Cationic rhodium(I)-diolefin complexes containing an optically active C2-symmetric bis(sulfoximine) ligand: Synthesis and catalytic activity

Article abstract of DOI:10.1016/j.poly.2010.09.017

A series of cationic rhodium(I) complexes [Rh(diene)(N^N)][BF₄] (diene = 1,5-cyclooctadiene (cod), norbornadiene (nbd), tetrafluorobenzobarralene (tfb)), containing the optically pure bis(sulfoximine) ligand 1,2-bis(S-methyl-S-phenylsulfonimidoyl)benzene, have been synthesized and fully characterized. The structure of the R,R enantiomer of the ligand, and that of its cyclooctadiene-Rh(I) complex, were confirmed by means of single-crystal X-ray diffraction techniques. Studies on the catalytic activity of these complexes in acetophenone hydrosilylation and dimethyl itaconate hydrogenation are also reported.

Full text of DOI:10.1016/j.poly.2010.09.017

Polyhedron 29 (2010) 3380–3386
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Cationic rhodium(I)–diolefin complexes containing an optically active
C2-symmetric bis(sulfoximine) ligand: Synthesis and catalytic activity
a
a
a,
b
Victorio Cadierno a, , Josefina Díez , Sergio E. García-Garrido , José Gimeno , Antonio Pizzano
⇑
⇑
a Departamento de Química Orgánica e Inorgánica, Instituto Universitario de Química Organometálica ‘‘Enrique Moles” (Unidad Asociada al CSIC), Facultad de Química,
Universidad de Oviedo, E-33071 Oviedo, Spain
b Instituto de Investigaciones Químicas, Consejo Superior de Investigaciones Científicas (CSIC), Avda Américo Vespucio no. 49, Isla de la Cartuja, E-41092 Sevilla, Spain
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of cationic rhodium(I) complexes [Rh(diene)(N^N)][BF4] (diene = 1,5-cyclooctadiene (cod), nor-
bornadiene (nbd), tetrafluorobenzobarralene (tfb)), containing the optically pure bis(sulfoximine) ligand
1,2-bis(S-methyl-S-phenylsulfonimidoyl)benzene, have been synthesized and fully characterized. The
structure of the R,R enantiomer of the ligand, and that of its cyclooctadiene–Rh(I) complex, were con-
firmed by means of single-crystal X-ray diffraction techniques. Studies on the catalytic activity of these
complexes in acetophenone hydrosilylation and dimethyl itaconate hydrogenation are also reported.
Ó 2010 Elsevier Ltd. All rights reserved.
Received 18 August 2010
Accepted 16 September 2010
Available online 11 October 2010
Keywords:
Rhodium complexes
Sulfoximine ligands
Hydrogenation
Hydrosilylation
X-ray molecular structures
1. Introduction
B [5e,l], and the isolated and X-ray structurally characterized com-
plexes D [6f] and E [9] (see Fig. 2). In all cases the expected N-coor-
Sulfoximines, the monoaza analogues of sulfones discovered by
Bentley and co-workers in 1950s [1], are nowadays recognized as
versatile reagents in synthetic organic chemistry [2]. In particular,
enantiopure derivatives are widely employed as chiral auxiliaries
in the stoichiometric preparation of a diverse range of optically ac-
tive compounds [2]. Recent works, mainly from Bolm’s group, have
also demonstrated the utility of sulfoximines in asymmetric cataly-
sis [3–4]. In this context, several N,N- [5], N,O- [6] and N,P-donor [7]
ligands containing chiral sulfoximidoyl cores have been designed
and successfully applied in different enantioselective metal-
catalyzed transformations. Among them, C2-symmetric bis(sulfox-
imine) derivatives of types A–C (see Fig. 1) proved to be highly
effective ligands in asymmetric copper-catalyzed Diels–Alder reac-
tions [5a,d,e,j,l] and palladium-catalyzed allylic alkylation processes
[5b,c], affording products with excellent enantiomeric excesses.
Surprisingly, despite the privileged C2-symmetry of these li-
gands which enables their potential use in further catalytic trans-
formations [8], efforts devoted to develop their coordination
chemistry have been scarce. In fact, in most of the catalytic studies
mentioned above the corresponding metal-complexes were not
isolated, the only information presently available on the coordina-
tion features of these ligands being restricted to some spectro-
scopic measurements on Cu(II) derivatives generated in situ from
dination of the sulfoximine units to the metal was observed [10].
We note that, while involvement in catalysis of E has not been de-
scribed, D is able to promote the catalytic oxidation of sulfides with
cumyl hydroperoxide, giving sulfoxides in very good yields, albeit
as racemates [6f].
As a contribution to filling this gap, we decided to explore the
suitability of these C2-symmetric bis(sulfoximines) to act as chelat-
ing ligands for rhodium. In particular, using enantiopure 1,2-bis(S-
methyl-S-phenylsulfonimidoyl)benzene 1 in both its (S,S) and (R,R)
forms as model (see Fig. 3), a series of cationic rhodium(I)–diolefin
complexes have been synthesized and tested as catalysts in ke-
tone-hydrosilylation and olefin-hydrogenation reactions. Results
from this study are presented herein. At this point, we must note
that, to the best of our knowledge, no sulfoximine–rhodium com-
plexes have been described to date in the literature [11].
2. Experimental
2.1. General information
All manipulations were performed under an atmosphere of dry
nitrogen using vacuum-line and standard Schlenk techniques. Sol-
vents were dried by standard methods and distilled under nitrogen
before use. All reagents were obtained from commercial suppliers
and used without further purification, with the exception of (R)-S-
methyl-S-phenylsulfoximine [12], the ligand (S,S)-1 [5a], and
⇑
Corresponding authors.
E-mail addresses: vcm@uniovi.es (V. Cadierno), jgh@uniovi.es (J. Gimeno).
0277-5387/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2010.09.017

V. Cadierno et al. / Polyhedron 29 (2010) 3380–3386
3381
Fig. 1. Generic structures of the C2-symmetric bis(sulfoximine) ligands used in asymmetric catalysis.
and in the absence of light, with AgBF4 (0.163 g, 0.84 mmol) for
1 h. The AgCl formed was then filtered off (over Kieselgühr) and
the resulting solution evaporated to dryness to afford a yellow
oily residue. A solution of (S,S)-1 (0.308 g, 0.8 mmol) in dichloro-
methane (20 mL) was then added and the mixture stirred at room
temperature overnight. The resulting solution was then filtered
over Kieselgühr, the filtrate evaporated to dryness, and the yellow
solid residue washed with diethyl ether (3 ꢃ 20 mL) and dried in
vacuo. [Rh(cod)(S,S)-1][BF4]: Yield: 77% (0.420 g); Anal. Calc. for
RhC28H32F4N2O2S2B (682.42 g molꢀ1): C, 49.28; H, 4.73; N, 4.11.
Found: C, 49.41; H, 4.72; N, 4.02%; Conductivity (acetone, 20 °C)
Fig. 2. The only isolated metal-complexes containing chiral C2-symmetric bis(sul-
foximine) ligands.
113
X
ꢀ1 cm2 molꢀ1
;
½
a 2D0
ꢁ
¼ ꢀ46:7ꢂ (c = 0.001 M in CHCl3). IR
(KBr)
m
= 3553 (m), 3097 (m), 3061 (m), 3019 (m), 2925 (m),
2881 (m), 2835 (m), 1997 (w), 1918 (w), 1830 (w), 1623 (w),
1581 (m), 1478 (s), 1448 (s), 1432 (m), 1405 (m), 1284 (s), 1222
(s), 1066 (s), 1010 (s), 957 (s), 872 (m), 812 (s), 755 (s), 687 (s),
626 (m), 565 (m), 536 (s), 522 (s), 498 (s), 463 (m); 1H NMR
(CD2Cl2) d = 1.38, 1.51, 1.90 and 2.17 (m, 2H each, CH2), 3.35
and 3.99 (br, 2H each, @CH), 3.58 (s, 6H, CH3), 6.83 (m, 4H,
CHarom), 7.68–8.68 (m, 10H, CHarom) ppm; 13C{1H} NMR (CD2Cl2)
d = 33.0 and 34.0 (s, CH2), 42.6 (s, CH3), 78.4 and 79.1 (d,
1JCRh = 13.5 Hz, @CH), 121.0, 124.8, 128.2, 129.4 and 134.9 (s,
CHarom), 138.5 and 141.0 (s, Carom) ppm. [Rh(nbd)(S,S)-1][BF4]:
Yield: 89% (0.474 g); Anal. Calc. for RhC27H28F4N2O2S2B
(666.37 g molꢀ1): C, 48.67; H, 4.24; N, 4.20. Found: C, 48.55; H,
Fig. 3. The C2-symmetric bis(sulfoximine) ligand employed in this work.
complexes [{Rh(l-Cl)(cod)}2] (2a) [13], [{Rh(l-Cl)(nbd)}2] (2b)
[14] and [{Rh( -Cl)(tfb)}2] (2c) [15], which were prepared by
l
following the methods reported in the literature. Infrared spectra
were recorded on a Perkin–Elmer 1720-XFT spectrometer. The
conductivities were measured at room temperature, in ca.
10ꢀ3 mol dmꢀ3 acetone solutions, with a Jenway PCM3 conductim-
eter. The C, H, and N analyses were carried out with a Perkin–Elmer
2400 microanalyzer. Optical rotations (a) at 20 °C at the sodium
D-line were measured in a Perkin–Elmer 343 polarimeter. Gas
chromatographic measurements were made on a Hewlett–Packard
4.31; N, 4.10%; Conductivity (acetone, 20 °C) 98
X
ꢀ1 cm2 molꢀ1
m = 3547 (m),
;
½
a 2D0
ꢁ
¼ ꢀ124:0ꢂ (c = 0.001 M in CHCl3). IR (KBr)
3017 (m), 2941 (s), 2862 (s), 2803 (m), 2017 (w), 1617 (w),
1581 (m), 1490 (s), 1447 (s), 1405 (m), 1371 (m), 1307 (m),
1222 (s), 1089 (s), 1058 (s), 1007 (s), 993 (s), 812 (m), 747 (m),
685 (m), 621 (w), 562 (w), 534 (m), 520 (s); 1H NMR (CD2Cl2)
d = 1.00 (s, 2H, CH2), 2.89 (br, 2H, CH), 3.43 and 3.83 (br, 2H each,
@CH), 3.66 (s, 6H, CH3), 6.74 and 6.94 (m, 2H each, CHarom), 7.85
(m, 6H, CHarom), 8.42 (m, 4H, CHarom) ppm; 13C{1H} NMR (CD2Cl2)
HP6890 equipment using
250 m) or a Gamma-Dex™ 225 (30 m, 250
spectra were recorded on
a
Supelco Beta-Dex™ 120 (30 m,
m) column. NMR
Bruker DPX-300 instrument at
l
l
a
300 MHz (1H), 282.4 MHz (19F), or 75.4 MHz (13C) using SiMe4 or
CFCl3 as standards. DEPT experiments have been carried out for
all the compounds reported.
1
d = 43.7 (br, CH), 50.7 (s, CH3), 54.2 and 54.6 (d, JCRh = 10.8 Hz,
3
@CH), 62.0 (d, JCRh = 7.7 Hz, CH2), 122.5, 125.2, 129.3, 130.5 and
136.0 (s, CHarom), 136.8 and 140.8 (s, Carom) ppm. [Rh(tfb)(S,S)-
1][BF4]: Yield: 90% (0.575 g); Anal. Calc. for RhC32H26F8N2O2S2B
(799.52 g molꢀ1): C, 48.07; H, 3.28; N, 3.50. Found: C, 48.12; H,
2.2. Preparation of (R,R)-1,2-bis(S-methyl-S-phenylsulfonimidoyl)
benzene ((R,R)-1)
3.31; N, 3.49%; Conductivity (acetone, 20 °C) 115
X
ꢀ1 cm2 molꢀ1
m = 3619 (m), 3545
;
a 2D0
ꢁ
¼ ꢀ97:3ꢂ (c = 0.001 M in CHCl3). IR (KBr)
Compound (R,R)-1, isolated as a white solid in 64% yield, was
synthesized from 1,2-dibromobenzene and (R)-S-methyl-S-phenyl-
sulfoximine following strictly the same method described by Bolm
½
(m), 3063 (m), 3027 (m), 2931 (m), 1706 (w), 1635 (w), 1581
(w), 1498 (s), 1448 (m), 1406 (w), 1376 (m), 1320 (w), 1303
(m), 1224 (s), 1122 (s), 1091 (s), 1039 (s), 1007 (s), 999 (s), 948
(m), 893 (m), 855 (m), 815 (m), 753 (s), 686 (m), 629 (w), 535
(m), 521 (m); 19F{1H} NMR (CD2Cl2) d = ꢀ159.8 and ꢀ147.2 (d,
´
and Simic for the preparation of its enantiomer (S,S)-1 [5a]. Anal.
Calc. for C20H20N2O2S2 (384.52 g molꢀ1): C, 62.47; H, 5.24; N,
7.29. Found: C, 62.51; H, 5.19; N, 7.33%;
(c = 0.001 M in CHCl3).
½
a 2D0
ꢁ
¼ 170:4ꢂ
3
2F each, JFF = 21.7 Hz, CFarom), ꢀ150.8 (s, BF4ꢀ); 1H NMR (CD2Cl2)
d = 2.59 and 3.23 (dd, 2H each, 3JHH = 5.9 and 5.9 Hz, @CH), 3.63 (s,
3
2.3. Preparationofcomplexes[Rh(diene){j
2(N,N)-(S,S)-1}][BF4](diene=
1,5-cyclooctadiene ([Rh(cod)(S,S)-1][BF4]), norbornadiene
([Rh(nbd)(S,S)-1][BF4]), tetrafluorobenzobarralene
([Rh(tfb)(S,S)-1][BF4])
6H, CH3), 5.18 (t, 2H, JHH = 5.9 Hz, CH), 7.05 and 7.21 (d, 2H each,
3JHH = 3.2 Hz, CHarom), 7.91 (m, 6H, CHarom), 8.46 (m, 4H, CHarom
)
ppm; 13C{1H} NMR (CD2Cl2) d = 40.6 and 40.7 (d, JCRh = 3.7 Hz,
2
1
CH), 43.9 (s, CH3), 55.2 and 55.4 (d, JCRh = 11.1 Hz, @CH), 123.1,
125.9, 129.5, 131.1 and 136.7 (s, CHarom), 137.2, 141.3 and 142.0
1
1
(s, Carom), 138.0 (d, JCF = 213.5 Hz, CF), 145.3 (d, JCF = 219.1 Hz,
CF) ppm.
A solution of the appropriate [{Rh(
(0.4 mmol) in acetone (20 mL) was treated, at room temperature
l-Cl)(diene)}2] dimer 2a–c

3382
V. Cadierno et al. / Polyhedron 29 (2010) 3380–3386
2.4. Preparation of complexes [Rh(diene){j
2(N,N)-(R,R)-1}][BF4]
Table 1
Crystal data and structure refinement for (R,R)-1 and [Rh(cod)(R,R)-1][BF4].
(diene = 1,5-cyclooctadiene ([Rh(cod)(R,R)-1][BF4]), norbornadiene
([Rh(nbd)(R,R)-1][BF4]), tetrafluorobenzobarralene ([Rh(tfb)(R,R)-
1][BF4])
(R,R)-1
[Rh(cod)(R,R)-
1][BF4]
Empirical formula
Formula weight
T (K)
C
20H20N2O2S2
RhC28H32F4N2O2S2B
682.40
293(2)
1.5418
monoclinic
P21
384.50
200(2)
1.5418
orthorhombic
P212121
These complexes, isolated as air-stable yellow solids, were pre-
pared through the same procedure starting from the appropriate
[{Rh(l-Cl)(diene)}2] dimer 2a–c (0.4 mmol) and the optically pure
ligand (R,R)-1 (0.308 g, 0.8 mmol). The IR and NMR data obtained
were identical to those of their (S,S)-enantiomers. [Rh(cod)(R,R)-
1][BF4]: Yield 74% (0.403 g); Anal. Calc. for RhC28H32F4N2O2S2B
(682.42 g molꢀ1): C, 49.28; H, 4.73; N, 4.11. Found: C, 49.47; H,
k (Å)
Crystal system
Space group
Unit cell dimensions
a (Å)
b (Å)
c (Å)
7.3744(2)
10.4101(3)
24.4433(5)
90
90
90
1876.47(8)
4
1.361
2.708
808
9.8455(1)
19.5481(3)
15.1618(2)
90
92.924(1)
90
2914.25(7)
4
1.555
4.75; N, 3.97%; Conductivity (acetone, 20 °C) 111
X ;
ꢀ1 cm2 molꢀ1
a
(°)
½
a 2D0
ꢁ
¼ 46:9ꢂ (c = 0.001 M in CHCl3). [Rh(nbd)(R,R)-1][BF4]: Yield
b (°)
91% (0.485 g); RhC27H28F4N2O2S2B (666.37 g molꢀ1): C, 48.67; H,
4.24; N, 4.20. Found: C, 48.45; H, 4.37; N, 4.07%; Conductivity (ace-
c
(°)
V (Å3)
Z
tone, 20 °C) 102
X
ꢀ1 cm2 molꢀ1
;
½
a 2D0
ꢁ
¼ 123:8ꢂ (c = 0.001 M in
Dcalc (g cmꢀ3
)
Absorption coefficient (mmꢀ1
F(0 0 0)
)
6.556
1392
CHCl3). [Rh(tfb)(R,R)-1][BF4]: Yield 84% (0.537 g); Anal. Calc. for
RhC32H26F8N2O2S2B (799.52 g molꢀ1): C, 48.07; H, 3.28; N, 3.50.
Found: C, 48.16; H, 3.35; N, 3.52%; Conductivity (acetone, 20 °C)
Crystal size (mm)
h Range for data collection (°)
Index ranges
0.30 ꢃ 0.23 ꢃ 0.03 0.2 ꢃ 0.175 ꢃ 0.1
116
X
ꢀ1 cm2 molꢀ1; ½a 2D0
ꢁ
¼ 97:2ꢂ (c = 0.001 M in CHCl3).
3.62–69.65
ꢀ8 6 h 6 8
ꢀ12 6 k 6 12
ꢀ29 6 l 6 29
27 800
2.92–69.59
ꢀ11 6 h 6 11
ꢀ23 6 k 6 23
ꢀ18 6 l 6 18
105 096
2.5. General procedure for the catalytic hydrosilylation of
acetophenone
Reflections collected
Independent reflections (Rint
Completeness to theta max. (%)
Absorption correction
Refinement method
)
3512 (0.0039)
99.9
10 907 (0.0081
99.8
To a solution of acetophenone (0.14 g, 1.2 mmol) and the corre-
sponding rhodium(I) complex (0.012 mmol, 1 mol%) in THF
(2.5 mL) a solution of Ph2SiH2 (0.25 g, 1.3 mmol) in THF (2.5 mL)
was added dropwise under nitrogen atmosphere. The mixture
was stirred at room temperature for 24 h and then evaporated to
dryness. The degree of conversion was determined by 1H NMR
analysis. The resulting residue was dissolved in CH2Cl2 and treated
with aqueous HCl (2 M, 3 mL) for 2 h, followed by neutralisation
with NaHCO3 and dilution with CH2Cl2 (10 mL). The organic phase
was then separated, the aqueous layer extracted with CH2Cl2
(3 ꢃ 15 mL), and the combined organic fractions collected and
dried over MgSO4. Purification of the resulting 1-phenylethanol
from Rh and Si impurities was accomplished by Kugelröhr distilla-
tion. The enantiomeric composition of the product was finally
determined by chiral GC.
empirical (XABS2)
full-matrix least-squares on F2
Data/restraints/parameters
3512/0/237
1.036
0.0296
0.0760
0.0305
10 907/0/723
1.049
Goodness-of-fit on F2
a
R1 [I > 2
r
(I)]
(I)]
R1 (all data)
0.0392
0.0989
0.0409
0.1006
0.004(6)
a
wR2 [I > 2
r
wR2 (all data)
0.0768
Absolute structure parameter
Largest difference in peak/hole
ꢀ0.003(13)
0.526 and ꢀ0.635 0.926 and ꢀ0.641
(e Åꢀ3
)
P
P
2
2 1=2
½wðF2o ꢀ Fc2Þ ꢁ= ½wðF2oÞ ꢁ
.
a
R1 = (Fo ꢀ Fc)/Fo; wR2
¼
lated with the program Collect [16]. Data reduction and cell refine-
ment were performed with the programs HKL DENZO and SCALEPACK
[17]. Absorption correction was applied by means of XABS2 [18].
The software package WINGX was used for space group determi-
nation, structure solution and refinement [19]. The structures were
solved by Patterson interpretation and phase expansion using DIRDIF
[20]. Isotropic least-squares refinement on F2 using SHELXL97 was
performed [21]. During the final stages of the refinements, all posi-
tional parameters and the anisotropic temperature factors of all
the non-H atoms were refined (except F atoms of the counteranion
in [Rh(cod)(R,R)-1][BF4]; these disordered atoms were located by
difference maps and isotropically refined). The H-atoms were
2.6. General procedure for the catalytic hydrogenation of dimethyl
itaconate
In a glovebox, a Fischer–Porter reactor (80 mL) was charged
with a solution of dimethyl itaconate (0.23 g, 1.45 mmol) and the
corresponding rhodium(I) complex (0.003 mmol, 0.2 mol%) in
CH2Cl2 (4 mL). The vessel was brought outside the glovebox, sub-
mitted to four vacuum-hydrogen cycles, and finally pressurized
to 4 atm. The reaction mixture was stirred at room temperature
for 24 h. Then, the reactor was depressurized, the mixture evapo-
rated to dryness, redissolved in an ethyl acetate–hexane (1:1) mix-
ture, and passed through a short pad of silica. The resulting residue
was analyzed by 1H NMR to determine conversion and by chiral GC
for enantiomeric excess.
geometrically located and their coordinates were refined riding
P
on their parent atoms. The function minimized was ½ wðF2o ꢀ
P
2
F2c Þ= wðF2oÞꢁ1=2 where w ¼ 1=½r2ðF2oÞ þ ðaPÞ þ bPꢁ (a = 0.0472
and b = 0.4108 for (R,R)-1, and a = 0.0692 and b = 1.1217 for
[Rh(cod)(R,R)-1][BF4]) with
r
ðF2oÞ from counting statistics and
P ¼ ðMaxðF2o; 0Þ þ 2F2c Þ=3. Atomic scattering factors were taken
from the International Tables for X-ray Crystallography [22]. Geo-
metrical calculations were made with PARST [23]. The crystallo-
graphic plots were made with PLATON [24].
2.7. X-ray crystallography
Crystals suitable for X-ray diffraction analysis were obtained by
slow diffusion of n-pentane into saturated solutions of (R,R)-1 and
[Rh(cod)(R,R)-1][BF4] in acetone. The most relevant crystal and
refinement data are collected in Table 1. Diffraction data were re-
corded on a Nonius Kappa CCD single-crystal diffractometer using
3. Results and discussion
Cu K
a
radiation with the crystal-to-detector distance fixed at
The optically pure bis(sulfoximine) ligand (S,S)-1,2-bis(S-
methyl-S-phenylsulfonimidoyl)benzene [(S,S)-1] was synthesized
29 mm, using the oscillation method, with 2° oscillation and 40 s
´
following the method described by Bolm and Simic [5a], i.e.
exposure time per frame. The data collection strategy was calcu-

V. Cadierno et al. / Polyhedron 29 (2010) 3380–3386
3383
Scheme 1. Preparation of the C2-symmetric bis(sulfoximine) ligand (R,R)-1.
through a Pd-catalyzed bis-amination of 1,2-dibromobenzene with
excess of (S)-S-methyl-S-phenylsulfoximine. Using the same ap-
proach, we also succeeded in the preparation of its enantiomer
(R,R)-1 from (R)-S-methyl-S-phenylsulfoximine (Scheme 1).
As expected, compound (R,R)-1, isolated as a white solid in 64%
yield, presented identical spectroscopic features (1H and 13C{1H}
solution of this compound in acetone. An ORTEP plot of the mole-
cule is shown in Fig. 4; selected bond distances and angles are
´
NMR and IR) to those described by Bolm and Simic for (S,S)-1. In
addition, its identity was unequivocally confirmed by means of
X-ray diffraction methods. Single-crystals suitable for X-ray analy-
sis were obtained by slow diffusion of n-pentane into a saturated
Fig. 5. ORTEP-type view of the structure of complex [Rh(cod)(R,R)-1][BF4]
showing the crystallographic labelling scheme. Tetrafluoroborate anion and
hydrogen atoms have been omitted for clarity. Thermal ellipsoids are drawn at
the 10% probability level. Selected bond distances (Å) and angles (°): Rh–
N(1) = 2.176(3); Rh–N(2) = 2.131(3); Rh–C* = 2.0011(7); Rh–C** = 2.002(2); C(1)–
C(2) = 1.412(6); C(1)–N(1) = 1.440(5); N(1)–S(1) = 1.570(3); S(1)–O(1) = 1.456(3);
S(1)–C(7) = 1.766(4); S(1)–C(13) = 1.774(5); C(2)–N(2) = 1.430(5); N(2)–S(2) =
1.565(4); S(2)–O(2) = 1.442(4); S(2)–C(14) = 1.762(5); S(2)–C(20) = 1.763(5);
Fig. 4. ORTEP-type view of the structure of the bis(sulfoximine) ligand (R,R)-1
showing the crystallographic labelling scheme. Hydrogen atoms have been omitted
for clarity. Thermal ellipsoids are drawn at the 10% probability level. Selected bond
distances (Å) and angles (°): C(1)–C(2) = 1.410(3); C(1)–N(1) = 1.412(2); N(1)–
S(1) = 1.5143(16); S(1)–O(1) = 1.4474(12); S(1)–C(7) = 1.7811(18); S(1)–C(13) =
1.777(2); C(2)–N(2) = 1.409(2); N(2)–S(2) = 1.5346(15); S(2)–O(2) = 1.4541(13);
*
N(1)–Rh–C = 98.67(15);
**
N(1)–Rh–C = 165.6(3);
N(1)–Rh–N(2) = 76.75(14);
*
**
*
**
N(2)–Rh–C = 175.0(2); N(2)–Rh–C = 96.70(10); C –Rh–C = 87.32(8); C(1)–
N(1)–S(1) = 116.3(3); N(1)–S(1)–O(1) = 119.9(2); N(1)–S(1)–C(7) = 103.16(19);
N(1)–S(1)–C(13) = 109.5(2); O(1)–S(1)–C(7) = 109.9(2); O(1)–S(1)–C(13) = 107.8(2);
C(7)–S(1)–C(13) = 105.8(2); N(1)–C(1)–C(2) = 117.4(4); C(1)–C(2)–N(2) = 114.8(4);
C(2)–N(2)–S(2) = 118.9(3); N(2)–S(2)–O(2) = 119.3(2); N(2)–S(2)–C(14) = 105.71(19);
S(2)–C(14) = 1.7816(19);
N(1)–S(1)–O(1) = 122.84(9);
S(2)–C(20) = 1.758(2);
C(1)–N(1)–S(1) = 132.01(13);
N(1)–S(1)–C(13) =
N(1)–S(1)–C(7) = 101.83(9);
113.55(9); O(1)–S(1)–C(7) = 106.68(8); O(1)–S(1)–C(13) = 107.26(9); C(7)–S(1)–
C(13) = 102.35(9); N(1)–C(1)–C(2) = 126.78(17); C(1)–C(2)–N(2) = 118.04(16);
N(2)–S(2)–C(20)
=
107.9(2); O(2)–S(2)–C(14) = 109.0(2); O(2)–S(2)–C(20) =
C(2)–N(2)–S(2) = 120.81(13);
110.63(9); N(2)–S(2)–C(20) = 102.76(9); O(2)–S(2)–C(14) = 106.73(9); O(2)–S(2)–
C(20) = 109.48(9); C(14)–S(2)–C(20) = 104.60(9).
N(2)–S(2)–O(2) = 121.42(8);
N(2)–S(2)–C(14) =
108.5(3); C(14)–S(2)–C(20) = 105.6(2). C* and C** centres of mass of the C@C
double bonds of the 1,5-cyclooctadiene ligand (C(21), C(22) and C(25), C(26),
respectively).
Scheme 2. Preparation of the cationic rhodium(I) complexes [Rh(diene)(S,S)-1][BF4] and [Rh(diene)(R,R)-1][BF4].

3384
V. Cadierno et al. / Polyhedron 29 (2010) 3380–3386
listed in the caption. Bond angles at the sulfur atoms (101.83(9)–
122.84(9)°) revealed the stereogenic centers to be in a distorted
tetrahedral environment, the S–N (1.5143(16) and 1.5346(15) Å)
and S–O (1.4474(12) and 1.4541(13) Å) bond lengths observed ly-
ing within the expected range for S@N and S@O double bonds [25].
All these structural features compare well with those previously
described in the literature for uncoordinated sulfoximine units
[2h]. Slight deviation of the nitrogen atoms N(1) and N(2) from
the main aromatic plane was also observed as indicated by the
N(1)–C(1)–C(2)–N(2) torsion angle (ꢀ6.1(3)°).
insoluble in n-alkanes and diethyl ether. The formulation proposed
for these species is based on analytical data, conductance measure-
ments (1:1 electrolytes; KM = 98–116
X
ꢀ1 cm2 molꢀ1) as well as IR
and multinuclear NMR (1H, 13C{1H} and 19F{1H}) spectroscopy,
their NMR spectra showing in all cases the expected resonances
for the corresponding diolefin and j
2(N,N)-coordinated bis(sulfox-
imine) ligand (details are given in Section 2). Specific optical rota-
tions were also determined and confirmed the enantiopurity of the
compounds synthesized.
Moreover, the structure of the cyclooctadiene derivative [(R,R)-
3a][BF4] could be unequivocally confirmed by means of X-ray dif-
fraction methods. As in the precedent case, single-crystals suitable
for X-ray analysis were obtained by slow diffusion of n-pentane
into a saturated solution of the complex in acetone. Two crystallo-
graphically independent molecules were found in the asymmetric
unit. An ORTEP-type view of one of these molecules, along with se-
lected structural parameters, is shown in Fig. 5 (the other does not
differ significantly, i.e. bond distances 0.01 Å and bond angles
1°). The sum of the angles around Rh, formed by the coordinated
bis(sulfoximine) nitrogen atoms (N(1) and N(2)) and the centres of
mass of the olefinic units (C* and C**) (359.4°), is in complete ac-
cord with the expected square planar geometry about the rhodium
center. The observed Rh-to-cod ligand distances and angles fall
also within the expected range for this type of compounds [28].
Concerning the bis(sulfoximine) ligand skeleton, its coordination
to rhodium is reflected in the elongation of the C–N and N–S bond
distances (ca. 0.03 and 0.04 Å, respectively) as compared to the
structure of the free ligand (R,R)-1, the Rh–N(1) (2.176(3) Å) and
Rh–N(2) (2.131(3) Å) bond lengths observed being typical for
Rh(I)–N(sp2) bonds [29]. Unlike the free ligand, the nitrogen atoms
N(1) and N(2) lie now exactly within the aromatic plane (N(1)–
C(1)–C(2)–N(2) torsion angle = 0.3(5)°). However, we must note
that in the second molecule a similar value to that found in
(R,R)-1 was observed (ꢀ5.5(6)°).
Reactions of the acetone–rhodium solvates [Rh(diene)(ace-
tone)2][BF4], generated in situ by treatment of the readily available
dimers [{Rh(l-Cl)(diene)}2] (diene = cod (2a), nbd (2b), tfb (2c))
with silver tetrafluoroborate in acetone [26], with (S,S)-1 or
(R,R)-1, in dichloromethane at room temperature, resulted in the
high-yield formation (74–91%) of the novel cationic rhodium(I)–
diolefin derivatives [Rh(diene)(S,S)-1][BF4] and [Rh(diene)(R,R)-
1][BF4], respectively (diene = cod, nbd, tfb), via displacement of
the coordinated acetone molecules and the selective
j
2(N,N)-
bidentate coordination of the bis(sulfoximine) ligand to the metal
(Scheme 2) [27].
Complexes [Rh(diene)(S,S)-1][BF4] and [Rh(diene)(R,R)-
1][BF4], isolated as air-stable yellow solids, are soluble in polar sol-
vents, such as acetone, dichloromethane, chloroform and THF, and
Table 2
Rh-catalyzed hydrosilylation of acetophenone.a
Entry
Catalyst
Yield (%)b
ee (%)c
1
2
3
4
5
6
7
8
[Rh(cod)(R,R)-1][BF4]
[Rh(nbd)(R,R)-1][BF4]
[Rh(tfb)(R,R)-1][BF4]
71
99
99
99
95
99
99
99
0
0
0
0
0
0
0
0
The transition metal-catalyzed asymmetric hydrosilylation of
ketones, followed by hydrolysis of the resulting silyl ethers, pro-
vides a useful route to optically active alcohols [30]. Based on the
known effectiveness of Rh(I) catalysts with chiral C2-symmetric
N,N-donor ligands [31], we decided to explore the behaviour of
the bis(sulfoximine)–rhodium complexes synthesized in this cata-
lytic transformation. As shown in Table 2, we found that the reac-
tions of acetophenone with diphenylsilane in the presence of
complexes [Rh(diene)(R,R)-1][BF4] (1 mol%) for 24 h at room tem-
perature afford, after the hydrolysis step, the desired 1-phenyleth-
anol in high yields (71–99%) but, in all cases, in complete racemic
form (entries 1–3). Similar results were obtained employing di-
2a (0.5 mol%)/(R,R)-1 (1.1 mol%)
2b (0.5 mol%)/(R,R)-1 (1.1 mol%)
2c (0.5 mol%)/(R,R)-1 (1.1 mol%)
[Rh(nbd)(R,R)-1][BF4]d
[Rh(nbd)(R,R)-1][BF4]e
a
Reactions were carried out at room temperature in THF (5 mL), under a dry
nitrogen atmosphere, using 1.2 mmol of acetophenone and 1.3 mmol of Ph2SiH2.
b
Determined by 1H NMR.
Determined by chiral GC.
Reaction performed in the presence of 2 mol% of (R,R)-1.
Reaction performed in the presence of 4 mol% of (R,R)-1.
c
d
e
Table 3
Rh-catalyzed hydrogenation of dimethyl itaconate.a
Entry
Catalyst
Yield (%)b
ee (%)c
1
2
3
7
8
[Rh(cod)(R,R)-1][BF4]
[Rh(nbd)(R,R)-1][BF4]
[Rh(tfb)(R,R)-1][BF4]
[Rh(nbd)(R,R)-1][BF4]d
[Rh(nbd)(R,R)-1][BF4]e
79
94
91
92
90
0
0
0
0
0
a
Reactions were carried out at room temperature in CH2Cl2 (4 mL) using 1.45 mmol of dimethyl
itaconate.
b
Determined by 1H NMR.
Determined by chiral GC.
Reaction performed in the presence of 0.5 mol% of (R,R)-1.
Reaction performed in the presence of 1 mol% of (R,R)-1.
c
d
e

V. Cadierno et al. / Polyhedron 29 (2010) 3380–3386
3385
(k) S. Nakamura, T. Toru, Sci. Synthesis 31a (2007) 833;
(l) H.-J. Gais, Heteroatom Chem. 18 (2007) 472;
rectly catalytic systems consisting of 1:2 mixtures of the dimeric
precursors [{Rh( -Cl)(diene)}2] (diene = cod (2a), nbd (2b), tfb
l
(m) C. Worch, A.C. Mayer, C. Bolm, in: T. Toru, C. Bolm (Eds.), Organosulfur
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(2c)) and the enantiopure ligand (R,R)-1 (1 mol% of Rh; entries
4–6). It is well documented that the enantioselectivity of the
hydrosilylation reactions with complexes containing N-donor li-
gands can be enhanced by the use of ligand excess [31]. However,
in our case such a beneficial effect was not observed, reactions per-
formed with [Rh(nbd)(R,R)-1][BF4] (1 mol%) in the presence of 2
and 4 mol% of (R,R)-1 resulting also in the formation of 1-phenyl-
ethanol as a racemate (entries 7 and 8).
(c) M. Mellah, A. Voituriez, E. Schulz, Chem. Rev. 107 (2007) 5133;
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asymmetric catalysis, see H. Okamura, C. Bolm, Chem. Lett. 33 (2004) 482;
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Chemical and Biological Methods, Wiley–VCH, Weinheim, 2007, p. 149.
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enantioselectivity were also observed when complexes [Rh(die-
ne)(R,R)-1][BF4] (0.2 mol%) were used as catalysts for the C@C
hydrogenation of the functionalized olefin dimethyl itaconate. In
all cases racemic 2-methyl-succinic acid dimethyl ester was
formed. Analysis of the crude reaction mixtures by 1H NMR spec-
troscopy showed in all cases the presence of free (R,R)-1. This fact,
along with absence of chiral induction observed, strongly suggests
that the bis(sulfoximine) ligand does not remain coordinated to
rhodium during the catalytic event.
(c) C. Bolm, O. Simic´, M. Martin, Synlett (2001) 1878;
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4. Conclusion
In summary, in this work a series of enantiopure cationic
rhodium(I)–diolefin complexes, containing the C2-symmetric
bis(sulfoximine) ligand 1,2-bis(S-methyl-S-phenylsulfonimidoyl)-
benzene, have been synthesized and fully characterized. These
compounds represent the first examples of isolated sulfoximine–
rhodium complexes described to date in the literature [11]. Unfor-
tunately, their use in catalytic asymmetric ketone-hydrosilylation
and olefin-hydrogenation reactions only afforded disappointing
results.
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(h) J. Sedelmeier, C. Bolm, J. Org. Chem. 72 (2007) 8859.
CCDC 784405 and 784406 contain the supplementary crystallo-
graphic data for (R,R)-1 and [Rh(cod)(R,R)-1][BF4]. These data can
be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/
retrieving.html, or from the Cambridge Crystallographic Data
Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-
336-033; or e-mail: deposit@ccdc.cam.ac.uk.
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Acknowledgments
(d) S. Castillón, C. Claver, Y. Díaz, Chem. Soc. Rev. 34 (2005) 702;
(e) G. Desimoni, G. Faita, K.A. Jørgensen, Chem. Rev. 106 (2006) 3561.
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of identity of sulfoximines. For representative examples of sulfoximine–metal
complexes isolated and characterized, see Ref. [5f,g], [6c,e], [7d–f]: M. Zehnder,
C. Bolm, S. Schaffner, D. Kaufmann, J. Müller, Liebigs Ann. (1995) 125;
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Financial support from the Spanish MICINN (Projects CTQ2006-
08485/BQU, CTQ2009-08746/BQU and Consolider Ingenio 2010
(CSD2007-00006)) and the Gobierno del Principado de Asturias (FI-
CYT Project IB08-036) is acknowledged. S.E.G.-G. also thanks MIC-
INN and the European Social Fund for the award of a Ramón y Cajal
contract.
(c) C. Bolm, J. Müller, M. Zehnder, M.A. Neuburger, Chem. Eur. J. 1 (1995) 312;
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