N-benzyl-N-phosphino-tert-butylsulfinamide and its coordination modes with Ir(I), Cu(I), Pd(II), and Pt(II): P,S or P,O?

Article abstract of DOI:10.1021/om200217j

Here we studied the coordination mode of optically pure N-benzyl-N-phosphino-tert-butylsulfinamide (1a) toward Ir(I), Cu(I), Pd(II), and Pt(II). Ligand 1a can work as a hemilabile bidentate P,O or P,S or monodentate P ligand depending on the nature of the metal and its electronic and steric environment. X-ray analysis confirmed that soft metals, such as Ir or Pt, favor the P,S coordination mode, while harder ones, such as Cu(I), favor the formation of P,O fivemembered-ring chelates. Finally, analysis of the resonances of the methylene and t-Bu groups in coordinated 1a allowed us to predict a P,S coordination mode for the corresponding (1a)PdCl₂ complex 7.

Full text of DOI:10.1021/om200217j

ARTICLE
pubs.acs.org/Organometallics
N-Benzyl-N-phosphino-tert-butylsulfinamide and Its Coordination
Modes with Ir(I), Cu(I), Pd(II), and Pt(II): P,S or P,O?
Thierry Achard,† Jordi Benet-Buchholz,‡ Eduardo C. Escudero-Adꢀan,‡
Antoni Riera,*,† and Xavier Verdaguer*,†
†Unitat de Recerca en Síntesi Asimꢁetrica (URSA-PCB), Institute for Research in Biomedicine (IRB Barcelona),
and Departament de Química Orgꢁanica, Universitat de Barcelona, c/Baldiri Reixac 10, E-08028 Barcelona, Spain
‡Institute of Chemical Research of Catalonia (ICIQ), Avinguda Països Catalans 16, 43007 Tarragona, Spain
S Supporting Information
b
ABSTRACT: Here we studied the coordination mode of
optically pure N-benzyl-N-phosphino-tert-butylsulfinamide
(1a) toward Ir(I), Cu(I), Pd(II), and Pt(II). Ligand 1a can
work as a hemilabile bidentate P,O or P,S or monodentate P
ligand depending on the nature of the metal and its electronic
and steric environment. X-ray analysis confirmed that soft
metals, such as Ir or Pt, favor the P,S coordination mode, while
harder ones, such as Cu(I), favor the formation of P,O five-
membered-ring chelates. Finally, analysis of the resonances of
the methylene and t-Bu groups in coordinated 1a allowed us to
predict a P,S coordination mode for the corresponding
(1a)PdCl2 complex 7.
’ INTRODUCTION
We also reported a series of rhodium(I) complexes with PNSO
ligands of types III and IV.6 These complexes are efficient catalysts
in intra- and intermolecular [2þ2þ2] cycloaddition reactions,
giving high yields and moderate enantiomeric excesses of
cycloadducts.7 Depending on the electronic environment around
the metal center, PNSO ligands work either as P,O ligands (III) or
as P,S chelating ligands (IV).
Given that only a few examples of phosphorusꢀsulfoxide
bidentate ligands have been reported,8ꢀ10 and considering the
success achieved with the use of PNSO complexes in the asym-
metric reaction using Co and Rh(I), here we studied the coordina-
tion mode of ligand 1a toward other metals. For this purpose, we
performed a systematic study of the coordination capacity of ligand
1a to iridium(I), copper(I), and palladium(II) precursors. The
structures of PNSOꢀmetal complexes [Ir(1a)2]OTf (2b),
[Cu(1a)2]OTf (4), [π-allyl-Pd(1a)Cl] (6), and [(1a)PtCl2] (8)
have been characterized by X-ray analysis.
Hemilabile phosphine-based ligands were introduced in the
1970s.1 These hybrid ligands of general formula P,Z have two
groups, P (phosphorus) and Z (heteroatom), which exhibit
different donor properties toward the metal center. When
coordinated to a transition metal, the phosphorus atom provides
a soft donor site that binds strongly to the metal; in contrast the
hard site (Z) acts as a labile group that binds weakly to the metal.
This equilibrium between the openꢀclosed forms creates a free
coordination site around the metal (see type A complexes,
Scheme 1). A number of labile groups have been reported in
the literature, and in general, oxygen-based substituents, such
as ethers, esters, and phosphine oxides, are among the most
labile.1a,b Some hybrid ligands containing nitrogen, sulfur, or
CdC functionalities also exhibit hemilabile properties.2
Recently, in our search for novel valuable chiral ligands, we
developed a new family of N-phosphine sulfinamide (PNSO)
ligands (I). This new class of chiral bidentate ligands represents
an efficient way of combining the easily accessible sulfur chirality3
with the coordinating capacity of phosphorus. Ligands I are
modular and can be conveniently assembled in three steps from
the commercially available enantiopure tert-butylsulfinamide or
p-tolylsulfinamide and an aldehyde, and a chlorophosphine.
Some of these ligands, such as 1a and 1b, have proved highly
efficient in the intermolecular asymmetric PausonꢀKhand reac-
tion, acting as bidentate P,S ligands (Figure 1).4,5 From these
studies, we reported the first example of a chiral sulfur atom
coordinated to a cobalt center (II).
’ RESULTS AND DISCUSSION
Synthesis of Iridium Complexes. Iridium(I) complexes are
highly efficient in catalytic asymmetric hydrogenation, and many
chiral ligands have been developed by incorporating different
types of chirality. However, only a few examples have been
Received: March 10, 2011
Published: May 05, 2011
r
2011 American Chemical Society
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Scheme 1. Possible Coordination Modes of the PNSO Ligand in Monometallic Complexes
the metal ion could be affected by the nature of the other ligands in
the coordination sphere.14b,15 In contrast, the monodentate DMSO
provides P,O and P,S bonding through cationic Rh(I) and Ir(I).11a
IR spectroscopy is a suitable tool to distinguish whether OꢀM or
SꢀM bonding occurs in sulfoxide metal complexes.9a,14c However,
as previously reported for rhodium complexes III and IV, no
diagnostic bands were observed for complexes 2a,b.16
Crystal Structure of Complex 2b. Finally, the P,S coordina-
tion mode was unambiguously indentified by X-ray analysis of a
suitable crystal obtained by layering Et2O over a CHCl3 solution
of 2b (Figure 2). To our knowledge, this represents a rare
example of a sulfinyl group coordinated to Ir(I)17 and the first
iridiumꢀPNSO complex isolated.
Figure 1
In the crystal structure of 2b (Figure 2), the Ir(I) center
presented a slightly distorted square-planar geometry, with the
two phosphorus atoms (and sulfur) in a cis arrangement, in close
analogy with other reported PꢀS, PꢀN, or PꢀO ligands.15ꢀ18
This X-ray structure is similar to the X-ray structure reported for
rhodium complex IV.6 The Ir, S, N, and P atoms adopt a planar
double-diamond disposition where the metal center is the
connection point of two identical four-membered rings. The
complex shows a C2 symmetry axis in the coordination plane of
the metal. The oxygen atoms and the t-Bu groups of the
sulfinamide are in anti position to each other to minimize steric
and electronic interactions. In this respect, the IrꢀS (2.284 and
2.281 Å) distances observed fall in the long range for an
S-bonding mode and are longer than the monodentate DMSO
ligand.14,11Furthermore, the SꢀO length, 1.469 and 1.466 Å,
fits the type of S-coordination observed for metal complexes
(average in several complexes 1.473 Å).14c
Determination of P,S or P,O Coordination of Ligand PNSO
1a in Complex 3. Alternatively, we attempted to synthesize
(PNSO)IrI(COD) in order to define the coordination mode of
PNSO ligand 1a when the metal center is more acidic. To this
end, ligand 1a (1 equiv) was added to a solution of cationic
iridium after chloride abstraction with AgOTf in dry THF, and
reaction mixture was stirred for 30 min. At this point 31P NMR
showed two singlets at 46 and 108 ppm respectively in 1:3 ratio
and total consumption of ligand 1a (Figure 3a). Layering the
reaction mixture overnight with Et2O then provided yellow
crystals. 31P NMR of this solid showed a signal at 49 ppm, which
is characteristic of the bis-PNSO complex 2a. When performed
under different conditions (varying solvent, both reaction time
and temperature), the reaction invariably gave of a mixture of 2a
and 3 in a different ratio.
reported for chiral sulfoxide groups bound to an iridium(I) metal
center.11
Synthesis of Bis-PNSO Iridium(I) Complexes 2a and 2b.
Optically pure PNSO ligand (þ)-(R)-1a was synthesized from
commercially available (þ)-tert-butylsulfinamide in an 80%
overall yield.7 [IrCl(COD)]2 was treated with AgOTf in dichlor-
omethane. The resulting solution was added to a solution of
ligand 1a (two equivalents) and left to stir for 24 h at room
temperature (Scheme 2). The resulting yellow mixture was
poured over Et2O and stirred to provide an air-stable yellow
precipitate (2a). Complex 2b was prepared similarly using AgBF4
in THF. The 1H NMR resonance for the t-Bu group (1.50 ppm)
of complex 2a is similar to those reported for rhodium complex
IV (1.47 ppm). Although the 31P NMR value (singlet at 45.9
ppm) of complex 2a is more shielded compared to complex IV
(doublet at 69.5 ppm), it is still consistent with a P,S coordination
(Scheme 2).
In complexes containing a sulfur atom bound to the metal, the
hydrogen atoms in β-position to sulfur undergo downfield
1
chemical shifts.12 In the H NMR spectra of complexes 2a,b,
the t-Bu signal was shifted downfield upon complexation (1.50
ppm).13 The Δδ 0.58ꢀ0.59 ppm is quite large but still consistent
for S-bonded complexes. The observed Δδ is slightly greater in
bis-PNSO iridium(I) than in those of rhodium(I), suggesting a
stronger S-bonding interaction in the former. In contrast,
methylene protons were shielded upon complexation, with a
Δδ of 0.15ꢀ0.25 ppm, similar to those observed for the Rh(I)-
III complexes (L = cod; nbd; 0.11ꢀ0.17 ppm).
The ambident character of the sulfoxide group for DMSO has
been widely studied. Initial trends showed a large preference to
coordinate “harder” metals through the oxygen atom and “softer”
metals via the sulfur center.14 However, the “hard/soft” character of
Not surprisingly, only a few X-ray structures of iridium(I)
complexes with O-bonded monodentate sulfoxide have been
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Scheme 2. Synthesis of Cationic Iridium(I) Complexes with Ligand 1a
Table 1. Selected Bond Lengths [Å] and Angles [deg] for 2b
with Estimated Standard Deviations in Parentheses
[(RS,RS)]-2b
Ir(1)ꢀP(2)
Ir(1)ꢀP(1)
Ir(1)ꢀS(1)
Ir(1)ꢀS(2)
O(1)ꢀS(1)
O(2)ꢀS(2)
S(1)ꢀC(20)
S(2)ꢀC(43)
2.2530(7)
2.2566(6)
2.2810(6)
2.2842(5)
1.468(2)
1.466(2)
1.837(3)
1.848(3)
P(2)ꢀIr(1)ꢀP(1)
P(2)ꢀIr(1)ꢀS(1)
P(1)ꢀIr(1)ꢀS(1)
P(2)ꢀIr(1)ꢀS(2)
P(1)ꢀIr(1)ꢀS(2)
S(1)ꢀIr(1)ꢀS(2)
S(1)ꢀN(1)ꢀP(1)
P(1)ꢀN(1)ꢀS(1)-O(1)
107.92(2)
175.56(3)
71.12(2)
71.17(2)
178.73(3)
109.85(2)
101.57(10)
ꢀ124.21(14)
dissociative mechanism (Scheme 3). This may involve first the
formation of P-coordinated complex A, which evolves to give P,
O complex B. Then ligand exchange involving the cycloctadiene
with a second molecule of ligand 1a leads to the formation of bis-
PNSO complexes. Indeed, bis-P complex C could generate P,O
complex E or P,S complex D. Coordination of the second labile
moiety on complex D releases the cyclooctadiene and leads to
the formation of the desired bis-P,S complex. The second route
supports the formation of hybrid P,OꢀP,S complex G in
equilibrium with bis-P,O complex F. Then complex F might
evolve by equilibration to the desired more stable bis-P,S
complex as a result of the hemilabile character of the sulfinyl
group. Other equilibria between P,O and P,S coordination could
occur, but the formation of the bis-P,S complex seems to be
irreversible under these reaction conditions.
Figure 2. ORTEP plot for X-ray structure of 2b with thermal ellipsoids
shown at 50% probability. Hydrogen atoms and counterion were
omitted for clarity.
reported in the literature, while none have been described for a
bidentate sulfoxide ligand.18 The reaction mixture of freshly
prepared iridium (2a and 3) or rhodium (III and IV) complexes
was analyzed by 31P NMR and compared with pure bis-PNSO 2a
and IV, respectively (Figure 3). In spectrum (a), the strong shift
to lower field (Δδ 48 ppm) compared to the S-bonded complex
2a (Δδ ꢀ11 ppm) suggested a P,O coordination for complex 3
(Figure 3a,b).19 Another strong indication of the O-bonding was
that similar deshielding was observed for the corresponding P,O
Rh(COD) complex III (Δδ 56.5 ppm) [see Figure 3c,d].20
After a few hours in THF, the mixture of 2a and 3 (Figure 3a)
31P NMR monitoring showed that, in the absence of free
ligand, a THF solution of complexes 2a and 3 yielded irreversibly
the formation of the bis-P,S complex 2a along with [Ir(cod)2]þ
(Figure 3). It is known that coordinating solvents cleave weak
metalꢀheteroatom bonds and so afford other open geometries.21
The situation could be more complex, involving more equilibrium
steps, which could allow the formation of bimetallic species. After
recombination, these species could afford two monometallic bis-
homoligated P,S and bis-cod complexes.22
1
was totally converted into the cationic bis-PNSO 2a. The H
NMR spectrum of the final mixture showed signals correspond-
ing to complex 2a but also to Ir(I) cationic bis-cod complex. No
1
other species were observed by either H or 31P NMR. The
formation of the P,S complex 2a and bis-cod Ir(I) appeared to be
irreversible under these reaction conditions. In the case of
dimeric Rh(I) complexes, the equilibrium was also shifted toward
the P,S coordination mode, but the process was much slower.
Proposed Mechanism for the Formation of Mono- and
Bis-PNSO Complexes. The formation of mono- and bis-PNSO
Ir(I) and Rh(I) complexes could be explained by an associative/
Synthesis of Copper Complexes. Copper complexes derived
from N-tert-butylsulfinylimine efficiently catalyze the DielsꢀAlder
reaction of cyclopentadiene with N-acryloyl oxazolidinone with
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Figure 3. 31P NMR spectrum of Rh complexes III-(cod) and IV and Ir complexes 2a and 3.
Scheme 3. Proposed Mechanism for the Formation of Mono- and Bis-PNSO Complexesa
a Counterion was omitted for clarity.
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Scheme 4. Synthesis of Copper(I) Complex with Ligand 1a
very high stereoselectivity.23 These complexes provide access to
synthesize complex molecules such as spirocyclic gymnodimine.23b
Some examples of O-bonded DMSO to a copper center have been
reported.14b These complexes are based mainly on copper(II), and
only one example of a copper(I) complex has been described to
date.24 These complexes exhibit several coordination modes, such
as square planar, distorted square pyramidal, octahedral, or trigonal.
Since various coordinating elements are present in PNSO ligands,
we addressed the behavior of these ligands toward a copper center.
We first focused on copper(II) complexes and began by mixing
ligand 1a with copper acetate in ethanol. We then followed the
reaction profile by 31P NMR and TLC. No complexation occurred
in ethanol, and ligand 1a was recovered unchanged. Switching the
copper source to CuCl2 gave no reaction either. Neither was
complexation of this ligand achieved when the reaction was
performed under different conditions (varying solvent, both reac-
tion time and temperature). These disappointing results prompted
us to shift our attention to copper(I), in spite of the knowledge that
sulfoxides are not efficient ligands for Cu(I) species. Thus, copper-
(I) triflate toluene complex was treated with ligand 1a in THF for a
few hours. The 31P NMR of the mixture showed only one singlet at
δ 18.3 ppm. THF volume was reduced to half, and the mixture was
left at 0 °C for 12 h, affording a white crystalline solid in 90% yield.
The 1H NMR showed a t-Bu signal at 1.03 ppm and methylene
protons as doublets at δ 4.62 and 4.74 ppm, respectively. With
regard to the uncoordinated ligand 1a, we observed a small
downfield shift for the t-Bu signal (Δδ 0.1 ppm), both methylene
protons were more deshielded (Δδ 0.16 and 0.14), and the
doublet of doublets was converted to two well-defined doublets.
These observations suggested O-coordination for the isolated
copper complex. Attempts to synthesize a mono-PNSO complex
under various conditions were unsuccessful, providing only the
bis-PNSO mononuclear complex 4, even when less than one
equivalent of ligand was used.
Figure 4. ORTEP plot for X-ray structure of 4 with thermal ellipsoids
shown at 50% probability. Hydrogen atoms, OTfꢀ, and CHCl3 were
omitted for clarity.
Table 2. Selected Bond Lengths [Å] and Angles [deg] for 4
with Estimated Standard Deviations in Parentheses
[(RS,RS)]-4
Cu(1)ꢀO(1)
Cu(1)ꢀO(2)
Cu(1)ꢀP(1)
Cu(1)ꢀP(2)
O(1)ꢀS(1)
O(2)ꢀS(2)
S(1)ꢀC(20)
2.1768(11)
2.1572(12)
2.2084(4)
2.2135(4)
1.5032(12)
1.5010(13)
1.8403(15)
S(2)ꢀC(43)
1.8487(16)
88.08(5)
O(2)ꢀCu(1)ꢀO(1)
O(2)ꢀCu(1)ꢀP(1)
O(1)ꢀCu(1)ꢀP(1)
O(2)ꢀCu(1)ꢀP(2)
O(1)ꢀCu(1)ꢀP(2)
P(1)ꢀCu(1)ꢀP(2)
O(2)ꢀS(2)ꢀN(2)ꢀP(2)
114.66(3)
88.16(3)
87.78(3)
110.16(3)
151.997(16)
26.24(10)
Cu(I) center presents a strong distorted square-planar pyramidal
geometry with an “empty coordination” site between the two
phosphorus atoms and an oxygen atom in a pseudo apical
position. The PꢀCuꢀP angle responsible for this strong distor-
tion is quite large (152.0°) to accommodate the severe steric
repulsions between the t-Bu and phenyl group of the phosphine.
Similar behavior was observed for the mixed bidentate phosphi-
neꢀphosphine oxide ligand bound to a Cu(I) center. Samuelson
reported a Cu complex that adopts a strong distorted tetrahedral
geometry (PꢀCuꢀP: 119°), and Charette described a Cu
complex with an angle (PꢀCuꢀP: 133°) that is between
Samuleson’s complex and complex 4.28
The Cu, O, S, N, and P atoms adopted a “spiro-like” disposition
where the metal center was the connection point of two identical
five-membered rings. The CuꢀO (2.157 and 2.177 Å) distances
observed are in the same range as those of monosulfoxide copper
complexes and are located between O-bonding Cu(I) (2.223 Å) and
Cu(II) (2.205Å) complexes.14,11 The O-bonding mode to the metal
led to a lengthening of the SdO bond (1.501(1) and 1.503(1) Å) in
comparison with noncoordinated DMSO 1.493(av) Å. These SꢀO
bonds are shorter than the one reported for monosulfoxide and
N-tert-butylsulfinyl imine copper complexes; this observation could
be attributable to the steric and cyclic constraints linked to the
bidentate properties of the PNSO ligand.14b,23c
In contrast to the bis-sulfoxide ligand, we did not observe PNSO
acting as a bridging ligand to form di- or polynuclear species.27a,b
Indeed BPSP-type ligands have been described to act as μ2-O-
bridging ligands for copper to form polymeric cations [Cu(BPSP)2-
(ClO4)]nþ intercalated by n [ClO4]ꢀ,25 and S-bridging ligands with
P and S atoms in cis positions for [{cis-PtCl2(PEt3)}2(1,2-bis-
(phenylsulfinyl)ethane)] bimetallic complexes.26 Elmann reported
an X-ray structure of a CuCl2-bis(sulfinyl)imidoamidine (SIAM)
complex with a M2L4-helicate structure, in which each ligand is
coordinated to a copper center via the oxygen atom of the sulfinyl
group.23c
Crystal Structure of Complex 4. Suitable crystals for X-ray
analysis were obtained by layering hexane over a CH2Cl2 solution
of 4. The X-ray analysis confirmed the P,O coordination mode to the
Cu(I) center (Figure 4), and the preference of sulfoxide for
27
ꢀ
ꢀ
O-bonding in hard acid metal ion complexes such as copper or tin.
The structure displays a C2 symmetry axis, which coincides
with intersection of the PꢀCuꢀP and OꢀCuꢀO planes. The
Synthesis of Palladium and Platinum Complexes. Pd(II) is
commonly considered a “soft” metal displaying a strong pre-
ference for soft ligands; for example [PdI4]2ꢀ was found to be
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Scheme 5. Synthesis of π-Palladium Complex 6
Figure 5. Diastereomers of (allyl)PdPCl-6. Chirality descriptors as-
sume that the priorities are allyl (first) > Cl > P and the centroid of the
allyl is out of the plane in the direction of the central carbon atom.
more stable than [PdCl4]2ꢀ. However, Pd(II) also forms “stable”
complexes with “hard” ligands, such as water [Pd(H2O)4]2þ 29
.
Figure 6. ORTEP diagram of (η3-allyl)Pd(PNSO) (6). The enantio-
mer found in the solid state has the (RS,SPd) absolute configuration.
In sulfoxide palladium complexes, both O- and S-coordination
have been reported, but the sulfoxide group is found mostly
S-bonded to the metal center.30,14b To this end, we studied the
capacity and coordination mode of PNSO ligands in palladium
complexes.
The 1H NMR and 31P NMR spectra for the allyl complex 6 at
room temperature showed broad signals due to their dynamic
behavior. Indeed, the 1H NMR spectrum was complex as a result
of the facile interconversion η3ꢀη1ꢀη3 of π-allyl, which allowed
formation of a mixture of two isomeric species in solution. The
t-Bu was placed too far from the allyl group, and therefore no
differentiation for its proton was detected. However, the 31P
NMR revealed two singlet signals at 69.9 and 65.9 ppm, respec-
tively, in a 1:2 ratio for the two isomeric palladium complexes
involving a different position of the allyl group (see Figure 5).
Meso ligands, such as allyl, which are not in the square plane of the
palladium, produce a potential element of chirality at the palla-
dium. Thus, two enantiomers occur (Figure 5) when no other
elements of chirality are present.32 The presence of a chiral
sulfinyl group in the PNSO ligand led to the formation of
diastereomers (RS,SPd) and (RS,RPd), which were present in
solution and observed as two singlet resonances by the 31P NMR.
X-ray Structure of Palladium Complex 6. Suitable crystals of
the new complex 6 for X-ray analysis were obtained by slow
evaporation of DCM at 0 °C. Complex 6 consisted of a slightly
distorted square plane centered on a palladium atom. Surpris-
ingly, in the solid state we observed only a single configuration of
the allyl relative to the chirality of the ligand corresponding to the
We first focused on the synthesis of a π-allyl cationic palladium
complex with PNSO ligand 1a. The synthesis was conducted
with ligand 1a (2 equiv) and [(η3-allyl)PdCl]2 (1 equiv) in
dry EtOH in the presence of NH4PF6. This procedure gave
the presumed complex 5a and/or 5b after crystallization
1
(Scheme 5). The H NMR spectrum of the reaction crude
product showed a small deshielding for the t-Bu group (0.95
ppm, Δδ = 0.02) and methylene protons (4.65 ppm, Δδ = 0.2),
indicative of a P,O coordination mode. High-resolution mass
spectrometry revealed the molecular ion [C26H34NOPPdS]þ
supporting the structures 5a,b. However, remarkably, the X-ray
analysis for this new complex (vide infra) did not exhibit the
expected P,S or P,O coordination but showed a monodentate
P-coordination mode (6). Accordingly, a straightforward synth-
esis of 6 was developed by mixing 1a with [(η3-allyl)PdCl]2 in
DCM in very good yield (93%). In this case, oxygen and sulfur
atoms were unable to displace the chlorine atom. Several η3-allyl-
Pd complexes have been described with an S-noncoordinating
atom,10b but in all these cases the presence of other coordinating
atoms in the backbone of the ligand competes with the S-bonding
capacity of the sulfinyl group.31
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ClꢀPdꢀP angle, ca. 100°, rather large. We attribute these
observations to the relatively large bulk of the ligand. The
SꢀO bond length (1.49 Å) is consistent with the S-noncoordi-
nating sulfinyl group.31 The palladiumꢀcarbon distance trans to
the phosphorus atom (2.211 Å) was longer than that trans to the
chloride (2.126 Å), which is in accordance with the stronger trans
influence of the phosphorus atom.33 These values are in the same
range as corresponding mono-PPh3 and monophosphoramidite
complexes, showing PdꢀC, trans-P, and trans-Cl bond length
values of 2.17, 2.18 and 2.10, 2.07 Å, respectively.34 It is well
established that when the σ-donor capacity of the ligands bound
to palladium is significantly different (Cl = poor σ-donor and
P = good σ-donor), an enhanced dissymmetry of the η3-allyl
ligands is observed.35
CH/π Interactions. A striking feature of the X-ray structure of
6 is that the allyl group lies in a perpendicular plane with respect
to the benzene ring of the benzyl group. This finding suggests the
presence of a weak interaction between one of the anti allyl
protons and the aromatic group. CH/π interactions, a type of
weak molecular force, play a crucial role in a variety of chemical
and biological phenomena. The CH/π interaction corresponds
to a hydrogen bond occurring between soft acids and soft bases.36
Evidence of these interactions has been reported from X-ray
crystallographic analyses of sulfoxide,37a manganese,37b and
cobalt37c complexes. CSD studies on transition metal complexes
highlighted the relevance of the CH/π hydrogen bond to control
the crystal packing and molecular structure of coordination and
organometallic compounds.38,39 CH/πPh bonds are involved in
controlling the conformational equilibrium of molecules.40 Metal
complexes bearing aromatic ligands display intraligand CH/π
interactions, which can orient the coordination around the
metal.41
Figure 7. ORTEP view of the solid-state structure of complex (RS,SPd)-
6. The dashed line shows the anti-allyl proton linked to C(26) and the
[C(18)---C(23)] phenyl ring.
Table 3. Selected Bond Lengths [Å] and Angles [deg] for 6
with Estimated Standard Deviations in Parentheses
[(RS,SPd)]-6
Pd(1)ꢀC(24) 2.210(3)
Pd(1)ꢀC(25) 2.154(3)
Pd(1)ꢀC(26) 2.126(3)
C(26)ꢀPd(1)ꢀC(24)
C(24)ꢀC(25)ꢀC(26)
P(1)ꢀPd(1)ꢀCl(1)
C(24)ꢀPd(1)ꢀP(1)
C(26)ꢀPd(1)ꢀCl(1)
67.45(12)
121.3(3)
100.40(2)
164.95(8)
161.18(8)
Pd(1)ꢀP(1)
Pd(1)ꢀCl(1)
S(1)ꢀO(1)
S(1)ꢀC(13)
2.3097(5)
2.3840(6)
1.4898(17) O(1)ꢀS(1)ꢀN(1)ꢀP(1) ꢀ123.54(11)
1.865(2)
Inspection of the crystal structure of 6 highlighted that both
electrostatic repulsion (between oxygen and chlorine atom) and
steric hindrance force the phenyl ring of the benzyl group close to
the allyl ligand (Figure 7). Indeed, the anti-H(26A) proton is
located at a short distance, viz., 2.795 Å, from the centroid Q1 of
the [(C18), C(19), C(20), C(21), C(22), C(23)] and closer to
the C19 and C20 atoms with lengths 2.859 and 2.955 Å,
respectively.42 The CH/π distance fits the usual range in
Nonbonding Interaction: CH/π
DꢀH
A
H
A
D
A
DꢀH
3 3 3
A
3 3 3
3 3 3
3 3 3
C26ꢀH(26A) C19
2.859
2.955
2.795
2.995
2.771
2.954
3.120
2.882
3.151
3.300
3.396
3.735
3.617
3.352
3.802
3.528
3.589
3.838
160.51
156.63
3 3 3
C26ꢀH(26A) C20
3 3 3
C26ꢀH(26A) Q1a
3 3 3
complexes featuring intramolecular sp2-CH πPh (2.83 (
3 3 3
C14ꢀH(14B) C1
122.53
118.53
3 3 3
0.16 Å) and is comparable to that reported by Scrivanti (2.66
and 2.83 Å).43,44 This is a rare example of an intramolecular CH/
π interaction involving a terminal hydrogen atom of an allyl
ligand in neutral palladium(II) complexes.
C14ꢀH(14B) C2
3 3 3
C14ꢀH(14B) Q2b
3 3 3
C25ꢀH(25) C18*
105.93
128.25
3 3 3
C25ꢀH(25) C19*
Crystal packing of 6 shows that the allyl group is sandwiched
between two benzyl groups (Figure 8). The anti proton (H26A)
is engaged in an intramolecular nonbonding interaction (Figure 7),
while the central proton (H25) is pointing toward one face of the
benzyl moiety of an adjacent molecule in an intermolecular
contact. The distance values between the central H25 and both
C18 and C19 are 2.882 and 3.120 Å, respectively, and are
consistent with a CH/π interaction.36,43 In the solid state 6
adopts a C-shaped conformation, which allows intra- and inter-
molecular CH/π interactions. This interesting cooperative CH/
π network is finally responsible for the selective formation of a
single diastereomer (RSRPd) of 6 in the solid state.
In order to observe other types of coordination modes with
palladium, we turned our attention to synthesizing some
palladium(II) chloride PNSO complexes. The addition of one
equivalent of ligand 1a to a THF solution of PdCl2(CH3CN)
provided a shiny yellow precipitate after 30 min of reaction.45
3 3 3
C25ꢀH(25) Q3*c
3 3 3
a Centroid of six-membered ring [(C18), C(19), C(20), C(21), C(22),
C(23)]. b Centroid of six-membered ring [(C1), C(2), C(3), C(4),
C(5), C(6)]. c Centroid of six-membered ring [(C1), C(2), C(3), C(4),
C(5), C(6)].
(RS,SPd) diastereomer (Figure 7). The allyl ligand bonds to the
palladium atom in an asymmetric η3-fashion (see Table 3), and
the PNSO ligand attaches to the metal only through the
phosphorus atom. The chlorine atom and the oxygen of the
sulfinyl moiety are in an anti-fashion disposition to minimize
electrostatic repulsion.
Both PdꢀP and PdꢀCl bond lengths, 2.310 and 2.384 Å,
respectively, are in the range for phosphineꢀpalladium and
chlorideꢀpalladium complexes. However, we noted that the
PdꢀCl bond length was modestly long, ca. 2.38 Å, and the
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ARTICLE
Figure 8. Crystalline intermolecular CH/π network (dashed lines) for 6. Most of the hydrogen atoms and both the Ph and t-Bu groups are omitted for
clarity.
Scheme 6. Synthesis of Palladium Complexes 7a,b and Platinum Complex 8
Table 4. Selected Bond Lengths [Å] and Angles [deg] for 8
with Estimated Standard Deviations in Parentheses
(RS)-8
PtꢀS
2.2011(9)
2.2141(10)
2.3614(9)
2.3142(10)
1.464(3)
PꢀPtꢀS
73.24(4)
102.08(16)
99.21(4)
97.57(4)
123.96
PtꢀP
PꢀNꢀS
PtꢀCl(1)
PtꢀCl(2)
OꢀS
PꢀPtꢀCl(1)
PꢀPtꢀCl(2)
PꢀNꢀSꢀO
SꢀC(1)
1.852(4)
first described in the late 1960s,47 are reported mainly for
platinum.48 PNSO ligand 1a reacted with PtCl2(cod) in DCM
to afford stable platinum complexes 8 as a crystalline white solid.
The 31P NMR showed one triplet signal at 19.6 ppm (J = 3272 Hz),
and 1H NMR showed a t-Bu signal at 1.63 ppm similar to that of the
palladium complex 7b. The methylene protons of 8, as doublets at
δ 4.30 and 4.46 ppm, respectively, are more shielded than those of
the corresponding palladium chloride 7b. Regarding uncoordi-
nated ligand 1a, we observed a strong deshielding for the t-Bu signal
at 1.63 ppm (Δδ 0.70 ppm), and both methylene protons were
found more shielded (Δδ 0.15 and 0.14). These observations agree
with the expected S-coordination for the isolated platinum com-
plex. The P,S coordination of PNSO ligand 1a through the Pt(II)
center was confirmed by X-ray diffraction analysis.
Figure 9. ORTEP view of the solid-state structure of complex (RS)-8.
Hydrogen atoms and CHCl3 were omitted for clarity.
This solid was then filtrated under vacuum to afford a pure yellow
solid as a palladium complex. The 31P NMR showed only
1
one signal at 39 ppm, and H NMR showed a t-Bu signal at
1.68 ppm and methylene protons as doublets of doublets at
δ 4.46 and 4.56 ppm, respectively. With regard to uncoordinated
ligand 1a, we observed a strong deshielding for the t-Bu signal
(Δδ 0.75 ppm), and both methylene protons were found slightly
shielded (Δδ 0.01 and 0.035) as a multiplet. These observations
suggest an S-coordination for the isolated palladium complex 7b.
The complex is air sensitive and unstable in solution and
decomposes after a few hours in CHCl3 or DCM solution.
The low stability of this palladium chloride complex prompted
us to synthesize similar platinum chloride complexes. Inspection
of various sulfoxide platinum complexes showed that almost all
the compounds are Pt(II) square-planar complexes, with an
S-coordination through the metal center.14 The O-coordination
is rare, and only a few examples have been reported in the
literature.46 Complexes of chelating bis-sulfoxides, which were
X-ray Structure of Platinum Complex 8. Suitable crystals of
the new complex 8 for X-ray analysis were obtained in hot
chloroform at 55 °C. The coordination around the Pt atom is
square planar. The PNSO ligand is bonded through its S and P
atoms. The [PtꢀSꢀNꢀP] atoms form a four-membered ring
similar to that depicted for Rh-IV and Ir-2b complexes. The
benzyl group faces one of the phenyl groups of the phosphorus
atom. The relatively short distance (3.612 Å)49 between the
benzyl and phenyl ring suggests a face-to-face πꢀπ stacking
interaction (distance range 3.2ꢀ3.8 Å).50
The PtꢀCl(1) bond distance (2.361 Å) trans to the phos-
phorus ligand is significantly longer than the PtꢀCl(2) distance
trans to sulfur (2.314 Å) (see Table 4). The PtꢀCl(2) bond
length in complex 8 is consistent with the average bond length of
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ARTICLE
2.323(38) Å reported by Orpen for various platinum
complexes.51 The PtꢀCl(1) (2.361 Å) bond length is consistent
with the low trans effect of chlorine.
at room temperature; then the yellow solution was evaporated under
vacuum to a small volume (2ꢀ3 mL) and poured over vigorously stirred
Et2O (50 mL). The resulting precipitate was filtered, washed with Et2O
(2 ꢁ 10 mL), and dried to give complex 2a as a shiny yellow powder
(0.205 g, 90%). Suitable crystals for X-ray analysis were obtained by
layering Et2O over a CH2Cl2 solution of 2a.
Platinumꢀsulfur coordination is generally highlighted by the
shortening of the SꢀO bond length from a free sulfoxide (dSꢀO
=
1.492 Å) to an S-coordinated platinumꢀsulfoxide complex
(dSꢀO = 1.467 Å).14b,c For complex 8, the distance is 1.464 Å,
which thus fits perfectly with such P,S coordination. As observed
for S-coordinated monodentate DMSO,52 the sulfur atom in the
PNSO ligand is slightly tetrahedral with a slightly larger
PtꢀSꢀO angle (120.64°) than the two PtꢀSꢀC and PtꢀSꢀN
angles (93.02° and 116.21°).
[R]D ꢀ184 (c 0.1, CHCl3); IR (KBr) νmax 1436, 1272,1148, 1093,
1031 cmꢀ1; 1H NMR (400 MHz, CDCl3) δ 1.50 (CH3, s, 18H), 4.35
(CH2, m, 2H), 6.69 (ArH, d, J = 7.2 Hz, 4H), 6.98 (ArH, m, 12H), 7.13
(ArH, t, J = 8 Hz, 2H), 7.52 (ArH, m, 10H), 7.72 (ArH, t, J = 8 Hz, 2H)
ppm; 13C NMR (100 MHz, CDCl3) δ 24.7 (6 ꢁ CH3), 51.5 (2 ꢁ CH2),
69.6 (2 ꢁ C), 125.1 (4 ꢁ C, d, J = 61 Hz), 127.6 (4 ꢁ C, dd, J = 65 Hz, J =
5 Hz), 128.5 (4 ꢁ CH), 128.6 (2 ꢁ CH); 129.0 (4 ꢁ CH), 129.4 (4 ꢁ
CH, t, J = 6 Hz), 130.2 (4 ꢁ CH, t, J = 6 Hz), 132.6 (4 ꢁ CH, t, J = 6 Hz),
133.1 (2 ꢁ CH), 133.7 (2 ꢁ C); 134.2 (2 ꢁ CH), 134.4 (4 ꢁ CH, t, J =
8.0 Hz) ppm; 31P NMR(121MHz, CDCl3) δ 45.9ppm; MS (ESI, H2O/
CH3CN (1:1), 1% formic) m/z 983 [100, (M ꢀ OTfꢀ)þ]; 922 (48);
HRMS (ESI) calcd for C46H52N2O2P2S2Irþ 983.2569, found 983.2579.
cis-[Ir(RS-PNSO)2][BF4] (2b). [IrCl(COD)]2 (0.136 g, 0.202 mmol)
and AgBF4 (0.079 g, 0.404 mmol) were placed in a Schlenk flask protected
from light with aluminum foil. The flask was then purged with N2, and dry
THF (2 mL) was added. The mixture was stirred for 2 h, and the resulting
white precipitate (AgCl) was removed by filtration over Celite under nitrogen
and subsequently washed with extra THF (3 ꢁ 2 mL). This yellow solution
was added dropwise into a Schlenk tube containing a solution of ligand 1a
(0.320 g, 0.808 mmol) in THF (2 mL), and the mixture turned yellow. The
reaction was stirred for 12 h at room temperature; then the yellow solution
was evaporated under vacuum to a small volume (2ꢀ3 mL) and poured over
vigorously stirred Et2O (50 mL). The resulting precipitate was filtered,
washed with Et2O (2 ꢁ 10 mL), and dried to give complex 2b as a shiny
yellow powder (0.311 g, 72%). Suitable crystals for X-ray analysis were
obtained by layering Et2O over a CH2Cl2 solution of 2b.
’ CONCLUSIONS
Here we studied the coordination behavior of the hemilabile
PNSO ligand N-benzyl-N-phosphino-tert-butylsulfinamide
(1a) toward Ir(I), Cu(I), Pd(II), and Pt(II). We observed P,
O or P,S coordination modes, depending on the nature of the
metal center (hard/soft) and on the electronic environment
around the metal. Ligand 1a provided a P,S coordination mode
with Ir, Pd, and Pt complexes, while P,O coordination was
observed in response to a harder Cu(I) center. For Ir, a
monomeric P,O intermediate was also observed by NMR, but
its stability precluded its isolation. On the basis of the 31P NMR
studies, we propose an associative/dissociative mechanism for
the formation of the thermodynamically favored dimeric com-
plex 2b.
Surprisingly, 1a was found to work as a monodentate P-ligand in
the π-allyl palladium complex 6. In this case, the sulfinyl moiety was
not able to displace the chloride atom from the Pd center. An
interesting cooperative CH/π network was unveiled in the crystal-
line structure of 6. The simultaneous action of both intra- and
intermolecular interactions of the π-allyl moiety with the aromatic
benzyl group is responsible for the observation of a single
diastereomer of the π-allyl complex in the solid state.
[R]D ꢀ33 (c 0.1, CHCl3);IR(KBr) νmax 1437, 1135, 1084, 1056 cmꢀ1
;
1H NMR (400 MHz, CDCl3) δ 1.51 (CH3, s, 18H), 4.35 (CH2, m, 4H),
6.69 (ArH, d, J = 7 Hz, 4H), 7.00 (ArH, m, 12H), 7.12 (ArH, t, J = 8 Hz,
2H), 7.52 (ArH, m, 10H), 7.72 (ArH, t, J = 7 Hz, 2H) ppm; 13C NMR
(100 MHz, CDCl3) δ 24.7 (6 ꢁ CH3), 51.55 (2 ꢁ CH2), 68.6 (2 ꢁ C, t,
J = 5 Hz), 125.1 (4 ꢁ C, dd, J = 66 Hz, J = 5 Hz), 127.6 (4 ꢁ C, dd, J = 64
Hz, J = 5 Hz), 128.5 (4 ꢁ CH), 128.6 (2 ꢁ CH), 129.0 (4 ꢁ CH), 129.4
(4 ꢁ C, t, J = 6 Hz), 130.13 (4 ꢁ C, t, J = 6 Hz), 132.6 (4 ꢁ C, t, J = 6 Hz),
133.1 (2 ꢁ CH), 133.8 (2 ꢁ CH), 134.2 (2 ꢁ CH), 134.5 (4 ꢁ CH, t, J =
8.0 Hz) ppm; 31P NMR (121 MHz, CDCl3) 45.8 ppm; MS (ESI, H2O/
CH3CN (1:1), 1% formic) m/z 983 [100, (M ꢀ OTfꢀ)þ]; 922 (48);
HRMS (ESI) calcd for C46H52N2O2P2S2Irþ 983.2569, found 983.2574.
cis-[Cu(RS-PNSO)2][TfO] (4). A solution of ligand 1a (0.2 g,
0.505 mmol) in DCM (5 mL) was added dropwise to a Schlenk flask
1H NMR analysis of the resonances of the methylene and
t-Bu groups could provide a useful tool to study and predict the
coordination mode of PNSO ligands toward transition metals.
The methylene protons in O-bonded PNSO ligands appear
downfield with respect to the free ligand 1a, while an upfield
shift is observed for S-bonded complexes. The multiplicity of
the methylene protons emerges as two doublets in O-coordi-
nation and as two doublets of doublets for S-coordination. For
the t-Bu group, O-bonded configurations provide a small
downfield shift (∼0.1 ppm), while in S-bonded configurations
a strong downfield shift (∼0.5 ppm) is observed. This analysis
allowed us to predict a P,S coordination mode for Pd dichlor-
ide complexes 7. New chiral PNSO complexes are currently
being tested as asymmetric catalysts in several reactions in our
laboratories.
containing a solution of [Cu(OTf) Tol]2 (0.130 g, 0.252 mmol) in
3
THF. The reaction was stirred for 5 h at room temperature, and solvent
was removed under vacuum. The crude mixture was then redisolved in
2 mL of THF and was left overnight at 0 °C. The resulting precipitate
was filtered, washed in cold THF, and dried to give complex 4 as a white
crystalline solid (0.228 g, 90%). Suitable crystals for X-ray analysis were
obtained by layering hexane over a CH2Cl2 solution of 4.
Mp 148ꢀ150 °C; [R]D ꢀ187 (c 0.1, CHCl3); IR (KBr) νmax 1436,
1267, 1151, 1031 cmꢀ1; 1H NMR (400 MHz, CDCl3) δ 1.03 (CH3, s,
18H), 4.62 (CH2, d, J = 15 Hz, 2H), 4.74 (CH2, d, J = 15 Hz, 2H), 6.94
(CH, d, J = 5 Hz, 4H), 7.18 (CH, s, 6H), 7.27 (CH, m, 4H), 7.37 (CH, t,
J = 7 Hz, 2H), 7.44 (CH, br, 4H), 7.58 (CH, s, 8H), 7.66 (CH, br, 2H)
ppm. 13C NMR (100 MHz, CDCl3) δ 22.9 (6 ꢁ CH3), 55.0 (2 ꢁ CH2),
61.8 (2 ꢁ C), 128.5 (2 ꢁ CH), 128.6 (4 ꢁ CH), 128.9 (4 ꢁ CH), 129.3
(4 ꢁ CH), 130.1 (4 ꢁ CH), 132.1,132.2 and 132.3 (m, 8 ꢁ CH), 134.6
(4 ꢁ CH), 134.9 (2 ꢁ C) ppm, the 4 CCꢀP were not observed; 31P
NMR (121 MHz, CDCl3) δ 18.3 ppm; MS (ESI, H2O/CH3CN (1:1),
1% formic) m/z 138 (60), 194 (27), 203 (100), 853 (40, [M]þ), 922
’ EXPERIMENTAL SECTION
cis-[Ir(RS-PNSO)2][TfO] (2a). [IrCl(COD)]2 (0.136 g, 0.202
mmol) and AgOTf (0.104 g, 0.404 mmol) were placed in a Schlenk
flask protected from light with aluminum foil. The flask was then purged
with N2, and dry DCM (2 mL) was added. The mixture was stirred for
2 h, and the resulting white precipitate (AgCl) was removed by filtration
over Celite under nitrogen and subsequently washed with extra DCM
(3 ꢁ 2 mL). This yellow solution was added dropwise into a Schlenk
tube containing a solution of ligand 1a (0.412 g, 0.808 mmol) in THF
(2 mL), and the mixture turned yellow. The reaction was stirred for 12 h
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ARTICLE
(10); HRMS (ESI) calcd for C46H52N2O2P2S2Cuþ 853.2202, found
853.2199.
’ ASSOCIATED CONTENT
[(η3-allyl)(RS-PNSO)PdCl] (6). The allylpalladium chloride dimer
(0.063 g, 0.063 mmol) and the ligand (0.05 g, 0.126 mmol) were added
to a flame-dried Schlenk flask. The contents were placed under inert
atmosphere, and CH2Cl2 was added. The resulting green solution was
stirred for 3 h at room temperature. The solution was then filtered
through a pad of Celite, evaporated to dryness, and triturated with Et2O
to leave the desired compound as a soft green powder. Green crystals
(34 mg) suitable for X-ray analysis were grown from slow evaporation of
a CH2Cl2 solution at 0 °C in 93% yield.
S
Supporting Information. Experimental procedures and
b
characterization data of all new compounds. Tables of crystal-
lographic data in cif file format. This material is available free of
charge via the Internet at http://pubs.acs.org.
’ AUTHOR INFORMATION
Corresponding Author
*E-mail: xavier.verdaguer@irbbarcelona.org.
Mp 158ꢀ160 °C; [R]D þ54 (c 0.1, CHCl3); IR (KBr) νmax 1433,
1079, 1053, 1000, 834 cmꢀ1; 1H NMR (400 MHz, CDCl3) δ 0.95 (CH3,
s, 9H), 1.28ꢀ1.31 (CHmaj, br, 0.78 H), 2.08 (CHmin, br, 0.38 H), 2.29
(CHmaj, br, 0.7 H), 2.51 (CHmin, br, 0.37 H), 3.27ꢀ3.38 (CHmaj, br,
0.71 H), 3.62 (CHmin, br, 0.37 H), 4.49ꢀ5.18 (CHþCH2, m, 4H), 5.39
(CHmaj, br, 0.67 H), 7.12ꢀ7.22 (CH, m, 3H), 7.3ꢀ7.5 (CH, m, 6H),
7.62ꢀ7.67 (CH, m, 3H), 7.85 (CH, br, 1H), 8.14ꢀ8.20 (CH, m, 2H)
ppm; 13C NMR (100 MHz, CDCl3) δ 22.9 (3 ꢁ CH3min); 24.6 (3 ꢁ
CH3maj); 47.6 (CH2min); 47.8 (CH2maj); 62.0 (Cmin); 65.8 (Cmaj); 78.4
(CH2maj); 78.8 (CH2min); 117.4 (Cmaj); 120.28 (Cmin); 127.9 and 128.1
(m, 4 ꢁ CH); 128.4 (4 ꢁ C, d, J = 11 Hz); 130.2 (CH); 131.1 (br, 2 ꢁ
CH) and 131.2 (br, 2 ꢁ CH); 131.9 (C, d, J = 2 Hz); 136.8 and 136.9
(br, 2 ꢁ CH); 138.4 (C) ppm; 31P NMR (121 MHz, CDCl3) δ 69.98
(minor) and 65.93 (major) ppm; MS (ESI, H2O/CH3CN (1:1), 1%
formic) m/z 121 (100), 540.08 (15), 541.09 (41), 542,08 (M ꢀ Clþ,
61.08), 543.09 (14), 544.08 (49), 545.09 (10), 546.09 (21); HRMS
(ESI) calcd for [M ꢀ Cl]þ C26H31NOPSPdþ 542.08933, found
542.08905.
[(RS-PNSO)PdCl2] (7b). In a Schlenk flask under nitrogen, a
solution of ligand 1a (0.2 g 0.504 mmol) in THF (2 mL) was added
dropwise to a yellow solution of PdCl2(CH3CN)2 (0.131 g, 0.504
mmol) in THF. This resulting yellow solution was stirred for 15ꢀ20 min
at room temperature to produce a strong yellow precipitate. This was
then filtered, washed with cold THF (2 ꢁ 1 mL), and dried to give
complex 7b as a yellow, shiny powder (0.245 g) in 85% yield.
[R]D ꢀ8 (c 0.6, CHCl3); IR (KBr) νmax 1435, 1107 cmꢀ1; 1H NMR
(400 MHz, CDCl3) δ 1.68 (CH3, 9H), 4.44ꢀ4.51 (CH2, dd, J = 16 Hz,
J = 12 Hz, 1H), 4.51ꢀ4.62 (CH2, dd, J = 16 Hz, J = 12 Hz, 1H),
6.73ꢀ6.75 (CH, d, J = 8 Hz, 2H), 7.05 (CH, t, J = 8 Hz, 2H), 7.16 (CH, t,
J = 7 Hz, 1H), 7.49ꢀ7.55 (CH, m, 4H), 7.62ꢀ7.66 (CH, tdd, J = 7 Hz,
J = 2 Hz, J = 1 Hz, 1H), 7.70ꢀ7.80 (CH, m, 3H), 7.85ꢀ7.91 (CH, m,
2H); 31P NMR (121 MHz, CDCl3) δ 38.1 ppm. 13C NMR spectra could
not be recorded due to the instability of the compound.
’ ACKNOWLEDGMENT
We thank the MEC (CTQ2008-00763), the Generalitat de
Catalunya (2009SGR-00901), and Enantia S. L. for financial
support. T.A. thanks Dr. Alphonse Tenaglia (IsM2-Chiros-
ciences, Marseille) for fruitful discussions.
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[(RS-PNSO)PtCl2] (8). In a dried Schlenk flask under nitrogen, a
solution of ligand 1a (0.05 g, 0.126 mmol) in DCM (2 mL) was added
dropwise to a THF solution of PtCl2(COD) (0.047 g, 0.126 mmol). The
resulting solution was stirred for 3 h at room temperature. Solvent was
removed under vacuum to afford quantitatively desired platinum com-
plexes as a white solid. The complex was recrystallized in DCM/hexane
to give a crystalline product (80 mg) in 96% yield.
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[R]D ꢀ42 (c 0.0014, CHCl3); IR (KBr) νmax 2914, 1429, 1179, 1087,
739, 679 cmꢀ1 1H NMR (400 MHz, CDCl3) δ 1.63 (CH3, 9H),
;
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4.42ꢀ4.34 (CH2, dd, J = 16 Hz, J = 14 Hz, 1H), 4.42ꢀ4.50 (CH2, dd, J =
16 Hz, J = 13 Hz, 1H), 6.74 (CH, d, J = 7 Hz, 2H), 7.08 (CH, t, J = 8 Hz,
2H), 7.19 (CH, t, J = 7 Hz, 1H), 7.47ꢀ7.52 (CH, m, 4H), 7.59ꢀ7.83
(CH, m, 6H); 13C NMR (100 MHz, CDCl3) δ:24.7 (3 ꢁ CH3), 50.7
(CH2, d, J = 4 Hz), 74.3 (C, d, J = 1.4 Hz), 123.5 (2 ꢁ C, dd, J = 69 Hz, J =
5 Hz), 128.7 (2 ꢁ CH), 128.80 (CH), 129.0 (2 ꢁ CH), 129.4 (2 ꢁ CH,
d, J = 13 Hz), 129.7 (2 ꢁ CH, d, J = 13 Hz), 132.6 (C), 133.9 (CH, d, J =
3 Hz), 134.10 (CH), 134.22 (2 ꢁ CH, d, J = 13 Hz), 134.25 (CH), 134.4
(2 ꢁ CH), 134.5 (CH); 31P NMR (121 MHz, CDCl3) δ 19.6 (J = 3272
Hz) ppm; HRMS (ESI, H2O/CH3CN (1:1), 1% formic) m/z calcd for
[M ꢀ Cl þ H2O]þ C23H28ClNO2PPtSþ 643.0915, found 643.0932.
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