Cationic iridium complexes with chiral dithioether ligands: Synthesis, characterisation and reactivity under hydrogenation conditions

Article abstract of DOI:10.1002/ejic.200400828

A series of cationic Ir^I complexes containing chiral dithioether ligands have been prepared in order to study the influence of the sulfur substituents and the metallacycle size on the acetamidoacrylate hydrogenation reaction. In the case of complexes 6, 7 and 10, a mixture of diastereomers is observed in solution due to the sulfur inversion processes. In contrast, this fluxional behaviour is efficiently controlled by using bicyclic ligands which inhibit the S-inversion in complexes 8 and 9. The solid-state structure of complex 10b shows only one diastereomer with the sulfur substituents in a relative anti disposition and in an overall configuration of S_CS _CS_SS_S at the coordinated dithioether ligand. Iridium com plexes containing seven- and six-membered metallacycles (6b-d, 7b,c, 10a,b) react with the substrate through S-ligand substitution, and the rate of this substitution is related to the position of the fluorine atom on the aromatic ring. On the contrary, complexes containing a bismetallacycle (8 and 9) are not displaced by the substrate. The catalytic hydrogenation activity of complexes 8 and 9 is analysed in terms of the high stability of the corresponding dihydride complexes (13 and 14). In both cases, only two of the four possible diastereomeric dihydride species are formed in solution. ( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005).

Full text of DOI:10.1002/ejic.200400828

FULL PAPER
Cationic Iridium Complexes with Chiral Dithioether Ligands: Synthesis,
Characterisation and Reactivity under Hydrogenation Conditions
Leticia Flores-Santos,[a] Erika Martin,*[a] Ali Aghmiz,[b] Montserrat Diéguez,[b]
Carmen Claver,[b] Anna M. Masdeu-Bultó,*[b] and Miguel Ángel Muñoz-Hernández[c]
Keywords: Chiral auxiliaries / S ligands / Iridium / Hydrides / Asymmetric catalysis
A series of cationic IrI complexes containing chiral dithio-
ether ligands have been prepared in order to study the in-
fluence of the sulfur substituents and the metallacycle size
on the acetamidoacrylate hydrogenation reaction. In the case
of complexes 6, 7 and 10, a mixture of diastereomers is ob-
served in solution due to the sulfur inversion processes. In
contrast, this fluxional behaviour is efficiently controlled by
using bicyclic ligands which inhibit the S-inversion in com-
plexes 8 and 9. The solid-state structure of complex 10b
shows only one diastereomer with the sulfur substituents in
a relative anti disposition and in an overall configuration of
SCSCSSSS at the coordinated dithioether ligand. Iridium com-
plexes containing seven- and six-membered metallacycles
(6b–d, 7b,c, 10a,b) react with the substrate through S-ligand
substitution, and the rate of this substitution is related to the
position of the fluorine atom on the aromatic ring. On the
contrary, complexes containing a bismetallacycle (8 and 9)
are not displaced by the substrate. The catalytic hydrogena-
tion activity of complexes 8 and 9 is analysed in terms of the
high stability of the corresponding dihydride complexes (13
and 14). In both cases, only two of the four possible dia-
stereomeric dihydride species are formed in solution.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2005)
ity to the metal coordination sphere may be advantageous
for enantioinduction; however, these centres are not config-
urationally stable, since sulfur inversion has a low energy
barrier. In the case of chiral dithioether complexes, the pres-
ence of two stereogenic centres at sulfur atoms, in addition
to the carbon stereogenic centres at the ligand backbone,
can lead to mixtures of diastereomers. The presence of mix-
tures of diasteromeric species and the difficulty to control
their interconversion in solution have been regarded as a
problem for asymmetric induction in catalytic reactions. In
spite of this behaviour, enantioinductions have been im-
proved when the configuration at the sulfur atom is con-
trolled by steric effects.[24,31,32] Unfortunately, having few
examples of S,S-homodonor ligands, which also differ con-
siderably in their skeleton size and rigidity, makes it difficult
to elucidate the structure-performance relationship.
In order to understand the influence of structural and
electronic factors on the reactivity of chiral dithioether-con-
taining catalysts, in the present work we prepared a series
of cationic iridium complexes with chiral dithioether li-
gands 1–5 (Figure 1) derived from l-(+)-diethyltartrate[33]
and (2R,4R)-2,4-pentanediol.[34] These ligands were selected
in order to study electronic and ring size effects and sulfur
inversion control, by the following strategies: (i) introduc-
tion of fluorine atoms at ortho- meta- or para- positions
of a thioether aromatic ring in order to change the donor/
acceptor electronic properties of sulfur atoms (ligands 1a–c
and 2a–c); (ii) evaluation of two ring sizes to tune the rigid-
ity of the molecular backbone (ligands 1a–d and 2a–c vs.
Introduction
The study of chiral sulfur transition-metal complexes as
asymmetric catalysts has notably increased during the last
decades.[1,2] In particular, complexes containing thioether
mixed-donor ligands such as the P,S-,[3–8] N,S-[9–17] and
O,S-[18–22] donors have been successfully applied in asym-
metric hydrogenation,[5,6,23] allylic substitutions[7–10,18] and
enantioselective hydrosilylation of ketones.[4,23] In contrast,
catalysts with chiral bidentate thioether ligands have been
scarcely investigated,[24–32] although some have shown
promising catalytic properties. In fact, we have recently
shown that metal complexes with chiral dithioether ligands
afford up to 81% ee in palladium-catalysed asymmetric al-
lylic substitutions[24] and 68% ee in iridium-catalysed asym-
metric hydrogenation reactions.[25,26]
Upon coordination to a metal, thioether ligands generate
a stereogenic centre at the sulfur atom, whose close proxim-
[a] Departamento de Química Inorgánica, Facultad de Química,
Universidad Nacional Autónoma de México, Cd. Universitaria,
04510 México DF, México
Fax: +52-55-5622-3720
E-mail: erikam@servidor.unam.mx
[b] Departament de Química Física i Inorgànica, Universitat Ro-
vira i Virgili,
c/Marcel·lí Domingo s/n, 43005 Tarragona, Spain
Fax: +34 977-559563
E-mail: masdeu@quimica.urv.es
[c] Centro de Investigaciones Químicas, Universidad Autónoma
del Estado de Morelos,
Av. Universidad 1001 Col. Chamilpa, Cuernavaca, México
Fax: +52-77-7329-7998
E-mail: mamund2@ciq.uaem.mx
Eur. J. Inorg. Chem. 2005, 2315–2323
DOI: 10.1002/ejic.200400828
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E. Martin, A. M. Masdeu-Bultó et al.
FULL PAPER
5); (iii) effective stereocontrol at sulfur atoms in metal inter- addition to the electron-withdrawing effect of the ortho-
mediates by using cyclic chiral thioether ligands which elim- fluoro substitution.
inate pyramidal inversion and also allow a backbone rigid-
ity modulation (ligands 3 and 4).
Scheme 1. Syntheses of complexes 6–10.
FAB mass spectra confirmed the formation of the mono-
nuclear species in all cases. Complexes were characterised
1
in solution by H and 13C NMR spectroscopy. 19F NMR
spectroscopy was also used for complexes 6b,c and 7b,c.
1
The full assignment of H and 13C NMR parameters was
performed by using homo- and heteronuclear two-dimen-
sional spectroscopy techniques (1H,1H-COSY, HETCOR
and NOESY).
The coordination of the dithioether ligands to the metal
generates a stereogenic centre at each sulfur atom. There-
Figure 1. Dithioether ligands 1–5.
fore, a mixture of diastereomers with different spatial arran-
The reactivity of the synthesised complexes [Ir(dithio-
gements of the sulfur substituents and conformations of the
ether)(cod)]BF4 towards acrylic acid derivatives and dihy-
chelate ring could exist in solution (Figure 2). Taking into
drogen is discussed in relation to the activity and selectivity
account that ligands 1 and 2 have absolute RR-configura-
observed under catalytic hydrogenation conditions.
tion at their asymmetric carbon centres and two possible
configurations at the sulfur atoms, three diastereomers
could be formed: RCRCRSRS and RCRCSSSS (both attrib-
Results and Discussion
uted to the anti isomers) and RCRCRSSS or RCRCSSRS
(corresponding to the syn isomer). This analysis applies also
for complexes with ligands 5, which have absolute SS con-
Iridium Complexes [Ir(cod)(dithioether)]BF4
figuration at their asymmetric carbon centres, therefore
three possible diastereomers, SCSCRSRS and SCSCSSSS
(anti isomers), and SCSCRSSS or SCSCSSRS (syn isomer)
can be formed. In contrast, for complexes containing li-
gands 3 and 4, there is only one possible syn isomer with
RCRCRSSS or RCRCSSRS configuration, since the inversion
at both sulfur atoms is inhibited.
Ligands 3, 4 and 5a,b reacted with dichloromethane
solutions of [Ir(cod)2]BF4 to form the corresponding [Ir-
(cod)(dithioether)]BF4 complexes 8, 9 and 10a,b by cod
substitution (Scheme 1). The complexes were isolated as
relatively air-stable, yellow or orange solids by addition of
hexane or diethyl ether with yields ranging from 50 to 99%.
In contrast, ligands 1a–d and 2a–c did not react with
dichloromethane solutions of [Ir(cod)2]BF4 unless hydrogen
was bubbled through the solution to reduce cod and pro-
mote its substitution. These results can be rationalised ac-
cording to the lower stability of the seven-membered metalla-
cycle formed in the case of ligands 1 and 2. A similar behav-
iour was observed for the non-fluorinated derivative of li-
gands 2.[25] In the case of ligands 3 and 4, the generation of
[7,5]- and [7,6]-membered rings, respectively, increases the
chelate stability. Dithioethers 1a and 2a did not form the
Figure 2. Possible diastereomers for metal complexes with ligands
iridium complexes, probably because of steric hindrance in 1–5.
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Cationic Iridium Complexes with Chiral Dithioether Ligands
In fact, variable temperature NMR studies (down to
FULL PAPER
The 13C NMR spectra for complexes 6b–d showed only
–80 °C) performed on complexes 8 and 9 are in accordance two signals for cod methylenic carbons and two signals for
with the presence of only one diastereomer in solution, cod methynic carbons, which can be attributed to the pres-
which corresponds to a C1-symmetry molecule with ence of only one anti diastereomer or a fast exchange be-
1
RCRCRSSS configuration. Full assignment of H and 13C tween both anti diastereomers. However, the 19F NMR ex-
spectra was achieved by homo- and heteronuclear 2D periments in the temperature range of +30 °C to –60 °C
NMR techniques and the conformation of both rings was show two different signals for complexes 6b and 6c in the
determined by using NOE experiments (Figure 3). The ratios 10:6 and 10:9.1, respectively, proving the presence of
seven-membered ring has a twisted chair conformation in two anti diastereomers in solution (I and II). The rate of
both complexes. The second ring is either a five-membered isomer interconversion for complex 6b was very low and
chelate ring with an envelope conformation in 8 (NOE con- invariant in the temperature range studied (k = 1.10–3 s–1)
tact between H4 with H1 and H2) or a six-membered ring [35], and for complex 6c the rate could not be calculated,
with a chair conformation in 9 (NOE contact between H1 since no significant change in the shape of the spectra was
and H7).
observed in the same range of temperatures. Although no
1
splitting of signals in H and 13C NMR spectra was ob-
served for complex 6d, by analogy with 6c,d, two dia-
stereomers could also be present in solution.
In the case of complexes 7b and 7c, two isomers, I and
II, were also detected at low temperature. The exchange
rates ranged from 5.26×102 s–1 (at –60 °C) to 1.22×104 s–1
(at 30 °C) for 7b and from 8.22×102 s–1 (–60 °C) to
5×104 s–1 (30 °C) for 7c. The values of the Gibbs activation
energy (ΔG϶, evaluated by the Eyring equation) are
50.4 1.0 kJmol–1 for 7b and 48.1 1.3 kJmol–1 for 7c, and
are in the range reported for sulfur inversion in thioether
complexes.[36,37] Therefore, the dynamic behaviour in solu-
tion of 7b and 7c is independent of the position of the fluor-
ine atom in the aromatic ring.
Crystal Structure of [Ir(cod)(5b)]BF4 (10b)
Figure 3. Structures proposed for complexes 8 and 9 showing the
NOE contacts.
Single crystals of 10b suitable for X-ray diffraction were
obtained by slow diffusion of n-hexane into an ethyl acetate
For complexes 10a,b containing a six-membered metalla- solution of the complex. The cationic structure is shown in
cycle, variable temperature 1H NMR spectra (–40 to Figure 4, and selected bond lengths and angles are listed in
+25 °C) exhibited patterns corresponding to the presence of Table 1. The iridium atom shows a slightly distorted square-
only one species with C2 symmetry, which may be attributed planar environment. The sulfur atoms are in a cis configu-
to one of the two possible anti diastereomers SSSCSCSS or ration and the cyclooctadiene ligand occupies the other two
RSSCSCRS with equatorial–equatorial or axial–axial con- coordination sites. For the latter ligand, using the centroids
formations, or to the chair equatorial–axial conformers in- of the C12–C13 and C16–C17 double bonds, X1a and X1b,
terchanging fast in solution. VT NMR spectra of 10b in respectively, a twist of 4.8o of the dihedral planes S1–Ir1–
CD2Cl2 were invariant in the temperature range studied. S2 and X1a–Ir1–X1b is found. A similar situation was ob-
NOE experiments suggested that an equatorial–equatorial served for the Ir complex [Ir(cod){C[P(S)(Ph)2]3}],[38] which
species was likely to be present in solution; nevertheless, the showed a twist of 9.0o. The distortion is also evident from
possibility of rapid equilibration with other species could the deviation from 90o observed in the following bond
not be discarded. Moreover, the structure in the solid state angles: X1a–Ir1–S1 86.8o, X1b–Ir1–S2 99.6o and X1a–Ir1–
of 10b, determined by X-ray diffraction (see following sec- X1b 85.6o, which is more pronounced than in [Ir(cod)-
tion), confirmed that the sulfur substituents were anti with {[P(S)(Ph)2]3C}] (89.5, 88.3 and 87.5o, respectively)[38] and
an equatorial–axial disposition.
the Rh complex [Rh(cod){CH[P(S)(Ph)2]2}] (86.4, 88.3 and
The 1H and 19F NMR spectra of complexes 6b,c and 7b,c 86.7o, respectively).[39] The Ir–S and Ir–C average bond
show in all cases broad signals at room temperature. It is lengths [2.3537(19) and 2.131(9) Å, respectively] are in the
interesting to note that the chemical shifts of the cod me- range reported for related IrI complexes.[38,40,41] Further-
thynic protons are not sensitive to the position of the fluoro more, similar Ir–S distances were reported for IrI cyclooc-
substituent on the dithioether ligands. Nevertheless, the re- tadiene complexes with thiolate bridging ligands.[42,43] The
activity towards acrylic acid derivatives depends on the po- average angle C–S–Ir [110.0(3)°] is close to the tetrahedral
sition of the fluorine atom in the aromatic ring.
angle, indicating sp3 hybridization at the sulfur atom.
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E. Martin, A. M. Masdeu-Bultó et al.
FULL PAPER
Scheme 2. Hydrogenation of acrylic acid derivatives 11a–d.
Figure 4. ORTEP representation (50% probability) of iridium com-
–
plex 10b. Hydrogen atoms and BF4 are omitted.
Table 1. Selected bond lengths [Å] and angles [°] for complex 10b.
Bond lengths [Å]
Bond angles
[°]
Ir(1)–C(16)
Ir(1)–C(12)
Ir(1)–C(17)
Ir(1)–C(13)
Ir(1)–S(2)
2.116(11)
C(16)–Ir(1)–C(12)
C(17)–Ir(1)–C(13)
C(16)–Ir(1)–S(2)
C(17)–Ir(1)–S(2)
C(12)–Ir(1)–S(1)
C(13)–Ir(1)–S(1)
S(2)–Ir(1)–S(1)
C(1)–S(1)–C(4)
C(1)–S(1)–Ir(1)
C(4)–S(1)–Ir(1)
C(3)–S(2)–C(9)
C(3)–S(2)–Ir(1)
C(9)–S(2)–Ir(1)
95.5(4)
88.4(4)
98.6(3)
99.6(3)
85.9(2)
87.9(2)
88.18(8)
105.0(4)
108.3(3)
111.3(3)
105.4(4)
104.4(3)
116.1(3)
2.126(8)
2.141(9)
2.141(8)
2.344(2)
2.3633(18)
Figure 5. Catalytic hydrogenation of methyl acetamidoacrylate
(11a) by using dithioether iridium complexes. Conditions: [{Ir-
(cod)L}BF4] = 4.3 mm, [Substrate] = 175 mm, T = 25 °C and p(H2)
= 1 atm.
Ir(1)–S(1)
tuted ligand showed higher conversion than the meta- and
para-fluoro complexes 6b and 6c.
The activity is also modified by the dithioether skeleton;
complexes 7b,c provided higher conversion than 6b,c and
complex 10a, with a smaller six-membered metallacycle,
showed lower conversion than the seven-membered chelate
complex 6d. Finally, complexes 8 and 9, which contain
metallabicycles, provided less active catalytic systems. In all
cases, the enantioinduction was practically nonexistent.
These catalytic results can be explained in terms of the
stability of the complexes. Catalytic systems 6, 7 and 10
decomposed gradually during the catalytic reaction to form
Ir0 with the consequent loss of the chiral ligand. This was
confirmed for the fluorinated precursors (6b,c and 7b,c) by
analysis of the catalytic mixture at the end of the hydrogen-
ation reactions through 19F NMR spectroscopy, which
The solid structure shows only one diastereomer with
the sulfur substituents in a relative anti disposition. The
metallacycle adopts a chair conformation with an overall
configuration SCSCSSSS.
Catalytic Experiments and Reactivity of the Iridium
Complexes
The catalytic activity of iridium complexes 6b–d, 7b,c, 8, showed the presence of the free ligand as a distinct species.
9, 10a,b in the hydrogenation of acrylic acid derivative 11a The decoordination of the dithioether ligands is promoted
at 25 °C and 1 atm of hydrogen pressure was examined by substrate coordination, since the addition of 11a to
(Scheme 2).
dichloromethane solutions of complexes 6, 7 and 10 under
All catalyst precursors show low conversions even at 12 h nitrogen generates free dithioether ligands and [Ir(11a)-
1
of reaction (Figure 5). Regarding the influence of the (cod)]+, detected by 19F NMR spectroscopy or by H and
fluoro-substitution on the aromatic ring, the meta-fluoro 13C NMR.
derivatives 6b and 7b showed higher conversion than their
In an attempt to recoordinate the dithioether ligand by
analogous para-fluoro derivatives 6c and 7c, in the same forcing cod reduction, H2 was bubbled into a solution con-
reaction time. The complex 6d without the fluoro-substi- taining 6b and 11a, but the signal of the free dithioether
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Cationic Iridium Complexes with Chiral Dithioether Ligands
FULL PAPER
remained unaltered, and the formation of metallic iridium
was observed.
For purposes of comparison, the catalytic activity of
complex [Ir(cod)2]+ (12) was studied under the same cata-
lytic conditions and was found to be the highest (45% con-
version at 1 h). Since the conversion obtained with 12 is
higher than that found with the dithioether complexes and
it has been demonstrated that these dithioether ligands are
replaced by the substrate to yield [Ir(11a)(cod)]+, the in-
creasing conversion can be related to a higher rate of dithi-
oether substitution. Thus, the less active systems are those
in which the rate of substitution is lower, suggesting that
the dithioether ligand is more strongly coordinated to the
metal. Consequently, in the case of seven-membered com-
plexes, catalytic precursors 6 lead to more active systems
probably because of the formation of weaker M–S bonds.
The same situation is observed when the more stable six-
membered complex 10a is compared with the seven-mem-
bered complex 6b. Concerning the electronic factors, the
lower activity of the fluorinated systems may be related to
a stronger M–S interaction due to an enhancement of the
π-acceptor ability of these ligands.
Figure 6. Attack of H2 (i) through the “upper” seven-membered
ring face with displacement of the (a) SS (13-I) and (b) SR atoms
(13-II); (ii) through the “lower” five-membered ring face with dis-
placement of the (c) SS (13-III) and (d) SR (13-IV) atoms.
In contrast to the above-mentioned behaviour, bicyclic
systems 8 and 9 do not decompose to Ir0 under catalytic
conditions, and the dithioether ligands are not replaced by
substrate 11a. Therefore, the catalytic hydrogenation of signals at δ = –13.83 and –13.78 ppm, suggesting similar
11b–d was studied by using 8 and 9. For these substrates, chemical environments for each couple sharing equal T1
the conversions ranged from modest to low and only for values.
the acid substrates 11b and 11d, the ee reached up to 15%
NOE experiments allowed identification of the major
(R), with 8 as catalyst precursor. In order to understand the isomer as 13-I, formed by the attack of H2 through the
catalytic performance of these bismetallacycles, we studied seven-membered ring face with displacement of the sulfur
the species formed in the presence of hydrogen.
with absolute S configuration (Figure 7). In particular,
NOE contacts between the methynic proton H5 with H3Ј
and the hydride ligand Hf, indicated the proximity of the
seven-membered ring face to the hydride ligand. The me-
thynic proton H4 showed contacts with the ethyl protons
H1and H2. The minor isomer corresponds to isomer 13-II,
formed also by the attack of H2 through the seven-mem-
bered ring face but with displacement of the sulfur with
absolute R configuration. The NOE contacts Hf–H5, H2–
H4–H1 and Hb-H3Ј allowed determination of the minor iso-
mer structure.
Reactivity of Complexes 8 and 9 with Hydrogen
Complexes 8 and 9 reacted with H2 at –70 °C to form
the corresponding dihydride species [Ir(H)2(8)(cod)]BF4
(13) and [Ir(H)2(9)(cod)]BF4 (14) (Scheme 3). Similar reac-
tivity was reported for other dithioether iridium com-
plexes.[25,26]
The dihydride complexes 13-I and 13-II were very stable;
1
the hydride signals remained in the H NMR spectra up to
25 °C after 24 h. The high stability of these complexes may
account for the very low activity of 8 in the hydrogenation
Scheme 3. Reaction of complexes 8 and 9 with H2.
Taking into account the two different faces of the coordi- of acrylic acid derivatives. Although the oxidative addition
nation plane (named seven-membered- and five-membered takes place readily at –70 °C, the 1,2-insertion of the hy-
ring faces) four diastereomers can be formed (Figure 6).
dride ligands in the M-alkene (cod) bond to hydrogenate
1
The hydride region of the H NMR spectra of complex the cod ligand is very slow.
13 showed four signals at –70 °C which were attributed to
Similar results were obtained in the reactivity study of
the presence of two different isomers: a major isomer (δ = complex 9 with H2 to form the dihydride complex 14. The
–11.37 and –13.83 ppm) and a minor one (δ = –11.56 and 1H NMR in the hydride region also showed four signals
–13.78 ppm) in a 5:3 ratio. The measurement of relaxation corresponding to two isomers in a 5:3 ratio. In this case,
times, T1 (see Experimental Section), confirmed the forma- the NOE contacts suggested that hydrogen attack also takes
tion of “classical hydride ligands”.[44–48] Moreover, signals place through the seven-membered ring face for both iso-
at δ = –11.37 and –11.56 ppm showed similar T1 values mers. The structure assignment of the major and minor iso-
(0.31 s) and the same was observed for T1 values (0.2 s) of mers was not possible because the hydride NOE signals
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E. Martin, A. M. Masdeu-Bultó et al.
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and enantioselectivities; (iv) the low activity of the bis-
metallacycles is directly related to the high stability of the
corresponding dihydride species; (v) only two dia-
stereomeric dihydride species (5:3) are formed in both cases;
(vi) in the bismetallacycle systems the enantioinduction is
slightly improved using the more rigid [7,5]- in comparison
to the [7,6]-bismetallacycle.
Experimental Section
General Remarks: All iridium complexes were prepared by standard
Schlenk techniques under nitrogen. The complex [Ir(cod)2]BF4 was
prepared by methods described in the literature.[49] The syntheses
of ligands 1a–d, 2a–c, 3 and 4 were reported previously.[33] The
syntheses of ligands 5a and 5b will be described elsewhere.[34] Sol-
vents were dried over standard drying agents and were freshly dis-
tilled and deoxygenated prior to use. All other reagents were used
as commercially supplied. 1H, 13C, and 19F NMR spectra were
measured with Varian 300 or 400 MHz spectrometers operating at
300 or 400 MHz (1H), 75 or 100 MHz (13C), 282 or 376 MHz (19F).
Chemical shifts are relative to TMS δ = 0 ppm (1H), CD2Cl2 δ =
55 ppm (13C) and CFCl3 δ = 0 ppm (19F). All species were studied
in deuterated dichloromethane unless otherwise indicated. Infrared
spectra were measured with a Nicolet AVATAR 320 FT-IR spec-
trometer. Electronic Impact and FAB+ mass spectra were recorded
with a Jeol SX102A inverse geometry spectrometer and VG Au-
tospect using a 3-nitrobenzyl alcohol matrix. Elemental analyses
were performed with an AE FISONS CHNS-0 equipment or a
Carlo–Erba EA-1108 microanalyser. Gas chromatography analyses
were performed with a Hewlett–Packard 5890A instrument. Enan-
tiomeric excesses (ee) were determined with a fused silica capillary
column Permabond l-Chirasil-Val (25 m×0.25 mm) for substrates
11a,b, and Chiraldex-G-TA (30 m×0.25 mm) for substrates 11c,d.
Figure 7. Representation of complexes of 13-I and 13-II, showing
the NOE contacts.
were superimposed. Upon increasing the temperature up to
0 °C, the hydride signals disappeared, and both signals of
cyclooctane and complex 9 were observed. This corre-
sponds to two parallel reactions, the hydrogenation of cod
and the reversible reductive elimination of H2.
As has been shown, the approach of dihydrogen to com-
plexes 8 and 9 takes place through the seven-membered ring
face, which is presumably the more hindered. Nevertheless,
upon formation of the dihydride complex, the reorganiza-
tion of the dithioether cyclic ligand leads to a less hindered
structure than when the approach is through the five- (for
complex 8) or six- (for complex 9) -membered ring face. In
this latter case, the bicyclic moiety of the resulting structure
would be bent towards the cod coordinated ligand while in
the other case, this fragment is launched outside the coordi-
nation sphere (Figure 6), which may favour the formation
of the observed isomers. The low enantioselectivity ob-
tained with both systems is probably related to the forma-
tion of different dihydrido complexes in solution.
Synthesis of Complexes [Ir(cod)(dithioether)]BF4 (dithioether =
1b–d, 2b,c, 3–5)
Procedure A: A solution of the corresponding ligand (1b–d, 2b,c,
0.08 mmol) in dichloromethane (3 mL) was added to a solution of
[Ir(cod)2]BF4 (40 mg, 0.08 mmol) in dichloromethane (5 mL) under
nitrogen. The solution was stirred for 30 min, and then hydrogen
was bubbled into the solution for 15 s in order to hydrogenate the
1,5-cyclooctadiene ligand and coordinate the dithioether to irid-
ium. The solution was filtered to remove Ir0, and the solvent was
evaporated. The residue was thoroughly washed with hexane and
recrystallised from dichloromethane/hexane to yield the products
as yellow microcrystalline solids.
Conclusion
Cationic iridium(i) complexes containing chiral dithio-
ether ligands were prepared and their fluxional behaviour in
solution was efficiently controlled by using bicyclic ligands,
which form configurationally stable sulfur stereocentres
upon coordination to the metal. The systematic study of
the reactivity of these complexes allowed to establish that:
(i) seven-membered chelating ligands are displaced in all
cases by methyl acetoamidoacrylate to form the species
[Ir(substrate)(cod)]+, which is responsible for the catalytic
activity in the hydrogenation of this substrate; (ii) the posi-
tion of the fluorine atoms in the aromatic rings affects the
substitution rate of the dithioether, thus modifying the cata-
lytic activity directly; (iii) the dithioether substitution does
not occur in the more rigid complexes containing cyclic di-
[Ir(cod)(1b)]BF4 (6b): Colour: yellow; yield: 33.5 mg, 46%. IR [KBr
1
(cm–1)]: (νB–F) 1064 (s). H NMR (400 MHz): δ = 7.59 (m, 18 H,
Har), 4.87 (m, 4 H, CH2–C6H5), 4.19 (m, 2 H, CH), 3.95 (m, 4 H,
CH2), 3.82 (m, 4 H, CH cod), 2.3 (m, 2 H, CH2 cod), 2.24 (m, 2
H, CH2 cod), 1.81 (m, 2 H, CH2 cod), 1.7 (m, 2 H, CH2 cod) ppm.
13C{1H} NMR (100 MHz): δ = 162.83 (Ci-F, JC,F = 250.4), 137.16
(Ci-S), 131.66 (Ci), 129.2 (Cm-S), 128.9 (Co), 128.7 (Cp), 128.56
(Cm), 118.19 (Co–S, Cp-S), 75.79 (CH), 74.65 (CH cod), 73.97 (CH
cod), 73.67 (CH2–C6H5), 31.14 (CH2 cod), 31.08 (CH2 cod), 29.46
(CH2) ppm. 19F NMR (376 MHz, –60 °C): δ = –109.45 (m, 6b-I),
–111.77 (m, 6b-II) ppm; 6b-I/6b-II = 5:3. FAB+: m/z (%) = 823 (M–
BF4). C38H40BF6IrO2S2 (909.88): calcd. C 50.16, H 4.43, S 7.05;
found C 49.74, H 4.40, S 7.00.
[Ir(cod)(1c)]BF4 (6c): Colour: yellow; yield: 26.2 mg, 36%. IR [KBr
1
thioligands; however, these systems show poor activities (cm–1)]: (νB–F) 1061 (s). H NMR (400 MHz): δ = 7.34 (m, 18 H,
2320
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Eur. J. Inorg. Chem. 2005, 2315–2323

Cationic Iridium Complexes with Chiral Dithioether Ligands
CHar), 4.57 (m, 4 H, CH2–C6H5), 3.87 (m, 2 H, CH), 3.68 (m, 4 1.34 (s, 3 H, CH3), 1.36 (s, 3 H, CH3) ppm; (20 °C): δ = 4.95 (m, 1
FULL PAPER
H, CH2), 3.6 (m, 4 H, CH cod), 2.4 (m, 2 H, CH2 cod), 2.1 (m, 1
H, CH2 cod), 1.99 (m, 1 H, CH2 cod), 1.58 (m, 2 H, CH2 cod),
1.46 (m, 2 H, CH2 cod) ppm. 13C{1H} NMR (100 MHz): δ =
H, CHa cod), 4.75 (m, 1 H, CHd cod), 4.68 (m, 1, CH 5), 4.61 (m,
1 H, CHb cod) 4.44 (m, 1 H, CHc cod), 4.19 (m, 1 H, CH 4), 3.83
(m, 1 H, CH2 3), 3.62 (m, 1 H, CH2 6), 3.36 (m, 3 H, CH2 6Ј,1,
137.67 (Ci), 134.68 (Co–S), 129.79 (Ci-S), 129.14 (Co), 128.87 (Cp), 2Ј), 3.17 (m, 1 H, CH2 2), 2.89 (m, 1 H, CH2 1Ј), 2.61 (m, 1 H,
128.79 (Cm), 117.63 (Cm-S), 76.43 (CH), 74.68 (CH cod), 73.87 CH2 3Ј) 2.26 (m, 4 H, CH2 cod), 2.05 (m, 4 H, CH2 cod), 1.41 (s,
(CH2–C6H5), 73.74 (CH cod), 31.38 (CH2 cod), 31.34 (CH2 cod), 6 H, CH3) ppm. 13C{1H} NMR (100 MHz): δ = 111.09 (C(CH3)2),
31.05 (CH2) ppm. 19F NMR (376 MHz, –60 °C): δ = –108.0 (m,
6c-I), –113.89 (m, 6c-II) ppm; 6c-I/6c-II = 10:9.1. FAB+: m/z (%) =
823 (M–BF4). C38H40BF6IrO2S2 (909.88): calcd. C 50.16, H 4.43,
S 7.05; found C 49.69, H 4.43, S 7.13.
83.43 (CHa cod), 83.14 (CH, 5), 81.29 (CHd cod), 78.61 (CHb cod),
76.73 (CHc cod), 76.31 (CH, 4), 46.54 (CH2 6), 41.04 (CH2 3),
36.55 (CH2 2), 33.08 (CH2 1), 32.41 (CH2 cod), 32.11 (CH2 cod),
31.66 (CH2 cod), 31.34 (CH2 cod), 28.56 (CH3) ppm. FAB+: m/z
(%) = 521 (M–BF4). High resolution FAB+: m/z (%) = 521.1226;
C17H28IrO2S2 (Err [ppm/mmu] = +12.7/+6.6). C17H28BF4IrO2S2
(607.56): calcd. C 33.61, H 4.65, S 10.56; found C 33.71, H 4.63, S
10.60.
[Ir(cod)(1d)]BF4 (6d): Colour: yellow; yield: 38.9 mg, 47%. IR [KBr
(cm–1)]: (νB–F) 1063(s). 1H NMR (400 MHz): δ = 7.42 (m, 20 H,
Har), 4.62 (m, 4 H, CH2–C6H5), 3.95 (m, 2 H, CH), 3.69 (m, 4 H,
CH2), 3.62 (m, 4 H, CH cod), 2.11 (m, 2 H, CH2 cod), 1.98 (m, 2
H, CH2 cod), 1.58 (m, 2 H, CH2 cod), 1.47 (m, 2 H, CH2 cod) ppm.
13C{1H} NMR (100 MHz): δ = 137.47 (Ci), 132.34 (Ci-S), 130.47
(Co), 129.58 (Co–S), 129.2 (Cm-S), 128.97 (Cp, Cp-S), 128.85 (Cm),
76.22 (CH), 74.84 (CH cod), 74.17 (CH cod), 73.82 (CH2–C6H5),
31.39 (CH2 cod), 31.33 (CH2 cod), 29.74 (CH2) ppm. FAB+: m/z
(%) = 787 (M–BF4). C38H42BF4IrO2S2 (873.9): calcd. C 52.23, H
4.84, S 7.34; found C 52.75, H 4.84, S 7.27.
[Ir(cod)(4)]BF4 (9): Colour: yellow-orange; yield: 49.3 mg, 99%. IR
[KBr (cm–1)]: (νB–F) 1053 (s). 1H NMR (300 MHz, refer to Figure 3
for assignments): δ = 4.91 (m, 1 H, CH 5), 4.61 (m, 1 H, CHa CHa
CHa CHa cod), 4.58 (m, 1 H, CH 6), 4.93 (m, 1 H, CHd cod), 4.21
(m, 1 H, CHb cod), 4.06 (m, 1 H, CHc cod), 3.75 (m, 1 H, CH2
7Ј), 3.54 (m, 1 H, CH2 4), 3.46 (m, 2 H, CH2 1,3), 3.44 (m, 1 H,
CH2 4Ј), 3.24 (m, 2 H, CH2 2,2Ј), 3.0 (m, 2 H, CH2 1,3), 2.71 (m,
CH2 7), 2.40–2.19 (m, 8 H, CH2 cod), 1.43 (s, 6 H, CH3) ppm.
13C{1H} NMR (75 MHz): δ = 106.06 (C(CH3)2), 79.31 (CHa cod),
78.46 (CH, 5), 77.94 (CHd cod), 73.84 (CHb cod), 73.71 (CHc cod),
72.04 (CH, 6), 38.28 (CH2, 7), 34.09 (CH2 4), 30.09 (CH2 2), 28.57
(CH2 1), 27.7 (CH2, cod), 27.03 (CH2 cod), 26.71 (CH2 cod), 24.96
(CH2 3), 24.62 (CH2 cod) 22.24 (CH3), 21.90 (CH3) ppm. FAB+:
m/z (%) = 535 (M–BF4). High resolution FAB+: m/z (%) =
535.1344; C18H30IrO2S2 (Err [ppm/mmu] = +5.1/+2.7).
[Ir(cod)(2b)]BF4 (7b): Colour: yellow; yield: 53 mg, 86%. IR [KBr
1
(cm–1)]: (νB–F) 1085 (s), (νB–F) 1055 (s). H NMR (400 MHz): 7.26
(m, 18 H, Har), 4.23 (m, 2 H, CH), 4.05 (m, 4 H, CH cod), 3.54
(m, 4 H, CH2), 2.25 (m, 4 H, CH2 cod), 1.76 (m, 4 H, CH2 cod),
1.42 (s, 6 H, CH3) ppm. 13C{1H} NMR (100 MHz): δ = 161.0 (Ci-
F, JC,F = 250.3), 132.17 (Cm), 130.17 (Ci), 127.03 (Cp-F), 118.11
(Cp), 117.88 (Co–S), 111.90 (C(CH3)2), 80.57 (CH cod), 80.31 (CH
cod), 78.52 (CH), 40.22 (CH3), 31.56 (CH2 cod), 27.22 (CH2) ppm.
19F NMR (376 MHz, –80 °C): δ = –108.3 (m, 7b-I), –111.41 (m,
Procedure C: The corresponding ligand (5a,b, 0.12 mmol) was
added to a solution of [Ir(cod)2]BF4 (40 mg, 0.08 mmol) in dichlo-
romethane (5 mL) under nitrogen. After stirring for 30 min, the
colour of the solution turned yellow-orange. Diethyl ether was
added to precipitate the product, which was collected by filtration,
washed with additional diethyl ether and vacuum dried.
7b-II) ppm; 7b-I/7b-II = 10:3.8. ΔH϶ = 16.4 1 kJmol–1, ΔS϶
=
–0.1 kJmol–1 K–1, ΔG϶
= 50.4 1 kJmol –1. FAB+: m/z (%) =
298.15
683 (M–BF4).
[Ir(cod)(2c)]BF4 (7c): Colour: yellow; yield: 50.5 mg, 82%. IR [KBr
1
(cm–1)]: (νB–F) 1084 (s), (νB–F) 1057 (s). H NMR (400 MHz) 7.62
(m, 4 H, Har), 7.19 (m, 4 H, Har), 4.2 (m, 2 H, CH), 3.96 (m, 4 H,
CH cod), 3.66 (m, 2 H, CH2), 3.47 (m, 2 H, CH2), 2.25 (m, 4 H,
CH2 cod), 1.77 (m, 4 H, CH2 cod), 1.41 (s, 6 H, CH3) ppm.
13C{1H} NMR (100 MHz): δ = 163.89 (Ci-F, JC,F = 249.5), 134.06
[Ir(cod)(5a)]BF4.CH2Cl2 (10a.CH2Cl2): Colour: yellow; yield:
29.2 mg, 48%. 1H NMR (CDCl3, 300 MHz): δ = 7.7 (m, 10 H,
C6H5), 4.0 (m, 6 H, CH + CH cod), 2.4 (t, 2 H, CH2, JH,H
=
5.1 Hz), 2.28 (m, 4 H, CH2 cod), 1.8 (m, 4 H, CH2 cod), 1.48 (d,
6 H, CH3, JH,H = 6.3 Hz) ppm. 13C{1H} NMR (CDCl3, 75 MHz):
δ = 133.68 (Co), 131.78 (Cm), 130.38 (Cp), 79.06 (CH cod), 78.52
(CH cod), 44.17 (CH), 38.83 (CH2), 31.58 (CH2 cod), 30.75 (CH2
3
4
2
(Co, JC,F = 6.3), 130.16 (Ci-S, JC,F = 2.3), 117.54 (Cm, JC,F
=
16.6), 111.12 (C(CH3)2), 79.72 (CH cod), 79.78 (CH cod), 78.59
(CH), 40.61 (CH3), 31.53 (CH2 cod), 31.23 (CH2) ppm. 19F NMR
(376 MHz, –80 °C): δ = –107.41 (m, 7c-I), –115.62 (m, 7c-II) ppm;
cod), 20.57 (CH3) ppm. FAB+: m/z (%)
= 589 (M–BF4).
7c-I/7c-II
=
10:3.5. ΔH϶
=
19.4 1.3 kJmol–1, ΔS϶
=
C25H32BF4IrS2·CH2Cl2 (760.63): calcd. C 41.06, H 4.51, S 8.44;
found C 41.30, H 4.70, S 8.04.
–0.1 kJmol–1 K–1, ΔG϶298.15 = 48.1 1.3 kJmol–1. FAB+: m/z (%) =
683 (M–BF4).
[Ir(cod)(5b)]BF4 (10b): Colour: orange; yield: 26.7 mg, 55%. 1H
NMR (CDCl3, 300 MHz,): δ = 4.37 (m, 2 H, CH cod), 4.13 (m, 2
H, CH cod), 3.76 (sextuplet, 2 H, CH, JH,H = 5.4 Hz), 3.55 (sept,
2 H, iPr CH, JH,H = 6.9 Hz), 2.56 (t, 2 H, CH2, JH,H = 5.4 Hz),
2.3 (m, 4 H, CH cod), 2.02 (m, 2 H, CH2 cod), 1.78 (m, 2 H, CH
cod), 1.61 (d, iPr CH3, JH,H = 6.6 Hz), 1.54 (d, 6 H, iPr CH3, JH,H
= 6.4 Hz) 1.53 (d, 6 H, iPr CH3, JH,H = 6.5 Hz) ppm. 13C{1H}
NMR (CDCl3, 75 MHz): δ = 78.24 (CH cod), 75.39 (CH cod),
41.53 (CH2), 41.0 (CH), 40.06 (iPr CH), 32.75 (CH2 cod), 30.42
(CH2 cod), 24.20 (CH3), 23.26 (iPr CH3), 22.84 (iPr CH3) ppm.
FAB+: m/z (%) = 521 (M–BF4). C19H36BF4IrS2 (607.65): calcd. C
37.56, H 5.97, S 10.55; found C 37.98, H 6.57, S 10.91.
Procedure B: A solution of the corresponding ligand (3, 4,
0.08 mmol) in dichloromethane (3 mL) was added to a solution of
[Ir(cod)2]BF4 (40 mg, 0.08 mmol) in dichloromethane (5 mL) under
nitrogen. After stirring for 40 min, the colour of the solution turned
yellow-orange. The volume was reduced, and hexane was added to
precipitate the product, which was collected by filtration, washed
with additional hexane and vacuum dried.
[Ir(cod)(3)]BF4 (8): Colour: yellow-orange; yield: 39.9 mg, 82%. IR
1
[KBr (cm–1)]: (νB–F) 1054 (s). H NMR (400 MHz, –80 °C, refer to
Figure 3 for assignments): δ = 4.87 (m, 1 H, CHa cod), 4.64 (m, 1
H, CHd cod), 4.64 (m, 1 H, CH 5), 4.50 (m, 1 H, CHb cod) 4.45
(m, 1 H, CHc cod), 4.14 (m, 1 H, CH 4), 3.77 (m, 1 H, CH2 3),
3.59 (m, 1 H, CH2 6), 3.28 (m, 3 H, CH2 6Ј,1, 2Ј), 3.07 (m, 1 H,
Synthesis of [Ir(H)2(cod)(dithioether)]BF4 (dithioether = 3, 4)
CH2 2), 2.82 (m, 1 H, CH2 1Ј), 2.58 (m, 1 H, CH2 3Ј) 2.17 (m, 4 General Procedure: Hydrogen was bubbled into an NMR tube con-
H, CH2 cod), 2.02 (m, 2 H, CH2 cod), 1.89 (m, 2 H, CH2 cod), taining a solution of [Ir(cod)(dithioether)]BF4 (ditihioether = 3, 4)
Eur. J. Inorg. Chem. 2005, 2315–2323
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© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
2321

E. Martin, A. M. Masdeu-Bultó et al.
FULL PAPER
(0.066 mmol) in deuterated dichloromethane at –72 °C for 20 min,
obtaining yellow solutions in both cases. The tube was introduced
into the NMR equipment at –80 °C and spectra were acquired.
The relaxation time, T1, was determined at –70 °C, and then the
temperature was increased by 10 °C intervals, recording spectra at
each successive temperature, until 25 °C was reached. 2D NMR
spectra were acquired at 25 °C for complex [Ir(H)2(cod)(3)]BF4 and
at 0 °C for complex [Ir(H)2(cod)(4)]BF4.
C19H36BF4IrS2, M = 607.61, Monoclinic space group P21, a =
9.2855(12), b = 12.5844(17), c = 10.0187(13) Å, β = 97.892(2)°, V
= 1159.6(3) Å3, Z = 2, Dc = 1.740 Mg/m3, 11295 reflections mea-
sured, 4057 unique (Rint = 0.0492) which were used in all calcula-
tions; the final R value was 0.0331 [F Ͼ 4σ(F)] and 0.0501 (all
data). The ORTEP diagram was generated using ORTEP-3.[50]
CCDC-239321 contains the supplementary crystallographic data
for this paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
[Ir(H)2(cod)(3)]BF4 (13): 1H NMR (300 MHz, –70 °C, refer to Fig-
ure 3 and Figure 7 for assignments): δ = 4.85 (m, 1 H, CHa cod),
4.64 (m, 1 H, CHd cod), 4.50 (m, 1, CH 5), 4.41 (m, 1 H, CHb cod)
4.41 (m, 1 H, CHc cod), 4.13 (m, 1 H, CH 4), 3.77 (m, 1 H, CH2
3), 3.59 (m, 1 H, CH2 6), 3.28 (m, 3 H, CH2 6Ј,1, 2Ј), 3.07 (m, 1
H, CH2 2), 2.80 (m, 1 H, CH2 1Ј), 2.59 (m, 1 H, CH2 3Ј) 2.06 (m,
4 H, CH2 cod), 1.91 (m, 4 H, CH2 cod), 1.34 (s, 3 H, CH3), 1.33
(s, 3 H, CH3), –11.37 [s, 1 H, complex 13-I, Hf, T1 = 0.3112 s
(err = 0.008368)], –11.56 [s, 1 H, complex 13-II, Hf, T1 = 0.3112 s
(err = 0.009975)], –13.78 [s, 1 H, complex 13-II, He, T1 = 0.222 s
(err = 0.006233)], –13.83 [s, 1 H, complex 13-I, He, T1 = 0.2087 s
(err = 0.003677)] ppm; 13-I/13-II = 5:3. 1H NMR (CD2Cl2,
300 MHz, 20 °C): δ = 4.93 (m, 1 H, CHa cod), 4.76 (m, 1 H, CHd
cod), 4.66 (m, 1, CH 5), 4.60 (m, 1 H, CHb cod) 4.43 (m, 1 H, CHc
cod), 4.17 (m, 1 H, CH 4), 3.81 (m, 1 H, CH2 3), 3.34 (m, 1 H,
CH2 6), 3.316 (m, 3 H, CH2, 6Ј,1, 2Ј), 3.15 (m, 1 H, CH2 2), 2.91
(m, 1 H, CH2 1Ј), 2.61 (m, 1 H, CH2 3Ј) 2.24 (m, 4 H, CH2 cod),
2.06 (m, 4 H, CH2 cod), 1.39 (s, 6 H, CH3), –11.39 (s, 1 H, complex
1, Hf), –11.59 (s, 1 H, complex 2, Hf), –13.87 (s, 1 H, complex 2,
He), –13.85 (s, 1 H, complex 1, He) ppm.
Acknowledgments
This work was financially supported by CONACyT from Mexico
(Ref. 34982), and Ministerio de Educación y Cultura from Spain
(PB97-0407-C05-01 and PB98-0641). L. F.-S. appreciates the fel-
lowship of DGEP-UNAM and CONACyT.
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[Ir(H)2(cod)(4)]BF4 (14): 1H NMR (400 MHz, 0 °C, refer to Fig-
ure 3 for assignments): δ = 4.91 (m, 1 H, CH 5), 4.6 (m, 2 H, CHa
cod + CH 6), 4.94 (m, 1 H, CHd cod), 4.18 (m, 1 H, CHb cod),
4.07 (m, 1 H, CHc cod), 3.76 (m, 1 H, CH2 7Ј), 3.57 (m, 1 H, CH2
4), 3.38 (m, 2 H, CH2 1,3), 3.35 (m, 1 H, CH2 4Ј), 3.29 (m, 2 H,
CH2 2, 2Ј), 3.03 (m, 2 H, CH2 1, 3), 2.78 (m, CH2 7), 2.38–1.91
(m, 8 H, CH2 cod), 1.43, 1.41 (s, 6 H, CH3, 0.5:1), –12.57 [s, 1 H,
complex 14-I/II, Hf, T1 = 0.4089 s (err = 0.01158)], –12.72 [s, 1 H,
complex 14-I/II, Hf, T1 = 0.3934 s (err = 0.009862)], –12.84 [s, 1
H, complex 14-I/II, He, T1 = 0.2825 s, (err = 0.009123)], –13.28 [s,
1 H, complex 14-I/II, He, T1 = 0.2846 s (err = 0.007316)] ppm.
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Catalysis: A standard hydrogenation experiment was performed in
the following manner.[25] A solution in dichloromethane (6 mL)
containing the complex [Ir(cod)L]BF4 (L = dithioether or cod,
0.026 mmol) and the substrate (1.05 mmol) was introduced into the
evacuated hydrogenation system which was filled up to atmospheric
pressure with hydrogen. The mixture was vigorously stirred using
a wrist-shaker and it was analysed directly by GC in the case of
substrates 11a and 11c. The final mixtures resulting from the hydro-
genation of acid substrates 11b and 11d were transformed into the
esters by the following procedure: trimethylsilyldiazomethane
(0.3 mL, 2 m in hexane) and MeOH (0.1 mL) were added to the
final catalytic solution (0.5 mL). This mixture was stirred for
30 min at room temperature, filtered through silica and analysed
by GC.
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Crystal Data for Complex 10b: Suitable crystals of complexes 10b
were grown by slow diffusion of n-hexane into a solution of the
complex in ethyl acetate and mounted on a glass fiber. The X-ray
data were collected at 293.5 K with a Bruker APEX instrument
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package was used for structure solution and refinement. An ab-
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2322
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Received: October 5, 2004
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