Chiral Xyliphos Complexes for the Catalytic Imine Hydrogenation Leading to the Metolachlor Herbicide: Isolation of Catalyst-Substrate Adducts

Article abstract of DOI:10.1002/chem.200305218

Iridium complexes relevant to the catalytic enantioselective hydrogenation of 2-methyl-6-ethylphenyl-1′-methyl-2′-methoxyethylimine (MEA-imine, 1) in the Syngenta Metolachlor (3) process were prepared and characterized. Reaction of the diphosphane (S)-1-[(R)-2-(diphenylphosphanyl)ferrocenyl]ethyldi(3,5-xylyl)phosphane ((S)-(R)-Xyliphos, (S)-(R)-4) with [Ir₂(μ-Cl) ₂(cod)₂] (cod = 1,5-cyclooctadiene) afforded [Ir(Cl)(cod){(S)-(R)-4}] (7), which reacted with AgBF₄ to form [Ir(cod){(S)-(R)-4}]BF₄ (8). Complexes 7 and 8 reacted with iodide to yield [Ir(I)(cod){(S)-(R)-4}] (9). When 9 was treated with one and two equivalents of HBF₄, two isomers of the cationic Ir^III iodo hydrido complex [Ir(I)(H)-(cod){(S)-(R)-₄}]BF₄ were isolated (10 and 11, respectively). Complex 9 was oxidized with one equivalent of I₂ to give the iodo-bridged dinuclear species [Ir ₂I₂(μ-I)₃{(S)-(R)-4}₂)] _I (12). [Ir₂(μ-Cl)₂(coe)₄] (coe=cyclooctene) reacted with (S)-(R)4 to yield the chlorobridged dinuclear complex [Ir₂(μ-Cl)₂{(S)-(R)-4}₂] (13). Complexes 7-12 were structurally characterized by single-crystal X-ray diffraction and tested as single-component catalyst precursors for enantioselective hydrogenation of MEA-imine. Complex 10 and dinuclear complex 12 gave the best catalytic results. Efforts were also directed at isolating substrate- or product-catalyst adducts: Treatment of 8 with 2,6-dimethylphenyl-1′-methyl-2′-methoxyethylimine (DMA-imine, 14, a model for 1) under H₂ allowed four isomers of [Ir(H) ₂{(S)-(R)-4}(14)]BF₄ (18-21) to be isolated. These analytically pure isomers were fully characterized by 2D NMR techniques. X-ray structural analysis of an Ir^I-imine adduct, namely, [Ir(C ₂H₄)₂(14)]BF₄ (25), which was prepared by reacting [IrCl(C₂H₄)₄] with [Ag(14)₂]BF₄ (16), confirmed the κ₂ coordination mode of imine 14.

Full text of DOI:10.1002/chem.200305218

FULL PAPER
Chiral Xyliphos Complexes for the Catalytic Imine Hydrogenation Leading
to the Metolachlor Herbicide: Isolation of Catalyst Substrate Adducts°
Romano Dorta,*[a] Diego Broggini,[b] Robert Stoop,[c] Heinz R¸egger,[c]
Felix Spindler,[d] and Antonio Togni[c]
Abstract: Iridium complexes relevant
to the catalytic enantioselective hydro-
genation of 2-methyl-6-ethylphenyl-1’-
methyl-2’-methoxyethylimine (MEA-
imine, 1) in the Syngenta Metolachlor
(3) process were prepared and charac-
terized. Reaction of the diphosphane
(S)-1-[(R)-2-(diphenylphosphanyl)fer-
rocenyl]ethyldi(3,5-xylyl)phosphane
IrIII iodo hydrido complex [Ir(I)(H)-
(cod){(S)-(R)-4}]BF4 were isolated (10
and 11, respectively). Complex 9 was
oxidized with one equivalent of I2 to
give the iodo-bridged dinuclear species
[Ir2I2(m-I)3{(S)-(R)-4}2)]I (12). [Ir2(m-
Cl)2(coe)4] (coe=cyclooctene) reacted
with (S)-(R)-4 to yield the chloro-
bridged dinuclear complex [Ir2(m-
Cl)2{(S)-(R)-4}2] (13). Complexes 7 12
were structurally characterized by
single-crystal X-ray diffraction and
tested as single-component catalyst
precursors for enantioselective hydro-
genation of MEA-imine. Complex 10
and dinuclear complex 12 gave the best
catalytic results. Efforts were also di-
rected at isolating substrate or prod-
uct catalyst adducts: Treatment of 8
with 2,6-dimethylphenyl-1’-methyl-2’-
methoxyethylimine (DMA-imine, 14, a
model for 1) under H2 allowed four
isomers of [Ir(H)2{(S)-(R)-4}(14)]BF4
(18 21) to be isolated. These analyti-
cally pure isomers were fully character-
ized by 2D NMR techniques. X-ray
structural analysis of an IrI imine
adduct, namely, [Ir(C2H4)2(14)]BF4
(25), which was prepared by reacting
[IrCl(C2H4)4] with [Ag(14)2]BF4 (16),
confirmed the k2 coordination mode of
imine 14.
((S)-(R)-Xyliphos,
(S)-(R)-4)
with
[Ir2(m-Cl)2(cod)2] (cod=1,5-cycloocta-
diene) afforded [Ir(Cl)(cod){(S)-(R)-4}]
(7), which reacted with AgBF4 to form
[Ir(cod){(S)-(R)-4}]BF4 (8). Complexes
7 and 8 reacted with iodide to yield
[Ir(I)(cod){(S)-(R)-4}] (9). When 9 was
treated with one and two equivalents
of HBF4, two isomers of the cationic
Keywords: asymmetric catalysis
hydrogenation ¥ iridium ¥ P ligands
¥
Introduction
Iridium is particularily efficient in the catalytic hydrogena-
tion of ™difficult∫ substrates such as tetrasubstituted al-
5]
Chiral amines constitute an important class of biologically
active molecules. Catalytic enantioselective hydrogenation
of imines is an efficient method to prepare chiral amines.[1]
kenes[2] and imines.[3 The key steps in the industrial syn-
theses of dextrometorphan (Lonza)[6] and (1S)-Metolachlor
(Syngenta)[7] are both enantioselective imine hydrogenations
catalyzed by soluble chiral iridium ferrocenyldiphosphane
complexes. The latter synthesis is outlined in Scheme 1 and
features the hydrogenation of 2-methyl-6-ethylphenyl-1’-
methyl-2’-methoxyethylimine (MEA-imine, 1) to the optical-
ly enriched (80% ee) (S)-MEA-amine (2). Nowadays, this
reaction represents the largest scale enantioselective catalyt-
ic process in industry. Compound 2 is the precursor to the
chiral herbicide (1S)-Metolachlor (3)[8,9] which is sold under
the trademark Dual-Magnum in amounts of more than 10
000 t per annum.[10]
[a] Prof. Dr. R. Dorta
Departamento de QuÌmica
Universidad SimÛn BolÌvar,
Caracas 1080A (Venezuela)
Fax : (+58)212-9063961
E-mail: rdorta@usb.ve
[b] Dr. D. Broggini
Department of Chemistry and Biochemistry, University of California
Santa Barbara, CA 93106-9510 (USA)
[c] Dipl. Chem. R. Stoop, Dr. H. R¸egger, Prof. Dr. A. Togni
Laboratory of Inorganic Chemistry,
The industrial catalyst system is prepared in situ and con-
sists of a mixture of [Ir2(m-Cl)2(cod)2] (cod=1,5-cycloocta-
diene), the chiral diphosphane (R)-(S)-Xyliphos ((R)-1-[(S)-
2-(diphenylphosphanyl)ferrocenyl]ethyldi(3,5-xylyl)phos-
phane, (R)-(S)-4), iodide (as tetrabutylammonium or
sodium salt), and a Br˘nsted acid (e.g., acetic or sulfuric
acid). The reaction is carried out under 80 bar of hydrogen
Swiss Federal Institute of Technology
ETH Hˆnggerberg, 8093Z¸rich (Switzerland)
[d] Dr. F. Spindler
Solvias AG, Postfach, CH-4002 Basel (Switzerland).
[°] The major part of this work was carried out by R.D. at ETH (ETH
Diss. No. 12739).
267
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DOI: 10.1002/chem.200305218
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FULL PAPER
Syntheses of complexes: The ™magic∫ catalyst mixture used
in industry to hydrogenate 1 consists of [Ir2(m-Cl)2(cod)2],
two equivalents of diphosphane 4, Bu4NI or NaI, and H2SO4
or AcOH. We expected that once the neutral IrI diphos-
phane complex bearing either ClÀ or IÀ ligands is formed in
situ it will readily be protonated to form cationic IrIII hydri-
do species. In fact, we observed the formation of several iri-
dium diphosphane hydride species when all four aforemen-
tioned ingredients were mixed under one-pot reaction con-
ditions. Unfortunately, no procedure was found to separate
the different components of these mixtures. We therefore
decided to synthesize such complexes in a step-by-step
manner and to test them subsequently as one-component
catalyst precursors for the hydrogenation of 1.
Scheme 1. Industrial synthesis of Metolachlor (Syngenta).
[Ir2(m-Cl)2(cod)2] reacted cleanly with two equivalents of
(S)-(R)-4 in toluene to afford [Ir(Cl)(cod){(S)-(R)-4}] (7) in
good yield as a yellow powder. The 31P{1H} NMR spectrum
indicated the formation of a sole diastereomer by the pres-
ence of only one pair of doublets (J=37 Hz) at d=16.4 and
À14.5 ppm. Complex 7 was treated with one equivalent of
AgBF4 in THF to afford the cationic compound 8 [see
Eq. (1)] as a brick-red powder in excellent yield. All 31P, 13C,
and 1H resonances were assigned by standard 2D NMR
techniques (see Experimental Section). A pair of doublets
(J=24 Hz) at d=3.2 (P(Ph)2) and at 37.9 ppm (P(Xyl)2) in
the 31P{1H} NMR spectrum characterized 8. In the 13C NMR
spectrum the C atoms of the coordinated olefins trans to the
xylyl- and phenyl-substituted P atoms resonated at d=92.3,
86.0 and 91.2, 84.7 ppm, respectively. This indicates that
electronically these latter donors are only modestly differ-
ent, the xylyl-substituted one exerting a slightly larger trans
influence. The electronic imbalance between the two ends
of each double bond is mainly a consequence of the twisted
conformation that the cod ligand adopts to fit into the chiral
pocket generated by the aryl groups of the Xyliphos ligand
(see X-ray structure analysis below). All observations were
in accord with results for analogous complexes characterized
by a number of selective NOEs and homo- and heteronu-
clear coupling constants[15] and
pressure at 323 K with a substrate/catalyst ratio of 106. Ini-
tial turnover frequency (TOF) is said to exceed 1.8î
106 hÀ1.[10] This makes it one of the fastest homogeneous sys-
tems known, second only to certain homogeneous Ziegler -
Natta polymerization catalysts[11] and Noyori×s ruthenium
hydrogenation catalysts.[12] Here we present the synthesis
and characterization (including X-ray crystal structures) of
iridium complexes that reflect the composition of the
™magic mixture∫ that is used in industry to hydrogenate
MEA-imine. These complexes were tested as single-compo-
nent catalyst precursors in the MEA-imine hydrogenation.
The best catalytic results were obtained with an iodo-bridg-
ed IrIII dimer which was synthesized by oxidation of an IrI
precursor with I2. Furthermore, we present the isolation and
full characterization of catalyst substrate adducts and an X-
ray analysis of a related iridium imine complex.
Results and Discussion
Ligand synthesis: The secondary phosphane (3,5-Xyl)2PH
(5) was obtained from PCl2(NEt2) in three steps in 59%
yield (Scheme 2). Condensation of 5 with commercially
by single-crystal X-ray diffrac-
tion study (see Figure 1). We
reasoned that the co-catalysts
[N(Bu)4]I and H2SO4 used in
the industrial system can form
HI in situ. Therefore, we stud-
ied the reactivity of 8 toward
commercially available aqueous
HI under different conditions,
and we invariably observed the
Scheme 2. Synthesis of (S)-(R)-4. i) 2 equiv 3,5-Xyl-Li, 203 K, Et2O; ii) 4 equiv, HCl(g), Et2O; iii) LAH, 195 K,
Et2O; iv) AcOH, 370 K.
formation of
a
mixture of
mainly two hydride species. The
available (S)-N,N-dimethyl-1-[(R)-2-(diphenylphosphanyl)-
ferrocenyl]ethylamine (6)[13] was accomplished by following
the standard protocol[14] and gave 75% of yellow microcrys-
talline (S)-(R)-4. The 31P{1H} NMR spectrum showed a pair
of doublets at d=À25.2 and 6.5 ppm (J=19 Hz). Note that
this is the enantiomer of the ligand that is used in the tech-
nical application, but this does not affect the scope of this
work.
1H NMR spectra of the resulting solutions showed a doublet
of doublets at d=À13.8 ppm and a pseudotriplet at d=
À12.6 ppm in varying ratios, along with signals for small
amounts of other hydrides. Disappointingly, these reactions
were neither clean nor could the products be separated. A
stepwise synthesis in which 8 was first treated with iodide
and then protonated proved to be more successful. Thus, the
IrI iodide 9 was prepared from 8 by adding one equivalent
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Iridium Hydrogenation Catalysts
267 278
of [N(Bu)4]I in THF [Eq. (1)]. Alternatively, halogen ex-
change of 7 with one equivalent of KI in acetone directly
led to 9, which was isolated as a yellow powder. Remarka-
bly, both routes to 9 involved absolute (at the NMR-sensi-
tivity level) diastereoselectity of the IÀ addition. Single-crys-
tal X-ray diffraction on 9 revealed that the IrÀI bond is ori-
ented endo with respect to the ferrocene moiety (see
Figure 2). Compounds 7, 8, and 9 were easily prepared on
gram scales.
contains four molecules. There are two crystallographically
distinct molecules. Figure 2 shows the square-pyramidal co-
ordination environment of one of the two independent mol-
Single crystals of 8 suitable for an X-ray diffraction study
were grown from THF. Figure 1 shows the expected square-
planar coordination environment of iridium. The iridium
Figure 2. Structure of one of the two independent molecules of
9
(ORTEP plot; 30% thermal isotropic ellipsoids). Selected bond length-
s [ä] and angles [8]: Ir(1)ÀI(1) 2.888(4), Ir(1)ÀP(1) 2.357(12), Ir(1)ÀP(2)
2.353(13), Ir(1)ÀC(36) 2.15(5), Ir(1)ÀC(37) 2.16(5), Ir(1)ÀC(40) 2.19(4),
Ir(1)ÀC(41) 2.23(5), C(36)ÀC(37) 1.25(6), C(40)ÀC(41) 1.40(6); I(1)-
Ir(1)-P(1) 97.2(3), I(1)-Ir(1)-P(2) 90.6(3), P(1)-Ir(1)-P(2) 98.9(5), I(1)-
Ir(1)-C(36) 122.9(14), P(1)-Ir(1)-C(36) 86.5(15), I(1)-Ir(1)-C(41)
120.9(12), P(2)-Ir(1)-C(41) 86.5(15), I(1)-Ir(1)-C(40) 85.1(12).
ecules of 9. The iodine atom is oriented in the direction of
the ferrocenyl moiety, which is a recurring feature in ferro-
cenyl diphosphane iridium complexes[16,17] (vide infra). The
iridium atom is displaced 0.37 ä along the Ir(1)ÀI(1) vector
out of the best plane fitted through P(1), P(2), and the mid-
points of the C=C bonds of the cod ligand. The Ir(1)ÀI(1)
distance of 2.888(4) ä is significantly longer than in the cor-
responding IrIII species (vide infra). The double bond
C(36)=C(37) (1.25(6) ä) trans to the more basic phosphane
P atom P(2) is shorter than C(40)=C(41) (1.40(6) ä). How-
ever, the large standard deviations of the bond lengths pre-
clude a more detailed discussion of the bonding parameters.
We note that no significant difference in the trans influence
of the phosphanes in the X-ray structure of the correspond-
ing cationic complex 8 was detected.
Figure 1. Structure of the cation of 8 (ORTEP plot; 30% probability el-
lipsoids). Selected bond lengths [ä] and angles [8]: Ir(1)ÀP(1) 2.318(4),
Ir(1)ÀP(2) 2.325(4), Ir(1)ÀC(36) 2.243(15), Ir(1)ÀC(40) 2.221(18), Ir(1)À
C(37) 2.183(13), Ir(1)ÀC(41) 2.180(18), C(36)ÀC(37) 1.37(3), C(40)À
C(41) 1.35(2); P(1)-Ir(1)-P(2) 92.76(15), P(1)-Ir(1)-C(40) 89.1(5), P(1)-
Ir(1)-C(41) 94.8(5), P(2)-Ir(1)-C(36) 89.4(4), P(2)-Ir(1)-C(37) 95.2(5).
The well-characterized, diastereomerically pure, neutral
iodo complex 9 was then used in protonation studies. Reac-
tion of 9 with H2SO4, CH3COOH, and CF3SO3H in different
solvents invariably led to mixtures of hydrides. However,
slow addition of a solution of HBF4 in Et2O to a solution of
9 in CH2Cl2 at 195 K afforded one hydrido species in 90%
yield, based on NMR measurements. The pseudotriplet at
atom lies within 0.02 ä of the best plane fitted through P(1),
P(2), and the midpoints of the C=C bonds. The cod ligand is
appreciably twisted out of the P(1)-Ir(1)-P(2) plane. This is
best illustrated by the distances of C(37) and C(41) from
this plane of À1.05 and +1.12 ä, respectively, or, alterna-
tively, by the closeness of C(36) and C(40) to this plane
(0.26 and À0.17 ä, respectively). Thus, the solid-state struc-
ture is in accord with the electronic imbalance of the two
double bonds of the cod ligand that was observed in NMR
experiments.
1
d=À12.6 ppm in the H NMR spectrum corresponded to a
pair of doublets (J=18 Hz) at d=À12.4 and 23.5 ppm in the
31P{1H} NMR spectrum. After workup, 10 (Scheme 3) was
isolated as a pink powder and fully characterized. Its struc-
ture is in accordance with standard 2D NMR data. Treat-
ment of 9 with two equivalents of HBF4 or, alternatively, of
Single crystals of 9 were obtained from a THF/Et2O mix-
ture. Complex 9 crystallized in a very large unit cell that
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R. Dorta et al.
FULL PAPER
moiety. The Ir(1)ÀI(1) bond
length of 2.803(5) ä compares
well with that of one of the rare
structurally characterized mon-
onuclear iridium iodo hy-
drides.[19] Figure 4 is a superpo-
sition of the core structures of 9
Scheme 3. Synthesis of 10 and 11.
10 with a further equivalent of HBF4 gave a new iridium hy-
dride complex which was isolated in acceptable yields as an
orange powder. This compound was characterized by a dou-
blet of doublets (J1 =15.8, J2 =9.3Hz) at d=À13.8 ppm in
1
the hydrido region of the H NMR spectrum and by a pair
of doublets (J=23Hz) at d=À31.9 and À1.5 ppm in the
31P{1H} NMR spectrum. Full characterization, including a
single-crystal X-ray diffraction analysis (see Figure 3), al-
lowed us to formulate the product as 11 (Scheme 3). The
protonation mechanism has not yet been elucidated and is
far from clear.[18] However, most important for the scope of
this study is the fact that we succeeded in isolating and char-
acterizing two monomeric iridium hydrido iodo isomers in
pure form that are the formal oxidative addition products of
HI to 8. These two isomers, 10 and 11, were also present in
the above mentioned ™magic mixture∫ when typical precata-
lyst preparation protocols were followed. Indeed, both 10
and 11 were excellent precatalysts for the hydrogenation of
MEA-imine 1 (vide infra).
Figure 4. Superposition of the coordination environments of iridium in
complexes 9 and 11.
and 11. The presence of the hydride ligand in 11 forces the
cod ligand to twist by 158 into the equatorial plane relative
to its orientation in 9. Alternatively, this situation may be
described by the smaller distance of the iridium atom from
the best plane fitted through P(1), P(2), and the midpoints
of the C=C bonds of cod in 11, that is, 0.23in 11 versus
0.37 ä in 9.
Single crystals of 11 suitable for an X-ray study were
grown from a THF/CH2Cl2 mixture. Figure 3shows a pseu-
dooctahedral coordination environment of iridium, with the
axial iodide ligand pointing in the direction of the ferrocenyl
The attempted oxidative addition of I2 to 8 led to an un-
precedented enantioselective activation and subsequent io-
dination of an allylic CÀH bond of the coordinated cod
ligand with concomitant formation of an IrIII hydrido iodo
cation. This chemistry has been described in detail else-
where.[17] When complex 9 was treated with an equimolar
amount of I2 in toluene at 333 K, a new species formed
quantitatively according to NMR spectroscopy [Eq. (2)].
1
The H NMR spectrum revealed the absence of coordinated
cod and coordinated solvent molecules. Elemental analyses
were in agreement with a compound of the composition
Ir¥I3¥4. Molecular weight determination indicated a dinuclear
structure. Conductometric measurements in acetone were in
agreement with a 1:1 electrolyte. The 31P{1H} NMR spec-
trum showed a sharp pair of doublets (J=11 Hz) at d=
À22.0 and 2.0 ppm and thus suggested a C2-symmetric dinu-
clear complex. Finally, a single-crystal X-ray analysis (see
Figure 5) was in agreement with these findings and allowed
us to draw structure 12. This complex reacted neither with
Tl and Ag salts nor with strong Br˘nsted acids. Nonetheless,
12 turned out to be the most efficient single-component cat-
alyst for MEA-imine hydrogenation (vide infra).
Crystals of 12 suitable for an X-ray crystallographic analy-
sis were grown from a CH2Cl2/Et2O mixture. In view of the
large dimensions of the structure the R values are high, and
the accuracy of the bonding parameters is correspondingly
low (in fact, no meaningful esd values were calculated).
Figure 5 confirms the dinuclear monocationic nature of 12
Figure 3. Structure of the cation of 11 (ORTEP plot; 30% probability el-
lipsoids). Selected bond lengths [ä] and angles [8]: Ir(1)ÀI(1) 2.803(5),
Ir(1)ÀP(1) 2.357(16), Ir(1)ÀP(2) 2.349(16), Ir(1)ÀC(36) 2.22(4), Ir(1)À
C(37) 2.22(4), Ir(1)ÀC(40) 2.28(4), Ir(1)ÀC(41) 2.22(4), C(36)ÀC(37)
1.26(8), C(40)ÀC(41) 1.28(8); P(1)-Ir(1)-P(2) 90.9(5), I(1)-Ir(1)-P(1)
94.9(4), I(1)-Ir(1)-P(2) 90.4(4), C(36)-Ir(1)-I(1) 116.3(16), C(37)-Ir(1)-
I(1) 83.7(16), C(41)-Ir(1)-I(1) 113.5(18), C(40)-Ir(1)-I(1) 80.9(17), C(36)-
Ir(1)-P(2) 153.4(16), C(36)-Ir(1)-P(2) 153.4(16), C(41)-Ir(1)-P(2)
88.0(18), C(40)-Ir(1)-P(2) 92.8(18), C(36)-Ir(1)-P(1) 86.6(16), C(37)-Ir(1)-
P(1) 94.5(17), C(41)-Ir(1)-P(1) 151.5(18), C(40)-Ir(1)-P(1) 174.5(17).
270
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Chem. Eur. J. 2004, 10, 267 278

Iridium Hydrogenation Catalysts
267 278
the other at d=À1.0 and
26.7 ppm (2JPP’ +4JPP’ =31 Hz).
The cis/trans ratio (ca. 30/70)
appeared to be independent of
the reaction conditions (differ-
ent solvents, temperatures, and
ways
of
mixing
[Ir2(m-
Cl)2(coe)4] with 4). Complex 13
is air-sensitive (sometimes pyro-
phoric), and it did not react
with iodides (e.g., Bu4NI). We
recently discovered that olefin-
free IrI dimers such as 13 readi-
ly and reversibly react with
CÀH and OÀH bonds,[16] and
their catalytic potential was
demonstrated in enantioselec-
tive olefin hydroamination (via
NÀH activation)[23] and olefin
hydroarylation (via CÀH activa-
tion)[24] reactions.
Figure 5. Structure of one of the two independent cations of 12 (ORTEP plot; 30% probability ellipsoids). For
clarity only the ipso-C atoms of the phenyl groups are drawn. Selected bond lengths [ä] and angles [8]: Ir(C)À
Ir(D) 3.669, Ir(C)ÀI(1C) 2.671(4), Ir(C)ÀI(2C) 2.770(4), Ir(C)ÀI(3C) 2.776(4), Ir(C)ÀI(5C) 2.721(4), Ir(C)À
P(1C) 2.249(15), Ir(C)ÀP(2C) 2.263(15), Ir(D)ÀI(1C) 2.720(4), Ir(D)ÀI(2C) 2.697(4), Ir(D)ÀI(3C) 2.758(4),
Ir(D)ÀI(4C) 2.693(4), Ir(D)ÀP(1D) 2.356(15), Ir(D)ÀP(2D) 2.278(16); P(1C)-Ir(C)-I(1C) 95.7(4), P(1C)-Ir(C)-
I(3C) 91.6(4), P(1C)-Ir(C)-I(5C) 93.4(4), P(1C)-Ir(C)-P(2C) 95.5(6), P(2C)-Ir(C)-I(1C) 98.8(4), P(2C)-Ir(C)-
I(2C) 93.7(4), P(2C)-Ir(C)-I(5C) 90.2(4), I(1C)-Ir(C)-I(2C) 77.62(12), I(1C)-Ir(C)-I(3C) 81.71(13), I(2C)-Ir(C)-
I(3C) 79.40(12), I(2C)-Ir(C)-I(5C) 91.86(13), I(3C)-Ir(C)-I(5C) 88.13(13), Ir(C)-I(1C)-Ir(D) 85.76(12), Ir(C)-
I(2C)-Ir(D) 84.30(12), Ir(C)-I(3C)-Ir(D) 83.07(12).
Catalytic hydrogenation of
MEA-imine (1): Complexes 7
12 were tested as catalyst pre-
cursors for the enantioselective,
solvent-free hydrogenation of
MEA-imine (1) to MEA-amine
(2) (Table 1). Unfortunately,
the pronounced sensitivity of
13 to air and moisture preclud-
ed its use under the experimen-
tal conditions chosen here.
and gives a selection of bond parameters. The triple iodo
bridge, along with the two terminal iodides and the two di-
phosphane ligands, define the two octahedral coordination
environments of Ir(1C) and Ir(1D). The terminal iodides
I(1C) and I(1D) again point in the direction of the ferrocen-
yl moieties. Their distances to the iridium centers of about
2.7 ä compare well with other IrIIIÀI bond lengths[19,21,22]
and are shorter than the corresponding distances in the IrI
and IrIII complexes 9 and 11 (vide supra). The IrÀI bonds
trans to the P atoms are slightly longer than those trans to
the I atoms. Figure 6 is a view along the molecular C2 axis
that passes through I(3C), and thus shows agreement with
solution 31P NMR data (pair of doublets). Structually, 12 ap-
pears to be a diphosphane analogue of the nonahalogenoiri-
Figure 6. View along the molecular C2 axis of 12 passing through I(3C)
(PowerMoMo line drawing).
dates [Ir2X9]3À[20] in which four of the terminal XÀ ligands
correspond to the two diphosphane ligands in 12.
We found that [Ir2(m-Cl)2(coe)4] (coe=cyclooctene) react-
ed cleanly with diphosphane (S)-(R)-4 in benzene, toluene,
or THF to give mixtures of the chloro-bridged dinuclear
complexes cis- and trans-13 in good yields. The 31P NMR
spectrum showed two pairs of multiplets, as expected for
two AA’BB’ systems. One pair of multiplets is at d=À4.2
and 22.7 ppm (only 2JPP’ +4JPP’ =38 Hz was resolved), and
Enantioselectivities did not vary significantly with the dif-
ferent precatalysts, but the activities were a function of the
Cl, I, or H ligands and the oxidation state of the precata-
lysts. Notably, the halide-free compound 8 was a very poor
hydrogenation catalyst (Table 1, entry 3). The influence of
the chloride versus the iodide ligand is evident in entries 2
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R. Dorta et al.
FULL PAPER
sessed. In its free state at room
temperature imine 14 exists as
a mixture of E and Z isomers
in a ratio of 86:14. Complexes 7
and 8 reacted neither with 14
nor with its immonium tetra-
fluoroborate salt 15. Complex 9
was protonated by 15 to give a
mixture of the hydrido com-
plexes 10 and 11 (along with
other minor hydrides) and free
imine 14. Elimination of HI
from 10 and 11 took place in
part in the presence of 14 (and
Table 1. Iridium-catalyzed hydrogenation of 1[a]
Entry
Catalyst precursor
Yield [%]
TOF [hÀ1
]
ee [%] (config.)
1
reference system[b]
100
31.2
<1
23.6
70.0
66.0
75.0
2778
867
<28
656
1944
1375
208379 (
80 (R)
77 (R)
not determined
78 (R)
2
3
7
8
4
9
5
10
11
12
77 (R)
81 (R)
6[c]
7[d]
S)
[a] 20.5 mL 1, no solvent, substrate/catalyst=50000, p=100 bar, 303 K, 18 h reaction time. See Experimental
Section for a typical protocol and analytical methods. [b] [Ir2(m-Cl)2(cod)2]+2(S)-(R)-4+[Bu4N]I+AcOH.
[c] 24 h reaction time. [d] Precatalyst of opposite chirality, that is, bearing ligand (R)-(S)-4.
and 4, whereby the latter ligand had a slightly detrimental
effect on activity. The IrI complexes performed poorly, while
the trivalent iridium precatalysts 10 12 displayed markedly
higher activities. The best mononuclear single-component
precatalyst was the cationic iodo hydrido species 10
(Table 1, entry 5), whereas its isomer 11 was less active
(Table 1, entry 6). Surprisingly, the dinuclear IrIII precatalyst
12 gave the best results in terms of activity, and selectivity
even in the absence of a source of protons (Table 1,
entry 7). In fact, under the hydrogenation conditions used in
this study, iridium hydrido iodo species may be formed
along with HI. Likewise, Zhang et al. recently used iodine
as an efficient in situ co-catalyst in the iridium-catalyzed
other bases) to give cationic 8. Complex 12 did not react
with 14 16. The chloro bridge of 13 was not split even in
neat imine 14, nor was any other type of imine coordination
observed in NMR experiments. However, as expected, 13
activated the NÀH bond of the immonium salt 15 to give
complicated and inseparable mixtures of hydrido imino
complexes. Treating 13 with silver salt 16 invariably formed
complex mixtures and a silver mirror on the walls of the re-
action flask.
When the cationic complex 8 was treated with H2 in the
presence of a large excess of DMA-imine (14) in CH2Cl2,
imine adducts 18 21 formed [Eq. (3)]. These compounds
were isolated as an analytically pure mixture in a ratio of
18:19:20:21 of 45:42:3:10. The diastereoselectivity of this re-
action varied little with the reaction conditions employed,
such as solvent and temperature. Reactions in CH2Cl2 were
cleaner than in CH3OH, THF, or neat 14. At 195 K, the re-
action was considerably slower, but with no beneficial effect
on the diastereoselectivity of DMA-imine complexation. Al-
though separation of isomers 18 21 was not possible, their
solution structures were fully established by a combination
of multinuclear 1D and 2D NMR techniques. The k2 coordi-
nation mode of imine 14 in another iridium complex was
confirmed by an X-ray structure analysis (25, vide infra).
Characteristic NMR parameters are summarized in Table 2.
A phase-sensitive 31P, 1H COSY experiment 1) established
the type of substituents on the phosphorus donors, 2) as-
signed the resonances of the hydride ligands trans to P from
the magnitudes of the J(31P, 1H) coupling constants, and
3) identified the second hydride ligand. The stereochemistry
of this hydride followed from a short triangulation based on
enantioselective hydrogenation of arylimines. They pro-
_
posed heterolytic H2 activation by an Ir(PP)(Cl)(I)2 species
to form an iridium hydrido chloro iodo complex with HI
elimination.[5] It remains to be demonstrated, though, that
HI elimination is favored over HCl elimination. None of the
single-component catalysts tested here approached the ex-
ceptional activity of the reference system (Table 1,
entry 1).[25] These results seem to indicate that both halide li-
gands, ClÀ as well as IÀ, must be present in the reaction mix-
ture.
Isolation and characterization of catalyst substrate com-
plexes: We were interested in isolating and characterizing
complexes that could serve as model compounds for inter-
mediates in the catalytic MEA-imine hydrogenation cycle.[3]
We chose to use the slightly simpler model substrate DMA-
imine (14). Iridium complexes containing both ligand 4 and
imine 14 within their coordination spheres are of particular
interest since they allow the interplay of steric and electron-
ic factors between the ligand and the substrate to be as-
1
cross-peaks observed in the H NOESY experiment. There-
fore, in the two major isomers 18 and 19 short internuclear
272
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Chem. Eur. J. 2004, 10, 267 278

Iridium Hydrogenation Catalysts
267 278
groups are caused by the shielding anisotropy of the perpen-
dicular aromatic rings which sandwich the methoxy group.
The orientation of the imine ligand with respect to the
IrH2P2 core was established following two short triangula-
tions based on the short internuclear distances that were ob-
served in the NOESY spectrum. The hydrides located cis to
both P donors exhibited spatial closeness to one of the
methyl groups of the 2,6-dimethylaniline unit, whereas ortho
protons of aromatic moieties assigned to the other hemi-
sphere with respect to the mentioned hydrides are close to
the methoxy groups.
A chemically relevant conformational aspect of the dia-
stereomeric mixture 18 21 is its solution dynamics. In the
room-temperature NOESY spectrum with an exchange
mixing time of 600 ms, selective exchange between diaster-
eomers 18 and 21 was observed. An exchange mechanism
must be consistent with the observation that the hydride
originally trans to PXyl2 must end up in the cis-cis position
_
(with respect to PP) while the other becomes trans to PXyl2.
Therefore, we suggest dissociation of the ether group, move-
ment of the PXyl2 donor to this vacant position and recoor-
dination of the ether group in the position where PXyl2 left.
Although we did not observe further interconversions
among the diastereomers it is
conceivable that they occur at
somewhat slower rates and
Table 2. Selected NMR data for 18 21 (relative abundances).
18 (45%)
À4.4
19 (42%)
20 (3%)
21 (10%)
À1.0
would explain why constant di-
astereomer ratios were ob-
served and why the mixtures
were inseparable.
Note that migratory insertion
of the C=N bonds into the IrÀH
bonds of 18 and 20 on the one
hand, and of 19 and 21 on the
other hand would give rise to
amines (R)-17 and (S)-17, re-
d(31P) (PPh2)
d(31P) (PXyl2)
d(1H) (Jtrans, Jcis
À30.2
5.4
22.311.9 0.8
3
42.1
)
À6.95 (147, 21.5)
À6.14 (149.9, 19.3)
À7.35 (145.2, 22.7)
À30.63 (13.9, 21.8)
not observed
not observed
not observed
3.58
À8 06 (153.5, 20.0)
d(1H) (Jcis, Jcis
)
À29.86 (13.2, 24.7)
À30.19 (12.6, 25.6)
À31.69 (8.5, 28.1)
d(1H) (OCH3)
d(1H) (OCH2)
d(1H) (CH3)
d(1H) (C5H5)
1.39
4.48, 4.02
1.60
1.72
4.47, 4.20
1.67
2.18
3.94, 3.07
1.41
3.50
3.45
3.46
separations of these hydrides from 1) the methine protons at
the stereogenic center of the phosphorus chelate, 2) the un-
substituted Cp ring, and 3) two types of aromatic ortho pro-
tons were found. In diastereomers 20 and 21 only the last-
named type of interactions was observed, consistent with
the remoteness of these hydrides from the aforementioned
functional groups. Coordination of the imine ligand in 18
and 19 was proven by the presence of a phosphorus-induced
doublet of doublets in the 13C NMR spectrum of the imine
C atoms resonating at d=180.00 and 180.64 ppm, respec-
tively. Furthermore, the chiral environment around iridium
rendered the methylene protons of the coordinated imine
diastereotopic. These were individually assigned in 18, 19,
and 21 from selective NOEs to the trans-cis hydride (rela-
tive to the P donors) and to the characteristic ortho protons
of the respective aromatic moieties. The observed selectivity
also pointed to a coordination of the ether functionality, as
free rotation of the ÀCH2OCH3 group is expected to lead to
a series of nonselective distance-dependent interactions. The
proposed coordination through oxygen is independently sup-
ported by the remarkable chemical shifts of the methoxy
groups resonating at d=1.39, 1.72, and 2.18 ppm for 18, 19,
and 21, respectively. These fairly low values for methoxy
spectively. However, under these conditions (i.e., in absence
of halides and at low H2 pressure) no reaction took place.
Although pre-coordination of the imine appears not to be
the enantioselective step, structures 18 21 allow for some
important stereochemical observations:
1) The relative abundances of the diastereomers indicate
that the half of the iridium coordination octahedron into
which the FeCp moiety points is sterically less accessible
for the substrate molecule. In all crystal structures of oc-
tahedral or square-pyramidal iridium ferrocenyldiphos-
phane complexes this position is occupied by a halogen
atom.[16,17,26] Structures 9, 11, and 12 in this work are ex-
amples thereof. In solution, however, complexes with op-
posite configuration are sometimes observed (cf. pair 10
and 11).
2) The methyl ether function of 14 always occupies the po-
sition trans to a hydride.
3) The imine function binds in a s fashion trans to one of
the P atoms. Both steric and electronic effects govern
the orientation of DMA-imine on iridium. The orienta-
tion is consistent with the relative trans influences of the
H, N, O and P donors and the requirement that either
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R. Dorta et al.
FULL PAPER
the N or the O substituent must fit between two aromat-
ic rings of the phosphorus chelate.
(imine) complex 16 at 195 K, clean metathesis occurred to
afford the iridium ethylene DMA imine complex 25 in very
good yield [Eq. (4)] along with one equivalent of AgCl and
free imine 14. Complex 16 was obtained as a white powder
on a gram scale in excellent yield by treating a solution of
AgBF4 in toluene with two equivalents of imine 14.The
1H NMR spectrum confirmed the presence of a sole isomer.
Broad signals for the ethylene ligands indicated dynamic be-
havior at room temperature, and the sharp signals for the
imine ligand 14 were all shifted to lower fields with respect
to those of the free imine. The resonance of the methoxy
protons of coordinated 14 was shifted downfield by about
0.5 ppm to d=3.98 ppm. The imino methyl protons resonat-
ed at d=1.93ppm and the methylene protons at d=
5.49 ppm, as compared to d=1.66 and 4.20 ppm, respective-
ly, in free 14. The 1H NMR data thus support a bidentate co-
ordination mode of 14.[31]
4) It may be assumed that the migratory insertion of the
hydride is the enantioselective step. Structures 18 and 20
are at the origin of the observed stereoselectivity of the
catalysis (i.e., (S)-(R)-Xyliphos gives predominantly the
(R)-amine and vice versa for the actual industrial proc-
ess). Migratory insertion of the hydrides cis to the imine
functions in 18 and 20 lead to the postulated IrIII amide
intermediates 22 and 23, respectively, containing a new
stereogenic center (Scheme 4). It has been shown that
Scheme 4. Proposed intermediates after migratory insertion of the hy-
drides cis to the imine functions in complexes 18 and 20. X=I, Cl, OAc,
HSO4, H etc. and Ar=2,6-dimethylaryl or 2-ethyl-6-methylaryl
H2 readily adds across such IrIII amide bonds to form a
coordinated amine, regenerate an IrÀH function,[27] and
thus close the catalytic cycle. Structure 18 (in the real
catalytic system, I, Cl, OAc, HSO4, etc. may actually
occupy the position trans to the methyl ether function in-
stead of a hydride ligand) should thermodynamically
favor migratory insertion to form the new CÀH bond
due to a synergistic effect caused by the electronic asym-
metry of the Xyliphos ligand. In 18 the hydride ligand is
more nucleophilic (it is trans to the more basic phos-
phane)[28] and the imine is more electrophilic (it is trans
to the less basic phosphane) as compared to 19. Also,
the result of the migratory insertion of 18, the postulated
pentacoordinate IrIII amido complex 22, is expected to
be stabilized by the coordination of the highly basic
amide function trans to the less basic phosphane. On the
other hand enantioselectivity could be kinetically con-
trolled, and an analogue of the minor (3%) component
20 may lead to the thermodynamically less stable postu-
lated intermediate 23. Hydrogenolysis of the iridium
amide bond (in this case trans to the more basic phos-
phane) or amine decoordination would then be the rate-
limiting steps. Detailed kinetic studies are necessary at
this stage.
Crystals of 25 were grown from a CH2Cl2/Et2O mixture
and an X-ray diffraction study was performed. The unit cell
contains two independent molecules. Figure 7 confirms the
k2 coordination mode of imine 14,[32] which has a bite angle
of 788, and
a square-planar coordination environment
around the iridium center. The iridium atom lies 0.01 ä
from the best plane fitted through the N and O atoms of 14
and the midpoints of the ethylene ligands. Similarly, the
Since we were interested in structurally assessing the coor-
dination behavior of the imine 14 by X-ray analysis and
since it was not possible to grow X-ray quality single crystals
from the mixtures 18 21, we opted for the synthesis of a
simple iridium imine adduct that would display a better
crystallinity. The goal was to synthesize an iridium imine
complex with labile spectator ligands that could be easily
substituted by diphosphane 4.[29] When the thermally labile
tetraethylene complex 24[30] was treated with the silver bis-
Figure 7. Structure of one of the two independent cations of 25 (ORTEP
plot; 30% probability ellipsoids). Selected bond lengths [ä] and
angles [8]: Ir(1)ÀN(116) 2.060(8), Ir(1)ÀO(112) 2.093(7), Ir(1)ÀC(102)
2.083(12), Ir(1)ÀC(101) 2.091(12), Ir(1)ÀC(103) 2.081(11), Ir(1)ÀC(104)
2.112(13), N(116)ÀC(114) 1.288(12), N(116)ÀC(121) 1.445(12), C(111)À
O(112) 1.446(12), C(113)ÀO(112) 1.406(12), C(114)ÀC(115) 1.519(13),
C(114)ÀC(113) 1.466(13), C(101)ÀC(102) 1.399(17), C(103)ÀC(104)
1.387(15), N(116)-Ir(1)-O(112) 77.7(3), N(116)-Ir(1)-C(102) 97.2(4),
O(112)-Ir(1)-C(103) 90.8(4), C(101)-Ir(1)-C(104) 86.7(5).
274
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Iridium Hydrogenation Catalysts
267 278
DMA backbone lies well within the plane defined by Ir, O,
and N, with the ipso-C(221) atom of the aryl group showing
the largest deviation of 0.05 ä. The dihedral angle between
the N,O,Ir plane and the plane fitted through the six C
atoms of the aryl ring is 878. The IrÀN bond length (2.06 ä)
lies within the expected range, and the IrÀO distance
(2.09 ä) is comparable to the length of an IrÀO single
bond.[33] Such tight ether coordination was previously ob-
served in a similar IrI complex.[34] The CÀN distance
(1.29 ä) does not indicate any appreciable amount of met-
al imine p backbonding.[35]
Experimental Section
General aspects: All experiments were performed under purified N2 in a
MBraun glovebox or under purified Ar using standard Schlenk techni-
ques. All glassware and stirbars were oven-dried at 413K. Pentane and
hexane were distilled from Na/K (50% w/w)/tetraglyme/benzophenone,
THF and diethyl ether from Na/K, benzene from Na/benzophenone, tolu-
ene and heptane from Na, and CH2Cl2 from Pb/Na alloy (Aldrich). Ace-
tone (Merck, puriss. p.a.) was dried over activated (553K, 0.001 mbar,
12 h) 4 ä molecular sieves. C6D6 and [D8]THF were dried over Na/K,
and CD2Cl2 and CDCl3 over Na/Pb alloy. The solvents were freshly distil-
led before use or kept in dispenser flasks in the glovebox. NMR spectra
were recorded on Bruker AC250 and Bruker dpx250 spectrometers
(same magnet, 1H: 250.133 MHz, 31P: 101.256 MHz). Chemical shifts are
given in ppm relative to internal TMS and to external H3PO4 (85%).
Coupling constants J are reported in hertz. Elemental analyses (EA)
were carried out at the Mikroelementaranalytisches Laboratorium at
ETH Zurich. All reactions involving silver salts were carried out in the
dark. The synthesis of enantiopure (R)-17 will be reported elsewhere.[26]
(R)-17 and (S)-17 were also obtained by separation on a preparative-
scale chiral Daicel OD-H column.
Attempts to isolate adducts of iridium with the hydroge-
nation product, that is, model amine 17, under conditions
analogous to those that allowed isolation of 18 21 failed.
Neither (R)- nor (S)-17 reacted cleanly with (S)-(R)-8 under
H2. This is because imine 14 is a much better ligand for iridi-
um than amine 17.[36] Note that amine 17 is a close model of
MEA-amine (2). Complex (S)-(R)-13 reacted with amine
(R)-17 to form complicated mixtures of hydrides. We
showed that chloro-bridged iridium complexes closely relat-
ed to 13 cleanly react with LiHNPh to afford IrI amido com-
plexes and IrI bis-amidate Li salts of the general formulae
Bis(3,5-xylyl)phosphane (5): A slightly turbid, yellowish solution of 3,5-
dimethylphenyllithium (9.25 g, 82.5 mmol) in Et2O (150 mL) was added
dropwise at 203K to
a colorless solution of PCl 2(NEt2) (7.18 g,
41.3mmol) in Et 2O (150 mL). The mixture was allowed to reach room
temperature. Then HCl(g) (ca. 160 mmol, liberated by treating 8.5 g of
NH4Cl with H2SO4) was slowly bubbled through the vigorously stirred
solution. The white precipitate was filtered off and the yellowish solution
pumped down. Fresh Et2O (50 mL) was added, and the resulting solution
was added dropwise to a slurry of LiAlH4 (5.56 g, 147 mmol) in Et2O
(150 mL) at 195 K. This mixture was warmed to room temperature over
4 h and stirred overnight. Refluxing for 2 h reflux, filtration, extraction of
the gray residue with Et2O, and subsequent evaporation of the combined
Et2O solutions gave a yellowish oil and a white precipitate. Distillation
(Tbath ꢀ430 K; Tvap ꢀ398 405 K; pꢀ0.04 mbar) gave 5.89 g (59%) of a
yellowish oil. 31P NMR (CDCl3): d=À40.0 ppm (s).
_
_
[{(PP)Ir(m-HNPh)}2] and [(PP)Ir(HNPh)2]Li, respectively.[37]
This prompted us to probe the reactivity of complex 13 with
various amounts of the corresponding lithium amide of 17
(obtained by deprotonation of 17 with LiBu) in [D8]THF.
Unfortunately, only complicated mixtures of products were
obtained. The dinuclear IrIII iodo complex 12 did not react
with this lithium amide.
(S)-(R)-Xyliphos
((S)-1-[(R)-2-(diphenylphosphanyl)ferrocenyl]ethyl-
Conclusion
bis(3,5-xylyl)phosphane, (S)-(R)-4): An orange-red solution of (S)-N,N-
dimethyl-1-[(R)-2-(diphenylphosphany)ferrocenyl]ethylamine (6, 8.86 g,
20.1 mmol) in AcOH (160 mL) was degased by two freeze pump thaw
cycles. Then PH(3,5-Xyl)2 (5, 5.35 g, 22.1 mmol) was added and the mix-
ture was heated to 370 K for 3 h. The volatile substsances were removed
in vacuo at 370 K, and EtOH (800 mL) was added to afford a limpid
orange solution at reflux temperature. Concentration to 400 mL, filtra-
tion, and washing with cold EtOH yielded 9.55 g (69%) of a yellow mi-
crocrystalline solid. From the mother liquor another crop of crystals was
recovered (0.80 g, 6%). Elemental analysis calcd (%) for C40H40P2Fe¥
C2H6O: C 73.68, H 6.77; found: C 73.54, H 6.80. 1H NMR (CDCl3): d=
1.46 (m, 3H), 2.19 (s, 6H), 2.27 (s, 6H), 3.72 (m, 1H), 3.84 (s, 5H), 4.03
(m, 2H), 4.24 (m, 1H), 6.77 (m, 1H), 6.85 7.00 (m, 5H), 7.10 7.20 (m, 5
H), 7.35 7.45 (m, 3H), 7.60 7.70 ppm (m, 2H). The spectrum indicated
one equivalent of EtOH of cocrystallization. 31P{1H} NMR (CDCl3): d=
À25.2 (d, J=19 Hz), 6.5 ppm (d, J=19 Hz).
[Ir(Cl)(cod){(S)-(R)-Xyliphos)}] (7): Warm toluene (50 mL) was added
to [Ir2(m-Cl)2(cod)2] (417 mg, 0.621 mmol) and (S)-(R)-Xyliphos ((S)-(R)-
4, 794 mg, 1.244 mmol), and the resulting limpid orange solution was stir-
red overnight. The volatile substances were evaporated and the remain-
ing orange glassy solid was treated with diethyl ether (20 mL) to give a
yellow crystalline solid. The mother liquor was filtered off and the solid
dried in vacuo. Yield: 950 mg (78%). Elemental analysis calcd (%) for
C48H52ClFeIrP2: C 59.17, H 5.38; found: C 58.95, H 5.57. 1H NMR
(C6D6): d=1.70 1.85 (m, 2H), 1.83(m, 3H), 2.10 2.30 (m, 2H), 2.12 (m,
6H), 2.19 (m, 6H), 2.35 2.55 (m, 2H), 2.55 2.75 (m, 2H), 3.78 (m, 1H),
3.85 4.10 (m, 4H), 3.96 (s, 5H), 4.42 (m, 2H), 6.45 7.05 (m, 8H), 7.20
7.30 (m, 2H), 7.30 7.40 (m, 2H), 7.82 (br, 2H), 8.86 ppm (m, 2H);
31P NMR (C6D6): d=À14.5 (d, J=37 Hz), 16.4 (d, J=37 Hz). [a]2D0 =144
(c=0.78, THF).
We prepared and characterized a series of complexes that
reflect the composition of the ™magic catalyst mixture∫ used
in the Syngenta MEA-imine hydrogenation process. Nota-
bly, complexes 10 and 11 contain all the ingredients in the
coordination sphere of iridium, namely, Xyliphos (4), iodide,
and a hydride originating from a Br˘nstedt acid. Not sur-
prisingly, these compounds, along with the unprecedented
dinuclear iodo bridged IrIII complex 12, were the best single-
component catalysts for the hydrogenation of imine 1. The
last-named complex is an excellent catalyst precursor even
though it does not have an IrIIIÀH bond. Coordination of
imine 14 [a close model for MEA-imine (1)] to 8 under
1 bar H2 pressure was not diastereoselective and led to a
mixture of two major (18, 19) and two minor isomers (20,
21). Two of them (18 and 20) were in accord with the stereo-
chemical outcome of the catalysis, and migratory insertion
leads to the postulated thermodynamic (22) or kinetic (23)
intermediates. Finally, we proved by an X-ray structure anal-
ysis of model compound 25 that imine 14 coordinates in an
k2 fashion to an IrI center. It was shown that the ether
group of the imine binds quite tightly to the iridium center.
The coordination behavior of amine 17 on iridium and its
exchange kinetics with imine 14 have been the object of in-
vestigation in our laboratory and will be reported in due
course.[36]
[Ir(cod)((S)-(R)-Xyliphos)]BF4 (8): An orange solution of [Ir2(m-
Cl)2(cod)2] (0.976 g, 1.45 mmol) and (S)-(R)-Xyliphos ((S)-(R)-4, 1.856 g,
2.91 mmol) in THF (130 mL) was stirred for 0.5 h (slightly turbid). Then
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R. Dorta et al.
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AgBF4 (0.570 g, 2.93mmol) was added, and the resulting deep red mix-
ture was stirred overnight. The finely divided white precipitate was al-
lowed to settle at 253K for 2 h. The mother liquor was then decanted off
over a Celite filterstick and stripped to a deep red glassy solid. Slurrying
and washing with n-hexane (25 mL) and drying in vacuo yielded a brick-
red powder (2.73g, 92%). Elemental analysis calcd (%) for
C48H52BF4FeIrP2: C 56.21, H 5.11; found: C 56.12, H 5.20; 31P NMR
(C6D6): d=3.2 (d, J=24 Hz, P1), 37.9 ppm (d, J=24, P2). 13C NMR
(CD2Cl2): d=14.52 (d, J=6.0 Hz, C7), 21.45 (s, C14, C15), 21.70 (s, C22,
C23), 28.05 (dd, J=J=1.6, 1.6 Hz, C42), 28.49 (dd, J=1.6, 1.8 Hz, C38),
33.02 (dd, J=26.0, 4.2 Hz, C6), 33.38 (dd, J=4.5, 2.2 Hz, C39), 33.68 (dd,
J=4.5, 2.3Hz, C43), 68.75 (d, J=8.0 Hz, C4), 69.63(dd, J=8.5, 1.6 Hz),
70.97 (s, C1’ C5’), 73.27 (dd, J=54.7, 5.9 Hz, C1), 74.94 (d, J=5.7 Hz,
C5), 84.74 (d, J=10.8 Hz, C36), 85.96 (d, J=10.1 Hz, C40), 89.42 (dd, J=
18.9, 4.1 Hz, C2), 91.21 (d, J=10.5 Hz, C37), 92.25 (d, J=11.1 Hz, C41),
127.15 (dd, J=44.7 Hz, 0.9, Cipso), 127.37 (d, J=50.8 Hz, Cipso), 128.89 (d,
J=10.0, C32 Hz, C34), 129.01 (dd, J=55.6, 1.1 Hz, Cipso)), 129.48 (d, J=
5.6 Hz, C17, C21), 129.56 (d, J=8.5 Hz, C25, C29), 131.44 (d, J=2.4 Hz,
C33), 132.85 (d, J=2.5 Hz, C27), 133.01 (d, J=9.2 Hz, C31, C35), 133.38
(d, J=2.5 Hz, C19), 134.29 (d, J=11.3 Hz, C9, C13), 134.37 (d, J=
2.6 Hz, C11), 135.10 (d, J=56.5 Hz, Cipso), 136.83 (d, J=13.5 Hz, C24),
138.77 (d, J=11.1 Hz, C10, C11), 139.45 ppm (d, J=9.9 Hz, C18, C20);
1H NMR (CD2Cl2): d=1.50 (dd, 3H7), 1.56 (m, H42), 1.61 (m, H38), 1.66
(m, H42), 1.88 (m, H38), 2.06 (m, H43), 2.30 (s, 3 H14, 3 H15), 2.32 (m,
H43), 2.34 (m, 2 H39), 2.40 (s, 3 H22, 3 H23), 3.28 (m, H41), 3.60 (dq,
H6), 3.65 (m, H37), 3.73 (s, H1’ H5’), 4.03(m, H3), 4.15 (dt, H4), 4.19
(m, H36), 4.20 (m, H40), 4.33 (td, H5), 7.04 (md, H17, H21), 7.19 (m,
H19), 7.20 (m, H11), 7.34 (md, H9, H13), 7.37 (m, H31, H35), 7.51 (m,
H33), 7.52 (m, H32, H34), 7.77 (m, H27), 7.81 (m, H26, H28), 8.35 ppm
(m, H25, H29). Single crystals suitable for X-ray diffraction analysis were
grown from a saturated, filtered solution of the complex in THF.
Dropwise addition of Et2O (4 mL) caused the precipitation of a brick-red
solid. The mother liquor was syphoned off, and the solid washed with
Et2O (4 mL) and dried in vacuo to give a pink powder (98 mg, 41%). El-
emental analysis calcd (%) for C48H53BF4FeIIrP2¥CH2Cl2: C 47.52, H
4.48,I 10.25; found: C 47.91 , H 4.42, I 10.34; IR: n˜(IrH)=2259 cmÀ1
(CsI). 31P NMR (CD2Cl2): dÀ12.4 (d, J=18 Hz), 23.5 ppm (d, J=18 Hz);
13C NMR (CD2Cl2): d=13.80 (d, J=5.6 Hz, C7), 21.73(s, C14, C15),
21.78 (s, C22, C23), 31.69 (dd, J=3.8, 0.9 Hz, *), 31.75 (dd, J=4.3,
2.2 Hz, *), 32.08 (dd, J=3.4, 1.0 Hz, *), 32.21 (4.1, 2.5 Hz, *), 37.64 (dd,
J=26.3, 4.1 Hz, C6), 69.48 (d, J=9.4 Hz, C4), 71.49 (s, C1’-C5’), 71.50
(dd, J=9.0, 1.0 Hz, C3), 75.95 (d, J=6.3Hz, C5), 89.16 (dd, J=7.6,
0.9 Hz, C37), 90.83 (dd, J=8.1, 1.4 Hz, C42), 95.81 (d, J=15.3Hz, C38),
98.95 (d, J=15.3Hz, C41), 125.83 (d, J=51.2 Hz, Cipso), 126.52 (dd, J=
59.4, 1.0 Hz, Cipso), 127.22 (d, J=53.3 Hz, Cipso), 128.41 (d, J=10.9 Hz,
C26, C28), 129.45 (d, J=10.7 Hz, C32, C34), 131.20 (d, J=60.7 Hz, Cipso),
131.70 (d, J=9.4 Hz, C9, C13), 132.04 (d, J=6.3Hz, C17, C21), 132.72
(d, J=2.8 Hz, C27), 133.28 (d, J=2.6 Hz, C33), 133.77 (d, J=2.9 Hz,
C19), 134.46 (d, J=2.6 Hz, C11), 134.7 (br, C25, C29), 135.2 (br, C31,
C35), 137.48 (d, J=10.9 Hz, C10, C12 or C18, C20), 139.56 ppm (d, J=
10.9 Hz, C18, C20 or C10, C12); *=C39, C40, C43, C44, not specifically
assigned. 1H NMR (CD2Cl2): d=À12.58 (dd, J=10.7, 10.7 Hz, IrH), 1.52
(dd, 3H6), 2.29 (s, 3H18, 3H20), 2.32 (m, H39), 2.41 (s, 3H10, 3H12),
2.43 (m, H40), 2.44 (m, H43), 2.52 (m, H44), 2.53 (m, H43), 2.67 (qd,
H6), 2.73 (2m, H39, H40), 2.81 (m, H44), 3.94 (m, H38), 3.99 (s, H1’-
H5’), 4.15 (m, H41), 4.71 (2 m, H4, H5), 4.76 (m, H37), 4.83 (m, H42),
4.91 (m, H3), 6.90 (md, H17, H21), 7.10 (m, H19), 7.26 (m, H11), 7.44
(m, H26, H28), 7.53 (m, H27), 7.56 (md, H9, H13), 7.79 (m, H33), 7.84
(m, H32, H34), 7.85 (vbr, H25, H29), 8.75 ppm (m, H31, H35).
[Ir(I)(H)(cod)((S)-(R)-Xyliphos)]BF4¥0.5CH2Cl2 (11):
HBF4 in Et2O (54 wt%, d=1.19, 260 mL, 1.90 mmol) was slowly added to
deep red solution of [Ir(I)(cod)((S)-(R)-Xyliphos)] (9, 1.015 g,
A solution of
a
[Ir(I)(cod)((S)-(R)-Xyliphos)] (9): Acetone (150 mL) was added to
[Ir2(m-Cl)2(cod)2] (0.959 g, 1.428 mmol), (S)-(R)-Xyliphos ((S)-(R)-4,
1.823g, 2.855 mmol), and KI (0.498 g, 3.002 mmol). Stirring for 3h af-
forded a yellow slurry, which was pumped down. Toluene (150 mL) was
added and the mixture was filtered over Celite. The volatile substances
were removed in vacuo leaving an orange glassy solid. Washing with
hexane and drying in vacuo yielded a yellow powder (2.81 g, 92%). Ele-
mental analysis calcd (%) for C48H52P2FeIIr: C 54.09, H 4.92; found: C
54.34, H 5.08; 31P NMR (C6D6): d=À24.0 (d, J=41 Hz, P1), 7.5 ppm (d,
J=41 Hz, P2); 13C NMR (C6D6): d=17.09 (d, J=7.4 Hz, C7), 21.40 (s,
MeXyl), 21.42 (s, MeXyl), 32.59 (d, J=3.7 Hz, C39, C43), 32.77 (d, J=
3.5 Hz, C38, C42), 35.30 (d, J=28.1 Hz, C6), 67.20 (dd, J=10.8, 1.6 Hz,
C37, C41), 68.33 (d, J=4.9 Hz, C4), 69.05 (dd, J=8.1, 2.6 Hz, C3), 70.13
(d, J=12.5 Hz, C36, C40), 71.46 (s, C1’ C5’), 73.61 (dd, J=47.4, 7.9 Hz,
C1), 74.21 (d, J=1.4 Hz, C5), 94.48 (dd, J=18.9, 5.8 Hz, C2), 126.51 (d,
J=8.7 Hz, C32, C34), 127.44 (s, C33), 127.48 (d, J=8.3Hz, C26, C28),
130.37 (d, J=2.3 Hz, C27), 131.55 (br, C9, C13), 131.93 (d, J=2.4 Hz,
C19), 131.96 (d, J=2.3Hz, C11), 132.49 (dd, J=40.5, 3.9 Hz, Cipso),
133.51 (d, J=8.0 Hz, C31, C35), 134.60 (dd, J=44.1, 2.2 Hz, Cipso), 135.20
(br, C17, C21), 136.35 (d, J=10.3Hz, C25, C29), 137.09 (br, C10, C12),
137.51 (d, J=10.0 Hz, C18, C20), 140.65 (d, J=51.2 Hz, Cipso), one Cipso
masked by C6D6, 127.16 ppm (dd, J=44.6, 1.6 Hz) in CDCl3). 1H NMR
(C6D6): d=1.79 (dd, 3H7), 1.96 (m, H38, H42), 2.01 (s, 3H22, 3H23),
2.03 (m, H39, H43), 2.14 (br, 3 H14, 3 H15), 2.53 (m, H39, H43), 2.65 (m,
H38, H42), 3.67 (m, H36, H40), 3.80 (m, H5), 3.84 (m, H4), 4.06 (s, H1’-
H5’), 4.26 (m, H37, H41), 4.35 (m, H3), 6.65 (m, H31, H35), 6.68 (qd,
H6), 6.74 (m, H11), 6.78 (m, H32, H34), 6.83 (m, H19), 6.97 (m, H33),
7.15 (m, H27), 7.27 (m, H26, H28), 7.50 (md, H17, H21), 8.75 ppm (m,
0.952 mmol) in CH2Cl2 (40 mL), and the mixture stirred for 60 h. Con-
centration (4 mL), addition of Et2O (16 mL), and stirring overnight
caused the formation of a yellow microcrystalline precipitate. After
standing at 253K for 4 h, the deep red mother liquor was decanted off,
and the solid washed with Et2O (30 mL) and dried in vacuo to yield an
orange powder (660 mg, 58%). From the mother liquor another crop of
crystals was recovered (68 mg, 6%). Elemental analysis calcd (%) for
C48H53BF4FeIIrP2¥0.5CH2Cl2: C 48.70, H 4.55, I 10.61; found: C 48.76, H
4.67, I 10.87; IR: n˜(IrH)=2256 cmÀ1 (CsI); 31P{H} NMR (CD2Cl2): d=
À31.9 (d, J=23Hz), À1.5 (d, J=23); 13C NMR (CD2Cl2): d=16.02 (br,
C7), 21.56, 21.58, 21.61 (3s, 4 Me Xyl), 30.33 (m, C44), 30.49 (m, C40),
32.40 (d, J=2.8 Hz, C43), 33.78 (m, C39), 34.37 (d, J=33.3 Hz, C6), 69.55
(dd, J=64.2, 6.1 Hz, C1), 70.34 (br, C4), 71.20 (br, C3), 72.44 (br, C1’
C5’), 74.54 (br, C5), 91.38 (br, C42), 94.13 (d, J=7.7 Hz, C37), 97.75 (d,
J=13.5 Hz, C38), 99.36 (d, J=11.8 Hz, C41), 124.80 (d, J=55.9 Hz,
Cipso), 126.43(d, J=49.0 Hz, Cipso), 128.22 (d, J=10.1 Hz, C26, C28),
128.24 (d, J=56.9 Hz, Cipso), 128.87 (d, J=10.7 Hz, C32,C34), 130.38 (dd,
J=5 Hz, 6, C9), 130.66 (s, C27), 130.87 (d, J=9.9 Hz, C13), 131.20 (d,
J=9.1 Hz, C25, C29), 132.18 (m, C17, C21), 132.81 (d, J=2.2 Hz, C33),
134.31 (m, C11), 134.43 (m, C19), 134.90 (d, J=9.5 Hz, C31, C35), 139.04
(d, J=10.3Hz, C10 or C12), 139.11 (d, J=65.2 Hz, Cipso), 139.14 (d, J=
11.7 Hz, C12 or C10), 139.72 ppm (d, J=10.9 Hz, C32, C34); 1H NMR
(CD2Cl2): d=À13.84 (dd, J=15.8, 9.2 Hz, IrH), 1.61 (dd, 3H7), 2.10 (s, 3
H14), 2.19 (s, 3 H22, 3 H23), 2.39 (3 m, H40, 2 H44), 2.46 (s, 3 H15), 2.47
(m, H43), 2.62 (m, H43), 2.98 (m, H39), 3.02 (m, H40), 3.42 (m, H39),
3.86 (m, H5), 4.12 (H1’ H5’), 4.26 (m, H41), 4.43(m, H4), 4.55 (m, H42),
4.92 (m, H3), 5.13 (m, H37), 5.51 (m, H38), 6.10 (md, H9), 6.46 (m, H25,
H29), 6.48 (qd, H6), 7.03(m, H26, H28), 7.04 (md, H17, H21), 7.10 (m,
H11), 7.11 (m, H19), 7.29 (m, H27), 7.57 (m, H32, H34), 7.62 (m, H33),
8.34 (md, H13), 8.35 ppm (m, H31, H35). Single crystals suitable for X-
ray diffraction analysis were grown from a filtered solution of 82 mg com-
plex in CH2Cl2 (0.3mL) and THF (0.6 mL).
H25, H29), H9 and H13too broad to be observed (7.2 in CDCl with D1/
3
2 =150 Hz). Single crystals suitable for X-ray diffraction analysis were ob-
tained as follows: 150 mg of the complex was dissolved in THF (7 mL),
Et2O was added to just induce precipitation, and subsequent warming re-
dissolved the precipitate. The resulting limpid solution was allowed to
slowly cool to room temperature.
[Ir2I2(m-I)3((S)-(R)-Xyliphos)2]I (12):
A solution of I2 (72.23mg,
0.2845 mmol) in toluene (20 mL) was added dropwise to a stirred solu-
tion of [Ir(I)(cod)((S)-(R)-Xyliphos)] (9, 303.3 mg, 0.2845 mmol) in tolu-
ene (30 mL) at 203 K. The resulting dark red solution was allowed to
slowly reach room temperature. Then it was heated at 323 K for 0.5 h.
The solution turned red-brown and a small amount of an oily precipitate
formed. After evaporation of the volatile substances the residue was
washed and slurried with hexane (2î60 mL). Drying in vacuo afforded a
[Ir(H)(I)(cod)((S)-(R)-Xyliphos)]BF4¥CH2Cl2 (10): A solution of HBF4
in Et2O (54 wt%, d=1.19, 26 mL, ca. 0.19 mmol) was slowly added to a
red solution of [Ir(I)(cod)((S)-(R)-Xyliphos)] (9, 203mg, 0.191 mmol) in
CH2Cl2 (10 mL) at 195 K. The solution turned yellow and was allowed to
slowly reach room temperature. The resulting orange solution was strip-
ped to a red oily solid, which was redissolved in fresh CH2Cl2 (1 mL).
276
¹ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
Chem. Eur. J. 2004, 10, 267 278

Iridium Hydrogenation Catalysts
267 278
brown powder (276 mg, 80%). Elemental analysis calcd (%) for
C80H80Fe2I6Ir2P4: C 39.66, H 3.33, I 31.43; found: C 39.52, H 3.07, I 31.37;
1H NMR (CD2Cl2): d=1.15 (m, 6H), 1.81 (s, br, 12H), 2.05 (s, br, 6H),
2.12 (s, br, 6H), 3.76 (s, 10H), 4.47 (m, 2H), 4.55 (m, 2H), 4.86 (s, 2H),
5.19 (m, 2H), 6.35 (m, 4H), 6.69 (m, 4H), 6.87 (s, 2H), 7.01 (s, 2H), 7.16
(m, 2H), 7.20 7.70 (m, br, 12H), 8.40 (m, 2H), 8.61 ppm (m, 4H); 31P{H}
NMR (CD2Cl2/C6D6): d=À22.0 (d, J=11 Hz), 2.0 ppm (d, J=11 Hz).
Crystals suitable for X-ray crystallographic analysis were grown from
CH2Cl2/Et2O.
[Ir(H)2((S)-(R)-Xyliphos)(DMA-imine)]BF4 (18, 19, 20, 21): A stream of
H2 (pꢀ2 bar) was slowly bubbled for 0.2 h through a deep red solution
of [Ir(cod)((S)-(R)-Xyliphos)]BF4 (8, 76.9 mg, 0.0750 mmol) and DMA-
imine 14 (143mg, 0.75 mmol) in CH 2Cl2 (7.5 mL). The solution turned
orange within seconds. Then the solution was pumped down to an orange
oil. Treatment of the oil with pentane (10 mL) afforded a pale yellow
powder, which was washed with another portion of pentane and dried in
vacuo (65 mg, 75%). Elemental analysis calcd (%) for C52H59BF4FeIr-
NOP2¥0.5CH2Cl2: C 54.67, H 5.24, N 1.21; found: C 54.94, H 5.35, N 1.21;
18: 31P NMR (CD2Cl2): d=À4.4 (d, J=8.5 Hz, P1), 23.2 ppm (d, J=
8.5 Hz, P2); 13C NMR (CD2Cl2): d=15.33 (d, J=5.7 Hz, C7), 17.17 (s,
C47), 17.96 (d, J=2.4, C38), 20.71 (d, J=2.2, C46), 21.39 (s, C22, C23),
21.75 (s, C14, C15), 38.16 (dd, J=27.3, 2.1, C6), 61.26 (s, C39), 69.65 (d,
J=6.8, C4), 71.18 (s, C1’ C5’), 71.4 (C3), 74.61 (d, J=3.5, C5), 83.17 (dd,
J=1.2, 1.2, C37), 95.24 (dd, J=17.8, 3.7), aromatic C atoms not assigned,
180.64 (dd, J=2.4, 1.0, C37). 1H NMR (CD2Cl2): d=À29.86 (ddd, J=
24.7, 13.5, 4.8, IrH), À6.95 (ddd, J=147.2, 21.8, 4.8, IrH), 0.99 (dd, J=
H7), 1.25 (s, 3H47), 1.37 (s, 3H39), 1.60 (s, 3H38), 2.09 (s, 3H14, 3
H15), 2.23 (s, 3 H22, 3 H23), 2.67 (s, 3 H46), 3.38 (qd, H6), 3.50 (s, H1’
H5’), 4.02 (d, J=36 Hz), 4.45 (2 m, H4, H5), 4.48 (d, J=36 Hz), 4.79 (m,
H3), ortho-protons: 6.81 (md, H31, H35), 7.00 (md, H17, H21), 7.23 (m,
H25, H29), 8.06 ppm (md, H9, H13); 19: 31P NMR (CD2Cl2): d=2.6 (d,
J=8.5 Hz, P1), 11.9 ppm (d, J=8.5 Hz, P2); 13C NMR (CD2Cl2): d=16.87
(d, J=5.7 Hz, C7), 17.67 (d, J=2.8 Hz, C38), 18.01 (s, C47), 20.79 (d, J=
2.6 Hz, C46), 21.53 (s, C14, C15, C22, C23), 36.04 (dd, J=33.9, 1.9 Hz,
C6), 62.75 (s, C39), 69.47 (d, J=5.6 Hz, C4), 71.0 (C3), 71.03 (s, C1’ C5’),
75.02 (d, J=1.3Hz, C5), 82.72 (d, J=1.9 Hz, C37), 93.59 (dd, J=19.4,
2.5 Hz, C2), aromatic C atoms not assigned, 180.00 ppm (dd, J=2.5,
1.2 Hz, C37); 1H NMR (CD2Cl2): d=À30.19 (ddd, J=25.6, 12.6, 4.8 Hz,
IrÀH), À6.14 (ddd, J=150.1, 19.3, 4.8 Hz, IrH), 1.14 (dd, J=7 Hz), 1.30
(s, 3 H47), 1.67 (s, 3 H38), 1.71 (s, 3 H39), 2.24 (s, 3 H22, 3 H23), 2.39 (s,
3H14, 3H15), 2.71 (s, 3H46), 3.45 (s, H1 ’-H5’), 3.52 (qd, H6), 4.16 (m,
H5), 4.20 (d, J=H36), 4.41 (m, H4), 4.48 (d, J=H36), 4.73 (m, H3),
ortho-protons: 7.14 (m, H25, H29), 7.17 (md, H17, H21), 7.43(m, H31,
H35), 7.55 ppm (md, H9, H13); 20: 31P NMR (CD2Cl2): d=5.4 (P1), 30.8
cis- and trans-[Ir2(m-Cl)2((S)-(R)-Xyliphos)2] (13): A red solution of (S)-
(R)-Xyliphos ((S)-(R)-4, 2.001 g, 3.133 mmol) in benzene (40 mL) was
added dropwise over 20 min to a stirred bright orange slurry of [Ir2Cl2(-
coe)4] (1.416 g, 1.566 mmol) in benzene (40 mL) to afford a limpid deep
red solution. After stirring for 15 min the solvent was removed in vacuo
leaving an orange solid. Washing with pentane and drying in vacuo af-
forded a yellow powder (2.40 g, 88%). Elemental analysis calcd (%) for
C80H80Cl2Fe2Ir2P4): C 55.46, H 4.65; found: C 55.18, H 4.80; 31P{1H} NMR
(C6D6), AA’XX’ spin system, two isomers: d=À4.22 (2JPP’ +4JPP’
=
38.3 Hz, isomer A), À1.01 (2JPP’ +4JPP’ =30.6 Hz, isomer B), 22.70 (2JPP’
+
4JPP’ =38.2 Hz, isomer A), 26.73 ppm (2JPP’ +4JPP’ =30.6 Hz, isomer B);
1H NMR (C6D6): d=1.05 À1.20 (m, 6H, isomer A), 1.25 1.35 (m, 6H,
isomer B), 2.12 (s, 12H, isomer B), 2.17 (s, 12H, isomer B), 2.22 (s, 12H,
isomer A), 2.38 (s, 12H, isomer A), 3.57 (s, 10H, isomer B), 3.68 (s, 10H,
isomer A), 3.75 4.20 (m, 8H, isomers A and B), 6.75 À8.55 ppm (m, 32
H, isomers A and B).
Typical hydrogenation protocol: MEA-imine (20.5 mL, 0.1 mol) was
transferred under argon to a magnetically stirred 50 mL steel autoclave
containing (R)-(S)-12 (2.4 mg, 0.001 mmol). The autoclave was purged
five times with 5 bar H2 (99.5%) and finally pressurized to 100 bar (this
pressure was maintained throughout the experiment). Stirring at
1500 rpm and warming to 303 K initiated the hydrogenation reaction,
which was left for 18 h. The reaction solution was diluted in CH2Cl2 (1%
v/v) and analyzed by GC (Varian 3700, OV-101 column, temperature pro-
gram: Tinit =373 K, 10 KminÀ1 up to 593K; retention times: MEA-amine
8.05 min, MEA-imine 7.65 min); 75.0% yield of MEA-amine 2. The ee
was determined by HPLC on a Daicel Chiracel OD-H column with
1
(P2); H NMR (CD2Cl2): d=À30.63 (ddd, J=22.0, 13.9, 4.5, Ir-H), À7.35
(ddd, J=145.2, 22.0, 4.5 Hz, IrH), 1.19 (dd, 3H7), ortho-protons: 6.59
(H17, H21), 6.98 (H25, H29), 7.30 (H9, H13), 8.16 ppm (H31, H35); 21:
hexane/iPrOH (99.65/0.35) as eluent (1.0 mLminÀ1
times: (R)-2 6.9 min, (S)-2 8.0 min; 79% ee (S)).
; 298 K; retention
1
31P NMR (CD2Cl2): d=À1.0 (P1), 42.1 ppm (P2); H NMR (CD2Cl2): d=
À31.69 (ddd, J=28.7, 8.5, 5.9 Hz, IrH), À8.06 (ddd, J=153.3, 20.0,
5.9 Hz, IrH), 1.36 (dd, 3 H7), ortho-protons: 6.66 (H17, H21), 7.06 (H9,
H13), 7.85 (H25, H29), 8.06 ppm (H31, H35).
DMA-imine (2,6-dimethylphenyl-1’-methyl-2’-methoxyethyl-imine, 14): A
mixture of methoxyacetone (41.2 g, 467 mmol) and 2,6-dimethylaniline
(57.9 g, 478 mmol) in toluene (100 mL) was heated to reflux on a water
separator for 24 h. About 8.5 mL of H2O was collected. The volatile sub-
stances were evaporated. Acetic anhydride (3.6 mL, 38 mmol) was added
to the yellowish residue to scavenge excess 2,6-dimethylaniline, and the
mixture was stirred at room temperature overnight. Fractionation (70 74
8C, 0.007 mbar) yielded a yellowish oil (71 g, 79%). Elemental analysis
calcd (%) for C12H17NO: C 75.35, H 8.96, N 7.32; found: C 75.00, H 9.10,
N 7.25; 1H NMR (250.13MHz, CDCl 3): d=1.66 (s, 3H, E isomer); 2.00
(brs, 6H, both isomers); 2.29 (s, 3H, Z isomer); 3.25 (s, 3H, Z isomer);
3.48 (s, 3H, E isomer); 3.62 (s, 2H, Z isomer); 4.20 (s, 2H, E isomer);
6.85 6.90 (m, 1H, both isomers); 6.95 7.00 ppm (m, 2H, both isomers).
Z:Eꢀ0.16.
2,6-Dimethylphenyl-1’-methyl-2’-methoxyethyliminium tetrafluoroborate
(15). A solution of HBF4 (54 wt% in Et2O, 3.50 mL, 25.7 mmol) was
added dropwise to a solution of DMA-imine (14, 4.92 g, 25.7 mmol) in
Et2O (125 mL) at À408C. A white flocculating solid formed, and the mix-
ture was left stirring overnight to slowly reach room temperature. The su-
pernatant was filtered off, and the residue washed with Et2O (2î50 mL)
and dried in vacuo affording a white powder (6.74 g, 94%). 1H NMR
(250.13MHz, CD 2Cl2): d=2.22 (s, 6H), 2.39 (s, 3H), 3.67 (s, 3H), 4.85 (s,
2H), 7.20 7.30 (m, 2H), 7.35 7.45 (m, 1H), 11.90 ppm (br, 1H).
[Ir(DMA-imine)(C2H4)2]BF4 (25): Ethylene (1 bar) was bubbled through
a slurry of [Ir2(m-Cl)2(coe)4] (1.044 g, 1.165 mmol) in heptane (5 mL) for
0.2 h at 273K. The resulting off-white slurry was cooled to 195 K, and
pentane (20 mL) was added at this temperature. The supernatant solution
was decanted off, and CH2Cl2 (10 mL) was added to give a turbid green-
ish solution.
A
solution of [Ag(DMA-imine)2]BF4 (16, 1.344 g,
2.328 mmol) in CH2Cl2 (10 mL) was then added over 0.2 h at 195 K. The
resulting greenish limpid solution was allowed to reach room tempera-
ture overnight, and a white finely divided precipitate and an orange su-
pernatant solution formed. This mixture was evaporated to dryness,
washed with Et2O (2î30 mL), and extracted with CH2Cl2 (3î10 mL)
over a Celite filterstick. Concentration of the mother liquor to 15 mL
and addition of Et2O precipitated an orange microcrystalline solid, which
was filtered off and dried in vacuo (1.08 g, 87%). Elemental analysis
calcd (%) for C16H25BF4IrNO¥0.5CH2Cl2: C 34.84, H 4.61, N 2.46; found:
C 35.19, H 4.64, N 2.47; 1H NMR (CD2Cl2): d=1.2 3.9 (br, 8H), 1.93 (s,
3H), 2.22 (s, 6H), 3.98 (s, 3H), 5.49 (s, 2H), 7.16 ppm (s, 3H). The spec-
trum indicated the presence of 0.5 equiv of CH2Cl2. Crystals suitable for
X-ray analysis were grown by vapor diffusion of Et2O into a CH2Cl2 solu-
tion that was prepared by first washing 185 mg of the complex in THF
(3mL), drying in vacuo, and then dissolving it in CH 2Cl2 (2 mL).
[Ag(DMA-Imine)2]BF4 (16): DMA-imine (14, 5.5 mL, 28.2 mmol) was
added by syringe to a solution of AgBF4 (1.11 g, 5.70 mmol) in toluene
(120 mL). After stirring at room temperaure for 3h a white precipitate
formed. The mother liquor was filtered off and the solid dried in vacuo
overnight. Washing the solid with pentane (2î60 mL) and drying in
vacuo afforded an off-white solid (2.96 g, 90%). Elemental analysis calcd
(%) for C24H34N2BO2F4Ag: C 49.94, H 5.94, N 4.85; found: C 50.19, H
6.04, N 4.81; 1H NMR (250.13MHz, CD 2Cl2): d=1.69 (s, 3H); 1.99 (s, 6
H); 3.23 (s, 3H); 4.22 (s, 2H); 7.08 7.10 ppm (m, 3H).
CCDC-189331, CCDC-189332, CCDC-189329, CCDC-189330, and
CCDC-134961 contain the supplementary crystallographic data for com-
pounds 8, 9, 11, 12, and 25, respectively. These data can be obtained free
of charge via www.ccdc.cam.ac.uk/conts/retrieving.html (or from the
Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge
CB2 1EZ, UK; fax: (+44)1223-336-033; or deposit@ccdc.cam.uk).
277
Chem. Eur. J. 2004, 10, 267 278
www.chemeurj.org
¹ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

R. Dorta et al.
FULL PAPER
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[18] In fact, one would expect 11 to be the product of simple protonation
of 9. Moreover, it is still uncertain whether the isomerization of 10
to 11 is catalytic in HBF4.
Received: June 10, 2003
Revised: September 16, 2003[F5218]
278
¹ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
Chem. Eur. J. 2004, 10, 267 278