the analysis, which was again performed on the LCMS (Shimadzu LCMS-QP8000)
using the same chiral column (CHIRALCEL OJ-R, DAICEL).
3
in
2
2
(

Helvetica Chimica Acta ± Vol. 86 (2003)
1759
À1
Crystal Data of 2b: C28
H
32Cl
2
F
3
N
2
O
5
RhS, 739.43 g mol , monoclinic, space group P2(1), a ˆ 10.3924(3),
3
À1
b ˆ 11.2263(4), c ˆ 13.8107(4) ä, b ˆ 102.276(2)8, Vˆ 1574.43(9) ä , Tˆ 180(2) K, Z ˆ 2, m ˆ 0.835 mm , 9885
reflections measured 6122 independent, R [I > 2s(I)] ˆ 0.1162, R (all data) ˆ 0.0795,
[I > 2s(I)] ˆ 0.0492 R
(all data) ˆ 0.1543. CCDC Ref. No. 199872.
Crystal Data of 2c: C20
RhS, 488.37 g mol , orthorhombic, space group P2(1)2(1)2(1), a ˆ
.3462(2), b ˆ 13.2369(3), c ˆ 15.8161(4) ä, b ˆ 908, Vˆ 1956.68(8) ä , Tˆ 180(2) K, Z ˆ 4, m ˆ 1.025 mm
8061 reflections measured 4471 independent, R [I > 2s(I)] ˆ 0.0633, R (all data) ˆ
[I > 2s(I)] ˆ 0.0350 R
.0499, R
(all data) ˆ 0.0676. CCDC Ref. No. 199871.
Crystal data of 2d: C24
RhS, 657.37 g mol , monoclinic, space group P2(1), a ˆ 12.9486(3),
1
2
1
R
2
À1
28 3 2 3
H F N O
3
À1
9
1
0
,
1
2
1
2
À1
H
2 3 2 5
30Cl F N O
3
À1
b ˆ 9.9939(2), c ˆ 21.3221(6) ä, b ˆ 98.4060(10)8, Vˆ 2729.59(11) ä , Tˆ 180(2) K, Z ˆ 4, m ˆ 0.947 mm
,
1
0
6134 reflections measured 8957 independent, R
.0552, R
1
[I > 2s(I)] ˆ 0.0450, R
2
[I > 2s(I)] ˆ 0.1122, R (all data) ˆ
1
2
(all data) ˆ 0.1186. CCDC Ref. No. 199870. Single-crystal data were collected using a Nonius CCD
a
diffractometer with a sealed-tube MoK
source. All structures were solved with SHELXS-97 and refined using
2
full-matrix least-squares on F using SHELXS-97 software. The CCDC contains supplementary crystallographic
data for this paper. This data maybe obtained, free of charge, via http:/www.ccdc.cam.ac.uk/conts/
retrieving.html (or free from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge
CB2 1EZ, UK; fax: ‡441223336033; e-mail: deposit@ccdc.cam.ac.uk).
REFERENCES
[1] M. T. Reetz, Centenary Lecture of the Royal Society of Chemistry, 12th March, 2003, at the University of
Cambridge, UK.
[2] −Catalytic Asymmetric Synthesis×, Ed. I. Ofima, VCH Publishers, Weinheim, 1993.
[3] R. Noyori, −Asymmetric Catalysis in Organic Synthesis×, John Wiley & Sons, New York, 1994.
[4] F. M. de Rege, D. K. Morita, K. C. Ott, W. Tumas, R. D. Broene, Chem. Commun. 2000, 1797.
[5] C. Claver, E. Fernandez, A. Gillon, K. Heslop, D. J. Hyett, A. Martorell, A. G. Orpen, P. G. Pringle, Chem.
Commun. 2000, 961.
[6] C. S. Stinson, Chem. Eng. News 2000, 55.
[
7] H. Brunner, in −Applied Homogeneous Catalysis with Organometallic Compound×, Eds. B. Cornils and
W. A. Herrmann, Wiley-VCH, Weinheim, 1996, Vol. 1, pp. 206, and refs. cit. therein.
8] B. F. G. Johnson, S. A. Raynor, D. S. Shephard, T. Mashmeyer, J. M. Thomas, G. Sankar, S. Bromley, R.
Oldroyd, L. Gladden, M. D. Mantle, Chem. Commun. 1999, 1167.
[
[
9] S. A. Raynor, J. M. Thomas, R. Raja, B. F. G. Johnson, R. G. Bell, M. D. Mantle, Chem. Commun. 2000,
1925.
[
[
[
[
10] M. D. Jones, R. Raja, J. M. Thomas, B. F. G Johnson, D. W. Lewis, J. Rouzaud, K. D. M. Harris, submitted.
11] J. M. Thomas, Angew. Chem., Int. Ed. 1999, 38, 3588.
12] J. M. Thomas, R. Raja, G. Sankar, B. F. G. Johnson, D. W. Lewis Chem.±Eur. J. 2001, 7, 2973.
13] C. Bianchini, D. G. Burnaby, J. Evans, P. Frediani, A. Meli, W. Oberhauser, R. Psaro, L. Sordelli, F. Vizza, J.
Am. Chem. Soc. 1999, 121, 5961.
[14] J. M. Thomas, T. Maschmeyer, B. F. G. Johnson, D. S. Shephard, J. Mol. Catal. A± Chem. 1999, 141, 139.
Received March 28, 2003