Phosphino-(α-sulfinylalkyl)phosphonium ylide complexes (Rh, Pd) with a configurationally stable asymmetric ylidic carbon

Article abstract of DOI:10.1016/j.tetasy.2010.05.045

The synthesis and structure of Rh(I) and Pd(II) complexes of chiral P,C-chelating phosphino-(α-sulfinylalkyl)phosphonium ylide ligands with a trisubstituted asymmetric ylidic center P⁺-CR(S(O)p-Tol)-M (R = alkyl group) have been investigated, and compared to those of the analogous disubstituted ylide complexes (R = H). Reaction of the ethyl onium ylide of o-bis(diphenylphosphino)benzene with (-)-menthyl-(S)-p-tolylsulfinate afforded the corresponding racemic erythro phosphino-(α-sulfinylethyl)phosphonium in 90% de (R = Me). The racemization process is interpreted by a Berry-like pseudorotation mechanism driven by the steric repulsion between the α-methyl substituent and the bulky menthyloxy S-substituent or sulfur lone pair in the intermediate ylide-sulfinyl adduct. The ylide of phosphino-(α-sulfinylethyl)phosphonium reacts with [Rh(cod) ₂][PF₆] and PdCl₂(MeCN)₂ to afford the corresponding P,C-chelated threo-Rh(I) and erythro-Pd(II) mononuclear complexes in 70% yield and total diastereoselectivity. These respective complexes act as efficient catalytic precursors for the hydrogenation of (Z)-α-acetamidocinnamic acid and allylic substitution of 3-acetoxy-1,3-diphenyl-1-propene with sodium dimethyl malonate. The bonding features of the erythro-Pd(II) complex exhibiting a sulfinyl O...Pd interaction are studied theoretically at the DFT level using ELF and MESP analyses. The η²-P,C haptomeric form of the ylide ligand is estimated to compete at 19% with the η¹-C haptomeric form dominating at 81%.

Full text of DOI:10.1016/j.tetasy.2010.05.045

Tetrahedron: Asymmetry 21 (2010) 1777–1787
Contents lists available at ScienceDirect
Tetrahedron: Asymmetry
journal homepage: www.elsevier.com/locate/tetasy
Phosphino-(
a-sulfinylalkyl)phosphonium ylide complexes (Rh, Pd)
with a configurationally stable asymmetric ylidic carbon
Remigiusz Zurawinski a,b,c, Christine Lepetit a,b, Yves Canac a,b, Laure Vendier a,b, Marian Mikolajczyk c,
,
*
Remi Chauvin a,b,
*
a CNRS, LCC (Laboratoire de Chimie de Coordination), 205, route de Narbonne, F-31077 Toulouse, France
b Université de Toulouse, UPS, INPT, LCC, F-31077 Toulouse, France
c Centre of Molecular and Macromolecular Studies, Department of Heteroorganic Chemistry, Polish Academy of Sciences, 90-363 Lodz, Sienkiewicza 112, Poland
a r t i c l e i n f o
a b s t r a c t
Article history:
The synthesis and structure of Rh(I) and Pd(II) complexes of chiral P,C-chelating phosphino-(
a
*
-sul-
+
Received 14 April 2010
Accepted 28 May 2010
Available online 28 June 2010
*
finylalkyl)phosphonium ylide ligands with a trisubstituted asymmetric ylidic center P –C R(S (O)p-
Tol)–M (R = alkyl group) have been investigated, and compared to those of the analogous disubstituted
ylide complexes (R = H). Reaction of the ethyl onium ylide of o-bis(diphenylphosphino)benzene with
(ꢀ)-menthyl-(S)-p-tolylsulfinate afforded the corresponding racemic erythro phosphino-(
yl)phosphonium in 90% de (R = Me). The racemization process is interpreted by a Berry-like pseudorota-
tion mechanism driven by the steric repulsion between the -methyl substituent and the bulky
menthyloxy S-substituent or sulfur lone pair in the intermediate ylide-sulfinyl adduct. The ylide of phos-
phino-( -sulfinylethyl)phosphonium reacts with [Rh(cod)2][PF6] and PdCl2(MeCN)2 to afford the corre-
a-sulfinyleth-
Dedicated to Professor Henri Kagan on the
occasion of his 80th birthday
a
a
sponding P,C*-chelated threo-Rh(I) and erythro-Pd(II) mononuclear complexes in 70% yield and total
diastereoselectivity. These respective complexes act as efficient catalytic precursors for the hydrogena-
tion of (Z)-
sodium dimethyl malonate. The bonding features of the erythro-Pd(II) complex exhibiting a sulfinyl
2-P,C
1-C haptomeric form dom-
a-acetamidocinnamic acid and allylic substitution of 3-acetoxy-1,3-diphenyl-1-propene with
Oꢁ ꢁ ꢁPd interaction are studied theoretically at the DFT level using ELF and MESP analyses. The
g
haptomeric form of the ylide ligand is estimated to compete at 19% with the
inating at 81%.
g
Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction
ylides the rotation about the P+–Cꢀ bond is also very small),7
non-salt-free non-stabilized ylides are intrinsically chiral, albeit
configurationally labile through exchange of the alkali cation. The
configurational stability can however be enhanced by increasing
the covalent character of the carbon–metal interaction (Fig. 1). This
is achieved with less electropositive metal centers, such as transi-
tion metal centers Mt (in the Pauling scale of electronegativity:
For more than 50 years, phosphonium ylides have been widely
used as reactants in the Wittig olefination reaction of carbonyl
compounds (aldehydes, ketones, lactones, etc.).1 These ylides can
be classified according to the olefination stereoselectivity:2 while
stabilized and salt-free non-stabilized ylides (R3P@CHZ) lead pref-
erentially to trans-olefination products,3 non-salt-free non-stabi-
lized ylides (R3P@CHR0 + LiX) lead to cis-olefination products.4 In
the ‘trans’ category, the configuration of the ylidic carbon atom is
quasi-planar (for Z = CO2R0, even in the presence of salt with Oꢁ ꢁ ꢁLi
interaction) or pyramidal with a very small pyramidalization bar-
rier of ca. 1 kcal/mol (for Z = H or alkyl group).5 In the ‘cis’ category
(generated byꢀin situ deprotonation of a phosphonium precursor
R3P+–CH2R0, X with a lithium base),6 the carbon center is made
tetrahedral through a Cꢁ ꢁ ꢁLi interaction.7 Although free ylidic car-
bon centers are thus non-stereogenic (in salt-free non-stabilized
v
(Li) = 1.0 ꢂ 1.6 6
The strength of the C?Mt complexation of the neutral ylides is
indeed illustrated by a rich coordination chemistry, previously re-
viewed by Schmidbaur.9 All ylide complexes exhibit a 1-sp3-C-
coordination mode (the
2-P,C-coordination mode is not known),
which is basically similar to the
1-sp2-C-coordination mode of
v (Mt) 6 2.2 < 2.5 = v
(C)).8
g
g
g
the famous neutral diaminocarbene ligands.10 This remarkable sta-
bility has been however only recently exploited in catalysis, where
the coordinated ylides act as spectator ligands.11 Most of the exam-
ples focus on asymmetric catalytic processes (hydrogenation,
hydroformylation,12 allylation,13 and hydrosilylation,14) involving
chiral ylide ligands with the atropochiral 1,10-binaphthyl backbone
of (R)- or (S)-binap (‘binapium’ ylides and ‘yliphos’).15,16 As the chi-
rality element of chiral phosphines can be located at either the
backbone (e.g., in diop),17 or the coordinating P atom (e.g., in
* Corresponding authors. Tel.: +48 42 681 58 32; fax: +48 42 684 71 26 (M.M.);
tel.: +33 (0)5 61 33 31 13; fax: +33 (0)5 61 55 30 03 (R.C.).
E-mail addresses: marmikol@bilbo.cbmm.lodz.pl (M. Mikolajczyk), chauvin@lcc-
toulouse.fr (R. Chauvin).
0957-4166/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetasy.2010.05.045

1778
R. Zurawinski et al. / Tetrahedron: Asymmetry 21 (2010) 1777–1787
X
X
X
M
C
X
M
C
M
M
P
C
P
P
P C
salt free
non-salt-free
M = Li
η1-C-coordination
η2-P,C-coordination
(unknown)
M = Na, K
M = transition metal
Figure 1. Schematic bonding typology of phosphonium ylides based on the relative electrostatic versus covalent components of interaction with neighboring metal salts.
When the deprotonation of the phosphonium precursor is carried out with a sodium or potassium base, the resulting salt is insoluble and the ylide is said ‘salt-free’ (left). All
X-ray crystal data of transition metal complexes of ylides indicate that the Pꢁ ꢁ ꢁM distance is non-bonding (right).9
dipamp),18 the chirality element of chiral ylide ligands can also be
located not only at the backbone12,15b,16,19 but also at the coordi-
nating C atom. Complexes with asymmetric ylidic carbon atoms
(derived from R3P+–CHR0R00 phosphoniums where R0 – R00 and
R,R0 – +PR3) are numerous, but the first enantiomerically resolved
examples have been reported in 2003 in the rhodium series,20
and in 2004 in the palladium series.21 These ligands are stabilized/
semi-stabilized ylides of chiral (sulfinylmethyl)triarylphosphoni-
ums,22 based on the 1,2-bis(diphenylphosphino)benzene (o-dppb)
core, and more precisely on Schmidbaur’s phosphino-methylphos-
phonium 1a.23,15b The chiral phosphonium precursor 2a is stereo-
This carbon center remains however acidic, and in the rhodium
series, the kinetic diastereoisomer (SC)-3a was shown to epimer-
ize to the thermodynamic diastereoisomer (RC)-3a under basic
conditions.20 The putative yldiide intermediate 5 was finally iso-
lated after treatment of (RC)-3a with NaH at low temperature
(Scheme 1).24
In order to prevent the stereochemical lability of the asymmet-
ric ylidic carbon, the analogous complexes 3b–c and 4b–c of the
ylides of phosphoniums 2b–c were targeted (Scheme 2), where
the acidic hydrogen atom of 3a and 4a is replaced by an alkyl group
(R = Me, i-Pr). The results are detailed below.
genic at the sulfinyl center, but not at the
a-carbon atom. When
treated with 1 equiv of n-BuLi followed with one equivalent of
transition metal salt ([Rh(cod)2][PF6] or PdCl2(MeCN)2), the result-
ing mononuclear complex 3a or dinuclear complex 4a is formed
diastereoselectively at the asymmetric ylidic carbon atom.20,21
2. Results and discussion
Two strategies for accessing ylide complexes with a resolved
asymmetric trisubstituted ylidic carbon atom could be envisaged
p-Tol
H
p-Tol
O
p-Tol
p-Tol
S
S
H
S
O
S
O
O
Ph2P
C
NEt3
Ph2P CH2
1) n-BuLi
Ph2P
C
Ph2P C
Rh(cod)
PPh2
[M]
Rh(cod)
PPh2
PPh2
PPh2
2) [M]-X
[M] = Rh(cod)
(SS,RC)-3a
(thermodynamic epimer, also formed by
complexation of 2a at 20ºC in 80 % de)
2a
(SS,SC)-3a: M = Rh(cod)
(kinetic epimer formed at 45ºC in 80 % de)
–
(SS,SC)-4a: M = (PdCl)1/2
(epimer formed at 20ºC in 75 % de
p-Tol
and at –60ºC in 67 % de)
S
O
NaH
Ph2P CH3
Ph2P
C
Rh(cod)
THF,
–78ºC
PPh2
PPh2
75%
1a
(SS)-5
(yldiide complex)
Scheme 1. Coordination chemistry of chiral phosphino-(sulfinylmethyl)phosphonium ylide ligands from Rh(I) and Pd(II) precursors [M]–X = [Rh(cod)2][PF6] or
PdCl2(MeCN)2.20,21 In the rhodium series, epimerization of the ylidic carbon center occurs through an yldiide complex 5 where this carbon atom is no longer stereogenic.24
p-Tol
p-Tol
p-Tol
*
*
*
S
Ph2P C *
H
R
R
R
S
S
O
O
O
Ph2P CH2
Ph2P
C
Ph2P C
*
*
R
Rh(cod)
PPh2
[PdCl]
PPh2
PPh2
PPh2
2b: R = Me
2c: R = i-Pr
1b: R = Me
1c: R = i-Pr
3b: R = Me
3c: R = i-Pr
4b: R = Me
4c: R = i-Pr
Scheme 2. Targeted phosphonium precursors and rhodium and palladium complexes of phosphino-(
a-sulfinylalkyl)phosphonium ylide ligands with a trisubstituted a-
carbon center.

R. Zurawinski et al. / Tetrahedron: Asymmetry 21 (2010) 1777–1787
1779
(Scheme 2): (i) through direct
scribed complexes 3a, 4a, or their phosphonium precursor 2a (with
a disubstituted -carbon atom: Scheme 1) and (ii) through -sulf-
a
-alkylation of the previously de-
2.2.
a
-Sulfinylation of alkylphosphoniums 1b–c
a
a
The second strategy relies on a possible a
-sulfinylation of high-
inylation of higher alkyl-phosphonium precursors 1b or 1c
(Scheme 2).
er alkylphosphoniums 1b–c, followed by complexation of the
ylides of the resulting phosphoniums 2b–c to rhodium or palla-
dium centers. The alkylphosphoniums 1b–c were first targeted
by monoalkylation of o-dppb.
2.1. Attempted a-alkylation of the (sulfinylmethyl)
phosphoniums 2a and 3a
2.2.1. Attempted
1c
a-sulfinylation of the iso-butylphosphonium
In a first approach to complex 3b (R = Me), the yldiide rhodium
complex 5 (generated by treatment of enantiomerically pure com-
Reaction of o-dppb with iso-butyl iodide followed by anion ex-
change of the formed phosphonium iodide afforded iso-butylphos-
phonium 1c (31P NMR: d (ppm) = 22.51 (d) and ꢀ14.81 (d),
JPP+ = 22.3 Hz) in 90% yield. The ylide generated from 1c by treat-
ment with a base was then reacted with menthyl-(S)-p-tolylsulfi-
nate, but regardless the conditions, the corresponding alkenyl
phosphonium salt 7 was isolated in up to 46% yield (31P NMR: d
(ppm) = 11.07 (d) and ꢀ14.04 (d), JPP+ = 32.4 Hz. Scheme 4). The
ꢀ
plex 3aꢁPF6 with NaH or KHMDS) was reacted with different
methylating agents (MeOTf and [Me3O][BF4]). An unidentified
product, exhibiting broad 31P NMR signals at 27.4 and 20.6 ppm,
could be purified by flash column chromatography, but underwent
decomposition in acidic medium (slowly in CDCl3 and quickly in the
presence of HBF4) to give another unidentified rhodium complex
(
31P NMR: d (ppm) = 61.0 (d), 1JRhP = 150 Hz). Facing these difficul-
ties which can be due to a poor regioselectivity of the alkylation
reaction (four nucleophilic sites are a priori possible: C, S, O, and
Rh), the phosphonium precursor 2b was then targeted by methyla-
tion of the free ylide of phosphonium 2aꢁPF6ꢀ, generated by treat-
ment with n-BuLi or NaH. Different conditions using MeI and
MeOTf as methylating agents were investigated, but in most cases
only starting phosphonium 2a and phosphonio-phosphine oxide 6
were observed.23a In one case only (NaH and MeOTf), the desired
steric strain of the putatively formed a-sulfinylalkylphosphonium
intermediate 2c thus likely promotes elimination of sulfenic acid
to the trisubstituted phosphonioalkene 7. A less bulky alkyl group
than iso-butyl was therefore desired at the phosphonium center:
the methylphosphonium 2b was thus targeted.
2.2.2. a-Sulfinylation of ethylphosphonium 1b
P-Ethylation of o-dppb was carried out by addition of ethyl io-
a
-methylated phosphonium 2b (later synthesized in good yield
dide, and after metathesis with potassium hexafluorophosphate,
ꢀ
and fully characterized: see below) was obtained diastereoselec-
tively in minute quantity and in a racemic form (Scheme 3).
the salt 1bꢁPF6 was isolated in 97% overall yield. Treatment of
1b by a stoichiometric amount of n-Buli, followed by addition of
p-Tol
p-Tol
S
S
O
O
Ph2P
CH3
Ph2P
C
Ph2P CH2
1) NaH
Me
+...
+
O
P
H
2) MeOTf
PPh2
PPh2
Ph2
( )-2b
one isolated diastereoisomer
6
2a
Scheme 3. Attempted preparation of the phosphino-(a-sulfinylethyl)phosphonium 2b (obtained in trace amounts under the indicated conditions).
1) n-BuLi
PPh2
Ph2P
Ph2P
PF6
[NH4][PF6]
1) i-Bu-I
2) p-Tol-S(O)OMenth
PF6
PPh2
[2c]
PPh2
PPh2
2) [NH4][PF6]
-p-TolSOH
7•PF6
o-dppb
1c•PF6
Scheme 4. Outcome of the attempted synthesis of (S)-
a-sulfinylisopropylphosphonium 2c (Scheme 2).
•
p-Tol
•
S
Me
O
Ph2P CH2
Ph2P C
PPh2
PPh2
1) n-BuLi
2) p-Tol-S(O)OMenth
Me
PPh2
PF6
H
1) Et-I
( )
PPh2
PF6
2) KPF6
3) [NH4][PF6]
–
–
97 %
1b.PF6
2b.PF6
o-dppb
74 %
89 % d.e.
Scheme 5. Straightforward preparation of the (a-sulfinylethyl)phosphonium 2b from o-ddpb.

1780
R. Zurawinski et al. / Tetrahedron: Asymmetry 21 (2010) 1777–1787
menthyl-(S)-(p-tolyl)sulfinate afforded the sulfinylethylphospho-
nium 2b in 74% yield (Scheme 5).
The triclinic space group (Pꢀ1) is however achiral, and both the
enantiomers (RS,RC)-2b and (SS,SC)-2b are present in the racemate
crystal. Racemization was confirmed by the specific rotation of a
The 31P NMR spectrum of the crude product exhibited two sys-
tems at dP = 31.5, ꢀ10.3 ppm (JPP = 14.2 Hz) and dP = 30.0, ꢀ11.0 ppm
(JPP = 20.2 Hz) in a 94.5/5.5 ratio, which were assigned to the two
epimers of 2b. The major epimer was purified by column chroma-
tography and fully characterized by 1H and 13C NMR spectroscopy.
In particular, the P+–CH(CH3)–S(O) protons resonate at 5.67 ppm
(dq, JHH = 7.2 Hz, JHP+ = 14.0 Hz) and 1.35 ppm (dd, JHH = 6.9 Hz,
JHP+ = 17.5 Hz). The stereochemistry of 2b was finally assigned to
polycrystalline sample (½a D25
¼ 0). This unexpected racemization
ꢃ
of the sulfinyl fragment can be tentatively explained by a Berry-
like pseudorotation mechanism26 of the intermediate pentacoordi-
nated sulfurane adduct resulting from nucleophilic attack of
menthyl-(S)-p-tolylsulfinate (Scheme 6).27 In this mechanism, the
steric strain specifically induced by the methyl substituent of 1b
(as compared to the unsubstituted phosphonium 1a from which
racemization does not occur20,21), would be the driving force of
the epimerization at the sulfur center. In parallel, the control of
*
*
the R ,R (erythro) configuration by X-ray diffraction analysis of a
single crystal (Fig. 2).25
*
*
the relative configuration of the ylidic carbon of (R ,R )-2b in 89%
de would correspond to the thermodynamic equilibrium between
the racemic
a-sulfinylethylphosphonium acid and the released
lithium menthoxide base (Schemes 5 and 6).
3. Complexation of the ylide of ethylphosphonium 2b
Attempts at complexation of the phosphonio-phosphine (R*,R*)-
2b with [Rh(cod)2]+ failed to produce a stable complex, probably
because of electrostatic repulsion between the cationic charges
(the ethandiyl-bridged diphosphonium salt of o-dppb was ob-
tained instead).23b By contrast, the neutral ylide of (R*,R*)-2b gen-
erated by addition of n-Buli in THF (detected by 31P NMR
spectroscopy at d (ppm) = ꢀ14.7 (d), +27.3 (d), JPP = 22 Hz, in the
same range as the ylide of 2a),20 was expected to react with either
cationic Rh(I) or neutral Pd(II) precursors to give the corresponding
ylide complexes.
3.1. Rhodium(I) complex of the ylide of ethylphosphonium 2b
The transient ylide of rac-2b was first reacted with 0.5 equiva-
lent of [RhCl(cod)]2 in THF at room temperature to give the rho-
dium complex 3b in 70% yield (Scheme 7). The 31P NMR
spectrum of the reaction mixture indicated the presence of a single
isomer at dP = 31.2 and 21.7 ppm (JPP+ = 25.0 Hz, JRhP+ = 8.1 Hz). The
product was purified by flash column chromatography and fully
Figure 2. ORTEP view of the X-ray crystal structure of the (SS,SC)-enantiomer of the
sulfinylethylphosphonium (R*,R*)-2b with thermal ellipsoids drawn at the 30%
probability level (H atoms are omitted for clarity). Space group: Pꢀ1 (triclinic),
R1[I > 2r(I)] = 0.0516. Selected bond distances (Å): C–Me = 1.539(4); C–
P+ = 1.845(3); C–S = 1.842(3); S–O = 1.489(2).25
O
S
+
Ph2P
CHMe
PPh2
O
p-Tol
= R
Ar =
OR
S
OR
Berry pseudorotations
[……]
CHMe
PPh2Ar
p-Tol
p-Tol
S
O
O
CHMe
ArPh2HP
–
RO
–RO
CHMe
PPh2Ar
p-Tol
p-Tol
O
S
S
CHMe
O
ArPh2P
(SS)-2b
(RS)-2b
Scheme 6. Representative possible intermediates, interconverting via Berry pseudorotation processes, accounting for the racemization of the sulfur center during the
formation of -sulfinylethylphosphonium 2b from menthyl-(SS)-p-tolylsulfinate and the ylide of ethylphosphonium 1b.
a

R. Zurawinski et al. / Tetrahedron: Asymmetry 21 (2010) 1777–1787
1781
p-Tol
p-Tol
p-Tol
O
S
S
S
O
O
[Rh(cod)2][PF6]
Me
n-BuLi
Ph2P
C
Ph2P
C
Me
PPh2
Ph2P C
( )
( )
( )
Me
Rh(cod)
H
PPh2
THF
70 %
PPh2
rac-(R*,S*)-3b•PF6
-sulfinylethyl)phosphonium 2b at a ‘soft’ Rh(I) fragment.
100 % d.e.
PF6
–
–
.
rac-(R*,R*)-2b PF6
Scheme 7. Complexation reaction of the ylide of rac-(
a
characterized. The 1H NMR signal of the methyl group is slightly
deshielded at 1.63 ppm (d, JHP+ = 19.5 Hz), compared to the starting
phosphonium 2b at 1.35 ppm (see above). The stereochemistry of
complex 3b was unambiguously assigned to the (R*,S*) (threo) con-
figuration by X-ray diffraction analysis of a single crystal (Fig. 3).25
It shows that the rhodium center entered the same side from
which the proton was abstracted by the base. The diastereoselec-
tivity of the complexation process (100% de) is thus induced by
the sulfinyl moiety: it is qualitatively identical to the 90:10 diaste-
reoselectivity (80% de) of the formation, at 20 °C, of the analogous
the rhodium series, the corresponding complex 4b was obtained
as a single isomer (31P NMR: dP = 26.3 and 19.3 ppm, JPP+ = 30.6 Hz)
in 70% yield (Scheme 8).
The stereochemistry of 4b was assigned to the (R*,R*) configura-
tion by X-ray diffraction analysis of a single crystal (Fig. 4),25 show-
ing that the palladium center entered the opposite side from which
*
*
the proton was abstracted from (R ,R )-2b.
Rh(I) complex (SS,RC)-3a from optically pure
a-disubstituted meth-
ylphosphonium 2a (Scheme 1).20
Figure 4. ORTEP view of the X-ray crystal structure of the (SS,SC)-enantiomer of the
erythro palladium complex salt (R*,R*)-4bꢁPF6ꢀ, with thermal ellipsoids drawn at
the 30% probability level (H atoms are omitted for clarity). Space group: P21/n
(monoclinic), R1[I > 2r(I)] = 0.0532. Selected bond distances (Å): C–Me = 1.542(6),
MeC–P+ = 1.792(5), MeC–S = 1.818(5), Pd–CMe = 2.072(5), Pd–O = 2.162(3), Pd–
S = 2.7243(16), S–O = 1.565(4).25
Figure 3. ORTEP view of the X-ray crystal structure of the (SS,RC)-enantiomer of the
threo rhodium complex salt (R*,S*)-3bꢁPF6ꢀ, with thermal ellipsoids drawn at the
30% probability level (H atoms are omitted for clarity). Space group: P21,21,21
The total erythro diastereoselectivity of the complexation pro-
(orthorhombic), R1[I > 2r(I)] = 0.0849. Selected bond distances (Å): C–
Me = 1.552(14), MeC–P+ = 1.818(12), MeC–S = 1.864(13), Rh–CMe = 2.231(11), S–
O = 1.497(8).25
*
*
cess leading to (R ,R )-4b is thus qualitatively identical to the dia-
stereoselectivity of the formation of the analogous Pd(II) complex
(SS,SC)-4a from enantiomerically pure a-disubstituted methylphos-
phonium 2a (Scheme 1).21 The diastereoselectivity is also opposite
to the threo diastereoselectivity observed in the formation of the
rhodium complex (R*,S*)-3b (see above). This difference might be
related to the stabilizing interaction occurring between the sulfinyl
oxygen atom and the ‘hard’ Pd(II) center of 4b (in contrast, the
3.2. Palladium(II) complex of the ylide of ethylphosphonium 2b
The transient ylide of rac-2b was then treated with a stoichiom-
etric amount of PdCl2(MeCN)2 in THF. As previously observed in
p-Tol
•
p-Tol
p-Tol
S
S
S
O
O
O
PdCl2(MeCN)2
n-BuLi
Ph2P
C
H
Ph2P
C
Ph2P
C
( )
( )
( )
Me
Pd
PPh2
Me
PPh2
Me
THF
Cl
70 %
PPh2
100 % d.e.
PF6
PF6
–
–
rac-(R*,R*)-2b.PF6
rac-(R*,R*)-4b•PF6
-sulfinylethylphosphonium 2b at a ‘hard’ Pd(II) fragment.
Scheme 8. Complexation of the ylide of rac-
a

1782
R. Zurawinski et al. / Tetrahedron: Asymmetry 21 (2010) 1777–1787
Rh(I) center of 3b can be classified as ‘soft’). This interaction indeed
provides the mononuclear 2b-PdCl2 complex 4b with a formal 16-
V(O) : 3.69 + 2.88
[–1.1]
V(Cl) : 5.00 + 3.00
Cl
valence electron count (this count was fulfilled by
l–chloro
[–0.5]
O
p-Tol
0.15
bridges in the dinuclear [2a-PdCl2]2 complex (SS,SC)-4a: see
Scheme 1).21 The unusual bonding features of 4b are analyzed in
detail below.
1.40
1.62
[+1.1]
[+0.4]
S
1.99
Pd
2.21
2.36
[–1.0]
1.91
C
Ph2P
[+1.8]
V(S) : 2.55
3.3. Analysis of electrostatic versus covalent interactions in the
PPh2
Me
a-sulfinyl-ylide-Pd(II) complex 4b
[+2.7]
*
*
The S–O bond of (R ,R )-4b (ꢄ1.565 Å) is strongly elongated as
Figure 6. Scaled populations of selected ELF valence basins of complex (SC,SC)-4b.
*
AIM charges in square brackets. B3PW91/6-31G /DZVP(Pd) level of calculation.
compared to the S–O bond of the free ligand 2b (ꢄ1.489 Å), and
falls in the 1.50–1.60 Å range of previously reported O-bonded or
g
2-S,O-bonded transition metal sulfinyl complexes.28 In a related
area in common with the border of the Pd ELF basin but also by
the formal ‘core’ character of the Pd ELF basin: the latter indeed
contains the 4d OA population, which actually corresponds to va-
lence electrons of a Pd(II) center (the so-called V(O) and V(Cl) ba-
sins of oxygen and chlorine lone pairs also appear formally
‘disynaptic’ through their large common borders with the Pd ba-
sin). This situation is clearly visible on the ELF basin partition
map (Fig. 7), where the white Pd basin and the green disynaptic
V(S,O) basin have a negligible common border anyway. A two-cen-
ter Pdꢁ ꢁ ꢁO interaction can therefore be envisioned.
Pd-sulfinyl complex, the sulfinyl O-coordination has been claimed
to be preferred to the alternative free sulfinyl arrangement that
would result in electronic repulsion between the sulfur lone pair
and the filled non-bonding d2z orbital of the palladium atom.28c
AIM atomic charges29 of the Pd complex (SC,SC)-4b have been
*
calculated at the B3PW91/6-31G /DZVP(Pd) level on the crystal
geometry. They reveal a one-electron polarization of the S–O bond
and a residual positive charge at the Pd atom (Fig. 5). Considering
the quite long Pdꢁ ꢁ ꢁO distance (longer by 0.1 Å than the Pd–C dis-
tance), this charge separation suggests a strong electrostatic com-
ponent of the Pdꢁ ꢁ ꢁO interaction. Recently, a related sulfinyl-Pd
interaction was reported in the lowest energy transition state (de-
noted as 5-SN2) of the nucleophilic substitution-determining step
in a Suzuki–Miyaura cross-coupling reaction (Fig. 5).30 On the basis
of natural population analysis (NPA), the Pd-sulfinyl interaction
was claimed to be of electrostatic nature and to be responsible
for the stabilization of the transition state. Although (SC,SC)-4b
and 5-SN2 have not been studied at the same DFT level, the geom-
etry and atomic charges appear to be similar in both complexes
(Fig. 5). These hybrid DFT calculations, which essentially differ in
basis set, can thus be qualitatively compared to support a strong
electrostatic component of the Pd-sulfinyl interaction.
Metal-ligand bonding in (R*,R*)-4b was further investigated
using the topological electron localization function (ELF).31 ELF
analysis is indeed particularly suited for the discrimination be-
tween electrostatic and covalent interactions because it provides
a selective criterion of covalent bonding through the occurence
of disynaptic basins and corresponding attractors. Moreover ELF
populations are also much less sensitive to the level of calculation
than NBO analysis. The populations of ELF valence basins in the Pd
coordination sphere of (SC,SC)-4b are shown in Figure 6.
Figure 7. ELF basins partition map in the plane containing the palladium, sulfur and
ylide carbon nuclei of complex (SC,SC)-4b. Core basins are highlighted in white. The
‘monosynaptic’ valence basins of chlorine and oxygen atoms are highlighted in gray
and orange color, respectively (the corresponding core basins are hidden below the
mapping plane). The ‘disynaptic’ valence basin of the S–O bond is colored in green.
*
B3PW91/6-31G /DZVP(Pd) level of calculation.
The zero atomic contribution of Pd (namely the contribution of
the corresponding AIM basin) to the disynaptic ELF valence basin
The absence of valence attractor between the palladium and
oxygen core basins (Fig. 7), and the negligible atomic contribution
of Pd to the monosynaptic valence basins of oxygen V(O) indicate
that the Pdꢁ ꢁ ꢁO interaction is of electrostatic nature. This is sup-
ported by the AIM charge values (Fig. 6), showing that the S–O
V(S,O) of the S–O bond confirms the absence of a three-center
p-
interaction between the sulfinyl ligand and the Pd atom (the Pdꢁ ꢁ ꢁS
distance of ca. 2.724 Å is indeed non-bonding: see Fig. 5). This disy-
naptic character is supported not only by the negligible surface
[–1.0]
[–1.1]
Cl
1.568
O
Me
O
1.565
p-Tol
[+1.1]
2.148
Pd
2.162
2.972
2.724
[+1.2]
S
[+0.1]
2.252
Me3P
Pd
S
[+0.4]
2.203
Ph2P
1.796
2.466
2.072
C
1.818
[–0.7]
C
[–1.0]
2.404
Br
H
H
PPh2
Me
Figure 5. Selected experimental geometrical data (in the crystal state: see Fig. 4) and calculated AIM atomic charges (in square brackets) of the Pd complex (SC,SC)-4b at the
*
B3PW91/6-31G /DZVP(Pd) level (left). Calculated geometry and NPA charges of the analogous transition state 5-SN2 of Ref. 30 at the B3LYP/6-31+G(d,p)/SDD(Pd) level (right).
Bond distances in Å.

R. Zurawinski et al. / Tetrahedron: Asymmetry 21 (2010) 1777–1787
1783
bond is strongly polarized (qO = ꢀqS = ꢀ1.1 e; qPd = +0.4 e). This is
also in line with the analogous interaction observed in the transi-
tion state of Ref. 30 (see above). The very low population of the
disynaptic basin V(Pd,Cl) is also in favor of a mostly ionic Pd–Cl
bond (Fig. 6).
question is quantitatively addressed for the ylide-Pd(II) complex
(R*,R*)-4b from the above-described ELF analysis. As an alternative
to the valence bond (VB) method for weighting resonance on the
basis of the electronic wave functions,35 the populations of the
ELF valence basins can indeed be used for weighting resonance
on the basis of electron density.36 The meaning of the ELF meso-
meric forms (based on the observable electron density) is however
more direct (or crude) than that of VB resonance structures. In par-
Beyond the S+ꢁ ꢁ ꢁOꢀꢁ ꢁ ꢁPd+ꢁ ꢁ ꢁClꢀ electrostatic interactions evi-
denced above, the global ionic character of the bonding in complex
(R*,R*)-4b can be finally appraised by the molecular electrostatic
potential (MESP), generated by the molecular charge
distribution:32
ticular, as the
p orbital of the P@C double bond results from the
overlap of a 2pC AO with a combination of the rꢅP—C localized
MOs, the hypervalent resonance structure R3P@CHR0 should be re-
placed by the zwitterionic structure Rꢀ,R2P+@CHR0. This structure
may also be invoked as a complementary ELF mesomeric form in
the description of free ylides.24 In the Pd complex (R*,R*)-4b how-
ever, the three P–C bonds are equivalent in terms of length (1.800,
1.801, 1.798 Å) and scaled ELF population (2.37). Contributions of
the corresponding all-octet forms Phꢀ,Ph2P+@C cannot account
for the calculated P–C populations higher than 2.0, and are there-
fore discarded from the present analysis.
Z
X
ZA
jr ꢀ RAj
q
ðr0Þ
VðrÞ ¼
ꢀ
d3r0
jr ꢀ r0j
A
where ZA are the nuclear charges, RA the position of the nuclei, and
q
(r) the electron density.
The topological analysis of the MESP, proposed by Gadre et al.,33
is a highly valuable tool for exploring the reactive sites of a mole-
cule as well as their relative strengths. The minima of the MESP
indicate localization of electron density and the most favorable
sites for electrophilic attack, whereas the MESP textured on
isodensity surfaces is convenient for exploring the regions of posi-
tive MESP and finding the most favorable sites for nucleophilic at-
tack. Such a surface is shown in Figure 8 for the Pd complex (R*,R*)-
4b. This plot shows that the most positive MESP regions (in blue)
are located at the P and S nuclei, whereas the most negative MESP
values (in red) are obtained at the lone pairs of the chlorine and
oxygen atoms, thus illustrating the conclusion of ELF analysis.
Calculations show that the ELF populations of the disynaptic ba-
sins V(Pd,ylidicC) and V(P, ylidicC) of 4b (Fig. 6) are in reliable
agreement with the description of Figure 9, where the weight of
the minor
to the
1-C form (81%). Lower contributions of 6% and 11% of this
2-P,C haptomeric form were found from ELF analysis of models of
g
2-P,C haptomeric remains sizeable (19%), as compared
g
g
the (SS,RC)-3a rhodium phosphonium ylide complex and corre-
sponding (SS)-5 yldiide complex, respectively.24 To the best of
our knowledge, the
g
2-P,C ‘haptomeric’ form is suggested here
for the first time on the basis of the valuable tool of ELF analysis,
and might deserve to be investigated by alternative methods.
Cl
Cl
O
C
p-Tol
O
C
p-Tol
S
Pd
Pd
S
Ph2P
Ph2P
PPh2
PPh2
81%
Me
Me
19%
Figure 9. Weighted resonance forms for the description of the phosphonium ylide–
Pd(II) interaction in complex (SC,SC)-4b. The weights were obtained from ELF
analysis of Figure 6.36
4. Conclusion
The results show that chiral transition metal complexes (Rh(I)
and Pd(II)) of (a-sulfinylethyl)phosphonium ylide ligands bearing
an asymmetric trisubstituted ylidic carbon atom are chemically
and configurationally stable. In spite of the racemization occurring
during the complexation process, the configuration of these asym-
metric ylidic centers is totally controlled by the stereogenic sulfi-
Figure 8. Isodensity surface (0.02 a.u.) color-coded with the MESP of the phospho-
nium ylide-Pd(II) complex (SC,SC)-4b. Color scale: red MESP <0.0; yellow
MESP = 0.05; green MESP = 0.10; light-blue MESP = 0.20; dark-blue MESP >0.35.
*
*
nyl substituent. The racemic rhodium complex (R ,S )-3b was
shown to be active at a 1% catalytic ratio in the hydrogenation of
(Z)-a-acetamidocinnamic acid (89% yield after 72 h under 15 bar
3.4. Relevance of the
ylide complexes
g
2-P,C ‘haptomeric’ form in phosphonium
H2: see Experimental section). This activity is thus similar to that
of the corresponding rhodium complex (SS,RC)-3a with an epimer-
izable ylidic center.20 The racemic palladium complex (R*,R*)-4b
was also shown to be active at a 4% catalytic ratio in allylic substi-
tution of 3-acetoxy-1,3-diphenyl-1-propene with sodium dimethyl
malonate (99% yield after 16 h at room temperature: see experi-
mental section). The enantioselectivity of the catalysts 3b and 4b
with a non-epimerizable asymmetric ylidic center now deserves
to be investigated after achievement of their optical resolution
(e.g., by semi-preparative chiral HPLC techniques).
As emphasized in the introduction, the
g
2-P,C coordination
mode of phosphonium ylide is not known (Fig. 1). Although free
ylides ꢀare classically described by two resonance structures
(R3P+– CHR0MR3P = CHR0), only the zwitterionic one thus prefig-
ures the generally assigned
onding analysis however, the contribution of the apolar
g
1-C ‘haptomeric’ form.34 In a preb-
phosphoraalkene structure raises the question of the—anyway
minor—exact contribution of the
g
2-P,C haptomeric form. This

1784
R. Zurawinski et al. / Tetrahedron: Asymmetry 21 (2010) 1777–1787
Beyond the chemical and stereochemical results, joint experi-
gave [2-(diphenylphosphino)phenyl]-(ethyl)diphenylphosphoni-
ꢀ
mental–theoretical insights have gained into the bonding features
of phosphonium ylide ligands. ELF and MESP analyses show that
electrostatics plays an important role in governing the structure
um hexafluorophosphate 1bꢁPF6 as a white solid. Yield: 0.675 g
(97%), mp 148–149 °C. 31P NMR (CDCl3, 293 K): d 26.53 (d,
JPP+ = 22.6 Hz, P+), ꢀ14.65 (d, JPP+ = 22.6 Hz, P), ꢀ144.18 (septet,
of the highly polar Pd(II) complex (R ,R )-4b. On the basis of ELF
JPF = 712.9 Hz, PF6ꢀ). 13C NMR (CDCl3, 293 K):
d 143.02 (dd,
*
*
weighting of resonance in complex 4b, a
g
2-P,C haptomeric form
JCP+ = 11.4 Hz, JCP = 18.8 Hz), 139.18 (d, JCP+ = 11.5 Hz), 136.49 (dd,
JCP+ = 11.9 Hz, JCP = 10.0 Hz), 135.11 (d, JCP+ = 2.9 Hz), 134.59 (d,
JCP+ = 2.9 Hz), 133.46 (d, JCP = 6.7 Hz), 133.00 (d, JCP = 19.1 Hz),
132.97 (dd, JCP+ = 9.0 Hz, JCP = 2.2 Hz), 131.54 (d, JCP+ = 12.4 Hz),
130.25 (d, JCP+ = 12.6 Hz), 129.51, 128.88 (d, JCP = 7.3 Hz), 124.79
(dd, JCP+ = 87.0 Hz, JCP = 35.8 Hz), 119.29 (dd, JCP+ = 86.3 Hz,
JCP = 2.8 Hz), 19.21 (dd, JCP+ = 53.3 Hz, JCP = 15.0 Hz, CH2), 7.84
(dd, JCP+ = 5.3 Hz, JCP = 1.3 Hz, CH3). 1H NMR (CDCl3, 293 K): d
7.83–7.65 (m, 3H), 7.66–7.60 (m, 6H), 7.56–7.49 (m, 5H), 7.34–
7.29 (m, 2H), 7.27–7.22 (m, 4H), 6.90–6.84 (m, 4H), 3.57 (dq,
JHH = 7.4 Hz, JHP+ = 12.7 Hz, 2H, CH2), 1.37 (dt, JHH = 7.5 Hz,
JHP+ = 20.2 Hz, 3H, CH3). IR (KBr): 3054, 2984, 1436, 1114, 840,
694 cmꢀ1. FAB-MS m/z (relative intensity): 475 (100), 397 (5),
is suggested for the first time to contribute significantly to the
coordination mode of phosphonium ylide ligands (up to ca. 20%,
versus 80% for the
g
1-C haptomeric form).
5. Experimental
5.1. General remarks
THF and diethyl ether were dried and distilled over sodium/
benzophenone, pentane, dichloromethane, and acetonitrile over
CaH2. All other reagents were used as commercially available. All
reactions were carried out under argon atmosphere, using schlenk
and vacuum line techniques. Column chromatography was carried
þ
369 (16), 183 (17). HRMS calcd for C32H29P2 475.1745, found
475.1745. Anal. Calcd for C32H29F6P3: C, 61.94; H, 4.71; F, 18.37;
P, 14.98. Found: C, 61.90; H, 4.77; P, 15.18.
out on silica gel (60 Å, C.C 70–200 lm). The following analytical
instruments were used. 1H, 13C and 31P NMR: Bruker ARX 250,
DPX 300, AV 500. NMR chemical shifts d are in parts per million
(ppm), with positive values to high frequency relative to the tetra-
methylsilane reference for 1H and 13C and to H3PO4 for 31P.
5.1.3. [2-(Diphenylphosphino)phenyl](iso-butyl) diphenylphos-
ꢀ
phonium hexafluorophosphate 1cꢁPF6
To 1,2-bis(diphenylphosphino)benzene (0.48 g, 1.08 mmol) was
added iodo-2-methylpropane (3.2 g, 17.4 mmol) in DMF (4 mL)
and the mixture was stirred for 12 h at 80 °C. After evaporation
of the solvent under vacuum, the crude residue was extracted with
CH2Cl2 (10 mL) and the organic layer was washed with H2O
(20 mL). The resulting salt dissolved in CH2Cl2 (50 mL) was then
vigorously stirred with a saturated solution of potassium hexa-
fluorophosphate (1.0 g, 5.4 mmol) in water (20 mL) for 30 min.
The organic layer was separated and the procedure was repeated
using the same amount of saturated aqueous solution of potassium
hexafluorophosphate. The layers were separated and the organic
one was dried over Na2SO4. After filtration, evaporation of the sol-
vent gave [2-(diphenylphosphino)phenyl](iso-butyl)diphenylphos-
5.1.1. [2-(Diphenylphosphino)phenyl](ethyl) diphenylphosphon-
ium iodide 1bꢁIꢀ
To 1,2-bis(diphenylphosphino)benzene (2.7 g, 6.0 mmol) was
added ethyl iodide (29.0 g, 0.186 mmol) and the mixture was stir-
red for 16 h at room temperature. Excess of ethyl iodide was evap-
orated under reduced pressure and the residue was washed with
diethyl ether (7 mL). To remove the remaining ethyl iodide, the
crude product was dissolved in dichloromethane (10 mL), the sol-
vent was evaporated, and the residue was dried under reduced
pressure (100 °C/0.005 mmHg) for 3 h. Yield: 3.60 (99%),
mp = 196 °C. 31P NMR (CDCl3, 293 K): d 26.92 (d, JPP+ = 22.6 Hz,
P+), ꢀ14.95 (d, JPP+ = 22.7 Hz, P). 13C NMR (CDCl3, 293 K): d
142.89 (dd, JCP = 19.0 Hz, JCP+ = 11.3 Hz), 139.14 (d, JCP+ = 10.9 Hz),
136.99 (dd, JCP+ = 12.2 Hz, JCP = 10.0 Hz), 135.07 (d, JCP+ = 2.9 Hz),
134.45 (d, JCP+ = 2.9 Hz), 133.54 (d, JCP = 6.9 Hz), 133.27 (dd,
JCP+ = 9.7 Hz, JCP = 2.5 Hz), 132.96 (d, JCP = 19.0 Hz), 131.70 (d,
JCP+ = 12.3 Hz), 130.19 (d, JCP+ = 12.6 Hz), 129.45, 128.84 (d,
JCP = 7.2 Hz), 124.87 (dd, JCP+ = 86.8 Hz, JCP = 35.6 Hz), 119.40 (dd,
JCP+ = 86.2 Hz, JCP = 3.0 Hz), 20.17 (dd, JCP+ = 52.2 Hz, JCP = 13.3 Hz,
CH2), 8.09 (d, JCP+ = 5.1 Hz, CH3). 1H NMR (CDCl3, 293 K): d 8.02–
7.95 (m, 1H), 7.82–7.72 (m, 6H), 7.65–7.59 (m, 2H), 7.54–7.47
(m, 5H), 7.32–7.27 (m, 2H), 7.21 (dt, JHH = 7.5 Hz, JHP = 1.6 Hz,
4H), 6.86–6.80 (m, 4H), 3.88 (dq, JHH = 7.5 Hz, JHP+ = 15.0, 2H,
CH2), 1.35 (dt, JHH = 7.5 Hz, JHP+ = 20.2 Hz, 3H, CH3). IR (KBr):
3041, 2979, 2871, 2794, 1478, 1434, 1112, 996, 771, 749, 738,
718, 694 cmꢀ1. FAB-MS m/z (relative intensity): 475 (100), 369
ꢀ
phonium hexafluorophosphate 1cꢁPF6 as a white solid. Yield:
0.63 g (90%). 31P NMR (CD2Cl2, 293 K): d 22.51 (d, JPP+ = 22.3 Hz,
P+), ꢀ14.81 (d, JPP+ = 22.3 Hz, P), ꢀ144.44 (septet, JPF = 710.9 Hz,
PF6ꢀ). 13C NMR (CD2Cl2, 293 K):
d 143.10 (dd, JCP+ = 12.6
Hz, JCP = 20.1 Hz), 139.70 (d, JCP+ = 11.3 Hz), 135.90 (dd, JCP+
=
11.3 Hz, JCP = 10.1 Hz), 135.11 (d, JCP+ = 2.5 Hz), 134.64 (d,
JCP+ = 2.5 Hz), 133.43 (d, JCP = 6.3 Hz), 133.06 (dd, JCP+ = 10.1 Hz,
JCP = 2.5 Hz), 133.00 (d, JCP = 20.1 Hz), 131.18 (d, JCP+ = 12.6 Hz),
130.14 (d, JCP+ = 12.5 Hz), 129.54, 128.84 (d, JCP = 7.5 Hz), 125.75
(dd, JCP+ = 86.8 Hz, JCP = 35.2 Hz), 119.69 (dd, JCP+ = 85.6 Hz,
JCP = 2.5 Hz), 33.06 (dd, JCP+ = 47.8 Hz, JCP = 13.8 Hz, CH2), 25.23
(dd, JCP+ = 5.0 Hz, JCP = 2.5 Hz, CH), 23.96 (d, JCP+ = 8.8 Hz, CH3). 1H
NMR (CD2Cl2, 293 K): d 7.87–7.77 (m, 3H), 7.72–7.61 (m, 7H),
7.57–7.53 (m, 4H), 7.39–7.36 (m, 2H), 7.31–7.27 (m, 4H), 6.94–
6.90 (m, 4H), 3.46 (dd, JHH = 6.6 Hz, JHP+ = 13.1 Hz, 2H, CH2), 2.19
(m, 1H, CH), 1.05 (dd, JHH = 6.7 Hz, JHP+ = 1.1 Hz, 6H, CH3).
þ
(13). HRMS calcd for C32H29OP2 475.1738, found 475.1745. Anal.
Calcd for C32H29IP2: C, 63.80; H, 4.85; P, 10.28. Found: C, 63.71;
H, 4.71; P, 10.20.
5.1.4. [2-(Diphenylphosphino)phenyl][10-(p-tolylsulfinyl)ethyl]
ꢀ
diphenylphosphonium hexafluorophosphate 2bꢁPF6
5.1.2. [2-(Diphenylphosphino)phenyl](ethyl) diphenylphos-
To
a
stirred suspension of [2-(diphenylphosphino)phenyl]
ꢀ
ꢀ
phonium hexafluorophosphate 1bꢁPF6
(ethyl)diphenylphosphonium hexafluorophosphate 1bꢁPF6 (1.57 g,
2.53 mmol) in diethyl ether (130 mL) at ꢀ30 °C was added a solu-
tion of n-BuLi (1.01 mL of 2.5 M solution in hexane, 2.53 mmol).
The cooling bath was removed, and the mixture was allowed to
warm to room temperature. After 30 min the mixture was cooled
to ꢀ5 °C and (S)-(ꢀ)-menthyl p-toluenesulfinate (0.41 g, 1.4 mmol)
in diethyl ether (40 mL) was added. After stirring for 10 min at ꢀ5 °C
and 30 min at room temperature a precipitate of [2-(diphenylphos-
phino)phenyl](ethyl)diphenylphosphonium hexafluorophosphate
[2-(Diphenylphosphino)phenyl](ethyl)diphenylphosphonium
iodide 1bꢁIꢀ (0.674 g, 1.12 mmol) in dichloromethane (50 mL) was
vigorously stirred with saturated solution of potassium hexa-
fluorophosphate (0.8 g, 4.3 mmol) in water (6 mL) for 30 min. The
organic layer was separated and the procedure was repeated using
the same amount of saturated aqueous solution of potassium hexa-
fluorophosphate (0.8 g, 4.3 mmol). The layers were separated and
the organic one was dried over MgSO4. Evaporation of the solvent

R. Zurawinski et al. / Tetrahedron: Asymmetry 21 (2010) 1777–1787
1785
was filtered off, and the reaction was quenched with a solution of
ammonium hexafluorophosphate (1.5 g, 9 mmol) in THF (40 mL)
at ꢀ78 °C. Then the solvents were evaporated under reduced pres-
sure, water was added (40 mL), and the mixture was extracted with
CH2Cl2 (3 ꢆ 40 mL). The organic layer was dried over Na2SO4. The
solvent was evaporated, and the crude product was purified by flash
column chromatography using dichloromethane–acetone (40:1) as
the eluent. Yield: 0.79 g (74%), de = 89%, mp 114–123 °C (dec.). Ma-
jor isomer: 31P NMR (CDCl3, 213 K): d 31.49 (d, JPP+ = 14.2 Hz, P+),
ꢀ10.28 (d, JPP+ = 14.2 Hz, P), ꢀ144.47 (septet, JPF = 713.8 Hz, PF6ꢀ).
13C NMR (CDCl3, 213 K): d 143.64 (dd, JCP = 12.2 Hz, JCP+ = 12.2 Hz),
143.34, 139.25 (d, JCP+ = 11.6 Hz), 138.15 (dd, JCP = 10.7 Hz,
JCP+ = 10.7 Hz), 135.95, 135.77, 135.57, 135.35 (d, JCP+ = 10.9 Hz),
134.98 (d, JCP = 3.7 Hz), 134.20 (d, JCP = 20.6 Hz), 134.12 (d,
JCP+ = 11.3 Hz), 133.93 (d, JCP+ = 10.1 Hz), 132.04 (d, JCP = 14.8 Hz),
131.75 (d, JCP+ = 12.6 Hz), 131.03, 130.83 (d, JCP+ = 13.0 Hz), 130.37
(d, JCP+ = 9.8 Hz), 130.27, 129.45 (d, JCP+ = 15.3 Hz), 129.39, 129.20
(d, JCP = 5.6 Hz), 129.08 (d, JCP = 8.8 Hz), 124.55, 123.31 (dd,
JCP+ = 83.7 Hz, JCP = 36.6 Hz), 116.46 (d, JCP+ = 85.8 Hz), 114.85 (d,
JCP+ = 85.1 Hz), 54.19 (dd, JCP+ = 47.1 Hz, JCP = 19.6 Hz, P+CH), 22.01
(C6H4CH3), 9.17 (d, JCP = 3.5 Hz, P+CHCH3). 1H NMR (CDCl3, 213 K):
d 8.62–8.53 (m, 1H), 8.03–7.96 (m, 1H), 7.94–7.78 (m, 4H), 7.73 (t,
JHH = 6.6 Hz, 1H), 7.68–7.62 (m, 1H), 7.60–7.48 (m, 4H), 7.46 (t,
JHH = 7.4 Hz, 1H), 7.40 (d, JHH = 8.1 Hz, 2H), 7.36–7.30 (m, 2H), 7.26
(t, JHH = 7.1 Hz, 2H), 7.18 (t, JHH = 7.1 Hz, 2H), 7.04 (dd, JHH = 7.4 Hz,
JHP = 7.4 Hz, 2H), 6.87 (dd, JHH = 8.1 Hz, JHP = 8.1 Hz, 2H), 6.77–6.63
(m, 2H), 6.55 (dd, JHH = 7.6 Hz, JHP+ = 13.3 Hz, 1H), 5.67 (dq,
JHH = 7.2 Hz, JHP+ = 14.0 Hz, 1H, P+CHCH3), 2.42 (s, 3H, CH3C6H4),
1.35 (dd, JHH = 6.9 Hz, JHP+ = 17.5 Hz, 3H). IR (KBr): 3056, 2924,
1482, 1438, 1185, 1108, 1088, 1045, 839, 724, 691 cmꢀ1. FAB-MS
m/z (relative intensity): 613 (44), 473 (44), 397 (100), 369 (16).
HRMS calcd for C39H35OP2S+ 613.1884, found 613.1884. Anal. Calcd
for C39H35F6OP3S: C, 61.74; H, 4.65; P, 12.25. Found: C, 61.62; H,
4.70; P, 12.31.
JCP+ = 12.7 Hz), 129.39 (d, JCP = 9.5 Hz), 129.06 (d, JCP = 9.9 Hz),
128.89, 127.23, 124.83 (dd, JCP+ = 82.2 Hz, JCP = 19.8 Hz), 123.78
(d, JCP+ = 97.2 Hz), 120.85 (dd, JCP+ = 67.4 Hz, JCP = 1.6 Hz), 104.35
(dd, JCRh = 8.2 Hz, JCP = 8.2 Hz, cod-CH), 98.58 (dd, JCRh = 7.4 Hz,
JCP = 9.8 Hz, cod-CH), 89.92 (d, JCRh = 8.7 Hz, cod-CH), 87.12 (d,
JCRh = 8.7 Hz, cod-CH), 40.57 (ddd, JCRh = 24.9 Hz, JCP = 7.7 Hz,
JCP+ = 16.9 Hz, P+CRh), 31.04 (cod-CH2), 30.51 (d, JCP = 3.4 Hz, cod-
CH2), 29.37 (d, JCP = 2.4, cod-CH2), 28.66 (cod-CH2), 21.54
(CH3C6H4), 13.67 (P+CCH3). IR (KBr): 3057, 2921, 1436, 1090,
1028, 841, 744, 695, 558 cmꢀ1. FAB-MS m/z (relative intensity):
823 (16), 715 (23), 684 (15), 549 (40), 369 (20), 154 (100). HRMS
calcd for C47H46OP2RhS+ 823.1820, found 823.1793. Anal. Calcd
for C47H46F6OP3RhS: C, 58.27; H, 4.79; P, 9.59. Found: C, 58.305;
H, 4.71, P, 9.64.
ꢀ
5.1.6. Palladium(II) complex salt 4bꢁPF6
To a stirred solution of [2-(diphenylphosphino)phenyl][10-(p-
tolylsulfinyl)ethyl]diphenylphosphonium
(150 mg, 0.2 mmol) 2b in THF (8 mL) at ꢀ30 °C was added n-BuLi
(83 L of 2.4 M solution in hexane, 0.2 mmol). The cooling bath
hexafluorophosphate
l
was removed, and the mixture was allowed to warm to room tem-
perature. After 15 min bis(acetonitrile)dichloropalladium(II)
(52 mg, 0.22 mmol) was added and stirring was continued for
additional 3 h. The solvent was evaporated and a crude mixture
was purified by flash column chromatography (dichloromethane–
acetonitrile gradient) giving complex 4b as a yellow solid. Yield:
87 mg (70%), de = 100% (only 1 diastereomer), mp: 141–143 °C
(dec.). 31P NMR (CD2Cl2, 293 K): d 26.32 (d, JPP+ = 30.6 Hz, P+),
19.33 (d, JPP+ = 30.5 Hz, P), ꢀ144.47 (septet, JPF = 710.8 Hz, PF6ꢀ).
1H NMR (CD2Cl2, 293 K): d 8.23 (ddd, JHH = 8.3 Hz, JHP+ = 1.2 Hz,
JHP = 13.8, 2H), 8.05–7.95 (m, 4H), 7.77 (ddt, JHH = 7.6 Hz,
JHP+ = 0.7 Hz, JHP = 3.6 Hz, 2H), 7.71–7.62 (m, 2H), 7.59–7.38 (m,
12H), 7.31–7.22 (m, 4H), 6.72 (br d, JHH = 6.1 Hz, 2H), 2.43 (s, 3H,
C6H4CH3), 1.63 (dd, JHP+ = 3.7 Hz, JHP = 16.7 Hz, 3H, CH3). 13C NMR
(CD2Cl2, 293 K): d 145.81, 137.82 (dd, JCP+ = 3.3 Hz, JCP = 8.8 Hz),
137.03 (dd, JCP+ = 8.3 Hz, JCP = 10.4 Hz), 135.97 (d, JCP = 2.9 Hz),
135.92 (dd, JCP+ = 6.0 Hz, JCP = 2.6 Hz), 135.40 (d, JCP = 3.1 Hz),
134.77 (d, JCP+ = 12.0 Hz), 134.10 (d, JCP = 9.8 Hz), 133.86 (d,
JCP = 10.2 Hz), 133.85 (d, JCP = 12.0 Hz), 133.30 (d, JCP+ = 11.9 Hz),
132.48 (d, JCP+ = 3.1 Hz), 132.27 (d, JCP+ = 3.0 Hz), 132.08 (d
JCP = 2.0 Hz), 131.08 (d, JCP = 12.1 Hz), 130.96 (dd, JCP+ = 40.7 Hz,
JCP = 6.4 Hz), 130.83, 130.64 (d, JCP = 12.9 Hz), 129.27 (d,
JCP+ = 12.5 Hz), 129.09 (d, JCP+ = 12.2 Hz), 128.45 (d, JCP+ = 62.8 Hz),
124.29, 123.80 (d, JCP+ = 61.4 Hz), 122.70 (dd, JCP+ = 12.3 Hz,
JCP = 91.7 Hz), 118.81 (dd, JCP+ = 2.7 Hz, JCP = 75.9 Hz), 118.38 (d,
JCP = 95.8 Hz), 21.48 (C6H4CH3), 20.06 (dd, JCP+ = 5.4 Hz,
JCP = 54.4 Hz, P+CPd), 15.20 (P+CCH3). IR (KBr): 3057, 2923, 1438,
1100, 841, 746, 691 cmꢀ1. FAB-MS m/z (relative intensity): 755
(5), 473 (20), 307 (16), 154 (100). Anal. Calcd for
ꢀ
5.1.5. Rhodium(I) complex salt 3bꢁPF6
To a stirred solution of [2-(diphenylphosphino)phenyl][10-(p-
tolylsulfinyl)ethyl]diphenylphosphonium
hexafluorophosphate
ꢀ
2bꢁPF6 (100 mg, 0.132 mmol) in THF (8 mL) at ꢀ30 °C was added
n-BuLi (57 lL of 2.3 M solution in hexane, 0.132 mmol). The cool-
ing bath was removed, and the mixture was allowed to warm to
room temperature. After 15 min, bis(1,5-cyclooctadiene) rho-
dium(I) hexafluorophosphate (70 mg, 0.152 mmol) was added
and stirring was continued for additional 3 h. The solvent was
evaporated and a crude mixture was purified by flash column chro-
matography (dichloromethane–acetone gradient) to give complex
3b as an orange solid. Yield: 87 mg (70%), de = 100% (only 1 diaste-
reomer), mp 139–144 °C (dec.). 31P NMR (CDCl3, 273 K): d 31.25
(dd, JPP+ = 25.0 Hz, JRhP+ = 8.1 Hz, P+), 21.67 (dd, JPP+ = 25.0 Hz,
JPRh = 154.8 MHz, P), ꢀ144.24 (septet, JPF = 712.6 Hz, PF6ꢀ). 1H
NMR (CDCl3, 273 K): d 9.26 (dd, JHH = 8.4 Hz, JHP+ = 11.3 Hz, 1H),
7.97 (t, JHH = 7.5 Hz, 1H), 7.86 (t, JHH = 7.6 Hz, 1H), 7.81–7.73 (m,
5H), 7.72–7.66 (m, 2H), 7.65–7.50 (m, 5H), 7.48–7.38 (m, 2H),
7.37–7.26 (m, 6H), 7.20–7.13 (m, 4H), 6.40 (dd, JHH = 8.2 Hz,
JHP+ = 11.4 Hz, 1H), 4.95–4.87 (m, 1H, cod-CH), 3.86–3.76 (m, 2H,
cod-CH), 3.74–3.68 (m, 1H, cod-CH), 2.36 (s, 3H, C6H4CH3), 2.40–
2.18 (m, 2H, cod-CH2), 2.21–1.68 (m, 6H, cod-CH2), 1.63 (d,
JHP+ = 19.5 Hz, 3H, P+CCH3). 13C NMR (CDCl3, 273 K): d 141.99,
138.52 (d, JCP+ = 8.4 Hz), 138.44 (d, JCP+ = 12.5 Hz), 137.15–136.85
(m, 2C), 136.08 (dd, JCP+ = 7.1 Hz, JCP = 35.9 Hz), 135.89 (d,
JCP+ = 10.0 Hz), 135.34 (dd, JCP+ = 2.7 Hz, JCP = 4.9 Hz), 135.11 (d,
JCP+ = 2.7 Hz), 133.81 (d, JCP+ = 2.7 Hz), 133.14 (d, JCP = 13.0 Hz),
133.06 (d, JCP = 11.2 Hz), 132.37 (dd, JCP+ = 11.9 Hz, JCP = 1.3 Hz),
132.13 (d, JCP+ = 8.8 Hz), 131.37 (d, JCP = 45.4 Hz), 131.24 (d,
JCP = 1.8 Hz), 131.12 (d, JCP = 1.9 Hz), 130.43 (d, JCP+ = 12.4 Hz),
130.05 (d, JCP = 43.6 Hz), 129.91 (d, JCP+ = 9.2 Hz), 129.67 (d,
C39H34ClF6OP3PdS: C, 52.07; H, 3.81; P, 10.33. Found: C, 52.21; H,
3.88; P, 10.20.
5.1.7. [2-(Diphenylphosphoryl)ethyl]triphenylphosphonium
ꢀ
hexafluorophosphate 6ꢁPF6
[2-(Diphenylphosphino)phenyl][10-(p-tolylsulfinyl)ethyl]diphe-
ꢀ
nylphosphonium hexafluorophosphate 2aꢁPF6
(70 mg, 0.092
mmol) in THF (4 mL) was heated at 50 °C for 66 h. The solvent
was evaporated and the crude mixture was purified by column
chromatography (dichloromethane–methanol gradient) to give
[2-(diphenylphosphoryl)ethyl]triphenylphosphonium hexafluoro-
phosphate 6 as a white solid. Yield: 35 mg (60%), mp 237 °C. 31P
NMR (CD3CN, 293 K):
d 29.5 (d, JPP+ = 50.7 Hz, P), 25.5 (d,
JPP+ = 50.7 Hz, P+), ꢀ144.5 (septet, JPF = 706.5 Hz, PF6ꢀ). 1H NMR
(CD3CN, 293 K): d 7.92–7.86 (m, 3H), 7.75–7.66 (m, 16H), 7.65–
7.60 (m, 2H), 7.57–7.52 (m, 4H), 3.47–3.37 (m, 2H, P(O)CH2),
2.65–2.55 (m, 2H, CH2P+). 13C NMR (CD3CN, 293 K): d 135.36 (d,

1786
R. Zurawinski et al. / Tetrahedron: Asymmetry 21 (2010) 1777–1787
JCP+ = 3.0 Hz), 133.84 (d, JCP+ = 10.1 Hz), 132.43 (d, JCP = 2.7 Hz),
131.28 (d, JCP = 100.3 Hz), 130.75 (d, JCP = 9.6 Hz), 130.34 (d,
JCP+ = 12.7 Hz), 128.98 (d, JCP = 11.9 Hz), 117.50 (d, JCP+ = 86.8 Hz),
21.91 (dd, JCP = 66.7 Hz, JCP+ = 4.5 Hz), 15.43 (d, JCP+ = 53.8 Hz). IR
(KBr): 3060, 2928, 1439, 1185, 1123, 838, 691 cmꢀ1. FAB-MS
m/z (relative intensity): 491 (100), 289 (60), 147 (48). HRMS
5.2. Computational details
AIM29 and ELF31 analyses of the experimental structure of the
Pd(II) complex (SC,SC)-4b of the phosphino-(sulfinylethyl)phospho-
nium ylide ligand were performed with the TOPMOD program37 at
the B3PW91/6-31G*/DZVP(Pd)38 level of calculation.39
The gas phase molecular electrostatic potential (MESP) was
computed for the experimental geometries at the same level as
mentioned above using GAUSSIAN03.39 Visualization of the isodensity
surfaces colour coded with the MESP was performed using
Molden.40
þ
calcd for C32H29OP2 491.1694, found 491.1694. Anal. Calcd for
C32H29F6OP3: C, 60.39; H, 4.59; P, 14.60. Found: C, 60.42; H, 4.70;
P, 14.72.
5.1.8. 2-(Diphenylphosphino)phenyl](20-methylpropen-10-
ꢀ
yl)diphenylphosphonium hexafluorophosphate 7ꢁPF6
Acknowledgments
2-(Diphenylphosphino)phenyl](iso-butyl)diphenylphosphonium
hexafluorophosphate 1cꢁPF6 (0.15 g, 0.23 mmol) was dissolved in
ꢀ
This work was performed with the support of the Laboratoire
Européen Associé (LEA) financed by the CNRS (France), and by
the Ministry of Science and Higher Education in Poland. The
authors thank CALMIP (Calcul intensif en Midi-Pyrénées, Tou-
louse—France), IDRIS (Institut du Développement et des Ressourc-
es en Informatique Scientifique—Orsay—France), and CINES
(Centre Informatique de l’Enseignement Supérieur—Montpellier—
France) for computing facilities.
Et2O (30 mL). After treatment with n-BuLi (0.103 mL of 2.5 M solu-
tion in hexane, 0.256 mmol) at ꢀ60 °C, the reaction mixture was
allowed to warm to room temperature. After addition of a solution
of (ꢀ)-menthyl-(S)-p-toluenesulfinate (34 mg, 0.115 mmol) in
Et2O (5 mL) at ꢀ60 °C, the solution was stirred at room tempera-
ture for 30 min. After filtration, the reaction was quenched by
addition of a solution of NH4PF6 in THF. After evaporation of the
solvent, the crude product was purified by column chromatogra-
phy (CH2Cl2/acetone gradient). Recrystallization of the dried resi-
due from THF with a few drops of Et3N afforded phosphonium 7
as a white solid. Yield: 34 mg (46%). 31P NMR (CD2Cl2, 293 K): d
11.07 (d, JPP+ = 32.4 Hz, P+), ꢀ14.04 (d, JPP+ = 32.4 Hz, P), ꢀ144.36
(septet, JPF = 710.9 Hz, PF6ꢀ). 13C NMR (CD2Cl2, 293 K): d 169.13
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18.9 Hz), 139.33 (d, JCP+ = 11.3 Hz), 136.33 (dd, JCP+ = 12.6 Hz,
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