Chiral amino alcohol derived bis-phosphoramidite pincer palladium complexes and their applications in asymmetric allylation of aldimines

Article abstract of DOI:10.1021/om100021p

Novel P-stereogenic bis-phosphoramidite pincer palladium complexes 1 and 2 derived from (S)-(-)-α,α-diphenyl-2-pyrrolidinemethanol and (S)-(+)-indolinemethanol, respectively, were synthesized in reasonable yields (i.e., 55-62%) by using a flexible, modular synthetic approach and were characterized by X-ray crystal structure determination. Reacting (S)-(+)-indolinemethanol with PCl₃ leads to the formation of a novel P-chiral building block, which exhibits good thermal stability of its stereochemical features. This enabled the design and development of new P-chiral bisphosphoramidite pincer arene ligands and their corresponding metal complexes. The molecular structure of the new indolinemethanol-derived phosphoramidite pincer metal complex screens quadrants I and III, which is in contrast to the previously reported L-proline-derived P-chiral ligands that screen quadrants II and IV. The bis-phosphoramidite pincer palladium, complexes 1 and 2 are active catalysts for asymmetric homoallylation of sulfonimines, where low (ee 33%) or no enantioselectivity was observed for reactions catalyzed by 2 and 1, respectively. Preliminary catalytic results revealed that enantiomeric excess values varied by using differently functionalized sulfonimines, suggesting that, both electronic properties and steric congestion of sulfonimines affect, the transition state of the electrophilic attack of the ¹nallyl Pd intermediate in the allylation.

Full text of DOI:10.1021/om100021p

Organometallics 2010, 29, 1379–1387 1379
DOI: 10.1021/om100021p
Chiral Amino Alcohol Derived Bis-phosphoramidite Pincer Palladium
Complexes and Their Applications in Asymmetric Allylation of Aldimines
Jie Li,† Martin Lutz,‡ Anthony L. Spek,‡ Gerard P. M. van Klink,†,§ Gerard van Koten,†
and Robertus J. M. Klein Gebbink*,†
†Organic Chemistry & Catalysis, Debye Institute for Nanomaterials Science, Faculty of Science, Utrecht
University, Padualaan 8, 3584 CH Utrecht, The Netherlands, and ‡Crystal and Structural Chemistry, Bijvoet
Center for Biomolecular Research, Faculty of Science, Utrecht University, Padualaan 8, 3584 CH Utrecht,
The Netherlands. §Present address: DelftChemTech, Faculty of Applied Sciences, Delft University of
Technology, Julianalaan 136, 2628 BL Delft, The Netherlands.
Received January 7, 2010
Novel P-stereogenic bis-phosphoramidite pincer palladium complexes 1 and 2 derived from
(S)-(-)-R,R-diphenyl-2-pyrrolidinemethanol and (S)-(þ)-indolinemethanol, respectively, were syn-
thesized in reasonable yields (i.e., 55-62%) by using a flexible, modular synthetic approach and were
characterized by X-ray crystal structure determination. Reacting (S)-(þ)-indolinemethanol with
PCl3 leads to the formation of a novel P-chiral building block, which exhibits good thermal stability
of its stereochemical features. This enabled the design and development of new P-chiral bis-
phosphoramidite pincer arene ligands and their corresponding metal complexes. The molecular
structure of the new indolinemethanol-derived phosphoramidite pincer metal complex screens
quadrants I and III, which is in contrast to the previously reported L-proline-derived P-chiral ligands
that screen quadrants II and IV. The bis-phosphoramidite pincer palladium complexes 1 and 2 are
active catalysts for asymmetric homoallylation of sulfonimines, where low (ee 33%) or no enantio-
selectivity was observed for reactions catalyzed by 2 and 1, respectively. Preliminary catalytic results
revealed that enantiomeric excess values varied by using differently functionalized sulfonimines,
suggesting that both electronic properties and steric congestion of sulfonimines affect the transition
state of the electrophilic attack of the 1η-allyl Pd intermediate in the allylation.
Introduction
catalysts, sensors, or switches, has attracted considerable
attention due to their unique reactivities and structural
properties.1 The synthesis of chiral pincer metal complexes
and their applications in asymmetric catalysis have more
recently been reported. Some representative frameworks of
these complexes documented to date are summarized in
Figure 1. Various groups independently developed a series
of NCN-bisoxazolinyl-phenyl pincer metal complexes bear-
ing as the metal, for example, rhodium, ruthenium, palla-
dium, or platinum, and explored their catalytic properties in,
for example, asymmetric allylation, asymmetric hydrosilyla-
tion, and asymmetric hydrogen transfer reactions. (Figure 1,
type A).2 The heterocyclic oxazoline skeleton supplies a
tunable and rigid chiral pocket to the metal coordination
sphere of bisoxazolinyl-phenyl pincer metal complexes,
including chiral centers at the 4- and 5-positions by using
various β-amino alcohols. Besides the well-developed chiral
NCN-pincer metal complexes, the development of chiral
PCP-pincer metal complexes has recently attracted much
attention. Zhang and co-workers reported a practical syn-
thesis of chiral PCP-pincer metal complexes bearing stereo-
genic benzylic methylene centers by using Corey’s chiral
reduction of 1,3-diacetylbenzene (Figure 1, type B).3 Alter-
natively, van Koten and co-workers developed the first
example of a PCP-pincer palladium complex bearing
In the past decades, the chemistry of pincer metal
complexes, especially their application as homogeneous
*Corresponding author. Fax: (þ31)-30-252-3615. E-mail: r.j.m.
kleingebbink@uu.nl.
(1) For reviews: (a) Albrecht, M.; van Koten, G. Angew. Chem., Int. Ed.
2001, 40, 3750. (b) Singleton, J. T. Tetrahedron 2003, 59, 1837. (c) van der
Boom, M. E.; Milstein, D. Chem. Rev. 2003, 103, 1759. (d) Morales-Morales, D.
ꢀ
Mini-Rev. Org. Chem. 2008, 5, 141. (e) Szabo, K. J. Synlett 2006, 6, 811.
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metallics 1999, 18, 3584. (h) Denmark, S. E.; Stravenger, R. A.; Faucher, A. M.;
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r
2010 American Chemical Society
Published on Web 02/17/2010
pubs.acs.org/Organometallics

1380 Organometallics, Vol. 29, No. 6, 2010
Li et al.
Figure 1. Representative framework of chiral pincer metal complexes.
P-stereogenic tert-butylphenylphosphine moieties by using a
(-)-sparteine-assisted asymmetric lithiation step4a and sub-
sequently reported its analogous ruthenium pincer metal
complexes (Figure 1, type C).4b Szabo and Bedford indepen-
ꢀ
dently reported a series of easily accessible and tunable 1,10-
bi-2-naphthol- and biphenanthrol-based chiral PCP-pincer
palladium complexes and demonstrated their application in
the asymmetric homoallylation of benzaldehyde and sulfo-
nimines with ee’s up to 85% (Figure 1, type D).5,6 The
synthesis of chiral phosphite pincer metal complexes benefits
from the structual diversity of easily available chiral diols
and an efficient modular synthesis. Accordingly, chiral
phosphite or bis(diamidophosphinite)pincer metal com-
plexes derived from chiral diols or chiral diamines have been
reported by several groups.5-7 In contrast to the extensive
use of chiral diols, especially members of the BINOL family,
little is known about the use of other chiral building blocks.
Inspiring results have recently been reported for the
successful use of L-proline and chiral amino alcohol deriva-
tives, which has expanded the library of new P-chiral ligands
and their corresponding metal complexes. The possibility to
shape the molecular environment of the phosphorus atom(s)
provides an excellent opportunity for the facile construction
of tunable chiral pockets at the metal center from which
catalysts could emerge with improved regio- and stereo-
selectivity.8,9 There are two major synthetic routes for acces-
sing L-proline-derived P-chiral ligands (Figure 2), and we
have explored both for the synthesis of new P-chiral pincer
ligands and metal complexes.
Figure 2. L-Proline-derived P-chiral building blocks.
resulting compounds can be used to prepare P-chiral bis-
phosphoramidite arene ligands through further organic
transformations. Actually, this protocol has led to the
efficient synthesis of a novel P-chiral pincer palladium
complex, 1 (vide infra). Alternatively, the carboxylic acid
group can be converted to arrive at functionalized chiral
secondary amines bearing bulky functional groups (e.g., aryl
groups) through stepwise organic transformations (Figure 2,
route B).11 In this case, the chiral pockets are supposed to be
improved by taking advantage of a closer proximity of bulky
substituents with respect to the phosphorus donor. In an
attempt to apply this protocol to synthesize the correspond-
ing pincer palladium complexes, however, we were not able
to obtained analytically pure samples, because their isolation
was hampered by the high moisture sensitivity of the
N-P-N manifold of the bis(diamidophosphinite)pincer
ligand.
Starting from L-proline, the carboxylic acid group can be
converted to arrive at functionalized amino alcohols bearing
bulky functional groups (e.g., aryl groups) with the corres-
ponding Grignard reagents (Figure 2, route A).10 The
(4) (a) Williams, B. S.; Dani, P; Lutz, M.; Spek, A. L.; van Koten, G.
Helv. Chim. Acta 2001, 84, 3519. (b) Medici, S.; Gagliardo, M.; Williams,
S. B.; Chase, P. A.; Gladiali, S.; Lutz, M.; Spek, A. L.; van Klink, G. P. M.;
van Koten, G. Helv. Chim. Acta 2005, 88, 694.
ꢀ
(5) (a) Wallner, O. A.; Olsson, V. J.; Eriksson, L.; Szabo, K. J. Inorg.
Chim. Acta 2006, 359, 1767. (b) Aydin, J.; Kumar, K. S.; Sayah, M. J.;
ꢀ
Wallner, O. A.; Szabo, K. J. J. Org. Chem. 2007, 72, 4689.
(6) Baber, R. A.; Bedford, R. B.; Betham, M.; Blake, M. E.; Coles,
S. J.; Haddow, M. F.; Hursthouse, M. B. A.; Orpen, A. G.; Pilarski,
L. T.; Pringle, P. G.; Wingad, R. L. Chem. Commun. 2006, 3880.
(7) (a) Benito-Garagorri, D.; Bocokic, V.; Mereiter, K.; Kirchner, K.
Organometallics 2006, 25, 3817. (b) Benito-Garagorri, D.; Kirchner, K. Acc.
Chem. Res. 2008, 41, 201.
(8) (a) Edwards, C. W.; Shipton, M. R.; Alcock, N. W.; Clase, H.;
Wills, M. Tetrahedron 2003, 59, 6473. (b) Breeden, S.; Cole-Hamilton,
D. J.; Foster, D. F.; Schwarz, G. J.; Wills, M. Angew. Chem., Int. Ed. 2000,
39, 4106. (c) Brunel, J. M.; Constantieux, T.; Buono, G. J. Org. Chem. 1999,
64, 8940. (d) Kimura, M.; Uozumi, Y. J. Org. Chem. 2007, 72, 707.
(9) (a) Bondarev, O. G.; Goddard, R. Tetrahedron Lett. 2006, 47,
9013. (b) Reetz, M. T.; Mehler, G.; Bondarev, O. Chem. Commun. 2006,
2292. (c) Benetsky, E. B.; Zheglov, S. V.; Grishina, T. B.; Macaev, F. Z.; Bet,
L. P.; Davankov, V. A.; Gavrilov., K. N. Tetrahedron Lett. 2007, 48, 8326.
(10) (a) Price, M. D.; Kurth, M. J.; Schore, N. E. J. Org. Chem. 2002,
67, 7769. (b) Zhou, Y.; Wang, W. H.; Dou, W.; Tang, X. L.; Liu, W. S.
Chirality 2008, 20, 110. (c) Corey, E. J.; Bakshi, R. K.; Shibata, S.; Chen,
C. P.; Singh, V. K. J. Am. Chem. Soc. 1987, 109, 7925.
In order to expand the library of P-chiral building blocks,
new starting materials are of key interest. So far, much less
effort has been put into the modification of the cyclic
pyrrolidine moiety of proline. To this end we have explored
the use of (S)-2-hydroxymethylindoline (Figure 2, route C),
which can be easily prepared by reducing commercially
(11) (a) Dunina, V. V.; Gorunova, O. N.; Stepanova, V. A.; Zykov,
P. A.; Livantsov, M. V.; Grishin, Y. K.; Churakov, A. V.; Kuzmina,
L. G. Tetrahedron: Asymmetry 2007, 18, 2011. (b) Tsarev, V. N.;
Lyubimov, S. E.; Bondarev, O. G.; Korlyukov, A. A.; Antipin, M. Y.;
Petrovskii, P. V.; Davankov, V. A.; Shiryaev, A. A.; Benetsky, E. B.;
Vologzhanin, P. A.; Gavrilov, K. N. Eur. J. Org. Chem. 2005, 2097. (c)
Koehn, U.; Schramm, A.; Kloss, F.; Goerls, H.; Arnold, E.; Anders, E.
Tetrahedron: Asymmetry 2007, 18, 1735. (d) Basavaiah, D.; Rao, K. V.;
Reddy, B. S. Tetrahedron: Asymmetry 2007, 18, 968.

Article
Organometallics, Vol. 29, No. 6, 2010 1381
Scheme 1. Synthesis of Pincer Palladium Complex 1
Figure 3. P-Chiral pincer palladium complexes 1 and 2.
available (S)-indoline-2-carboxylic acid with BH3 Me2S12 as
3
a new starting material to access a novel P-chiral building
block and its corresponding P-chiral pincer palladium com-
plex 2 (vide infra).
In this paper, we report on the development of a novel
P-chiral building block derived from (S)-2-hydroxymethyl-
indoline and the synthesis of two amino alcohol-derived,
chiral bis-phosphoramidite pincer palladium complexes 1
and 2 via a modular synthetic approach (Figure 3). The
potential of stereocontrol of the novel P-chiral pincer metal
complexes has been tested by using 1 and 2 as catalysts in
asymmetric allylation reactions.
Scheme 2. Synthesis of the Racemic Pincer Arene Ligand 6
Results and Discussion
Synthesis of Chiral Pincer Palladium Complex 1. Complex
1 was prepared via a straightforward synthetic route by using
optically active (S)-(-)-2-[diphenyl(hydroxylmethyl)]pyrro-
lidine 5 as starting material. This synthetic route is very
suitable for a modular approach allowing the synthesis of a
small library of P-chiral ligands starting from L-proline
derivatives (Scheme 1). Optically active amino alcohol 5
was phosphonated by using PCl3 in the presence of triethyl-
amine to afford the corresponding phosphorochloridate
adduct 4, which was subsequently coupled with 2-iodore-
sorcinol in toluene at 110 °C to yield pincer arene ligand 3 in
good yield. The diastereomeric ratio (dr) of a sample of crude
3 in solution after filtration was roughly estimated as 98:2 by
comparing the integral values of the large singlet at 141.1
ppm and a tiny singlet at 138.7 ppm in the 31P NMR, which
were assigned to the two phosphoramidite diastereoisomers.
The fact that 3 was obtained with high dr while being pre-
pared at 110 °C indicated that epimerization on the P-stereo-
genic phoshorus donors was not taking place, which proved
that the epimerization energy barrier at the P-centers is high
enough for the retention of their stereochemistry under most
practical conditions.13
5b
ꢀ
warming to 60 °C as was reported by Szabo et al., the
present P-stereogenic pincer arene ligand is superior to
commonly used building blocks having axial chirality in
terms of retention of configuration of the stereocenters.
The pincer palladium complex 1 was obtained in reason-
able yield (55%) and with excellent diastereoselectivity (dr >
99:1) after fractional crystallization from concentrated
CH2Cl2 solution by the addition of hexanes. The complex
can also be purified by flash chromatography, although this
does require the use of predried silica gel and eluent to
prevent hydrolysis of the complex.
Bedford and co-workers developed an alternative app-
roach to prepare diol-derived pincer metal complexes invol-
ving C-H activation by using sterically encumbered 2,4-
di-tert-butylbenzene-1,3-diol as a backbone.6 In an attempt
to use this particular approach for the diastereoselective
synthesis of P-chiral pincer arene ligand 6, we found instead
that it led to a complete loss of stereospecificity on phos-
phorus (Scheme 2). Two sharp singlets of equal intensity at
145.3 and 147.6 ppm were found in the 31P NMR spectra of
ligand 6.
Ligand 3 was directly used in the next step after filtering
over a short plug of Celite to remove any [HNEt3]Cl salt.
Palladation of pincer arene ligand 3, with complete retention
of the stereospecificity, was achieved via an oxidative addi-
tion reaction of 3 with a zerovalent Pd species (i.e., Pd2-
X-ray Crystal Structure of 1 (Et2O). The detailed struc-
3
ture of pincer palladium complex 1 in the solid state was
established by X-ray crystal structure determination
(Figures 4 and 5). Compound 1 (Et2O) crystallizes in the
(dba)3 CHCl3) under mild conditions (20 °C, 16 h). Warm-
3
ing the reaction mixture to 80 °C can shorten the reaction
time to 4 h without loss of any stereospecificity. However,
under these conditions a substantial amount of side products
was formed. In contrast to the partial racemization of the
functionalized BINOL or biphenanthrol moieties upon
3
non-centrosymmetric space group P21, and its enantiopurity
was confirmed by the Flack x parameter (see Experimental
Section). The molecular geometry of the complex consists of
a P-chiral meridonal-tridentate ligand and contains a direct
σ-carbon-metal bond to the palladium metal center. The
Pd-P (2.2628(8) and 2.2609(8) A) and Pd-C (1.981(3) A)
bond lengths are very close to the corresponding bond
lengths in the previously reported 1,10-bi-2-naphthol pincer
palladium complex (Table 1).5a The bond angle P-Pd-P
˚
˚
ꢀ
(12) Pasquier, C.; Naili, S.; Mortreux, A.; Agbossou, F.; Pelinski, L.;
Brocard, J.; Eilers, J.; Reiners, I.; Peper, V.; Martens, J. Organometallics
2000, 19, 5723.
(13) Hersh, W. H.; Klein, L.; Todaro, L. J. J. Org. Chem. 2004, 69,
7355.

1382 Organometallics, Vol. 29, No. 6, 2010
Li et al.
Scheme 3. Synthesis of Pincer Palladium Complex 2
Figure 4. Displacement ellipsoid plot of complex 1 (Et2O)
(50% probability level). Hydrogen atoms and the noncoordi-
nated Et2O molecule are omitted for clarity.
3
Synthesis of Chiral Pincer Palladium Complex 2. Follow-
ing a similar synthesis route to that reported for 1, (S)-(þ)-
indolinemethanol 9 was treated with PCl3 in the presence of
triethylamine to form the corresponding phosphorochlori-
date 8 at low temperature (Scheme 3). Without isolation and
purification, 8 was subsequently reacted with 2-iodoresorci-
nol at 110 °C to yield pincer arene ligand 7 in good yield and
acceptable purity after a simple filtration. The diastereo-
meric ratio of crude 7 in solution after filtration was roughly
estimated at 95:5 by comparing the integral values of the
large singlet at 142.3 ppm and a tiny singlet at 139.4 ppm in
the 31P NMR. Palladation of the resulting pincer aryl iodide
ligand 7 was smoothly achieved through oxidative addition
with [Pd2(dba)3 CHCl3] under mild conditions (20 °C, 16 h).
3
Complex 2 was obtained in promising yield (62%) with
excellent diastereoselectivity (dr > 99:1) after fractional
recrystallization from CH2Cl2/hexanes.
Figure 5. Molecular plot of 1 (Et2O) in the crystal, viewed
3
along the I1-Pd1 bond. Hydrogen atoms and the Et2O mole-
cule are omitted for clarity.
Besides the synthetic method mentioned above, also the
alternative synthetic approach following Bedford’s protocol
was investigated in this case. In contrast to the unsuccessful
synthesis of pincer arene ligand 6, pincer arene ligand 10
was obtained in good yield (85%) with excellent diastereo-
selectivity (dr = 96:4 estimated by 31P NMR; Scheme 4).
Subsequent metalation of modified pincer ligand 10 through
a C-H activation reaction with PdCl2(MeCN)2 occurred
very sluggishly but yielded some of the desired pincer metal
complex 11. Maximum conversion to 11 as estimated by 31P
NMR was merely about 30%. From the crude reaction
mixture no analytically pure sample of complex 11 could
be isolated.
˚
Table 1. Selected Bond Lengths [A], Angles [deg], and Torsion
Angles [deg] in 1 (Et2O)
3
Pd1-I1
2.6254(3)
2.2628(8)
1.651(3)
1.627(2)
1.598(2)
160.24(3)
79.58(9)
105.02(13)
103.90(13)
97.15(12)
120.5(2)
109.5(2)
106.8(2)
118.3(3)
-15.1(2)
Pd1-C1
1.981(3)
2.2609(8)
1.646(3)
1.630(2)
1.594(2)
176.97(9)
80.68(9)
105.64(12)
103.80(14)
96.77(12)
121.7(2)
110.3(2)
107.8(3)
119.7(3)
-11.8(2)
Pd1-P1
Pd1-P2
P1-N1
P2-N2
P1-O1
P2-O3
P1-O2
P2-O4
P1-Pd1-P2
C1-Pd1-P1
O1-P1-O2
O1-P1-N1
O2-P1-N1
P1-N1-C7
P1-N1-C10
C7-N1-C10
C9-C10-C11
Pd1-P1-O1-C2
C1-Pd1-I1
C1-Pd1-P2
O3-P2-O4
O3-P2-N2
O4-P2-N2
P2-N2-C24
P2-N2-C27
C24-N2-C27
C26-C27-C28
Pd1-P2-O3-C6
X-ray Crystal Structure of 2 (Et2O). We succeeded in
3
growing single crystals of 2, and an X-ray crystal structure
determination was carried out (Figures 6 and 7). Complex
2 (Et2O) crystallizes enantiomerically pure in the non-
3
centrosymmetric space group P1 with two independent
molecules in the unit cell. These molecules are related by
an approximate, noncrystallographic 2-fold rotation axis
roughly about the crystallographic c-axis, which is probably
the reason for the observed formation of twinned crystals
(see Experimental Section).
(160.24(3)°) derivates from 180° due to the steric strain in the
five-membered chelate rings. The ligand has the expected
pseudoequatorial orientation of the exocyclic substituents at
the phosphorus atoms (i.e., S-configuration at the P-stereo-
centers) and has two pairs of bulky diphenyl groups indepen-
dently situated in quadrants II and IV, respectively (Figure 5).
The phospholidine ring at P2 has an envelope conformation,
while the other phospholidine and pyrrolidine cycles are best
described as twisted conformations. The P-N-C (at N1 and
N2) and C-C-C (at C10 and C27) angles are 120.5(2)/
121.7(2)° and 118.3(3)/119.7(3)°, respectively.
Much like complex 1, complex 2 possesses the typical
structural features of ECE-pincer metal complexes. The
˚
Pd-P (2.2574(14)-2.2701(14) A) and Pd-C (1.981(5) and
˚
1.988(5) A) bond lengths and P-Pd-P bond angles
(161.11(6)° and 159.87(5)°) are very close to the correspond-
ing bond lengths and bond angles for complex 1 (Table 2)

Article
Organometallics, Vol. 29, No. 6, 2010 1383
Scheme 4. Synthesis of Pincer Palladium Complex 11
phosporus atoms (i.e., S-configuration at both P-stereo-
centers). One phospholidine ring within the unit cell has a
twisted conformation, and three phospholidine rings are best
described with an envelope conformation. The pyrrolidine
rings are essentially flat. The C-C-C angles at C8x and
C17x are 116.0(6)-118.2(5)°, which is comparable to the
corresponding angles in complex 1 (118.3(3)/119.7(3)°), but
the P-N-C angles of 123.0(4)-129.8(4)° are significantly
larger than in complex 1 (120.5(2)/121.7(2)°). Interestingly,
the two phenyl moieties are independently situated in quad-
rants I and III, respectively (Figure 7), which is exactly
opposite of complex 1 (Figure 5).
Catalytic Asymmetric Allylation. Since electron-deficient
ECE-pincer palladium complexes are known to be efficient
catalysts in the (asymmetric) homoallylation of aldehydes and
aldimines,5,6,14 we embarked on testing the stereocontrolling
potential of the two novel complexes 1 and 2. These tests were
carried out for the reaction of allyltributyltin with sulfoni-
mines, i.e., withprotected arylaldimines, atroom temperature
in dry DMF without additives (Table 2, reaction 1).
The data in Table 3 show that both 1 and 2 are active
catalysts in the homoallylation reaction of various aldimines
bearing N-sulfonyl protecting groups. The allyl products
were obtained in 60-81% yield, which is consistent with
previous reports.5
Figure 6. Displacement ellipsoid plot of complex 2 (Et2O) in
3
the crystal (50% probability level). Only one of two independent
molecules is shown. Hydrogen atoms and noncoordinated Et2O
molecules are omitted for clarity.
Although both 1 and 2 afforded the desired allylic product
12a in similar yields (about 60%), they exhibited very
different stereoselectivities for the same substrate. For sub-
strate 12, complex 1 gave no ee, whereas complex 2 gave
moderate ee’s of 11% (Table 3, entries 1 and 2). The mole-
cular geometries of 1 and 2 in the solid state (see Figures 5
and 7, respectively) show that in the case of complex 1 the
bulky diphenyl moieties are not oriented toward the metal
center. Differently, for complex 2, the two P-ring skeletons
form a more defined chiral pocket where the catalytic con-
version takes place. This is reflected by the observation that
no stereoselctivity has been obtained for the reaction with
benchmark substrate 12 catalyzed by 1, whereas in the case of
2 the product was formed at least with moderate ee’s. More-
over, in the latter case the nature of the substituents in both
the aldimine aryl ring and the N-sulfonyl group did have an
effect on the ee levels.
Mechanistic studies of ECE-pincer Pd-catalyzed homoally-
lation reactions by Szabo et al.,14 showed that (1) the crucial
Figure 7. Quaternion fit of the two independent residues in the
crystal structure of 2 (Et2O). Only the metal coordination plane
and the coordinated phenyl ring were used for the fit. The first
residue is drawn in red, the second residue in black. Hydrogen
atoms and Et2O molecules are omitted for clarity.
ꢀ
Pd η1-allyl moiety formed upon transmetalation of the allyl-
stannane undergoes an electrophilic attack by an aldimine at
the allyl γ-position, (2) N-coordination of the sulfonylimine
3
and the adopted slightly distorted square-planar geometries.
The molecular structure found in the solid state con-
firms that the new P-chiral ligand has two P-stereogenic
ꢀ
(14) (a) Solin, N.; Kjellgren, J.; Szabo, K. J. J. Am. Chem. Soc. 2004,
ꢀ
126, 7026. (b) Solin, N.; Wallner, O. A.; Szabo, K. J. Org. Lett. 2005, 7, 689.
(c) Wallner, O. A.; Szabꢀo, K. J. Chem. Eur. J. 2006, 12, 6976.

1384 Organometallics, Vol. 29, No. 6, 2010
Li et al.
˚
Table 2. Selected Bond Lengths [A], Angles [deg], and Torsion Angles [deg] for the Two Independent Molecules (x = 1, 2) in 2 (Et2O)
3
x = 1
x = 2
x = 1
x = 2
Pdx-Ix
2.6442(5)
2.2640(14)
1.657(5)
1.632(4)
1.596(5)
161.11(6)
80.64(16)
100.7(2)
106.9(2)
96.2(2)
111.4(4)
123.9(4)
108.9(5)
116.0(6)
7.6(4)
2.6468(5)
2.2574(14)
1.665(5)
1.636(4)
1.614(4)
159.87(5)
80.54(15)
100.1(2)
107.0(2)
95.1(2)
111.9(4)
128.5(4)
110.7(4)
116.7(6)
4.6(4)
Pdx-C1x
1.981(5)
2.2616(15)
1.657(5)
1.632(4)
1.596(5)
176.02(16)
80.48(16)
101.0(2)
107.0(2)
95.0(2)
113.4(4)
129.8(4)
109.1(5)
117.5(6)
3.4(4)
1.988(5)
2.2701(14)
1.673(5)
1.632(4)
1.595(5)
178.86(15)
80.06(16)
104.4(2)
103.5(2)
97.2(2)
110.3(4)
123.0(4)
107.3(4)
118.2(5)
-8.6(4)
Pdx-P1x
Pdx-P2x
P1x-N1x
P2x-N2x
P1x-O1x
P2x-O3x
P1x-O2x
P2x-O4x
P1x-Pdx-P2x
C1x-Pdx-P1x
O1x-P1x-O2x
O1x-P1x-N1x
O2x-P1x-N1x
P1x-N1x-C8x
P1x-N1x-C15x
C8x-N1x-C15x
C7x-C8x-C9x
Pdx-P1x-O1x-C2x
C1x-Pdx-Ix
C1x-Pdx-P2x
O3x-P2x-O4x
O3x-P2x-N2x
O4x-P2x-N2x
P2x-N2x-C17x
P2x-N2x-C24x
C17x-N2x-C24x
C16x-C17x-C18x
Pdx-P2x-O3x-C6x
Table 3. Asymmetric Homoallylation of Sulfonimines Catalyzed by P-Chiral Pincer Metal Complexes 1 and 2
a Reaction conditions: 0.15 mmol of sulfonimine, 0.18 mmol of allyltributyltin, 5 mol % of pincer Pd complex, 1 mL of DMF, room temperature, 96 h.
b Isolated yields. c Detected by chiral HPLC. d The absolute configurations of the allylic products have not been assigned.

Article
Organometallics, Vol. 29, No. 6, 2010 1385
Scheme 5. Reaction Pathway for the Pincer Pd-Catalyzed Ally-
lation of Aldimines
optically active amino alcohols as starting materials via
template synthesis. A novel P-chiral building block derived
from (S)-(þ)-indolinemethanol was reported, which offers a
nice perspective for employing this building block in further
P-chiral ligand design. Through X-ray diffraction analysis, it
was found that the new indoline-derived P-chiral building
block provides an opposite steric congestion with respect to
previously reported L-proline-derived P-chiral ligands. This
opens the possibility of making use of opposite steric con-
gestion through appropriate modifications on various posi-
tions of the L-proline skeleton.
The novel P-chiral pincer metal complexes were shown to
be active catalysts for the homoallylation of aldimines, with
complex 2 outperforming complex 1 in terms of product
enantioselectivity, which is possibly due to its more defined
chiral pocket. It has also been found that both the geometries
and the electronic properties of the aryl and the protecting
groups on the aldimine substrates have a strong influence on
both the product yield and enantioselectivity. It seemed that
good stereocontrolling requires relatively bulkier ligand
substituents in order to form a deeper chiral pocket. To
further improve enantioselectivities and yields in these reac-
tions, the synthesis of novel P-chiral pincer metal complexes
bearing well-tailored bulkier substituents is currently on-
going in our lab.
electrophile does not take place in the transition state, and (3)
the enantioselectivity of the product is predominantly deter-
mined by steric interactions in the transition state; see Scheme 5.
Accordingly, we assumed that both the geometries and electro-
nic properties of aryl and the protecting groups could have
strong influences on yield and enantioselectivity.
Substrates 13 and 14, bearing electron-withdrawing nitro
groups on meta and para positions, were tested under the
same conditions with complex 2, and the corresponding
allylic products were obtained in reasonable 75% and 81%
yields, respectively. It seemed the yields were improved due to
the enhanced electrophilicity of the sulfonimines. Interest-
ingly, for product 13a, the ee was improved to 20%, whereas it
did not improve for product 14a (Table 3, entries 3 and 4).
Besides varying the substitution pattern on the aldimine
phenyl ring, different protecting groups were also attempted
to reveal their influences on the ee values. It was found that
larger protecting groups resulted in better enantioselectivities,
which could be explained by an enhanced recognition by the
rigid chiral pockets due to the steric bulk of the protecting
groups. For instance, the ee was slightly impoved to 14.5% for
2-mesitylenesulfonimine 15 as substrate and was further im-
proved to29% for 2,4,6-triisopropylbenzenesulfonimine16 as
substrate (Table 3, entries 5 and 6).
Recently, we reported on the use of the N,N-dimethylsulfa-
moyl group as a new low molecular weight and easily remo-
vable protecting/activating group for ECE-pincer metal
complex catalyzed allylation reactions with a wide range of
functional group tolerance.15 Remarkably, application of this
protecting group increased the ee of the products to 28% and
33% for substrates 17 and 18, respectively (Table 3, entries 7
and 8), which are better than the reaults obtained with the
arylsulfonimine protecting groups (Table 3, entries 5 and 6).
Apparently, it is not only the size of the protecting groups but in
particular their electronic properties that can somehow influ-
ence enantioselectivity, as the smaller sized N,N-dimethysulfa-
moyl protecting groups resulted in higher ee’s than the con-
siderably larger triisopropylbenzenesulfonyl protecting group.
Unfortunately, although P-chiral pincer metal complexes
showed comparable activities to BINOL- and biphenan-
throl-based chiral pincer metal complexes,5 the enantioselec-
tivities were overall rather moderate. As shown in Scheme 5,
electrophilic attack of aldimines takes place at the γ-position
of an η1-allyl Pd moiety, and this position is rather far away
from the Pd center. Plausibly, good stereocontrolling re-
quires relatively bulkier substituents such as BINOL or
biphenanthrol to afford deeper chiral pockets.
Experimental Section
General Remarks. All reactions were performed under a dry
N2 atmosphere by using standard Schlenk techniques. DMF
and Et3N were distilled over CaH2 in a conventional heating
bath and were then stored under N2 at -30 °C on molecular
sieves. Toluene was freshly dried over sodium. PCl3 was freshly
distilled and stored under N2 prior to use. (S)-(þ)-Indoline-
methanol was prepared as previously reported.12 Substrates 15,
16, 17, and 18 were synthesized according to reported proce-
dures.16 All other reagents were purchased from ACROS Or-
ganics and Sigma-Aldrich Chemical Co. Inc. and used as
received. 1H NMR (400.0 MHz), 13C NMR (100.6 MHz), and
31P NMR (161.9 MHz) spectra were recorded at room tempera-
ture in CDCl3 on a Varian 400 MHz INOVA spectrometer.
Chemical shift values are reported in ppm (δ) relative to
(CH3)4Si (1H and 13C NMR) or a capillary containing 85%
H3PO4 in D2O (31P{1H} NMR). Optical rotations were re-
corded on a Perkin-Elemer 241 polarimeter at 20 °C. Flash
chromatography was performed using ACROS silica gel,
0.06-0.200 mm, pore diameter ca. 6 nm. Elemental microana-
lyses were performed by Dornis and Kolbe, Mikroanalytisches
€
Laboratorium, Mulheim a/d Ruhr, Germany. MS measure-
ments were carried out on an Applied Biosystems Voyager
DE-STR MALDI-TOF MS. Enantiomeric excess values (ee)
were measured by means of chiral-phase HPLC (Daicel Chiracel
AD or AS-H) at the Department of Organic and Molecular
Inorganic Chemistry, University of Groningen, Groningen, The
Netherlands.
General Procedure for Synthesis of P-Chiral Pincer Metal
Complexes 1 and 2. (S)-(-)-R,R-Diphenyl-2-pyrrolidinemetha-
nol (0.507 g, 2 mmol) or (S)-(þ)-indolinemethanol (0.300 g, 2
mmol) was azeotropically dried with dry toluene (3 ꢀ 2 mL) and
was suspended in dry toluene (15 mL) at -78 °C. In a separated
flame-dried Schlenk flask, PCl3 (2 mmol, 175 μL) and Et3N (4
mmol, 553 μL) were diluted in dry toluene (10 mL), and this
solution was added dropwise to the -78 °C precooled solution
of amino alcohol with vigorous stirring. After addition, the
Conclusion
In this paper, we have reported the preparation of two
novel P-chiral pincer palladium complexes, 1 and 2, by using
(16) (a) Hayashi, T.; Kawai, M.; Tokunaga, N. Angew. Chem., Int.
Ed. 2004, 43, 6125. (b) Huisman, M.; ten Have, R.; van Leusen, A. M. Synth.
Commun. 1997, 27, 945.
(15) Li, J.; Minnaard, A. J.; Klein Gebbink, R. J. M.; van Koten, G.
Tetrahedron Lett. 2009, 50, 2232.

1386 Organometallics, Vol. 29, No. 6, 2010
Li et al.
cooling bath was removed and the reaction mixture was allowed
to slowly warm to ambient temperature, at which time it was
stirred for an additional 2 h. Afterward, a solution of azeotro-
pically predried iodoresorcinol (1 mmol, 0.236 g) and Et3N (2.2
mmol, 304 μL) in toluene (5 mL) was slowly added to the
reaction mixture, which was then heated to 110 °C for 1 h. After
cooling, a white salt was rapidly filtered off over a short plug of
Celite, and the filter cake was washed with toluene (2 ꢀ 5 mL).
The combined toluene fractions were concentrated under re-
duced pressure and were thoroughly dried under vacuum to
yield an off-white solid. 31P NMR spectra indicated that the
purity of the crude products was higher than 90%, so that they
were directly used in the next step without further purification.
Thereafter, the off-white solid was redissolved in toluene (20
6.88 (d, J=7.6 Hz, 2H, PhH), 6.94 (t, J=7.6 Hz, 2H, PhH), 7.07
(d, J=7.6 Hz, 2H, ArH), 7.12 (t, J=8 Hz, 2H, PhH), 7.22-7.25
(m, 1H, ArH). 13C{1H} NMR (CDCl3, 100.6 Hz): δ 34.0, 62.5,
75.6, 107.6 (t, J=10 Hz), 114.5, 123.7, 125.6, 128.0, 130.5, 132.0,
142.4 (t, J =6.64 Hz), 156.9 (t, J =10.8 Hz). 31P{1H} NMR
(CDCl3, 161.9 Hz): δ 150.2 (s). [R]20D -470 (c 0.1, CHCl3). MS
(MALDI-TOF): m/z calcd for C24H21N2O4P2Pd 569.00 [M -
I]þ, found 569.03. Anal. Calcd for C24H21IN2O4P2Pd: C, 41.37;
H, 3.04; N, 4.02; P, 8.89. Found: C, 41.41; H, 3.01; N, 3.98; P,
8.93.
General Procedure for P-Chiral Palladium Pincer Metal Com-
plex Catalyzed Allylation of Aldimines. Allyltributylstannane
(56 μL, 0.18 mmol) was added to a mixture of sulfonimine (0.15
mmol), pincer Pd complex 1 or 2 (0.0075 mmol), and dry DMF
(1 mL). The reaction mixture was then stirred for 96 h at room
temperature and was quenched by the addition of a saturated
aqueous KF solution (1 mL). The resulting mixture was vigir-
ously stirred at room temperature for another 24 h. The crude
product was extracted with EtOAc (3 ꢀ 2 mL), and the
combined organic layers were dried over MgSO4. Analytically
pure allylic product was obtained by purification on a silica gel
column (hexanes/EtOAc, 7:3 (v/v)). The enantiomeric excess
was determined by chiral-phase HPLC (Daicel Chiracel OD-H
or AS-H columns).
mL), and this solution was added to Pd2(dba)3 CHCl3 (0.9
3
mmol, 0.932 g) in toluene (10 mL). The reaction mixture was
stirred at ambient temperature overnight in the absence of light.
The crude reaction mixture was then concentrated under re-
duced pressure, and the title complex was purified by repeating
precipitation out of a small amount of CH2Cl2 by the addition of
hexanes. Alternatively, the complex was directly subjected to
chromatography by using predried silica gel and eluent (EtOAc/
hexanes, 3:7 (v/v)).
Spectral Data for Crude Product of Compound 3. Yield:
quantitative (0.805 g). 1H NMR (CDCl3, 400 MHz): δ 1.40
(m, 2H, CH2), 1.53 (m, 4H, CH2), 1.71 (m, 2H, CH2), 2.85
(apparent t, J=8.4 Hz, 2H, NCH2), 3.15 (m, 2H, NCH2), 4.11
(m, 2H, NCH), 6.18 (d, J=6.8 Hz, 2H, ArH), 6.85 (t, J=7.2 Hz,
1H, ArH), 7.20 (t, J=7.8 Hz, 4H, PhH), 7.22-7.38 (m, 8H,
PhH), 7.43 (d, J=6.4 Hz, 4H, PhH), 7.55 (d, J=7.2 Hz, 4H,
PhH). 13C{1H} NMR (CDCl3, 100.6 Hz): δ 24.8, 30.73, 47.9 (t,
J=9.0 Hz), 69.8, 94.5 (t, J=4.0 Hz), 105.8 (t, J=9.6 Hz), 125.5,
126.3, 127.8, 128.5, 128.9, 129.0, 129.2, 129.4, 129.7, 133.5, 139.4
(t, J=4.0 Hz), 143.9, 146.5. 31P{1H} NMR (CDCl3, 161.9 Hz): δ
141.1 (s).
N1-[1-(4-Nitrophenyl)-3-butenyl]-2,4,6-trimethyl-1-benze-
nesulfonamide, 15a. 1H NMR (CDCl3, 400 MHz): δ 2.21 (s, 3H,
Me), 2.43 (t, J=6.8 Hz, 2H, CH2CHdCH2), 2.48 (s, 6H, Me),
4.40 (q, J=7.2 Hz, 1H, CH=CH2), 5.08-5.12 (apparent t, 2H,
CHdCH2), 5.30 (br s, 1H, NH), 5.47-5.54 (m, 1H, ArCH-
(NH)), 6.78 (s, 2H, mesityleneH), 7.22 (d, J=8 Hz, 2H, ArH),
7.94 (d, J=8 Hz, 2H, ArH). 13C NMR (CDCl3, 100.6 MHz): δ
21.1, 23.2, 42.0, 56.7, 120.8, 123.6, 127.7, 132.0, 132.4, 133.9,
139.1, 143.0, 147.3, 148.1. Anal. Calcd for C19H22N2O4S: C,
60.94; H, 5.92; N, 7.48; S, 8.56. Found: C, 60.99; H, 5.88; N,
7.45; S, 8.51. The enantiomeric excess of 15a was determined by
chiral-phase HPLC (Daicel Chiracel AD, hexane/iPrOH, 9:1
(v/v), flow rate 1.0 mL/min): major enantiomer tR=13.4 min,
minor enantiomer tR=11.0 min.
Spectral Data for Complex 1. 1 was obtained as a light yellow
solid (0.497 g, 0.55 mmol). Yield: 55%. The single crystals were
grown by slow diffusion of diethyl ether into a solution of
1
CH2Cl2. H NMR (CDCl3, 400 MHz): δ 1.44 (m, 2H, CH2),
N1-[1-(4-Nitrophenyl)-3-butenyl]-2,4,6-triisopropyl-1-benzene-
sulfonamide, 16a. 1H NMR (CDCl3, 400 MHz): δ 1.13 (d, J=6.8
1.79 (m, 4H, CH2), 2.18 (m, 2H, CH2), 3.33 (apparent t, J=9.2
Hz, 2H, NCH2), 4.26 (m, 2H, NCH2), 4.79 (m, 2H, NCH), 6.26
(d, J=7.6 Hz, 2H, ArH), 6.93 (t, J=8.0 Hz, 1H, ArH), 7.26 (t, J=
8 Hz, 4H, PhH), 7.32-7.40 (m, 8H, PhH), 7.47 (d, J=7.2 Hz,
4H, PhH), 7.61 (d, J = 6.8 Hz, 4H, PhH). 13C{1H} NMR
(CDCl3, 100.6 Hz): δ 25.8, 30.7, 48.0 (t, J=9.6 Hz), 71.0, 94.4
(t, J=3.3 Hz), 106.8 (t, J=9.5 Hz), 126.5, 127.3, 127.8, 128.1,
128.3, 128.4, 128.6, 128.7, 129.7, 141.4 (t, J=3.7 Hz), 143.7,
157.1 (t, J=11 Hz). 31P{1H} NMR (CDCl3, 161.9 Hz): δ 160.3
(s). [R]20D -83, (c 0.1, CHCl3). MS (MALDI-TOF): m/z calcd
for C40H37N2O4P2Pd 777.13 [M - I]þ, found 777.11; Anal.
Calcd for C40H37IN2O4P2Pd: C, 53.09; H, 4.12; N, 3.10; P, 6.84.
Found: C, 53.12; H, 4.16; N, 3.07; P, 6.82.
Spectral Data for Crude Product of Compound 7. Yield:
quantitative (0.601 g). 1H NMR (CDCl3, 400 MHz): δ 3.10
(d, J=7.2 Hz, 1H, CH2), 3.14 (d, J=7.0 Hz, 1H, CH2), 3.18 (d,
J=8.4 Hz, 1H, CH2), 3.26 (d, J=8.8 Hz, 1H, CH2), 3.65 (m, 4H,
OCH2), 4.30 (apparent t, J=8.8 Hz, 2H, NCH), 6.70 (d, J=7.6
Hz, 2H, PhH), 6.78 (d, J=7.0 Hz, 2H, PhH), 6.88 (t, J=7.7 Hz,
2H, PhH), 7.15 (d, J=7.2 Hz, 2H, ArH), 7.18 (t, J=7.8 Hz, 2H,
PhH), 7.24-7.28 (m, 1H, ArH). 13C{1H} NMR (CDCl3, 100.6
Hz): δ 34.2, 62.1, 74.5, 105.8 (t, J=8 Hz), 112.4, 114.5, 121.7,
123.4, 125.4, 127.9, 130.1, 132.5, 141.7 (t, J=6.0 Hz), 148.9.
31P{1H} NMR (CDCl3, 161.9 Hz): δ 142.3 (s).
i
i
Hz, 7H, PrH), 1.21-1.24 (m, 14H, PrH), 2.45-2.52 (m, 2H,
CH2CHdCH2), 4.60 (q, J=5.2 Hz, 1H, CHdCH2), 4.99 (d, J=
4.4 Hz, 1H, NH), 5.10-5.16 (apparent t, 2H, CHdCH2),
5.21-5.60 (m, 1H, ArCH(NH)), 7.06 (s, 2H, (iPr)3ArH), 7.27
(d, J=8.4 Hz, 2H, ArH), 8.00 (d, J=8.4 Hz, 2H, ArH). 13C
NMR (CDCl3, 100.6 MHz): δ 9.3, 13.9, 23.8, 25.0, 27.5, 29.3,
30.0, 34.4, 42.2, 56.5, 120.7, 123.7 (d, J=19 Hz), 127.9, 132.4,
133.2, 147.4, 148.4, 150.2, 153.5. Anal. Calcd for C25H34N2O4S:
C, 65.47; H, 7.47; N, 6.11; S, 6.99. Found: C, 65.51; H, 7.55; N,
6.13; S, 7.01. The enantiomeric excess of 16a was determined by
chiral-phase HPLC (Daicel Chiracel AD, hexane/iPrOH, 9:1
(v/v), flow rate 1.0 mL/min): major enantiomer tR =9.0 min,
minor enantiomer tR=7.1 min.
N1-[1-(3-Nitrophenyl)-3-butenyl]-N,N0-dimethylsulfamoyla-
1
mide, 17a. H NMR (CDCl3, 400 MHz): δ 2.53-2.60 (m, 8H,
NMe2 þ CH2CHdCH2), 4.54 (q, J=6.0 Hz, 1H, CH=CH2),
4.81 (d, J=5.2 Hz, 1H, NH), 5.17-5.21 (m, 2H, CHdCH2), 5.63
(m, 1H, ArCH(NH)), 7.54 (t, J=7.6 Hz, 1H, ArH), 7.54 (d, J=
7.2 Hz, 1H, ArH), 8.13 (d, J=7.2 Hz, 1H, ArH), 8.20 (s, 1H,
ArH). 13C NMR (CDCl3, 100.6 MHz): δ 37.8, 42.1, 57.0, 120.5,
121.8, 122.9, 129.8, 132.6, 133.2, 144.3, 148.6. Anal. Calcd for
C12H17N3O4S: C, 48.15; H, 5.72; N, 14.04; O, 21.38; S, 10.71.
Found: C, 48.11; H, 5.77; N, 14.40; S, 10.74. The enantiomeric
excess of 17a was determined by chiral-phase HPLC (Daicel
Chiracel AS-H, hexane/iPrOH, 9:1 (v/v), flow rate 1.0 mL/min):
major enantiomer tR =23.1 min, minor enantiomer tR =26.0
min.
Spectral Data for Complex 2. 2 was obtained as an off-white
solid (0.431 g, 0.62 mmol). Yield: 62%. The single crystals were
grown by slow diffusion of hexanes into a solution of diethyl
ether. 1H NMR (CDCl3, 400 MHz): δ 3.09 (d, J=6.8 Hz, 1H,
CH2), 3.13 (d, J=7.6 Hz, 1H, CH2), 3.26 (d, J=9.2 Hz, 1H,
CH2), 3.30 (d, J=8.4 Hz, 1H, CH2), 4.34 (t, J=8.4 Hz, 2H,
NCH), 4.83-4.95 (m, 4H, OCH2), 6.77 (d, J=8 Hz, 2H, PhH),
N1-[1-(4-Nitrophenyl)-3-butenyl]-N,N0-dimethylsulfamoyla-
1
mide, 18a. H NMR (CDCl3, 400 MHz): δ 2.50-2.54 (m, 2H,
CH2CHdCH2), 2.58-2.59 (m, 6H, NMe2), 4.52 (q, J=6.8 Hz,

Article
Organometallics, Vol. 29, No. 6, 2010 1387
Table 4. Selected Crystallographic Data for Complexes 1 (Et2O)
3
temperature of 150 K up to a resolution of (sin θ/λ)max=0.65
-1. Integration of the reflections was performed with
˚
A
and 2 (Et2O)
3
1 (Et2O)
EvalCCD.17 The structures were solved with automated Patter-
son methods (program DIRDIF-9918 for 2 (Et2O)) or direct
2 (Et2O)
3
3
3
methods (SHELXS-9719 for 1 (Et2O)). Refinement was per-
formula
C
40H37IN2O4P2Pd
0.85(C4H10O)
C
24H21IN2O4-
3
3
formed with SHELXL-9719 against F2 of all reflections. Non-
hydrogen atoms were refined with anisotropic displacement
parameters. All hydrogen atoms were introduced in calculated
positions and refined with a riding model. Geometry calcula-
tions and checking for higher symmetry was performed with the
P2Pd C4H10
O
3
fw
967.96
770.79
colorless
cryst color
cryst size [mm3]
cryst syst
space group
colorless
0.39 ꢀ 0.21 ꢀ 0.12
monoclinic
P21 (no. 4)
13.5613(5)
9.5680(2)
17.5560(9)
90
108.878(2)
90
2155.43(14)
2
1.491
40 685/9826
1.265
multiscan
0.42-0.86
498/4
0.0293/0.0577
0.0428/0.0618
-0.027(12)
1.035
0.63 ꢀ 0.39 ꢀ 0.09
triclinic
PLATON20 program. In 1 (Et2O) the diethyl ether solvent
P1 (no. 1)
10.3714(3)
11.8544(2)
13.0540(3)
89.198(1)
84.462(2)
68.804(1)
1489.01(6)
2
1.719
18 348/11 751
1.807
multiscan
0.41-0.85
708/3
3
˚
a [A]
molecule was refined with a partial occupancy of 0.85. The
crystal of 2 (Et2O) was non-merohedrally twinned with a 2-fold
˚
b [A]
˚
c [A]
3
rotation about hkl (001) as twin operation. This twin law was
taken into account during intensity integration and the HKLF5
structure refinement.21 The twin fraction refined to 0.5361(6).
Further details about the crystal structure determinations are
given in Table 4.
R [deg]
β [deg]
γ [deg]
3
˚
V [A ]
Z
Dx [g/cm3]
reflns measd/unique
μ [mm-1
abs corr
]
Acknowledgment. This work was financially supported
by University Utrecht and was supported in part (M.L.,
A.L.S.) by the Council for the Chemical Sciences of The
Netherlands Organization for Scientific Research (CW-
NWO). Prof. Dr. Adriaan J. Minnaard and Mrs. Theo-
dora Tiemersma at University of Groningen are greatly
thanked for their kind help with chiral HPLC measure-
ments.
abs corr range
params/restraints
R1/wR2 [I > 2σ(I)]
R1/wR2 [all reflns]
Flack x param22
S
0.0298/0.0768
0.0319/0.0786
0.007(15)
1.102
3
˚
res density [e/A ]
-0.90/0.71
-0.98/1.05
Supporting Information Available: CIF files giving crystal-
lographic data for complexes 1 and 2. This material is available
free of charge via the Internet at http://pubs.acs.org.
1H, CH=CH2), 5.01 (d, J=6.4 Hz, 1H, NH), 5.13-5.18 (m, 2H,
CHdCH2), 5.60-5.70 (m, 1H, ArCH(NH)), 7.48 (d, J=6.8 Hz,
2H, ArH), 8.20 (d, J=6.8 Hz, 2H, ArH). 13C NMR (CDCl3,
100.6 MHz): δ 37.9, 42.1, 57.1, 120.6, 124.0, 127.8, 132.5, 147.6,
149.4. Anal. Calcd for C12H17N3O4S: C, 48.15; H, 5.72; N,
14.04; O, 21.38; S, 10.71. Found: C, 48.23; H, 5.70; N, 14.11; S,
10.64. The enantiomeric excess of 18a was determined by chiral-
phase HPLC (Daicel Chiracel AS-H, hexane/iPrOH, 9:1 (v/v),
flow rate 1.0 mL/min): major enantiomer tR=25.3 min, minor
enantiomer tR=30.1 min.
(17) Duisenberg, A. J.; Kroon-Batenburg, L. M.; Schreurs, A. M. J.
Appl. Crystallogr. 2003, 36, 220.
(18) Beurskens, P. T.; Admiraal, G.; Beurskens, G.; Bosman, W. P.;
Garcia-Granda, S.; Gould, R. O.; Smits, J. M.; Smykalla, C. The
DIRDIF99 program system; Technical Report of the Crystallography
Laboratory, University of Nijmegen, The Netherlands, 1999.
(19) Sheldrick, G. M. Acta Crystallogr. 2008, A64, 112.
(20) Spek, A. L. J. Appl. Crystallogr. 2003, 36, 7.
(21) Herbst-Irmer, R.; Sheldrick, G. M. Acta Crystallogr. 1998, B54,
443.
X-ray Crystal Structure Determinations. X-ray reflections
˚
were measured with Mo KR radiation (λ = 0.71073 A) on a
Nonius KappaCCD diffractometer with rotating anode at a
(22) Flack, H. D. Acta Cryst. 1983, A39, 876.