Ir(I) complexes with oxazoline-thioether ligands: Nucleophilic attack of pyridine on coordinated 1,5-cyclooctadiene and application as catalysts in imine hydrogenation

Article abstract of DOI:10.1016/j.jorganchem.2004.03.015

Oxazoline-thioether ligands 6-11 react with [Ir(η⁴-COD)Py₂]PF₆ (COD=C₈H₁₂=1,5-cyclooctadiene) to give [Ir(σ-η²-C₈H₁₂ Py⁺)L] PF₆ (L=oxazoline-thio

Full text of DOI:10.1016/j.jorganchem.2004.03.015

Journal of Organometallic Chemistry 689 (2004) 1911–1918
www.elsevier.com/locate/jorganchem
Ir(I) complexes with oxazoline-thioether ligands: nucleophilic
attack of pyridine on coordinated 1,5-cyclooctadiene and
application as catalysts in imine hydrogenation
a b,
Ester Guiu , Carmen Claver , Sergio Castillon
a
*
ꢀ
a
Departament de Quꢀımica Analꢀıtica i Quꢀımica Orgꢁanica, Universitat Rovira i Virgili, Pl. Imperial Tꢁarraco 1, 43005 Tarragona, Spain
b
ꢀ
ꢀ
ꢁ
ꢁ
Departament de Quımica Fısica i Inorganica, Universitat Rovira i Virgili, Pl. Imperial Tarraco 1, 43005 Tarragona, Spain
Received 21 January 2004; accepted 15 March 2004
Abstract
Oxazoline-thioether ligands 6–11 react with [Ir(g4-COD)Py2]PF6 (COD ¼ C8H12 ¼ 1,5-cyclooctadiene) to give [Ir(r-g2-
C8H12Pyþ)L] PF6 (L ¼ oxazoline-thioether ligand) (12a–d) complexes resulted from the coordination of ligand to the metal and
subsequent nucleophilic attack of pyridine to one of the double carbon bond of COD with concomitant iridium–carbon bond
formation. When [Ir(g4-COD)2]BF4 was used as starting material, the reaction with ligands 7, 9 afforded the complexes [Ir(g4-
COD)L]BF4. Application of these iridium complexes to the reduction of N-(a-methyl)benzylidenbenzylamine gave low or negligible
enantioselectivity.
Ó 2004 Elsevier B.V. All rights reserved.
Keywords: Ir/oxazoline-thioether complexes; Ir/cyclooctenyl complexes; Iridium–carbon bond formation; Hydrogenation of imines
1. Introduction
The phosphino-oxazoline ligands (P\N), mainly
developed by Williams and co-workers [7], Pfaltz [8]
and Helmchen and co-workers [9], proved to be ver-
satile chiral ligands in a wide range of homogeneous
catalytic reactions such as imine [10] and olefin [11,12]
reductions with Ir(I) complexes as well as in
palladium-catalysed allylic substitution and Heck [9]
reaction.
Mixed ligands containing nitrogen and sulfur coor-
dinative atoms as oxazoline-thioether ligands were pre-
pared and used mainly by Pfaltz and his colleague [13],
Williams and co-workers [7a] and Helmchen and his
colleague [9a] in palladium-catalysed allylic alkylation
providing a high enantiocontrol [7a,14]. Besides, a
group of complexes fac-[ReX(CO)3(NS)] and fac-
[PtXMe3(NS)] with oxazoline-thioether ligands have
been described showing the presence of four diastereo-
isomers [15].
Chiral metal complexes containing oxazoline deriva-
tive ligands (1a–g) (Fig. 1) are efficient catalysts in
asymmetric reactions [1] such as enantioselective cooper
and ruthenium cyclopropanation [2], iron, magnesium,
copper-catalysed Diels Alder, copper-catalysed Michael
and Mannich reactions [3], rhodium-catalysed hydrosi-
lylation [4], iridium-catalysed hydrogenation [5] and
palladium-catalysed allylic substitution [6]. The asym-
metry induced by such heterobidentate systems is de-
termined by a combination of steric and electronic
interactions. Therefore, these ligands make it possible to
control the enantioselectivity in catalytic reactions by
creating an asymmetric environment provided by the
oxazoline moiety and by combining soft and hard donor
atoms (P, S, N) to modify the electronic properties on
the metal center. Moreover, modifying the chelate ring
size is another way of optimizing the effectiveness of the
catalytic system.
In this paper we report the preparation and structural
characterization of iridium complexes bearing oxazoline-
thioether ligands 6–9 (Scheme 2) and their application in
the hydrogenation of N-(a-methyl)benzylidenbenzyl-
amine.
* Corresponding author. Tel.: +34-977-559574; fax: +34-977-559563.
E-mail address: claver@quimica.urv.es (C. Claver).
0022-328X/$ - see front matter Ó 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2004.03.015

1912
E. Guiu et al. / Journal of Organometallic Chemistry 689 (2004) 1911–1918
R
R
PF6
R'
N
R
O
O
O
O
2X-
N
N
N
N
R
R'
R
O
O
O
Cu
N
R'
Rh
1c
N
N
Cu
N
iPr
R
R
1b
1a
BArF
R' R'
O
R
O
R
O
O
S
N
N
PAr2
Ph2P
N
Ph
R
Ir
Pd
iPr
R'
Pd
1e
R
R
1g
1d
Fig. 1. Chiral metal complexes bearing oxazoline derivative ligands.
2. Results and discussion
Complexes 12a–d were stable in air even in solution.
Mass spectroscopy analysis and NMR experiments al-
low us to elucidate the structure of compound 12a. The
presence of pyridine was confirmed by 1H and 13C
NMR, and also by MS spectroscopy. The highest peak
in the FAB spectrum at m=z ¼ 648:1 corresponds to the
iridium containing cation and another relevant peak
appears at m=z ¼ 570:1, which corresponds to Mþ ) Py.
The characteristic signals of the PFꢀ6 anion, which in this
case is the counterion of the pyridinium salt, were ob-
served in the 31P{1H} spectrum at )144.1 ppm (septu-
plet, JPꢀF ¼ 712:8 Hz) and in 19F{1H} spectrum at
)73.6 ppm (doublet, JFꢀP ¼ 711:7 Hz). 1H and 13C{1H}
NMR spectra showed signals corresponding to the COD
ligand and to the coordinated oxazoline-thioether li-
gand. The eight signals corresponding to the aliphatic
CH2 protons of COD were unambiguously assigned by
COSY and TOCSY experiments and by correlation with
their respective carbons. The assignment of the olefinic
COD protons revealed that whereas three of these sig-
nals appeared at the expected chemical shift (3–5 ppm),
a signal corresponding to H3 appeared at 2.59 ppm. The
With the aim of exploring the coordination chemistry
of the oxazoline-thioether ligands, we decided to prepare
ligands 6–11, which have methyl, phenyl or t-butyl
groups attached to the sulfur atom, and phenyl or iso-
propyl on the stereogenic center of the oxazoline ring
(Scheme 1). Compounds 6–9 have already been reported
[16] and ligands 10 and 11 have been synthesized and
characterized for the first time here following the re-
ported procedure [16].
We initially selected [Ir(g4-COD)(Py)2] PF6(COD ¼
C8H12 ¼ 1,5-cyclooctadiene, Py ¼ pyridine) which had
been used as a precursor to prepare several cationic Ir(I)
complexes [17]. The reaction of the chiral oxazoline-thi-
oether ligands 6–9 with [Ir(g4-COD)(Py)2]PF6 in anhy-
drous CH2Cl2 at room temperature was expected to occur
with the displacement of the two pyridine molecules af-
fording the corresponding cationic Ir(I) complexes [Ir(g4-
COD)L]PF6 (L ¼ oxazoline-thioetherligands). However,
the isolated complexes 12a–d showed the composition
depicted in Scheme 2.
(ii)
(i)
O
CN
CN
N
SR
SR
F
R'
2
R'=Ph
R'=i-Pr
R'=Ph
R'=i-Pr
R'=Ph
R'=i-Pr
6 R=Me
7 R=Me
8 R=Ph
9 R=Ph
10 R=t-Bu
11 R=t-Bu
3 R=Me
4 R=Ph
5 R=t-Bu
2-fluorobenzonitrile
Scheme 1. (i) RSNa, THF reflux. (ii) L-valinol or L-phenylglycinol, ZnCl2, C6H5Cl reflux.

E. Guiu et al. / Journal of Organometallic Chemistry 689 (2004) 1911–1918
1913
O
R'
N
2
+
[Ir(COD)Py ]PF
+
[Ir(σ−η -C H Py )L]PF
2
6
L=Ligand)
8
12
6
SR
12a R=Me, R'=Ph
94%
86%
98%
91%
6 R=Me, R'=Ph
i
i
12b R=Me, R'= Pr
7 R=Me, R'= Pr
12c R=Ph, R'Ph
8 R=Ph, R'Ph
i
i
12d R=Ph, R'= Pr
9 R=Ph, R'= Pr
Scheme 2. Synthesis of 12a–d.
Fig. 2. Proposed structure and a section of the HETCOR spectrum for 12a.
Table 1
NMR data of complex [Ir(r-g2-C8H12Pyþ)6]PF6 (12a)
HETCOR experiment showed a correlation of H3 with
the carbon appearing at 3.57 ppm (!) (Fig. 2). This
carbon must be directly bonded to the metal and since
there are no additional protons in the COD structure,
pyridine must be bonded to the neighbouring carbon. In
fact, the chemical shift of H4 and C4 are in agreement
with the values expected for a carbon bonded to a py-
ridinium salt.
Two isomers can be obtained for compounds 12a–d
depending on the formation of a C–Ir bond close to the
nitrogen of oxazoline ring or to the sulfur atom. Each of
them can give 16 diastereomers since three new stereo-
centres, apart from the one in the oxazoline ring, are
formed during the reaction. A NOE experiment carried
out in compound 12a showed a signal enhancement of
H11 and H12 of pyridine and H4 when the methyl group
was irradiated, confirming that the SMe group is close
to the C–Ir bond formed and at the same face as the
pyridinium substituent. Thus, considering a trans rela-
tionship between the C–Ir bond and the pyridinium
group, the resulting structure, [Ir(r-g2-C8H12Pyþ)L]
PF6 (12a), consists of monomeric units with an Ir atom
coordinated to a pyridinium-cyclooctenyl unit via r-C
and p-C@C bonds and to the oxazoline-thioether ligand
(Fig. 2). The relative stereochemistry of phenyl and SMe
groups was not determined. The NMR data for 12a are
collected in Table 1.
1H NMR (ppm)
13C NMR (ppm)
H1
H2
4.07
3.22
C1
C2
87.1
67.3
3.6
H3
2.59
4.66
C3
C4
H4
70.9
37.2
24.5
20.6
26.3
66.6
77.9
154.8
152.6
14.5
H5, H50
H6, H60
H7, H70
H8, H80
H9
2.43, 1.21
2.03, 1.74
1.74, 1.54
2.20, 1.46
5.81
C5
C6
C7
C8
C9
H10, H100
5.13, 4.94
8.95
8.54
C10
C11
C12
Me
H11
H12
Me
1.48
the coordinated cyclooctadiene takes place, resulting in
the formation of a pyridinium salt and a C–Ir bond.
Olefins, which are usually unreactive to nucleophiles, do
react with various nucleophiles such as malonates, ace-
tates, hydroxides, etc, leading to new carbon–carbon or
carbon–heteroatom bond formation when they are co-
ordinated to metals [18]. Transition metals such as pal-
ladium (II) or platinum (II) [19,20] are most suitable for
this reaction, since they withdraw electron density from
the olefins. Likewise, several examples were reported
with rhodium (I) [21] or iridium (I) [22] complexes, even
with NRnH3 ꢀ n as nucleophile agents.
A reasonable explanation for these observations is
that a nucleophilic attack of the pyridine to the C@C of

1914
E. Guiu et al. / Journal of Organometallic Chemistry 689 (2004) 1911–1918
1
The H NMR spectrum of complex 12b showed only
one species and the presence of pyridine, COD and
oxazoline-thioether ligands, as in 12a, although in this
case the signals were broad even at )50 °C and could not
be assigned unambiguously. 1H NMR of complexes
12c–d showed the presence of several species in equi-
librium, where pyridine signals were also present. Low-
ering the temperature did not result in the resolution of
one species. The presence of several species may be due
to the formation of several regioisomers as a conse-
quence of the nucleophilic attack of the pyridine on ei-
ther C3 or C4. Moreover, a new stereogenic center is
created when the sulfur is coordinated to the metal
center, which gives rise to diastereomeric mixtures. This
behaviour has previously been described for Rh [23] and
Pd [24] complexes with thioether ligands. Attempts to
obtain crystals suitable for X-ray diffraction were un-
successful. The formation of these regioisomeric or di-
astereomeric complexes seems to be favoured when a
phenyl substituent is attached to the sulfur atom.
Further investigation of the reaction of [Ir(g4-
COD)Cl]2 with ligand 7 in anhydrous CH2Cl2 at 50 °C
for 1–2 h under an inert atmosphere afforded the com-
plex [Ir(g4-COD)7]PF6 (13a) after anion exchange by
washing with an aqueous solution of NaPF6 and crys-
tallization from CH2Cl2/Et2O. Complex 13b was syn-
thesized by reacting [Ir(g4-COD)2]BF4 with ligand 9 in
anhydrous CH2Cl2.
The hydrogenation of C@N bond presents more
points of complexity that the corresponding reduction of
alkenes or ketones and most of the catalyst highly effi-
cient in C@C and C@O hydrogenation are ineffective in
imines reduction. Recently, the asymmetric hydrogena-
tion of prochiral imines has been received a great deal of
attention because it is a useful tool to obtain versatile
chiral auxiliaries [25]. Particularly, iridium complexes
containing chiral ligands have resulted to be highly ef-
ficient in this process [26].
In this context, the Ir/oxazoline-thioether ligands 6–
11 and complex 12a were tested as catalysts for the
asymmetric hydrogenation of imines. We focused on
reducing the imine N-(a-methyl)benzylidenbenzylamine
(14) (Scheme 3) by systems generated ‘in situ’ from
[Ir(COD)Cl]2/6–11 and under 50 bar of H2 pressure. The
results are collected in Table 2.
When the catalytic precursor was formed by [Ir(g4-
COD)Cl]2 in the presence of ligands 6–8 (entries 2–4),
conversions were lower than 50%. These results were
similar or lower than the conversion obtained with the
iridium precursor when no ligand was added (entry 1).
However, the iridium systems with ligands 9–11 (entries
5–7) provided conversions between 80% and 100% in the
same conditions. These results indicate that new cata-
lytic systems are formed at least when the oxazoline-
Elemental analysis of 13a and 13b showed that the
composition of these complexes was in agreement with
the proposed stoichiometry. The H NMR spectra of
1
*
[Ir]
N
N
H
13a,b were complex and signals broad, showing the
signals corresponding to the coordinated oxazoline-thi-
oether ligand and the g4-cyclooctadiene appearing at
the expected chemical shift.
[H2]
15
14
Scheme 3. Hydrogenation of N-(a-methyl)benzylidenbenzylamine.
Table 2
Hydrogenation of 14 catalysed by Ir/oxazoline-thioether ligands 6–11 and complex 12aa
Entry
Precursor/Ligand
Solvent
Additive
Conv [%]
1
2
[Ir(g4-COD)Cl]2/–
[Ir(g4-COD)Cl]2/6
[Ir(g4-COD)Cl]2/7
[Ir(g4-COD)Cl]2/8
[Ir(g4-COD)Cl]2/9
[Ir(g4-COD)Cl]2/10
[Ir(g4-COD)Cl]2/11
[Ir(g4-COD)Cl]2/6
[Ir(g4-COD)Cl]2/7
[Ir(g4-COD)Cl]2/8
[Ir(g4-COD)Cl]2/9
[Ir(g4-COD)Cl]2/10
[Ir(g4-COD)Cl]2/10
[Ir(g4-COD)Cl]2/10
[Ir(g4-COD)Cl]2/10
12a
MeOH/DCE (1:1)
MeOH/DCE (1:1)
MeOH/DCE (1:1)
MeOH/DCE (1:1)
MeOH/DCE (1:1)
MeOH/DCE (1:1)
MeOH/DCE (1:1)
MeOH/DCE (1:1)
MeOH/DCE (1:1)
MeOH/DCE (1:1)
MeOH/DCE (1:1)
MeOH/DCE (1:1)
MeOH
–
48
50
–
3
–
32
34
4
–
5
–
80
99
6
–
7
–
Bu4NI
100
73
8
9
Bu4NI
Bu4NI
44
28
10
11
12
13
14
15
16b
17
18
Bu4NI
Bu4NI
64
99
–
–
–
–
–
–
95
C6H6
100
100
13
MeOH/C6H6(1:1)
MeOH/DCE (1:1)
MeOH/DCE (1:1)
CH2Cl2
12a
12a
39
23
a 1% mol. [M], 1.25% mol. 6–11, 1% mol. Bu4NI, 50 bar H2, 25 °C, 24 h, DCE, dichloroethane.
b 30 bar.

E. Guiu et al. / Journal of Organometallic Chemistry 689 (2004) 1911–1918
1915
thioether ligands 9–11 are added to the iridium precur-
sor. Conversions were higher when a t-butyl group was
present at the sulfur atom.
Complex 12a was also active in the hydrogenation of
imine 14 although only in one instance, some enanti-
oselectivity (15%) was achieved.
It has been shown that in several Rh(I) [27] and Ir(I)
[28] systems, the presence of a co-catalyst improves the
catalytic activity and the enantioselectivity. Among the
most widely used co-catalysts are iodides and amines
[29]. The experiments with ligands 6 and 7 (Table 2,
entries 8 and 9) provided higher conversion when Bu4NI
was used as co-catalyst. The results obtained in the ex-
periments carried out with ligands 9 and 10 in the
presence of Bu4NI were maintained or were slightly
lower than in the absence of additive. No enantioselec-
tivity was observed with these catalytic systems in the
asymmetric hydrogenation of imine 14. Only ligand 6
provided 15% of ee (determined by 1H NMR using
mandelic acid). Such solvents as MeOH/C2H4Cl2,
MeOH, C6H6 and MeOH/C6H6 (Table 2, entries 12–15)
have been tested, and total conversion was obtained in
all cases.
4. Experimental
All reactions were carried out in an argon atmosphere
using standard Schlenk techniques. Solvents were dis-
tilled and degassed prior to use.
1H, 13C{1H}, 31P{1H} and 19F{1H} NMR spectra
were recorded on a Varian Gemini spectrometer at 300
and 400 MHz. Chemical shifts were reported relative to
tetramethylsilane for H and 13C{1H} as internal refer-
1
ence, H3PO4 85% for 31P{1H} and trichlorofluoro-
methane for 19F{1H} as external references. Optical
rotations were measured on a Perkin–Elmer 241 MC
polarimeter. Elemental analyses were carried out on a
Carlo Erba Microanalyser EA 1108. VG-Autospect
equipment was used for FAB mass spectral analyses
with 3-nitrobenzylalcohol as matrix. EI mass spectra
were obtained on an HP 5989 A spectrometer at an
ionizing voltage of 70 eV. The catalytic reactions were
monitored by GC on a Hewlett–Packard 5890A. Con-
version was measured in an Ultra-2 column (5%
diphenylsilicone/95% dimethylsilicone, 25 m ꢁ 0.2 mm
£). The enantiomeric excess of N-(a-methyl)phenyl-
The complex [Ir(r-g2-C8H12Pyþ)6]PF6 (12a) was
active in reducing imine 14 into the corresponding amine
(Table 2, entries 16–18). Conversions were similar to
those obtained with systems prepared in situ from
[Ir(g4-COD)Cl]2/7 and 8 (entries 3, 4 and 17). It has
been reported [30] that diolefin ligands in cationic irid-
ium complexes are hydrogenated before the substrate.
However, when we studied the hydrogenation of imine
1
idenbenzylamine (14) was determined by H NMR, us-
ing mandelic acid as resolution agent.
1
14 in the presence of the complex 12a by HP H NMR
4.1. 2-tert-Butylsulfanyl-benzonitrile (5)
at 298 K, we observed signals corresponding to the co-
ordinated Py-cyclooctenyl ligand after 24 h at 50 bar of
H2 pressure. That can be a reason of the low activity of
this catalytic system.
A solution of 2-methyl-2-propanethiol (9 mmol) in
THF (2 ml) was added to a stirred mixture of sodium
hydride (9 mmol) in THF (5 ml). To the resulting white
precipitate, a solution of 2-fluorobenzonitrile (8 mmol)
in THF (2 ml) was added. The mixture was stirred under
reflux for 48 h. The reaction mixture was poured into
dichloromethane (20 ml) and washed with 15% aqueous
NaOH (20 ml) and then with water (20 ml). The aqueous
layers were extracted with dichloromethane (2 ꢁ 30 ml)
and the combined extracts were dried (MgSO4), con-
centrated under reduced pressure and purified by col-
umn chromatography using hexane/ethyl acetate 3:1 as
solvent to give 1.3 g (86%) of compound 5.
3. Conclusions
In the preparation of iridium complexes containing
oxazoline-thioether ligands starting from the iridium
precursor [Ir(g4-COD)Py2]PF6, an unexpected nucleo-
philic attack of the pyridine on the coordinated cyclo-
octadiene with concomitant r-Ir–C bond formation
takes place, leading to the Ir(r-g2-C8H12Pyþ)L]PF6
(12a–d). When [Ir(g4-COD)Cl]2, followed by anion ex-
change, or [Ir(g4-COD)2]BF4 were used as precursors
the expected [Ir(g4-COD)L]A (A ¼ PF6, BF4) complexes
were obtained.
Hydrogenation of imine 14 with the catalytic systems
formed in situ from [Ir(g4-COD)Cl]2]/6–11 provided
conversions of 30–100% in 24 h, although no enanti-
oselectivity was achieved. The new stereogenic center
formed by the coordination of sulfur to the metal center
may be responsible for the existence of different diaste-
reomers during the catalytic cycle, which does not fa-
vour the stereoselectivity.
1H NMR (300 MHz, CDCl3, ppm) 7.7–7.5 (m, 4H,
arom.), 1.35 (s, 9H, C(CH3)3). 13C NMR (74.5 MHz,
CDCl3, ppm) 138.8 (arom., CH), 136.3 (arom., C),
133.6, 132.3, 129.3, 121.0 (arom., CH), 118.1 (CBN),
48.8 (C(CH3)3), 30.9 (C(CH3)3).
4.2. General procedure for the synthesis of oxazoline-
thioether ligands 6–11
In a 50-ml Schlenk flask, zinc chloride (0.5 mmol) was
melted under high vacuum and cooled under nitrogen to
room temperature. Chlorobenzene (25 ml) was then

1916
E. Guiu et al. / Journal of Organometallic Chemistry 689 (2004) 1911–1918
added followed by the corresponding thiobenzonitrile
(10 mmol) and the aminoalcohol (15 mmol -valinol or
-phenylglycinol). The mixture was heated under reflux
for 48 h. The solvent was removed under reduced
pressure to give an oily residue, which was dissolved in
dichloromethane (30 ml). The solution was extracted
with aqueous solution of NaCl (3 ꢁ 20 ml) and the
aqueous phase with dichloromethane (30 ml). The
combined organic extracts were dried (MgSO4) and
evaporated under reduced pressure.
hydrous dichloromethane was stirred for 2 h. Then cold
degassed diethylether was added and a precipitate ap-
peared. The solid was filtered off and washed with cold
degassed diethylether.
L
L
4.6. [Ir(r-g2-C8H12Pyþ)6]PF6 (12a)
Complex [Ir(g4-COD)Py2]PF6 (181 mg, 0.30 mmol)
was treated with 6 (107 mg, 0.40 mmol) following the
general procedure to obtain 221 mg (94% yield) of
complex 12a. Elemental Anal. Calc. for C29H32F6-
IrN2OPS: C, 43.88; H, 4.06; N, 3.53; S, 4.04. Found: C,
43.97; H, 4.19; N, 3.40, S, 3.49%. MS FAB: m=z (%):
648.1 (8.5, Mþ), 572.1 (19.8, Mþ ) C6H5), 570.1 (63.5,
Mþ ) Py), 462 (2.20, Mþ ) C13H17N), 136 (100,
C8H10NO). HRMS L-SIMS: m=z [C24H27NOSIr]þ:
570.14425. Found: 570.14537. 1H NMR (400 MHz,
CDCl3, ppm) 8.95 (m, 1H, arom.), 8.54 (m, 1H, arom.),
7.79 (m, 4H, arom.), 7.52 (m, 2H, arom.), 7.41 (m, 2H,
arom.), 7.30 (m, 3H, arom.), 7.05 (m 1H, arom.), 5.81
(m, 1H, CH), 5.13 (m, 1H, CH2), 4.96 (m, 1H, CH2),
4.66 (m, 1H, CH), 4.07 (m, 1H, CH), 3.22 (m, 1H, CH),
2.59 (m, 1H, CH), 2.43 (m, 1H, CH2), 2.22 (m, 1H,
CH2), 2.03 (m, 1H, CH2), 1.74 (m, 1H, CH2), 1.51 (s,
3H, CH3–S), 1.21 (m, 1H, CH2). 13C NMR (100.6 MHz,
CDCl3, ppm) 176.5 (C@N), 154.7 (arom., CH), 152.6
(arom., CH), 147.8–123.4 (arom.), 87.13 (@CH), 77.94
(CH2–O), 70.93 (@CH), 67.3 (@CH), 66.63 (CH–N),
37.21 (CH2), 26.29 (CH2), 24.50 (CH2), 20.57 (CH2),
14.47 (CH3–S), 3.57 (@CH). 31P NMR (161.9 MHz,
CDCl3, ppm) )144.1 (sept, JPꢀF ¼ 712:8 Hz). 19F NMR
(376 MHz, CDCl3, ppm) )73.6 (d, JFꢀP ¼ 711:7 Hz).
4.3. (4S)-2-(2-tert-Butylsulfanyl-phenyl)-4-phenyl-4,5-
dihydro-oxazole (10)
A total of 0.5 mmol (68 mg) of ZnCl2 reacted with 10
mmol (1.91 g) of 2-tert-butylthio-benzonitrile (5) and 15
mmol (1.37 g) of L-phenylglycinol by following the
general procedure described above. The residue was
purified by column chromatography using CH2Cl2/Et3N
as solvent to give 1.5 g (49% yield) of compound 10 as a
yellow oil was obtained. Compound 10 decomposed
slightly during the purification.
1H NMR (300 MHz, CDCl3, ppm) 7.7–7.1 (m, arom.,
9H), 5.40 (dd, 3J ¼ 8:4 Hz, J ¼ 1:8 Hz 1H, CH), 4.81, (dd,
3J ¼ 8:4 Hz, J ¼ 1:8 Hz, 1H, CH2), 4.30 (t, J ¼ 8:4 Hz,
1H, CH2), 1.25 (s, 9H, CH3 ꢁ 3). 13C NMR (75.4 MHz,
CDCl3, ppm) 166.1 (C@N), 142.5 (arom., C), 138.6
(arom., CH), 135.6, 130.4 (arom., C), 130.2, 128.9, 128.8,
128.6, 127.7, 127.1, 126.8, 126.8 (arom., CH), 75.2 (CH2–
O), 70.5 (CH–N), 47.6 (C(CH3)3), 31.4 (C(CH3)3).
4.4. (4S)-2-(2-tert-Butylsulfanyl-phenyl)-4-isopropyl-4,5-
dihydro-oxazole (11)
4.7. [Ir(r-g2-C8H12Pyþ)7]PF6 (12b)
A total of 0.25 mmol (68 mg) of ZnCl2 reacted with 5
mmol (950 g) of 2-tert-butylthio-benzonitrile (5) and 7.5
mmol (685 mg) of L-valinol following the general proce-
Complex [Ir(g4-COD)Py2]PF6 (90.5 mg, 0.15 mmol)
was treated with 7 (47 mg, 0.20 mmol) following the
general procedure to obtain 98 mg (86% yield) of com-
dure described above. The residue was purified by column
chromatography using CH2Cl2/Et3N as solvent to obtain
85.5 mg (55% yield) of compound 11 as a yellow oil.
1
plex 12b. H NMR (300 MHz, CDCl3, ppm) 8.68 (m,
1H, arom.), 8.48 (m, 1H, arom.), 7.70 (m, 3H, arom.),
7.19 (m, 3H, arom.), 6.94 (m, 1H, arom.), 4.68 (m, 2H,
CH), 4.54 (m, 3H, CH), 4.33 (m, 1H, CH), 2.65 (m, 1H,
CH), 2.51–0.82 (m, 8H, CH2), 1.43 (s, 3H, CH3–S), 1.07
20
[aDꢂ ¼ ꢀ28:0° (c ¼ 0:33, CH3COCH3). 1H NMR
(300 MHz, CDCl3, ppm) 7.7–6.8 (m, arom., 4H), 4.37
(dd, 3J ¼ 6:8 Hz, J ¼ 1:5 Hz, 1H, CH), 4.18 (t, 3J ¼ 6:8
Hz, CH2), 4.13 (m, 1H, CH2), 1.84 (m, 3J ¼ 6:6 Hz, 1H,
CH), 1.35 (s, 9H, CH3 ꢁ 3), 1.04 (d, 3H, CH3), 0.96 (d,
3H, CH3). 13C NMR (75.4 MHz, CDCl3, ppm) 161.6
(C@N), 137.6–125.0 (arom., C, CH), 73.3 (CH2–O), 69.7
(CH–N), 48.85 (C(CH3)3), 32.7 (CH), 30.68 (C(CH3)3),
18.6 (CH3), 18.2 (CH3). IR (NaCl, cmꢀ1) 3059, 2957
(@CH), 1648 (C@N).
3
3
(d, 3H, CH3, J ¼ 6:9 Hz), 0.64 (d, 3H, CH3, J ¼ 6:9
Hz). 13C NMR (74.5 MHz, CDCl3, ppm) 197.5 (C@N),
154.7 (arom., CH), 152.7 (arom., CH), 138.9–123.7
(arom.), 87.53 (@CH), 71.6 (CH2–O), 70.78 (@CH), 68.5
(@CH), 65.95 (CH–N), 37.49 (CH2), 30.32 (CH), 29.90
(CH2), 26.84 (CH2), 24.94 (CH2), 20.90 (CH3), 19.43
(CH3), 14.93 (CH3–S), 3.75 (@CH).
4.5. General procedure for the synthesis of [Ir(r-g2-
C8H12Pyþ)L]PF6 (12a–d)
4.8. [Ir(r-g2-C8H12Pyþ)8]PF6 (12c)
Complex [Ir(g4-COD)Py2]PF6 (71.3 mg, 0.118 mmol)
was treated with 8 (50.6 mg, 0.15 mmol) following the
general procedure to obtain 99 mg (98% yield) of com-
A solution of the corresponding ligand (0.40 mmol)
and [Ir(g4-COD)(Py)2]PF6 (0.30 mmol) in 1 ml of an-

E. Guiu et al. / Journal of Organometallic Chemistry 689 (2004) 1911–1918
1917
plex 12c. Elemental Anal. Calc. for C34H34F6IrN2OPS:
C, 47.71; H, 4.00; N, 3.27; S, 3.75. Found: C, 47.44; H,
4.08; N, 2.92; S, 3.75%. H NMR (400 MHz, CDCl3,
ppm) 8.33–6.81 (m, arom.), 5.89–4.22 (m, CH2–O, CH–
N, COD), 2.97–1.37 (m, COD).
oxazoline-thioether ligand (0.055 mmol) was then ad-
ded, followed by imine (4.4 mmol for a 100:1 imine:Ir
ratio). The solution was transferred under argon to the
autoclave via syringe.
1
4.13. In situ HP NMR hydrogenation of 14
4.9. [Ir(r-g2-C8H12Pyþ)9]PF6 (12d)
In a typical experiment, a sapphire tube (/ ¼ 10 mm)
was filled under argon with a solution of [Ir(r-g2-
C8H12Pyþ)7]PF6 (12b) (0.05 mmol) and imine 14 (0.52
mmol) in CH2Cl2-d8 (1.5 ml). The HP NMR tube was
purged twice with H2 and pressurized to the appropriate
pressure of H2 (50 bar). After shaking the sample for 24
h, the solution was analysed.
Complex [Ir(g4-COD)Py2]PF6 (181 mg, 0.3 mmol)
was treated with 9 (118.8 g, 0.4 mmol) following the
general procedure to obtain 224 mg (91% yield) of
complex 12d. Elemental Anal. Calc. for C31H36F6-
IrN2OPS: C, 45.30; H, 4.41; N, 3.41, S, 3.9. Found: C,
45.12; H, 4.42; N, 3.59; S, 3.61%. MS FAB: m=z (%)
598.1 (7.01, Mþ ) Py), 147 (100, C9H9NO). HRMS L-
SIMS m=z [C26H31NOSIr]þ: 598.1755. Found: 598.1752
1H NMR (400 MHz, CDCl3, ppm) 10.59–6.84 (m,
arom.), 5.51–3.81 (m, CH2–O, CH–N, COD), 2.50–0.45
(m, COD, CH, CH3). 31P NMR (161.9 MHz, CDCl3,
ppm) )143.9 (sept, JPꢀF ¼ 712:7 Hz). 19F NMR (376
MHz, CDCl3, ppm) )73.26 (d, JFꢀP ¼ 713:3 Hz).
Acknowledgements
Work was carried out in the frame of a Bayer A.G.
project. Financial support by A.G. Bayer and Ministerio
ꢀ
de Ciencia y Tecnologıa (PROFIT FIT-040000-2002-50)
is acknowledged. Technical assistance by the Servei de
Recursos Cientifics (URV) is acknowledged.
4.10. [Ir(g4-COD)7]PF6 (13a)
A solution of ligand 7 (71.4 mg, 0.3 mmol) and
[Ir(COD)Cl]2 (101.6 mg, 0.132 mmol) in dichlorome-
thane (5 ml) was heated for 2 h at 50 °C in a sealed tube
under argon. After cooling to room temperature, the
solution was washed twice with an aqueous solution of
NH4PF6 (0.4 M, two 10 ml portions). The red dichlo-
romethane solution was washed with water and dried
over Na2SO4. Crystallization from CH2Cl2/Et2O and
drying afforded 65.6 mg (73% yield) of complex 13a.
Elemental Anal. Calc for C21H29F6IrNOPS: C, 37.05;
H, 4.26; N, 2.06; S, 4.70. Found: C, 38.30; H, 4.13; N,
1.96; S, 4.46%.
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