Synthesis of Rh(I) and Ir(I) complexes with chiral C2-multitopic ligands: Structural and catalytic properties

Article abstract of DOI:10.1016/S0022-328X(01)01067-1

Four multitopic ligands, N,N′-bis[(S)-prolyl)phenylenediamine, N,N′-bis{[(S)-pyrrolidin-2-yl]methyl}phenylenediamine, N,N′-bis[(S)-N-benzylprolyl]phenylenediamine, N,N′-bis{[(S)-N-benzyl-pyrrolidin-2-yl]methyl}phenylenediamine, were synthesised and their co-ordination properties with Rh(I) and Ir(I) studied. The complexes were prepared by the reaction of [MCl(cod)]₂ with AgPF₆ and further treatment with the ligand. All ligands form one to one [ML] species with the above metal ions. The structures of these complexes were elucidated by analytical and spectroscopic data (elemental analysis, mass spectroscopy, IR, ¹H- and ¹³C-NMR). Complexes show excellent activities and enantioselectivities up to 30% for the hydrogenation of prochiral olefins under mild reaction conditions.

Full text of DOI:10.1016/S0022-328X(01)01067-1

Journal of Organometallic Chemistry 634 (2001) 25–33
www.elsevier.com/locate/jorganchem
Synthesis of Rh(I) and Ir(I) complexes with chiral C2-multitopic
ligands
Structural and catalytic properties
M.J. Alco´n a, M. Iglesias a,*, F. Sa´nchez b,*, I. Viani b
a Instituto de Ciencia de Materiales de Madrid, CSIC, Cantoblanco, 28049 Madrid, Spain
b Instituto de Qu´ımica Orga´nica, CSIC, Juan de la Cier6a, 3, 28006 Madrid, Spain
Received 2 April 2001; accepted 10 June 2001
Abstract
Four multitopic ligands, N,N%-bis[(S)-prolyl)phenylenediamine, N,N%-bis{[(S)-pyrrolidin-2-yl]methyl}phenylenediamine, N,N%-
bis[(S)-N-benzylprolyl]phenylenediamine, N,N%-bis{[(S)-N-benzyl-pyrrolidin-2-yl]methyl}phenylenediamine, were synthesised and
their co-ordination properties with Rh(I) and Ir(I) studied. The complexes were prepared by the reaction of [MCl(cod)]2 with
AgPF6 and further treatment with the ligand. All ligands form one to one [ML] species with the above metal ions. The structures
of these complexes were elucidated by analytical and spectroscopic data (elemental analysis, mass spectroscopy, IR, 1H- and
13C-NMR). Complexes show excellent activities and enantioselectivities up to 30% for the hydrogenation of prochiral olefins
under mild reaction conditions. © 2001 Elsevier Science B.V. All rights reserved.
Keywords: Rhodium; Iridium; Asymmetric hydrogenation; Multitopic ligands
1. Introduction
the chiral pool and as cheap industrial chemical inter-
mediates. The second advantage lies in the chemistry of
the nitrogen functional group itself. The chemistry of
nitrogen is not always easy but has received abundant
attention such that there exist, in most cases, numerous
synthetic solutions to each possible transformation of
these compounds. As a result, these synthetic facilities
allow tailor-made modifications toward the preparation
of ligands with specific physicochemical properties.
C2-symmetric diamines could be used in carbonyl
reduction by hydride transfer with more than 99% ee
[4]. It is noticeable that even groups known for their
work on the use of chiral phosphines have turned their
attention to nitrogen-containing ligands. Thus, in 1995,
Noyori and co-workers used a synergetic effect of di-
amines and phosphines in carbonyl reduction by hydro-
genation with molecular H2 [5]. Chiral diureas with the
C2-diamine basic structure also gave promising results
[6]. Nitrogen-containing ligands may be used in asym-
metric catalysis with transition metals less expensive
than the noble metals. Thus, semicorrins were used in
cobalt complexes by Pfaltz and co-workers [7] for the
reduction of a,b-unsaturated molecules with NaBH4.
Catalytic asymmetric synthesis using organometallic
complexes has become one of the most active areas of
research in modern organic synthesis [1]. In this area
the search for and development of new chiral com-
plexes and a better understanding of their properties,
play a fundamental role in revealing the mechanisms of
catalytic processes [2].
The most commonly studied and employed
organometallic complexes contain phosphorus ligands.
This is mainly due to the excellent results obtained with
phosphines in different catalytic reactions [1]. However,
interest in nitrogen ligands has increased over the recent
years because of their higher stability, easier prepara-
tion and promising results [3]. Nitrogen-containing lig-
ands present several distinct advantages. First, they are
largely available in enantiomerically pure form, both in
* Corresponding authors. Tel.: +34-913329032; fax: +34-
913720623.
E-mail addresses: marta.iglesias@icmm.csic.es (M. Iglesias), felix-
iqo@iqog.csic.es (F. Sa´nchez).
0022-328X/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved.
PII: S0022-328X(01)01067-1

26
M.J. Alco´n et al. / Journal of Organometallic Chemistry 634 (2001) 25–33
An extensive study of the synthesis of new chiral
ligands were characterised unequivocally by mass spec-
trometry, IR and 1H-, 13C-NMR spectroscopy and gave
satisfactory elemental analyses. Mass spectrometry
shows the highest ions at m/z 302, 275, 484 and 455,
which corresponds to the molecular weights of com-
ligands to be applied in asymmetric synthesis has been
carried out in our earlier papers. For that purpose,
special efforts have been taken toward the synthesis of
easily accessible ligands based on natural aminoacids
[8]. These ligands have been applied with success in
asymmetric catalysis like the addition of diethylzinc to
enones [9], hydrogenation [10], cyclopropanation [11]
and oxidation of olefins [12]. In this context we have
developed the synthesis of a family of chiral C2-multi-
topic ligands (Fig. 1) with rigidity in the backbone as
an alternative to the more flexible family of C2-nitrogen
ligands that we have described recently [13]. To direct
our research toward obtaining further information on
the stability and structure of catalyst precursors, we
report the preparation of new C2-chiral ligands and
their Rh(I) and Ir(I) complexes and investigate their
co-ordination chemistry and catalytic properties in
detail.
1
pounds 3–6, respectively. The H- and 13C-NMR spec-
tra obtained are in agreement with those expected for
these C2 symmetrical ligands. The ligands have two
optically active centres; both have the S absolute
configuration.
2.2. Preparation of complexes
The rhodium and iridium complexes [M(ligand)-
(L%)]PF6 (L%=cod, THF) (7–14), were obtained by
treating the dimeric [M(cod)Cl]2 with two equivalents
of AgPF6 in tetrahydrofurane. An equimolar amount of
the corresponding multitopic ligands was added to the
solution containing the cationic mononuclear
[M(cod)(THF)x]PF6 species (Scheme 2). The mononu-
clear complexes [M(L)(L%)]PF6 (M=Rh, Ir) were pre-
pared in good yield (\60%) by the ligand exchange of
L with [M(cod)(THF)2]PF6 in THF. The complexes
were isolated by precipitation from diethyl ether as
microcrystaline air stable solids. Rhodium and iridium
complexes were moderately unstable in solution and
13C-NMR could be obtained only in the solid state.
Elemental analysis of C, H, N and metal is consistent
with the proposed stoichiometry (Fig. 2). Mass spec-
trometry (ESI-MS and APCI-MS with positive mode)
indicated a monomeric formula in accordance with the
results of IR and NMR studies. The complexes have
their highest ions at m/z values corresponding to the
loss of F−, and PF−6 in the molecular species.
2. Results and discussion
2.1. Synthesis of ligands
The ligands were prepared and well characterised
following a modified procedure described in Ref. [13].
All reaction steps were fine-tuned for high yield and
selectivity. The preparation of diamides N,N%-bis[(S)-
prolyl]phenylenediamine (3), and N,N%-bis[(S)-N-ben-
zylprolyl]phenylenediamine (5), was achieved starting
from the easily available
L-proline protected as the
N-carbobenzyloxy (1a) or N-benzyl (1b) derivative, ac-
cording to Scheme 1. The corresponding amines N,N%-
bis{[(S)-pyrrolidin-2-yl]methyl}phenylenediamine (4),
N,N%-bis{[(S)-N-benzyl-pyrrolidin-2-yl]methyl}-
phenylenediamine (6) were obtained by the reduction of
the respective amide with lithium aluminium hydride or
alternatively with sodium borohydride/trifluoroacetic
acid in dioxane at reflux. All intermediates and final
products have been obtained with a total yield of
70–80%. Diamides 3 and 5 are white solids while
amines 4 and 6 were isolated as colourless oils that are
stable at low temperature in an inert atmosphere. The
The IR spectra of the free ligands exhibit the charac-
teristic bands of amides and amines. The amide I band
appears at about 1660–1680 cm−1 and amide II at
1520 cm−1. The IR spectra of amide complexes (7, 9)
show w(NꢀH) bands in the range of 3260–3376 cm−1
,
shifted with respect to the free ligands, due to RhꢀNH
coordination. The amide I band at 1682 cm−1 is at-
tributed to the uncoordinated keto function and the
band at 1600 cm−1 is due to the CꢁC frequency. The
amide II band appears in the same position as the free
ligand. Also, the IR spectra of Rh–amine complexes 8
and 10 show w(NꢀH) bands shifted at higher frequen-
cies (3400 cm−1). The w(PꢀF) frequency appears at 835
cm−1 as medium bands characteristic of the non-coor-
dinated PF−6 anion.
These complexes are moderately unstable in organic
solvents and we have obtained the 13C-MAS and CP/
MAS-NMR spectra of powdered samples. The 13C-
NMR spectra of free ligands exhibits a single signal for
the CꢁO at about 173–174 ppm and in the spectra of
Rh–amide complexes 7 and 9 two peaks are found for
the amide carbons. The spectrum of complex 7 displays
Fig. 1. C2-multitopic ligands.

M.J. Alco´n et al. / Journal of Organometallic Chemistry 634 (2001) 25–33
27
Scheme 1.
calised on the metal ion. At shorter wavelengths the
bands at 300 nm may be assigned to the Rh“ligand
charge transfer transition and intra-ligand transitions.
The conductivity data suggest 1:1 electrolytes for all
cationic complexes.
two separate resonances at 183.6 and 166.1 ppm. The
downfield shift is due to the Rh’NHꢀCO coordina-
tion and the signal high field shifted indicating that a
higher electron density in this complex may be due to
the hydrogen bond between the NH and the uncoordi-
nated CꢁO group. The 13C-NMR spectrum of 9 also
shows two carbonyl signals at 180.9 (+7.2) and 166.4
(−7.3) ppm. The 13C-NMR spectra of amine com-
plexes show only small chemical shift differences com-
pared with the free ligands.
The IR spectra of the mononuclear Ir complexes
show that the expected w(NꢀH) bands shift to higher
frequencies. There is also no doubt that in the Ir–amide
complexes 11 and 13 the CꢁO unit of the amide groups
is not involved in the coordination to the metal, as in
the IR spectra only one CꢁO stretching frequency at
1690, 1683 cm−1 appears. The band at 1540–1520
cm−1 is due to the amide–N coordination. The 13C-
NMR spectra of 11 and 13 exhibit only one signal for
the amide carbons at l 167.0, 172.0, 167.0 ppm shifted
at higher field (−7.1 ppm) which also indicates a high
electron density in these complexes. In the Ir–amine
complexes 12 and 14 the 13C-NMR signals show only
small chemical shift differences compared with the free
ligands.
2.3. Catalytic acti6ity
The use of cationic complexes with chiral nitrogen-
containing ligands is an attractive approach for the
catalytic hydrogenation of prochiral olefins. In the first
stage, metal complexes were evaluated as catalysts in
the hydrogenation of diethyl citraconate to investigate
the potential of ligands 3–6 for asymmetric catalysis
(Table 1, Fig. 3). In the presence of 0.2 mol% of
catalysts in ethanol at 313 K under a pressure of 4 bar
H2, the substrate was fully converted to alkane in 30
min. The results of these studies reveal that cationic
catalysts are very effective for this transformation form-
ing a product with higher rate and comparable enan-
tioselectivity to that achieved with the analogous
ethylenediamine derivative [13]. The results show that
iridium complexes are more efficient than rhodium
complexes. The hydrogenation is completed in less than
Electronic absorption spectra of rhodium and iridium
complexes, measured between 800 and 200 nm, show a
clear maximum at ca. 300 nm (m=6000–8000) and one
shoulder at ca. 400 nm (m=1500–2000). Taking into
account their energy position and intensity the bands at
400 nm could be assigned [14] to d–d transitions lo-
Scheme 2.

28
M.J. Alco´n et al. / Journal of Organometallic Chemistry 634 (2001) 25–33
Fig. 2. Proposed structures for the rhodium and iridium complexes 7–14.
are in progress and will be presented extensively in
future.
30 min with higher ee (30%). Changing the substituents
in the ligands produces an important effect on the
optical induction. Thus, the optical induction is higher
for the catalysts containing the benzyl groups as pyrro-
lidine substituents. The results of these studies reveal
that cationic catalysts are very effective for this trans-
formation forming a product with higher rate and
moderate enantioselectivity.
The effect of the characteristics of substrate (Fig. 4)
on reactivity and enantioselectivity was tested using 7
as a model catalyst and the results summarised in Fig.
5. The hydrogenation of diethyl mesaconate, diethyl
citraconate and citraconic anhydride was quantitative
in less than 20 min with modest enantioselectivity (ee=
13.4, 9.0, 26%), while the hydrogenation of more steric
demanding diethyl 2-benzylidene succinate proceeds
more slowly (ee=22%).
The iridium complexes have shown higher rates
(TOF) and enantioselectivity (ee 30%) than the Rh
complexes. The change of substituents on the pyrro-
lidine nitrogen plays a significant role on optical induc-
tion that increases when moving from hydrogen to
benzyl group, indicating that an enhanced steric volume
around the metallic centre is a decisive effect for high
enantioselectivity.
3. Conclusions
A series of new microcrystalline air-stable rhodium
and iridium complexes with multitopic C2-symmetry
nitrogen ligands has been synthesised and characterised
fully even in an optically pure form. The complexes are
mononuclear species with the ligand coordinated in a
tetradentate manner through the amine–amide groups.
The metal–nitrogen bond is sufficiently stable for a
transfer of chirality from the optically active catalyst to
the product. We have shown that these cationic Rh(I)
and Ir(I) complexes are efficient catalysts for the hydro-
genation of olefins. The complexes are handled easily
and the turnover numbers approaching up to 11 000
could be achieved with the diethyl 2-citraconate. These
results constitute a firm ground for the design of more
efficient enantioselective systems, based on C2-symme-
try nitrogen ligands.
4. Experimental
A study about the influence of structural characteris-
tics of ligand and substrates with these promising cata-
lysts in homogeneous media or supported on zeolites
The preparation of organometallic complexes were
carried out under dinitrogen by conventional Schlenk-
tube techniques. The starting complexes [Rh(cod)Cl]2

M.J. Alco´n et al. / Journal of Organometallic Chemistry 634 (2001) 25–33
29
Table 1
Asymmetric hydrogenation of diethyl citraconate
Catalyst
TOF (mmol substrate mmol
ee (%) a
catalyst−1 min−1
)
7
8
9
10
11
12
13
14
4062
8000
4070
10 000
3625
9600
9.1
13.4
13.6
19.4
13.4
16.5
25.8
29.3
9700
11 000
Fig. 4. Prochiral olefins for the catalytic hydrogenation.
All reactions were performed in EtOH at 40 °C, S/C=500 and 4 atm
H2. All reactions were complete after 30 min reaction time.
a Enantiomeric excess (ee) was determined by chiral GC using a
chiral column based on alkylated cyclodextrin [17].
tion 13C-MAS or CP/MAS-NMR spectra of powdered
samples, in some cases also with a Toss sequence, in
order to eliminate the spinning side bands, were
recorded at 100.63 MHz, 6 ms, 90° pulse width, 2 ms
contact time and 5–10 recycle delay, using a Bruker
MSL 400 spectrometer equipped with an FT unit. The
spinning frequency at the magic angle (54°44%) was 4
kHz. Optical rotation values were measured at the
sodium-D line (589 nm) with a Perkin–Elmer 241 MC
polarimeter. Gas chromatographic analysis was per-
formed using a Hewlett–Packard 5890 II with a flame
ionisation detector in a cross-linked methylsilicone
column [17].
[15] and [Ir(cod)Cl]2 [16] were prepared using the meth-
ods reported earlier. All solvents were carefully de-
gassed before use. C, H and N analysis was carried out
by the analytical department of the Institute of Materi-
als Science (CSIC). Metal contents were analysed by
atomic absorption using a Perkin–Elmer 1100 B ap-
paratus and a plasma ICP Perkin–Elmer 40. Mass
spectra were performed on a Hewlett–Packard 1100
MSD mass spectrometer (ESI-MS, APCI-MS) with
positive mode. IR spectra were recorded on a Nicolet
XR60 spectrophotometer (range 4000–200 cm−1) in
1
KBr pellets; H-, 13C-NMR spectra were taken on a
4.1. Synthesis of ligands
Varian XR300 and a Bruker 200 spectrometers. 1H-
NMR chemical shifts are given in parts per million
(ppm) using Me4Si as an internal standard. High resolu-
The amides 3 and 5 were prepared by modifying the
procedure
given
for
1,6-bis[2(S)-2-pyrrolidinyl-
Fig. 3. Catalytic activity of the complexes 7–14 in the asymmetric hydrogenation of ethyl citraconate (catalyst–substrate=1:500; T=313 K,
pH2=4 atm).

30
M.J. Alco´n et al. / Journal of Organometallic Chemistry 634 (2001) 25–33
Fig. 5. Kinetic profile of catalytic hydrogenation of prochiral olefins with 7. All reactions were performed in EtOH at 40 °C, S–C=500 and
pH2=4 atm.
methyl]ethylenediamine starting from phenylenedi-
amine [13].
136.39 (CPhꢀR o-phenylenediamine), 128.58–127.88
(CPhꢀH Cbz), 125.01–124.63 (CPhꢀH o-phenylenedi-
amine), 67.36 (OCH2Ph), 61.13 (C2), 47.22 (C5), 28.41
(C3), 24.59 (C4). MS; m/z: 324, 250, 220, 205, 154, 57.
4.1.1. N,N%-Bis[(S)-N-benzyloxycarbonyprolyl]-
phenylenediamine (2)
Ethyl chloroformate (1.41 ml, 14.8 mmol) was added
dropwise with vigorous stirring to an ice-cold solution
of (S)-N-benzyloxycarbonylproline (1a) (3.7 g, 14.9
mmol) and triethylamine (2.07 ml, 14.9 mmol) in THF
(80 ml). When the addition was complete the pasty
reaction mixture was stirred for 30 min (temperature
5–10 °C), and a very reactive mixed anhydride was
obtained. To the anhydride solution, recrystallised o-
phenylenediamine (0.8 g, 7.4 mmol) in cold THF (3 ml)
was added dropwise for 15 min and the mixture was
stirred for 2 h at 0 °C, and then filtered. The solvent
was evaporated and the residue extracted with EtOAc
and washed successively with water, aq. NaHCO3 and
brine. The organic layer was dried over magnesium
sulphate and evaporated in vacuo to give 3.39 g (80%)
of a white solid. The product was purified by flash-
chromatography with hexane–EtOAc (1:2). M.p. (dec.):
66–67 °C. [h]2D0−93.3 (CH2Cl2, 1). Anal. Found: C,
66.8; H, 6.8; N, 10.4. Calc. for C32H34N4O6 (MW 570):
C, 67.3; H, 6.8; N, 10.4%. IR (cm−1): w(NH) 3272,
w(CꢁOCbz) 1696, w(amide I) 1677; w(CꢁC) 1590; w(amide
4.1.2. N,N%-Bis[(S)-prolyl]phenylenediamine (3)
A mixture of N,N%-bis[(S)-N-benzyloxycarbonyl pro-
lyl]phenylenediamine (2) (7.3 g, 12.8 mmol), cyclohex-
ene (6 ml, 76 mmol) and 2 g of commercial Pd/C (10%)
in 160 ml of EtOH was heated under reflux for 1 h in
argon, cooled and filtered over celite. the catalyst was
washed with EtOH, and the filtrate and wash liquids
were evaporated under reduced pressure to give 3.64 g
of 3. Yield: 84%; m.p. (dec.): 123–125 °C. [h]2D0−27.7
(CH2Cl2, 1). Anal. Found: C, 62.5; H, 6.8; N, 17.9.
Calc. for C16H22N4O2 (MW 302): C, 63.6; H, 7.3; N,
18.5%. IR (KBr, cm−1): w(NH) 3304, 3238, w(amide I)
1662, w(CꢁC) 1590, w(amide II) 1522. 1H-NMR
(CDCl3, 50 °C): l 9.68–9.59 (s, br, 2H, NꢀH), 7.68–
7.63 (m, 2H, p-Ph), 7.21–7.11 (m, 2H, o-Ph), 3.86 (dd,
2H, H2, J=5.28 Hz, J=9.22 Hz), 3.07–2.99 (m, 2H,
H5), 2.97–2.93 (m, 2H, H5%), 2.37–2.13 (m, 4H, H3,
NꢀH), 2.06–1.97 (m, 2H, H3%), 1.82–1.69 (m, 4H, H4).
13C-NMR (CDCl3, 50 °C): l 174.09 (CꢁO), 129.72
(CPhꢀR), 125.59 (Co-Ph), 123.98 (Cp-Ph), 61.03 (C2), 47.35
(C5), 30.82 (C3), 26.23 (C4). MD; m/z: 302 ([M+]), 220,
205, 145, 57.
1
II) 1518. H-NMR (CDCl3, 50 °C): l 8.48–8.52 (m,
2H, NꢀH), 7.38–7.10 (m, 10H, Ph Cbz), 7.10–6.96 (m,
4H, Ph o-phenylenediamine), 5.18–5.07 (m, 4H,
OCH2), 4.41–4.20 (m, 2H, H2), 3.68–3.35 (m, 4H, H5),
2.46–2.04 (m, 2H, H3), 2.04–1.86 (m, 2H, H3%), 1.86–
1.74 (m, 4H, H4). 13C-NMR (CDCl3, 50 °C): l 170.97
(CꢁO amide), 156.29 (CꢁO ester), 140.22 (CPhꢀR Cbz),
4.1.3. N-N%-Bis{[(S)-pyrrolidin-2-yl]methyl}-
phenylenediamine (4)
Procedure a: to a solution of N,N%-bis[(S)-pro-
lyl]phenylenediamine (3) (1 g, 3.3 mmol) in ice-cold

M.J. Alco´n et al. / Journal of Organometallic Chemistry 634 (2001) 25–33
31
THF (25 ml), LiAlH4 (1.3 g, 34 mmol) was added
dropwise. When the addition was complete the reaction
mixture was stirred for 24 h under reflux. The reaction
products were analysed by GC-MS. The product was
isolated as an air sensitive oil. Yield: 0.62 g (70%).
Anal. Found: C, 69.8; H, 9.9; N, 20.7. Calc. for
C16H26N4 (MW 274): C, 70.1; H, 9.5; N, 20.4%. IR
(film, cm−1): w(NꢀH) 3288. 1H-NMR (CDCl3, D2O,
50 °C): l 7.03–6.58 (4H, CHPh.), 3.68–3.46 (m, 4H,
CH2ꢀNHPh), 3.26–3.17 (m, 2H, H2), 3.14–3.09 (m, 4H,
H5), 1.97–1.88 (m, 4H, H3), 1.86–1.72 (m, 4H, H4).
MS; m/z: 275 ([M++1]).
added dropwise to the mixture with vigorous stirring.
When the addition was complete the pasty reaction
mixture was stirred for 1 h (temperature 5–10 °C), and
a very reactive mixed anhydride was obtained. To the
anhydride filtered solution, recrystallised o-phenylene-
diamine (2.44 mmol) in cold THF (1 ml) was added for
15 min and the mixture was stirred at 0 °C for 10 h,
and washed successively with water, aq. NaHCO3 and
brine. The organic layer was dried over MgSO4 and
evaporated in vacuo to give a white solid. The product
was purified by flash-chromatography with hexane–
EtOAc (1/2). Yield:75%
Procedure b: to an ice-cold suspension of 2.19 g
(0.0579 mol) of NaBH4 in dry dioxane (30 ml), trifl-
uoroacetic acid was added dropwise (0.0579 mol or
28.95 ml of a 2 M dioxane solution) and the mixture
was stirred for 10 min at room temperature (r.t.). The
amide (3.86 mmol) was added to the solution and the
mixture was stirred for 48 h under reflux. The solvent
was evaporated under reduced pressure. Water was
carefully added to the residue, which was extracted with
CHCl3 and dried over MgSO4. The solvent was elimi-
nated and the final product was purified by flash chro-
matography. Yield: 79%.
4.1.5. N,N%-Bis{[(S)-N-benzyl-pyrrolidin-2-yl]methyl}-
phenylenediamine (6)
The diamine 6 was prepared through procedures (a
and b) similar to those given for 4 starting from N,N%-
bis[(S)-N-benzylprolyl]phenylenediamine (5) (1.20 g,
2.49 mmol). The product was purified by flash chro-
matography with EtOAc–NEt3 (95/5) and isolated as
an air sensitive colourless oil. Yield: procedure a: 1.02 g
(87%), procedure b: 80%. Anal. Found: C, 79.2; H, 8.7;
N, 12.6. Calc. for C30H38N4 (MW 454): C, 79.3; H, 8.4;
N, 12.3%. IR (film, cm−1): w(NꢀH) 3307, w(CꢁC) 1594.
1H-NMR (CDCl3, 50 °C): l 7.29–7.07 (m, 10H, Ph),
6.70–6.67 (m, 2H, CPh), 6.56–6.53 (m, 2H, CPh), 4.30
(s, br, NH), 3.92–3.89 (d, 2H, CH2Ph), 3.18–3.06 (m,
8H, CH2Ph, H2, H5, H8), 2.87–2.77 (m, 4H, H5, H8),
2.20–1.86 (m, 4H, H3,3%), 1.62–1.44 (m, 4H, H4,4%).
13C-NMR (CDCl3, 50 °C): l 139.56, 137.88 (CPhꢀNH),
128.62, 128.02, 126.74, 118.04, 109.62 (CPh.), 62.08 (C2),
58.00 (C5), 54.42 (CH2Ph), 44.08 (C8), 28.64 (C3), 23.46
(C4). MS; m/z: 455([M++1]), 91.
4.1.4. N,N%-Bis[(S)-N-benzylprolyl]phenylenediamine (5)
Procedure a: to a solution of N,N%-bis[(S)-pro-
lyl]phenylenediamine (3) (2.16 g, 4 mmol) and triethy-
lamine (2.37 ml, 2 mmol) in ice-cold THF (25 ml),
benzyl bromide (2 ml, 2 mmol), was added dropwise
with vigorous stirring. When the addition was complete
the reaction mixture was stirred for 6 h at 0 °C. The
solvent was evaporated and the residue extracted with
CHCl3 and washed successively with water, aq.
NaHCO3 and brine. The organic layer was dried over
MgSO4 and evaporated in vacuo to give 5 as a white
solid. The product was purified by flash chromatogra-
phy with 1:1 hexane–EtOAc. Yield: 3.4 g (93%); m.p.
4.2. Preparation of [M(C2-ligand)(THF)]PF6 complexes
(M=Rh, Ir) (7–14)
4.2.1. General procedure
(dec.): 101–102 °C; [h]2D0−58.1 (CHCl3, c=1); Anal.
The preparation of [Rh(3)]PF6·(THF) (7) is described
in detail, and the experimental procedure is a model for
all the other complexes. Silver hexafluorophosphate
(0.4 mmol) in THF (40 ml) was added to [Rh(cod)Cl]2
(0.2 mmol) in THF (10 ml) and the mixture was stirred
vigorously at r.t. for 30 min. Precipitated silver chloride
was filtered and the yellow solution was treated with
the ligand (0.4 mmol) in THF. The mixture was stirred
for 24 h under reflux. The solvent was evaporated
under reduced pressure to 2 ml. Careful addition of
Et2O caused the precipitation of a solid which was
collected by filtration, washed with Et2O and dried
under vacuum (10−3 mmHg) to give the wine cationic
complex. Yield: 85%; m.p. (dec.): \230 °C. Anal.
Found: C, 41.3; H, 5.2; N, 8.0; Rh, 14.5. Calc. for
C24H38F6N4O4PRh (MW 694): C, 41.5; H, 5.5; N, 8.1;
Rh, 14.8%. IR (KBr, cm−1): w(NꢀH) 3362, 3303,
w(amide I) 1682, w(CꢁC) 1594, w(amide II) 1549,
6
Found: C, 74.5; H, 7.1; N, 11.8. Calc. for C30H34N4O2
(MW 483): C, 74.7; H, 7.1; N, 11.6%. IR (KBr, cm−1):
w(NH) 3328, 3214, w(amide I) 1680, 1660, w(CꢁC) 1594,
1
w(amide II) 1520, 1510. H-NMR (CDCl3, 50 °C): l
9.32 (s, br, 2H, NꢀH), 7.34–7.05 (m, 14H, Ph), 3.80 (d,
2H, CH2Ph, J=15.16 Hz), 3.54 (d, 2H, CH2Ph, J=
14.99 Hz), 3.30–3.25 (m, 2H, H2), 3.03–2.97 (m, 2H,
H5), 2.41–2.32 (m, 2H, H5%), 2.21–2.11 (m, 2H, H3),
1.92–1.83 (m, 2H, H3%), 1.70–1.60 (m, 4H, H4). 13C-
NMR (CDCl3, 50 °C):
l
173.70 (CꢁO), 137.87
(CPhꢀNH), 129.97 (CPhꢀC), 129.04–124.64 (CPhꢀH),
67.52 (C2), 59.92 (CH2Ph), 53.99 (C5), 30.89 (C3), 24.03
(C4). MS; m/z: 484 ([M++1]), 160, 91.
Procedure b. a solution of (S)-N-benzylproline (1b)
(1 g, 4.88 mmol) and Et3N (685 ml, 4.88 mmol) in
CHCl3 (50 ml), was stirred at r.t. for 15 min and
cooled. Ethyl chloroformate (466 ml, 4.88 mmol) was

32
M.J. Alco´n et al. / Journal of Organometallic Chemistry 634 (2001) 25–33
w(amide II) 1520, w(PꢀF) 834. 13C-NMR (solid): l
183.6, 166.1 (CꢁO), 144.1 (CꢀOTHF), 142.1 (CPhꢀR),
129.2 (CPho), 126.0 (CPhp), 110.1 (CꢀCTHF), 78.7 (C2),
64.9, 60.3 (C5), 30.5 (C3, C4). UV–vis: umax (nm) (log m,
10−3 M) (DMF): 381.5 (3.06), 294.5 (3.77). \M
(V−1 cm2 mol−1, 10−3 M, CH3CN): 154–167. MS;
m/z: 405 ([Rh(3)]+), 303 ([(3)+1]).
Complexes 8–14 were prepared by a procedure simi-
lar to that given for 1 using 0.2 equivalents of the
appropriate ligand.
4.2.5. [Ir(3)(THF)]PF6 (11)
Beige. Yield: 85%; m.p. (dec.): \200 °C. Anal.
Found: C, 33.1; H, 4.0; N, 7.6; Ir, 27.1. Calc. for
C20H30F6IrN4O3P (MW 711): C, 33.7; H, 4.2; N, 7.9; Ir,
27.0%. IR (KBr, cm−1): w(NꢀH) 3402, 3184, w(amide I)
1690, w(CꢁC) 1604, w(amide II) 1540, w(PꢀF) 842. 13C-
NMR (solid): l 167.0 (CꢁO), 143.9 (CꢀOTHF), 142.4
(CPhꢀR), 128.2 (CPho), 126.9 (CPhp), 110.6 (CꢀCTHF),
76.7 (C2), 63.6, 59.9 (C5), 27.8, 25.7 (C3, C4). \M
(V−1 cm2 mol−1, 10−3 M, CH3CN): 110. MS; m/z
(
191Ir): 562 ([Ir(3)]PF6−4F), 303 ([(3)]+1).
4.2.2. [Rh(4)(THF)]PF6 (8)
4.2.6. [Ir(4)]PF6 (12)
Yellow. Yield: 75%; m.p. (dec.) \200 °C. Anal.
Found: C, 40.0; H, 6.3; N, 8.7; Rh, 16.9. Calc. for
C20H34F6N4PRh (MW 594): C, 40.4; H, 6.0; N, 8.9; Rh,
17.3%. IR (KBr, cm−1): w(NꢀH) 3400, 3296, w(PꢀF)
Light yellow. Yield: 75%; m.p. (dec.): \200 °C.
Anal. Found: C, 36.8; H, 4.8; Ir, 36.1; N, 10.4. Calc. for
C16H26F6IrN4P (MW 522): C, 36.8; H, 5.0; Ir, 36.8; N,
10.7%. IR (KBr, cm−1): w(NꢀH) 3394, w(PꢀF) 836.
13C-NMR (solid): l 140.1 (CPhꢀR), 129.39 (CPh), 66.7
(C2), 60.3 (C5), 28.5 (C3, C4). UV–vis: umax (nm) (log m,
10−3 M) (DMF): 378.5 (2.36), 289.5 (3.39), 290 (3.93).
836. 13C-NMR (solid):
l
144.1 (CPhꢀR), 142.7
(CꢀOTHF), 129.0 (CPho), 127.0 (CPhp), 109.3 (CꢀCTHF),
68.7 (C2), 64.9, 60.3 (C5), 28.5 (C3, C4). UV–vis: umax
(nm) (log m, 10−3 M) (DMF): 377.5 (2.36), 288.5 (3.39),
292 (3.93). \M (V−1 cm2 mol−1, 10−3 M, CH3CN):
122. MS; m/z: 503 ([Rh(4)]PF6−F), 377 ([Rh(4)]+).
\
(V−1 cm2 mol−1, 10−3 M, CH3CN): 103. MS; m/z
M
(
191Ir): 591 ([Ir(4)]PF6−F), 465 ([Ir(4)]+), 275 ([(4)]+
1).
4.2.7. [Ir(5)(cod)]PF6 (13)
4.2.3. [Rh(5)(cod)]PF6 (9)
Light brown. Yield: 80%; m.p. (dec.): 130–132 °C.
Anal. found: C, 49.4; H, 5.0; Ir, 20.1; N, 6.2. Calc. for
C38H46F6IrN4O2P (MW 927): C, 49.2; H, 5.0; Ir 20.7;
N, 6.0%. IR (KBr, cm−1): w(NꢀH) 3376, 3260, w(amide
I) 1683, 1679, w(CꢁC) 1600, w(amide II) 1548, w(PꢀF)
Yellow. Yield: 68%; m.p. (dec.): 120–122 °C. Anal.
Found: C, 54.4; H, 5.3; N, 6.4; Rh, 12.8. Calc. for
C38H46F6N4O2PRh (MW 839): C, 54.3; H, 5.5; N, 6.7;
Rh, 12.3%. IR (KBr, cm−1): w(NꢀH) 3376, 3260, 1686,
w(amide I) 1612, w(CꢁC) 1570, w(amide II) 1526, w(PꢀF)
840. 1H-NMR (CDCl3, 50 °C): l 7.8–6.6 (m, 14H,
Ph.), 4.3–4.0 (m, 6H, CHꢁ, CH2Ph), 3.50–3.48 (m, 2H,
CH2Ph), 2.95–1.50 (m, H5, H3, H4, CHcod).13C-NMR
(solid): l 180.9, 166.4 (CꢁO), 129.35 (CPh), 76.7 (C2),
68.82 (CꢁCcod), 66.62 (CH2Ph), 55.82 (C5), 31.68 (C3),
29.81 (CꢀCcod), 29.03 (C4). UV–vis: umax (nm) (log m,
10−3 M) (DMF): 348.0 (3.27), 289.0 (3.70). \M
(V−1 cm2 mol−1, 10−3 M, CH3CN): 124–127. MS;
m/z: 693 ([Rh(5)(cod)]+), 483 ([(5)+1]).
1
840. H-NMR (CDCl3, 50 °C): l 7.84–6.65 (m, 14H,
Ph), 4.25–4.05 (m, 6H, CHꢁ, CH2Ph), 3.50 (m, 2H,
CH2Ph), 2.90–1.60 (m, H5, H3, H4, CHcod). 13C-NMR
(solid): l 172.0, 167.0 (CꢁO), 129.60 (CPh), 78.7 (C2),
68.42 (CꢁCcod), 62.86 (CH2Ph), 56.82 (C5), 29.61(C3,
CꢀCcod), 26.33 (C4). UV–vis: umax (nm) (log m, 10−3 M)
(DMF): 346.0 (3.27), 292.0 (3.70). \M (V−1 cm2 mol−1
,
10−3 M, CH3CN): 114–117. MS; m/z (191Ir): 781
([Ir(5)(cod)]+), 484 ([(5)]+1).
4.2.8. [Ir(6)(cod)]PF6 (14)
Yellow. Yield: 75%; m.p. (dec.): 133–136 °C. Anal.
Found: C, 50.7; H, 5.3; Ir, 20.9; N, 6.4. Calc. for
C38H50F6IrN4O2P (MW 899): C, 50.7; H, 5.6; Ir, 21.4;
N, 6.2%. IR (KBr, cm−1): w(NꢀH) 3378, w(CꢁC) 1600,
w(PꢀF) 822. 13C-NMR (solid): l 135.6 (CPhꢀNH),
129.84 (CPh.), 67.52 (CꢁCcod), 60.68 (C5), 58.25 (C2),
50.07 (CH2Ph), 43.51 (C8), 29.37, 28.56, 26.45 (C3, C4,
CH2cod). UV–Vis: umax (nm) (log m, 10−3 M) (DMF):
345.0 (3.27), 288.0 (3.70). \M (V−1 cm2 mol−1, 10−3
M, CH3CN): 124–127. MS; m/z (191Ir) (MeOH–
CH3CN): 772 ([Ir(6)]PF6−F), 677 ([Ir(6)(MeOH)]+),
645 ([Ir(6)]+), 455 ([(6)]+1).
4.2.4. [Rh(6)(cod)]PF6 (10)
Yellow. Yield: 75%; m.p. (dec.): \210 °C. Anal.
Found: C, 56.0; H, 5.8; N, 7.2; Rh, 12.9. Calc. for
C38H50F6N4O2PRh (MW 810): C, 56.3; H, 6.2; N, 6.9;
Rh, 12.7%. IR (KBr, cm−1): w(NꢀH) 3350, 3260,
w(CꢁC) 1600, w(PꢀF) 836. 13C-NMR (solid): l 135.6
(CPhꢀNH), 128.99 (CPh.), 64.68 (C5), 59.10 (C2), 50.37
(CH2Ph), 41.51 (C8), 28.89 (C3, C4). UV–vis: umax (nm)
(log m, 10−3 M) (DMF): 345.0 (3.27), 288.0 (3.70). \M
(V−1 cm2 mol−1, 10−3 M, CH3CN): 114–117. MS;
m/z (MeOH–CH3CN): 714 ([Rh(6)(MeOH)]PF6]−F),
558 ([Rh(6)]++1), 455 ([(6)]+1).
The iridium complexes were prepared following the
general procedure starting from [IrCl(cod)]2 and the
corresponding ligand.
4.3. Catalytic experiments
The catalytic properties, in hydrogenation reactions,

M.J. Alco´n et al. / Journal of Organometallic Chemistry 634 (2001) 25–33
33
[3] (a) F. Fache, E. Schulz, M. Lorraine Tommasino, M. Lemaire,
Chem. Rev. 100 (2000) 2159;
of the above-mentioned Rh and Ir complexes were
examined under conventional conditions for batch reac-
tions in a reactor (Autoclave Engineers) of 100 ml
capacity at 313 K, 4 atm dihydrogen pressure and a
metal–substrate molar ratio of 1:500. The results were
monitored by GLC using an internal standard refer-
ence. The kinetics results are shown in Table 1.
(b) A. Togni, L.M. Venanzi, Angew. Chem. Int. Ed. Engl. 33
(1994) 497;
(c) F. Fache, B. Dunjic, P. Ga´mez, M. Lemaire, Top. Catal. 4
(1997) 201.
[4] P. Ga´mez, F. Fache, P. Mangeney, M. Lemaire, Tetrahedron
Lett. 34 (1993) 43 (see also p. 6897).
[5] T. Ohkuma, H. Ooka, S. Hashiguchi, T. Ikariya, R. Noyori, J.
Am. Chem. Soc. 117 (1995) 2675 (see also p. 10417).
[6] P. Ga´mez, B. Dunjic, M. Lemaire, J. Org. Chem. 61 (1996) 5196.
[7] U. Leutenegger, A. Madin, A. Pfaltz, Angew. Chem. Int. Ed.
Engl. 28 (1989) 60.
Acknowledgements
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(Eds.), Comprehensive Coordination Chemistry, vol. 2, Perga-
mon Press, Oxford, 1987, p. 739.
[9] A. Corma, M. Iglesias, M.V. Mart´ın, J. Rubio, F. Sa´nchez,
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[12] A. Corma, A. Fuerte, M. Iglesias, F. Sa´nchez, J. Mol. Catal. A:
Chemical 107 (1996) 225.
[13] M.J. Alco´n, M. Iglesias, F. Sa´nchez, I. Viani, J. Organomet.
Chem. 601 (2000) 284.
[14] R.D. Peacock, B. Steward, Coord. Chem. Rev. 46 (1982) 129.
[15] (a) J. Chatt, L.M. Venanzi, J. Chem. Soc. Chem. Commun.
(1957) 4715;
The authors are grateful to Mr J.A. Esteban-Percales
for his valuable help in ligand isolation and purification
and to Direccio´n General de Investigacio´n Cient´ıfica y
Te´cnica of Spain (Project MAT97-1016-C02-02;
MAT2000-1768-C02-02) for the financial support.
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